Quantitative Structure−Activity Relationship (5D-QSAR) Study of Combretastatin-like Analogues as Inhibitors of Tubulin Assembly

The concise synthesis of chalcone, indanone and indenone analogues of combretastatin A4

A series of aryl- and aroyl-substituted chalcone analogues of the tubulin binding agent combretastatin A4 (1) were prepared, using a recently introduced one-pot palladium-mediated hydrostannylation-coupling reaction sequence. These chalcones were converted to indanones by Nazarov cyclisation, followed by oxidation to give the corresponding indenones. Indenones were also prepared using a palladium-mediated formal [3+2]-cycloaddition process between ortho-halobenzaldehydes and diarylpropynones. All compounds were assessed as inhibitors of tubulin polymerisation, but only E-31 had activity similar to that of 1. However, compound E-31 did not exhibit antiproliferative activity against the MCF-7 cell line.

Highly potent triazole-based tubulin polymerization inhibitors

We describe the synthesis and biological evaluation of a series of tubulin polymerization inhibitors that contain the 1,2,4-triazole ring to retain the bioactive configuration afforded by the cis double bond in combretastatin A-4 (CA-4). Several of the subject compounds exhibited potent tubulin polymerization inhibitory activity as well as cytotoxicity against a variety of cancer cells including multi-drug-resistant (MDR) cancer cell lines. Attachment of the N-methyl-5-indolyl moiety to the 1,2,4-triazole core, as exemplified by compound 7, conferred optimal properties among this series. Computer docking and molecular simulations of 7 inside the colchicine binding site of tubulin enabled identification of residues most likely to interact strongly with these inhibitors and explain their potent anti-tubulin activity and cytotoxicity. It is hoped that results presented here will stimulate further examination of these substituted 1,2,4-triazoles as potential anti-cancer therapeutic agents.

Plant-based anticancer molecules: a chemical and biological profile of some important leads

A number of natural products, with diverse chemical structures, have been isolated as anticancer agents. Several potential lead molecules such as camptothecin, vincristine, vinblastine, taxol, podophyllotoxin, combretastatins, etc. have been isolated from plants and many of them have been modified to yield better analogues for activity, toxicity or solubility. Several successful molecules like topotecan, irinotecan, taxotere, etoposide, teniposide, etc. also have emerged as drugs upon modification of these natural leads and many more are yet to come. In this review, the authors have focused on four important anticancer leads, that is, camptothecin, taxol, combretastatin A-4 and podophyllotoxin. Their chemistry, structure and activity relationships, biological activities, modes of action, analogue synthesis and future prospects have been discussed.

Structure-Based Discovery of a Boronic Acid Bioisostere of Combretastatin A-4

Targeting the microtubule system represents an attractive strategy for the development of anticancer agents. In this study, we report a class of combretastatin A-4 (CA-4) analogs derivatized with a boronic acid moiety replacing the hydroxyl group on the C-ring of CA-4. Docking studies of the X-ray structures of our aryl-boronic analogs onto an X-ray structure of the alpha,beta-tubulin heterodimer suggested that cis-6 was a potent inhibitor of the colchicine binding. The model indicated that there would be strong hydrogen bonding between the boronic acid moiety and Thr-179 and Val-181 of alpha-tubulin. We demonstrate that the cis-6 boronic acid bioisostere of CA-4: (1) inhibits tubulin assembly, (2) competitively displaces colchicine, and (3) is a low-nanomolar inhibitor of human cancer cell lines. We present this isostere as a class of potent analogs of CA-4.