Conclusions
Inhibition of c-Met with crizotinib effectively sensitizes cetuximab-resistant KRAS mutant colorectal cancer cell lines to radiation. Crizotinib has the potential to improve outcomes in locally advanced rectal cancer patients undergoing chemoradiation.
Methods
A tissue microarray containing colorectal tumors was used to study the relationship between KRAS mutations and c-Met expression. For in vivo studies, we used the KRAS mutant cell lines HCT116, DLD1, and LoVo. Colony formation assays were performed to assess the effects of crizotinib and cetuximab. Immunoblot analysis was used to determine the effect of crizotinib on c-Met and downstream pathways and DNA damage response. We then selected noncytotoxic doses of crizotinib to assess clonogenic survival with radiation. To study potential mechanisms of radiosensitization, cell cycle analysis was performed using flow cytometry.
Results
Analysis of the tissue microarray revealed that KRAS mutant tumors had active c-Met signaling. KRAS mutant cell lines LoVo, HCT116, and DLD1 were resistant to cetuximab but sensitive to crizotinib. Pretreatment with crizotinib for 24 hours radiosensitized LoVo, DLD1, and HCT116 cell lines with enhancement ratios of 1.54, 1.23, and 1.30, respectively. Immunoblot analysis showed that crizotinib blocked radiation-induced c-Met phosphorylation and attenuated downstream signaling pathways. Cell cycle analysis revealed minimal G1 arrest with crizotinib. Additionally, crizotinib completely blocked HGF induced cell migration. Conclusions: Inhibition of c-Met with crizotinib effectively sensitizes cetuximab-resistant KRAS mutant colorectal cancer cell lines to radiation. Crizotinib has the potential to improve outcomes in locally advanced rectal cancer patients undergoing chemoradiation.