74 results on '"Burke, TG"'
Search Results
2. Plasma and tissue disposition of non-liposomal DB-67 and liposomal DB-67 in C.B-17 SCID mice
- Author
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Zamboni, WC, Jung, LL, Strychor, S, Joseph, E, Zamboni, BA, Fetterman, SA, Sidone, BJ, Burke, TG, Curran, DP, Eiseman, JL, Zamboni, WC, Jung, LL, Strychor, S, Joseph, E, Zamboni, BA, Fetterman, SA, Sidone, BJ, Burke, TG, Curran, DP, and Eiseman, JL
- Abstract
Purpose: DB-67 is a silatecan, 7-silyl-modified camptothecin, with enhanced lipophilicity and increased blood stability of the active-lactone ring. The generation of a liposomal formulation of DB-67 may be an attractive method of intravenous (IV) administration and may maintain DB-67 in the active-lactone form. We evaluated the tissue and plasma disposition of DB-67 lactone and hydroxy acid after administration of non-liposomal (NL) and liposomal (L) DB-67 in severe combined immunodeficient (SCID) mice. Methods: NL-DB-67 and L-DB-67 10 mg/kg IV×1 were administered via a tail vein in SCID mice. After dosing, mice (n=3 per time point) were euthanized and blood (∼1 ml) and tissue were collected from 5 min to 48 h after administration. DB-67 lactone and hydroxy acid concentrations in plasma and DB-67 total (sum of lactone and hydroxyl acid) concentrations in tissues were determined by high-performance liquid chromatography (HPLC) with fluorescence detection. Results: Clearance of DB-67 lactone after administration of NL-DB-67 and L-DB-67 were 1.6 and 3.5 l/h/m 2, respectively; DB-67 lactone half-lives after administration of NL-DB-67 and L-DB-67 were 1.4 and 0.9 h, respectively. The percentages of DB-67 lactone in plasma after administration of NL-DB-67 and L-DB-67 were 92% and 89%, respectively. Liver, kidney, spleen, and lung tissues had longer exposure times to DB-67 after administration of L-DB-67 compared with NL-DB-67. Conclusion: In plasma, the majority of DB-67 remained in the lactone form after administration of NL-DB-67 and L-DB-67. The plasma disposition of DB-67 was similar after administration of NL-DB-67 and L-DB-67, suggesting that most of the DB-67 is immediately released from the L-DB-67 formulation. Following administration of L-DB-67, the higher and longer exposure of DB-67 in the spleen, as compared with NL-DB-67, is consistent with splenic clearance of liposomes by the reticuloendothelial system. © 2007 Springer Science+Business Media, LLC.
- Published
- 2008
3. Analysis of human topoisomerase I inhibition and interaction with the cleavage site +1 deoxyguanosine, via in vitro experiments and molecular modeling studies
- Author
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Laco, GS, Du, W, Kohlhagen, G, Sayer, JM, Jerina, DM, Burke, TG, Curran, DP, Pommier, Y, Laco, GS, Du, W, Kohlhagen, G, Sayer, JM, Jerina, DM, Burke, TG, Curran, DP, and Pommier, Y
- Abstract
Human topoisomerase I Tyr723 (white) in covalent complex with DNA (light blue) via the -1 deoxythymidine (bottom), while the +1 deoxyguanosine with a free 5′-OH is rotated out of the helix (right). Homocamptothecin 9,10 diF (green) is docked in the active site (A-E rings, left to right). Active-site residues (yellow) that make H-bond/electrostatic contacts with either inhibitor, or the rotated +1 deoxyguanosine, are shown. Oxygen, red; nitrogen, blue; fluorine, magenta. Human topoisomerase I (Top1) plays a pivotal role in cell replication and transcription, and therefore is an important anti-cancer target. Homocamptothecin is a lead compound for inhibiting Top1, and is composed of five conjugated planar rings (A-E). The homocamptothecin E-ring β-hydroxylactone opens slowly to a carboxylate at pH < 7.0. We analyzed, which form of homocamptothecin was biochemically relevant in the following ways: (1) the homocamptothecin carboxylate was tested for activity in vitro and found to be inactive; (2) homocamptothecin was incubated with Top1 and dsDNA, and we found that the homocamptothecin β-hydroxylactone form was stabilized; (3) the homocamptothecin E-ring β-hydroxylactone was modified to prevent opening, and the derivatives were either inactive or had low activity. These results indicated that the homocamptothecin β- hydroxylactone was the active form, and that an E-ring carbonyl oxygen and adjacent unsubstituted/unprotonated ring atom were required for full activity. Homocamptothecin and derivatives were docked into a Top1/DNA active site model, in which the +1 deoxyguanosine was rotated out of the helix, in order to compare the interaction energies between the ligands and the Top1/DNA active site with the in vitro activities of the ligands. It was found that the ligand interaction energies and in vitro activities were correlated, while the orientations of the ligands in the Top1/DNA active site explained the importance of the E-ring β-hydroxylactone independently of E
- Published
- 2004
4. Synthesis and evaluation of a novel E-ring modified α-hydroxy keto ether analogue of camptothecin
- Author
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Du, W, Curran, DP, Bevins, RL, Zimmer, SG, Zhang, J, Burke, TG, Du, W, Curran, DP, Bevins, RL, Zimmer, SG, Zhang, J, and Burke, TG
- Abstract
The synthesis of a novel E-ring modified keto ether analogue of camptothecin and homocamptothecin by the cascade radical annulation route is reported. The analogue, Du1441, is an isomer of homocamptothecin, but includes the α-hydroxy carbonyl functionality that camptothecin possesses and homocamptothecin lacks. Despite these similarities, the new keto ether analogue is inactive in cell assays, and implications for the structure/activity relationship are discussed. Copyright © 2001 Elsevier Science Ltd.
- Published
- 2002
5. A versatile prodrug approach for liposomal core-loading of water-insoluble camptothecin anticancer drugs
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Liu, X, Lynn, BC, Zhang, J, Song, L, Bom, D, Du, W, Curran, DP, Burke, TG, Liu, X, Lynn, BC, Zhang, J, Song, L, Bom, D, Du, W, Curran, DP, and Burke, TG
- Abstract
We describe a versatile prodrug strategy for loading the liposomal lumen with water-insoluble camptothecins. The procedure involves conversion of an active camptothecin analogue to a 20-OR ω-aminoalkanoanic ester prodrug in which R = CO[CH2]nNH2 and n = 1-3. The basic amino group of the prodrug serves three roles. First, at pH ranges of 3-5, the amine enhances aqueous solubility. Second, it enhances responsiveness to a transmembrane ammonium sulfate gradient across the liposomal bilayer, thereby facilitating active loading of the agent into the liposomal aqueous core. Third, at a physiological pH of 7 or above (the pH to be encountered following drug release at the tumor site), the nucleophilicity of the amine manifests itself and cyclization to the C-21 carbonyl carbon occurs. This cyclization triggers a rapid and convenient nonenzymatic decomposition process that releases active camptothecin. Accordingly, this novel liposomal approach offers a potential system for tumor-targeting prodrugs of many water-insoluble camptothecins, including the highly lipophilic and clinically attractive analogues SN-38, 9-nitrocamptothecin and DB-67. The rate of formation of the active agent at the tumor site can be controlled through the selection of n (the length of the alkyl spacer group). Copyright © 2002 American Chemical Society.
- Published
- 2002
6. The highly lipophilic DNA topoisomerase I inhibitor DB-67 displays elevated lactone levels in human blood and potent anticancer activity
- Author
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Bom, D, Curran, DP, Zhang, J, Zimmer, SG, Bevins, R, Kruszewski, S, Howe, JN, Bingcang, A, Latus, LJ, Burke, TG, Bom, D, Curran, DP, Zhang, J, Zimmer, SG, Bevins, R, Kruszewski, S, Howe, JN, Bingcang, A, Latus, LJ, and Burke, TG
- Abstract
The novel silatecan 7-t-butyldimethylsilyl-10-hydroxycamptothecin (DB-67) is 25- to 50-times more lipophilic than camptothecin and readily incorporates into lipid bilayers. Using the method of fluorescence anisotropy titration, we determined that DB-67 bound to small unilamellar vesicles composed of dilaurylphosphatidylcholine (DLPC) with an association constant (K value) of 5000 M-1. This association constant is significantly higher than the KDLPC value observed for camptothecin (KDLPC value of 110 M-1). Using HPLC methods, we demonstrated that the presence of liposomal membranes readily stabilize the lactone form of DB-67. At drug and lipid concentrations of 10 μM and 0.3 mM, respectively, the lactone form of DB-67 persisted in liposome suspension after 3 h of incubation at 37°C. Thus an advantage of a liposomal formulation of DB-67 is that the presence of lipid bilayers assists with stabilizing the key pharmacophore of the agent. The highly lipophilic character of DB-67, in combination with its 10-hydroxy moiety (which functions to enhance lactone stability in the presence of human serum albumin), results in DB-67 having superior stability in human blood with a percent lactone at equilibrium value of 30 [Cancer Res. 59 (1999) 4898; J. Med. Chem. 43 (2000) 3970]. Potent cytotoxicities against a broad range of cancer cells were observed for DB-67, indicating that DB-67 is of comparable potency to camptothecin. The impressive human blood stability and cytotoxicity profiles for DB-67 indicate it is an excellent candidate for comprehensive in vivo pharmacological and efficacy studies. Based on these promising attributes, DB-67 is currently being developed under the NCI RAID program. Due to its potent anti-topoisomerase I activity and its intrinsic blood stability, DB-67 appears as an attractive novel camptothecin for clinical development. © 2001 Elsevier Science B.V. All rights reserved.
- Published
- 2001
7. The novel silatecan 7-tert-butyldimethylsilyl-10-hydroxycamptothecin displays high lipophilicity, improved human blood stability, and potent anticancer activity
- Author
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Bom, D, Curran, DP, Kruszewski, S, Zimmer, SG, Strode, JT, Kohlhagen, G, Du, W, Chavan, AJ, Fraley, KA, Bingcang, AL, Latus, LJ, Pommier, Y, Burke, TG, Bom, D, Curran, DP, Kruszewski, S, Zimmer, SG, Strode, JT, Kohlhagen, G, Du, W, Chavan, AJ, Fraley, KA, Bingcang, AL, Latus, LJ, Pommier, Y, and Burke, TG
- Abstract
We describe the rational design and synthesis of B- and A,B-ring-modified camptothecins. The key α-hydroxy-δ-lactone pharmacophore in 7-tert-butyldimethylsilyl-10-hydroxycamptothecin (DB-67, 14) displays superior stability in human blood when compared with clinically relevant camptothecin analogues. In human blood 14 displayed a t( 1/2 ) of 130 rain and a percent lactone at equilibrium value of 30%. The tert-butyldimethylsilyl group renders the new agent 25-times more lipophilic than camptothecin, and 14 is readily incorporated, as its active lactone form, into cellular and liposomal bilayers. In addition, the dual 7-alkylsilyl and 10-hydroxy substitution in 14 enhances drug stability in the presence of human serum albumin. Thus, the net lipophilicity and the altered human serum albumin interactions together function to promote the enhanced blood stability. In vitro cytotoxicity assays using multiple different cell lines derived from eight distinct tumor types indicate that 14 is of comparable potency to camptothecin and 10-hydroxycamptothecin, as well as the FDA-approved camptothecin analogues topotecan and CPT-11. In addition, cell-free cleavage assays reveal that 14 is highly active and forms more stable top1 cleavage complexes than camptothecin or SN-38. The impressive blood stability and cytotoxicity profiles for 14 strongly suggest that it is an excellent candidate for additional in vivo pharmacological and efficacy studies.
