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
Authors: Murphy Sean 
Published: December 2022

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.