Investigation of the mechanisms of resistance to targeted therapies is essential as resistance acquired during treatment may lead to relapse or refractoriness to the therapy. Our previous study identified the small molecule KRC-108 as a result of efforts to find an anticancer agent with c-Met-inhibitory activity. In the present study, the changes accompanying resistance to KRC-108 were investigated in the gastric cancer cell line MKN-45 and its KRC-108-resistant clones by western blot and immunofluorescence analyses. Increased expression of the c-Met protein was observed in KRC-108-resistant cells compared with that of the parental cells, and the phosphorylation of c-Met also increased in cell lines resistant to KRC-108. Resistance to the c-Met inhibitor was associated with cell morphological changes: MKN-45 parental cells, which had a round and poorly differentiated morphology, were altered to exhibit an epithelial cell-like phenotype in KRC-108-resistant clones. Consistent with the transition to an epithelial morphology, the expression of E-cadherin was increased in resistant cells. Using immunoprecipitation, an interaction between E-cadherin and the c-Met protein was observed in the KRC-108-resistant cells. Immunohistochemical analysis of human gastric carcinoma tissues revealed the co-expression of E-cadherin and c-Met. These results suggest that the epithelial transition in KRC-108-resistant cells is mediated by recruiting E-cadherin to c-Met protein. Thus, the present study identified a mechanism used by cancer cells to confer resistance to anticancer agents.
Keywords: E-cadherin; c-Met; drug resistance; epithelial transition.