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Stimulator of interferon genes (STING) is an innate immune receptor activated by natural or synthetic agonists to elicit antitumoral immune response via type I IFNs and other inflammatory cytokines. Bacillus Calmette-Guerin (BCG) is the standard of care as intravesical therapy for patients with high-risk non-muscle invasive bladder cancer (NMIBC). There are limited options available for patients with NMIBC who developed BCG unresponsiveness. In this study, we characterized in vitro and in vivo antitumor effects of E7766, a macrocyle-bridged STING agonist, via intravesical instillation in two syngeneic orthotopic murine NMIBC tumor models resistant to therapeutic doses of BCG and anti-PD-1 agents. E7766 bound to recombinant STING protein with a Kd value of 40 nmol/L and induced IFNβ expression in primary human peripheral blood mononuclear cells harboring any of seven major STING genotypes with EC50 values of 0.15 to 0.79 μmol/L. Intravesical E7766 was efficacious in both NMIBC models with induction of effective immunologic memory in the treated animals. Pharmacologic activation of the STING pathway in the bladder resulted in IFN pathway activation, infiltration of T cells and natural killer (NK) cells, dendritic cell activation, and antigen presentation in bladder epithelium, leading to the antitumor activity and immunity. In addition, measurements of the pharmacodynamic markers, Ifnβ1 and CXCL10, in bladder, urine, and plasma, and of STING pathway intactness in cancer cells, supported this mode of action. Taken together, our studies reveal an antitumor immune effect of pharmacologic activation of the STING pathway in bladder epithelium and thus provide a rationale for subsequent clinical studies in patients with NMIBC., (©2022 American Association for Cancer Research.)

A strategy for creating potent and pan-genotypic stimulator of interferon genes (STING) agonists is described. Locking a bioactive U-shaped conformation of cyclic dinucleotides by introducing a transannular macrocyclic bridge between the nucleic acid bases leads to a topologically novel macrocycle-bridged STING agonist (MBSA). In addition to substantially enhanced potency, the newly designed MBSAs, exemplified by clinical candidate E7766, exhibit broad pan-genotypic activity in all major human STING variants. E7766 is shown to have potent antitumor activity with long lasting immune memory response in a mouse liver metastatic tumor model. Two complementary stereoselective synthetic routes to E7766 are also described., (© 2021 Wiley-VCH GmbH.)

Background: Chlorotoxin (Cltx) isolated from scorpion venom is an established tumor targeting and antiangiogenic peptide. Radiolabeled Cltx therapeutic ( 131 I-TM601) yielded promising results in human glioma clinical studies, and the imaging agent tozuleristide, is under investigation in CNS cancer studies. Several binding targets have previously been proposed for Cltx but none effectively explain its pleiotropic effects; its true target remains ambiguous and is the focus of this study., Methods: A peptide-drug conjugate (ER-472) composed of Cltx linked to cryptophycin as warhead was developed as a tool to probe the molecular target and mechanism of action of Cltx, using multiple xenograft models., Results: Neuropilin-1 (NRP1), an endocytic receptor on tumor and endothelial cells, was identified as a novel Cltx target, and NRP1 binding by Cltx increased drug uptake into tumor. Metabolism of Cltx to peptide bearing free C-terminal arginine, a prerequisite for NRP1 binding, took place in the tumor microenvironment, while native scorpion Cltx with amidated C-terminal arginine did not bind NRP1, and instead acts as a cryptic peptide. Antitumor activity of ER-472 in xenografts correlated to tumor NRP1 expression. Potency was significantly reduced by treatment with NRP1 blocking antibodies or knockout in tumor cells, confirming a role for NRP1-binding in ER-472 activity. Higher cryptophycin metabolite levels were measured in NRP1-expressing tumors, evidence of NRP1-mediated enhanced drug uptake and presumably responsible for the superior antitumor efficacy., Conclusions: NRP1 was identified as a novel Cltx target which enhances tumor drug uptake. This finding should facilitate tumor selection for chlorotoxin-based therapeutics and diagnostics.

