Abstract A57: Killing cancer with keto: Beta-hydroxybutyrate the main metabolite produced by a ketogenic diet acts as an endogenous histone deacetylase inhibitor to sensitize immunotherapy resistant prostate cancer to immune checkpoint blockade


 Prostate cancer (Pca) 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 Pca 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 (BHB) an endogenous HDAC inhibitor derived from acetoacetate. In-vitro we noticed significant increases of MHC I when our ICB resistant prostate cancer cells are treated with either Vorinostat or BHB. In vitro and in-vivo we confirmed that epigenetic changes were occurring through an increase of H3K9 acetylation. We then developed two diets that increase BHB. One is through a cyclical ketogenic diet (CKD) that has over 90% fat in its chow and 1,3, Butanediol diet (BD). When mice bearing these ICB resistant tumor are treated with either Vorinostat, with a CKD, or with a BD, tumors are desensitized to ICB therapy. We analyzed changes in the tumor immune microenvironment of mice treated with Standard Diet (SD), BD, ICB, and BD+ICB through scRNA-seq. This showed vast changes in the tumor microenvironment. Strikingly BD and BD+ICB showed a significant decrease in Neutrophils. Both BD and BD+ICB treated groups had significant changes in total monocytes and in increase of M1 polarized macrophages but only combination treatment were CD8+ T-Cells increased. Given the significant changes in monocytes we further clustered on cells with monocytic markers. In BD + ICB we noticed a significant decrease in M2 polarized immunosuppressive macrophages and an increase of anti-tumor TNFa, iNOS, and p53 positive+ dendritic cells (TIP DC’s). These cells are derived from immunosuppressive monocytes which may explain the decrease of M2 Macrophages and increase of TIP-DC’s. There are also distinct signaling changes within the tumor microenvironment. BD and BD+ ICB increase MHC II and CD86 signaling to T-Helper cells and decrease Foxp3+ T-Regulatory Cell (T-Reg) signaling. Although there is no change to T-Reg proportions this suggests that they play a decreased role. ICB treatment appears to make up the majority of changes with increased interferon (IFN) and CD86 signaling from CD4 T-Helper Cells. In BD+ICB tumors TIP-DC’s make up the largest increase of IFN, CD86, and MHC II signaling to T-Helper Cells when compared to ICB. Our results indicate a novel mechanism in which a ketogenic diet and by extension BHB can be used to increase therapeutic efficacy of ICB therapy in Pca.
 Citation Format: Sean Murphy. Killing cancer with keto: Beta-hydroxybutyrate the main metabolite produced by a ketogenic diet acts as an endogenous histone deacetylase inhibitor to sensitize immunotherapy resistant prostate cancer to immune checkpoint blockade [abstract]. In: Proceedings of the AACR Special Conference: Tumor Immunology and Immunotherapy; 2022 Oct 21-24; Boston, MA. Philadelphia (PA): AACR; Cancer Immunol Res 2022;10(12 Suppl):Abstract nr A57.