β-Hydroxy-β-Methylbutyrate Enhances Anti-PD1 Immunotherapy in a Mouse Model of Pancreatic Ductal Adenocarcinoma

Background: Pancreatic ductal adenocarcinoma (PDAC) has a single digit five-year survival that is driven by a number of factors including limited effective therapeutic options for the management of PDAC. Immunotherapies such as inhibition of programmed death 1 (PD1) have proven effective in cancers with historically poor treatment options such as melanoma. But, PDAC has thus far proven unresponsive to immunotherapies. Development of effective anti-tumor immunity is in part limited by the metabolically hostile TME. β-Hydroxy-β-Methylbutyrate (HMB) is a leucine metabolite which has been shown to reduce cancer cachexia and tumor progression. We sought to determine if HMB treatment would alter immunotherapy response in PDAC via reduction of metabolic competition. Methods: C57BL/6 mice were injected with PANC02 cells subcutaneously to generate PDAC tumors, then fed either a control (AIN93G) or HMB supplemented diet. Once tumors were palpable, mice were further randomized for treatment with anti-PD1 immunotherapy or a control (n=6/group). Tumors were collected, measured and weighed; RNA isolated; and cDNA synthesized for global transcriptomic analysis. Gene set enrichment analysis followed by enrichment mapping was used to determine the pathway activation induced by HMB, anti-PD1, or the combination. CIBERSORTx deconvolution was used to determine TME immune cell composition. Results: As anticipated, neither HMB nor anti-PD1 therapies alone were sufficient to reduce tumor growth. The combination of HMB and anti-PD1; however, resulted in significantly smaller tumors than the anti-PD1 treated group, indicating that HMB was sufficient to enable PDAC response to ICI. Transcriptomic analysis revealed only moderate immunomodulatory effects of HMB or anti-PD1 alone; however, the combination induced a robust anti-tumor immune response. Deconvolution analysis indicated that the combination of HMB and anti-PD1 increased the abundance of anti-tumor immune cell types. Overall, HMB promotes efficacy of anti-PD1 immunotherapy in a model of PDAC. Discussion: Here, we report that the combination of HMB with anti-PD1 elicited significant anti-tumor response. This is particularly remarkable as many PDAC immunotherapy trials with or without other treatments did not result in significant benefit. HMB has been well tolerated in numerous cancer cachexia clinical trials and is both cheaply and commonly available. Thus, this combination is a highly promising avenue for the advancement of immunotherapy in PDAC.Bachelor of Science in Public Healt