Abstract 1845: Propranolol reduces hemangiosarcoma cell viability by disrupting lipid homeostatic pathways

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Abstract Angiosarcoma is a highly aggressive cancer of blood vessel-forming cells with few effective treatment options and high patient mortality. Recent studies have shown that the beta-adrenergic antagonist propranolol, a drug historically used for the treatment of cardiac disease, promotes regression of angiosarcomas when combined with standard chemotherapies and increases the overall survival of angiosarcoma patients. Because angiosarcomas are rare, undertaking studies to understand the susceptibility of these tumors to propranolol remains a challenge. In contrast, hemangiosarcoma is a common cancer in dogs that closely models the genetic landscape and the pathogenesis of human angiosarcoma, making it a powerful tool for investigating the susceptibility of angiosarcomas to propranolol. Treatment of an angiosarcoma and hemangiosarcoma cell line panel with propranolol or its receptor active S-(-), and inactive R-(+) enantiomers similarly reduced cell viability in all lines in a concentration dependent manner, suggesting the effects of propranolol are independent of adrenergic receptor activity. Lipin-1, an enzyme responsible for the conversion of phosphatidic acid (PA) to diacylglycerol (DAG), is a known target of propranolol. Inhibition of lipin-1 by propranolol rapidly increases the levels PA, which plays a key role in phospholipid synthesis, intracellular vesicle transport, and signaling pathways involved in regulation of metabolism. Hence, we tested the hypothesis that propranolol induces its detrimental effects in angiosarcomas by disrupting lipid metabolic pathways and vesicular transport. We found that propranolol induced synthesis of cholesterol and fatty acid pathways within 30 minutes via the activation of SREBP-1. Propranolol also blocked endocytosis of extracellular cholesterol, suggesting the rapid induction of lipid synthesis was used by cells to maintain lipid homeostasis. The rapid induction of lipid synthesis activated an ER stress response, contributing to a loss of cell viability. Propranolol also blocked autophagy, proteasomal degradation pathways, and vesicular transport of cholesterol, limiting access to essential metabolites and further exacerbating ER stress. Because mTORC1 is a key regulator of SREBP-1 and mTORC1 is stabilized by PA, we evaluate the effects of propranolol on mTORC1 activity. While propranolol rapidly increased PA levels, it modestly increased the phosphorylation of 4E-BP1, a downstream target of mTORC1, and results were not consistent across all cell lines. Instead, propranolol rapidly induced the phosphorylation and inhibition of GSK-3beta, a known inhibitor of SREBP-1, providing a mechanism for the activation of lipid synthesis pathways by propranolol. Our data suggest propranolol induces sarcoma cell death by disrupting lipid homeostatic pathways and inducing ER stress. Importantly, our findings identify a mechanistic pathway that can be targeted in combination with propranolol to further improve patient responses. Citation Format: Derek M. Korpela, Jhuma Saha, Ali Khammanivong, Shee Kwan Phung, David R. Brown, Erin B. Dickerson. Propranolol reduces hemangiosarcoma cell viability by disrupting lipid homeostatic pathways [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 1845.