Mismatch repair system decreases cell survival by stabilizing the tetraploid G1 arrest in response to SN-38

Functional mismatch repair and inactive p53 drive sensitization of colorectal cancer cells to irinotecan via the IAP antagonist BV6

A common strategy to overcome acquired chemotherapy resistance is the combination of a specific anticancer drug (e.g., topoisomerase I inhibitor irinotecan) together with a putative sensitizer. The purpose of this study was to analyze the cytostatic/cytotoxic response of colorectal carcinoma (CRC) cells to irinotecan, depending on the mismatch repair (MMR) and p53 status and to examine the impact of BV6, a bivalent antagonist of inhibitors of apoptosis c-IAP1/c-IAP2, alone or combined with irinotecan. Therefore, several MSH2- or MSH6-deficient cell lines were complemented for MMR deficiency, or MSH6 was knocked out/down in MMR-proficient cells. Upon irinotecan, MMR-deficient/p53-mutated lines repaired DNA double-strand breaks by homologous recombination less efficiently than MMR-proficient/p53-mutated lines and underwent elevated caspase-9-dependent apoptosis. Opposite, BV6-mediated sensitization was achieved only in MMR-proficient/p53-mutated cells. In those cells, c-IAP1 and c-IAP2 were effectively degraded by BV6, caspase-8 was fully activated, and both canonical and non-canonical NF-κB signaling were triggered. The results were confirmed ex vivo in tumor organoids from CRC patients. Therefore, the particular MMR+/p53mt signature, often found in non-metastasizing (stage II) CRC might be used as a prognostic factor for an adjuvant therapy using low-dose irinotecan combined with a bivalent IAP antagonist.

Role of Deficient Mismatch Repair in the Personalized Management of Colorectal Cancer

Colorectal cancer (CRC) represents the third most common type of cancer in developed countries and one of the leading causes of cancer deaths worldwide. Personalized management of CRC has gained increasing attention since there are large inter-individual variations in the prognosis and response to drugs used to treat CRC owing to molecular heterogeneity. Approximately 15% of CRCs are caused by deficient mismatch repair (dMMR) characterized by microsatellite instability (MSI) phenotype. The present review is aimed at highlighting the role of MMR status in informing prognosis and personalized treatment of CRC including adjuvant chemotherapy, targeted therapy, and immune checkpoint inhibitor therapy to guide the individualized therapy of CRC.

Association between mismatch repair gene and irinotecan-based chemotherapy in metastatic colon cancer

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.