- Published
- 2000
8. Novel A,B,E-ring-modified camptothecins displaying high lipophilicity and markedly improved human blood stabilities [3]
- Author
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Bom, D, Curran, DP, Chavan, AJ, Kruszewski, S, Zimmer, SG, Fraley, KA, Burke, TG, Bom, D, Curran, DP, Chavan, AJ, Kruszewski, S, Zimmer, SG, Fraley, KA, and Burke, TG
- Published
- 1999
9. Potent topoisomerase I inhibition by novel silatecans eliminates glioma proliferation in vitro and in vivo
- Author
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Pollack, IF, Erff, M, Bom, D, Burke, TG, Strode, JT, Curran, DP, Pollack, IF, Erff, M, Bom, D, Burke, TG, Strode, JT, and Curran, DP
- Abstract
Although topoisomerase inhibitors, such as camptothecin and topotecan, have been widely used in the treatment of nonglial tumors, their application for gliomas has been limited by poor efficacy relative to toxicity that may in part reflect limited bioavailability and blood stability of these agents. However, the potential promise of this class of agents has fostered efforts to develop new, more potent, and less toxic inhibitors that may be clinically relevant. Using a cascade radical annulation route to the camptothecin family, we developed a series of novel camptothecin analogues, 7- silylcamptothecins ('silatecans'), that exhibited potent inhibition of topoisomerase I, dramatically improved blood stability, and sufficient lipophilicity to favor blood-brain barrier transit. We explored the efficacy of a series of these agents against a panel of five high-grade glioma cell lines to identify a promising compound for further preclinical testing. One of the most active agents in our systems (DB67) inhibited tumor growth in vitro with an ED50 ranging between 2 and 40 ng/ml, at least 10-fold more potent than the effects observed with topotecan, and at least comparable with those of SN-38, the active metabolite of CPT-11. Because DB67 also exhibited the highest human blood stability of any of the agents examined, this agent was then selected for in vivo studies. A dose-escalation study of this agent in a nude mouse U87 glioma model system demonstrated a concentration- dependent effect, with tumor growth inhibition at day 28 postimplantation (the day control animals began to require sacrifice because of large tumor size) of 61 ± 7% and 73 ± 3% after administration of DB67 doses of 3 and 10 mg/kg/day, respectively, for 5 days beginning on postimplantation day 7. Animals that continued treatment with 10 mg/kg/day in three additional 21-day cycles all remained progression free after >90 days of follow-up but later developed enlarging tumors after treatment was stopped. Howeve
- Published
- 1999
10. Novel A,B,E-ring modified camptothecins displaying high lipophilicity and markedly improved human blood stabilities
- Author
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Bom, D., Du, W., Garbarda, A., Curran, Dp, Chavan, Aj, Stefan Kruszewski, Zimmer, Sg, Fraley, Ka, Bingcang, Al, Wallace, Vp, Tromberg, Bj, and Burke, Tg
11. Evidence for three morphotypes among anadromous Arctic char (Salvelinus alpinus) sampled in the marine environment.
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Burke TG, Pettitt-Wade H, Hollins JPW, Gallagher C, Lea E, Loseto L, and Hussey NE
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- Animals, Trout, Lakes, Climate Change, Seasons, Arctic Regions, Water Pollutants, Chemical analysis
- Abstract
Variable resource use and responses to environmental conditions can lead to phenotypic diversity and distinct morphotypes within salmonids, including Arctic char (Salvelinus alpinus). Despite the cultural and economic importance of Arctic char in the Inuvialuit Settlement Region (ISR), limited data exist on the extent and presence of morphological diversity in this region. This is of concern for management given climate change impacts on regional fish populations. The authors investigated morphological diversity in anadromous Arctic char sampled during their summer marine migration-residency period when seasonal harvesting occurs in a coastal mixed-stock fishery. Geometric morphometric analysis was conducted using digital photographs of live Arctic char (n = 103) of which a sub-set was subsequently implanted with acoustic transmitters (n = 90) and released, and their overwintering lakes determined using active acoustic telemetry surveys. Twenty-three morphological landmarks were established and overlaid on digital images, and nine linear measurements of the body and head were recorded. Principle component analysis and K-means clustering based on linear measurements categorised fish into three morphotypes: slender body and slim head (n = 31), small and short head with a small mouth (n = 46) and elongated head shape with large mouth (n = 26). Tagged individuals of the three morphotypes occupied all lakes with no distinction observed. The three Arctic char morphotypes detected in this coastal mixed-stock fishery could represent adaptation to specific feeding-movement behaviours potentially tied to juvenile residency in freshwater systems, efficient exploitation of the marine prey pulse, or are relicts from ancestral types. To the authors' knowledge, this study is the first to identify distinct Arctic char morphotypes occurring in sympatry in the marine environment. Identifying phenotypic diversity will assist management to promote the sustainability of this regional fishery., (© 2022 Fisheries Society of the British Isles.)
- Published
- 2022
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12. An in vitro study of liposomal curcumin: stability, toxicity and biological activity in human lymphocytes and Epstein-Barr virus-transformed human B-cells.
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Chen C, Johnston TD, Jeon H, Gedaly R, McHugh PP, Burke TG, and Ranjan D
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- Antineoplastic Agents chemistry, Antineoplastic Agents toxicity, B-Lymphocytes metabolism, Cell Line, Transformed, Cell Line, Tumor, Cell Proliferation drug effects, Cholesterol chemistry, Curcumin chemistry, Curcumin toxicity, Dimyristoylphosphatidylcholine chemistry, Dimyristoylphosphatidylcholine toxicity, Drug Stability, Herpesvirus 4, Human drug effects, Herpesvirus 4, Human metabolism, Humans, Liposomes, Lymphocytes metabolism, Phosphatidylglycerols chemistry, Phosphatidylglycerols toxicity, Spleen cytology, Spleen metabolism, Toxicity Tests, Antineoplastic Agents administration & dosage, B-Lymphocytes drug effects, Curcumin administration & dosage, Lymphocytes drug effects
- Abstract
Curcumin is a multi-functional and pharmacologically safe natural agent. Used as a food additive for centuries, it also has anti-inflammatory, anti-virus and anti-tumor properties. We previously found that it is a potent inhibitor of cyclosporin A (CsA)-resistant T-cell co-stimulation pathway. It inhibits mitogen-stimulated lymphocyte proliferation, NFkappaB activation and IL-2 signaling. In spite of its safety and efficacy, the in vivo bioavailability of curcumin is poor, and this may be a major obstacle to its utility as a therapeutic agent. Liposomes are known to be excellent carriers for drug delivery. In this in vitro study, we report the effects of different liposome formulations on curcumin stability in phosphate buffered saline (PBS), human blood, plasma and culture medium RPMI-1640+10% FBS (pH 7.4, 37 degrees C). Liposomal curcumin had higher stability than free curcumin in PBS. Liposomal and free curcumin had similar stability in human blood, plasma and RPMI-1640+10% FBS. We looked at the toxicity of non-drug-containing liposomes on (3)H-thymidine incorporation by concanavalin A (Con A)-stimulated human lymphocytes, splenocytes and Epstein-Barr virus (EBV)-transformed human B-cell lymphoblastoid cell line (LCL). We found that dimyristoylphosphatidylcholine (DMPC) and dimyristoylphosphatidylglycerol (DMPG) were toxic to the tested cells. However, addition of cholesterol to the lipids at DMPC:DMPG:cholesterol=7:1:8 (molar ratio) almost completely eliminated the lipid toxicity to these cells. Liposomal curcumin had similar or even stronger inhibitory effects on Con A-stimulated human lymphocyte, splenocyte and LCL proliferation. We conclude that liposomal curcumin may be useful for intravenous administration to improve the bioavailability and efficacy, facilitating in vivo studies that could ultimately lead to clinical application of curcumin.
- Published
- 2009
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13. Plasma and tissue disposition of non-liposomal DB-67 and liposomal DB-67 in C.B-17 SCID mice.
- Author
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Zamboni WC, Jung LL, Strychor S, Joseph E, Zamboni BA, Fetterman SA, Sidone BJ, Burke TG, Curran DP, and Eiseman JL
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- Animals, Camptothecin pharmacokinetics, Female, Half-Life, Hydroxy Acids blood, Lactones blood, Mice, Mice, SCID, Spleen metabolism, Tissue Distribution, Camptothecin analogs & derivatives, Liposomes pharmacokinetics, Organosilicon Compounds pharmacokinetics
- Abstract
Purpose: DB-67 is a silatecan, 7-silyl-modified camptothecin, with enhanced lipophilicity and increased blood stability of the active-lactone ring. The generation of a liposomal formulation of DB-67 may be an attractive method of intravenous (IV) administration and may maintain DB-67 in the active-lactone form. We evaluated the tissue and plasma disposition of DB-67 lactone and hydroxy acid after administration of non-liposomal (NL) and liposomal (L) DB-67 in severe combined immunodeficient (SCID) mice., Methods: NL-DB-67 and L-DB-67 10 mg/kg IV x 1 were administered via a tail vein in SCID mice. After dosing, mice (n = 3 per time point) were euthanized and blood ( approximately 1 ml) and tissue were collected from 5 min to 48 h after administration. DB-67 lactone and hydroxy acid concentrations in plasma and DB-67 total (sum of lactone and hydroxyl acid) concentrations in tissues were determined by high-performance liquid chromatography (HPLC) with fluorescence detection., Results: Clearance of DB-67 lactone after administration of NL-DB-67 and L-DB-67 were 1.6 and 3.5 l/h/m(2), respectively; DB-67 lactone half-lives after administration of NL-DB-67 and L-DB-67 were 1.4 and 0.9 h, respectively. The percentages of DB-67 lactone in plasma after administration of NL-DB-67 and L-DB-67 were 92% and 89%, respectively. Liver, kidney, spleen, and lung tissues had longer exposure times to DB-67 after administration of L-DB-67 compared with NL-DB-67., Conclusion: In plasma, the majority of DB-67 remained in the lactone form after administration of NL-DB-67 and L-DB-67. The plasma disposition of DB-67 was similar after administration of NL-DB-67 and L-DB-67, suggesting that most of the DB-67 is immediately released from the L-DB-67 formulation. Following administration of L-DB-67, the higher and longer exposure of DB-67 in the spleen, as compared with NL-DB-67, is consistent with splenic clearance of liposomes by the reticuloendothelial system.
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- 2008
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14. Analysis of human topoisomerase I inhibition and interaction with the cleavage site +1 deoxyguanosine, via in vitro experiments and molecular modeling studies.
