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In recent years, the endocannabinoid system has received great interest as a potential therapeutic target in numerous pathological conditions. Cannabinoids have shown an anticancer potential by modulating several pathways involved in cell growth, differentiation, migration, and angiogenesis. However, the therapeutic efficacy of cannabinoids is limited to the treatment of chemotherapy-induced symptoms or cancer pain, but their use as anticancer drugs in chemotherapeutic protocols requires further investigation. In this paper, we reviewed the role of cannabinoids in the modulation of signaling mechanisms implicated in tumor progression.

The endocannabinoid system regulates food intake, energy, and glucose metabolism at both central and peripheral levels. We have investigated the mechanism by which it may control glucose uptake in skeletal muscle cells. Detectable levels of the cannabinoid receptor type 1 (CB1) were revealed in L6 cells. Exposure of differentiated L6 myotubes to the CB1 antagonist rimonabant (SR141716) selectively increased 2-deoxyglucose uptake (2-DG) in a time-and dose-dependent manner. A similar effect was induced by genetic silencing of CB1 by small interfering RNA. Protein expression profiling revealed that both the regulatory p85 and the catalytic p110 subunits of the phosphatidylinositol-3-kinase (PI3K) were increased by SR141716. No significant change in the cellular content of other known molecules regulating PI3K was observed. However, phosphoinositidedependent kinase-1, Akt/protein kinase B, and protein kinase C activities were rapidly induced after SR141716 treatment of L6 cells in a PI3K-dependent manner. The stimulatory effect of SR141716 on PI3K expression and activity was largely prevented by

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Increasing evidence suggest the role of the cannabinoid receptors (CBs) in the control of cell survival or death and signaling pathways involved in tumor progression. Cancer cell lines are characterized by a subtle modulation of CB levels which produces a modified responsiveness to specific ligands, but the molecular mechanisms underlying these events are poorly and partially understood. We previously provided evidence that the endocannabinoid (EC) anandamide (AEA) exerts anti-proliferative effect likely by modulation of the expression of genes involved in the cellular fate. In this study we focused on the role of the CB1 receptor, ECs, and steroids in the mechanisms involved in colorectal cancer (CRC) cell growth inhibition in vitro. We demonstrated that, in DLD1 and SW620 cells, 17β-estradiol induced a specific and strong up-regulation of the CB1 receptor by triggering activation of the CB1 promoting region, localized at the exon 1 of the CNR1 gene. Moreover, treatment of DLD1 and SW620 cells with Met-F-AEA, a stable AEA-analogous, or URB597, a selective inhibitor of FAAH, induced up-regulation of CB1 expression by co-localization of PPARγ and RXRα at the promoting region. Finally, increased availability of AEA, of both exogenous and endogenous sources, induced the expression of estrogen receptor-beta in both cell lines. Our results partially elucidated the role of EC system in the molecular mechanisms enrolled by steroids in the inhibition of colon cancer cell growth and strongly suggested that targeting the EC system could represent a promising tool to improve the efficacy of CRC treatments.

