Anti-tumor Activity of the Novel Hexahydrocannabinol Analog LYR-8 in Human Colorectal Tumor Xenograft Is Mediated through the Inhibition of Akt and Hypoxia-Inducible Factor-1α Activation

Cannabinoid compounds have been shown to exert anti-tumor effects by affecting angiogenesis, invasion, and metastasis. In the present study, we examined the action mechanism by which LYR-8, a novel hexahydrocannabinol analog, exerts anti-angiogenic and anti-tumor activity in human cancer xenografts. In the xenografted tumor tissues, LYR-8 significantly reduced the expression of hypoxia-inducible factor-1 alpha (HIF-1α), a transcription factor responsible for induction of angiogenesis-promoting factors, and its target genes, vascular endothelial growth factor (VEGF) and cyclooxygenase-2 (COX-2). In HT-29 human colon cancer cells treated with a hypoxia-inducing agent (CoCl2), LYR-8 dose-dependently suppressed the induction of HIF-1α and subsequently its targets, VEGF and COX-2. In addition, highly elevated prostaglandin E2 (PGE2) concentrations in CoCl2-treated HT-29 cells were also significantly suppressed by LYR-8. However, LYR-8 alone in the absence of CoCl2 did not alter the basal expression of VEGF and COX-2, or PGE2 production. Furthermore, LYR-8 effectively suppressed Akt signaling, which corresponded to the suppression of CoCl2-induced HIF-1α accumulation. Taken together, LYR-8 exerts anti-tumor effects through the inhibition of Akt and HIF-1α activation, and subsequently suppressing factors regulating tumor microenvironment, such as VEGF and COX-2. These results indicate a novel function of cannabinoid-like compound LYR-8 as an anti-tumor agent with a HIF-1α inhibitory activity.