Abstract B42: Structure-activity study of tubulin precipitation by thiol-reactive compounds

Abstract

Abstract Tubulin, a major constituent of microtubules, has been established as an important chemotherapeutic target. Its expression is tightly regulated at the transcriptional level and not affected by tubulin targeting agents including taxanes and vinca alkaloids. Recently, we reported that benzyl isothiocyanate (BITC) and phenethyl isothiocyanate (PEITC), two isothiocyanates (ITCs) derived from cruciferous vegetables, induce rapid and significant precipitation and degradation of both α- and β-, but not γ-, tubulin at 10 μM through covalent binding to cysteine residues. In contrast, sulforaphane and erucin, two hydrophilic ITCs, and N-methylphenethylamine, an analog of PEITC without electrophilic functional group, show no activity as well as little downstream effects such as cell cycle arrest at mitosis and apoptosis induction at the same concentration. Because ITC are electrophiles, these findings suggest that thiol-reactivity may be the triggering event, the structure of compounds is associated with its activity, and tubulin precipitation and degradation are biologically important. In this study, we report that other thiol-reactive compounds, such as N-benzylmaleimide, phenylarsine oxide, and phenylmercuric chloride, also induce significant tubulin precipitation. They were much more potent than their hydrophilic counterparts, such as N-maleoyl-beta-alanine, arsenic oxide, and mercury chloride. These results shed lights onto structure-activity relationships. More importantly, their potencies of precipitating tubulin correlate well with not only their affinity to tubulin cysteines but also induction of G2/M phase arrest and apoptosis in human lung cancer cells A549. The results support the notion that cysteine modification is an upstream event for tubulin instability and cytotoxicity. The study presents critical knowledge on the rational design and screening of thiol-reactive compounds targeting the stability of tubulin. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the Second AACR International Conference on Frontiers in Basic Cancer Research; 2011 Sep 14-18; San Francisco, CA. Philadelphia (PA): AACR; Cancer Res 2011;71(18 Suppl):Abstract nr B42.