Pancreatic cancer, the fourth leading cause of cancer death in the United States, has a negative prognosis because metastasis occurs before symptoms manifest. Leiodermatolide, a polyketide macrolide with antimitotic activity isolated from a deep water sponge of the genus Leiodermatium, exhibits potent and selective cytotoxicity toward the pancreatic cancer cell lines AsPC-1, PANC-1, BxPC-3, and MIA PaCa-2, and potent cytotoxicity against skin, breast and colon cancer cell lines. Induction of apoptosis by leiodermatolide was confirmed in the AsPC-1, BxPC-3 and MIA PaCa-2 cells. Leiodermatolide induces cell cycle arrest but has no effects on in vitro polymerization or depolymerization of tubulin alone, while it enhances polymerization of tubulin containing microtubule associated proteins (MAPs). Observations through confocal microscopy show that leiodermatolide, at low concentrations, causes minimal effects on polymerization or depolymerization of the microtubule network in interphase cells, but disruption of spindle formation in mitotic cells. At higher concentrations, depolymerization of the microtubule network is observed. Visualization of the growing microtubule in HeLa cells expressing GFP-tagged plus end binding protein EB-1 showed that leiodermatolide stopped the polymerization of tubulin. These results suggest that leiodermatolide may affect tubulin dynamics without directly interacting with tubulin and hint at a unique mechanism of action. In a mouse model of metastatic pancreatic cancer, leiodermatolide exhibited significant tumor reduction when compared to gemcitabine and controls. The antitumor activities of leiodermatolide, as well as the proven utility of antimitotic compounds against cancer, make leiodermatolide an interesting compound with potential chemotherapeutic effects that may merit further research., Competing Interests: ◆ Conflict of Interest Disclosure: Guzmán, Pitts, Linley, Winder, Baker and Wright have no conflicts of interest to disclose. Xu, Tendyke, Oestreicher, Mitsuhashi and Suh are either current or former employees of Eisai, Inc., (© 2016 UICC.)

Apratoxin A is a natural product with potent antiproliferative activity against many human cancer cell lines. However, we and other investigators observed that it has a narrow therapeutic window in vivo Previous mechanistic studies have suggested its involvement in the secretory pathway as well as the process of chaperone-mediated autophagy. Still the link between the biologic activities of apratoxin A and its in vivo toxicity has remained largely unknown. A better understanding of this relationship is critically important for any further development of apratoxin A as an anticancer drug. Here, we describe a detailed pathologic analysis that revealed a specific pancreas-targeting activity of apratoxin A, such that severe pancreatic atrophy was observed in apratoxin A-treated animals. Follow-up tissue distribution studies further uncovered a unique drug distribution profile for apratoxin A, showing high drug exposure in pancreas and salivary gland. It has been shown previously that apratoxin A inhibits the protein secretory pathway by preventing cotranslational translocation. However, the molecule targeted by apratoxin A in this pathway has not been well defined. By using a (3)H-labeled apratoxin A probe and specific Sec 61α/β antibodies, we identified that the Sec 61 complex is the molecular target of apratoxin A. We conclude that apratoxin A in vivo toxicity is likely caused by pancreas atrophy due to high apratoxin A exposure. Mol Cancer Ther; 15(6); 1208-16. ©2016 AACR., (©2016 American Association for Cancer Research.)

The design, synthesis, and biological evaluation of irciniastatin A (1) analogues, achieved by removal of three synthetically challenging structural units, as well as by functional group manipulation of the C(11) substituent of both irciniastatins A and B (1 and 2), has been achieved. To this end, we first designed a convergent synthetic route toward the diminutive analogue (+)-C(8)-desmethoxy-C(11)-deoxy-C(12)-didesmethylirciniastatin (6). Key transformations include an acid-catalyzed 6-exo-tet pyran cyclization, a chiral Lewis acid mediated aldol reaction, and a facile amide union. The absolute configuration of 6 was confirmed via spectroscopic analysis (CD spectrum, HSQC, COSY, and ROESY NMR experiments). Structure-activity relationship (SAR) studies of 6 demonstrate that the absence of the three native structural units permits access to analogues possessing cytotoxic activity in the nanomolar range. Second, manipulation of the C(11) position, employing late-stage synthetic intermediates from our irciniastatin syntheses, provides an additional five analogues (7-11). Biological evaluation of these analogues indicates a high functional group tolerance at position C(11).

