Background: Chemical compounds from natural sources continue to serve as important pharmacological tools for the understanding of biological pathways and also provide chemical platform for new drug discovery. The utility of various anti-microtubule agents from natural origins are the best examples that continuously serve these two purposes. In this study, we have identified a novel tubulin-targeting activity of a natural product Withaferin-A. Though several groups have already shown that Withaferin-A is a potent anti-cancer agent, can kill variety of carcinomas by inducing apoptosis, but not much is known about its molecular targets inside the cell. This study is to evaluate the therapeutic efficacy of WA towards human cancer, in relation to its ability to directly targeting microtubule dynamics within cell.

Methods: The IC-50 value of WA was determined by MTT assay, apoptosis and cell cycle assay was performed by FACS analysis, wound healing assay was done to see cellular migration, immune fluorescent detection was done to check microtubular network of WA treated cells. Effect of WA on tubulin polymerization in cell free system was studied by light scattering assay, binding measurements of WA to tubulin was determined by flurometric assay and probable WA-tubulin interaction site was proposed by molecular modeling method.

Results: We have identified WA as a novel anti-microtubule agent that inhibits proliferation, migration and cellular progression by affecting mitosis in HeLa and MCF-7 cells. Brief incubation with nontoxic concentrations of WA induced significant depolymerization of interphase and mitotic spindle microtubules. It inhibits tubulin polymerization, induces conformational changes in tubulin by directly binding to purified tubulin. Both in silico and in-vitro studies indicated that WA preferably binds to a novel site on tubulin.

Conclusion: It is evident that WA suppresses microtubule dynamics by directly binding to tubulin which sheds light on mechanisms behind its anti-proliferative activity towards cancer cells.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2011 Nov 12-16; San Francisco, CA. Philadelphia (PA): AACR; Mol Cancer Ther 2011;10(11 Suppl):Abstract nr C218.