A ketogenic diet can revert acquired resistance to immunotherapy in prostate cancer through β-hydroxybutyrate-mediated inhibition of histone deacetylases

Prostate cancer is the second leading cause of cancer deaths in men in the US. In the past decade, immune checkpoint blockade (ICB) drugs targeting programmed death 1 (PD-1) and cytotoxic T-lymphocyte antigen 4 (CTLA-4) have revolutionized the field of cancer therapeutics, but the objective response rate in prostate cancers is in the low single digits. A major complicating issue is that immunotherapies can have significant adverse effects, so there is a clinical need for novel combinatorial strategies that do not involve additional or compounding adverse effects. We developed a model system of advanced prostate cancer that has acquired resistance to ICB therapy. The PD-1 resistant sublines showed strong downregulation of the mouse major histocompatibility complex (MHC-I), which was reversed by treating cells with either the pan-histone deacetylase (HDAC) inhibitor Vorinostat or β-hydroxybutyrate. When mice bearing these ICB resistant tumor are treated with either Vorinostat, with a cyclical ketogenic diet (CKD), or with a 1,3-butanediol diet (BD), tumors are resensitized to ICB therapy. We analyzed changes in the tumor immune microenvironment and showed that this effect is driven by a shift in monocyte differentiation, changing from M2 polarized immunosuppressive macrophages into iNOS+ dendritic cells instead. This differentiation is dependent on an ICB-induced increase in CD40L+ CD8+ T-cells in the tumor immune microenvironment. Our results indicate a novel mechanism in which a ketogenic diet can be used to increase therapeutic efficacy of ICB therapy. Samples consist of single cell suspensions, derived from 3 different tumors per treatment group (standard diet (SD), butanediol diet (BD), immune checkpoint blockade (ICB), and BD + ICB.