- Author
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Laco GS, Du W, Kohlhagen G, Sayer JM, Jerina DM, Burke TG, Curran DP, and Pommier Y
- Subjects
- Binding Sites, DNA, Humans, Hydrophobic and Hydrophilic Interactions, Ligands, Nucleic Acid Conformation, Protein Binding, Static Electricity, Thermodynamics, Topoisomerase I Inhibitors, Camptothecin analogs & derivatives, DNA Topoisomerases, Type I chemistry, Deoxyguanosine chemistry, Models, Molecular
- Abstract
Human topoisomerase I (Top1) plays a pivotal role in cell replication and transcription, and therefore is an important anti-cancer target. Homocamptothecin is a lead compound for inhibiting Top1, and is composed of five conjugated planar rings (A-E). The homocamptothecin E-ring beta-hydroxylactone opens slowly to a carboxylate at pH>7.0. We analyzed, which form of homocamptothecin was biochemically relevant in the following ways: (1) the homocamptothecin carboxylate was tested for activity in vitro and found to be inactive; (2) homocamptothecin was incubated with Top1 and dsDNA, and we found that the homocamptothecin beta-hydroxylactone form was stabilized; (3) the homocamptothecin E-ring beta-hydroxylactone was modified to prevent opening, and the derivatives were either inactive or had low activity. These results indicated that the homocamptothecin beta-hydroxylactone was the active form, and that an E-ring carbonyl oxygen and adjacent unsubstituted/unprotonated ring atom were required for full activity. Homocamptothecin and derivatives were docked into a Top1/DNA active site model, in which the +1 deoxyguanosine was rotated out of the helix, in order to compare the interaction energies between the ligands and the Top1/DNA active site with the in vitro activities of the ligands. It was found that the ligand interaction energies and in vitro activities were correlated, while the orientations of the ligands in the Top1/DNA active site explained the importance of the E-ring beta-hydroxylactone independently of E-ring opening. An essential component of this Top1/DNA active site model is the rotated +1 deoxyguanosine, and in vitro experiments and molecular modeling studies supported rotation of the +1 deoxyguanosine out of the helix. These results allow for the rational design of more potent Top1 inhibitors through engineered interactions with as yet unutilized Top1 active-site residues including: Glu356, Asn430, and Lys751.
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- 2004
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15. The effect of DB-67, a lipophilic camptothecin derivative, on topoisomerase I levels in non-small-cell lung cancer cells.
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Bence AK, Mattingly CA, Burke TG, and Adams VR
- Subjects
- Camptothecin chemistry, Drug Screening Assays, Antitumor, Humans, Organosilicon Compounds chemistry, Time Factors, Camptothecin analogs & derivatives, Camptothecin pharmacology, Carcinoma, Non-Small-Cell Lung enzymology, DNA Topoisomerases, Type I metabolism, Lung Neoplasms enzymology, Organosilicon Compounds pharmacology
- Abstract
Purpose: To determine the in vitro drug sensitivity of two non-small-cell lung cancer cell lines after treatment with the novel lipophilic camptothecin derivative, 7- tert-butyldimethylsilyl-10-hydroxycamptothecin (DB-67), to determine if topoisomerase I protein levels decrease after treatment with DB-67, and to assess the duration and extent of topoisomerase I modulation after DB-67 exposure, in order to provide information about drug resistance that may be useful in determining an appropriate dosing schedule for DB-67., Methods: The growth inhibition of the non-small-cell lung cancer cell lines A549 and H460 after exposure to DB-67 was evaluated with the MTS assay. A549 and H460 cells were treated for various times with DB-67 and topoisomerase I levels were determined by western blot analysis. In addition, A549 and H460 cells were treated with DB-67 for 24 h and topoisomerase I levels were determined by western blot analysis daily for 1 week after drug removal., Results: DB-67 inhibited the growth of both A549 and H460 cells grown in culture; the A549 cells were more resistant to the cytotoxic effects of DB-67 than H460 cells. Notably, A549 cells had approximately one-half the baseline topoisomerase I than H460 cells. Topoisomerase I protein levels significantly decreased after 8-18 h of exposure to DB-67. Both A549 and H460 cells treated with DB-67 for 24 h had only negligible amounts of topoisomerase I at the end of treatment. However, within 24 h of drug removal topoisomerase I levels returned to near baseline levels in both cell lines., Conclusions: The decrease in topoisomerase I levels caused by DB-67 may represent a mechanism of resistance to this novel camptothecin derivative. Dosing DB-67 once every 48-72 h may maximize the interaction of the drug with topoisomerase I and should be considered as a potential dosing schedule in the preclinical and clinical development of this compound.
- Published
- 2004
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16. Degradation of camptothecin-20(S)-glycinate ester prodrug under physiological conditions.
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Liu X, Zhang J, Song L, Lynn BC, and Burke TG
- Subjects
- Antineoplastic Agents, Phytogenic blood, Antineoplastic Agents, Phytogenic chemistry, Camptothecin blood, Chromatography, Liquid, Drug Stability, Glycine blood, Hydrogen-Ion Concentration, Hydrolysis, Molecular Structure, Spectrometry, Mass, Electrospray Ionization, Time Factors, Camptothecin analogs & derivatives, Camptothecin chemistry, Glycine analogs & derivatives, Glycine chemistry, Prodrugs chemistry
- Abstract
We have compared the strikingly different decomposition pathways for camptothecin-20(S)-acetate -acetate and camptothecin-20(S)-glycinate in phosphate buffered saline, human plasma and blood. The aliphatic ester analog camptothecin-20(S)-acetate demonstrated excellent stability in the above fluids for many hours with minimal hydrolysis, while the camptothecin-20(S)-glycinate analog (differing solely by the presence of an amino group) underwent rapid and essentially complete decomposition. Reversed-phase high performance liquid chromatography (RP-HPLC) with electrospray ionization-mass spectral (ESI-MS) detection was then used to correlate structural information for camptothecin-20(S)-glycinate decomposition products. ESI-MS detection indicated the ring-opened carboxylate form of camptothecin and the ring-opened degradation product co-elute near the solvent front, while the latest eluting decomposition product was the closed-ring lactone form of camptothecin. A novel decomposition product with intermediate retention time displayed an identical mass-to-charge ratio as camptothecin-20(S)-glycinate ester but a strikingly different fragmentation pattern. The LC-ESI-MS evidence of a novel camptothecin prodrug degradation pathway is provided in this report.
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- 2004
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17. The novel highly lipophilic topoisomerase I inhibitor DB67 is effective in the treatment of liver metastases of murine CT-26 colon carcinoma.
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Lopez-Barcons LA, Zhang J, Siriwitayawan G, Burke TG, and Perez-Soler R
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- Animals, Antineoplastic Agents administration & dosage, Antineoplastic Agents pharmacokinetics, Camptothecin administration & dosage, Camptothecin pharmacokinetics, Cell Line, Tumor, Colonic Neoplasms pathology, Female, Injections, Intraperitoneal, Injections, Intravenous, Irinotecan, Liposomes, Mice, Organosilicon Compounds administration & dosage, Organosilicon Compounds pharmacokinetics, Splenectomy, Tissue Distribution, Antineoplastic Agents therapeutic use, Camptothecin analogs & derivatives, Camptothecin therapeutic use, Carcinoma drug therapy, Carcinoma secondary, Colonic Neoplasms drug therapy, Liver Neoplasms, Experimental drug therapy, Liver Neoplasms, Experimental secondary, Organosilicon Compounds therapeutic use, Topoisomerase I Inhibitors
- Abstract
Colorectal carcinoma occurs in 1 of 20 individuals in most developed countries. The relapse after resection with metastatic liver disease is a major cause of death. 7-t-Butyldimethylsilyl-10-hydroxycamptothecin (DB67) has been incorporated into liposomes allowing for intravenous (i.v.) administration. A preclinical efficacy study of liposomal DB67 was performed using the colon carcinoma CT-26 cell line. The therapeutic dose for DB67 and liposomal DB67 was found to be 7 mg/kg per day using the qdx5/1 schedule. The results are compared with those obtained with irinotecan. The treatment with liposomal DB67 administered intravenously was more effective in reducing the weight and volume of primary spleen tumors and the weight and extent of liver metastases than free DB67 or liposomal DB67 administered intraperitoneally, but less effective than irinotecan. When the primary tumor was resected, treatment with liposomal DB67 administered intravenously was more effective in reducing the weight and extent of liver metastases than DB67 or liposomal DB67 administered intraperitoneally, and irinotecan. DB67 showed a higher accumulation in spleen and liver after its i.v. administration in liposomal form compared with its free or liposomal form administered intraperitoneally. DB67 and liposomal DB67 are more effective than irinotecan in the treatment of liver metastases after resection of the primary tumor.
- Published
- 2004
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18. Determination of 9-nitrocamptothecin by precolumn derivatization and its metabolite 9-aminocamptothecin in a biological fluid using reversed-phase high-performance liquid chromatography with fluorescence detection.
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Zhang J, Burke TG, and Latus LJ
- Subjects
- Animals, Calibration, Dogs, Reproducibility of Results, Sensitivity and Specificity, Camptothecin analogs & derivatives, Camptothecin blood, Chromatography, High Pressure Liquid methods, Spectrometry, Fluorescence methods
- Abstract
A novel insoluble topoisomerase I inhibitor, 9-nitrocamptothecin (9-NC), is in advanced stages of clinical development and has been used to treat a diverse array of tumor types, including breast, ovarian, pancreatic and haematological malignancies. We have established a sensitive high-performance liquid chromatography method using fluorescence detection for the quantitation of 9-NC. Non-fluorescent 9-NC is converted to fluorescent 9-aminocamptothecin (9-AC) via a one-step pre-column derivative reaction. The quantitative limit of 9-NC was 1 ng/ml and the method was reproducible with the respective intra- and inter-day variability falling below 5.0 and 9.0%. The determination of both 9-NC and its metabolite 9-AC in dog plasma was also achieved using the same chromatographic and detection conditions. In dog plasma, the quantitative limits of 9-AC and 9-NC were 0.25 and 1 ng/ml, respectively. The presence of 9-AC in the samples yielded no interference with the determination of 9-NC. However, individual matrices can affect the conversion efficiency of 9-NC, thus indicating that standard samples should be run for each matrix.
