Cannabinoid Receptors As A Target For Therapy Of Ovarian Cancer

[Truth Seeker]

Ovarian cancer represents one of the leading cause of cancer-related deaths for women and is the most common gynecologic malignancy. In spite of relative low morbidity, ovarian cancer has a high fatality ratio, with overall 5-year survival of less than 30%. At present, there are inadequate treatment options for the management of advanced ovarian cancer, and therefore development of novel approaches for treatment of this disease are needed. Cannabinoids, the active components of Cannabis sativa linnaeous and their derivatives have received considerable attention in recent years due to their diverse pharmacological activities such as cell growth inhibition and tumor regression. To date, two different cannabinoid receptors have been characterized and cloned from mammalian tissues: the "central" CB1 receptor and the "peripheral" CB2 receptor. We found that compared to normal Chinese hamster ovarian (CHO) cells, the expression levels of both cannabinoid receptors CB1 and CB2 were significantly higher in human ovarian cancer cells OVCAR-3 and SKOV-3. We then determined expression levels of the cannabinoid receptors in different grades of human ovarian cancer specimens and employing western blot analysis found that both CB1 and CB2 receptors were expressed. To evaluate the cell growth response of WIN-55,212-2 (a mixed CB1/CB2 agonist) on CHO, OVCAR-3 and SKOV-3 cells, we employed MTT assay. Of interest, our results demonstrated that treatment of CHO cells with WIN-55,212-2 (5-20 µM; 48 h), did not affect cell viability. In sharp contrast, treatment of OVCAR-3 and SKOV-3 cells with WIN-55,212-2 under similar conditions significantly decreased the viability of cells. The decrease in cell viability in OVCAR-3 and SKOV-3 cells suggests the involvement of either or both CB1 and CB2 receptors in the antiproliferative action of cannabinoids. To evaluate the possible implication of CB1 and CB2 receptors in WIN-55,212-2-mediated decrease in cell viability, the effect of selective receptor antagonists was studied. Blocking of both receptors by their antagonists SR141716 (CB1) and SR144528 (CB2) significantly prevented this growth inhibitory effect. Further, WIN-55,212-2 treatment of both OVCAR-3 and SKOV-3 cells resulted in G1 arrest in cell cycle progression, which was associated with a marked decrease in the protein expression of cyclin D1, D2, and E and their activating partner cdk2, 4 and 6. In addition WIN-55,212-2 treatment of both OVCAR-3 and SKOV-3 cells was found to result in induction of apoptosis as determined by PARP cleavage and flow cytometry. We also found that treatment of both OVCAR-3 and SKOV-3 cells with WIN-55,212-2 resulted in down-regulation of the expression of PCNA and VEGF. These results support a new therapeutic approach for the treatment of ovarian cancer. It is also conceivable that with available cannabinoids as lead compounds, non-habit forming agents that have higher biological effects could be developed.

Source: Cannabinoid receptors as a target for therapy of ovarian cancer -- Afaq et al. 2006 (1): 1084 -- AACR Meeting Abstracts