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 Cannabis -vs- Brain Cancer 

http://www.ncbi.nlm.nih.gov/pubmed/17934890: Gliomas are the most important group of malignant primary brain tumors and one of the most aggressive forms of cancer, exhibit high resistance to conventional chemotherapies. In glioblastoma endothelial cells, CB1 and CB2 receptors were present in about 38% and 54% of the cells respectively, analyzed by immunohistochemistry. CB2 expression levels were higher in glioblastoma tissues in comparison to CB1. Selective CB2 agonists may become important targets for the treatment of glioma. Cannabinoids, inhibit tumor growth in animal models by inducing apoptosis of tumor cells and impairing tumor angiogenesis. Administration of Δ9-THC and JWH-133 inhibits MMP-2 expression in in vivo model of glioma [101-103]. The growth inhibitory effect of these cannabinoids is prevented by blocking ceramide synthesis, and the expression of the stress protein p8 [102-103]. Both Δ9-THC and WIN-55,212-2 resulted in sustained activation of ERK1/2 and inhibition of AKT [104]. Furthermore, Δ9-THC induced eukaryotic translation initiation factor 2alpha (eIF2alpha) phosphorylation and thereby activated an ER stress response that promoted autophagy via tribbles homolog 3-dependent (TRB3-dependent) inhibition of the Akt/mammalian target of rapamycin complex 1 (mTORC1) axis [105]. The activation of this pathway was necessary for the antitumor action of cannabinoids in vivo [105]. In contrast to that CBD treatment induces apoptosis in glioma cells in vitro and tumor regression in vivo through activation of caspases and reactive oxygen species via receptor-independent manner Furthermore, studies revealed that CBD induced TRPV2-dependent Ca2+ influx which triggers the drug uptake and synergizes with cytotoxic agents to induce apoptosis of glioma cells [106]. Authors thought that CBD which do not specifically interact with CB1/CB2 receptors, can modulate the activity of Δ9-THC. On that basis Marcu et al determined the growth inhibitory effect of CBD in combination with Δ9-THC in the U251 and SF126 glioblastoma cell lines [107]. Furthermore, the combined treatment of Δ9-THC and temozolomide (TMZ) exert a strong antitumoral action in glioma xenografts by inducing autophagy [108]. The submaximal doses of Δ9-THC and CBD in combination with TMZ produced a strong antitumoral action in both TMZ-sensitive and TMZ-resistant tumors [108]. Treatment of KM-233 (novel cannabinoid ligand) caused a time dependent change in the phosphorylation profiles of MEK, ERK1/2, Akt, BAD, STAT3, and p70S6K in U87MG human GBM cells [109]. At 12mg/kg daily dose of KM-233 for 20 days revealed around 80% reduction in tumor size in the orthotopic model of U87MG [109]. Glioma cells develop resistance to cannabinoid treatment due to the upregulation of Amphiregulin (EGFR family ligand) and the growth factor midkine (Mdk) [110-111]. Amphiregulin expression was associated with increased ERK activation and Mdk mediated its protective effect through ALK which interferes with autophagic cell death [112]. The silencing of amphiregulin and Mdk or ALK pharmacological inhibition can overcome drug resistance of glioma to cannabinoids antitumoral action. Furthermore, to improve the efficacy of cannabinoids action, microencapsulation methods were used which facilitates a sustained release of the two cannabinoids for several days [113]. Administration of CBD- and THC-loaded poly-ε-caprolactone microparticles reduced tumor growth, cell proliferation and increased apoptosis in mice bearing glioma xenografts with the same efficacy than a daily local administration of these drugs in solution [113].

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4171598 The active components of Cannabis sativa L., Cannabinoids, traditionally used in the field of cancer for alleviation of pain, nausea, wasting and improvement of well-being have received renewed interest in recent years due to their diverse pharmacologic activities such as cell growth inhibition, anti-inflammatory activity and induction of tumor regression. Here we used several experimental approaches, which identified delta-9-tetrahydrocannabinol (Delta(9)-THC) as an essential mediator of cannabinoid antitumoral action.

METHODS AND RESULTS:  Administration of Delta(9)-THC to glioblastoma multiforme (GBM) cell lines results in a significant decrease in cell viability. Cell cycle analysis showed G(0/1) arrest and did not reveal occurrence of apoptosis in the absence of any sub-G(1) populations. Western blot analyses revealed a THC altered cellular content of proteins that regulate cell progression through the cell cycle. The cell content of E2F1 and Cyclin A, two proteins that promote cell cycle progression, were suppressed in both U251-MG and U87-MG human glioblastoma cell lines, whereas the level of p16(INK4A), a cell cycle inhibitor was upregulated. Transcription of thymidylate synthase (TS) mRNA, which is promoted by E2F1, also declined as evident by QRT-PCR. The decrease in E2F1 levels resulted from proteasome mediated degradation and was prevented by proteasome inhibitors.