In continuation of our ongoing search for bioactive compounds from microbial extracts, we performed antiproliferative and/or antimalarial assays on extracts of 806 microbial species isolated from Madagascan marine organisms, on 1317 species isolated from Madagascan soil samples and on a Streptomyces species (S.4) from a marine sponge collected from the Florida Keys. This work identified active extracts from four Streptomyces isolates (S.1, S.2, S.3 and S.4). The extracts of Streptomyces S.1 and S.2 showed antiproliferative activity against the A2780 ovarian cancer cell line, while those of S.3 and S.4 displayed both antiproliferative and antimalarial activity. Bioassay-guided fractionation coupled with dereplication of the active extracts led to the identification and isolation of nonactin (1), monactin (2), dinactin (3), ±-nonactic acid (4), toyocamycin (5), piperafizine A (6) and a new dipeptide named xestostreptin (7). The structures of all isolated compounds 1-7 were elucidated by analyses of their NMR spectroscopic and mass spectrometric data, and were confirmed by comparison with the data reported in the literature. Compound 6 was crystallized and subjected to X-ray diffraction analysis to confirm its structure as piperafizine A (6). Compounds 1-3 displayed strong antiproliferative activity against A2780 ovarian cancer cells (IC50 values of 0.1, 0.13 and 0.2 μM, respectively), A2058 melanoma cells (IC50 values of 0.2, 0.02 and 0.02 μM, respectively), and H522-T1 non small-cell cancer lung cells (IC50 values of 0.1, 0.01 and 0.01 μM, respectively), while compounds 4 and 7 exhibited weak antiplasmodial activity against the Dd2 strain of Plasmodium falciparum, with IC50 values of 6.5 and 50 μM, respectively., (Copyright © 2015 Elsevier Ltd. All rights reserved.)

The cystine-glutamate antiporter (system xc-) is a Na+-independent amino acid transporter that exchanges extracellular cystine for intracellular glutamate. It is thought to play a critical role in cellular redox processes through regulation of intracellular glutathione synthesis via cystine uptake. In gliomas, system xc- expression is universally up-regulated while that of glutamate transporters down-regulated, leading to a progressive accumulation of extracellular glutamate and excitotoxic cell death of the surrounding non-tumorous tissue. Additionally, up-regulation of system xc- in activated microglia has been implicated in the pathogenesis of several neurodegenerative disorders mediated by excess glutamate. Consequently, system xc- is a new drug target for brain cancer and neuroinflammatory diseases associated with excess extracellular glutamate. Unfortunately no potent and selective small molecule system xc- inhibitors exist and to our knowledge, no high throughput screening (HTS) assay has been developed to identify new scaffolds for inhibitor design. To develop such an assay, various neuronal and non-neuronal human cells were evaluated as sources of system xc-. Human glioma cells were chosen based on their high system xc- activity. Using these cells, [14C]-cystine uptake and cystine-induced glutamate release assays were characterized and optimized with respect to cystine and protein concentrations and time of incubation. A pilot screen of the LOPAC/NINDS libraries using glutamate release demonstrated that the logistics of the assay were in place but unfortunately, did not yield meaningful pharmacophores. A larger, HTS campaign using the 384-well cystine-induced glutamate release as primary assay and the 96-well 14C-cystine uptake as confirmatory assay is currently underway. Unexpectedly, we observed that the rate of cystine uptake was significantly faster than the rate of glutamate release in human glioma cells. This was in contrast to the same rates of cystine uptake and glutamate release previously reported in normal human fibroblast cells.

The two new lignans 3α-O-(β-D-glucopyranosyl)desoxypodophyllotoxin (1) and 4-O-(β-D-glucopyranosyl)dehydropodophyllotoxin (2) were isolated from Cleistanthus boivinianus, together with the known lignans deoxypicropodophyllotoxin (3), (±)-β-apopicropodophyllin (4), (-)-desoxypodophyllotoxin (5), (-)-yatein (6), and β-peltatin-5-O-β-D-glucopyranoside (7). The structures of all compounds were characterized by spectroscopic techniques. Compounds 1, 4, and 5 showed potent antiproliferative activities against the A2780 ovarian cancer cell line, with IC50 values of 33.0 ± 3.6, 63.1 ± 6.7, and 230 ± 1 nM, respectively. Compounds 2 and 7 showed only modest A2780 activities, with IC50 values of 2.1 ± 0.3 and 4.9 ± 0.1 μM, respectively, while compounds 3 and 6 had IC50 values of >10 μM. Compound 1 also had potent antiproliferative activity against the HCT-116 human colon carcinoma cell line, with an IC50 value of 20.5 nM, and compound 4 exhibited modest antiproliferative activity against the A2058 human caucasian metastatic melanoma and MES-SA human uterine sarcoma cell lines, with IC50 values of 4.6 and 4.0 μM, respectively.

