HDAC inhibitors target IRS4 to enhance anti-androgen receptor (AR) therapy in AR-positive triple negative breast cancer

Triple negative breast cancer (TNBC) is the most malignant subtype of breast cancer. Androgen receptor (AR)-positive TNBC has been identified as a potential therapeutic target; however, clinical trials have not produced an effective treatment. This study aimed to identify a new treatment regimen to improve the prognosis of AR-positive TNBC. First, we used a combination of an AR inhibitor (enzalutamide, Enz) and selective histone deacetylase inhibitor (chidamide, Chid) to treat AR-positive TNBC cell lines and observed a synergistic effect of the drugs. The combination treatment inhibited cell growth and migration by arresting the cell cycle at the G2/M phase. We used next-generation sequencing to detect changes in gene regulation. The results showed that the PI3K/Akt signalling pathway was significantly inhibited by the combination treatment of Enz and Chid, and gene set enrichment analysis (GSEA) revealed that KRAS signalling was significantly enriched. Analysis of associated genes revealed that insulin receptor substrate 4 (IRS4) plays a critical role in blocking the activation of KRAS signalling. In a mouse xenograft model, combination treatment also inhibited the PI3K/Akt signalling pathway by upregulating the expression of IRS4 and thereby suppressing tumour growth. In conclusion, we found that Enz and Chid combination treatment upregulates IRS4, which results in the blocking of KRAS signalling and suppression of tumour growth. We hypothesize that the expression level of IRS4 can be used as a biomarker for screening patients with AR-positive TNBC using enzalutamide and chidamide combination therapy.