Abstract 4896: Synergistic Anti-Tumor Activity of CDK4/6 Inhibitor Combined with Paclitaxel in NSCLC Cells Harboring Mutant KRAS

Abstract Background: Deregulation of the p16INK4A-cyclin D-cyclin-dependent kinases (CDK) 4/6-retinoblastoma (RB) pathway is frequently observed in various cancers and represents one of the attractive therapeutic targets. The gain of function mutation in KRAS gene confers intrinsic resistance to targeted anti-cancer drugs as well as cytotoxic chemotherapeutic agents leading to treatment failure. More effective treatment for adenocarcinomas harboring KRAS mutations should be developed to improve clinical outcomes. Purpose: CINK4, a chemical inhibitor of cyclin-dependent kinase 4, has demonstrated potent anti-proliferative activity in the presence of pRb. Herein, when combined with paclitaxel, we investigated that CINK4 may increase its anti-proliferative activity in the NSCLC cells harboring KRAS mutant. Methods: We measured the anti-proliferative activities of CINK4 in A549 (KRAS mutant), H358 (KRAS mutant), SK-LU-1 (KRAS mutant), H23 (KRAS mutant), PC14 (KRAS wild), and Calu-3 (KRAS wild) cell lines using SRB assay, cell cycle distribution quantified by flow cytometric analysis, and the expression of cell cycle regulators and apoptosis-related proteins was evaluated by Western blotting. Multiple drug effect was analyzed to study an interaction between two drugs. The nature of the interaction between two agents was calculated for the combination index (CI). Results: Concentration- and time- dependent anti-proliferative effects of CINK4 (0.1∼ 40 µM concentration range) and paclitaxel (0.1∼300 nM) alone were observed in six NSCLC cell lines, and were not significantly different between each cell line (48 h IC50: 10.4 ± 0.2 µM and 5.5 ± 0.9 nM, 10.1± 1.9 µM and 5.2 ± 0.9 nM, 6.6 ± 0.8 µM and 3.6 ± 1.0 nM, 8.6 ± 0.8 µM and >10 nM, 8.9 ± 0.5 µM and 3.5 ± 0.2 nM, and 8.4 ± 0.2 µM and > 10 nM, in A549, H358, PC14, and Calu-3, SKLU-1, and H23 cells, respectively). After 48 h CINK4 treatment alone, the G0/G1phase cell population increased with increment of subG1 faction in concentration-dependent manner. CINK4 reduced cyclinD1 and Rb phosphorylation and increase the expression of cleaved PARP in concentration-dependent manner in A549, H358, and PC14 cells. The CINK4 combined with paclitaxel in four KRAS mutant cell lines enhanced anti-proliferative activity of paclitaxel. The CI values of CINK4 and palitaxel in A549, H358, SKLU-1 and H23 were 0.51 ± 0.16, 0.63± 0.12, 0.60 ± 0.15, and 0.55 ± 0.15, respectively. Conclusions: Taken together, our data suggest that CINK4 alone has promising anti-tumor activity in NSCLC cells with or without KRAS mutation. In addition, CDK4/6 inhibitor in combined with paclitaxel demonstrated more enhanced anti-tumor activity in NSCLC cells harboring mutant KRAS. 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 4896. doi:1538-7445.AM2012-4896