- Published
- 2003
- Full Text
- View/download PDF
19. A versatile prodrug approach for liposomal core-loading of water-insoluble camptothecin anticancer drugs.
- Author
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Liu X, Lynn BC, Zhang J, Song L, Bom D, Du W, Curran DP, and Burke TG
- Subjects
- Antineoplastic Agents, Phytogenic administration & dosage, Camptothecin administration & dosage, Camptothecin chemistry, Drug Carriers chemistry, Liposomes chemistry, Prodrugs administration & dosage, Solubility, Water chemistry, Antineoplastic Agents, Phytogenic chemistry, Camptothecin analogs & derivatives, Prodrugs chemistry
- Abstract
We describe a versatile prodrug strategy for loading the liposomal lumen with water-insoluble camptothecins. The procedure involves conversion of an active camptothecin analogue to a 20-OR omega-aminoalkanoanic ester prodrug in which R = CO[CH(2)](n)()NH(2) and n = 1-3. The basic amino group of the prodrug serves three roles. First, at pH ranges of 3-5, the amine enhances aqueous solubility. Second, it enhances responsiveness to a transmembrane ammonium sulfate gradient across the liposomal bilayer, thereby facilitating active loading of the agent into the liposomal aqueous core. Third, at a physiological pH of 7 or above (the pH to be encountered following drug release at the tumor site), the nucleophilicity of the amine manifests itself and cyclization to the C-21 carbonyl carbon occurs. This cyclization triggers a rapid and convenient nonenzymatic decomposition process that releases active camptothecin. Accordingly, this novel liposomal approach offers a potential system for tumor-targeting prodrugs of many water-insoluble camptothecins, including the highly lipophilic and clinically attractive analogues SN-38, 9-nitrocamptothecin and DB-67. The rate of formation of the active agent at the tumor site can be controlled through the selection of n (the length of the alkyl spacer group).
- Published
- 2002
- Full Text
- View/download PDF
20. Synthesis and evaluation of a novel E-ring modified alpha-hydroxy keto ether analogue of camptothecin.
- Author
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Du W, Curran DP, Bevins RL, Zimmer SG, Zhang J, and Burke TG
- Subjects
- Camptothecin chemical synthesis, Camptothecin pharmacology, Chromatography, High Pressure Liquid, Ethers chemistry, Humans, Molecular Structure, Spectrum Analysis, Tumor Cells, Cultured, Antineoplastic Agents, Phytogenic chemical synthesis, Antineoplastic Agents, Phytogenic pharmacology, Camptothecin analogs & derivatives
- Abstract
The synthesis of a novel E-ring modified keto ether analogue of camptothecin and homocamptothecin by the cascade radical annulation route is reported. The analogue, Du1441, is an isomer of homocamptothecin, but includes the alpha-hydroxy carbonyl functionality that camptothecin possesses and homocamptothecin lacks. Despite these similarities, the new keto ether analogue is inactive in cell assays, and implications for the structure/activity relationship are discussed.
- Published
- 2002
- Full Text
- View/download PDF
21. The highly lipophilic DNA topoisomerase I inhibitor DB-67 displays elevated lactone levels in human blood and potent anticancer activity.
- Author
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Bom D, Curran DP, Zhang J, Zimmer SG, Bevins R, Kruszewski S, Howe JN, Bingcang A, Latus LJ, and Burke TG
- Subjects
- Anisotropy, Antineoplastic Agents, Phytogenic chemistry, Camptothecin chemistry, Camptothecin therapeutic use, Chemical Phenomena, Chemistry, Physical, Chromatography, High Pressure Liquid, Drug Screening Assays, Antitumor, Enzyme Inhibitors chemistry, Humans, Lipid Bilayers, Organosilicon Compounds chemistry, Spectrometry, Fluorescence, Tumor Cells, Cultured, Antineoplastic Agents, Phytogenic pharmacology, Camptothecin analogs & derivatives, Camptothecin pharmacology, Enzyme Inhibitors pharmacology, Lactones blood, Organosilicon Compounds pharmacology, Topoisomerase I Inhibitors
- Abstract
The novel silatecan 7-t-butyldimethylsilyl-10-hydroxycamptothecin (DB-67) is 25- to 50-times more lipophilic than camptothecin and readily incorporates into lipid bilayers. Using the method of fluorescence anisotropy titration, we determined that DB-67 bound to small unilamellar vesicles composed of dilaurylphosphatidylcholine (DLPC) with an association constant (K value) of 5000 M(-1). This association constant is significantly higher than the K(DLPC) value observed for camptothecin (K(DLPC) value of 110 M(-1)). Using HPLC methods, we demonstrated that the presence of liposomal membranes readily stabilize the lactone form of DB-67. At drug and lipid concentrations of 10 microM and 0.3 mM, respectively, the lactone form of DB-67 persisted in liposome suspension after 3 h of incubation at 37 degrees C. Thus an advantage of a liposomal formulation of DB-67 is that the presence of lipid bilayers assists with stabilizing the key pharmacophore of the agent. The highly lipophilic character of DB-67, in combination with its 10-hydroxy moiety (which functions to enhance lactone stability in the presence of human serum albumin), results in DB-67 having superior stability in human blood with a percent lactone at equilibrium value of 30 [Cancer Res. 59 (1999) 4898; J. Med. Chem. 43 (2000) 3970]. Potent cytotoxicities against a broad range of cancer cells were observed for DB-67, indicating that DB-67 is of comparable potency to camptothecin. The impressive human blood stability and cytotoxicity profiles for DB-67 indicate it is an excellent candidate for comprehensive in vivo pharmacological and efficacy studies. Based on these promising attributes, DB-67 is currently being developed under the NCI RAID program. Due to its potent anti-topoisomerase I activity and its intrinsic blood stability, DB-67 appears as an attractive novel camptothecin for clinical development.
- Published
- 2001
- Full Text
- View/download PDF
22. Images in preventive medicine. Cause and effect.
- Author
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Lowenstein SR, Burke TG, Stone S, and Orzel JA
- Subjects
- Aged, Humans, Male, Ultrasonography, Carcinoma, Squamous Cell diagnostic imaging, Lung Neoplasms diagnostic imaging, Tomography, X-Ray Computed
- Published
- 2001
- Full Text
- View/download PDF
23. The novel silatecan 7-tert-butyldimethylsilyl-10-hydroxycamptothecin displays high lipophilicity, improved human blood stability, and potent anticancer activity.
- Author
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Bom D, Curran DP, Kruszewski S, Zimmer SG, Thompson Strode J, Kohlhagen G, Du W, Chavan AJ, Fraley KA, Bingcang AL, Latus LJ, Pommier Y, and Burke TG
- Subjects
- Animals, Antineoplastic Agents chemistry, Antineoplastic Agents pharmacology, Camptothecin chemistry, Camptothecin pharmacology, DNA drug effects, Drug Screening Assays, Antitumor, Drug Stability, Electrophoresis, Agar Gel, Humans, Hydrolysis, Kinetics, Mice, Mice, Nude, Organosilicon Compounds chemistry, Organosilicon Compounds pharmacology, Spectrometry, Fluorescence, Structure-Activity Relationship, Tumor Cells, Cultured, Antineoplastic Agents chemical synthesis, Camptothecin analogs & derivatives, Camptothecin chemical synthesis, Organosilicon Compounds chemical synthesis
- Abstract
We describe the rational design and synthesis of B- and A, B-ring-modified camptothecins. The key alpha-hydroxy-delta-lactone pharmacophore in 7-tert-butyldimethylsilyl-10-hydroxycamptothecin (DB-67, 14) displays superior stability in human blood when compared with clinically relevant camptothecin analogues. In human blood 14 displayed a t(1/2) of 130 min and a percent lactone at equilibrium value of 30%. The tert-butyldimethylsilyl group renders the new agent 25-times more lipophilic than camptothecin, and 14 is readily incorporated, as its active lactone form, into cellular and liposomal bilayers. In addition, the dual 7-alkylsilyl and 10-hydroxy substitution in 14 enhances drug stability in the presence of human serum albumin. Thus, the net lipophilicity and the altered human serum albumin interactions together function to promote the enhanced blood stability. In vitro cytotoxicity assays using multiple different cell lines derived from eight distinct tumor types indicate that 14 is of comparable potency to camptothecin and 10-hydroxycamptothecin, as well as the FDA-approved camptothecin analogues topotecan and CPT-11. In addition, cell-free cleavage assays reveal that 14 is highly active and forms more stable top1 cleavage complexes than camptothecin or SN-38. The impressive blood stability and cytotoxicity profiles for 14 strongly suggest that it is an excellent candidate for additional in vivo pharmacological and efficacy studies.
- Published
- 2000
- Full Text
- View/download PDF
24. Treatment of thoracic disc herniation: evolution toward the minimally invasive thoracoscopic technique.
- Author
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Burke TG and Caputy AJ
- Subjects
- Animals, Diskectomy trends, Humans, Intervertebral Disc anatomy & histology, Intervertebral Disc diagnostic imaging, Intervertebral Disc Displacement diagnosis, Intervertebral Disc Displacement physiopathology, Minimally Invasive Surgical Procedures adverse effects, Minimally Invasive Surgical Procedures trends, Postoperative Complications etiology, Postoperative Complications physiopathology, Postoperative Complications prevention & control, Radiography, Thoracic Vertebrae anatomy & histology, Thoracic Vertebrae diagnostic imaging, Thoracoscopy adverse effects, Thoracoscopy trends, Treatment Outcome, Diskectomy instrumentation, Diskectomy methods, Intervertebral Disc surgery, Intervertebral Disc Displacement surgery, Minimally Invasive Surgical Procedures methods, Thoracic Vertebrae surgery, Thoracoscopy methods
- Abstract
Thoracic disc herniation has always carried with it the potential for serious adverse neurological consequences if not treated appropriately. The authors review the historical evolution of treatment for thoracic disc herniation from the early surgical series using dorsal approaches (which were known to involve a significant risk of paraplegia) to later surgical series in which lateral and then ventral approaches to the disc were increasingly emphasized, with significant improvement in patient outcome. The evolution of minimally invasive thoracoscopic techniques is discussed, together with the results of several surgical series demonstrating significant reductions in morbidity compared with more traditional methods. The technique of thoracoscopic discectomy is presented in detail.
- Published
- 2000
- Full Text
- View/download PDF
25. Microendoscopic posterior cervical foraminotomy: a cadaveric model and clinical application for cervical radiculopathy.
- Author
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Burke TG and Caputy A
- Subjects
- Adult, Cadaver, Decompression, Surgical, Endoscopes, Feasibility Studies, Hospitalization, Humans, Intervertebral Disc Displacement complications, Intraoperative Care, Length of Stay, Male, Micromanipulation instrumentation, Micromanipulation methods, Middle Aged, Minimally Invasive Surgical Procedures instrumentation, Minimally Invasive Surgical Procedures methods, Pain, Postoperative prevention & control, Radiculopathy etiology, Recovery of Function, Spinal Nerve Roots surgery, Spinal Stenosis complications, Cervical Vertebrae surgery, Endoscopy, Radiculopathy surgery
- Abstract
Object: Cervical radiculopathy caused by either soft herniated disc material or foraminal stenosis is a common problem. Anterior and posterior surgical approaches are commonly used to decompress the nerve root. The authors undertook a study to establish the feasibility of performing a microendoscopic posterior approach for cervical foraminotomy in the clinical setting., Methods: The authors performed an endoscopic posterior foraminotomy technique in which they used a rigid endoscope, in both a cadaver model and in three clinical cases, including one in which a multiple-level procedure was undertaken. Postoperatively, all patients returned to functional work status within 4 weeks. The mean length of hospitalization was 1.3 days., Conclusions: The advantages to this technique include improved intraoperative visualization, a smaller incision, and significantly less postoperative discomfort compared with a traditional keyhole approach.
