Abstract 1204: Enhanced efficacy of selumetinib by pretreatment of 5-FU in preclinical Ras/Raf-mutant colorectal cancer models

Abstract

Abstract Optimal strategy for the application of MEK inhibitor as combination therapy has not been established in Ras/Raf-mutant colorectal cancer (CRC). As we preliminary observed that 5-FU-induced pharmacodynamic changes were restored by ERK inhibition, we hypothesized that post-treatment of MEK inhibitor would enhance antitumor activity of 5-FU. Treatment of 5-FU for 2 days followed by selumetinib for another 2 days (FS schedule) exhibited synergism for cell viability, whereas reverse or concomitant combination showed antagonism or inconsistent response, respectively, in 8 kinds of CRC cell lines including BRAFV600E colo205, BRAFV600E RKO, or KRASG13D HCT8 cells. Combination as FS schedule persistently down-regulated the phosphorylation of ERK and pS6 throughout treatment period, whereas selumininib alone or reverse combination transiently decreased within 24 hr. The cells treated as FS schedule exhibited higher apoptosis and lower capacity of anchorage-independent cell growth than the cells under single or reverse combination. Microarray analysis revealed the distinct groups of genes underlying different efficacy by schedule-dependent treatment. Tumor growth in mice administered 5-FU at 10 mg/kg/day for colo205 and at 30 mg/kg/day for HCT8 for 7 days followed by selumetinib at 10 mg/kg/day for colo205 and 25 mg/kg/day for HCT8 for another 7 days was significantly retarded than that in mice treated with single agents. But the combination in reverse sequence induced comparable tumor growth to single agents. Decreased expression of Ki67 was observed in tumors from mice treated as FS scheduling. Our results suggest that the schedule-dependent combination of 5-FU and selumetinib may be benefit in patients having CRC with hyper-activation of Ras/RAF pathway. Citation Format: Hye Yeon Jang, Haeng Jung Lee, Yeo Jin Nam, Won Dong Kim, Yong Ju Bae, Jin Hwang Jung, Seung Jin Lee, Dae Hyuk Moon. Enhanced efficacy of selumetinib by pretreatment of 5-FU in preclinical Ras/Raf-mutant colorectal cancer models [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 1204. doi:10.1158/1538-7445.AM2017-1204