Introduction

Canine hemangiosarcoma is an aggressive and lethal tumor in dogs that closely mimics the clinical presentation of human angiosarcoma. The beta-adrenergic receptor antagonist, propranolol, has recently been shown to promote tumor regression and increase the overall survival of angiosarcoma patients. Preclinical models suggest propranolol may also be effective against hemangiosarcoma. Our objective was to determine if pathways vital to hemangiosarcoma cell survival are vulnerable to propranolol inhibition.

Methods

RNA-sequencing (RNA-seq) was used to identify altered transcriptional programs. Fluorescent-based assays in combination with flow cytometry and confocal microscopy were used to confirm inhibition of autophagic flux, endocytosis, and metabolic pathways in hemangiosarcoma cell lines. Immunoblotting and qRT-PCR were used to confirm activation of the lipid synthesis and endoplasmic reticulum (ER) stress pathways.

Results

Our data suggest that propranolol prevents hemangiosarcoma cells from obtaining the essential lipid building blocks needed for cell proliferation and viability. Propranolol blocked endocytosis and autophagic flux, preventing the uptake and processing of exogenous cholesterol and fatty acids. In response, cells rapidly increased the expression of genes and proteins involved in fatty acid and cholesterol synthesis via activation of the transcription factor SREBP-1. In addition, propranolol induced the ER stress pathways; we associated the extent of activation of these pathways in hemangiosarcoma cell lines with propranolol sensitivity.

Conclusion

We conclude that propranolol inhibits hemangiosarcoma cell proliferation and induces cell death by disrupting lipid homeostasis and inducing ER stress. Targeting these pathways in combination with propranolol may provide new opportunities for strategic intervention.

Funding Information

This work was supported by grants D17CA-059 and D18CA-017 from Morris Animal Foundation, the Sarcoma Foundation of America (Dr. Richard and Valerie Aronsohn Memorial Research Award), and P30 CA077598 from the National Institutes of Health.