Selective Estrogen Receptor Modulators: Cannabinoid Receptor Inverse Agonists with Differential CB1 and CB2 Selectivity

Computational and Experimental Drug Repurposing of FDA-Approved Compounds Targeting the Cannabinoid Receptor CB1

The cannabinoid receptor 1 (CB1R) plays a pivotal role in regulating various physiopathological processes, thus positioning itself as a promising and sought-after therapeutic target. However, the search for specific and effective CB1R ligands has been challenging, prompting the exploration of drug repurposing (DR) strategies. In this study, we present an innovative DR approach that combines computational screening and experimental validation to identify potential Food and Drug Administration (FDA)-approved compounds that can interact with the CB1R. Initially, a large-scale virtual screening was conducted using molecular docking simulations, where a library of FDA-approved drugs was screened against the CB1R's three-dimensional structures. This in silico analysis allowed us to prioritize compounds based on their binding affinity through two different filters. Subsequently, the shortlisted compounds were subjected to in vitro assays using cellular and biochemical models to validate their interaction with the CB1R and determine their functional impact. Our results reveal FDA-approved compounds that exhibit promising interactions with the CB1R. These findings open up exciting opportunities for DR in various disorders where CB1R signaling is implicated. In conclusion, our integrated computational and experimental approach demonstrates the feasibility of DR for discovering CB1R modulators from existing FDA-approved compounds. By leveraging the wealth of existing pharmacological data, this strategy accelerates the identification of potential therapeutics while reducing development costs and timelines. The findings from this study hold the potential to advance novel treatments for a range of CB1R -associated diseases, presenting a significant step forward in drug discovery research.

Mechanism of regulating macrophages/osteoclasts in attenuating wear particle-induced aseptic osteolysis

Joint replacement surgery is the most effective treatment for end-stage arthritis. Aseptic loosening caused by periprosthetic osteolysis is a common complication after joint replacement. Inflammation induced by wear particles derived from prosthetic biomaterials is a major cause of osteolysis. We emphasize that bone marrow-derived macrophages and their fusion-derived osteoclasts play a key role in this pathological process. Researchers have developed multiple intervention approaches to regulate macrophage/osteoclast activation. Aiming at wear particle-induced periprosthetic aseptic osteolysis, this review separately discusses the molecular mechanism of regulation of ROS formation and inflammatory response through intervention of macrophage/osteoclast RANKL-MAPKs-NF-κB pathway. These molecular mechanisms regulate osteoclast activation in different ways, but they are not isolated from each other. There is also a lot of crosstalk among the different mechanisms. In addition, other bone and joint diseases related to osteoclast activation are also briefly introduced. Therefore, we discuss these new findings in the context of existing work with a view to developing new strategies for wear particle-associated osteolysis based on the regulation of macrophages/osteoclasts.

Supraphysiologic doses of 17β-estradiol aggravate depression-like behaviors in ovariectomized mice possibly via regulating microglial responses and brain glycerophospholipid metabolism

BACKGROUND

17β-Estradiol (E2) is generally considered neuroprotective in humans. However, the current clinical use of estrogen replacement therapy (ERT) is based on the physiological dose of E2 to treat menopausal syndrome and has limited therapeutic efficacy. The efficacy and potential toxicity of superphysiological doses of ERT for menopausal neurodegeneration are unknown.

METHODS

In this study, we investigated the effect of E2 with a supraphysiologic dose (0.5 mg/kg, sE2) on the treatment of menopausal mouse models established by ovariectomy. We performed the open field, Y-maze spontaneous alternation, forced swim tests, and sucrose preference test to investigate behavioral alterations. Subsequently, the status of microglia and neurons was detected by immunohistochemistry, HE staining, and Nissl staining, respectively. Real-time PCR was used to detect neuroinflammatory cytokines in the hippocampus and cerebral cortex. Using mass spectrometry proteomics platform and LC-MS/ MS-based metabolomics platform, proteins and metabolites in brain tissues were extracted and analyzed. BV2 and HT22 cell lines and primary neurons and microglia were used to explore the underlying molecular mechanisms in vitro.

RESULTS

sE2 aggravated depression-like behavior in ovariectomized mice, caused microglia response, and increased proinflammatory cytokines in the cerebral cortex and hippocampus, as well as neuronal damage and glycerophospholipid metabolism imbalance. Subsequently, we demonstrated that sE2 induced the pro-inflammatory phenotype of microglia through ERα/NF-κB signaling pathway and downregulated the expression of cannabinoid receptor 1 in neuronal cells, which were important in the pathogenesis of depression.

CONCLUSION

These data suggest that sE2 may be nonhelpful or even detrimental to menopause-related depression, at least partly, by regulating microglial responses and glycerophospholipid metabolism.

