Design, synthesis and biological evaluation of quinoline-2-carbonitrile-based hydroxamic acids as dual tubulin polymerization and histone deacetylases inhibitors.

A series of quinoline and quinazoline analogs were designed and synthesized as new tubulin polymerization (TP) and histone deacetylases (HDAC) inhibitors. Compounds 12a and 12d showed the best cytotoxicity activities against a panel of human cancer cell lines with an averaged IC50 value of 0.6 and 0.7 nM, respectively. Furthermore, these lead compounds showed good activities against CA-4-resistant colon-carcinoma and multidrug-resistant leukemia cells. In addition, compounds 12a and 12d induced HT29 cell cycle arrest in the G2/M phase and produced caspase-induced apoptosis of HT29 cells through mitochondrial dysfunction. Also, 12a and 12d inhibited HDAC8, 6, and 11 activities. Furthermore, lead compound 12a exhibited higher metabolic stability than isoCA-4 and was highly potent in suppressing tumor growth in the fibrosarcoma MCA205 tumor model. Collectively, these studies suggest that 12a represents a new dual inhibitor of TP and HDAC activities, which makes it a suitable candidate for further investigations in clinical development.

Alkyl-Resorcinol Derivatives as Inhibitors of GDP-Mannose Pyrophosphorylase with Antileishmanial Activities.

Leishmaniasis is a vector-borne disease caused by the protozoan parasite Leishmania found in tropical and sub-tropical areas, affecting 12 million people around the world. Only few treatments are available against this disease and all of them present issues of toxicity and/or resistance. In this context, the development of new antileishmanial drugs specifically directed against a therapeutic target appears to be a promising strategy. The GDP-Mannose Pyrophosphorylase (GDP-MP) has been previously shown to be an attractive therapeutic target in Leishmania. In this study, a chemical library of 5000 compounds was screened on both L. infantum (LiGDP-MP) and human (hGDP-MP) GDP-MPs. From this screening, oncostemonol D was found to be active on both GDP-MPs at the micromolar level. Ten alkyl-resorcinol derivatives, of which oncostemonols E and J (2 and 3) were described for the first time from nature, were then evaluated on both enzymes as well as on L. infantum axenic and intramacrophage amastigotes. From this evaluation, compounds 1 and 3 inhibited both GDP-MPs at the micromolar level, and compound 9 displayed a three-times lower IC50 on LiGDP-MP, at 11 µM, than on hGDP-MP. As they displayed mild activities on the parasite, these compounds need to be further pharmacomodulated in order to improve their affinity and specificity to the target as well as their antileishmanial activity.

Cyclic bridged analogs of isoCA-4: Design, synthesis and biological evaluation.

In this work, a series of cyclic bridged analogs of isocombretastatin A-4 (isoCA-4) with phenyl or pyridine linkers were designed and synthesized. The synthesis of the desired analogs was performed by the formation of nitro-vinyl intermediates, followed by a Cadogan cyclization. Structure activity relationship (SAR) study demonstrates the critical role of the combination of quinaldine as ring A, pyridine as the linker, and indole as ring B in the same molecule, for the cytotoxic activity. Among all tested compounds, compound 42 showed the highest antiproliferative activity against a panel of cancer cell lines with average IC50 values of 5.6 nM. Also, compound 42 showed high antiproliferative activity against the MDR1-overexpressing K562R cell line; thus, it was 1.5- and 12-fold more active than the reference compounds, isoCA-4 and CA-4, respectively. Moreover, 42 displayed a strong antiproliferative activity against the colon-carcinoma cells (HT-29), which are resistant to combretastatin A-4 and isoCA-4, and it was found to be 8000-fold more active than natural CA-4. Compound 42 also effectively inhibited tubulin polymerization both in vitro and in cells, and induced cell cycle arrest in G2/M phase. Next, we demonstrated that compound 42 dose-dependently caused caspase-induced apoptosis of K562 cells through mitochondrial dysfunction. Finally, we evaluated the effect of compound 42 in human no cancer cells compared to the reference compound. We demonstrated that 42 was 73 times less cytotoxic than isoCA-4 in quiescent peripheral blood lymphocytes (PBLs). In summary, these results suggest that compound 42 represents a promising tubulin inhibitor worthy of further investigation.

Synthesis and Anticancer Properties of Oxazepines Related to Azaisoerianin and IsoCoQuines.

In this article, we report the synthesis and biological properties of a series of novel oxazepines related to isoCA-4 having significant antitumor properties. Among them, three oxazepin-9-ol derivatives display a nanomolar or a sub-nanomolar cytotoxicity level against five human cancer cell lines (HCT116, U87, A549, MCF7, and K562). It was demonstrated that the lead compound in this series inhibits tubulin assembly with an IC50 value of 1 µM and totally arrests the cellular cycle in the G2/M phase at the low concentration of 5 nM in HCT116 and K562 cells. Molecular modeling studies perfectly corroborates these promising results.

