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Background: All-trans retinoic acid (ATRA) is widely employed in the treatment of various proliferative and inflammatory diseases. However, its therapeutic efficacy is imperiled due to its poor solubility and stability. Latter was surmounted by its incorporation into a solid matrix of lipidic nanoparticles (SLNs)., Methods: ATRA loaded SLNs (ATRA-SLNs) were prepared using a novel microemulsification technique (USPTO 9907758) and an optimal composition and were characterized in terms of morphology, differential scanning calorimetry (DSC), and powder X-ray diffraction studies (PXRD). In vitro release, oral plasma pharmacokinetics (in rats) and stability studies were also done., Results: Rod-shaped ATRA-SLNs could successfully incorporate 3.7 mg/mL of ATRA, increasing its solubility (from 4.7 μg/mL) by 787 times, having an average particle size of 131.30 ± 5.0 nm and polydispersibility of 0.283. PXRD, DSC, and FTIR studies confirmed the formation of SLNs. Assay/total drug content and entrapment efficiency of ATRA-SLNs was 92.50 ± 2.10% and 84.60 ± 3.20% (n=6), respectively, which was maintained even on storage for one year under refrigerated conditions as an aqueous dispersion. In vitro release in 0.01 M phosphate buffer (pH 7.4) with 3% tween 80 was extended 12 times from 2h for free ATRA to 24 h for ATRA-SLNs depicting Korsmeyer Peppas release. Oral administration in rats showed 35.03 times enhanced bioavailability for ATRA-SLNs., Conclusion: Present work reports preparation and evaluation of bioenhanced ATRA-SLNs containing a high concentration of ATRA (>15 times than that reported by others). Latter is attributed to the novel preparation process and intelligent selection of components. Lay Summary: All-trans retinoic acid (ATRA) shows an array of pharmacological activities but its efficacy is limited due to poor solubility, stability and side effects. In present study its solubility and efficacy is improved by 787 and 35.5 times, respectively upon incorporation into solid lipid nanoparticles (ATRA-SLNs). Latter extended its release by 12 times and provided stability for at least a year under refrigeration. A controlled and sustained release will reduce dose related side effects. ATRA-SLNs reported presently can thus be used in treatment /prophylaxis of disorders like cancers, tuberculosis, age related macular degeneration and acne and as an immune-booster., (Copyright© Bentham Science Publishers; For any queries, please email at epub@benthamscience.net.)

Aim: Multicompartmental lipid-protein nanohybrids (MLPNs) were developed for combined delivery of the anticancer drugs tretinoin (TRE) and genistein (GEN) as synergistic therapy of lung cancer. Materials & methods: The GEN-loaded lipid core was first prepared and then coated with TRE-loaded zein shell via nanoprecipitation. Results: TRE/GEN-MLPNs demonstrated a size of 154.5 nm. In situ ion pair formation between anionic TRE and the cationic stearyl amine improved the drug encapsulation with enhanced stability of MLPNs. TRE/GEN-coloaded MLPNs were more cytotoxic against A549 cancer cells compared with combined free GEN/TRE. In vivo , lung cancer bearing mice treated with TRE/GEN-MLPNs displayed higher apoptotic caspase activation compared with mice-treated free combined GEN/TRE. Conclusion: TRE/GEN-MLPNs might serve as a promising parenteral nanovehicles for lung cancer therapy.

The intestinal lymphatic system plays an important role in the pathophysiology of multiple diseases including lymphomas, cancer metastasis, autoimmune diseases, and human immunodeficiency virus (HIV) infection. It is thus an important compartment for delivery of drugs in order to treat diseases associated with the lymphatic system. Lipophilic prodrug approaches have been used in the past to take advantage of the intestinal lymphatic transport processes to deliver drugs to the intestinal lymphatics. Most of the approaches previously adopted were based on very bulky prodrug moieties such as those mimicking triglycerides (TG). We now report a study in which a lipophilic prodrug approach was used to efficiently deliver bexarotene (BEX) and retinoic acid (RA) to the intestinal lymphatic system using activated ester prodrugs. A range of carboxylic ester prodrugs of BEX were designed and synthesised and all of the esters showed improved association with chylomicrons, which indicated an improved potential for delivery to the intestinal lymphatic system. The conversion rate of the prodrugs to BEX was the main determinant in delivery of BEX to the intestinal lymphatics, and activated ester prodrugs were prepared to enhance the conversion rate. As a result, an 4-(hydroxymethyl)-1,3-dioxol-2-one ester prodrug of BEX was able to increase the exposure of the mesenteric lymph nodes (MLNs) to BEX 17-fold compared to when BEX itself was administered. The activated ester prodrug approach was also applied to another drug, RA, where the exposure of the MLNs was increased 2.4-fold through the application of a similar cyclic activated prodrug. Synergism between BEX and RA was also demonstrated in vitro by cell growth inhibition assays using lymphoma cell lines. In conclusion, the activated ester prodrug approach results in efficient delivery of drugs to the intestinal lymphatic system, which could benefit patients affected by a large number of pathological conditions., (Copyright © 2018 The Authors. Published by Elsevier B.V. All rights reserved.)

All-trans-retinoic acid (ATRA) exhibits potent cytotoxicities against different cancer cells by binding to retinoic acid receptors (RARs), which is regarded as the first example of targeted therapy in acute promyelocytic leukemia (APL). However, its extensive clinical applications have been limited because of poor aqueous solubility, short half-life time and side effects. In this report, dimeric ATRA phosphorylcholine prodrug (Di-ATRA-PC) was designed and assembled into nanoliposomes to improve its pharmacokinetic properties. Di-ATRA-PC prodrug was synthesized by a facile esterification and characterized by mass spectrometry (MS) and nuclear magnetic resonance spectroscopy (NMR). The Di-ATRA-PC assembled liposomes were prepared by thin film hydration method with ATRA loading efficiency up to 73wt%. The liposomes have a uniform particle size (73.1±3.6nm) with negatively charged surface (-20.5±2.5mV) and typical lipid bilayer structure as measured by dynamic light scattering (DLS), transmission electron microscope (TEM) and cryogenic transmission electron microscope (cryo-TEM). In vitro drug release study confirmed that Di-ATRA-PC liposomes could sustainedly release free ATRA in a weakly acidic condition. Furthermore, cellular uptake, MTT and cell apoptosis analysis demonstrated that the liposomes could be successfully internalized into tumor cells to induce apoptosis of MCF-7 and HL-60 cells. More importantly, in vivo pharmacokinetic assay indicated that Di-ATRA-PC liposomes had much longer retention time in comparison with ATRA. In conclusion, Di-ATRA-PC liposomal formulation could be a potential drug delivery system of ATRA with enhanced pharmacokinetic properties., (Copyright © 2017 Elsevier B.V. All rights reserved.)

Hepatocellular carcinoma (HCC) is the second leading cause of cancer deaths worldwide largely due to lack of effective targeted drugs to simultaneously block multiple cancer-driving pathways. The identification of all-trans retinoic acid (ATRA) as a potent Pin1 inhibitor provides a promising candidate for HCC targeted therapy because Pin1 is overexpressed in most HCC and activates numerous cancer-driving pathways. However, the efficacy of ATRA against solid tumors is limited due to its short half-life of 45min in humans. A slow-releasing ATRA formulation inhibits solid tumors such as HCC, but can be used only in animals. Here, we developed a one-step, cost-effective route to produce a novel biocompatible, biodegradable, and non-toxic controlled release formulation of ATRA for effective HCC therapy. We used supercritical carbon dioxide process to encapsulate ATRA in largely uniform poly L-lactic acid (PLLA) microparticles, with the efficiency of 91.4% and yield of 68.3%, and ~4-fold higher C max and AUC over the slow-releasing ATRA formulation. ATRA-PLLA microparticles had good biocompatibility, and significantly enhanced the inhibitory potency of ATRA on HCC cell growth, improving IC 50 by over 3-fold. ATRA-PLLA microparticles exerted its efficacy likely through degrading Pin1 and inhibiting multiple Pin1-regulated cancer pathways and cell cycle progression. Indeed, Pin1 knock-down abolished ATRA inhibitory effects on HCC cells and ATRA-PLLA did not inhibit normal liver cells, as expected because ATRA selectively inhibits active Pin1 in cancer cells. Moreover ATRA-PLLA microparticles significantly enhanced the efficacy of ATRA against HCC tumor growth in mice through reducing Pin1, with a better potency than the slow-releasing ATRA formulation, consistent with its improved pharmacokinetic profiles. This study illustrates an effective platform to produce controlled release formulation of anti-cancer drugs, and ATRA-PLLA microparticles might be a promising targeted drug for HCC therapy as PLLA is biocompatible, biodegradable and nontoxic to humans., (Copyright © 2017 Elsevier B.V. All rights reserved.)

