Introduction

Despite existing combination therapies, local and systemic control of canine urothelial carcinoma (UC) remains challenging. Increasingly, cannabidiol (CBD) has been evaluated for anti-neoplastic effects in vitro and in vivo, yielding encouraging results. However, the mechanisms through which these occur remain incompletely understood. Although these effects have been studied in various human malignancies, including urogenital tumors, there is a lack of such information available for veterinary patients. This study aimed to evaluate expression of various cannabinoid receptors in canine UC cell lines, examine the anti-neoplastic effects of CBD, and investigate their underlying mechanisms.

Methods

Three canine UC cell lines and one immortalized canine kidney epithelial cell line were evaluated. Expression of cannabinoid receptors CB1, CB2, PPAR-gamma, GPR55, and TRPV1 was evaluated via western blotting. Crystal violet colorimetric assays were used to establish IC50 concentrations for CBD and assess the effects of known cannabinoid receptor antagonists on cell viability. Flow cytometry was used to measure apoptosis and autophagy to characterize the mechanisms through which CBD induces cytotoxicity.

Results

The expression of cannabinoid receptors was detected in all cell lines. Treatment with CBD resulted in dose dependent reduction of cell viability in all cell lines; however, apoptosis and autophagy were not significantly increased compared to vehicle control at 8 and 24 hours respectively. Treatment with receptor antagonists did not alter cell viability in comparison to treatment with CBD alone.

Conclusion

Further investigation into possible underlying mechanisms of CBD as a novel therapeutic agent is necessary before its role in improving patient outcomes can be established.

Funding Information

Funding for this project was provided by Greywolf Animal Health and Ontario Veterinary College Pet Trust.