- Published
- 2000
- Full Text
- View/download PDF
26. Camptothecin design and delivery approaches for elevating anti-topoisomerase I activities in vivo.
- Author
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Burke TG and Bom D
- Subjects
- Animals, Antineoplastic Agents, Phytogenic pharmacokinetics, Camptothecin administration & dosage, Camptothecin pharmacokinetics, Drug Design, Drug Stability, Enzyme Inhibitors pharmacokinetics, Humans, Liposomes, Structure-Activity Relationship, Antineoplastic Agents, Phytogenic administration & dosage, Antineoplastic Agents, Phytogenic chemistry, Camptothecin analogs & derivatives, Enzyme Inhibitors administration & dosage, Enzyme Inhibitors chemistry, Topoisomerase I Inhibitors
- Abstract
The camptothecins as a class have exhibited unique dynamics and reactivity in vivo, with respect to both drug hydrolysis and blood protein interactions. These factors have confounded their pharmaceutical development and clinical implementation. Recent bench and clinical research alike indicates that the combination of medicinal chemical and drug delivery approaches has been and will continue to be highly valuable in improving the overall therapeutic indices of camptothecin-based anti-topoisomerase I therapies. In the future the development of camptothecin analogues that exhibit highly specific human albumin interactions will likely be avoided, and agents such as the highly lipophilic DB-67 analogue with improved tissue stability will be evaluated. Drug delivery scientists will also devise better ways of targeting camptothecin therapies to solid tumors by using carriers such as tumor-targeted long-circulating liposomes.
- Published
- 2000
- Full Text
- View/download PDF
27. Lack of latex allergen contamination of solutions withdrawn from vials with natural rubber stoppers.
- Author
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Thomsen DJ and Burke TG
- Subjects
- Drug Compounding, Drug Contamination, Allergens analysis, Drug Packaging, Latex analysis, Latex Hypersensitivity prevention & control, Pharmaceutical Solutions analysis
- Abstract
The effect on latex allergen contamination and microbial growth of a latex-allergy precaution technique for preparing injectable products was studied. The study consisted of three parts: (1) preparation of 20 samples from vials with latex-containing stoppers in accordance with conventional guidelines, (2) preparation of 20 samples in accordance with latex-allergy precaution guidelines, and (3) preparation of 5 latex-free samples and 1 latex-contaminated sample as negative and positive controls, respectively. The conventional method involved swabbing a vial top with an alcohol prep pad, puncturing the dry natural rubber stopper with an 18-gauge needle attached to a latex-free syringe, and withdrawing the contents of the vial into the syringe. The latex-allergy precaution preparation technique was similar, except that the stopper was removed before the vial contents were withdrawn. There was essentially no difference in latex allergen concentrations between the two drug preparation methods. None of the samples prepared with the standard method supported any microbial growth. One sample prepared with the latex-allergy precaution method grew bacteria. Removal of the dry rubber stopper from vials did not yield solutions with less latex allergen than solutions prepared according to conventional guidelines.
- Published
- 2000
- Full Text
- View/download PDF
28. Potent topoisomerase I inhibition by novel silatecans eliminates glioma proliferation in vitro and in vivo.
- Author
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Pollack IF, Erff M, Bom D, Burke TG, Strode JT, and Curran DP
- Subjects
- Animals, Antineoplastic Agents, Phytogenic toxicity, Camptothecin toxicity, Cell Division drug effects, Cell Survival drug effects, Genes, p53, Humans, Irinotecan, Mice, Mice, Nude, Mutation, Structure-Activity Relationship, Topotecan therapeutic use, Topotecan toxicity, Transplantation, Heterologous, Tumor Cells, Cultured, Antineoplastic Agents, Phytogenic therapeutic use, Camptothecin analogs & derivatives, Camptothecin therapeutic use, Glioma drug therapy, Glioma pathology, Topoisomerase I Inhibitors
- Abstract
Although topoisomerase inhibitors, such as camptothecin and topotecan, have been widely used in the treatment of nonglial tumors, their application for gliomas has been limited by poor efficacy relative to toxicity that may in part reflect limited bioavailability and blood stability of these agents. However, the potential promise of this class of agents has fostered efforts to develop new, more potent, and less toxic inhibitors that may be clinically relevant. Using a cascade radical annulation route to the camptothecin family, we developed a series of novel camptothecin analogues, 7-silylcamptothecins ("silatecans"), that exhibited potent inhibition of topoisomerase I, dramatically improved blood stability, and sufficient lipophilicity to favor blood-brain barrier transit. We explored the efficacy of a series of these agents against a panel of five high-grade glioma cell lines to identify a promising compound for further preclinical testing. One of the most active agents in our systems (DB67) inhibited tumor growth in vitro with an ED50 ranging between 2 and 40 ng/ml, at least 10-fold more potent than the effects observed with topotecan, and at least comparable with those of SN-38, the active metabolite of CPT-11. Because DB67 also exhibited the highest human blood stability of any of the agents examined, this agent was then selected for in vivo studies. A dose-escalation study of this agent in a nude mouse U87 glioma model system demonstrated a concentration-dependent effect, with tumor growth inhibition at day 28 postimplantation (the day control animals began to require sacrifice because of large tumor size) of 61 +/- 7% and 73 +/- 3% after administration of DB67 doses of 3 and 10 mg/kg/day, respectively, for 5 days beginning on postimplantation day 7. Animals that continued treatment with 10 mg/kg/day in three additional 21-day cycles all remained progression free after >90 days of follow-up but later developed enlarging tumors after treatment was stopped. However, a slightly higher dose (30 mg/kg/day) induced complete tumor regression after only two cycles in all study animals and was effective even if treatment was delayed until large, bulky tumors had developed. Application of the 30 mg/kg/day dose to treat established intracranial glioma xenografts led to long-term (>90 day) survival in six of six animals, whereas all controls died of progressive disease (P < 0.00001). No apparent toxicity was encountered in any of the treated animals. In summary, the present studies indicate that silatecans may hold significant promise for the treatment of high-grade gliomas and provide a rationale for proceeding with further preclinical evaluation of their efficacy and safety versus commercially available camptothecin derivatives.
- Published
- 1999
29. Novel A,B,E-ring-modified camptothecins displaying high lipophilicity and markedly improved human blood stabilities.
- Author
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Bom D, Curran DP, Chavan AJ, Kruszewski S, Zimmer SG, Fraley KA, and Burke TG
- Subjects
- Camptothecin blood, Camptothecin chemistry, Chromatography, High Pressure Liquid, Dimyristoylphosphatidylcholine chemistry, Drug Stability, Enzyme Inhibitors chemistry, Enzyme Inhibitors pharmacology, Fluorescence Polarization, Humans, Hydrolysis, Phosphatidylglycerols chemistry, Spectrometry, Fluorescence, Structure-Activity Relationship, Camptothecin analogs & derivatives, Camptothecin chemical synthesis, Enzyme Inhibitors chemical synthesis, Topoisomerase I Inhibitors
- Published
- 1999
- Full Text
- View/download PDF
30. Fluorescence spectral properties of the anticancer drug topotecan by steady-state and frequency domain fluorometry with one-photon and multi-photon excitation.
- Author
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Gryczynski I, Gryczynski Z, Lakowicz JR, Yang D, and Burke TG
- Subjects
- Antineoplastic Agents metabolism, DNA metabolism, Fluorescence Polarization, Humans, In Vitro Techniques, Photochemistry, Photons, Spectrometry, Fluorescence, Topotecan metabolism, Antineoplastic Agents chemistry, Antineoplastic Agents radiation effects, Topotecan chemistry, Topotecan radiation effects
- Abstract
Topotecan is an antitumor agent with activity against a variety of cancers. We examined the steady-state and time-resolved fluorescence spectral properties of topotecan with one- and two-photon excitation. Topotecan was found to display a high two-photon cross section near 20 GM for wavelengths within the fundamental output of a Ti:sapphire laser, 800-880 nm. In frozen solution the anisotropies of topotecan are near the theoretical maxima for one-photon and two-photon excitation with colinear electronic transitions. The intensity and anisotropy decays of topotecan fluorescence were found to be homogeneous (single exponentials) in phosphate-buffered saline and propylene glycol. The steady-state and time-resolved data indicate that topotecan binds to a double-helical DNA oligomer d(AT)10 resulting in increased anisotropies and multiexponential intensity and anisotropy decays. Subnanosecond components in the anisotropy decay of the DNA-topotecan complex suggest loose binding of the drug to DNA. Loose binding of topotecan to DNA is also revealed by accessibility of topotecan to collisional quenching by iodide.
- Published
- 1999
31. The acidic microclimate in poly(lactide-co-glycolide) microspheres stabilizes camptothecins.
- Author
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Shenderova A, Burke TG, and Schwendeman SP
- Subjects
- Drug Carriers, Drug Interactions, Electrodes, Fluorescent Dyes, Hydrogen-Ion Concentration, Lactones chemistry, Magnesium Hydroxide chemistry, Microclimate, Microspheres, Polyglactin 910 chemistry, Water chemistry, Antineoplastic Agents chemistry, Camptothecin analogs & derivatives, Camptothecin chemistry, Drug Stability
- Abstract
Purpose: The camptothecin (CPT) analogue, 10-hydroxycamptothecin (10-HCPT) has been shown previously to remain in its acid-stable (and active) lactone form when encapsulated in poly(lactide-co-glycolide) (PLGA) microspheres (1). The purpose of this study was to determine the principal mechanism(s) of 10-HCPT stabilization., Methods: CPTs were encapsulated in PLGA 50:50 microspheres by standard solvent evaporation techniques. Microspheres were eroded in pH 7.4 buffer at 37 degrees C. The ratio of encapsulated lactone to carboxylate was determined by HPLC as a function of time, initial form of drug encapsulated, fraction of co-encapsulated Mg(OH)2, CPT lipophilicity, and drug loading. Two techniques were developed to assess the microclimate pH, including: i) measurement of H+ content of the dissolved microspheres in an 80:20 acetonitrile/H2O mixture and ii) confocal microscopy of an encapsulated pH-sensitive dye, fluorescein., Results: The encapsulated carboxylate converted rapidly to the lactone after exposure to the release media, indicating the lactone is favored at equilibrium in the microspheres. Upon co-encapsulation of Mg(OH)2, the trend was reversed, i.e., the lactone rapidly converted to the carboxylate form. Measurement of -log(hydronium ion activity) (paH*) of dissolved microspheres with pH-electrode and pH mapping with fluorescein revealed the presence of an acidic microclimate. From the measurements of H+ and water contents of particles hydrated for 3 days, a microclimate pH was estimated to be in the neighborhood of 1.8. The co-encapsulation of Mg(OH)2 could both increase the paH* reading and neutralize pH in various regions of the microsphere interior. Varying the drug lipophilicity and loading revealed that the precipitation of the lactone could also stabilize CPT., Conclusions: PLGA microspheres prepared by the standard solvent evaporation techniques develop an acidic microclimate that stabilizes the lactone form of CPTs. This microclimate may be neutralized by co-encapsulating a base such as Mg(OH)2, as suggested by previous work with poly(ortho esters) (2).
