Pathways mediating the effects of cannabidiol on the reduction of breast cancer cell proliferation, invasion, and metastasis

Id-1 is a key transcriptional regulator of glioblastoma aggressiveness and a novel therapeutic target

Glioblastoma is the most common form of primary adult brain tumors. A majority of glioblastomas grow invasively into distant brain tissue, leading to tumor recurrence, which is ultimately incurable. It is, therefore, essential to discover master regulators that control glioblastoma invasiveness and target them therapeutically. We show here that the transcriptional regulator Id-1 plays a critical role in modulating the invasiveness of glioblastoma cell lines and primary glioblastoma cells. Id-1 expression levels positively correlate with glioma cell invasiveness in culture and with histopathologic grades in patient biopsies. Id-1 knockdown dramatically reduces glioblastoma cell invasion that is accompanied by profound morphologic changes and robust reduction in expression levels of "mesenchymal" markers, as well as inhibition of self-renewal potential and downregulation of glioma stem cell markers. Importantly, genetic knockdown of Id-1 leads to a significant increase in survival in an orthotopic model of human glioblastoma. Furthermore, we show that a nontoxic compound, cannabidiol, significantly downregulates Id-1 gene expression and associated glioma cell invasiveness and self-renewal. In addition, cannabidiol significantly inhibits the invasion of glioblastoma cells through an organotypic brain slice and glioma progression in vivo. Our results suggest that Id-1 regulates multiple tumor-promoting pathways in glioblastoma and that drugs targeting Id-1 represent a novel and promising strategy for improving the therapy and outcome of patients with glioblastoma.

Towards the use of cannabinoids as antitumour agents

Various reports have shown that cannabinoids (the active components of marijuana and their derivatives) can reduce tumour growth and progression in animal models of cancer, in addition to their well-known palliative effects on some cancer-associated symptoms. This Opinion article discusses our current understanding of cannabinoids as antitumour agents, focusing on recent insights into the molecular mechanisms of action, including emerging resistance mechanisms and opportunities for combination therapy approaches. Such knowledge is required for the optimization of preclinical cannabinoid-based therapies and for the preliminary clinical testing that is currently underway.

Cannabinoids, endocannabinoids, and cancer

The endocannabinoid system consists of an array of endogenously produced bioactive lipids that activate cannabinoid receptors. Although the primary focus of endocannabinoid biology has been on neurological and psychiatric effects, recent work has revealed several important interactions between the endocannabinoid system and cancer. Several different types of cancer have abnormal regulation of the endocannabinoid system that contributes to cancer progression and correlates to clinical outcomes. Modulation of the endocannabinoid system by pharmacological agents in various cancer types reveals that it can mediate antiproliferative and apoptotic effects by both cannabinoid receptor-dependent and -independent pathways. Selective agonists and antagonists of the cannabinoid receptors, inhibitors of endocannabinoid hydrolysis, and cannabinoid analogs have been utilized to probe the pathways involved in the effects of the endocannabinoid system on cancer cell apoptosis, proliferation, migration, adhesion, and invasion. The antiproliferative and apoptotic effects produced by some of these pharmacological probes reveal that the endocannabinoid system is a promising new target for the development of novel chemotherapeutics to treat cancer.

The endocannabinoid system and cancer: therapeutic implication

The endocannabinoid system is implicated in a variety of physiological and pathological conditions (inflammation, immunomodulation, analgesia, cancer and others). The main active ingredient of cannabis, Δ(9) -tetrahydrocannabinol (Δ(9) -THC), produces its effects through activation of CB(1) and CB(2) receptors. CB(1) receptors are expressed at high levels in the central nervous system (CNS), whereas CB(2) receptors are concentrated predominantly, although not exclusively, in cells of the immune system. Endocannabinoids are endogenous lipid-signalling molecules that are generated in the cell membrane from phospholipid precursors. The two best characterized endocannabinoids identified to date are anandamide (AEA) and 2-arachidonoylglycerol (2-AG). Here we review the relationship between the endocannabinoid system and anti-tumour actions (inhibition of cell proliferation and migration, induction of apoptosis, reduction of tumour growth) of the cannabinoids in different types of cancer. This review will focus on examining how activation of the endocannabinoid system impacts breast, prostate and bone cancers in both in vitro and in vivo systems. The therapeutic potential of cannabinoids for cancer, as identified in clinical trials, is also discussed. Identification of safe and effective treatments to manage and improve cancer therapy is critical to improve quality of life and reduce unnecessary suffering in cancer patients. In this regard, cannabis-like compounds offer therapeutic potential for the treatment of breast, prostate and bone cancer in patients. Further basic research on anti-cancer properties of cannabinoids as well as clinical trials of cannabinoid therapeutic efficacy in breast, prostate and bone cancer is therefore warranted.