Cannabinoid Receptor-Mediated Apoptosis Induced by R(+)- Methanandamide and Win55,212-2 Is Associated with Ceramide Accumulation and p38 Activation in Mantle Cell Lymphoma

We have recently shown that cannabinoids induce growth inhibition and apoptosis in mantle cell lymphoma (MCL), a malignant B-cell lymphoma that expresses high levels of cannabinoid receptor types 1 and 2 (CB1 and CB2). In the current study, the role of each receptor and the signal transduction triggered by receptor ligation were investigated. Induction of apoptosis after treatment with the synthetic agonists R()- methanandamide [R()-MA] and Win55,212-2 (Win55; (R)-()- [2,3-dihydro-5-methyl-3-(4-morpholinylmethyl) pyrrolo-[1,2,3- d,e]-1,4-benzoxazin-6-yl]-1-naphthalenyl-methanone) was dependent on both cannabinoid receptors, because pretreatment with N-(piperidin-1-yl)-5-(4-chlorophenyl)-1-(2,4-dichlorophenyl)-4-methyl-1H-pyrazole-3-carboximide hydrochloride (SR141716A) and N-((1S)-endo-1,3,3-trimethyl bicyclo heptan2-yl]-5-(4-chloro-3-methylphenyl)-1-(4-methylbenzyl)-pyrazole-3-carboxamide) (SR144528), specific antagonists to CB1 and CB2, respectively, abrogated caspase-3 activity. Preincubation with the inhibitors 4-(4-fluorophenyl)-2-(4-methylsulfinylphenyl)-5-(4-pyridyl)1H-imidazole (SB203580) and 4-(4- fluorophenyl)-2-(4-hydroxyphenyl)-5-(4-pyridyl)-1H-imidazole (SB202190) showed that phosphorylation of MAPK p38 was implicated in the signal transduction leading to apoptosis. Treatment with R()-MA and Win55 was associated with accumulation of ceramide, and pharmacological inhibition of ceramide synthesis de novo prevented both p38 activation and mitochondria depolarization assessed by binding of 3,3-dihexyloxacarbocyanine iodide (DiOC6). In contrast, the pancaspase inhibitor z-Val-Ala-Asp(Ome)-CH2F (z-VAD-FMK) did not protect the mitochondrial integrity. Taken together, these results suggest that concurrent ligation of CB1 and CB2 with either R()-MA or Win55 induces apoptosis via a sequence of events in MCL cells: accumulation of ceramide, phosphorylation of p38, depolarization of the mitochondrial membrane, and caspase activation. Although induction of apoptosis was observed in both MCL cell lines and primary MCL, normal B cells remained unaffected. The present data suggest that targeting CB1/ CB2 may have thererapeutic potential for the treatment of
mantle cell lymphoma.