Cannabinoid Receptor Type II Ligands from Sandalwood Oil and Synthetic α-Santalol Derivatives

Bioassay-guided fractionation of the essential oil of Santalum album led to the identification of α-santalol (1) and β-santalol (2) as new chemotypes of cannabinoid receptor type II (CB2) ligands with Ki values of 10.49 and 8.19 μM, respectively. Nine structurally new α-santalol derivatives (4a-4h and 5) were synthesized to identify more selective and potent CB2 ligands. Compound 4e with a piperazine structural moiety demonstrated a Ki value of 0.99 μM against CB2 receptor and did not show binding activity against cannabinoid receptor type I (CB1) at 10 μM. Compounds 1, 2, and 4e increased intracellular calcium influx in SH-SY5Y human neuroblastoma cells that were attenuated by CB2 antagonism or inverse agonism, supporting the results that these compounds are CB2 agonists. Molecular docking showed that 1 and 4e had similar binding poses, exhibiting a unique interaction with Thr114 within the CB2 receptor, and that the piperazine structural moiety is required for the binding affinity of 4e. A 200 ns molecular dynamics simulation of CB2 complexed with 4e confirmed the stability of the complex. This structural insight lays a foundation to further design and synthesize more potent and selective α-santalol-based CB2 ligands for drug discovery.

Cannabidiol as a Promising Adjuvant Therapy for Estrogen Receptor-Positive Breast Tumors: Unveiling Its Benefits with Aromatase Inhibitors

BACKGROUND

Estrogen receptor-positive (ER⁺) breast cancer is the most diagnosed subtype, with aromatase inhibitors (AIs) being one of the therapeutic drug types used in the clinic. However, endocrine resistance may develop after prolonged treatment, and different approaches, such as combining endocrine and targeted therapies, have been applied. Recently, we demonstrated that cannabidiol (CBD) induces anti-tumor actions in ER⁺ breast cancer cells by targeting aromatase and ERs. Considering this, we studied, in vitro, whether CBD when combined with AIs could improve their effectiveness.

METHODS

MCF-7aro cells were used and the effects on cell viability and on the modulation of specific targets were investigated.

RESULTS

CBD when combined with anastrozole (Ana) and letrozole (Let) caused no beneficial effect in comparison to the isolated AIs. In contrast, when combined with the AI exemestane (Exe), CBD potentiated its pro-cell death effects, abolished its estrogen-like effect, impaired ERα activation, and prevented its oncogenic role on the androgen receptor (AR). Moreover, this combination inhibited ERK_1/2 activation, promoting apoptosis. The study of the hormonal microenvironment suggests that this combination should not be applied in early stages of ER⁺ breast tumors.

CONCLUSIONS

Contrary to Ana and Let, this study highlights the potential benefits of combining CBD with Exe to improve breast cancer treatment and opens up the possibility of new therapeutic approaches comprising the use of cannabinoids.

Tocilizumab-coated solid lipid nanoparticles loaded with cannabidiol as a novel drug delivery strategy for treating COVID-19: A review

Commonly used clinical strategies against coronavirus disease 19 (COVID-19), including the potential role of monoclonal antibodies for site-specific targeted drug delivery, are discussed here. Solid lipid nanoparticles (SLN) tailored with tocilizumab (TCZ) and loading cannabidiol (CBD) are proposed for the treatment of COVID-19 by oral route. TCZ, as a humanized IgG1 monoclonal antibody and an interleukin-6 (IL-6) receptor agonist, can attenuate cytokine storm in patients infected with SARS-CoV-2. CBD (an anti-inflammatory cannabinoid and TCZ agonist) alleviates anxiety, schizophrenia, and depression. CBD, obtained from Cannabis sativa L., is known to modulate gene expression and inflammation and also shows anti-cancer and anti-inflammatory properties. It has also been recognized to modulate angiotensin-converting enzyme II (ACE2) expression in SARS-CoV-2 target tissues. It has already been proven that immunosuppressive drugs targeting the IL-6 receptor may ameliorate lethal inflammatory responses in COVID-19 patients. TCZ, as an immunosuppressive drug, is mainly used to treat rheumatoid arthritis, although several attempts have been made to use it in the active hyperinflammatory phase of COVID-19, with promising outcomes. TCZ is currently administered intravenously. It this review, we discuss the potential advances on the use of SLN for oral administration of TCZ-tailored CBD-loaded SLN, as an innovative platform for managing SARS-CoV-2 and related infections.

Identification of CB1 Ligands among Drugs, Phytochemicals and Natural-Like Compounds: Virtual Screening and In Vitro Verification

Cannabinoid receptor type 1 (CB1) is an important modulator of many key physiological functions and thus a compelling molecular target. However, safe CB1 targeting is a non-trivial task. In recent years, there has been a surge of data indicating that drugs successfully used in the clinic for years (e.g. paracetamol) show CB1 activity. Moreover, there is a lot of promise in finding CB1 ligands in plants other than Cannabis sativa. In this study, we searched for possible CB1 activity among already existing drugs, their metabolites, phytochemicals, and natural-like molecules. We conducted two iterations of virtual screening, verifying the results with in vitro binding and functional assays. The in silico procedure consisted of a wide range of structure- and ligand-based methods, including docking, molecular dynamics, and quantitative structure-activity relationship (QSAR). As a result, we identified travoprost and ginkgetin as CB1 ligands, which provides a starting point for future research on the impact of their metabolites or preparations on the endocannabinoid system. Moreover, we found five natural-like compounds with submicromolar or low micromolar affinity to CB1, including one mixed partial agonist/antagonist viable for hit-to-lead phase. Finally, the computational procedure established in this work will be of use for future screening campaigns for novel CB1 ligands.

