Abstract 2794: Cytotoxic and vascular disrupting activity of EHT 6706, a novel tubulin polymerization inhibitor

Abstract

Among cytotoxics commonly used for cancer treatment, microtubule-targeting agents harbor a broad clinical anti-tumor efficacy. Microtubule-targeting agents act by their direct cytotoxic actions on tumor cells but also by their anti-angiogenic and vascular-disrupting actions. In contrast to classical antiangiogenic agents, vascular disrupting agents can, at the same time, block cell survival, prevent the formation of new vessels and damage the existing tumor vasculature. Here we describe EHT 6706, the current lead compound of a novel chemical class of tubulin targeting agents. EHT 6706 inhibits in a dose-dependent manner microtubule formation in an in vitro tubulin polymerization assay. EHT 6706 binds at or near the colchicine binding site of the tubulin-colchicine complex, hence displacing the [3]H-colchicine tracer. This binding competition is comparable to that of combretastain A-4, an established colchicine site binder with a higher affinity for tubulin than colchicine. At low concentrations, EHT 6706 decreases the amount of microtubular materials and induces alteration in tumor cell morphology. Perturbing microtubule dynamics with EHT 6706 halts the rapid cancer cells division by blocking cells in the metaphase/anaphase transition of the cell cycle and leads to apoptosis. EHT 6706 exhibits broad cytotoxicity in vitro with potency at sub-nanomolar/low nanomolar concentrations (0.3-10nM) in multiple cancer types (more than 60 cell lines, including the NCI60 panel) such as breast, melanoma, colorectal, renal, ovarian, non-small cell lung, leukaemia, as well as pancreatic cancer cells. EHT 6706 exerts this growth inhibition of human tumor cells independently of the type of main multidrug resistance mechanisms (ABC transporter MDR-1 (Pgp-1), MRP-1…). Furthermore, EHT 6706 retains cytotoxic activity against all of the resistant cell lines tested (combretastatin, vinblastin, imatinib), thus indicating the potential of this agent for the treatment of resistant tumors. EHT 6706 carries a potential for enhancing antitumor effects of radiation. In H460 and MiaPaca2 cell lines, indeed, EHT 6706 treatment inhibits clonogenic survival synergistically with ionizing radiation and exerts additive inhibition of proliferation when given in combination with conventional chemotherapeutic agents. Finally, in vitro experiments demonstrate that EHT 6706 has anti-angiogenic and vascular disrupting effects. Endothelial cell tube formation inhibition, pre-established vessels disruption, and vascular permeability increase were observed in a concentration- and time-dependent manner. These studies demonstrate that EHT 6706 has potent in vitro efficacy as a novel tubulin-targeted anti-proliferative and anti-vascular agent. EHT 6706 is a candidate for in vivo pharmacokinetic and efficacy studies. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 2794. doi:1538-7445.AM2012-2794