In this paper, we describe the synthesis, physicochemical characterization, drug release kinetics and preliminary biological evaluation of several N-(2-hydroxypropyl)methacrylamide (HPMA)-based polymer-retinoid conjugates designed for solid tumor immunotherapy. The conjugates are supposed to inhibit the immunosuppressive activity of myeloid-derived suppressor cells (MDSC) accumulated in the solid tumor microenvironment. All-trans retinoic acid (ATRA) was derivatized to hydrazide (AtrHy) and then attached to the polymer backbone via a spacer that is stable at the normal pH of blood (7.4) and hydrolytically degradable in mildly acidic environments (e.g. in endosomes or lysosomes, pH~5.0-6.5). Polymer-AtrHy conjugates were designed to achieve prolonged blood circulation and release of the immunomodulator intracellularly or extracellularly in solid tumor tissue. Three types of polymer precursors, differing in the structure of the keto acid-containing side chains, were synthesized. A linkage susceptible to hydrolytic cleavage was formed by the conjugation reaction of the carbonyl group-terminated side chains of the polymer precursors with the hydrazide group of a drug derivative. In vitro incubation of the conjugates in buffers resulted in much faster release of the drugs or their derivatives from the polymer at pH 5.0 than at pH 7.4, with the rate depending on the detailed structure of the spacer. Both the AtrHy derivative and its polymer conjugates showed the ability to induce the differentiation of retinoid-responsive HL-60 cells, thus demonstrating the required biological activity.

Resistance to aromatase inhibitors is a major concern in the treatment of breast cancer. Long-term letrozole cultured (LTLC) cells represent a model of resistance to aromatase inhibitors. The LTLC cells were earlier generated by culturing MCF-7Ca, the MCF-7 human breast cancer cell line stably transfected with human placental aromatase gene for a prolonged period in the presence of letrozole. In the present study the effect of RAMBA, VN/14-1 on the sensitivity of LTLC cells upon multiple passaging and the mechanisms of action of VN/14-1 in such high passage LTLC (HP-LTLC) cells was investigated. We report that multiple passaging of LTLC cells (HP-LTLC cell clones) led to profound decrease in their sensitivity to VN/14-1. Additionally, microarray studies and protein analysis revealed that VN/14-1 induced marked endoplasmic reticulum (ER) stress and autophagy in HP-LTLC cells. We further report that VN/14-1 in combination with thapsigargin exhibited synergistic anti-cancer effect in HP-LTLC cells. Preliminary pharmacokinetics in rats revealed that VN/14-1 reached a peak plasma concentration (Cmax) within 0.17h after oral dosing. Its absolute oral bioavailability was >100%. Overall these results indicate potential of VN/14-1 for further clinical development as a potential oral agent for the treatment of breast cancer., (Copyright © 2014 Elsevier B.V. All rights reserved.)

Tretinoin is a retinoid derivative that has an antiproliferative effect on several kinds of tumours. Human lung adenocarcinoma epithelial cell lines (A549) exhibit a profound resistance to the effects of tretinoin. Nanocarriers seem to be a good alternative to overcomecellular resistance to drugs. The aim of this study was to test whether tretinoin-loaded lipid-core nanocapsules exert anantitumor effect on A549 cells. A549 cells were incubated with free tretinoin (TTN), blank nanocapsules (LNC) and tretinoin-loaded lipid-core nanocapsules (TTN-LNC). Data from evaluation of DNA content and Annexin V binding assay by flow cytometry showed that TTN-LNC induced apoptosis and cell cycle arrest at the G1-phase while TTN did not. TTN-LNC showed higher cytotoxic effects than TTN on A549 cells evaluated by MTT and LIVE/DEAD cell viability assay. Gene expression profiling identified up-regulated expression of gene p21 by TTN-LNC, supporting the cell cycle arrest effect. These results showed for the first time that TTN-LNC are able to overcome the resistance of adenocarcinoma cell line A549 to treatment with TTN by inducing apoptosis and cell cycle arrest, providing support for their use in applications in lung cancer therapy., (Copyright © 2014 Elsevier B.V. All rights reserved.)

The objective of this study was to investigate the effects of drug amounts (0.1%, 0.2% and 0.3% w/w), amounts of the oil (10%, 15% and 20% w/w of lipid matrix) and types of the oil (soybean oil (S), medium chain triglycerides (M), oleic acids (O) and linoleic acids (L)) in lipid matrix of all-trans retinoic acid (ATRA)-loaded nanostructured lipid carriers (NLCs) for transdermal drug delivery. The ATRA-loaded solid lipid nanoparticles (SLNs) were formulated with 30% w/w cetyl palmitate. All lipid nanoparticles had average sizes between 130 and 241 nm and had negative zeta potentials. The drug loading of all formulations was higher than 95%. The release of drug from all lipid nanoparticles followed zero-order kinetics. The amount of drug released from all the NLCs and SLNs was significantly greater than the drug released from the ATRA suspension. The ATRA flux of the SLNs was higher than the NLCs. The flux of the NLCs containing oleic acid was significantly higher than the other types of oils. The chemical stability at 4 °C, the percentage of ATRA remaining in all the lipid nanoparticles tested was higher than 80%. It can be concluded that both the SLNs and NLCs are promising dermal drug delivery systems for ATRA.

Poly(amino acid)s are well-known as biodegradable and environmentally acceptable materials. In this study, a series of poly(L-aspartic acid)-b-poly(L-phenylalanine) (PAA-PPA) compounds with different degrees of polymerization were used to prepare copolymer micelles for a poorly water-soluble drug 4-amino-2-trifluoromethyl-phenyl retinate (ATPR, a novel all-trans retinoic acid derivative) and in vivo pharmacokinetics, biodistribution and antitumor efficacy of ATPR delivered by PAA-PPA micelles were evaluated. The area under the plasma concentration time curve AUC0→∞ of ATPR-loaded PAA20PPA20 micelles was 2.23 and 1.97 times higher than that of ATPR solution and ATPR CrmEL solution, respectively; In addition, the mean residence time (MRT) was increased 1.67 and 1.97-fold, respectively and the total body clearance (CL) was reduced 2.25 and 1.98-fold, respectively. The biodistribution study indicated that most of the ATPR in the ATPR-M group was distributed in the liver and there was delayed liver aggregation compared with the ATPR solution and ATPR CrmEL solution groups. Furthermore, the antitumor efficacy of ATPR-loaded PAA20PPA20 micelles was demonstrated in in vivo antitumor models involving mice inoculated with the human gastric cancer cell line SGC-7901. At the same dose of 7mg/kg, the ATPR-loaded micelles group demonstrated a better tumor growth inhibition and induced differentiation than the groups given ATPR solution and ATPR CrmEL solution. Therefore, the ATPR-loaded PAA-PPA micelles appear to be a potentially useful drug delivery system for ATPR and suitable for the chemotherapy of gastric cancer., (Copyright © 2013 Elsevier B.V. All rights reserved.)

A sensitive, reliable and specific LC-MS-MS method was developed and validated for the identification and quantitation of all-trans retinoic acid (ATRA) in human plasma. Acitretin was used as the internal standard (IS). After liquid-liquid extraction of 500 μL plasma with methyl tert-butyl ether (MTBE), ATRA and the IS were chromatographed on a HyPURITY C18 column (150 mm×2.1 mm, 5 μm) with the column temperature set at 40 °C. The mobile phase was consisted of 40% phase A (MTBE-methanol-acetic acid, 50:50:0.5, v/v) and 60% phase B (water-methanol-acetic acid, 50:50:0.5, v/v) with a flow rate of 0.3 mL/min. The API 4000 triple quadrupole mass spectrometer was operated in multiple reaction monitoring (MRM) mode via the positive electrospray ionization interface using the transition m/z 301.4→123.1 for ATRA and m/z 326.9→177.1 for IS, respectively. The calibration curve was linear over the range of 0.45-217.00 ng/mL (r≥0.999) with a lower limit of quantitation (LLOQ) of 0.45 ng/mL. The intra- and inter-day precisions values were below 8% relative standard deviation and the accuracy was from 98.98% to 106.19% in terms of relative error. The validated method was successfully applied in a bioequivalence study of ATRA in Chinese healthy volunteers.

