P2.14-66 Combination ALK and MEK Inhibition in ALK-Positive Lung Cancer

Abstract

ALK positive lung cancer can be treated with ALK inhibitors, but resistance typically develops within 1 or 2 years. One strategy to overcome drug resistance is combination therapy. In particular, MEK has been suggested as a target for combination therapy with ALK inhibitors. We investigated this hypothesis with in vitro and in vivo experiments. Human lung adenocarcinoma cells harbouring the ELM4-ALK rearrangement (H3122) we exposed to varying concentrations of the ALK inhibitor crizotinib, and the MEK inhibitor selumetinib, and cytotoxicity assayed using the SRB assay. Cell cycle, apoptosis, and Western blot assays were used to further investigate mechanisms of co-action. Balb/c mice were then dosed with crizotinib (5 or 25mg/kg, po) and/or selumetib (25 mg/kg, po) for 14 days and toxicity assessed. Nude mice were then injected with H3122 cells to produce a flank tumour, and the effects of treatment with crizotinib (25 mg/kg, po) and/or selumetinib (25 mg/kg, po) ascertained. Combination crizotinib and selumetinib killed both crizotinib naieve and crizotininb resistant H3122 cells in a synergistic manner. The combination treatment caused a small increase in apoptosis, and a large decrease in cells in S phase. Western blot showed strong combination effects on suppression of phoshpo-ERK, and cyclin DI, and upregulation of BIM. No toxicity for liver or kidney function was detected with 25 mg/kg crizotinib and selumetinib. In xenograft experiments, the combination suppressed tumour growth to a greater extent than either drug alone. This work has successfully replicated recent findings for combination ALK and MEK inhibition in ALK lung cancer experiments, but using different specific drugs than previously. The drugs were were well tolerated in combination. Cell based experiments shed further light on mechanisms of action for this drug combination, and revealed two further druggable targets: BIM and CDK1.