Histamine receptor 1 (HRH1): A new therapeutic target for pancreatic cancer?

Pancreatic ductal adenocarcinoma (PDAC) is the most common and lethal (5‐year survival <10%) type of pancreatic cancer and the 3 rd leading cause of cancer death in the U.S. Current treatment options (surgery, radiotherapy, and chemotherapy) rarely produce a cure. New and effective therapies for PDAC are thus an important, urgent need. As a novel approach to address this unmet need, we explored whether G protein‐coupled receptors (GPCRs), in particular GPCRs with FDA‐approved drugs (which could be repurposed), have altered expression in PDAC compared to healthy pancreatic tissue or cells. We undertook a comprehensive analysis of GPCRs (comparing GPCR expression in PDAC samples in The Cancer Genome Atlas [TCGA] with that in The Genotype‐Tissue Expression [GTEx] database) and identified numerous GPCRs with higher expression in PDAC. One such GPCR, histamine receptor H1 (HRH1), which is targeted by many FDA‐approved antihistamines, has ~30‐fold higher mRNA expression in PDAC. We found that high HRH1 expression is an unfavorable prognostic marker for PDAC. However, the roles of HRH1 in PDAC are unknown. We hypothesized that HRH1 is functional and contributes to the phenotype of PDAC. We initially assessed the mRNA and protein expression of HRH1 in human PDAC cell lines. RNAseq data from The Cancer Cell Line Encyclopedia (CCLE) database revealed that HRH1 is the main histamine receptor expressed in multiple human PDAC cell lines: AsPC‐1, MIA PaCa‐2, PANC‐1 and BxPC‐3 (5‐19 transcripts/million [TPM] compared to the other 3 HRHs [≤ 0.6 TPM]). We confirmed those results by qPCR. Proteomic analysis (PMID: 31978347 and PMID: 28375945) has identified HRH1 protein expression in AsPC‐1, MIA PaCa2 and PANC‐1: HRH1 had a strong protein‐RNA correlation (Pearson correlation= 0.64 and Spearman correlation= 0.72). We next tested if HRH1 is functional in PDAC cells. We treated BxPC‐3 cells with histamine (10µM) and with the FDA‐approved HRH1 inhibitors/antihistamines loratadine or clemastine (both 1µM) in a wound healing assay. We found that histamine, via HRH1, increased BxPC‐3 cell migration. Moreover, histamine (in a time‐ and concentration‐dependent manner) increased intracellular Ca 2+ in BxPC‐3, AsPC‐1 and Capan‐2 cells. Multiple HRH1 antagonists blocked this response. We also found high expression of HRH1 (by qPCR) in pancreatic tumors of KPC (LSL‐KrasG12D/+; Trp53f/f; Ptf1a‐Cre) mice, which spontaneously develop pancreatic cancer. We isolated cancer cell lines from the KPC pancreatic tumors by multiple passage of the cells and found that: 1) the cells highly express HRH1 mRNA and 2) histamine increases intracellular Ca 2+ via HRH1, i.e., inhibition by multiple HRH1 antihistamines. Together, these data indicate the presence and functional activity of HRH1 in human PDAC and a mouse model and suggest that HRH1 may be a novel therapeutic target for PDAC.