- Published
- 1999
- Full Text
- View/download PDF
32. Phase I and pharmacokinetic study of GI147211, a water-soluble camptothecin analogue, administered for five consecutive days every three weeks.
- Author
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Eckhardt SG, Baker SD, Eckardt JR, Burke TG, Warner DL, Kuhn JG, Rodriguez G, Fields S, Thurman A, Smith L, Rothenberg ML, White L, Wissel P, Kunka R, DePee S, Littlefield D, Burris HA, Von Hoff DD, and Rowinsky EK
- Subjects
- Adult, Aged, Antineoplastic Agents administration & dosage, Camptothecin administration & dosage, Camptothecin adverse effects, Camptothecin pharmacokinetics, Drug Administration Schedule, Female, Humans, Infusions, Intravenous, Male, Middle Aged, Neoplasms blood, Neutropenia chemically induced, Thrombocytopenia chemically induced, Antineoplastic Agents adverse effects, Antineoplastic Agents pharmacokinetics, Camptothecin analogs & derivatives, Neoplasms drug therapy
- Abstract
GI1147211 is a 7-substituted 10,11-ethylenedioxy-20(S)-camptothecin analogue that inhibits the nuclear enzyme topoisomerase I. In this Phase I and pharmacological study, 24 patients with advanced solid malignancies received a total of 72 courses of GI147211 as a 30-min infusion daily for 5 consecutive days, at doses ranging from 0.3 to 1.75 mg/m2/day. Severe neutropenia precluded dose escalation above 1.5 mg/m2/day in minimally pretreated patients, and both severe neutropenia and thrombocytopenia were dose limiting in heavily pretreated patients at doses above 1.0 mg/m2/day. These doses are, therefore, recommended for subsequent Phase II evaluations of GI147211 in patients with comparable prior therapy. Nonhematological toxicities, including nausea, vomiting, fatigue, and anorexia, were mild to moderate. The disposition of GI147211 in blood was described by a linear three-compartment model, with renal elimination accounting for only 11% of drug distribution. No relationship was observed between the pharmacological exposure to GI147211 and effects on neutrophils; however, patients who developed dose-limiting myelosuppression did experience greater exposure to both the lactone and total forms of the drug. The hydrolysis kinetics of GI147211 revealed not only a shift of the drug to the inactive carboxylate form in human serum albumin but also stabilization of the lactone in erythrocytes, perhaps accounting for the observed lactone:total area under the concentration-time curve ratio of 0.27. These results indicate that GI147211 exhibits predictable toxicities and that further studies are warranted to determine the distinct role of this compound among currently available camptothecin analogues.
- Published
- 1998
33. Stabilization of 10-hydroxycamptothecin in poly(lactide-co-glycolide) microsphere delivery vehicles.
- Author
-
Shenderova A, Burke TG, and Schwendeman SP
- Subjects
- Antineoplastic Agents, Phytogenic administration & dosage, Camptothecin administration & dosage, Camptothecin chemistry, Delayed-Action Preparations, Drug Stability, Microscopy, Confocal, Microscopy, Electron, Scanning, Microspheres, Molecular Weight, Pharmaceutical Vehicles, Polylactic Acid-Polyglycolic Acid Copolymer, Antineoplastic Agents, Phytogenic chemistry, Camptothecin analogs & derivatives, Lactic Acid chemistry, Polyglycolic Acid chemistry, Polymers chemistry
- Abstract
Purpose: The purpose of this study was to investigate the potential of poly(lactide-co-glycolide) (PLGA) microspheres to stabilize and deliver the analogue of camptothecin, 10-hydroxycamptothecin (10-HCPT)., Methods: 10-HCPT was encapsulated in PLGA 50:50 microspheres by using an oil-in-water emulsion-solvent evaporation method. The influence of encapsulation conditions (i.e., polymer molecular weight (Mw), polymer concentration, and carrier solvent composition) on the release of 10-HCPT from microspheres at 37 degrees C under perfect sink conditions was examined. Analysis of the drug stability in the microspheres was performed by two methods: i) by extraction of 10-HCPT from microspheres and ii) by sampling release media before lactone--carboxylate conversion could take place., Results: Microspheres made of low Mw polymer (inherent viscosity 0.15 dl/g) exhibited more continuous drug release than those prepared from polymers of higher Mw (i.v. = 0.58 and 1.07 dl/g). In addition, a high polymer concentration and the presence of cosolvent in the carrier solution to dissolve 10-HCPT were both necessary in the microsphere preparation in order to eliminate a large initial burst of the released 10-HCPT. An optimal microsphere formulation released 10-HCPT slowly and continuously for over two months with a relatively small initial burst of the released drug. Both analytical methods used to assess the stability of 10-HCPT revealed that the unreleased camptothecin analogue in the microspheres remained in its active lactone form (> 95%) over the entire 2-month duration of study., Conclusions: PLGA carriers such as those described here may be clinically useful to stabilize and deliver camptothecins for the treatment of cancer.
- Published
- 1997
- Full Text
- View/download PDF
34. Simple and versatile high-performance liquid chromatographic method for the simultaneous quantitation of the lactone and carboxylate forms of camptothecin anticancer drugs.
- Author
-
Warner DL and Burke TG
- Subjects
- Acetonitriles, Buffers, Camptothecin analogs & derivatives, Ethylamines, Humans, Hydrogen-Ion Concentration, Irinotecan, Osmolar Concentration, Topotecan, Antineoplastic Agents, Phytogenic blood, Camptothecin blood, Carboxylic Acids blood, Chromatography, High Pressure Liquid methods, Lactones blood
- Abstract
The well documented hydrolysis of the alpha-hydroxy-delta-lactone ring moiety in camptothecin and related analogues is routinely monitored using high-performance liquid chromatography (HPLC). Previous HPLC separations of the lactone and carboxylate forms of camptothecins have often required mobile phases containing three to four components; ion-pairing reagent to provide adequate retention of the carboxylate form of the drug; buffer to control the ionic strength and pH of the mobile phase; acetonitrile to control the retention of the lactone form and, in some instances, sodium dodecyl sulfate to reduce peak tailing. Because of the complexity of the mobile phases employed, development of these assays can be a laborious process, requiring re-optimization for each new analogue. In this study, we have developed a simple HPLC methodology for the simultaneous separation of the lactone and carboxylate forms of numerous camptothecin analogues. The mobile phase employed includes only triethylamine acetate (TEAA) buffer and acetonitrile. In this application, triethylamine serves multiple roles; as the ion-pairing reagent, as a masking agent for underivatized silanols and as the major buffer component. By altering only the composition of TEAA buffer with respect to acetonitrile, method development becomes a more streamlined and time efficient process. In this publication, we present the simultaneous separation of the lactone and carboxylate forms of camptothecin and four related analogues, namely, topotecan, GI147211, 10-aminocamptothecin and the CPT-11-SN-38 drug-metabolite pair. It is proposed that this new mobile phase, consisting of only triethylamine acetate buffer and acetonitrile, can be used for the analysis of the several camptothecin derivatives presently in clinical trials as well as the numerous other analogues in preclinical development.
- Published
- 1997
- Full Text
- View/download PDF
35. Drug allergy assessment at a university hospital and clinic.
- Author
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Pilzer JD, Burke TG, and Mutnick AH
- Subjects
- Adolescent, Adult, Aged, Documentation, Drug Hypersensitivity classification, Drug Monitoring, Female, Hospitals, Teaching, Humans, Male, Middle Aged, Pharmacy Service, Hospital, Drug Hypersensitivity diagnosis, Pharmacists
- Abstract
The accuracy of drug allergies reported in patients' medical records and the cost-effectiveness of pharmacist interviews to clarify these reports were studied. Fourteen pharmacists interviewed hospital and clinical patients about reported allergies and noted their assessments in the patients' charts. The patient's physician was notified of discrepancies between previous allergy documentation and the pharmacist's assessment. The pharmacy resident re-interviewed a convenience sample of the patients to determine consistency among the pharmacists. The reported reactions were classified as true allergies, severe adverse effects, or vague reactions (drug should be avoided); drug intolerance and mild or moderate adverse effects; excessive pharmacologic effects; or no reaction experienced. The medication profile for each patient was reviewed after discharge to identify the pharmacists' prevention of adverse effects or allergic reactions; cost avoidance was then estimated. The pharmacists assessed 347 reports of allergies in 195 patients. Anti-infective agents accounted for 53% of the stated allergies, followed by narcotics (18%), psychotropic medications (7%), nonsteroidal anti-inflammatory drugs (6%), cardiovascular medications (5%), and others (11%). For more than 80% of the reports of allergies to beta-lactam antibiotics and sulfonamides, pharmacists either found or could not rule out true allergies; this was the case for only 31% of reported allergies to narcotics. Nine percent of patients who reported allergy to a beta-lactam or sulfonamide had never experienced a reaction to the drug. Pharmacists intervened in four cases to prevent adverse reactions and a total of 4.4 additional hospital days, and in five instances the use of a less suitable or more expensive drug was avoided. Pharmacists found a large discrepancy between reported allergies and true allergies and helped prevent uses of drugs that could have prolonged patients' hospital stay.
- Published
- 1996
- Full Text
- View/download PDF
36. Chemistry of the camptothecins in the bloodstream. Drug stabilization and optimization of activity.
- Author
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Burke TG
- Subjects
- Antineoplastic Agents, Phytogenic chemistry, Antineoplastic Agents, Phytogenic pharmacokinetics, Camptothecin analogs & derivatives, Camptothecin chemistry, Camptothecin pharmacokinetics, Humans, Lactones blood, Antineoplastic Agents, Phytogenic blood, Camptothecin blood
- Published
- 1996
- Full Text
- View/download PDF
37. Fluorescence detection of the anticancer drug topotecan in plasma and whole blood by two-photon excitation.
- Author
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Burke TG, Malak H, Gryczynski I, Mi Z, and Lakowicz JR
- Subjects
- Antineoplastic Agents chemistry, Camptothecin blood, Camptothecin chemistry, Chemistry Techniques, Analytical methods, Humans, Infrared Rays, Lasers, Male, Photons, Plasma chemistry, Skin blood supply, Topotecan, Antineoplastic Agents blood, Blood Chemical Analysis methods, Camptothecin analogs & derivatives, Spectrometry, Fluorescence methods
- Abstract
The anticancer drug topotecan was detected in human plasma and whole blood using two-photon excitation at 730 or 820 nm. These wavelengths are longer than the main absorption bands of hemoglobin. Two-photon excitation of topotecan was demonstrated by a quadratic dependence of the emission intensity on the incident power, compared to a linear dependence for one-photon excitation at 410 nm. The observed emission centered at 525 nm was shown to be topotecan from the similarity of the emission spectrum and decay times observed for one-photon and two-photon excitation. Topotecan was detected at concentrations as low as 0.05 and 1 microM in plasma and whole blood, respectively. Since skin blood and tissues are translucent at long wavelengths, these results suggest the possibility of homogeneous or noninvasive clinical sensing with two-photon excitation.