CONCLUSIONS:  Delta(9)-THC is shown to significantly affect viability of GBM cells via a mechanism that appears to elicit G(1) arrest due to downregulation of E2F1 and Cyclin A. Hence, it is suggested that Delta(9)-THC and other cannabinoids be implemented in future clinical evaluation as a therapeutic modality for brain tumors.

http://www.ncbi.nlm.nih.gov/pubmed/22879071Cannabinoids are a group of structurally heterogeneous but pharmacologically related compounds, including plant-derived cannabinoids, synthetic substances and endogenous cannabinoids, such as anandamide and 2-arachidonoylglycerol. Cannabinoids elicit a wide range of central and peripheral effects mostly mediated through cannabinoid receptors. There are two types of specific G(i/o)-protein-coupled receptors cloned so far, called CB1 and CB2, although an existence of additional cannabinoid-binding receptors has been suggested. CB1 and CB2 differ in their predicted amino acid sequence, tissue distribution, physiological role and signaling mechanisms. Significant alterations of a balance in the cannabinoid system between the levels of endogenous ligands and their receptors occur during malignant transformation in various types of cancer, including gliomas. Cannabinoids exert anti-proliferative action in tumor cells. Induction of cell death by cannabinoid treatment relies on the generation of a pro-apoptotic sphingolipid ceramide and disruption of signaling pathways crucial for regulation of cellular proliferation, differentiation or apoptosis. Increased ceramide levels lead also to ER-stress and autophagy in drug-treated glioblastoma cells. 

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5964193:  The antineoplastic effects of cannabinoids have been investigated in a number of in vitro and in vivo studies (reviewed in Ladin et al., 2016). A pilot phase I clinical trial for the treatment of GBM patients indicated a good safety profile for THC (Velasco et al., 2007). The intra-tumor administration of THC in nine patients with actively growing recurrent GBM decreased tumor cell proliferation (Guzmán et al., 2006) and induced apoptosis (Carracedo et al., 2006). In contrast, cannabinoids promoted the survival of healthy oligodendrocytes (Molina-Holgado et al., 2002), astrocytes (Gómez Del Pulgar et al., 2002), and neurons (Howlett et al., 2002; Mechoulam, 2002). A tumor-specific cytostatic/cytotoxic effect of cannabinoids would, therefore, have great relevance for the treatment of GBM.

Pre-clinical studies have also investigated the anti-tumor effects of cannabinoid combinations (in particular THC:CBD) and found that the anti-neoplastic effect of THC was enhanced when combined with CBD (reviewed in Ladin et al., 2016). The therapeutic potential of THC:CBD combinations was, furthermore, tested in combination with standard GBM chemotherapy, such as the alkylating anti-neoplastic drug TMZ or with ionizing radiotherapy. In a GBM xenograft model in nude mice, the reduction of tumor size could be enhanced by co-administration of THC with CBD and TMZ in comparison to the effects of THC, CBD and TMZ alone (Torres et al., 2011). In a further study, THC:CBD co-treatment of orthotopic GBM tumors in C57BL/6 mice enhanced the killing effect of ionizing radiation (Scott et al., 2014; Ladin et al., 2016).

In conclusion, cannabinoids show promising anti-neoplastic functions in GBM by targeting multiple cancer hallmarks such as resistance to programmed cell death, neoangiogenesis, tissue invasion or stem cell-induced replicative immortality. The effects of cannabinoids can be potentially enhanced by combination of different cannabinoids with each other or with chemotherapeutic agents. This requires, however, a detailed understanding of cannabinoid-induced molecular mechanisms and pharmacological effects. Ultimately, these findings might foster the development of improved therapeutic strategies against GBM and, perhaps, other diseases of the nervous system as well.

https://www.ncbi.nlm.nih.gov/pubmed/11479216The development of new therapeutic strategies is essential for the management of gliomas, one of the most malignant forms of cancer. We have shown previously that the growth of the rat glioma C6 cell line is inhibited by psychoactive cannabinoids (I. Galve-Roperh et al., Nat. Med., 6: 313-319, 2000). These compounds act on the brain and some other organs through the widely expressed CB(1) receptor. By contrast, the other cannabinoid receptor subtype, the CB(2) receptor, shows a much more restricted distribution and is absent from normal brain. Here we show that local administration of the selective CB(2) agonist JWH-133 at 50 microg/day to Rag-2(-/-) mice induced a considerable regression of malignant tumors generated by inoculation of C6 glioma cells. The selective involvement of the CB(2) receptor in this action was evidenced by: (a) the prevention by the CB(2) antagonist SR144528 but not the CB(1) antagonist SR141716; (b) the down-regulation of the CB(2) receptor but not the CB(1) receptor in the tumors; and (c) the absence of typical CB(1)-mediated psychotropic side effects. Cannabinoid receptor expression was subsequently examined in biopsies from human astrocytomas. A full 70% (26 of 37) of the human astrocytomas analyzed expressed significant levels of cannabinoid receptors. Of interest, the extent of CB(2) receptor expression was directly related with tumor malignancy. In addition, the growth of grade IV human astrocytoma cells in Rag-2(-/-) mice was completely blocked by JWH-133 administration at 50 microg/day. Experiments carried out with C6 glioma cells in culture evidenced the internalization of the CB(2) but not the CB(1) receptor upon JWH-133 challenge and showed that selective activation of the CB(2) receptor signaled apoptosis via enhanced ceramide synthesis de novo. These results support a therapeutic approach for the treatment of malignant gliomas devoid of psychotropic side effects.