Identification of a new series of flavopiridol-like structures as kinase inhibitors with high cytotoxic potency.

In this work, unique flavopiridol analogs bearing thiosugars, amino acids and heterocyclic moieties tethered to the flavopiridol via thioether and amine bonds mainly on its C ring have been prepared. The analogs bearing thioether-benzimidazoles as substituents have demonstrated high cytotoxic activity in vitro against up to seven cancer cell lines. Their cytotoxic effects are comparable to those of flavopiridol. The most active compound 13c resulting from a structure-activity relationship (SAR) study and in silico docking showed the best antiproliferative activity and was more efficient than the reference compound. In addition, compound 13c showed significant nanomolar inhibition against CDK9, CDK10, and GSK3ß protein kinases.

Pyrrolo-imidazo[1,2-a]pyridine Scaffolds through a Sequential Coupling of N-Tosylhydrazones with Imidazopyridines and Reductive Cadogan Annulation, Synthetic Scope, and Application.

A new strategy for the construction of 3-phenyl-1H-pyrrolo-imidazo[1,2-a]pyridine backbone is described. The reaction starts from the coupling between N-tosylhydrazones and 2-chloro-3-nitroimidazo[1,2-a]pyridines leading to the formation of 3-nitro-2-(arylvinyl)imidazo[1,2-a]pyridine derivatives. Optimization of Cadogan-reductive conditions allowed the conversion of the obtained nitro derivative to a new scaffold of the type 3-aryl-1H-pyrrolo-imidazo[1,2-a]pyridine. This method provides rapid access to new libraries in the context of diversity-oriented synthesis, which intends to generate small molecules with a large structure diversity in an efficient manner. Screening of the biological activity of the newly generated compounds leads to the identification of a new promising compound 5cc, which exhibits good antiproliferative activity in the submicromolar range against a human colon cancer cell line.

N,N-bis-heteroaryl methylamines: Potent anti-mitotic and highly cytotoxic agents.

The synthesis and evaluation of a series of N,N-bis-heterocyclic-methylamines 1 as isoazaerianin analogues are described. It was demonstrated that the replacement of the 3,4,5-trimethoxyphenyl A-ring present in CA-4, isoCA-4 and isoazaerianin by a quinoline or a quinazoline ring is possible and often beneficiary for a high level of cytotoxicity. We have also showed that a carbazole or an indole nucleus are very effective as B-rings in this series, leading to anti-cancer drugs 1 having a sub-nanomolar level of cytotoxicity (1a: IC50 = 70 pM against HCT116 cells). 1a also display a high level of cytotoxicity against four other human cancer cells and inhibited tubulin assembly at a micromolar level. Moreover, at a concentration of 5 nM, 1a arrested the cellular cycle in G2/M phase of the cellular cycle and induced apoptosis of HCT116 cells. It was also showed that after few hours 1a at a concentration of 10 nM totally disrupted endothelial network formation on Matrigel.

1,1-Diheterocyclic Ethylenes Derived from Quinaldine and Carbazole as New Tubulin-Polymerization Inhibitors: Synthesis, Metabolism, and Biological Evaluation.

We report the synthesis and metabolic and biological evaluation of a series of 17 novel heterocyclic derivatives of isocombretastatin-A4 (iso-CA-4) and their structure-activity relationships. Among these derivatives, the most active compound, 4f, inhibited the growth of a panel of seven cancer cell lines with an IC50 in the low nanomolar range. In addition, 4f showed interesting activity against CA-4-resistant colon-carcinoma cells and multidrug-resistant leukemia cells. It also induced G2/M cell-cycle arrest. Structural data indicated binding of 4f to the colchicine site of tubulin, likely preventing the curved-to-straight tubulin structural changes that occur during microtubule assembly. Also, 4f disrupted the blood-vessel-like assembly formed by human umbilical-vein endothelial cells in vitro, suggesting its function as a vascular-disrupting agent. An in vitro metabolism study of 4f showed its high human-microsomal stability in comparison with that of iso-CA-4. The physicochemical properties of 4f may be conducive to CNS permeability, suggesting that this compound may be a possible candidate for the treatment of glioblastoma.

One-Pot Synthesis of 2-Styrylindoles from Ortho-Substituted Chloroenynes.

A facile one-pot synthesis of 2-styrylindoles, through Suzuki arylation of ortho-substituted chloroenynes followed by N-cyclization and N-demethylation, has been developed. A variety of 2-styrylindoles were obtained in good to excellent yields and were evaluated for their anticancer properties.

Design and Synthesis of Tubulin and Histone Deacetylase Inhibitor Based on iso-Combretastatin A-4.