Natural compound schweinfurthins are of considerable interest for novel therapy development because of their selective anti-proliferative activity against human cancer cells. We previously reported the isolation of highly active schweinfurthins E-H, and in the present study, mechanisms of the potent and selective anti-proliferation were investigated. We found that schweinfurthins preferentially inhibited the proliferation of PTEN deficient cancer cells by indirect inhibition of AKT phosphorylation. Mechanistically, schweinfurthins and their analogs arrested trans-Golgi-network trafficking, an intracellular vesicular trafficking system, resulting in the induction of endoplasmic reticulum stress and the suppression of both lipid raft-mediated PI3K activation and mTOR/RheB complex formation, which collectively led to an effective inhibition of mTOR/AKT signaling. The trans-Golgi-network traffic arresting effect of schweinfurthins was associated with their in vitro binding activity to oxysterol-binding proteins that are known to regulate intracellular vesicular trafficking. Moreover, schweinfurthins were found to be highly toxic toward PTEN-deficient B cell lymphoma cells, and displayed 2 orders of magnitude lower activity toward normal human peripheral blood mononuclear cells and primary fibroblasts in vitro. These results revealed a previously unrecognized role of schweinfurthins in regulating trans-Golgi-network trafficking, and linked mechanistically this cellular effect with mTOR/AKT signaling and with cancer cell survival and growth. Our findings suggest the schweinfurthin class of compounds as a novel approach to modulate oncogenic mTOR/AKT signaling for cancer treatment.

The new triterpene turranoic acid (1) and the new N-containing nor-triterpene turraenine (2), along with triptocallic acid B (3) and esculentoic acid (4) were isolated from leaves of a Turraea sp. Compounds 1-3 showed weak to moderate in vitro antiplasmodial activity against the chloroquine-resistant Plasmodium falciparum strain FCM29. Compound 1 also displayed weak cytotoxic activity against the nonsmall lung cancer cell line H522-T1 with an IC50 value of 16.4 μM.

Antiproliferative bioassay-guided fractionation of the ethanol extract of the stems of Anisocycla grandidieri led to the isolation of the known alkaloids stebisimine (1), (+)-1,2-dehydrotelobine (2), (+)-2'-norcocsuline (3) and puetogaline B (4). Herein, we report the full NMR assignments of all compounds and the X-ray crystallography of single crystals of compounds 1 and 3. Compounds 2 and 3 showed moderate antiproliferative activity against the A2780 human ovarian cancer cell line with IC50 values of 4.1 ± 0.3 and 2.7 ± 0.3 μM, respectively, and they also displayed selective activity toward the H460 (large cell lung cancer), MCF-7 (breast ductal carcinoma), and UACC-257 (melanoma) cell lines., (Copyright © 2013 John Wiley & Sons, Ltd.)

Dereplication of the antiproliferative ethyl acetate fraction of the Madagascan sponge Carteriospongia sp. led to the detection and isolation of the two known homoscalarane-type sesterterpenes 1 and 2. Investigation of a similar sponge containing closely related compounds afforded the four new antiproliferative homoscalarane sesterterpenes (3 and 5-7). The structures of all isolated compounds were elucidated by spectroscopic methods, including UV, IR and 1D and 2D NMR. Compounds 1, 3 and 5 displayed submicromolar antiproliferative activity against the A2780 ovarian cell line with IC50 values of 0.65, 0.26 and 0.28 μM, respectively, while compounds 6 and 7 showed moderate activity (4.5 and 8.7 μM, respectively). Compounds 3 and 5 also displayed anti-proliferative activity against the H522-T1 non-small cell lung and A2058 human melanoma cancer cell lines., (Copyright © 2013 Elsevier Ltd. All rights reserved.)

Investigation of the South African plant Urginea depressa Baker (Asparagaceae Juss.) for antiproliferative activity against the A2780 ovarian cancer cell line led to the isolation of the six new homoisoflavonoids urgineanins A-F (1-6), the two known bufatrienolides 7 and 9, and the new bufatrienolides urginins B and C (8 and 10). Structures were elucidated based on analysis of their 1D and 2D NMR spectra, electronic circular dichroism, and mass spectrometric data. Five of the six new homoisoflavonoids had good antiproliferative activity against the A2780 ovarian cancer, A2058 melanoma, and H522-T1 human non-small-cell lung cancer cells, and urgineanin A (1) had submicromolar activity against all three cell lines. The four bufatrienolides 7-10 had strong antiproliferative activity against the same cell line, with IC50 values of 24.1, 11.2, 111, and 40.6 nM, respectively.

Two novel reddish-orange alkaloids, mycoleptodiscin A (1) and mycoleptodiscin B (2), were isolated from liquid cultures of the endophytic fungus Mycoleptodiscus sp. that had been isolated from Desmotes incomparabilis in Panama. Elucidation of their structures was accomplished using 1D and 2D NMR spectroscopy in combination with IR spectroscopic and MS data. These compounds are indole-terpenes with a new skeleton uncommon in nature. Mycoleptodiscin B (2) was active in inhibiting the growth of cancer cell lines with IC50 values in the range 0.60-0.78 μM.