https://www.ncbi.nlm.nih.gov/pubmed/17952650Cannabinoids, the active components of Cannabis sativa L., act in the body by mimicking endogenous substances--the endocannabinoids--that activate specific cell surface receptors. Cannabinoids exert various palliative effects in cancer patients. In addition, cannabinoids inhibit the growth of different types of tumor cells, including glioma cells, in laboratory animals. They do so by modulating key cell signaling pathways, mostly the endoplasmic reticulum stress response, thereby inducing antitumoral actions such as the apoptotic death of tumor cells and the inhibition of tumor angiogenesis. Of interest, cannabinoids seem to be selective antitumoral compounds, as they kill glioma cells, but not their non-transformed astroglial counterparts. On the basis of these preclinical findings, a pilot clinical study of Delta(9)-tetrahydrocannabinol (THC) in patients with recurrent glioblastoma multiforme has been recently run. The good safety profile of THC, together with its possible growth-inhibiting action on tumor cells, justifies the setting up of future trials aimed at evaluating the potential antitumoral activity of cannabinoids.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1576089In conclusion, the present study demonstrates, for the first time, that CBD can inhibit the migration of tumoral cells. Although the mechanism of this action is not clear at the moment, we can exclude any engagement of classical cannabinoid receptors and/or Gi/o-coupled receptors. Our data further support the use of cannabinoids as antimetastatic drugs as previously demonstrated for met-fluoro-anandamide on rat thyroid cancer cell (Portella et al., 2003). This antimigratory property, together with the known antiproliferative and apoptotic features of CBD (Massi et al., 2004), strengthen the evidence for its use as a potential antitumoral agent.

https://www.ncbi.nlm.nih.gov/pubmed/24204703:  In the present study, we found that CBD inhibited U87-MG and T98G cell proliferation and invasiveness in vitro and caused a decrease in the expression of a set of proteins specifically involved in growth, invasion and angiogenesis. In addition, CBD treatment caused a dose-related down-regulation of ERK and Akt prosurvival signaling pathways in U87-MG and T98G cells and decreased hypoxia inducible factor HIF-1α expression in U87-MG cells. Taken together, these results provide new insights into the antitumor action of CBD, showing that this cannabinoid affects multiple tumoral features and molecular pathways. As CBD is a non-psychoactive phytocannabinoid that appears to be devoid of side effects, our results support its exploitation as an effective anti-cancer drug in the management of gliomas.

https://www.ncbi.nlm.nih.gov/pubmed/16804518 Delta(9)-Tetrahydrocannabinol (THC) and other cannabinoids inhibit tumour growth and angiogenesis in animal models, so their potential application as antitumoral drugs has been suggested. However, the antitumoral effect of cannabinoids has never been tested in humans. Here we report the first clinical study aimed at assessing cannabinoid antitumoral action, specifically a pilot phase I trial in which nine patients with recurrent glioblastoma multiforme were administered THC intratumoraly. The patients had previously failed standard therapy (surgery and radiotherapy) and had clear evidence of tumour progression. The primary end point of the study was to determine the safety of intracranial THC administration. We also evaluated THC action on the length of survival and various tumour-cell parameters. A dose escalation regimen for THC administration was assessed. Cannabinoid delivery was safe and could be achieved without overt psychoactive effects. Median survival of the cohort from the beginning of cannabinoid administration was 24 weeks (95% confidence interval: 15-33). Delta(9)-Tetrahydrocannabinol inhibited tumour-cell proliferation in vitro and decreased tumour-cell Ki67 immunostaining when administered to two patients. The fair safety profile of THC, together with its possible antiproliferative action on tumour cells reported here and in other studies, may set the basis for future trials aimed at evaluating the potential antitumoral activity of cannabinoids.