- Published
- 1996
- Full Text
- View/download PDF
38. Biomechanical comparison of the dewar and interspinous cervical spine fixation techniques.
- Author
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Simmons ED Jr, Burke TG, Haley T, and Medige J
- Subjects
- Biomechanical Phenomena, Elasticity, Humans, In Vitro Techniques, Spinal Fusion instrumentation, Stress, Mechanical, Torsion Abnormality, Cervical Vertebrae surgery, Orthopedic Fixation Devices, Spinal Fusion methods
- Abstract
Study Design: This study evaluates and compares the stiffness of two cervical spine fixation techniques., Objectives: This biomechanical study was carried out to compare the interspinous and Dewar cervical spine fixation techniques., Summary of Background Data: Interspinous wiring is a commonly used method of fixation in the cervical spine. The Dewar technique is less commonly known and practiced, and clinical experience has suggested that it may be a more stable technique., Methods: Cervical spine specimens stabilized with the interspinous and "Dewar" techniques were biomechanically tested in flexion and in torsion. Stiffness and energy absorption under moderate loads were compared. The Dewar technique uses contoured double corticocancellous iliac grafts as internal grafts/splints fixed to the spine with threaded pins and wire. The interspinous technique is a single interspinous wire loop. Eleven fresh human cervical spines were harvested from cadavers. The spines were destabilized at C4-C5 by sectioning all tissue except the anterior longitudinal ligament. Each fixation technique was applied alternatively and tested on each spine., Results: In torsion testing (n = 5), the Dewar fusion was 61% stiffer than the interspinous technique (P < 0.02). Dewar: 11.3 N/mm (s.d. 4.9 N/mm) and interspinous: 8.4 N/mm (SD 3.3 N/mm). In flexion testing (n = 6), the Dewar technique was 35% stiffer than the interspinous technique (P < 0.10). Dewar: 655.4 Nmm/degree (SD 293 Nmm/degree) and interspinous: 406.8 Nmm/degree (SD 113.0 Nmm/degree). Energy absorption with the interspinous technique was greater in flexion (P < 0.10) and in torsion (P < 0.005), indicating more deformation with the interspinous technique. There was no statistically significant difference between the means of specimens tested first and those tested second independently of the fixation technique., Conclusions: These tests indicate that the Dewar cervical spine fixation is stiffer than the single interspinous wire in both flexion and particularly torsion. This project is the only biomechanical study of the Dewar technique that we are aware of, and the results support the clinical findings regarding the effectiveness of this technique.
- Published
- 1996
- Full Text
- View/download PDF
39. Molecular structure of the halogenated anti-cancer drug iododoxorubicin complexed with d(TGTACA) and d(CGATCG).
- Author
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Berger I, Su L, Spitzner JR, Kang C, Burke TG, and Rich A
- Subjects
- Crystallography, X-Ray, Doxorubicin chemistry, Models, Molecular, Molecular Conformation, Antibiotics, Antineoplastic chemistry, Doxorubicin analogs & derivatives, Intercalating Agents chemistry, Oligodeoxyribonucleotides chemistry
- Abstract
4'-Deoxy-4'-iododoxorubicin, a halogenated anthracycline derivative, is an anticancer agent currently under Phase II clinical trials. In preclinical studies, it has demonstrated significantly reduced levels of cardiotoxicity compared to currently employed anthracyclines. It also has modified pharmacological properties resulting in an altered spectrum of experimental antitumor activity. The iodine atom at the 4' position of the sugar ring reduces the basicity and enhances the lipophilicity of this compound as compared to related anthracycline drugs. We report here single crystal X-ray diffraction studies of the complexes of 4'-deoxy-4'-iododoxorubicin with the hexanucleotide duplex sequences d(TGTACA) and d(CGATCG) at 1.6 and 1.5 A, respectively. The iodine substituent does not alter the geometry of intercalation as compared to previously solved anthracycline complexes, but appears to markedly affect the solvent environment of the structures. This could have consequences for the interaction of this drug with DNA and DNA binding proteins in cells.
- Published
- 1995
- Full Text
- View/download PDF
40. Reduced albumin binding promotes the stability and activity of topotecan in human blood.
- Author
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Mi Z, Malak H, and Burke TG
- Subjects
- Antineoplastic Agents chemistry, Antineoplastic Agents metabolism, Apoptosis drug effects, Camptothecin blood, Camptothecin chemistry, Camptothecin metabolism, Camptothecin pharmacology, DNA, Neoplasm drug effects, Drug Stability, Electrophoresis, Agar Gel, Flow Cytometry, Fluorescence Polarization, HL-60 Cells, Humans, Irinotecan, Lactones metabolism, Molecular Structure, Serum Albumin pharmacology, Topoisomerase I Inhibitors, Topotecan, Antineoplastic Agents blood, Antineoplastic Agents pharmacology, Camptothecin analogs & derivatives, Serum Albumin metabolism
- Abstract
Topotecan, a semisynthetic water-soluble analogue of camptothecin, is the first topoisomerase I targeting anticancer agent to enter comparative phase III clinical trials. Here we elucidate the biophysical factors underlying the markedly improved bloodstream stability and cytotoxic activity of topotecan relative to camptothecin. Each agent contains an alpha-hydroxy-delta-lactone ring that hydrolyzes under physiological pH to yield a biologically-inactive carboxylate form. In human plasma, camptothecin lactone converts rapidly and completely to its carboxylate form due to a 200-fold binding preference by serum albumin (HSA) for the latter [Mi, Z., & Burke, T.G. (1994) Biochemistry 33, 10540-12545]. Time-resolved fluorescence anisotropy measurements reveal that neither topotecan lactone nor carboxylate associates with HSA, thereby resulting in a significantly higher level of lactone stability in plasma for topotecan (t1/2 = 23.1 min, percent lactone at equilibrium of 17.6) relative to camptothecin (t1/2 = 10.6 min, percent lactone at equilibrium of < 0.2). Moreover, studies with HL-60 human promyelocytic leukemia cells reveal that a physiologically-relevant level (40 mg/mL) of HSA dramatically attenuates the cytotoxic activity of camptothecin in excess of 2600-fold (for a 72 h exposure, the IC50 value of 1.5 nM in the absence of HSA increased to 4 microM in the presence of HSA). The activities of other clinically relevant anticancer analogues, 9-aminocamptothecin and SN-38, were also strongly modulated by the presence of 40 mg/mL HSA. In marked contrast, the presence of HSA effected no change on the cytotoxic activity of topotecan (IC50 = 12 nM both in the absence and in presence of HSA).(ABSTRACT TRUNCATED AT 250 WORDS)
- Published
- 1995
- Full Text
- View/download PDF
41. Thrombolytic-associated cholesterol emboli syndrome: case report and literature review.
- Author
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Geraets DR, Hoehns JD, Burke TG, and Grover-McKay M
- Subjects
- Central Nervous System Diseases etiology, Female, Humans, Kidney Diseases etiology, Middle Aged, Retinal Diseases etiology, Risk Factors, Skin Diseases etiology, Syndrome, Thrombolytic Therapy adverse effects, Embolism, Cholesterol etiology, Fibrinolytic Agents adverse effects
- Abstract
Thrombolytics can cause cholesterol embolization syndrome (CES). This adverse effect has received less attention than other risks of thrombolytic therapy, such as systemic bleeding and hemorrhage, with only sporadic reports of CES in the literature. Risk factors have not been consistently identified and emphasized; therefore, occurrence of CES after thrombolysis remains difficult to predict, it results in substantial morbidity and mortality, and it lacks effective pharmacologic treatment. Heightened awareness of the disorder can aid in its correct identification and reporting.
- Published
- 1995
42. The important role of albumin in determining the relative human blood stabilities of the camptothecin anticancer drugs.
- Author
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Burke TG, Munshi CB, Mi Z, and Jiang Y
- Subjects
- Camptothecin pharmacokinetics, Humans, Camptothecin blood, Serum Albumin chemistry
- Published
- 1995
- Full Text
- View/download PDF
43. Marked interspecies variations concerning the interactions of camptothecin with serum albumins: a frequency-domain fluorescence spectroscopic study.
- Author
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Mi Z and Burke TG
- Subjects
- Animals, Cattle, Dogs, Drug Stability, Humans, Kinetics, Mice, Models, Chemical, Protein Binding, Rabbits, Rats, Species Specificity, Spectrometry, Fluorescence, Camptothecin blood, Serum Albumin metabolism
- Abstract
Camptothecin, an anticancer agent reknown for its novel mechanism of action and outstanding murine in vivo activity, has to date displayed only modest therapeutic utility against human cancers. The drug contains an delta-lactone ring moiety which, at pH7.4, hydrolyzes to yield a biologically inactive carboxylate form. Comparison of drug stability in both plasma and purified serum albumin samples revealed that ring opening occurred to a much greater extent in human samples versus those of other species. Multifrequency phase-modulation spectroscopic analyses of the intrinsic fluorescence emissions of the two drug forms revealed a physical explanation for the extensive ring opening observed in the presence of human serum albumin (HSA): the protein exhibited a marked 200-fold binding preference for the carboxylate (K = 1.2 x 10(6) M-1) relative to the lactone (K approximately 5.5 x 10(3) M-1). Serum albumins from other species were found to bind camptothecin carboxylate not nearly as tightly as HSA. Due to the unique capacity of human albumin to bind camptothecin carboxylate, resulting in extensive conversion of the drug to its biologically inactive form, it appears that the success of the agent in eradicating cancer in animal models may be inherently more difficult to duplicate in man.
- Published
- 1994
- Full Text
- View/download PDF
44. Differential interactions of camptothecin lactone and carboxylate forms with human blood components.
- Author
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Mi Z and Burke TG
- Subjects
- Binding Sites, Camptothecin chemistry, Carboxylic Acids blood, Carboxylic Acids chemistry, Chromatography, High Pressure Liquid, Drug Stability, Erythrocyte Membrane metabolism, Humans, In Vitro Techniques, Kinetics, Lactones blood, Lactones chemistry, Liposomes, Male, Molecular Conformation, Molecular Structure, Serum Albumin metabolism, Spectrometry, Fluorescence, Camptothecin blood
- Abstract
The intrinsic fluorescent emissions from the lactone and carboxylate forms of camptothecin have been exploited in order to elucidate their markedly different interactions with the various components of human blood. In phosphate-buffered saline (PBS) at pH 7.4, human serum albumin (HSA) preferentially binds the carboxylate form with a 150-fold higher affinity than the lactone form; these interactions result in camptothecin opening more rapidly and completely in the presence of HSA than in the protein's absence [Burke, T.G., & Mi, Z. (1993) Anal. Biochem. 212, 285-287]. In human plasma, at pH 7.4 and 37 degrees C, we have observed camptothecin lactone to open rapidly and fully to the carboxylate form (t1/2 = 11 min; % lactone at equilibrium, 0.2%). Substitution of a 10-hydroxy moiety into the camptothecin fluorophore makes the agent's emission spectrum highly sensitive to microenvironment polarity; we have observed pronounced blue shifting (from 530 to 430 nm) in the emission spectra of the hydroxy-substituted carboxylate both upon HSA association as well as upon drug dissolution in organic solvents of low dielectric strength. Hence, it appears that camptothecin carboxylate's fluorophore locates in a hydrophobic binding pocket in native HSA. Ionic interactions also appear to strongly affect binding between camptothecin carboxylate and the HSA binding pocket, since a 6-fold increase in solution salt concentration diminished camptothecin carboxylate binding by 10-fold. Our findings that HSA denaturation abolishes high-affinity binding indicate that interactions of the carboxylate drug form are specific for the native HSA conformation. Interestingly, high-affinity binding of the carboxylate appeared not to occur in the presence of other blood proteins, such as gamma-globulin, alpha 1-acid glycoprotein, fibrinogen, and the oxy and deoxy forms of hemoglobin. In whole blood versus plasma, camptothecin was found to display enhanced stability (t1/2 value of 22 min and a lactone concentration at equilibrium value of 5.3%). The enhanced stability of camptothecin in human blood was found to be due to drug associations with the lipid bilayers of red blood cells. Camptothecin lactone partitions into the lipid bilayers of erythrocytes, with the drug locating in a hydrophobic environment protected from hydrolysis.
