Canine urothelial carcinoma (UC) is an invasive epithelial neoplasm and is the most common urogenital tumour in dogs. Despite the use of multimodal therapies, local and systemic control of this disease remain challenging. A particular difficulty with UC relates to the frequency of local treatment failure, which often results in urinary obstruction, however distant metastases also occur, highlighting the need for novel therapies to help improve outcomes. Increasingly, cannabidiol (CBD) has been evaluated for anti-neoplastic effects in vitro and in vivo, yielding encouraging results. However, the mechanisms through which these effects occur remain incompletely understood. Although these effects have been studied in various human malignancies, including urogenital tumours, there is a lack of such information available for veterinary patients. The present work aimed to evaluate expression of various cannabinoid receptors in canine UC cell lines, examine the anti-neoplastic effects of CBD and investigate potential underlying mechanisms. Three canine UC cell lines and one immortalized canine kidney epithelial cell line were evaluated. A major band was observed in all cell lines using an antibody directed against cannabinoid receptors CB1, CB2, PPARγ, GPR55 and TRPV1 via western blotting. Additionally, treatment with CBD resulted in dose dependent reduction of cell viability in all cell lines. However, apoptosis and autophagy were found not to be significantly increased compared to vehicle controls at 8 and 24 hours following administration of CBD, respectively. Lastly, treatment with cannabinoid receptor antagonists, to investigate whether the anti-neoplastic effects of CBD are mediated by these receptors, did not alter cell viability in comparison to treatment with CBD alone.
Based on this information, it can be concluded that while these cannabinoid receptors are expressed in canine UC in vitro, their biologic role and role in any potential anti-neoplastic effects remain unclear. Further investigation into possible underlying mechanisms of action of CBD is necessary prior to defining its role as a potential novel therapeutic agent for canine UC.