Purpose: All-trans retinoic acid (RA)-incorporated nanoparticles were prepared using deoxycholic acid-conjugated dextran (DexDA). Anticancer activity of RA-incorporated DexDA nanoparticles were tested in vitro and in vivo., Methods: RA-incorporated nanoparticles were prepared by dialysis. Antiproliferative and anti-invasive potential of RA-incorporated nanoparticles were studied using CT26 colorectal carcinoma cells., Results: RA-incorporated nanoparticles have small particle sizes of around 70-300 nm and spherical shapes. The higher drug-feeding ratio and higher substitution degree of deoxycholic acid in the conjugates resulted in higher drug contents, lower loading efficiency, and larger particle size. RA release rate became slower at higher drug contents and higher substitution degree of deoxycholic acid in the DexDA conjugates. The antiproliferation activity, anti-invasive activity, and matrix metalloproteinase 2 expression of RA-incorporated nanoparticles against CT26 cells in vitro was similar to RA. However, RA-incorporated nanoparticles had superior antimetastatic activity in an animal pulmonary metastatic model of CT26 cells compared to RA itself., Conclusion: RA-incorporated nanoparticles showed similar anticancer activity in vitro and superior antimetastatic activity in vivo in a pulmonary metastatic model of CT26 cells. We suggest that RA-incorporated nanoparticles are promising vehicles for efficient delivery of RA.

Purpose: Novel retinoic acid metabolism blocking agent (RAMBA), VN/12-1, is a highly potent anti-cancer agent that induces autophagy. Its combination with autophagy inhibitor chloroquine (CHL) has been shown to synergistically enhance apoptosis in breast cancer cells. The purpose of this study was to determine the toxicity and pharmacokinetic profile of VN/12-1 and its combination with CHL., Methods: Preliminary toxicology of VN/12-1 was determined using female SCID mice (n = 4 for each group). ATRA was used for comparison. We selected four different doses of VN/12-1 and ATRA. Two of the doses were low and less frequent (2.5 and 5 mg/kg twice a week), and the remaining doses were high and more frequent (10 and 20 mg/kg every day). The dose of CHL was 50 mg/kg twice a week. For pharmacokinetic (PK) study, 20 mg/kg of VN/12-1 was injected subcutaneously (s.c.) into the mice, and their plasma was collected at various intervals (n = 2) and analyzed by HPLC., Results: The lower and less frequent doses of VN/12-1 and ATRA were found to be least toxic. However, high and more frequent doses of these compounds were toxic to the mice. PK results showed that VN/12-1 has a half-life of 6 h. The area under the curve (AUC) for VN/12-1 was 83.78 h μg/ml., Conclusions: VN/12-1 and ATRA are non-toxic when used as 5 mg/kg twice a week as single agents or in combination with CHL. The favorable PK properties of VN/12-1 can potentially be used for its further advanced pre-clinical and clinical development.

Systemic therapies with retinoic acid (RA) can result in toxic side effects without yielding biologically effective levels in target tissues such as lung. The authors adapted a PARI LC Star nebulizer to create a tubular system for short-term inhalation treatment of guinea pigs using a water-miscible formulation of all-trans RA (ATRA) or vehicle. Based on the initial average weight, animals received an estimated average ATRA doses of either 0.32 mg·kg(-1) (low dose, 1.4 mM), or 0.62 mg·kg(-1) (medium dose, 2.8 mM), or 1.26 mg·kg(-1) (high dose, 5.6 mM) 20 minutes per day for 6 consecutive days. This system led to a rise of ATRA levels in lung, but not liver or plasma. Cellular lung levels of retinol, retinyl palmitate, and retinyl stearate also appeared to be unaffected (245.6 ± 10.7, 47.4 ± 3.4, and 132.8 ± 7.7 ng·g(-1) wet weight, respectively). The application of this aerosolized ATRA also induced a dose-dependent protein expression of the cellular retinol-binding protein 1 (CRBP-1) in lung, without apparent harmful side effects.

Retinoic acid derivatives have shown their greatest benefit in acute promyelocytic leukemia, but have also demonstrated pre-clinical anti-cancer effects in some solid tumors. Histone deacetylase inhibitors, by upregulating gene expression, are able to limit cancer cell proliferation and induce apoptosis. The combination of all-trans retinoic acid (ATRA) and the histone deacetylase inhibitor valproic acid has been previously studied in hematologic malignancies. We conducted a phase I two-step dose escalation trial of the liposomal ATRA analog ATRA-IV and divalproex sodium (Depakote) in nine patients with advanced solid tumors refractory to prior therapy. Side effects attributed to therapy had a severity

Although all-trans retinoic acid (ATRA) is widely used in acute promyelocytic leukemia (APL), there is little data as to whether or not ATRA is useful for patients with liver and renal failure. A 63-year-old APL patient, complicated by Child-Pugh class A liver cirrhosis and chronic renal failure (creatinine 3.2 mg/dL), was successfully treated with 45 mg/m(2)/day of ATRA. With three courses of chemotherapy, complete remission has been maintained for four years in this patient. Serum trough and maximum ATRA concentration, and the area under the curve (AUC) were not elevated. These observations suggest that full-dose ATRA therapy might be safely applicable to such a complicated case with APL.

The pharmacokinetics of all-trans-retinoic acid (ATRA), an anti-cancer drug was highly variable due to its poor aqueous solubility. In this study, we investigated the pharmacokinetics of ATRA in male Wistar rats following intravenous administration of the ATRA loaded tributyrin emulsion. In vitro, the ATRA emulsion was proved binding to apolipoprotein(s). In vivo, the clearance of ATRA was significantly reduced by formulating into the tributyrin emulsion, leading to higher AUCs. Co-administration with 17alpha-ethynylestradiol, a compound known to upregulate the activity of low-density lipoprotein receptors in tissues, significantly increased the K(e), V, and CL of ATRA. The variation of plasma AUCs after administering the ATRA emulsion to the healthy rats was two times less than that after the ATRA solution. The IC(50) in ATRA of the ATRA emulsion for the Caco-2 carcinoma cells was 3.8 microg/mL lower than 6 microg/mL of the ATRA solution. The IC(50) of the emulsion for the HepG2 carcinoma cells was 2.8 microg/mL, while IC(50) was not achieved with the ATRA solution over the test concentration range. The finding indicated that the tributyrin emulsion could be used as a carrier for ATRA and enhances the drug effect by reducing the clearance and increasing the in vitro activity.

Active derivatives of vitamin A are essential in physiological processes such as cell growth, differentiation, morphogenesis and development. The biological functions of vitamin A are mediated through the retinoid acid receptors (RARs) and retinoid X receptors (RXRs). Aryl hydrocarbon receptor (AhR) agonists such as planar halogenated compounds are known to interfere with vitamin A homeostasis in both field and laboratory studies. In this study, we have investigated the molecular interactions between vitamin A and AhR signalling pathways using juvenile Atlantic salmon and agonists for both receptor pathways. Groups of juvenile salmon were treated with all-trans- and 9-cis-retinoic acid mixture (7:3 ratio) dissolved in DMSO (dimethyl sulfoxide) at 0.1, 1 and 10 mg/kg fish weight. The mixture was force fed singly or in combination with 0.1 mg 3,3',4,4'-tetrachlorobiphenyl (co-planar congener 77)/kg fish weight dissolved in DMSO. Liver samples were collected 3 days after PCB-77 exposure. A separate group exposed to combined retinoic acid (1 mg/kg for 5 days) and PCB-77, was sampled at 3, 7 and 14 days after PCB-77 exposure. Liver samples collected from all exposure groups were analyzed for gene (RARalpha, AhR2alpha, AhR2beta, CYP1A1, UGT1 and GSTpi) expression using real-time PCR and activity (7-ethoxyresorufin O-deethylase (EROD), UGT and GST) using biochemical methods with specific substrates. Our data showed that exposure to RA alone did not produce a significant increase of RARalpha mRNA levels, and the presence of PCB-77 attenuated the expression of RARalpha in RA dose- and time-specific manner. In addition, RA produced a dose-dependent increase of CYP1A1 mRNA and activity (EROD) levels without concomitant increase in AhR2 isoforms. When administered alone, PCB-77 produced increased CYP1A1, UGT1 and GSTpi mRNA and enzyme levels. The PCB-77-induced CYP1A1, UGT1 and GSTpi (mRNA and activity) levels were modulated by RA, in a parameter and dose-specific manner. In general, our data show an interaction between vitamin A and AhR signalling that may affect retinoid homeostasis in fish.

