Abstract 2678: Molecular signature of drug action for microtubule stabilizing agents

Microtubule-stabilizing agents (MSAs) comprise a class of drugs that bind to polymerized microtubules (MTs), thereby inhibiting their dynamic properties and leading to arrest in mitosis. The prototype of this group of drugs, Taxol, is an effective chemotherapeutic agent used extensively in the treatment of human ovarian, breast, and lung carcinomas. Although electron crystallography and photoaffinity labeling studies led to the identification of the binding site for Taxol in the β-tubulin subunit of the MT polymer, the effect of the drugs on MT conformation was only recently deciphered in our laboratory using hydrogen deuterium exchange (HDX) coupled to high-pressure liquid chromatography and mass spectrometry (HPLC-MS). We have also utilized this technique to determine the binding mode and conformational effects of discodermolide, another MSA with potential to become a useful anti-tumor drug. We found that in tubulin isolated from chicken erythrocytes, discodermolide bound to an overlapping binding site with Taxol, but had a distinct pose within the pocket, such that it oriented itself away from the M-loop and toward the N-terminal H1-S2 loop of β-tubulin. Evidence of conformational effects on the C-terminal H12 helix in the α-tubulin subunit and of complementary MT stabilization between Taxol and discodermolide was found. These results provide the molecular basis for the ability of the two drugs to modulate interactions with endogenous microtubule associated proteins (MAPs) and for the synergy observed between them in vivo. Preliminary analysis of the data with four other MSAs, epothilone B, ixabepilone, peloruside A, and laulimalide, suggests a very similar mode of MT stabilization by all the drugs in this class, with some drug-specific, and more importantly, binding-mode-specific MT-stabilizing effects. Careful examination and qualitative comparison of the conformational effects of all the aforementioned MSAs is currently in progress, and will allow us to determine a molecular signature for drug action that may correlate with the corresponding therapeutic benefits.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 2678.