Abstract 2620: Combination of growth hormone receptor antagonist and gemcitabine leads to highly efficacious tumor clearance in a mouse model of pancreatic ductal adenocarcinoma

Pancreatic cancer is responsible for more than 48,000 deaths and 60,000 new cancer cases every year in the United States while the overall 5-year survival rate is only 10%. These numbers point towards an urgent need for new therapeutic approaches wherein therapy resistance poses a tremendous challenge. We and others have identified the role of growth hormone (GH) and its cognate receptor (GHR), overexpressed in pancreatic ductal adenocarcinoma patients (PDAC; >90% of pancreatic cancer cases), in driving therapy resistance by directly upregulating multidrug efflux, phenotype switch via epithelial-to-mesenchymal transition (EMT) and inhibition of apoptosis. Our laboratory had pioneered the discovery of pharmacologic GHR antagonists including the only approved and prescribed GHR antagonist, pegvisomant, and a new antagonist candidate named compound-G. Here, we used in vitro, in vivo and in silico analyses to assess the feasibility and efficacy of a treatment regimen including GHR antagonist and chemotherapy to manage PDAC. Both pegvisomant and compound-G exhibit significant suppression of cancer cellular viability, invasive potential, drug efflux rate and apoptosis in PDAC cell cultures. In male and female Nude mice with human PDAC xenografts, GHR inhibition by either pegvisomant or compound-G markedly re-sensitized the tumors towards both low and high doses of gemcitabine treatment. Compound G plus high doses of gemcitabine lead to almost complete tumor clearance in 40% of the mice. Also, tissue analyses reveal increased production of GH in tumors treated with chemotherapy. In the GHR antagonist treated tumors, significantly lower expression of ABC transporter (Abcb1, Abcg5, Abcc2, Abcg2), EMT mediator (Cdh2, Zeb1, Snai2, Epas1) and apoptosis marker (Bcl2) genes compared to control were observed - accounting for the observed sensitization to gemcitabine. In the human PDAC patient datasets, increased expression of GHR correlates strongly with increased expression of multidrug efflux transporters, anti-apoptotic markers, and EMT transcription factors. Therefore, we provide robust pre-clinical validation for a treatment regimen combining GHR antagonist and chemotherapy leading to highly efficacious tumor clearance. Acknowledgement: This work was supported in part by the State of Ohio’s Eminent Scholar Program that includes a gift from Milton and Lawrence Goll, by the AMVETS, and Ohio University’s Student Enhancement Award and Edison Biotechnology Institute. Citation Format: Reetobrata Basu, Prateek Kulkarni, Emily Davis, Silvana Duran, John J. Kopchick. Combination of growth hormone receptor antagonist and gemcitabine leads to highly efficacious tumor clearance in a mouse model of pancreatic ductal adenocarcinoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 2620.