Abstract 4427: Efficacy of a novel mitotic kinesin Eg5 inhibitor in docetaxel-resistant non-small cell lung cancer cells

Abstract

Abstract Lung cancer is the leading cause of cancer-related deaths in Japan and worldwide. Non-small cell lung cancer (NSCLC) accounts for a majority of lung cancer and docetaxel is one of the key drugs in the treatment of metastatic NSCLC in combination with platinum agents as first-line therapy and is also given as second-line monotherapy. However, most of the patients acquire resistance and fail to respond not long after the initial treatment. Development of novel therapeutics which is active in docetaxel-resistant NSCLC is necessary. Mitotic kinesin Eg5 is critical for proper bipolar spindle assembly during mitosis. It also plays an important role in cancer cell proliferation and has been thought to be a good target for cancer therapeutics. We have synthesized an S-trityl-L-cysteine (STLC) derivative Compound3 as a novel Eg5 inhibitor and previously demonstrated potent growth-inhibitory effect in a wide variety of cancer cell lines. In this study, we evaluated the efficacy of Compound3 in docetaxel-resistant NSCLC cell line PC-14/TXT. Compound3 showed potent growth-inhibitory effect in PC-14/TXT cells by MTT assay without cross-resistance to docetaxel. In order to study the mechanism of growth inhibition by Compound3, we performed flow cytometry analysis and evaluated the effects of docetaxel and Compound3 on cell cycle progression in PC-14 and PC-14/TXT cells. Docetaxel induced G2/M cell cycle arrest only in PC-14 cells but it did not in PC-14/TXT cells. Compound3 induced G2/M cell cycle arrest not only in PC-14 cells but also in PC-14/TXT cells. Compound3 induced increase of sub-G1 fraction in PC-14 cells, suggesting Compound3 induced apoptosis in PC-14 cells. On the other hand, we did not observe increase of sub-G1 fraction by Compouond3 treatment in PC-14/TXT cells. These results suggest Compound3 exerts growth-inhibitory effect in PC-14/TXT cells by cell cycle arrest and it has a differential growth-inhibitory property between PC-14 and PC-14/TXT cells. Effect of docetaxel and Compound3 on spindles formation was evaluated by immunocytochemistry. Docetaxel induced multipolar spindles formation in PC-14 cells but did not show any effect in PC-14/TXT cells. On the other hand, Compound3 induced distinctive monoastral spindles formation in both PC-14 and PC-14/TXT cells as early as 8 hours after the treatment. We performed immunoblot analyses to further investigate the effect of Compound3 on molecules relevant to Eg5. There was no correlation observed between the growth-inhibitory effect and the basal Eg5 expression level between two cell lines. No significant difference was observed between the cells in the status of spindle checkpoint kinases such as MAD2 and BubR1. Taken together, a novel mitotic kinesin Eg5 inhibitor Compound3 should be considered for further exploration and development as a novel therapeutic option for the patients with non-small cell lung cancer who failed docetaxel treatment. 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 4427.