Abstract 4430: A novel mitotic kinesin Eg5 inhibitor exerts the growth-inhibitory effect in cancer cells in a manner independent of induction of monoastral formation but dependent on KRAS mutation status

Abstract

Abstract Mitotic kinesin Eg5 plays an important role in mitosis, as it is critical for proper bipolar spindle assembly. After the discovery of the first Eg5 inhibitor monastrol, a number of Eg5 inhibitors have been developed as anticancer drugs. We have previously synthesized a series of S-trityl-L-cysteine (STLC) derivatives as Eg5 inhibitors and demonstrated potent inhibitory effect on Eg5 ATPase activity and induction of mitotic arrest with characteristic monoastral spindles in HeLa cells. In this study, we evaluated the growth-inhibitory acitivities of novel STLC derivatives, Compound1, Compound2, and Compound3 by MTT assay in a wide range of human cancer cell lines derived from gastric (MKN1, MKN45, MKN74, NUGC3, NUGC4, NCI-N87), colon (C170, DLD1, HCT15, COLO205), pancreatic (AsPC1, BxPC3, SUIT2) and lung (PC-9, PC-14, H1975, H441, A549) cancers and investigated potential predictive biomarkers. Among the derivatives, Compound3 showed the most potent growth-inhibitory effect and sensitivity between cell lines showed marked differences, with IC50 values ranging from 0.134 to 7.14 μM. Pancreatic cancer cell line AsPC1 and non-small cell lung cancer (NSCLC) cell lines H441 and A549 which harbor KRAS mutation showed relatively high IC50 values compared to other cell lines without KRAS mutation. Compound3 induced G2/M arrest in all cell lines as early as 8 hours after the treatment by flowcytometry, while the increase of the apoptotic sub-G1 fraction was not observed in these AsPC1, H441 and A549 cells harboring KRAS mutation. These results suggested that differential sensitivity to Compound3 and attenuated induction of apoptosis by Compound3 were attributed to KRAS mutation. Induction of monoastral spindles formation by Compound3 was observed as early as 8 hours after the treatment not only in sensitive cell lines but in refractory cell lines such as AsPC1 and H441 cells by immunocytochemistry, suggesting the induction of monoastral spindles formation does not work as a predictive biomarker for clinical development. There was no correlation observed between the growth-inhibitory effect and the basal Eg5 expression level of each cell line by western blot analysis. No significant difference was observed in the induction of a spindle checkpoint kinase BubR1 phosphorylation among the cells, a potential predictive biomarker in response to the Eg5 inhibitor treatment by western blot analysis. Taken together, a novel mitotic kinesin Eg5 inhibitor Compound3 should be considered for further exploration and development and KRAS mutation status was suggested to be a candidate for a predictive biomarker of poor response to Eg5 inhibitors. 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 4430.