Four new compounds, (-)-petrosynoic acids A-D (1-4), and five known congeners, pellynols A (5), C (6), D (7), F (8), and I (9), were isolated from a Petrosia sp. marine sponge collected in American Samoa. Isolation work was guided by cytotoxicity against human lung cancer cells (H460). The structures of the C31-C33 polyacetylenes (1-9) were determined on the basis of 1D- and 2D-NMR analysis, mass spectrometry, and comparison of specific rotation values. Compounds 1-9 were found to be broadly cytotoxic with limited selectivity for cancer cells, as they were all moderately active against the A2058 (melanoma), H522-T1 (lung), and H460 (lung) human cancer cell lines as well as IMR-90 quiescent human fibroblast cells.

Investigation of the endemic Madagascan plant Nematostylis anthophylla (Rubiaceae) for antiproliferative activity against the A2780 ovarian cancer cell line led to the isolation of the known triterpene saponin randianin (1), and the two new bioactive triterpene saponins 2"-O-acetylrandianin (2) and 6"-O-acetylrandianin (3). The structures of the two new compounds were elucidated based on analysis of their 1D- and 2D-NMR spectra, and mass spectrometric data. The three isolated triterpene saponins displayed moderate but selective antiproliferative activities, with IC(50) values of 1.2, 1.7, and 2.2 μM, respectively, against the A2780 ovarian cancer, but only weak inhibitions of the proliferation of A2058 melanoma and the H522 lung cancer cell lines., (Copyright © 2013 Verlag Helvetica Chimica Acta AG, Zürich.)

A series of eribulin analogues was evolved in silico through iterative atom-based enumeration employing a genetic algorithm-derived survival function to minimize predicted PgP-mediated drug efflux. Representatives of the virtual series were subsequently synthesized in the laboratory and tested in vitro for PgP-susceptibility. These new computer-inspired derivatives were found to exhibit high cell growth inhibitory activity and to be among the least sensitive to P-glycoprotein-mediated drug efflux in the eribulin series, thereby validating this approach to in silico molecular design., (Copyright © 2012 Elsevier Ltd. All rights reserved.)

Investigation of the endemic Madagascan plant Uvaria sp. for antiproliferative activity against the A2780 ovarian cancer cell line led to the isolation of two new acetogenins. The structures of these two compounds were elucidated on the basis of analysis of their 1D and 2D NMR spectra, circular dichroism, and mass spectrometric data, together with chemical modification. The two acetogenins display weak antiproliferative activity against the A2780 ovarian cancer, the A2058 melanoma, and the H522 lung cancer cell lines.

The design, synthesis, and biological evaluation of two diminutive forms of (+)-spongistatin 1, in conjunction with the development of a potentially general design strategy to simplify highly flexible macrocyclic molecules while maintaining biological activity, have been achieved. Examination of the solution conformations of (+)-spongistatin 1 revealed a common conformational preference along the western perimeter comprising the ABEF rings. Exploiting the hypothesis that the small-molecule recognition/binding domains are likely to comprise the conformationally less mobile portions of a ligand led to the design of analogues, incorporating tethers (blue) in place of the CD and the ABCD components of the (+)-spongistatin 1 macrolide, such that the conformation of the retained (+)-spongistatin 1 skeleton would mimic the assigned solution conformations of the natural product. The observed nanomolar cytotoxicity and microtubule destabilizing activity of the ABEF analogue provide support for both the assigned solution conformation of (+)-spongistatin 1 and the validity of the design strategy.

The marine natural product (+)-spongistatin 1 is an extremely potent growth inhibitory agent having activity against a wide variety of cancer cell lines, while exhibiting low cytotoxicity against quiescent human fibroblasts. Consistent with a microtubule-targeting mechanism of action, (+)-spongistatin 1 causes mitotic arrest in DU145 human prostate cancer cells. More importantly, (+)-spongistatin 1 exhibits significant in vivo antitumor activity in the LOX-IMVI human melanoma xenograft model. (+)-Spongistatin 1 is, thus, an important class of microtubule targeting anticancer agent that warrants further investigation.

Investigation of the Madagascan endemic plant Ambavia gerrardii for antiproliferative activity against the A2780 ovarian cancer cell line led to the isolation of the three new alkaloids 8-hydroxyeupolauridine (1), 9-methoxyeupolauridine 1-oxide (2), and 11-methoxysampangine (3) and the three known alkaloids 4-6. The structures of 1 and 2 were confirmed by synthesis. Compounds 3, 4, and 6 showed moderate to good antiproliferative activities, with IC50 values of 10.3, 3.5, and 0.60 μM, respectively, against the A2780 human ovarian cancer cell line and with IC50 values of 0.57, 1.77, and 0.58 μM, respectively, against the H460 human lung cancer cell line.

