Modification of the epigenome as a potential therapy for breast cancer

Despite progress in prevention, diagnosis and treatment, breast cancer remains the first cause of cancer-related death in women worldwide. Novel therapeutic strategies are needed especially for triple-negative breast cancers (TNBC), which do not benefit from targeted/endocrine therapies. This research study aimed to investigate the benefit of combining epigenetic drugs used at low concentrations to enhance the effects of DNA methyltransferase (DNMT) inhibitors against breast cancer cells, potentially broadening therapeutic options. Two treatments combining DNMT inhibitors with either histone deacetylase (HDAC) inhibitors or vitamin C were tested in a panel of breast cancer cell lines. Combining DNMT and HDAC inhibitors enhanced the effects induced by DNMT inhibitors such as the up-regulation of SFRP1 and UCHL1 potential tumour suppressor genes, associated with promoter and global DNA demethylation up to 17.7% compared to controls. Combination DNMT/HDAC inhibitors also up-regulated PD-L1 (also known as CD274), a target of immune-checkpoint inhibitor up to 32.5-fold, and induced early and prolonged reduction of spheroid growth. The second combination treatment tested, using DNMT inhibitor decitabine and vitamin C, enhanced loss of cell viability at Day 10 in MCF-7 and 4T1 cells. This combination treatment led to early increase in double- stranded RNA, characteristic of viral mimicry effects by a factor of 1.3 to 1.8 at Day 4. Combination decitabine/vitamin C also up-regulated type I/II interferon genes up to 114-fold in breast cancer cell lines including TNBC cells MDA-MB-231 and MDA-MB- 468. Whole-genome expression analysis confirmed the increased up-regulation of immune-related genes and also showed the up-regulation of 51 to 98 of Cancer/Testis Antigen genes in MDA-MB-231 and MCF-7 respectively, after treatment combining decitabine and vitamin C. In conclusion, combining epigenetic drugs can improve the efficacy of DNMT inhibitor against breast cancer cells in vitro. The main novelty of this study is the enhancement of decitabine effects on loss of cell viability and immune-stimulation in breast cancer cells including TNBC, by combining decitabine with vitamin C. Combining epigenetic therapies could provide additional therapeutic options to TNBC and sensitise breast cancer cells to subsequent immunotherapy.