Designing multitarget drugs have raised considerable interest due to their advantages in the treatment of complex diseases such as cancer. Their design constitutes a challenge in antitumor drug discovery. The present study reports a dual inhibition of tubulin polymerization and HDAC activity. On the basis of 1,1-diarylethylenes ( isoCA-4) and belinostat, a series of hybrid molecules was successfully designed and synthesized. In particular compounds, 5f and 5h were proven to be potent inhibitors of both tubulin polymerization and HDAC8 leading to excellent antiproliferative activity.

A fluorine scan of a tubulin polymerization inhibitor isocombretastatin A-4: Design, synthesis, molecular modelling, and biological evaluation.

A novel series of tubulin polymerization inhibitors, based on fluorinated derivatives of isocombretastatin A-4 was synthesized with the goal of evaluating the effect of these compounds on the proliferative activity. The introduction of fluorine atom was performed on the phenyl ring or at the linker between the two aromatic rings. The modification of isoCA-4 by introduction of difluoromethoxy group at the para-position (3i) and substitution of the two protons of the linker by two fluorine atoms (3m), produced the most active compounds in the series, with IC50 values of 0.15-2.2 nM (3i) and 0.1-2 nM (3m) respectively, against a panel of six cancer cell lines. Compounds 3i and 3m had greater antiproliferative activity in comparison with references CA-4 or isoCA-4, the presence of fluorine group leads to a significant enhancement of the antiproliferative activity. Molecular docking studies indicated that compounds 3i and 3m occupy the colchicine binding site of tubulin. Evaluation of cytotoxicity in Human noncancer cells indicated that the compounds 3i and 3m were practically ineffective in quiescent peripheral blood lymphocytes, and may have a selective antiproliferative activity against cancer cells. Analyses of cell cycle distribution, and morphological microtubules organization showed that compound 3m induced G2/M phase arrest and, dramatically disrupted the microtubule network.

Cytotoxic Prenylated Stilbenes Isolated from Macaranga tanarius.

With the aim of discovering new cytotoxic prenylated stilbenes of the schweinfurthin series, Macaranga tanarius was selected for detailed phytochemical investigation among 21 Macaranga species examined by using a molecular networking approach. From an ethanol extract of the fruits, seven new prenylated stilbenes, schweinfurthins K-Q (7-13), were isolated, along with vedelianin (1), schwenfurthins E-G (2-4), mappain (5), and methyl-mappain (6). The structures of the new compounds were established by spectroscopic data analysis. The relative configurations of compounds 8, 12, and 13 were determined based on ROESY NMR spectroscopic analysis. The cytotoxic activities of compounds 1-13 were evaluated against the human glioblastoma (U87) and lung (A549) cancer cell lines.

Palladium-Catalyzed One-Pot Reaction of Hydrazones, Dihaloarenes, and Organoboron Reagents: Synthesis and Cytotoxic Activity of 1,1-Diarylethylene Derivatives.

A new three-component assembly reaction between N-tosylhydrazones, dihalogenated arenes, and boronic acids or boronate esters was developed, producing highly substituted 1,1-diarylethylenes in good yields. The two C-C bonds formed through this coupling have been catalyzed by a single Pd-catalyst in a one-pot fashion. It is noted that the one-pot pinacol boronate cross-coupling reaction generally provides products in high yields, offers an expansive substrate scope, and can address a broad range of aryl, styrene, vinyl, and heterocyclic olefinic targets. The scope of this one-pot coupling has been also extended to the synthesis of the 1,1-diarylethylene skeleton of the natural product ratanhine. The new compounds were evaluated for their cytotoxic activity, and this allowed the identification of compound 4ab that exhibits excellent antiproliferative activity in the nanomolar concentration range against HCT116 cancer cell lines.

Synthesis and biological evaluation of C-13' substituted 7'-homo-anhydrovinblastine derivatives.

Recent publications highlighted that vinca derivatives either functionalized on C-12' or enlarged on cycle C' could be more cytotoxic than vinblastine or vinorelbine, both used in anti-cancer therapy. By combining these two results, nine new 7'-homo-anhydrovinblastine derivatives functionalized on C-13' were elaborated. The synthesis of key intermediates, their one-step transformation into final products in mild conditions and their biological activities are presented.

Pipestelides A-C: cyclodepsipeptides from the Pacific marine sponge Pipestela candelabra.

