Anti-tumor activity and mechanisms of a novel vascular disrupting agent, (Z)-3,4′,5-trimethoxylstilbene-3′-O-phosphate disodium (M410)

Vascular disrupting agents (VDAs) have emerged as a new kind of anti-cancer drug in recent years. Structural modification of an active parent compound is an effective approach to developing new agents with more activity and fewer adverse reactions. In our study, six synthesized stilbene derivatives were screened for their cytotoxic activity against human tumor cells, and their mechanisms of action were investigated. The MTT assay was used to determine the anti-proliferative activity of these compounds. Polymerization of tubulin was detected by a tubulin assembly assay, and the cellular microtubule network was observed by immunocytochemical analyses. Cell-cycle distribution was detected by flow cytometry. A nude mouse model with xenografted colon cancer was used to demonstrate the in vivo anti-tumor activity, and microvessel density (MVD) was determined by immunohistochemistry. The expression levels of protein and mRNA were detected by Western blot and RT-PCR, respectively. Among the six newly synthesized compounds, (Z)-3,4′,5-trimethoxylstilbene-3′-O-phosphate disodium (M410) showed potent cytotoxic activity toward proliferating tumor cells and exhibited a similar cytotoxicity against multi-drug resistant (MDR) tumor cells. M410 inhibited bovine brain tubulin polymerization in a way similar to that of colchicine. In proliferating human umbilical vein endothelial cells (HUVECs), 20 nM of M410 induced cellular tubulin depolymerization within 4 h, which led to M phase arrest. Systemic administration of M410 at nontoxic doses in nude mice resulted in inhibition of tumor growth of human colon cancer LoVo xenografts. The tumor vessel density also decreased after M410 treatment, as determined by immunohistochemical staining for CD31. M410 downregulated hypoxia-inducible factor-1 alpha (HIF-1α) expression, reduced nuclear HIF-1α, and downregulated vascular endothelial cell growth factor (VEGF) mRNA. Our results indicate that M410 is a potent microtubule inhibitor that is cytotoxic, angiogenesis inhibiting and vascular targeting.