Eribulin mesylate (Halaven™), a totally synthetic analog of the marine polyether macrolide halichondrin B, has recently been approved in the United States as a treatment for breast cancer. It is also currently under regulatory review in Japan and the European Union. Our continuing medicinal chemistry efforts on this scaffold have focused on oral bioavailability, brain penetration and efficacy against multidrug resistant (MDR) tumors by lowering the susceptibility of these compounds to P-glycoprotein (P-gp)-mediated drug efflux. Replacement of the 1,2-amino alcohol C32 side chain of eribulin with fragments neutral at physiologic pH led to the identification of analogs with significantly lower P-gp susceptibility. The analogs maintained low- to sub-nM potency in vitro against both sensitive and MDR cell lines. Within this series, increasing lipophilicity generally led to decreased P-gp susceptibility. In addition to potency in cell culture, these compounds showed in vivo activity in mouse xenograft models., (Copyright © 2011 Elsevier Ltd. All rights reserved.)

Eribulin mesylate is a newly approved treatment for locally advanced and metastatic breast cancer. We targeted oral bioavailability and efficacy against multidrug resistant (MDR) tumors for further work. The design, synthesis and evaluation of novel amine-containing analogs of eribulin mesylate are described in this part. Attenuation of basicity of the amino group(s) in the C32 side-chain region led to compounds with low susceptibility to PgP-mediated drug efflux. These compounds were active against MDR tumor cell lines in vitro and in xenograft models in vivo, in addition to being orally bioavailable., (Copyright © 2011 Elsevier Ltd. All rights reserved.)

Novel second generation analogs of eribulin mesylate, a tubulin agent recently approved for the treatment of breast cancer, are reported. Our recent efforts have focused on expanding the target indications for this class of compounds to other tumor types. Herein, we describe the design, synthesis and evaluation of eribulin analogs active against brain tumor cell lines in vitro and corresponding brain tumor models in mice. Attenuation of basicity of the amino group(s) in the C32 side-chain region led to compounds with lower susceptibility to P-gp mediated drug efflux, allowing these compounds to permeate through the blood-brain barrier. In preclinical in vivo studies, these compounds showed significantly higher levels in the brain and cerebrospinal fluid as compared to eribulin. In addition, analogs within this series showed antitumor activity in an orthotopic murine model of human glioblastoma., (Copyright © 2011 Elsevier Ltd. All rights reserved.)

Investigation of the endemic Madagascar plant Leptadenia madagascariensis Decne. (Apocynaceae) for antiproliferative activity against the A2780 ovarian cancer cell line led to the isolation of the four new cardenolides 1-4. The structure elucidations of these compounds were based on analyzes of their 1D and 2D NMR spectra and mass spectrometric data. The cardenolides were strongly antiproliferative to the A2780 ovarian cancer cell line, with IC(50) values of 0.18, 0.21, 0.17, and 0.29μM line, and to the H460 human lung cancer cell line, with IC(50) values of 0.16, 0.68, 0.37, and 0.48μM, respectively., (Copyright © 2010 Elsevier Ltd. All rights reserved.)

Bioassay-guided fractionation of an ethanol extract of the roots of the endemic Malagasy plant Pongamiopsis pervilleana led to the isolation of the three new compounds (2'R)-4'-hydroxyemoroidocarpan (1), pongavilleanine (3), and epipervilline (4) together with two known compounds, identified as emoroidocarpan (2) and rotenolone (5). The structures of all compounds were determined by physical, chemical, and spectroscopic evidence. The stereochemistry at C-2' of the previously reported compound emoroidocarpan was determined to be R by the observation of a negative Cotton effect at 474 nm in the CD spectrum of its osmate ester derivative. Compounds 2-5 displayed moderate antiproliferative activity against the A2780 human ovarian cancer cell line, and rotenolone also showed micromolar antiproliferative activity toward the breast cancer BT-549, prostate cancer DU 145, NSCLC NCI-H460, and colon cancer HCC-2998 cell lines.

The design, synthesis, and biological evaluation of two potential (+)-spongistatin 1 analogues have been achieved. The analogues, incorporating tethers (red) in place of the ABCD and the CD components of the (+)-spongistatin 1 macrolide, were designed such that the conformations of the retained skeleton (blue) would mimic the assigned major solution conformation of the natural product The nanomolar cytotoxicity observed for the ABEF analogue provides strong support for the assigned solution conformation.

