Is Adjuvant Chemotherapy Necessary for Patients with Deficient Mismatch Repair Gastric Cancer?-Autophagy Inhibition Matches the Mismatched

Abstract

Purpose: The use of microsatellite instability (MSI) and mismatch repair (MMR) as predictive biomarkers for fluorouracil-based adjuvant chemotherapy in colorectal cancer has been a paradigm shift. However, whether this applies to gastric cancer is questionable. Furthermore, we herein investigated whether and how autophagy plays a role in MSI-relevant chemoresistance.

Materials and methods: A total of 929 patients with deficient MMR (dMMR) and proficient MMR (pMMR) gastric cancers who underwent curative-intent gastrectomy were enrolled. We compared clinicopathological variables and survival among dMMR and pMMR cohorts and tested the responses of MSI-high and microsatellite stable (MSS) gastric cancer cell lines to 5-fluorouracil (5-FU) with or without chloroquine, an autophagy inhibitor.

Results: We identified an 8.9% prevalence of dMMR cases (83 out of 929) in our cohort. This was associated with old age, tumor site at the distal stomach, an intestinal phenotype, fewer nodal metastasis, and early pathological stages. MMR was an independent prognostic factor after multivariate adjustment. Overall survival (OS) of dMMR patients was better than that of the pMMR patients but was only applicable to stage III patients. There was no difference in OS between dMMR patients treated with or without adjuvant chemotherapy, although the latter showed more medical morbidities. The MSI-high gastric cancer cell lines, versus the MSS counterparts, displayed increased resistance to 5-FU and increased autophagy. Interestingly, autophagy inhibition abrogated the chemoresistance.

Conclusion: Our data show that fluorouracil-based adjuvant chemotherapy does not work for dMMR cases, if not worse. Autophagy inhibition and/or immune checkpoint inhibition might be promising alternative strategies for gastric cancer treatment.

Implications for practice: The use of microsatellite instability (MSI) and mismatch repair (MMR) as predictive biomarkers for adjuvant chemotherapy in colorectal cancer has caused a paradigm shift in cancer therapy, although its implications in gastric cancer are still questionable. The data obtained in the current study indicate that MSI-MMR is an independent prognostic factor for gastric cancer. Standard fluorouracil-based adjuvant chemotherapy did not work for deficient MMR cases, and was likely worse. Instead, strategies like autophagy inhibition and/or immune checkpoint inhibition should be taken into consideration in the future.

Keywords: Autophagy; Gastric cancer; Microsatellite instability; Mismatch repair.

Figure 1

OS of gastric cancers stratified by MMR status. OS at stage II–IV (A), stage II (B), stage III (C), and stage IV (D).Abbreviations: CI, confidence interval; dMMR, deficient mismatch repair; HR, hazard ratio; OS, overall survival; pMMR, proficient mismatch repair.

Figure 2

DFS of gastric cancers stratified by mismatch repair (MMR) status. MMR status at stage II–III (A), stage II (B), and stage III (C).Abbreviations: CI, confidence interval; DFS, disease‐free survival; dMMR, deficient mismatch repair; HR, hazard ratio; pMMR, proficient mismatch repair.

Figure 3

OS and DFS of gastric cancers stratified by mismatch repair (MMR) status and adjuvant chemotherapy. OS of stage II–IV gastric cancers stratified by MMR status and adjuvant chemotherapy (A). OS of stage III gastric cancers stratified by MMR status and adjuvant chemotherapy (B). DFS of stage III gastric cancers stratified by MMR status and adjuvant chemotherapy (C). C/T (+) and C/T (−) indicate with and without adjuvant chemotherapy, respectively.Abbreviations: CI, confidence interval; DFS, disease‐free survival; dMMR, deficient mismatch repair; HR, hazard ratio; OS, overall survival; pMMR, proficient mismatch repair.

Figure 4

In vitro test of gastric cancer cell lines. (A): Proliferation assay of MSI‐H (SNU1 and SNU638) and MSS (SNU601 and SNU719) gastric cancer cell lines treated by 5‐FU with various concentrations. All experiments were in triplicate. (B): Representative Western blotting of LC3B and p62 of MSI‐H (SNU1 and SNU638) and MSS (SNU601 and SNU719) gastric cancer cell lines treated by 5‐FU with various concentrations, where LC3B‐II indicated lipidization of LC3B‐I, surrogate of autophagy activation, whereas p62 represented autophagy flux. (C): Proliferation assay of MSI‐H SNU1 gastric cancer cell line treated by 5‐FU and CQ with various concentrations. All experiments were in triplicate. *, p < .05 versus control; ‡, p < .01 versus control.Abbreviations: CQ, chloroquine; ctrl, control; 5‐FU, 5‐fluorouracil; MSI‐H, microsatellite instability high; MSS, microsatellite stable.