Pipestelides A-C (2-4) are three new NRPS-PKS hybrid macrolides containing uncommon moieties, isolated from the Pacific marine sponge Pipestela candelabra. Their structures were elucidated on the basis of spectroscopic data. These cyclodepsipeptides appear to be biosynthetically related to jaspamide (aka jasplakinolide) (1) by chemical modification of the building blocks of the polyketide or peptide chains. Pipestelides A-C (2-4) contain a bromotyrosine [3-amino-3-(bromo-4-hydroxyphenyl)propanoic acid] unit, a polypropionate with a Z double bond, and a 2-hydroxyquinolinone, respectively. Revised chemical shift assignments are provided for the co-isolated known jasplakinolide C(a) (5). In addition, compounds 2 and 3 exhibited cytotoxic activities in the micromolar range.

Isolation, structure elucidation and biological activity of metabolites from Sch-642305-producing endophytic fungus Phomopsis sp. CMU-LMA.

Eight polyketide compounds were isolated from the cultivation broth of Phomopsis sp. CMU-LMA. We have recently described LMA-P1, a bicyclic 10-membered macrolide, obtained as a bioconversion derivative of Sch-642305, the major compound isolated in this study. Benquinol is the ethyl ester derivative of the 13-dihydroxytetradeca-2,4,8-trienoic acid produced by Valsa ambiens. This compound is concomitantly produced with the 6,13-dihydroxytetradeca-2,4,8-trienoic acid (DHTTA) previously isolated from Mycosphaerellarubella. The absolute configuration of the new compound, (2R,3R,4S,5R)-3-hydroxy-2,4-dimethyl-5-[(S,Z)-3-methylpentenyl]-tetrahydro-pyranone LMA-P2 was confirmed by X-ray crystallography. The δ-lactone 2,3-dihydroxytetradecan-5-olide (DHTO) was previously isolated from Seiridium unicorne. This compound may form through the cyclization of the methyl-2,3,5-trihydroxytridecanoate LMA-P3, a new linear polyketide isolated in this study. Benquoine, a new 14-membered lactone generated from the cyclization of benquinol, is proposed as the key precursor for the biosynthesis of Sch-642305. Antimicrobial activity and cancer cell viability inhibition by the new compounds were investigated. Benquoine exhibits antimicrobial activity against Gram positive bacteria, and cytotoxicity against HCT-116 cancer cell line.

Biotransformation of natural compounds. Oxido-reduction of Sch-642305 by Aspergillus ochraceus ATCC 1009.

Sch-642305 is the major compound produced by the endophytic fungi Phomopsis sp. CMU-LMA. Incubation of Sch-642305 with Aspergillus ochraceus ATCC 1009 resting cells leads to three new derivatives through an oxido-reduction of the six-membered ring of the molecule. Reduction of the double bound leads to compound (1), which subsequently undergoes carbonyl reduction to (2) and ring hydroxylation to (3). According to the previously solved crystal structure of Sch-642305 coupled with (1)H NMR NOE correlation and the crystal structure of compound 1, the absolute configurations of the new derivatives were established. In contrast to the parent compound Sch-642305, compound (1) exhibits antimicrobial activity against gram-negative bacteria. Furthermore, while all derivatives exhibit cytotoxic activity against various cancer cell lines, compound (2) achieved an IC(50) of 4 nM against human myelogenous leukemia K 562, compared to 20 nM for the parent Sch-642305.

ATP hydrolysis and pristinamycin IIA inhibition of the Staphylococcus aureus Vga(A), a dual ABC protein involved in streptogramin A resistance.

In Gram-positive bacteria, a large subfamily of dual ATP-binding cassette proteins confers acquired or intrinsic resistance to macrolide, lincosamide, and streptogramin antibiotics by a far from well understood mechanism. Here, we report the first biochemical characterization of one such protein, Vga(A), which is involved in streptogramin A (SgA) resistance among staphylococci. Vga(A) is composed of two nucleotide-binding domains (NBDs), separated by a charged linker, with a C-terminal extension and without identified transmembrane domains. Highly purified Vga(A) displays a strong ATPase activity (K(m) = 78 mum, V(m) = 6.8 min(-1)) that was hardly inhibited by orthovanadate. Using mutants of the conserved catalytic glutamate residues, the two NBDs of Vga(A) were shown to contribute unequally to the total ATPase activity, the mutation at NBD2 being more detrimental than the other. ATPase activity of both catalytic sites was essential for Vga(A) biological function because each single Glu mutant was unable to confer SgA resistance in the staphylococcal host. Of great interest, Vga(A) ATPase was specifically inhibited in a non-competitive manner by the SgA substrate, pristinamycin IIA (PIIA). A deletion of the last 18 amino acids of Vga(A) slightly affected the ATPase activity without modifying the PIIA inhibition values. In contrast, this deletion reduced 4-fold the levels of SgA resistance. Altogether, our results suggest a role for the C terminus in regulation of the SgA antibiotic resistance mechanism conferred by Vga(A) and demonstrate that this dual ATP-binding cassette protein interacts directly and specifically with PIIA, its cognate substrate.