2276P - Regulation of major histocompatibility class-I gene methylation using DNA methyltransferase inhibitor and PD-L1 inhibitor in triple-negative breast cancer

Background

There are many studies on gene methylation and immunotherapy in breast cancer, but there are few studies on the effect of DNA methyltransferase (DNMT) inhibitors and immunotherapy on major histocompatibility (MHC) class-I gene methylation in triple-negative breast cancer (TNBC).

Methods

The relationship between the expression of the MHC class-I gene and DNA methylation was analyzed using data from The Cancer Genome Atlas (TCGA). The expression of DNMTs and MHC class-I genes was analyzed in breast cancer tissue from TNBC patients and TNBC cell lines. DNA methylation analysis of the MHC class-I gene was performed with pyrosequencing in TNBC tissues and methylation specific PCR in TNBC cell lines. TNBC cell lines were treated with DNMT inhibitors Decitabine and Zebularine and PD-L1 inhibitor Atezolizumab, and then changes in the expression of DNMT, MHC-I gene, and methylation patterns of MHC class-I gene were analyzed.

Results

TCGA data analysis confirmed that there was an inverse correlation between DNA methylation and mRNA expression of the MHC class-I gene, but analysis in TNBC patients in this study did not show this correlation. After treating TNBC cell lines with DNMT inhibitors and PD-L1 inhibitor alone and in combination, the DNA methylation pattern of the HLA-B and HLA-C gene was suppressed, but there was no significant change in the DNA methylation of the HLA-A gene. The expression of the MHC class-I gene increased in BT-20 after Decitabine treatment, and only in BT-549 after Zebularine treatment. It increased in BT-549 after Atezolizumab treatment, and in MDA-MB231 after combination of Decitabine and Atezolizumab. After each drug treatment, the cell viability of TNBC cell lines was reduced due to the drug's own cancer treatment effect, which limited the analysis of the outcome of changes.

Conclusions

The treatment responses to DNMT inhibitors and PD-L1 inhibitor were different depending on the characteristics of TNBC and the types of drugs, suggesting that the treatment target needs to be applied differently. Further study is needed to determine specific treatment targets and appropriate drugs according to the characteristics of TNBC.

Clinical trial identification

Editorial acknowledgement

Legal entity responsible for the study

The author.

Funding

This work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIT) (No. 2020R1G1A1099646).

Disclosure

The author has declared no conflicts of interest.