Cannabinoids are the active components of Cannabis sativa. The interest in cannabinoid research has triggered only two decades ago following the discovery of the endocannabinoid system, mainly from the molecular characterization of endogenous receptors: CB1 (mostly expressed in the central nervous system) and CB2 (in immune cells). In the last few years, several groups have described their use as potential therapeutic agents in the treatment of pain, multiple sclerosis or Alzheimer. Moreover, increasing evidences have suggested their potential role as antitumor drugs.
Despite the abundant expression of CB2 in immune cells, very few studies have examined its use in hematological malignancies. Considering the high expression levels of CB2 in B-cells, we hypothesized that plasma cells (PCs) could also express high levels of CB2 and therefore might be an excellent target for cannabinoids.
DEVELOPMENT: Our objective was to evaluate the anti-tumor effect of cannabinoids in MM and identify the mechanisms involved. We use the synthetic cannabinoids WIN-55 (CB1 and CB2 mixed agonist) and JWH-133 (CB2 selective agonist). We used MM cell lines U266, MM1R, MM1S and RPMI8226 and primary PCs from patients and CD34+ cells from patients and healthy donors. Viability studies were carried out by MTT and cytometric analyses and the expression of receptors and the study of signaling pathways by Western blot (WB). Further, we tested the cannabinoid effects in vivo in murine models (NSG xenograft mice). We observed a high expression of CBs in CPs and a remarkable proapoptotic effect of cannabinoids on myelomatous cells. By contrast, the viability of the CD34 + hematopoietic progenitor cells remained unaffected irrespective of the dose used. In this regard, in MM cells lines and primary cells from patients we observed cleavage of PARP as well as activation of caspases 8, 9, 3 and 2, the latter related to endoplasmic reticulum stress induced by the cannabinoids. This cannabinoid-induced apoptotic effect was also mediated by AKT and MAPKs signaling pathways, as assessed by WB. In addition, Fluorometric analyses confirmed that cannabinoids induce an early mitochondrial damage. Next we confirmed that cannabinoids increase the expression of SPT, the limiting enzyme for the synthesis of ceramides (membrane sphingolipids). The upregulation of SPT following cannabinoid incubation induced accumulation of ceramide, as assessed by immunohistochemistry. Furthermore, the incubation with myoricine, an SPT inhibitor, partially inhibited caspase 3 activation. Finally, we checked the antimyeloma effect of the cannabinoids in vivo, using a model of human MM xenografted in immunodeficient mice NOD/SCID. Our results demonstrate a significant reduction in tumor growth, even tumor regression, as well as a significant increase of survival of cannabinoid-treated as compared to mice receiving vehicle.
CONCLUSIONS: Cannabinoids have a very selective antitumor effect against MM cells. This effect involves activation of apoptosis processes and alterations in the composition of membrane sphingolipids (ceramides). In vivo studies confirmed the efficacy of these agents in the treatment of MM. This study lays the groundwork for the design of new anti-myeloma therapies.
No relevant conflicts of interest to declare.
Asterisk with author names denotes non-ASH members.