Abstract 856: Combination of crizotinib and radiation in the treatment of ALK-positive and cetuximab-resistant lung cancer

Abstract

Abstract Approximately 4% of patients with non-small cell lung carcinoma (NSCLC) carry the EML4-ALK chromosomal rearrangement. Crizotinib, a c-MET and ALK inhibitor, has shown significant therapeutic benefit as a single agent with FDA approval for the treatment of patients with ALK-positive NSCLC. Since radiation commonly plays a key role in lung cancer treatment, we sought to evaluate the potential of crizotinib as a radiation sensitizer and the role of ALK in cellular radiation sensitivity. We examined the effect of crizotinib in combination with radiation on ALK signaling, cell proliferation, cell cycle distribution and radiosensitivity in ALK-positive NSCLC cell lines H3122 and H2228 in vitro. We also examined the in-vivo effects of crizotinib in combination with radiation in H3122 and H2228 xenograft models. Crizotinib blocked phosphorylation of ALK and its downstream effectors and inhibited cell proliferation in a dose-dependent manner. The combination of crizotinib and radiation resulted in increased inhibition of cell growth. Although cells were sensitized to radiation by crizotinib, molecular knockdown of ALK by siRNA had only modest impact on cell radiosensitivity. Cell cycle analysis by flow cytometry showed that ALK-siRNA induced G1 arrest. Interestingly, low dose crizotinib induced G1 arrest, while doses above 2µM induced G2 arrest. Combination treatment induced arrest in G1 and G2 phases and decreased the cell population in S-phase. Moreover, in xenograft tumor models, we observed combined treatment to produce additive tumor growth inhibition over that observed with either drug or radiation alone. We further examined the capacity of crizotinib overcome cetuximab resistance in our established in vitro resistance models. Compared with parental cells, cetuximab-resistant cells showed cross-resistance to radiation. Crizotinib inhibited the growth of cetuximab-resistant cells and resensitized cells to radiation. Compared with single-agent treatment, the combination of crizotinib and erlotinib resulted in increased growth inhibition and further re-sensitization to radiation. These data suggest that crizotinib in combination with radiation can enhance the inhibitory effect on ALK-positive tumor cell growth in vitro and in-vivo and also suggest the potential value of using crizotinib in combination with other EGFR-targeting therapeutics. Ultimately however, the potential value of crizotinib as a radiation sensitizer requires systematic clinical investigation. Citation Format: Chunrong Li, Shyhmin Huang, Noah Walters, Eric A. Armstrong, Paul M. Harari. Combination of crizotinib and radiation in the treatment of ALK-positive and cetuximab-resistant lung cancer. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 856. doi:10.1158/1538-7445.AM2014-856