- Published
- 1994
- Full Text
- View/download PDF
45. Stabilization of topotecan in low pH liposomes composed of distearoylphosphatidylcholine.
- Author
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Burke TG and Gao X
- Subjects
- Antineoplastic Agents blood, Buffers, Camptothecin administration & dosage, Camptothecin blood, Chemical Phenomena, Chemistry, Physical, Chromatography, High Pressure Liquid, Drug Carriers, Drug Stability, Humans, Hydrogen-Ion Concentration, Lactones administration & dosage, Lactones blood, Lactones chemistry, Liposomes, Topotecan, Antineoplastic Agents administration & dosage, Camptothecin analogs & derivatives, Phosphatidylcholines
- Abstract
Topotecan is a promising anticancer agent presently undergoing clinical evaluation worldwide. Topotecan, camptothecin, 9-aminocamptothecin, and CPT-11 have aroused considerable interest in recent years for their ability to halt the growth of a wide range of human tumors. For each analogue an important structural requirement for biological activity is a closed alpha-hydroxy lactone ring moiety. Unfortunately, this functionality hydrolyses rapidly in aqueous solution under physiological conditions (i.e. pH 7 or above), resulting in an inactive carboxylate form of the drug. In this report, we demonstrate that topotecan's half-life in human plasma (pH 7.6) can be enhanced dramatically by packaging the drug within the aqueous, pH 5-adjusted confines of lipid vesicles composed of diasteroylphosphatidylcholine. We have also demonstrated that drug sequestration within the liposomal particles can be efficiently accomplished. Thus, our preliminary experiments suggest that liposomes may be of potential utility for markedly improving the stability of topotecan in circulation.
- Published
- 1994
- Full Text
- View/download PDF
46. The structural basis of camptothecin interactions with human serum albumin: impact on drug stability.
- Author
-
Burke TG and Mi Z
- Subjects
- Camptothecin analogs & derivatives, Carboxylic Acids chemistry, Chromatography, High Pressure Liquid, Half-Life, Irinotecan, Kinetics, Lactones chemistry, Molecular Structure, Spectrometry, Fluorescence, Structure-Activity Relationship, Topotecan, Camptothecin blood, Camptothecin chemistry, Serum Albumin metabolism
- Abstract
The intense intrinsic fluorescence emissions from several clinically relevant camptothecin drugs have been exploited in order to study the structural basis of drug binding to human serum albumin. Both HPLC and time-resolved fluorescence spectroscopic methodologies were employed to characterize the associations of camptothecins with HSA in phosphate-buffered saline (pH 7.4) at 37 degrees C. The alpha-hydroxy delta-lactone ring moiety of camptothecin (C), 10-hydroxycamptothecin (HC), 10,11-(methylenedioxy)camptothecin (MC) and 9-chloro-10,11-(methylenedioxy)camptothecin (CMC) was in each case observed to hydrolyze more rapidly and completely in the presence of HSA than in the protein's absence. Binding isotherms constructed by the method of fluorescence lifetime titration showed that HSA bound preferentially the carboxylate forms of C, HC, MC, and CMC over their lactone forms, thereby providing an explanation for the shift to the right in the lactone-carboxylate equilibrium observed for each compound upon HSA addition. In marked contrast, three analogues (SN-38, CPT-11, and topotecan) all displayed enhanced stabilities in the presence of HSA. While the lifetimes of CPT-11, topotecan, and the carboxylate forms of both drugs were insensitive to the addition of HSA, the lifetimes of both SN-38 and its carboxylate form did titrate upon HSA addition. Analysis of binding isotherms constructed for the albumin interactions of SN-38 and its carboxylate form demonstrated a higher overall association constant for the lactone form [640 (M amino acid (aa) residues)-1] relative to the carboxylate form [150 (M aa)-1]. Our studies indicate that specific modifications at the 7- and 9-positions of the quinoline nucleus, such as those contained in CPT-11, topotecan, and SN-38, enhance drug stability in the presence of HSA. In the case of SN-38, the enhanced stability was shown to be due to preferential associations between the drug's lactone form and the blood protein.
- Published
- 1994
- Full Text
- View/download PDF
47. Ethyl substitution at the 7 position extends the half-life of 10-hydroxycamptothecin in the presence of human serum albumin.
- Author
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Burke TG and Mi Z
- Subjects
- Antineoplastic Agents, Phytogenic metabolism, Antineoplastic Agents, Phytogenic pharmacokinetics, Binding Sites, Camptothecin chemical synthesis, Camptothecin metabolism, Camptothecin pharmacokinetics, Half-Life, Humans, Irinotecan, Lactones metabolism, Serum Albumin metabolism, Structure-Activity Relationship, Antineoplastic Agents, Phytogenic chemical synthesis, Camptothecin analogs & derivatives
- Published
- 1993
- Full Text
- View/download PDF
48. Preferential binding of the carboxylate form of camptothecin by human serum albumin.
- Author
-
Burke TG and Mi Z
- Subjects
- Binding Sites, Camptothecin analogs & derivatives, Camptothecin chemistry, Carboxylic Acids, Humans, In Vitro Techniques, Kinetics, Protein Binding, Spectrometry, Fluorescence, Camptothecin metabolism, Serum Albumin metabolism
- Published
- 1993
- Full Text
- View/download PDF
49. Lipid bilayer partitioning and stability of camptothecin drugs.
- Author
-
Burke TG, Mishra AK, Wani MC, and Wall ME
- Subjects
- Binding Sites, Camptothecin analogs & derivatives, Camptothecin chemistry, Dimyristoylphosphatidylcholine metabolism, Drug Stability, Fluorescence Polarization, Hydrogen-Ion Concentration, Kinetics, Phosphatidylcholines metabolism, Phosphatidylglycerols metabolism, Spectrometry, Fluorescence, Spectrophotometry, Structure-Activity Relationship, Camptothecin metabolism, Lipid Bilayers metabolism
- Abstract
The intense intrinsic fluorescence emissions from several clinically relevant camptothecin drugs have been exploited in order to determine (1) the structural basis of drug binding to lipid bilayers, (2) the lipid bilayer stability of each drug's alpha-hydroxylactone moiety, a pharmacophore which is essential for antitumor activity, and (3) the site of drug binding in the bilayer. Equilibrium affinities of camptothecin and related congeners for small unilamellar vesicles composed of electroneutral dimyristoylphosphatidylcholine (DMPC) or negatively-charged dimyristoylphosphatidylglycerol (DMPG) were determined using the method of fluorescence anisotropy titration. Experiments were conducted in phosphate-buffered saline (PBS) at 37 degrees C and overall association constants (K values) were determined. Of the seven compounds studied, the new compound 9-chloro-10,11-methylenedioxy-(20S)-camptothecin (CMC) was found to display the highest membrane affinities (KDMPC = 400 M-1, KDMPG = 320 M-1), followed by 10,11-methylenedioxy-camptothecin and camptothecin, which exhibited KDMPC and KDMPG values of 100 M-1 or greater. Topotecan displayed markedly reduced binding to lipid bilayers (KDMPC = 10 M-1, KDMPG = 50 M-1). HPLC assays were subsequently employed to assess the relative stabilities of the lactone ring of membrane-bound drugs. Our results clearly indicate that lipid bilayer interactions stabilize the lactone moiety of camptothecin drugs. In comparison to half-lives in PBS (37 degrees C) of 17 and 19 min for camptothecin and CMC, respectively, DMPC- or DMPG-bound drugs were found to be stable even for periods up to 72 h. Iodide quenching data indicate that membrane-bound camptothecin intercalates between the lipid acyl chains, in a protected environment well removed from the aqueous interface. In this manner lipid bilayer interactions stabilize the lactone ring structure of camptothecins and thereby conserve the biologically active form of each medication.
- Published
- 1993
- Full Text
- View/download PDF
50. In vitro cytotoxicity, cellular pharmacology, and DNA lesions induced by annamycin, an anthracycline derivative with high affinity for lipid membranes.
- Author
-
Ling YH, Priebe W, Yang LY, Burke TG, Pommier Y, and Perez-Soler R
- Subjects
- Animals, Doxorubicin pharmacokinetics, Drug Resistance, Drug Screening Assays, Antitumor, In Vitro Techniques, Leukemia P388 drug therapy, Leukemia P388 metabolism, Mice, DNA Damage, DNA, Neoplasm drug effects, Doxorubicin analogs & derivatives, Doxorubicin pharmacology
- Abstract
Annamycin (AN) is an anthracycline antibiotic with high affinity for lipid membranes which is being developed for clinical studies formulated in liposomes. We studied the in vitro cytotoxicity, cellular pharmacology, and DNA damage induced by AN in P388 cells sensitive and resistant to doxorubicin (DOX). AN was as cytotoxic as DOX against P388-sensitive cells and about 50 times more cytotoxic than DOX against P388-resistant cells (resistance index 5 for AN versus 250 for DOX). Cellular uptake of AN by sensitive cells was 2-3-fold higher than that of DOX. In resistant cells, cellular uptake of AN and DOX was approximately 65% and 30%, respectively, of the cellular uptake in sensitive cells. As a result, cellular uptake of AN by resistant cells was higher than uptake of DOX by sensitive cells. DOX was fully retained in sensitive cells while it was effluxed rapidly from resistant cells. In contrast, efflux of AN was similar in sensitive and resistant cells, thus suggesting that it is not mediated by P-glycoprotein. AN was more effective than DOX in inducing single DNA breaks, double DNA breaks, and DNA-protein cross-links, both in sensitive and resistant cells, although DNA damage was lower in resistant cells than in sensitive cells. DNA lesions induced by AN in resistant cells were similar to or greater than those induced by DOX in sensitive cells. These studies indicate that the lack of cross-resistance between DOX and AN appears to be related, at least in part, to the relatively higher cellular uptake of AN compared with DOX and is associated with the ability of AN to induce significant DNA damage in resistant cells.
- Published
- 1993
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