Abstract PO-091: Histamine receptor 1 (HRH1): A potentially novel G protein-coupled receptor (GPCR) therapeutic target in pancreatic adenocarcinoma (PDAC) cells and tumors

A recent study reported that patients taking HRH1 antihistamines have decreased progression of various tumors, including PDAC; the authors inferred that this was an immune effect (Fritz et al., PMID: 33550204). We have initiated studies to test an alternative hypothesis: HRH1 expressed by PDAC cells may contribute to the malignant phenotype and if so, FDA-approved HRH1 antihistamines might be therapeutics to treat or perhaps prevent PDAC. We have undertaken bioinformatic and experimental approaches to test this hypothesis. Our bioinformatic analysis revealed that PDAC tumors in The Cancer Genome Atlas (TCGA) have >30-fold higher HRH1 expression than in normal pancreas (GTEx database) and is highly expressed in PDAC cell lines in the Cancer Cell Line Encyclopedia (CCLE). HRH1 expression was selectively associated with markers of PDAC cells and not with markers of other cell types in the tumor microenvironment. Higher expression of HRH1 in TCGA-PDAC tumors negatively impacts on patient survival. Our experimental studies indicate that human and mouse PDAC cells express HRH1 mRNA, protein and signaling and that HRH1 is present on the surface of PDAC cells. We found that histamine prominently increases calcium [Ca2+] in multiple human PDAC cell lines with EC50 values comparable to that in other cell types. The histamine-stimulated increase in [Ca2+] occurs via a Gq/11 (heterotrimeric GTP binding protein)-dependent mechanism and is blocked by multiple FDA-approved HRH1 antihistamines (with pKi values similar to those of HRH1 inhibition of other cell types). HRH1 activation by histamine increases PDAC cell migration. Histamine also increases the production of numerous cytokines (including VEGF) from PDAC cells, and in preliminary studies, stimulates growth of multiple PDAC cell lines at low concentrations (1-10 nM). Together with published data indicating that mast cells (which synthesize and release histamine) in PDAC tumors are associated with PDAC cell growth/invasion, angiogenesis and worse prognosis, our findings suggest that independent of immune cells, a "mast cell-histamine-PDAC cell HRH1 axis" may contribute to the malignant phenotype of PDAC tumors. Importantly, HRH1 on PDAC cells could be targeted by repurposing approved HRH1 antihistamines as a novel therapeutic approach for PDAC tumors. Supported by grants from the University of California Cancer Research Coordinating Committee and Tobacco-Related Disease Research Program. Citation Format: Cristina Salmeron, Krishna Sriram, Mehrak Javadi-Paydar, Paul A. Insel. Histamine receptor 1 (HRH1): A potentially novel G protein-coupled receptor (GPCR) therapeutic target in pancreatic adenocarcinoma (PDAC) cells and tumors [abstract]. In: Proceedings of the AACR Virtual Special Conference on Pancreatic Cancer; 2021 Sep 29-30. Philadelphia (PA): AACR; Cancer Res 2021;81(22 Suppl):Abstract nr PO-091.