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Cannabis -vs- Leukemia

http://www.ncbi.nlm.nih.gov/pubmed/15978942:  Targeting cannabinoid receptors has recently been shown to trigger apoptosis and offers a novel treatment modality against malignancies of the immune system. However, the precise mechanism of apoptosis in such cancers has not been previously addressed. In this study, we used human Jurkat leukemia cell lines with defects in intrinsic and extrinsic signaling pathways to elucidate the mechanism of apoptosis induced by Delta9-tetrahydrocannabinol (THC). We observed that Jurkat cells deficient in FADD or caspase-8 were partially resistant to apoptosis, while dominant-negative caspase-9 mutant cells were completely resistant to apoptosis. Use of caspase inhibitors confirmed these results. Furthermore, overexpression of Bcl-2 rendered the cells resistant to THC at early time points but not upon prolonged exposure. THC treatment led to loss of Deltapsi(m), in both wild-type and FADD-deficient Jurkat cells thereby suggesting that THC-induced intrinsic pathway was independent of FADD. THC treatment of wild-type Jurkat cells caused cytochrome c release, and cleavage of caspase-8, -9, -2, -10, and Bid. Caspase-2 inhibitor blocked THC-induced caspase-3 in wild-type Jurkat cells but not loss of Deltapsi(m). Together, these data suggest that the intrinsic pathway plays a more critical role in THC-induced apoptosis while the extrinsic pathway may facilitate apoptosis via cross-talk with the intrinsic pathway.

http://www.ncbi.nlm.nih.gov/pubmed/16754784:  In the current study, we examined the effects of the nonpsychoactive cannabinoid, cannabidiol, on the induction of apoptosis in leukemia cells. Exposure of leukemia cells to cannabidiol led to cannabinoid receptor 2 (CB2)-mediated reduction in cell viability and induction in apoptosis. Furthermore, cannabidiol treatment led to a significant decrease in tumor burden and an increase in apoptotic tumors in vivo. From a mechanistic standpoint, cannabidiol exposure resulted in activation of caspase-8, caspase-9, and caspase-3, cleavage of poly(ADP-ribose) polymerase, and a decrease in full-length Bid, suggesting possible cross-talk between the intrinsic and extrinsic apoptotic pathways. The role of the mitochondria was further suggested as exposure to cannabidiol led to loss of mitochondrial membrane potential and release of cytochrome c. It is noteworthy that cannabidiol exposure led to an increase in reactive oxygen species (ROS) production as well as an increase in the expression of the NAD(P)H oxidases Nox4 and p22(phox). Furthermore, cannabidiol-induced apoptosis and reactive oxygen species (ROS) levels could be blocked by treatment with the ROS scavengers or the NAD(P)H oxidase inhibitors. Finally, cannabidiol exposure led to a decrease in the levels of p-p38 mitogen-activated protein kinase, which could be blocked by treatment with a CB2-selective antagonist or ROS scavenger. Together, the results from this study reveal that cannabidiol, acting through CB2 and regulation of Nox4 and p22(phox) expression, may be a novel and highly selective treatment for leukemia.

http://www.ncbi.nlm.nih.gov/pubmed/15454482: Delta9-Tetrahydrocannabinol (THC) is the active metabolite of cannabis. THC causes cell death in vitro through the activation of complex signal transduction pathways. However, the role that the cannabinoid 1 and 2 receptors (CB1-R and CB2-R) play in this process is less clear. We therefore investigated the role of the CB-Rs in mediating apoptosis in 3 leukemic cell lines and performed microarray and immunoblot analyses to establish further the mechanism of cell death. We developed a novel flow cytometric technique of measuring the expression of functional receptors and used combinations of selective CB1-R and CB2-R antagonists and agonists to determine their individual roles in this process. We have shown that THC is a potent inducer of apoptosis, even at 1 x IC(50) (inhibitory concentration 50%) concentrations and as early as 6 hours after exposure to the drug. These effects were seen in leukemic cell lines (CEM, HEL-92, and HL60) as well as in peripheral blood mononuclear cells. Additionally, THC did not appear to act synergistically with cytotoxic agents such as cisplatin. One of the most intriguing findings was that THC-induced cell death was preceded by significant changes in the expression of genes involved in the mitogen-activated protein kinase (MAPK) signal transduction pathways. Both apoptosis and gene expression changes were altered independent of p53 and the CB-Rs.

