Abstract 3773: Preclinical evaluation of the CDK4/6 inhibitor LEE011 in nasopharyngeal carcinoma (NPC) cell lines

Abstract LEE011 is a specific CDK4/6 inhibitor that induces G1 cycle arrest by blocking the formation of cyclin D1-CDK4/6 complex and inhibiting Rb phosphorylation. Cyclin D1 is overexpressed in > 90% of NPC and CCND1 gene activation is implicated in pathogenesis. The preclinical activity of LEE011 was evaluated in 4 NPC cell lines (C666-1, HK1, HK1-LMP1, HONE-1) and the immortalized nasopharyngeal epithelial cell line NP69. Under basal condition, phosphorylated (p) Rb was strongly expressed in HK1 and HK1-LMP1, moderately in HONE-1 and NP69, and weakly in C666-1. Cyclin D1, CDK4 and 6 were expressed in all cell lines. The IC50 concentrations for cell growth inhibition after 72 hours of exposure to LEE011 in the respective cell lines were: HK1-LMP1 = 4.10±1.12μM; HK1 = 5.07±1.37μM, C666-1 = 12.25±1.63μM, NP69 = 15.23±1.93μM, HONE-1 = 19.58±1.54μM. LEE011 could induce over 95% cell growth inhibition in all NPC cell lines. Three representative cell lines (HK1 as the most sensitive to LEE011, and C666-1 and HONE-1 as less sensitive) were chosen to evaluate the effect of LEE011 on kinase signaling, apoptosis and cell cycle. Treatment of these cell lines at or above their respective IC50 concentrations for up to 48 hrs showed a dose-dependent reduction in p- and total Rb expression. A slight increase in the expression of CDK4, CDK6 and cyclinD1 were observed in HK1 and HONE1 cells, but not in C666-1 cells. G0/G1 population was increased by more than 20% in C666-1 and HK-1 cells at up to 48 hrs of exposure to LEE011. The effect of combining LEE011 with the alpha-specific PI3K inhibitor BYL719 on cell growth was studied in C666-1, HK1 and HONE-1 cells. A strong synergistic effect on growth inhibition was seen in C666-1 and HK1, but not HONE-1 at 72hrs, with the respective combination index (CI) of ED50 less than 0.5. Additionally, the combination of LEE011 and cisplatin at different sequences was investigated on their effect on cell growth. The sequential administration of cisplatin followed by LEE011 was the most optimal sequence on cell growth inhibition in C666-1 and HONE-1, but not in HK1 cells. Preliminary result suggests that this schedule was associated with better pRB inhibition than other schedules in C666-1 cells. The IC50 of LEE011 for a cisplatin-resistant HK1-LMP1-cis cell line at 72 hr was similar to its parental HK1-LMP1 cell line. In summary, LEE011 displayed dose- and time-dependent growth inhibitory effect in over 95% of NPC cells examined. A synergistic inhibitory effect on cancer cell growth was observed when LEE011 was combined with BYL719 in vitro and sequential administration of cisplatin followed by LEE011 has shown an optimal inhibitory effect. These results should be confirmed in xenograft models of NPC. Citation Format: Brigette B. Ma, Chi-Hang Wong, Connie Hui, Edwin P. Hui, Anthony T.C. Chan. Preclinical evaluation of the CDK4/6 inhibitor LEE011 in nasopharyngeal carcinoma (NPC) cell lines. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 3773.