https://www.ncbi.nlm.nih.gov/pubmed/17239827The efficacy of cannabinoids against high-grade glioma in animal models, mediated by two specific receptors, CB1 and CB2, raised promises for targeted treatment of the most frequent and malignant primary brain tumors. Unlike the abundantly expressed CB1, the CB2 receptor shows a restricted distribution in normal brain. Although brain tumors constitute the second most common malignancy in children and the prevalence of histological types of brain tumors vary significantly between the adult and pediatric populations, cannabinoid receptor expression in pediatric tumors remains unknown. In the present study, we compared the expression of the CB2 receptor in paraffin-embedded sections from primary brain tumors of adult and pediatric patients. Most glioblastomas expressed very high levels of CB2 receptors and the expression correlated with tumor grade. Interestingly, some benign pediatric astrocytic tumors, such as subependymal giant cell astrocytoma (SEGA), which may occasionally cause mortality owing to progressive growth, also displayed high CB2 immunoreactivity. The high levels of CB2 expression would predestine those tumors to be vulnerable to cannabinoid treatment. In contrast, all examined cases of embryonal tumors (medulloblastoma and S-PNET), the most frequently diagnosed malignant brain tumors in childhood, showed no or trace CB2 immunoreactivity. Our results suggest that the CB2 receptor expression depends primarily on the histopathological origin of the brain tumor cells and differentiation state, reflecting the tumor grade.

https://www.ncbi.nlm.nih.gov/pubmed/20307616Gliomas are the most important group of malignant primary brain tumors and one of the most aggressive forms of cancer. During the last years, several studies have demonstrated that cannabinoids induce apoptosis of glioma cells and inhibit angiogenesis of gliomas in vivo. As the effects of cannabinoids rely on CB(1) and CB(2) receptors activation, the aim of the present study was to investigate both receptors protein expression in cellular membrane homogenates of human glial tumors using specific antibodies raised against these proteins. Additionally, we studied the functionality of the cannabinoid receptors in glioblastomas by using WIN 55,212-2 stimulated [(35)S]GTPgammaS binding. Western blot analysis showed that CB(1) receptor immunoreactivity was significantly lower in glioblastoma multiforme (-43%, n=10; p<0.05) than in normal post-mortem brain tissue (n=16). No significant differences were found for astrocytoma (n=6) and meningioma (n=8) samples. Conversely, CB(2) receptor immunoreactivity was significantly greater in membranes of glioblastoma multiforme (765%, n=9; p<0.05) and astrocytoma (471%, n=4; p<0.05) than in control brain tissue (n=10). Finally, the maximal stimulation of [(35)S]GTPgammaS binding by WIN 55,212-2 was significantly lower in glioblastomas (134+/-4%) than in control membranes (183+/-2%; p<0.05). The basal [(35)S]GTPgammaS binding and the EC(50) values were not significantly different between both groups. The present results demonstrate opposite changes in CB(1) and CB(2) receptor protein expression in human gliomas. These changes may be of interest for further research about the therapeutic effects of cannabinoids in glial tumors.

https://www.ncbi.nlm.nih.gov/pubmed/17105950 Two well-characterized cannabinoid receptors (CBrs), CB1 and CB2, mediate the effects of cannabinoids and marijuana use, with functional evidence for other CBrs. CB1 receptors are expressed primarily in brain and peripheral tissues. For over a decade several laboratories were unable to detect CB2 receptors in brain and were known to be intensely expressed in peripheral and immune tissues and have traditionally been referred to as peripheral CB2 CBrs. We have reported the discovery and functional presence of CB2 cannabinoid receptors in mammalian brain that may be involved in depression and drug abuse and this was supported by reports of identification of neuronal CB2 receptors that are involved in emesis. We used RT-PCR, immunoblotting, hippocampal cultures, immunohistochemistry, transmission electron microscopy, and stereotaxic techniques with behavioral assays to determine the functional expression of CB2 CBrs in rat brain and mice brain exposed to chronic mild stress (CMS) or those treated with abused drugs. RT-PCR analyses supported the expression of brain CB2 receptor transcripts at levels much lower than those of CB1 receptors. In situ hybridization revealed CB2 mRNA in cerebellar neurons of wild-type but not of CB2 knockout mice. Abundant CB2 receptor immunoreactivity (iCB2) in neuronal and glial processes was detected in brain and CB2 expression was detected in neuron-specific enolase (NSE) positive hippocampal cell cultures. The effect of direct CB2 antisense oligonucleotide injection into the brain and treatment with JWH015 in motor function and plus-maze tests also demonstrated the functional presence of CB2 cannabinoid receptors in the central nervous system (CNS). Thus, contrary to the prevailing view that CB2 CBrs are restricted to peripheral tissues and predominantly in immune cells, we demonstrated that CB2 CBrs and their gene transcripts are widely distributed in the brain. This multifocal expression of CB2 immunoreactivity in brain suggests that CB2 receptors may play broader roles in the brain than previously anticipated and may be exploited as new targets in the treatment of depression and substance abuse.