Abstract 5193: Cholecystokinin-B receptor mediates growth of hepatocellular carcinoma

Abstract Background: The fastest-growing cause of cancer-related death is hepatocellular carcinoma (HCC), which is in part attributable to the obesity epidemic and nonalcoholic steatohepatitis (NASH). The gastrointestinal (GI) peptides, gastrin and cholecystokinin (CCK), regulate digestive functions and growth of the GI tract through the G-protein coupled receptors CCK- receptors (CCK-Rs). Both peptides activate the CCK-B receptor (CCK-BR) whereas only CCK peptide activates the CCK-A receptor (CCK-AR). CCK-Rs and gastrin are low or absent in normal mouse hepatocytes. We have previously shown that CCK blood levels increase and CCK-Rs become overexpressed in the livers of mice eating a high saturated fat diet that induced NASH and HCC. Hypothesis: CCK and gastrin mediate the growth of HCC through the CCK-R and that interruption of this signaling pathway could decrease growth of HCC. Methods: RNA was extracted from murine Hepa1-6, RIL-175, and human HepG2 cells and was evaluated by qRT-PCR for expression of CCK-AR, CCK-BR, and gastrin. CCK-R protein expression was analyzed by flow cytometry. In order to determine which CCK-R mediated the growth effects, growth was studied in vitro using selective receptor antagonists or CRISPR Cas9 technology to knock-out each receptor. HCC cells were treated in vitro with CCK peptide (1-10nM), the CCK-AR antagonist (L364,718), or the CCK-BR antagonist (L365,260). Proliferation of selective CCK-R KO cells was compared to that of wild-type cells. To determine the effect of a CCK-R antagonist on tumor growth in vivo, two cohorts of mice bearing subcutaneous Hepa1-6 or RIL-175 HCC tumors were treated with an oral bioavailable CCK-R antagonist, proglumide (1 mg/ml) or untreated water (controls) for 3-4 weeks. The mice bearing Hepa1-6 tumors were placed on a high-fat diet to raise blood CCK levels. Mice bearing RIL-175 tumors were fed standard chow to determine if proglumide could block autocrine growth by gastrin. Results: The mRNA expression of CCK-AR, CCK-BR and gastrin were increased 80-90-fold in all HCC cell lines compared to that of normal liver. CCK-BRs were detected on >85% of the cells by flow cytometry. CCK peptide (1nM) stimulated HCC growth in vitro in both wild-type cells and in CCK-AR KO cells but not in CCK-BR KO cells. CCK-BR antagonist blocked CCK-stimulated growth in vitro but the CCK-AR antagonist did not, suggesting that the CCK-BR was responsible for mediating proliferation. In vivo tumor growth was significantly reduced with proglumide treatment by 70% (p<0.05) in Hepa1-6 and by 73% (p<0.001) in RIL-75 tumors, respectively. Conclusion: CCK-Rs are overexpressed in HCC and proliferation appears to be mediated through the CCK-BR. Downregulation with CRISPR Cas9 or blockade of the CCK-BR with an antagonist decreases growth in vitro and proglumide therapy decreases tumor growth in vivo. Strategies that block signaling at the CCK-BR may provide a novel therapeutic option for HCC treatment. Citation Format: Martha D. Gay, Anita Safronenka, Hong Cao, Robin Tucker, Narayan Shivapurkar, Jill P. Smith. Cholecystokinin-B receptor mediates growth of hepatocellular carcinoma [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 5193.