Hypomethylation of mismatch repair genes MLH1 and MSH2 is associated with chemotolerance of breast carcinoma: Clinical significance.

BACKGROUND AND OBJECTIVES

The aim of the study was to understand the importance of mismatch repair genes MLH1 and MSH2 in chemotolerance and prognosis of breast carcinoma (BC).

METHODS

First, the alterations (deletion/methylation/expression) of MLH1 and MSH2 were analyzed in 45 neoadjuvant chemotherapy (NACT)-treated and 133 pretherapeutic BC samples. The chemotolerant BC cells were characterized by treating two BC cell lines MCF-7 and MDA MB 231 with two anthracycline antitumor antibiotics, doxorubicin and nogalamycin.

RESULTS

The deletion frequencies were 32% to 38% in MLH1/MSH2 genes and promoter methylation frequencies were 49% to 62% in MLH1 and 41% to 51% in MSH2 in both NACT-treated and pretherapeutic samples. The overall alteration of MLH1 and MSH2 was 58% to 71% in the samples. Reduced messenger RNA (mRNA) and protein expression were found in both the genes and it showed concordance with the molecular alterations. NACT-treated patients showed better prognosis. The chemotherapeutic drug induced increased mRNA/protein expression of the genes in BC cell lines was due to their promoter hypomethylation, as analyzed by quantitative methylation assay. This phenomenon was also evident in NACT-treated BC samples.

CONCLUSION

MLH1/MSH2 genes play a critical role in the development of BC. Hypomethylation of MLH1/MSH2 genes might be important in chemotolerance of the disease.