Histamine H1 Receptor: A potential therapeutic target for pancreatic ductal adenocarcinoma.

Patients diagnosed with pancreatic ductal adenocarcinoma (PDAC) have a dismal 5-year survival (∼13%). Thus, new, effective, and ideally, less toxic therapies are desperately needed. Epidemiologic studies have found that patients with PDAC prescribed H1-antihistamines have improved survival. Expression of the histamine H1 receptor (HRH1), a G protein-coupled receptor which is blocked by approved H1-antihistamines, is increased by ∼20-fold in PDAC tumors compared with normal pancreas. Here, we used bioinformatic and molecular biological techniques to identify the cellular localization of HRH1 in the PDAC tumor microenvironment, assess functional responses to HRH1 activation, and define its potential biological roles in PDAC. We found that HRH1 is primarily expressed in cancer cells of PDAC tumors in humans and KPC mice (mice engineered to develop PDAC) and signals via G protein q/11 to increase intracellular Ca²⁺. HRH1 activation increases migration and invasion by PDAC cancer cells. Orally administered fexofenadine, an H1-antihistamine, was bioavailable in the tumors of KPC mice and yielded smaller pancreatic tumor tissue weights and lower expression of immunomodulatory (interleukin 6 and PD-1) and fibrotic (Col1A1) genes than in vehicle-control KPC mice. Thus, PDAC cancer cells express HRH1, which is functional in vitro and in vivo, suggesting that the repurposing of approved H1-antihistamines may be an efficacious and safe therapeutic approach for patients with PDAC. SIGNIFICANCE STATEMENT: Pancreatic ductal adenocarcinoma (PDAC) has a ∼13% 5-year survival rate, highlighting the need for new therapies. The HRH1 (histamine) receptor, associated with poorer survival, is upregulated in PDAC tumors. This study found that HRH1 is functional in PDAC cells, increasing intracellular Ca²⁺ via G_q/11 and promoting tumorigenic responses. KPC mice treated with an H1-antihistamine have reduced pancreas weight and lower proinflammatory and fibrotic markers in PDAC tumors. Thus, HRH1 may be a potential target for repurposing approved H1-antihistamines to treat PDAC.