Folic acid, conjugated to poly(ethylene glycol)-distearoylphosphatidylethanolamine (folate-PEG-DSPE), was used to target emulsions of all-trans retinoic acid (ATRA) to folate receptor-overexpressing tumor cells. Two kinds of ATRA-incorporated folate-tethered emulsions (ATRA-FTE 2000/3400) were prepared using soybean oil, egg phosphatidylcholine and folate-PEG-DSPE with different PEG length. As a control, ATRA-incorporated non-tethered emulsion (ATRA-NTE) was prepared by using PEG2000-DSPE without folate instead of using folate-PEG-DSPE. The mean particle diameters of ATRA-FTE 2000/3400 were about 100-130 nm. The cellular uptake in KB cells of fluorescence-labeled ATRA-FTE 3400 was determined with HPLC (for ATRA) and confocal microscopy (for lipid emulsion). The growth inhibitory activity of ATRA was evaluated by MTT assay. The folate ligands in emulsion increased the cellular uptake of ATRA about 3-fold and 1.6-fold in ATRA-FTE 3400 and ATRA-FTE 2000, respectively. Growth inhibitory activity of ATRA-FTE 3400 in KB cells was higher than that of ATRA-NTE at the same dose. Whereas the growth inhibitory effect in MCF-7 cells of ATRA was similar between ATRA-NTE and ATRA-FTE 3400. The addition of free folate significantly reduced the uptake of ATRA regardless of the length of PEG attached to folate. Folate-tethered lipid emulsion showed effective and selective delivery to the folate receptor-abundant carcinomas, suggesting a potential for targeted delivery of anticancer agents.

Purpose: Novel potent C-4 azolyl retinoic acid metabolism blocking agents (RAMBAs)-VN/14-1, VN/50-1, VN/66-1, VN/67-1, and VN/69-1, have been synthesized and investigated for their in vitro and in vivo effects against breast and prostate cancers. These RAMBAs, in addition to being potent inhibitors of all-trans-retinoic acid (ATRA) metabolism have potent anti-cancer properties and in vivo anti-tumor efficacies as characterized in breast and prostate cancer models. Here we determined the toxicity and pharmacokinetics (PK) of these various RAMBAs., Methods: Preliminary acute toxicity studies of these RAMBAs were carried out using Swiss NIH mice. The toxicity profile of the RAMBAs was evaluated relative to ATRA. Three different doses (8.3, 33, and 100 micromol/kg/day) of ATRA and RAMBAs were administered on a daily basis subcutaneously for 14 days to the mice. Clinical signs of toxicity alopecia, scaly skin, and loss of body weight in the mice were observed during the study and the maximum tolerated dose was determined. PK of selected agents (VN/14-1, VN/50-1, and VN/66-1) was studied in Balb/C mice after a single dose subcutaneous administration. Plasma concentrations of the agents were quantitatively determined using a high-performance liquid chromatographic method with ultraviolet detection. Plasma concentration versus time profiles were fit to various PK structural models and relevant PK parameters were estimated., Results: VN/66-1 and VN/69-1 were found to be the least toxic even at the highest doses when compared to the other RAMBAs and ATRA. VN/66-1 had the longest half-life, the slowest clearance, and the greatest exposure., Conclusions: Based on PK characteristics and toxicity studies, VN/66-1 appeared to be the most favorable agent. However, both VN/14-1 and VN/66-1 are our leads based on the fact that VN/14-1 has been found to be highly effective in endocrine-sensitive and -resistant breast cancer cells and tumors with little toxicity. Our findings provide valuable information that will be used to select RAMBAs and establish therapeutic regimens that provide optimal efficacy with minimal toxicity.

All-trans retinoic acid (ATRA) was incorporated into lipid emulsions in an attempt to alter its distribution characteristics and improve its inhibition of liver cancer metastasis. Lipid emulsions composed of egg phosphatidylcholine, cholesterol, and soybean oil were the optimized carriers for ATRA delivery, as shown by the submicron particle size and high incorporation efficiency. The particle size and zeta potential of ATRA incorporated into emulsions were about 133 nm and -11 mV, respectively. In vitro drug release study demonstrated that the release of ATRA from emulsions was sustained in the absence and present of bovine serum albumin, suggesting that ATRA was stable when incorporated in emulsions. After intravenous administration in mice, [3H]cholesteryl hexadecyl ether incorporated into emulsion, which is the inherent distribution of emulsions, accumulated gradually mainly in the liver. The blood concentration and hepatic accumulation of [3H]ATRA incorporated into emulsion was significantly higher than that of serum dissolving [3H]ATRA, which represent the original distribution characteristic of free ATRA. In a murine liver metastasis model by colon adenocarcinoma, the liver metastasis number and liver weight were significantly reduced and the survival time of mice was prolonged following intravenous injection of ATRA incorporated into emulsions.

Retinoids are known to suppress carcinogenesis in various epithelial tissues. Among them, all-trans-retinoic acid (atRA) is recognized as one such active retinoid. However, despite the known anticarcinogenic activity of atRA, it exhibits its short plasma half-life during repeated oral administration due to the "acute retinoid resistance" in the liver. This has been the major limitation in clinical applications of atRA. Therefore, in order to render atRA more suitable for clinical uses, sustained delivery of atRA using biodegradable microspheres is suggested in this study. When 50 mg atRA/kg of atRA-loaded microspheres were subcutaneously administered to rats once, the atRA concentration in plasma was maintained around 6.5 ng/ml for 7 weeks, with only minor signs of toxicity. When the chemopreventive efficacy of atRA-loaded microspheres was evaluated using a model of 4-nitroquinoline 1-oxide-induced oral carcinogenesis in F344 rats, a single injection of atRA-loaded microspheres significantly suppressed oral carcinogenesis. Additional injections of atRA-loaded microspheres, however, did not indicate further suppression of carcinogenesis.

Purpose: To determine single-and multiple-dose pharmacokinetics of liposomal-all- trans -retinoic acid (Atragen) following intravenous and oral ATRA (Vesanoid) administration in healthy volunteers., Methods: This was a randomized, prospective, open-label, parallel pharmacokinetic study in which 29 subjects were given 90 mg/m (2) i.v. liposomal (L)-ATRA (16 subjects) every other day or 45 mg/m (2) oral ATRA (13 subjects) daily over 15 days. Pharmacokinetic parameters were assessed on days 1, 9, and 15., Results: Twenty-two subjects (11 in each group) completed the study and were evaluated. Area under the plasma concentration-time curve [AUC(0, infinity)] and maximum plasma concentration (C(max) ) of ATRA did not decrease during the 15 days of L-ATRA treatment. However, the oral ATRA regimen resulted in a significant decrease in the AUC(0, infinity) and C(max) of 45.3% and 31.8%, respectively, on day 9 as compared with that to day 1 (p< 0.05). In addition, the mean AUC(0, infinity) was 13- and 22-fold greater for L-ATRA than for oral ATRA on days 1 and 9, respectively. Despite the significantly higher plasma concentrations after L-ATRA treatment, the side effects of each formulation were similar, except for dermal exfoliation, which was seen in 31% of the subjects after L-ATRA dosing, and abnormal liver function tests that were seen in 23% of the subjects after oral ATRA administration., Conclusions: These findings suggest that i.v. administration of L-ATRA maintains higher and stable plasma ATRA concentrations than oral ATRA in healthy subjects after repetitive administration. L-ATRA with a favorable pharmacokinetic profile may have potential advantages over oral ATRA and may be more efficacious in the treatment of acute promyelocytic leukemia or other retinoid-responsive cancers.

Background: Due to severe side effects in virtually all children treated with a standard dose of 45 mg/m(2)/day all-trans-retinoic acid (ATRA) for acute promyelocytic leukemia (APL) the AML-BFM study group reduced the dosage to 25 mg/m(2)/day. For the lack of data on the use of ATRA at this dosage in children with APL, the study group further decided to evaluate the pharmacokinetics and metabolism of ATRA in children., Procedure: Twenty-three pharmacokinetic and metabolic profiles of ATRA were studied in 14 children (aged 0.9-18.4 years) with APL. Eleven plasma samples were collected over a period of 8 hr and analyzed for ATRA and its metabolites by high-performance liquid chromatography., Results: Peak plasma concentrations of ATRA were characterized by wide interpatient variability (range: 28.6-513.0 nM). Compared to adults the same metabolic pathways were observed in children. Even though peak plasma concentrations were in the lower range of those considered effective in vitro, ATRA side effects, notably neurotoxicity, still required dose reduction, treatment break, or drug withdrawal in eight patients. In this small number of patients, neurotoxicity could not be related to age or any specific level of ATRA or metabolites in the plasma. Plasma concentrations of vitamin A, however, were significantly higher in those patients, who developed signs of neurotoxicity (P = 0.03, Mann-Whitney Rank Sum test)., Conclusions: Considering the low plasma concentrations and the persistence of toxicity in spite of dose reduction intermittent dosing schedules might be considered as an alternative to further dose reduction of ATRA in the treatment of APL especially in children, who might be at risk of ATRA-induced neurotoxicity., (Copyright 2003 Wiley-Liss, Inc.)

