Mismatch repair (MMR) gene is closely related to the pathogenesis of
colon cancer. This study aimed to evaluate the association between MMR status and efficacy of
irinotecan-based
chemotherapy. As a target of
5-FU,
thymidylate synthase (TS) expression level might be influenced by
irinotecan. Understanding whether this influence of TS is related with MMR status is helpful to the further exploration of the mechanism of
irinotecan sensitivity in metastatic
colon cancer with different MMR status. One hundred eighty-four patients with metastatic
colon cancer receiving
irinotecan-based
chemotherapy for the first-line treatment were included. Correlations between MMR and clinicopathological characteristics and prognosis were determined. Two pairs of
colon cancer cell lines (HCT-116-hMLH1(Vector) (deficient MMR, dMMR) versus HCT-116-hMLH1(+) (proficient MMR, pMMR); SW480-
shRNA-hMLH1 (dMMR) versus SW480-
shRNA-Control (pMMR)) were established by regulating MMR status. Sensitivity of these cell lines to
irinotecan was determined by MTT assay. Regulation of TS by
irinotecan was evaluated by western blotting and quantitative real-time PCR assay. dMMR accounted for 18.5 % and was related with proximal
colon cancer (p = 0.005), poorly differentiated
tumors (p = 0.018) and favorable efficacy with a higher disease control rate (DCR), a longer progression-free survival (PFS) and a trend of longer overall survival (OS). dMMR
colon cancer cells were more sensitive to
irinotecan. TS expression level was reduced more in dMMR cells after
irinotecan treatment (p < 0.05). Our study favors an increased sensitivity of
irinotecan in
colon cancer with dMMR status. MMR status may be a predictive
biomarker of response to
irinotecan-based
chemotherapy in metastatic
colon cancer.