Fatty acid amide hydrolase drives adult mammary gland development by promoting luminal cell differentiation.

Mammary gland development occurs primarily in adulthood, undergoing extensive expansion during puberty followed by cycles of functional specialization and regression with every round of pregnancy/lactation/involution. This process is ultimately driven by the coordinated proliferation and differentiation of mammary epithelial cells. However, the endogenous molecular factors regulating these developmental dynamics are still poorly defined. Endocannabinoid signaling is known to determine cell fate-related events during the development of different organs in the central nervous system and the periphery. Here, we report that the endocannabinoid-degrading enzyme fatty acid amide hydrolase (FAAH) plays a pivotal role in adult mammary gland development. Specifically, it is required for luminal lineage specification in the mammary gland, and it promotes hormone-driven secretory differentiation of mammary epithelial cells by controlling the endogenous levels of anandamide and the subsequent activation of cannabinoid CB1 receptors. Together, our findings shed light on the role of the endocannabinoid system in breast development and point to FAAH as a therapeutic target in milk-production deficits.

Neuronal Cannabinoid CB1 Receptors Suppress the Growth of Melanoma Brain Metastases by Inhibiting Glutamatergic Signalling.

Melanoma is one of the deadliest forms of cancer. Most melanoma deaths are caused by distant metastases in several organs, especially the brain, the so-called melanoma brain metastases (MBMs). However, the precise mechanisms that sustain the growth of MBMs remain elusive. Recently, the excitatory neurotransmitter glutamate has been proposed as a brain-specific, pro-tumorigenic signal for various types of cancers, but how neuronal glutamate shuttling onto metastases is regulated remains unknown. Here, we show that the cannabinoid CB1 receptor (CB1R), a master regulator of glutamate output from nerve terminals, controls MBM proliferation. First, in silico transcriptomic analysis of cancer-genome atlases indicated an aberrant expression of glutamate receptors in human metastatic melanoma samples. Second, in vitro experiments conducted on three different melanoma cell lines showed that the selective blockade of glutamatergic NMDA receptors, but not AMPA or metabotropic receptors, reduces cell proliferation. Third, in vivo grafting of melanoma cells in the brain of mice selectively devoid of CB1Rs in glutamatergic neurons increased tumour cell proliferation in concert with NMDA receptor activation, whereas melanoma cell growth in other tissue locations was not affected. Taken together, our findings demonstrate an unprecedented regulatory role of neuronal CB1Rs in the MBM tumour microenvironment.

Identification of fatty acid amide hydrolase as a metastasis suppressor in breast cancer.

Clinical management of breast cancer (BC) metastasis remains an unmet need as it accounts for 90% of BC-associated mortality. Although the luminal subtype, which represents >70% of BC cases, is generally associated with a favorable outcome, it is susceptible to metastatic relapse as late as 15 years after treatment discontinuation. Seeking therapeutic approaches as well as screening tools to properly identify those patients with a higher risk of recurrence is therefore essential. Here, we report that the lipid-degrading enzyme fatty acid amide hydrolase (FAAH) is a predictor of long-term survival in patients with luminal BC, and that it blocks tumor progression and lung metastasis in cell and mouse models of BC. Together, our findings highlight the potential of FAAH as a biomarker with prognostic value in luminal BC and as a therapeutic target in metastatic disease.

Therapeutic targeting of HER2-CB2R heteromers in HER2-positive breast cancer.

Although human epidermal growth factor receptor 2 (HER2)-targeted therapies have dramatically improved the clinical outcome of HER2-positive breast cancer patients, innate and acquired resistance remains an important clinical challenge. New therapeutic approaches and diagnostic tools for identification, stratification, and treatment of patients at higher risk of resistance and recurrence are therefore warranted. Here, we unveil a mechanism controlling the oncogenic activity of HER2: heteromerization with the cannabinoid receptor CB2R. We show that HER2 physically interacts with CB2R in breast cancer cells, and that the expression of these heteromers correlates with poor patient prognosis. The cannabinoid Δ9-tetrahydrocannabinol (THC) disrupts HER2-CB2R complexes by selectively binding to CB2R, which leads to (i) the inactivation of HER2 through disruption of HER2-HER2 homodimers, and (ii) the subsequent degradation of HER2 by the proteasome via the E3 ligase c-CBL. This in turn triggers antitumor responses in vitro and in vivo. Selective targeting of CB2R transmembrane region 5 mimicked THC effects. Together, these findings define HER2-CB2R heteromers as new potential targets for antitumor therapies and biomarkers with prognostic value in HER2-positive breast cancer.

Appraising the "entourage effect": Antitumor action of a pure cannabinoid versus a botanical drug preparation in preclinical models of breast cancer.

Breast cancer is the second leading cause of death among women. Although early diagnosis and development of new treatments have improved their prognosis, many patients present innate or acquired resistance to current therapies. New therapeutic approaches are therefore warranted for the management of this disease. Extensive preclinical research has demonstrated that cannabinoids, the active ingredients of Cannabis sativa, trigger antitumor responses in different models of cancer. Most of these studies have been conducted with pure compounds, mainly Δ9-tetrahydrocannabinol (THC). The cannabis plant, however, produces hundreds of other compounds with their own therapeutic potential and the capability to induce synergic responses when combined, the so-called "entourage effect". Here, we compared the antitumor efficacy of pure THC with that of a botanical drug preparation (BDP). The BDP was more potent than pure THC in producing antitumor responses in cell culture and animal models of ER+/PR+, HER2+ and triple-negative breast cancer. This increased potency was not due to the presence of the 5 most abundant terpenes in the preparation. While pure THC acted by activating cannabinoid CB2 receptors and generating reactive oxygen species, the BDP modulated different targets and mechanisms of action. The combination of cannabinoids with estrogen receptor- or HER2-targeted therapies (tamoxifen and lapatinib, respectively) or with cisplatin, produced additive antiproliferative responses in cell cultures. Combinations of these treatments in vivo showed no interactions, either positive or negative. Together, our results suggest that standardized cannabis drug preparations, rather than pure cannabinoids, could be considered as part of the therapeutic armamentarium to manage breast cancer.