We previously developed a murine model of acute promyelocytic leukemia (APL) by using human cathepsin G gene regulatory elements to direct the expression of promyelocytic leukemia (PML)/retinoic acid receptor alpha (RAR alpha) and RAR alpha/PML fusion cDNAs to the early myeloid compartment of transgenic mice. To study the efficacy of noncytotoxic therapy in this animal model, cohorts of naive immunocompetent mice were inoculated with primary murine APL cells from a frozen tumor bank. Arsenic trioxide and liposomally encapsulated all-trans-retinoic acid (Lipo ATRA), alone or in combination, were administered for 21 days by i.p. injection using doses that yielded plasma levels similar to those observed in human APL patients treated with these agents. Lipo ATRA was highly effective in inducing durable molecular remissions in immunocompetent mice [C57BL/6 x C3H F(1) (B6C3HF1)]; arsenic therapy was much less effective, and did not clearly synergize with Lipo ATRA to increase the remission rate in immunocompetent mice. The survival of Lipo ATRA-treated severe combined immunodeficient (SCID) animals (lacking functional T and B cells) was inferior to that of immunocompetent B6C3HF1 recipients (40% vs. 88% survival at 1 y, P < 0.001). These data suggest that adaptive immunity cooperates with pharmacologic therapy to induce or maintain remissions in murine APL. It also implies that immunosuppressive anti-leukemia therapies could paradoxically blunt effective anti-leukemia immune responses that are important for clearing small numbers of residual tumor cells after chemotherapy-mediated cytoreduction.

Neuroblastoma, the most common extracranial solid tumour in children, may undergo spontaneous differentiation or regression, but the majority of metastatic neuroblastomas have poor prognosis despite intensive treatment. Retinoic acid regulates growth and differentiation of neuroblastoma cells in vitro, and has shown activity against human neuroblastomas in vivo. The retinoid 9-cis RA has been reported to induce apoptosis in vitro, and to inhibit the growth of human neuroblastoma xenografts in vivo. However, at given dosage, the treatment with 9-cis RA caused significant toxic side effects. In the present study we investigated the bioavailability of 9-cis RA in rat. In addition, we compared two different dose schedules using 9-cis RA. We found that a lower dose of 9-cis RA (2 mg day(-1)) was non-toxic, but showed no significant effect on tumour growth. The bioavailability of 9-cis RA in rat was 11% and the elimination half-life (t1/2) was 35 min. Considering the short t1/2, we divided the toxic, but tumour growth effective dose 5 mg day(-1) into 2.5 mg p.o. twice daily. This treatment regimen showed no toxicity but only limited effect on tumour growth. Our results suggest that 9-cis RA may only have limited clinical significance for treatment of children with poor prognosis neuroblastoma.

Purpose: To determine the maximum tolerated dose and describe the toxicities of 9-cis-retinoic acid (9cRA, ALRT1057) administered p.o. tid in pediatric patients with refractory cancer and to study the pharmacokinetics of 9cRA and determine whether systemic drug exposure changes with chronic dosing., Patients and Methods: Children with refractory cancer (stratified by age, < or =12 and >12 years) were treated with p.o. 9cRA for 28 consecutive days. The starting dose was 50 mg/m(2)/day divided into 3 doses with planned escalations to 65, 85, and 110 mg/m(2)/day. Pharmacokinetic sampling was performed on days 1 and 29 of the first cycle., Results: Of the 37 patients entered, 18 patients < or =12 years of age and 11 patients >12 years of age were evaluable for toxicity. In patients >12 years of age, dose-limiting headache occurred in 2/2 patients at the 110 mg/m(2)/day dose level; 1/8 patients at 85 mg/m(2)/day developed dose-limiting pseudotumor cerebri. In patients < or =12 years of age, 3/5 patients at the starting dose level of 50 mg/m(2)/day developed dose-limiting pseudotumor cerebri; and 0/6 patients experienced dose-limiting toxicity at 35 mg/m(2)/day. Reversible non-dose-limiting hepatotoxicity was observed in 15 patients across all of the dose levels. There was considerable interpatient variability in 9cRA plasma concentrations. Peak plasma concentrations of 9cRA occurred at a median of 1.5 h after a p.o. dose, and the harmonic-mean terminal half-life was 43 min. By day 29 of 9cRA administration, the plasma 9cRA area under the curve declined by an average of 65% from day 1 values., Conclusions: The dose-limiting toxicity of 9cRA in pediatric patients was neurotoxicity, primarily pseudotumor cerebri. Younger children tolerate significantly lower doses of 9cRA than older children. Similar to all-trans-retinoic acid, the pharmacokinetics of 9cRA demonstrated a wide degree of interpatient variability and decreased over time when administered on a daily basis. The recommended Phase II dose of 9cRA in patients < or =12 and >12 years of age is 35 and 85 mg/m(2)/day, respectively.

We report that all- trans retinoic acid (ATRA) enhanced the toxicity of docetaxel against DU145 and LNCaP prostate cancer cells, and that the nature of the interaction between ATRA and docetaxel was highly synergistic. Docetaxel-induced apoptotic cell death was associated with phosphorylation and hence inactivation of Bcl-2. ATRA enhanced docetaxel-induced apoptosis and combined treatment with ATRA and docetaxel resulted in down-regulation of Bcl-2. Docetaxel caused phosphorylation and hence inactivation of cdc2 kinase result ing in G2/M arrest. ATRA inhibited docetaxel-induced phosphorylation of cdc2 resulting in activation of cdc2 kinase and partial reversal of the G2/M arrest. ATRA also inhibited docetaxel-induced activation of MAPK indicating that the effects of docetaxel and ATRA on cdc2 phosphorylation are dependent on MAPK. We conclude that ATRA synergistically enhances docetaxel toxicity by down-regulating Bcl-2 expression and partially reverses the docetaxel-induced G2/M arrest by inhibiting docetaxel-induced cdc2 phosphorylation in a pathway that is dependent on MAPK., (Copyright 2001 Cancer Research Campaign.)

Purpose: To determine the overall and dose-limiting toxicities (DLTs) of alitretinoin (9-cis-retinoic acid) in combination with tamoxifen and the pharmacokinetics of alitretinoin alone and when combined with tamoxifen in patients with metastatic breast cancer. The effect of tamoxifen and alitretinoin on MIB-1, a marker of proliferation, in unaffected breast tissue was explored., Patients and Methods: Eligible patients had metastatic breast cancer. Previous tamoxifen therapy was allowed. Planned dose levels for alitretinoin ranged from 50 to 140 mg/m2/d with 20 mg/d tamoxifen in all patients after 4 weeks of alitretinoin as a single agent. Plasma concentrations of alitretinoin and retinol were measured at baseline and after 1, 2, and 3 months. Breast core biopsies were obtained at baseline and after 2 months of therapy., Results: Twelve patients with metastatic breast cancer received a total of 86 cycles of therapy. At 90 mg/m2/d, three of five patients experienced a DLT: grade 3 headache, grade 3 hypercalcemia, and grade 3 noncardiogenic pulmonary edema. At 70 mg/m2/d, one of six patients experienced a DLT (headache), and this level was considered the maximal tolerated dose in this study. Three toxicities occurred that had not been reported previously with alitretinoin: an asymptomatic delay in dark adaptation, a marked decrease in high-density lipoprotein cholesterol, and the occurrence of enthesopathy. Two of the nine assessable patients had a durable clinical response: one partial response and stable disease for 18 months and one complete response in continuous remission for 48+ months. Both responding patients were estrogen receptor-positive and had had previous tamoxifen therapy. There was a high degree of interpatient variability of plasma alitretinoin concentrations, although a significant decline in alitretinoin plasma levels over time was observed. MIB-1 scores declined in four of the eight paired breast specimens obtained., Conclusion: The combination of tamoxifen and alitretinoin is well tolerated and has antitumor activity in metastatic breast cancer. The recommended phase II dose is 70 mg/m2/d with 20 mg/d tamoxifen.

