Abstract 1565: β-hydroxy-β-methylbutyrate enhances anti-PD1 immunotherapy in a mouse model of pancreatic ductal adenocarcinoma
Authors: Etigunta Suhas K. , Coleman Michael F. , Pfeil Alex J. , Lashinger Laura M. , Cui Zhengrong , Hursting Stephen D. 
Published: July 2021

Abstract
Background: Pancreatic ductal adenocarcinoma (PDAC) has a five year survival rate in single digits.This 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 provided dramatic benefit to cancers with historically poor treatment options such as melanoma. However, PDAC has thus far proven unresponsive to immunotherapies. It is well understood that the development of effective anti-tumor immunity is in part limited by the metabolically hostile tumor microenvironment. 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 vehicle control. 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 microenvironment 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 immunotherapy. Transcriptomic analysis demonstrated only moderate immunomodulatory effects of HMB or anti-PD1 alone; however, the combination potently induced putatively anti-tumor immune response. Deconvolution analysis indicated that the combination of HMB and anti-PD1 increased the abundance of anti-tumor immune cell types. HMB treatment, as expected, was very well tolerated by all animals with no adverse effects detected. 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, without the need for the prior induction of immunological cell death via chemotherapy or radiation. 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. This research was supported by R35CA197627 to S. Hursting.
Citation Format: Suhas K. Etigunta, Michael F. Coleman, Alex J. Pfeil, Laura M. Lashinger, Zhengrong Cui, Stephen D. Hursting. β-hydroxy-β-methylbutyrate enhances anti-PD1 immunotherapy in a mouse model of pancreatic ductal adenocarcinoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 1565.