Fractionation of an ethanol extract of a Madagascar collection of the leaves and fruit of Cassipourea lanceolata Tul. led to the isolation of three euphane triterpenoids 1-3. The (1)H and (13)C NMR spectra of all compounds were fully assigned using a combination of 2D NMR experiments, including COSY, TOCSY, HSQC (HMQC), HMBC and ROESY sequences. The three compounds showed weak antiproliferative activities against the A2780 human ovarian cancer cell line, with IC(50) values of 25, 25 and 32 microM, respectively., (Copyright 2009 Elsevier Ltd. All rights reserved.)

A new 1-imidazoyl-3-carboxy-6-hydroxy-beta-carboline alkaloid, named hyrtiocarboline (1), was isolated from a Papua New Guinea marine sponge, Hyrtios reticulatus. The structure was elucidated from spectroscopic data, including (1)H-(15)N HMBC NMR experiments, which provided complementary (15)N chemical shift information in support of the structure. This compound showed selective antiproliferative activity against H522-T1 non-small cell lung, MDA-MB-435 melanoma, and U937 lymphoma cancer cell lines.

E7974 is a synthetic analogue of the marine sponge natural product hemiasterlin. Here, we show that E7974, such as parental hemiasterlin, acts via a tubulin-based antimitotic mechanism. E7974 inhibits polymerization of purified tubulin in vitro with IC(50) values similar to those of vinblastine. In cultured human cancer cells, E7974 induces G(2)-M arrest and marked disruption of mitotic spindle formation characteristic of tubulin-targeted anticancer drugs. Extensive hypodiploid cell populations are seen in E7974-treated cells, indicating initiation of apoptosis after prolonged G(2)-M blockage. Consistent with this observation, E7974 induces caspase-3 activation and poly ADP ribose polymerase cleavage, typical biochemical markers of apoptosis. Only a short cellular exposure to E7974 is sufficient to induce maximum mitotic arrest, suggesting that E7974's antitumor effects in vivo may persist even after blood levels of the drug decrease after drug administration. Interactions of E7974 with purified tubulin were investigated using two synthetic tritiated photoaffinity analogues incorporating a benzophenone photoaffinity moiety at two different positions of the E7974 scaffold. Both analogues preferentially photolabeled alpha-tubulin, although minor binding to beta-tubulin was also detected. E7974 thus seems to share a unique, predominantly alpha-tubulin-targeted mechanism with other hemiasterlin-based compounds, suggesting that, unlike many tubulin-targeted natural products and related drugs, the hemiasterlins evolved to mainly target alpha-tubulin, not beta-tubulin subunits.

Bioassay-guided fractionation of an EtOH extract obtained from the roots of the Madagascan plant Dodonaea viscosa led to the isolation of two new antiproliferative oleanane-type triterpenoid saponins, dodoneasides A and B (1 and 2). The structures of these two new compounds were elucidated using 1D and 2D NMR experiments and mass spectrometry. Compounds 1 and 2 showed antiproliferative activity against the A2780 human ovarian cancer cell line with IC(50) values of 0.79 and 0.70 muM, respectively.

We report here that des-methyl, des-amino pateamine A (DMDA-PatA), a structurally simplified analogue of the marine natural product pateamine A, has potent antiproliferative activity against a wide variety of human cancer cell lines while showing relatively low cytotoxicity against nonproliferating, quiescent human fibroblasts. DMDA-PatA retains almost full in vitro potency in P-glycoprotein-overexpressing MES-SA/Dx5-Rx1 human uterine sarcoma cells that are significantly resistant to paclitaxel, suggesting that DMDA-PatA is not a substrate for P-glycoprotein-mediated drug efflux. Treatment of proliferating cells with DMDA-PatA leads to rapid shutdown of DNA synthesis in the S phase of the cell cycle. Cell-free studies show that DMDA-PatA directly inhibits DNA polymerases α and γ in vitro albeit at concentrations considerably higher than those that inhibit cell proliferation. DMDA-PatA shows potent anticancer activity in several human cancer xenograft models in nude mice, including significant regressions observed in the LOX and MDA-MB-435 melanoma models. DMDA-PatA thus represents a promising natural product-based anticancer agent that warrants further investigation.

The first total synthesis of ipomoeassin F was carried out using a convergent approach that relied upon the use of Schmidt glycosidation technology for the coupling of two suitably protected monosaccharide fragments. After two steps, ring-closing metathesis was used to form the macrocyclic ring, and seven more steps then furnished ipomoeassin F. In vitro inhibitory activity against a four-panel cell line showed low nanomolar inhibitory activity.