In addition to suppressing breast cancer cell growth, retinoids potentiate growth inhibition in human breast cancer when tested in vitro and in vivo with tamoxifen and/or interferon. The purpose of this study was to ascertain the biologic effects of all-trans-retinoic acid (ATRA) administered alone and with tamoxifen +/- interferon and to identify the relationship between ATRA plasma concentrations and optimal biological dose (the lowest dose that produces a biological response). Three consecutive groups of 15 patients with locally advanced operable breast cancer were treated, in accordance with good clinical practice (GCP) requirements, with ATRA at 3 dose levels alone or with tamoxifen +/- alpha-interferon 2a at flat doses. After 3 weeks, the tumors were surgically removed. Biological parameters measured at the beginning (in biopsy tissue) and end (in surgical tissue) of the study were compared. The optimal biological dose for ATRA was 15 mg/m2/day. Treatments influenced tumor grade but not cell cycle kinetics (G0-G1 phase) or proliferation (Ki67 levels). ATRA induced progesterone receptors independent of dose level and co-administered drugs, but did not induce estrogen receptors when administered alone. Retinoic acid receptor (RAR)-alpha was not affected by treatment and RAR-alpha was moderately influenced whereas RAR-beta (concomitantly with transforming growth factor-beta) was induced in 33% of patients by ATRA alone. ATRA pharmacokinetics were dose- and time-dependent. Neither the ATRA + tamoxifen nor the ATRA + tamoxifen + interferon combinations potentiated the ATRA-induced biological changes. Future studies evaluating the role of RAR-beta as a biological marker of retinoid activity are warranted.

Although advanced renal-cell carcinoma (RCC) responds poorly to standard therapies, phase I-II trials have shown activity for combinations of interferon-alpha2b (IFN) with a retinoid. Alitretinoin (9-cis RA) is an endogenous retinoid with high binding affinity for both RAR and RXR receptor families. This phase I-II study enrolled 38 patients with RCC in a dose-escalation study of tolerability, pharmacokinetics (PK), and efficacy of twice daily oral 9-cis RA with subcutaneous IFN. In contrast to studies with similar doses of daily 9-cis RA, PK studies found a consistent reduction in 9-cis RA concentrations of about 50% after multiple b.i.d. doses of 30 or 50 mg/m2, independent of cotreatment with IFN. In the phase I portion, toxicities included systemic symptoms typical of IFN and biochemical abnormalities previously associated with retinoids. Two patients experienced dose-limiting toxicity at 50 mg/m2 b.i.d. of 9-cis RA, thus the recommended phase II dose was 30 mg/m2 b.i.d. One of twenty-six evaluable patients achieved a durable objective partial remission, and repeated dosing with this regimen was poorly tolerated. This combination of retinoid and interferon is not recommended for further study in RCC.

Background: All-trans-retinoic acid (ATRA, vitamin A acid or tretinoin) is effective in the treatment of acute promyelocytic leukaemia (APL). Unfortunately, the oral absorption of ATRA is highly variable. Its poor aqueous solubility also makes it difficult to be formulated into parenteral formulation. To date, there is no parenteral formulation of ATRA available commercially., Objective: To undertake the preformulation work necessary for developing such a product., Method: We investigated the solubility and stability profile of ATRA in various formulations., Results: The aqueous solubility of ATRA could be greatly increased by the inclusion of ATRA in 2-hydroxypropyl-beta-cyclodextrin (HP-beta-CD). Adjusting the pH value further improved the water solubility of ATRA. The photostability of HP-beta-CD-based formulation of ATRA was evaluated and it was found that inclusion ATRA into HP-beta-CD did improve the photostability of ATRA., Conclusion: These results showed that it is possible to develop a parenteral formulation and/or an aqueous oral formulation of all-trans-retinoic acid by using 2-hydroxypropyl-beta-cyclodextrin. However, the biopharmaceutical properties of such a formulation would be necessary before its use.

The resistance to all trans retinoic acid (ATRA) differentiating treatment is a consequence, in most of the cases, of either increased catabolism or down regulation of ATRA uptake. Recently, we have shown that ATRA efficiency to differentiate HL-60 cells was enhanced about 30 times after its incorporation into Low Density Lipoprotein (ATRA-LDL). Here, we attempted to differentiate the ATRA-resistant HL-60 cells by ATRA-LDL at high concentrations up to 10 microM. No significant differentiating effect was observed, although the LDL receptor sites were evidenced in these cells. To increase the number of LDL receptors, the cells were pre-incubated in lipoprotein-deprived serum medium and compactin (2 microM), both ATRA and ATRA-LDL induced gradual increase of cell differentiation (35%+/-1 and 51.5%+/-5 at 10 microM of ATRA and ATRA-LDL respectively). At 2 and 8 microM, the intracellular concentrations of ATRA were respectively three and four times higher when incorporated into LDL. In addition, ATRA-LDL, in the medium, was better protected against degradation than ATRA. The surprising restoration of free ATRA sensitivity after treatment with compactin suggested the implication of new mechanisms unrelated to the LDL-receptor endocytosis but involving the non-sterol pathway.

Although retinoids show promise for prevention of second primary upper aerodigestive tract tumors, the optimum retinoid, dose, and schedule are unknown. All-trans retinoic acid (ATRA) has greater affinity for retinoic acid receptors and may be more active than other retinoids but has a shorter plasma half life and may up-regulate its own metabolism. We defined the maximum long-term tolerable dose, dosing frequency, pharmacokinetics, and toxicity of ATRA in patients with treated squamous cell carcinoma of the head and neck (SCCHN). Twenty-one patients were randomized to 45, 90, or 150 mg/m2 ATRA either once daily, or as divided doses every 8 h, for 1 year. Pharmacokinetics were assessed periodically. Fourteen men and seven women with previous SCCHN of initial stage I-IV were treated. Grade > or =3 toxicities (reversible) included headache and hypertriglyceridemia in 5 and 6 patients each, mucositis in 2 patients, and hyperbilirubinemia, elevated alkaline phosphatase, colitis, lipasemia, xerostomia, eczema, and arthritis in 1 patient each. The 150-mg/m2 dose was not tolerable. Doses were reduced for grade > or =3 toxicity in seven of eight patients at 90 mg/m2 daily. Three of nine patients at 45 mg/m2/day required dose reduction, two at the once-daily dose. Day 1 ATRA area under the plasma concentration versus time curve (AUC) increased with dose, and after 1-2 months of continued dosing, the AUC declined in 7 of 13 patients (54%) studied. ATRA AUC did not correlate with toxicity severity or frequency. Fifteen mg/m2/day every 8 h is a tolerable dose for 1 year in patients with treated SCCHN. ATRA pharmacokinetics did not correlate with toxicity.

all-trans-Retinoic acid (ATRA, vitamin A acid, or tretinoin) is a potent chemotherapeutic agent for the treatment of acute promyelocytic leukemia (APL). Its poor aqueous solubility not only affects its oral absorption but also prevents it from forming an aqueous parenteral formulation. Recently, we developed a water-soluble formulation of ATRA with 2-hydroxypropyl-beta-cyclodextrin (HPbetaCD). In present study, this formulation was tested in Sprague-Dawley rats. Kinetic study of ATRA was carried out after oral or intravenous administration. Though there were no statistical differences in any of the estimated pharmacokinetic parameters between ATRA sodium salt and HPbetaCD-based ATRA after intravenous administration, inclusion of ATRA into HPbetaCD was found to greatly improve the oral absorption of ATRA., (Copyright 2000 Wiley-Liss, Inc.)

We have measured the pharmacokinetics of three retinoids, all-trans retinoic acid, 13-cis retinoic acid, and fenretinide in rat blood and rat brain [especially white matter (WM) and gray matter (GM)] to help select retinoids for treating human malignant glioma. All-trans retinoic acid permeated well into the WM, giving peak concentration in WM of 25.7 microg/g, 6 to 7 times higher than the peak serum concentration. There was less 13-cis retinoic acid in WM: area under the curve (AUC)(0-->infinity) WM/AUC(0-->infinity) serum = 18.00 microg ml(-1) h/32.67 microg ml(-1) h. The ratio WM/GM was over 1 for these two compounds, but the half-lives were short in the serum and cerebral tissue (0.57-1.02 h). Fenretinide had different pharmacokinetics: the peak concentrations were in serum (1.7 microg/ml) and WM (1.2 microg/ml)-low, but the AUC(0-->infinity) was large (25.55 microg ml(-1) in serum and 57.53 microg ml(-1) in WM) due to its long elimination half-life (13.78 h in serum and 17.77 h in WM). These findings provide information that may be used to select a retinoid and establish therapeutic regimens that provide optimal efficacy with minimal toxicity.