http://www.ncbi.nlm.nih.gov/pubmed/16139274:  Cannabinoids have been shown to inhibit the growth of a broad spectrum of tumour cells. However, the molecular mechanisms involved in that effect have not been completely elucidated. Here, we investigated the possible involvement of mitogen-activated protein kinases (MAPKs) in CB2 receptor-induced apoptosis of human leukaemia cells. Results show that stimulation of the CB2 receptor leads to p38 MAPK activation and that inhibition of this kinase attenuates CB2 receptor-induced caspase activation and apoptosis. These findings support a role for p38 MAPK in CB2 receptor-induced apoptosis of human leukaemia cells.

http://www.ncbi.nlm.nih.gov/pubmed/14692532:  Two non-psychotropic cannabinoids, cannabidiol (CBD) and cannabidiol-dimethylheptyl (CBD-DMH), induced apoptosis in a human acute myeloid leukemia (AML) HL-60 cell line. Apoptosis was determined by staining with bisBenzimide and propidium iodide. A dose dependent increase of apoptosis was noted, reaching 61 and 43% with 8 microg/ml CBD and 15 microg/ml CBD-DMH, respectively, after a 24 h treatment. Prior exposure of the cells to gamma-irradiation (800 cGy) markedly enhanced apoptosis, reaching values of 93 and 95%, respectively. Human monocytes from normal individuals were resistant to either cannabinoids or gamma-irradiation. Caspase-3 activation was observed after the cannabinoid treatment, and may represent a mechanism for the apoptosis. Our data suggest a possible new approach to treatment of AML.   

http://www.ncbi.nlm.nih.gov/pubmed/3037549:    Monocyte maturation markers were induced in cultured human myeloblastic ML-2 leukemia cells after treatment for 1-6 days with 0.03-30 microM delta 9-tetrahydrocannabinol (THC), the major psychoactive component of marijuana. After a 2-day or longer treatment, 2- to 5-fold increases were found in the percentages of cells exhibiting reactivity with either the murine OKM1 monoclonal antibody or the Leu-M5 monoclonal antibody, staining positively for nonspecific esterase activity, and displaying a promonocyte morphology. The increases in these differentiation markers after treatment with 0.03-1 microM THC were dose dependent. At this dose range, THC did not cause an inhibition of cell growth. The THC-induced cell maturation was also characterized by specific changes in the patterns of newly synthesized proteins. Pronounced among these changes was an increase in the synthesis of at least 10 proteins that are found abundantly in monocytes. The THC-induced differentiation did not, however, result in cells with a highly developed mature monocyte phenotype; the THC-treated cells failed to exhibit other monocyte markers such as attachment to the surface of tissue culture dishes or morphological maturation beyond the promonocyte stage. However, treatment of these "incompletely" matured cells with either phorbol 12-myristate 13-acetate or 1 alpha,25-dihydroxycholecalciferol, which are inducers of differentiation in myeloid leukemia cells (including ML-2 cells), produced cells with a mature monocyte morphology. Two other cannabinoids, cannabidiol and cannabinol, which were more cytotoxic than THC at comparable doses, also caused an increase in the expression of maturation markers, but at doses higher than those required for THC. The ML-2 cell system described here may be a useful tool for deciphering critical biochemical events that lead to the cannabinoid-induced "incomplete" cell differentiation of ML-2 cells and other related cell types. Findings obtained from this system may have important implications for studies of cannabinoid effects on normal human bone-marrow progenitor cells.