Bioassay-guided fractionation of an ethanol extract of a Madagascar collection of Elaeodendron alluaudianum led to the isolation of two new cardenolide glycosides (1 and 2). The (1)H and (13)C NMR spectra of both compounds were fully assigned using a combination of 2D NMR experiments, including (1)H-(1)H COSY, HSQC, HMBC, and ROESY sequences. Both compounds 1 and 2 were tested against the A2780 human ovarian cancer cell line and the U937 human histiocytic lymphoma cell line assays, and showed significant antiproliferative activity with IC(50) values of 0.12 and 0.07 microM against the A2780 human ovarian cancer cell line, and 0.15 and 0.08 microM against the U937 human histiocytic lymphoma cell line, respectively.

Bioassay-guided fractionation of an ethanol extract of a Malleastrum sp. afforded three new limonoids, malleastrones A-C ( 1- 3), respectively. Each limonoid contained a rare tetranortriterpenoid skeleton. Structure elucidation of the isolates was carried out by analysis of one- and two-dimensional NMR and X-ray diffraction data. The novel isolates 1 and 2 were tested for antiproliferative activity against a panel of cancer cell lines and exhibited IC 50 values ranging from 0.19 to 0.63 microM.

Bioassay-guided fractionation of an ethanol extract of Artabotrys madagascariensis led to the isolation of the new compound artabotrene (1), two butenolides (2 and 3), and the tetracyclic triterpene polycarpol (4). Structure elucidation was determined on the basis of one and two-dimensional NMR, and absolute configuration of compounds 2-4 was verified by analysis of CD and optical rotation spectra. Two of the isolates, melodorinol (2) and acetylmelodorinol (3), were found to display antiproliferative activity against five different tumour cell lines with IC50 values ranging from 2.4 to 12 microM.

Bioassay-guided fractionation of an ethanol extract obtained from the Madagascar plant Elaeodendron sp. led to the isolation of two new cardenolides, elaeodendrosides T and U (1 and 2). The structures of the new compounds were elucidated using 1D and 2D NMR experiments and mass spectrometry. Compounds 1, 3, 4, and 5 showed significant antiproliferative activity against A2780 human ovarian cancer cells with IC50 values of 0.085, 0.019, 0.19, and 0.10 microM, respectively, while compounds 2 and 6 were less active.

Bioassay-guided fractionation of an EtOH extract obtained from the roots of the Madagascan plant Albizia gummifera led to the isolation of three new cytotoxic oleanane-type triterpenoid saponins, gummiferaosides A-C (1-3). The structures of these new compounds were elucidated using 1D and 2D NMR experiments and mass spectrometry. Compounds 1-3 showed cytotoxicity against the A2780 human ovarian cancer cell line with IC50 values of 0.8, 1.5, and 0.6 microg/mL, respectively.

E7389, a macrocyclic ketone analog of the marine natural product halichondrin B, currently is undergoing clinical trials for cancer. This fully synthetic agent exerts its highly potent in vitro and in vivo anticancer effects via tubulin-based antimitotic mechanisms, which are similar or identical to those of parental halichondrin B. In an attempt to understand the impressive potency of E7389 in animal models of human cancer, its ability to induce apoptosis following prolonged mitotic blockage was evaluated. Treatment of U937 human histiocytic lymphoma cells with E7389 led to time-dependent collection of cells in the G2-M phase of the cell cycle, beginning as early as 2 h and becoming maximal by 12 h. Increased numbers of hypodiploid events were seen beginning at 12 h, suggesting initiation of apoptosis after prolonged E7389-induced mitotic blockage. The identity of hypodiploid events as apoptotic cells under these conditions was confirmed by two additional morphologic criteria: green to orange/yellow shifts on acridine orange/ethidium bromide staining, and cell surface annexin V binding as assessed by flow cytometry. Several biochemical correlates of apoptosis also were seen following E7389 treatment, including phosphorylation of the antiapoptotic protein Bcl-2, cytochrome c release from mitochondria, proteolytic activation of caspase-3 and -9, and cleavage of the caspase-3 substrate poly(ADP-ribose) polymerase (PARP). In LNCaP human prostate cancer cells, treatment with E7389 also led to generation of hypodiploid cells, activation of caspase-3 and -9, and appearance of cleaved PARP, indicating that E7389 can activate cellular apoptosis pathways under anchorage-independent and -dependent cell culture conditions. These results show that prolonged mitotic blockage by E7389 can lead to apoptotic cell death of human cancer cells in vitro and can provide a mechanistic basis for the significant in vivo anticancer efficacy of E7389.