Unraveling AMPK and BET regulation of immune checkpoint biology: implications for personalized medicine

Abstract

Triple negative breast cancer (TNBC) patients with comorbid Type 2 diabetes (T2D) show worse survival compared to nondiabetic TNBC patients. Immune checkpoint blockade (ICB) has unclear benefit in TNBC. Immune suppression in T2D, and use of metformin, an activator of 5 Adenosine Monophosphate-activated Protein Kinase (AMPK), in such patients, prompted us to examine AMPK regulation of immune checkpoint expression. Improved ICB efficacy may optimize outcomes for certain TNBC patients. We have also been exploring the role of Bromodomain and ExtraTerminal domain (BET) proteins (BRD2, BRD3, BRD4) in regulation of checkpoint molecules in immune cell subsets, including CD4+, CD8+ T cells, and NK cells. BET proteins are important transcriptional co-regulators, critical for proliferation and metastasis in many cancer types, including TNBC. We observed differential BET regulation of immune checkpoint proteins, specifically TIM-3, TIGIT, PD-1 and CTLA-4, on CD3/CD28-stimulated peripheral blood mononuclear cells by flow cytometry. Chemical inhibition of AMPK with Compound C, and with the pan-BET inhibitor JQ1 or the BRD4-selective PROTAC inhibitor MZ-1, revealed that BET proteins regulate PD-1 and CTLA-4 through an AMPK-dependent pathway and TIM-3 and TIGIT through an AMPK-independent pathway. Personalized approaches to ICB treatment of TNBC patients with comorbid T2D should improve outcomes.