The biotransformation and tissue distribution of 9-cis-retinoic acid was investigated in hairless rats. Indeed, only limited information is available about the pharmacokinetics of 9-cis-retinoic acid. Assuming that the target site for retinoids is the skin, tissue distribution study is therefore particularly justified. Following single oral administration of 30 mg/kg of 9-cis-retinoic acid, the parent drug and five metabolites were detected in plasma. Additionally, concentrations of 9-cis-retinoic acid and metabolites were determined in the skin and seven other tissues. The distribution of 9-cis-retinoic acid was rapid in all of the organs studied (T(max)

We analysed the relationship between all-trans retinoic acid (ATRA) resistance and P-glycoprotein (P-gp)-associated multidrug resistance (MDR) in acute promyelocytic leukaemia (APL). There was no difference in the intracellular ATRA accumulation between NB4 cells and an MDR1 cDNA-transduced NB4 subline and between ATRA-resistant NB4 cells (NB4/RA) and an MDR1 cDNA-transduced NB4/RA subline. PSC833, a MDR modifier, did not increase the intracellular accumulation of ATRA or affect the expression of CD11b, the nitroblue tetrazolium (NBT) reduction activity, the proportion of apoptotic cells or the morphology of these four ATRA-treated cell lines. Similar results were obtained in the analysis of APL cells from five patients relapsed after ATRA-induced complete remission.

Solagé is a combination product composed of 2% mequinol (4-hydroxyanisole) and 0.01% tretinoin (all-trans-retinoic acid) in an ethanolic solution, which is being studied for its safety and efficacy as a topical treatment for disorders of skin hyperpigmentation. The purpose of this study was to evaluate the extent of percutaneous absorption of [3H]tretinoin and to estimate the systemic exposure to mequinol from this combination product when topically applied to the backs of healthy subjects. Eight subjects received bid topical applications of nonradiolabelled 2% mequinol/0.01% tretinoin solution on a 400 cm2 area of the back for 14 days. The subjects then received a single topical application of 2% mequinol/0.01% [3H]tretinoin solution. After 12 h, the radiolabelled dose was removed and bid treatment with nonradiolabelled 2% mequinol/0.01% tretinoin solution was continued for 7 days. Plasma, urine and faecal samples were analysed for total radioactivity and plasma was analysed for both mequinol and tretinoin by GC/MS procedure. Mean percutaneous absorption of [3H]tretinoin based on the cumulative recoveries of radioactivity in the urine and faeces was about 4.5% (median 2.18%). Tretinoin concentrations in plasma did not increase above endogenous levels. This was consistent with the concentrations of radioactivity in plasma, which showed an average Cmax of 91 pg-eq/mL (median 26 ng/mL). Average Cmax and AUC(0-12 h) values for mequinol were 10 ng/mL and 33 ng h/mL, respectively. Based on the results of this study, systemic toxicity from topical application of tretinoin in this formulation is unlikely, because percutaneous absorption of tretinoin is minimal and because endogenous levels of tretinoin are not increased following bid dosing with this combination formulation. The safety of mequinol in this combination formulation is supported by the low systemic exposures of the subjects in this study compared with the systemic exposures at the highest doses in the dermal toxicity studies in mice (16.6-fold) and rats (34.6-fold).

Purpose: 9-cis retinoic acid (ALRT 1057; 9cRA) is a promising new retinoid that binds to all known retinoic acid receptors (RAR and RXR), potentially providing it with a broader spectrum of biologic activity than either 13-cis retinoic acid or all-trans retinoic acid. It has been shown to be at least as active as all-trans retinoic acid as a differentiation-inducing and antiproliferative agent in both in vivo and in vitro tumor model systems., Methods: The New York Gynecologic Oncology Group undertook a prospective, multi-institutional phase II clinical and pharmacokinetic trial of 9cRA in patients with advanced or recurrent squamous cell or adenosquamous cell carcinoma of the uterine cervix. Patients received daily oral doses of 140 mg/m2 of 9cRA. 9cRA and its metabolites were determined by reversed-phase HPLC in plasma samples drawn at 0.5 to 8 hours., Results: Sixteen patients with advanced or recurrent carcinoma of the cervix were enrolled. Therapy was well tolerated with no unexpected toxicities. There were no complete or partial responses observed, indicating that a response rate of 20% or greater to this agent could be ruled out with 95% confidence. Pharmacokinetic parameters for 9cRA on day 1 were in agreement with previous studies. The area under the plasma versus time curves for 9cRA declined by 69% between days 1 and 8 with daily 9cRA dosing and remained at this low level in those patients evaluated on day 28. 4-oxo-9-cis retinoic acid (4-oxo-9cRA) was identified as a major plasma metabolite of 9cRA. Plasma levels of 4-oxo-9-cRA were initially 71% of those of 9cRA, but in contrast to 9cRA, there was no decline in plasma levels on days 8 and 28. The ratio of the area under the curve for the 4-oxo metabolite relative to that of the parent compound increased from less than 1 on day 1 to approximately 2.4 on days 8 and 28. Thus, despite early induction of its own metabolism, levels of total retinoid metabolites persisted at pharmacologic levels at day 28., Conclusions: 9cRA with this dose and schedule was inactive in women with advanced carcinoma of the cervix. Despite a decline in plasma levels of 9cRA over time, levels of the 4-oxo metabolite tended to persist. While the 4-oxo metabolite is less potent than the parent compound, these data nevertheless suggest that the lack of clinical activity in this patient population may not be attributable exclusively to suboptimal pharmacokinetic parameters.

9-cis-Retinoic acid (9-cis-RA) and all-trans-RA (ATRA) are naturally occurring hormones. The nuclear receptors that mediate the effects of retinoids are the retinoic acid receptors (RARs) and the retinoid X receptors (RXRs). ATRA binds RAR with high affinity but does not bind to RXR, whereas 9-cis-RA, an isomer of ATRA, is a ligand that binds and transactivates both RARs and RXRs. The goals of this study were to determine the safety, tolerability, pharmacokinetics, and metabolic profile of 9-cis-RA in advanced cancer patients. Forty-one patients received oral 9-cis-RA (ALRT1057; Panretin capsules) at doses ranging from 5-140 mg/m2/day. Twenty-six patients were treated once daily with up to 140 mg/m2; a subsequent cohort of 15 patients were treated twice daily (b.i.d.) at 100-140 mg/m2/day (50, 60, and 70 mg/m2 b.i.d.) to evaluate a b.i.d. dosing regimen. Headache was the most frequent adverse event and was dose limiting in 3 of 41 patients. Skin toxicity was the next most common toxicity and was seen in 11 of 41 patients; it was typically mild and limited to skin dryness and erythema. Other toxicities included conjunctivitis, flushing, diarrhea, transaminitis, hypercalcemia, and asymptomatic hypertryglyceridemia. Toxicities were typically dose related, occurred primarily above 83 mg/m2/day, and were not ameliorated by b.i.d. dosing. No tumor responses were observed. The mean day 1 area under the plasma concentration-time curve and peak plasma concentration values were dose-proportional over all dose levels, whereas day 15 area under the plasma concentration-time curve and peak plasma concentration values were nonlinear above 83 mg/m2/day, suggesting that 9-cis-RA induced its own metabolism at doses equal to and above 140 mg/m2/day. 9-cis-RA is a retinoid receptor pan agonist with a more favorable pharmacokinetic and toxicity profile than that observed with previously studied retinoids and merits further investigation.

Since in vitro observations indicated that all-trans retinoic acid (ATRA), especially in combination with IFNalpha, can exert significant suppressive effects on Ph+ cells, we investigated the effects and the pharmacokinetic profile of ATRA in a selected cohort of patients with Ph+ chronic myeloid leukemia (CML) in chronic phase. Eighteen patients were treated with ATRA at a dose of 80 mg/m2/day (p.o.), divided into two equal doses after meals, for 7 consecutive days every other week for a maximum of 12 courses (1 course = 1 week on and 1 week off). Pharmacokinetic profiles of ATRA were evaluated during intermittent therapy on days 1 and 7 of course 1; on day 1 of course 2; on day 1 of course 6. Out of the 18 patients treated with ATRA, 11 (61%) went off study before the sixth course of treatment because of progressive hyperleukocytosis (seven cases), or thrombocytosis (one case), or refusal (three cases). Seven (39%) patients completed the first six courses (12 weeks) of treatment with ATRA and two of them (11%) maintained a white blood cell (WBC) <10 x 10[9]/l which was induced by the pretreatment with hydroxyurea. One patient completed the 12th course of ATRA maintaining WBC <10 x 10(9)/l, platelets <500 x 10(9)/l and spleen not palpable. The treatment with ATRA was well tolerated and only one patient discontinued the therapy because of non-hematological side-effects. The area under the concentration-time curve (AUC) decreased significantly (P< 0.001) during the first week of therapy. By adopting an intermittent dosing regimen, 1 week on/ 1 week off (1 course), at the start of courses 2 and 6, we obtained the ATRA AUCs equivalent to the ones achieved on day 1 of course 1. In conclusion, our results showed that ATRA alone appeared to be unable to control the WBC expansion in the CML patients in chronic phase. Moreover, it did not induce any remarkable cytoreductive effects on the platelet count and on the hemoglobin level. The major interest of ATRA would be in combination with other therapies. If ATRA was given in combination with IFNalpha or other agents, dose reduction of these would not be planned. On the basis of the pharmacokinetic profile, ATRA should be administered intermittently rather than continuously.