The selective CB1 receptor antagonist rimonabant (SR141716) was shown to perform a number of biological effects in several pathological conditions. Emerging findings demonstrate that rimonabant exerts antitumor action in thyroid tumors and breast cancer cells. In our study, human colorectal cancer cells (DLD-1, CaCo-2 and SW620) were treated with rimonabant and analyzed for markers of cell proliferation, cell viability and cell cycle progression. Rimonabant significantly reduced cell growth and induced cell death. In addition, rimonabant was able to alter cell cycle distribution in all the cell lines tested. Particularly, rimonabant produced a G2/M cell cycle arrest in DLD-1 cells without inducing apoptosis or necrosis. The G2/M phase arrest was characterized by a parallel enhancement of the number of mitoses associated to elevated DNA double strand breaks and chromosome misjoining events, hallmarks of mitotic catastrophe. Protein expression analyses of Cyclin B1, PARP-1, Aurora B and phosphorylated p38/MAPK and Chk1 demonstrated that rimonabantinduced mitotic catastrophe is mediated by interfering with the spindle assembly checkpoint and the DNA damage checkpoint. Moreover, in the mouse model of azoxymethane-induced colon carcinogenesis, rimonabant significantly decreased aberrant crypt foci (ACF) formation, which precedes colorectal cancer. Our findings suggest that rimonabant is able to inhibit colorectal cancer cell growth at different stages of colon cancer pathogenesis inducing mitotic catastrophe in vitro. ' UICCKey words: rimonabant; colon cancer; mitotic catastrophe; ACF formation Rimonabant (SR141716) is the first described highly selective antagonist for the cannabinoid receptor type 1 (CB1).1 Because of its ability to block the CB1 receptor, which controls food intake at central and peripheral level, rimonabant has been in clinical development for the treatment of obesity and its metabolic complications, including dyslipidemia, type 2 diabetes and atherosclerosis. However, rimonabant shows a plethora of pharmacological effects in a number of physiopathological conditions including cancer. 3The first observation of a rimonabant potential antitumor action was provided by our group in rat thyroid cancer cells (KiMol) in vitro and in thyroid tumor xenografts induced by KiMol injection in athymic mice. In this model, rimonabant was able to partially prevent the antitumor effect of endocannabinoid degradation inhibitors as well as of a metabolically stable analogue of the endocannabinoid anandamide (2-methylarachidonyl-2 0 -fluoroethylamide, Met-F-AEA). However, rimonabant, when used alone in the same model and at the dose able to counteract the Met-F-AEA effect, did not enhance tumor growth but instead it exerted a small, although significant, antitumor effect on thyroid tumors both in vitro and in vivo.4 Other authors demonstrated a potential antiproliferative effect of rimonabant: it decreased viability of primary mantle lymphoma cells isolated from tumor biopsies, 5 whilst a 48 hr incubation of C6 gl...

In this study we investigated the role of CB1 receptor signaling in angiogenesis and the therapeutic exploitation of CB1 inactivation as an antiangiogenic strategy. We started from the observation that CB1 receptor expression is induced during angiogenesis and that the endocannabinoid anandamide stimulated bFGFinduced angiogenesis in the nanomolar physiologic range. To define the functional involvement of CB1 receptor signaling during angiogenesis, 2 different strategies have been carried out: siRNAmediated knockdown and pharmacologic antagonism of CB1 receptors. CB1 receptors inactivation resulted in the inhibition of bFGF-induced endothelial proliferation, migration, and capillary-like tube formation, through prosurvival and migratory pathways involving ERK, Akt, FAK, JNK, Rho, and MMP-2. To corroborate the potential therapeutic exploitation of CB1 blockade as an antiangiogenic strategy, we performed in vivo assays founding that CB1 blockade was able to inhibit bFGF-induced neovascular growth in the rabbit cornea assay. A relevant finding was the ability to reduce ocular pathologic neo-vascularization in mouse oxygen-induced retinopathy. These results demonstrate that CB1 signaling participates to the proliferative response elicited by proangiogenic growth factors in angiogenesis and that for this reason CB1 receptor could represent a novel target for the treatment of diseases where excessive neoangiogenesis is the underlying pathology. IntroductionThe endocannabinoid system, composed of 2 cannabinoid receptors CB1 and CB2, their endogenous ligands (endocannabinoids, eg, anandamide), and the enzymes for their metabolism, has been pointed out to be implicated in several pathophysiologic conditions ranging from neurologic and psychiatric diseases to eating, cardiovascular, reproductive disorders, and cancer. [1][2][3] The main effects of endocannabinoids rely on the activation of CB1, a 7-transmembranedomain protein belonging to the G ␣i protein-coupled receptor family (GPCR). 4 CB1 receptors are highly expressed in the central nervous system, especially in the cortex, cerebellum, hippocampus, and basal ganglia, and their involvement in processes of memory and learning, in diseases affecting movement, mood, and anxiety and in conditions related to altered brain reward mechanisms, has been ascertained. 5 Noteworthy, CB1 receptors are expressed also by a variety of peripheral tissues and cells and in the last years a role in several physiologic functions and pathologies is emerging. CB1 deficiency was reported to be associated to age-related osteoporosis 6 and preterm birth in mice, 7 highlighting a role for CB1 signaling in bone metabolism and in early pregnancy events. On the other hand, CB1 receptor antagonism and/or inactivation through genetic engineering as in CB1-deficient mouse strains, 8 were shown to be useful in several pathologies in which the endocannabinoid system is unbalanced or CB1 more than expressed (eg, obesity, metabolic syndrome, diabetes, Alzheimer disease). 9-11 Indeed, CB1 inactivation e...