Purpose: All-trans-retinoic acid (ATRA) is a retinoid analogue that has been shown to be effective in acute promyelocytic leukemia. It is currently being investigated for efficacy in the treatment and prevention of various types of cancer. One of the factors limiting its use is the observed increase in ATRA clearance and elimination which occurs shortly after treatment is started, leading to reduced levels of drug in the body and loss of effectiveness. ATRA efficacy may be enhanced if this autoinduction of metabolism can be overcome, for example through the inhibition of the activity of the induced specific metabolizing enzyme(s). This requires the identification of this induced enzyme(s) and development of approaches to selectively inhibit its activity., Methods: In the course of a phase II evaluation of ATRA in prostate cancer, we investigated the activities of five specific cytochrome P450 (CYP) (CYPs 1A2, 2C19, 2D6, 2E1 and 3A4) and N-acetyltransferase enzymes using a newly developed five-drug cocktail involving caffeine, mephenytoin, debrisoquine, chlorzoxazone and dapsone respectively. Enzyme activities were assessed in 17 patients with hormone-refractory prostate cancer before the initiation of ATRA therapy, after 14 days of continuous ATRA administration and 7 days after cessation of drug therapy., Results: After 14 days of ATRA therapy, the activities of CYP2E1 (chlorzoxazone hydroxylase) and N-acetyltransferase (in fast acetylators only) were increased by 83% and 29% (P < 0.05), respectively. Both activities returned to baseline by 7 days after cessation of therapy and the profiles were similar to the changes seen in the clearance of ATRA itself. There were no changes in the activities of any of the other enzymes investigated., Conclusion: This study shows that ATRA selectively modulates the activities of specific metabolizing enzymes and that this approach may be useful in identifying enzymes that can be explored in an attempt to mitigate ATRA autoinduction through selective modulation of enzyme activities. Further investigations are required to determine whether the elevated enzymes are also responsible for the increased clearance and elimination of ATRA.

A double-blind, placebo-controlled, randomized study using single ascending oral doses of 5 mg, 15 mg, 40 mg, 80 mg, and 150 mg of 9-cis-retinoic acid was performed to assess the single-dose pharmacokinetics, tolerability, and pharmacodynamic effects of 9-cis-retinoic acid in healthy men. Forty participants received treatment (six taking the active treatment and two taking placebo for each dose level). The pharmacokinetics of 9-cis-retinoic acid were linear over the dose range studied. Peak plasma concentrations were achieved within 3 to 4 hours on average. The half-life was in the range of 1.3 to 2.4 hours. Metabolism was the major pathway of elimination. 4-Oxo-9-cis-retinoic acid, one of four metabolites measured, which included all-trans-retinoic acid and 13-cis-retinoic acid, was the main metabolite in plasma, achieving peak plasma levels of 41% to 83% of those of 9-cis-retinoic acid. Dose-/concentration-dependent reductions of retinol in plasma, with a maximum of 30% from baseline, were observed 24 hours after administration. Baseline levels were recovered after 5 days. Concentrations of retinol binding protein remained unchanged. Overall, the drug was well tolerated at all dose levels. Adverse events observed were consistent with findings of other retinoids (all-trans-retinoic acid and 13-cis-retinoic acid) and included headache and xeroderma at high dose levels.

Recent reports of the dramatic antitumour effect of tretinoin (all-trans retinoic acid) in patients with acute promyelocytic leukaemia (APL) have generated a great deal of interest in the use of this drug as a chemopreventive and therapeutic agent. However, the biological efficacy of tretinoin is greatly impaired by (presumably) an induced hypercatabolism of the drug leading to reduced tretinoin sensitivity and resistance. Several pharmacokinetic studies have shown that plasma drug exposure [as measured by the plasma area under the concentration-time curve (AUC infinity)] declines substantially and rapidly when the drug is administered in a long term daily tretinoin regimen. These observations led to the hypothesis that the rapid development of acquired clinical resistance to tretinoin may have a pharmacological basis and result from an inability to present an effective drug concentration to the leukaemic cells during continuous treatment. The principal mechanisms proposed to explain the increased disappearance of tretinoin from plasma include: (i) decreased intestinal absorption; (ii) enhanced enzymatic catabolism; and (iii) the induction of cytoplasmic retinoic acid binding proteins (CRABP), which leads to increased drug sequestration. The most favoured explanation is that continuous tretinoin treatment acts to induce drug catabolism by cytochrome P450 (CYP) enzymes. Several strategies aimed at preventing or overcoming induced tretinoin resistance have been, and are being, planned. These strategies include intermittent dose administration, administration of pharmacological inhibitors of CYP oxidative enzymes, combination with interferon-alpha and intravenous administration of liposome-encapsulated tretinoin. As these strategies are now under investigation and the number of patients enrolled is small, further studies are needed to determine the efficacy and toxicity of these new schedules of drug administration. In this article we provide an overview of the relevant aspects of tretinoin physiology and pharmacokinetics, and summarise the current status of knowledge to help in the better optimisation of tretinoin administration.

We evaluated the utility of a 7-day drug holiday in the restoration of chronic dosing all-trans-retinoic acid (tRA) blood levels in 11 non-small cell lung carcinoma patients. Baseline kinetic studies (day 1) were compared to postchronic dosing (day 7) and drug holiday kinetics (day 14). High levels of baseline pharmacokinetic variability and variability in response to prolonged tRA therapy were evident. Median area under the curve (AUC) decreased from a baseline level of 1.2 to 0.69 microg/ml/h (p = 0.03). t (1/2) showed no significant alterations. A near-significant increase in T (lag) (p = 0.08) was noted, which suggests modulation of absorbance parameters. Trends in AUC were strongly correlated with C (max) as was T (max) with T (lag). After a 7-day drug holiday the median AUC significantly increased from the day 7 value to 1.8 microg/ml/h p = 0.01). Since post-drug holiday values for parameters were not statistically different from baseline pharmacokinetic values, this suggests a complete restoration of tRA bioavailability.

The aromatic retinoid (E)-4-[2-(5,6,7,8-tetrahydro-5,5,8,8-tetramethyl-2-naphthylenyl)-1 -propenyl] benzoic acid (TTNPB) is 1000-fold more potent as a teratogen than all trans-retinoic acid (tRA) in several species and in the inhibition of chondrogenesis in the mouse limb bud cell culture. Factors responsible for the potency of TTNPB were investigated including binding to nuclear retinoic acid receptors (RARs and RXRs), cytosolic binding proteins (CRABPs), and metabolic disposition of TTNPB. For competitive binding assays and saturation kinetics, nucleosol or cytosol fractions were obtained from COS-1 cells transfected with cDNAs encoding the appropriate nuclear receptor or binding protein. TTNPB binds to RAR alpha, beta, and gamma with Kds in the nanomolar range; however, these binding affinities are 10-fold less than those of tRA. Although the affinities are high for TTNPB, it is unlikely that the binding affinities to nuclear receptors alone account for the potency of TTNPB. The binding affinities of TTNPB for the CRABPs are significantly lower than those of tRA. TTNPB did not compete with [3H]9-cis RA for binding to RXR alpha, beta, or gamma. Mouse limb bud cell cultures, a well characterized model for retinoid teratogenesis, were used to compare the metabolic disposition of TTNPB and tRA. In the media of limb bud cell cultures treated with either retinoid, the disappearance of TTNPB was significantly slower than that of tRA over 72 hr. Both retinoids reached approximately equal concentrations in cell uptake experiments; however, TTNPB disappeared from the limb bud cell at a significantly slower rate than did tRA. Collectively, these results indicate that high affinity binding to RARs, lower affinity to CRABPs, and resistance to metabolism contribute to the potency of TTNPB.