Non-Canonical Cannabinoid Receptors with Distinct Binding and Signaling Properties in Prostate and Other Cancer Cell Types Mediate Cell Death

Cannabinoids exert anti-cancer actions; however, the underlying cytotoxic mechanisms and the cannabinoid receptors (CBRs) involved remain unclear. In this study, CBRs were characterized in several cancer cell lines. Radioligand binding screens surprisingly revealed specific binding only for the non-selective cannabinoid [³H]WIN-55,212-2, and not [³H]CP-55,940, indicating that the expressed CBRs exhibit atypical binding properties. Furthermore, [³H]WIN-55,212-2 bound to a single site in all cancer cells with high affinity and varying densities. CBR characteristics were next compared between human prostate cancer cell lines expressing low (PC-3) and high (DU-145) CBR density. Although mRNA for canonical CBRs was detected in both cell lines, only 5 out of 15 compounds with known high affinity for canonical CBRs displaced [³H]WIN-55,212-2 binding. Functional assays further established that CBRs in prostate cancer cells exhibit distinct signaling properties relative to canonical G_i/G_o-coupled CBRs. Prostate cancer cells chronically exposed to both CBR agonists and antagonists/inverse agonists produced receptor downregulation, inconsistent with actions at canonical CBRs. Treatment of DU-145 cells with CBR ligands increased LDH-release, decreased ATP-dependent cell viability, and produced mitochondrial membrane potential depolarization. In summary, several cancer cell lines express CBRs with binding and signaling profiles dissimilar to canonical CBRs. Drugs selectively targeting these atypical CBRs might exhibit improved anti-cancer properties.

Characterization of cannabinoid receptors expressed in Ewing sarcoma TC-71 and A-673 cells as potential targets for anti-cancer drug development

AIMS

Characterizing cannabinoid receptors (CBRs) expressed in Ewing sarcoma (EWS) cell lines as potential targets for anti-cancer drug development.

MAIN METHODS

CBR affinity and function were examined by competitive binding and G-protein activation, respectively. Cannabinoid-mediated cytotoxicity and cell viability were evaluated by LDH, and trypan blue assays, respectively.

KEY FINDINGS

qRT-PCR detected CB1 (CB1R) and CB2 receptor (CB2R) mRNA in TC-71 cells. However, binding screens revealed that CBRs expressed exhibit atypical properties relative to canonical receptors, because specific binding in TC-71 could only be demonstrated by the established non-selective CB1/CB2R radioligand [³H]WIN-55,212-2, but not CB1/CB2R radioligand [³H]CP-55,940. Homologous receptor binding demonstrated that [³H]WIN-55,212-2 binds to a single site with nanomolar affinity, expressed at high density. Further support for non-canonical CBRs expression is provided by subsequent binding screens, revealing that only 9 out of 28 well-characterized cannabinoids with high affinity for canonical CB1 and/or CB2Rs were able to displace [³H]WIN-55,212-2, whereas two ligands enhanced [³H]WIN-55,212-2 binding. Five cannabinoids producing the greatest [³H]WIN-55,212-2 displacement exhibited high nanomolar affinity (K_i) for expressed receptors. G-protein modulation and adenylyl cyclase assays further indicate that these CBRs exhibit distinct signaling/functional profiles compared to canonical CBRs. Importantly, cannabinoids with the highest affinity for non-canonical CBRs reduced TC-71 viability and induced cytotoxicity in a time-dependent manner. Studies in a second EWS cell line (A-673) showed similar atypical binding properties of expressed CBRs, and cannabinoid treatment produced cytotoxicity.

SIGNIFICANCE

Cannabinoids induce cytotoxicity in EWS cell lines via non-canonical CBRs, which might be a potential therapeutic target to treat EWS.

Sex differences in cocaine-associated memory: The interplay between CB1, mGluR5, and estradiol

We know surprisingly little about the sex differences in the neurobiology of cocaine addiction, except females are more susceptible to the rewarding effects of cocaine than their male counterparts. Only a handful of recent studies have examined the neurobiology of cocaine-induced conditioned place preference (CPP) memory among female rodents. We contribute to this emerging line of research by documenting sex differences in cocaine-associated memory and illustrating the underlying signaling pathways in five experiments. Rimonabant (Rim), a cannabinoid CB₁ antagonist and inverse agonist, exerted a facilitating effect for low-dose cocaine and an impairing effect for high-dose cocaine CPP memory in male mice, as in our previous study, but not in female mice. Nor did we observe the effect exist among CB₁ knockout male mice, which indicated that the CB₁ receptors played a mediating role. We also found that the metabotropic glutamate receptor 5 (mGluR5) was located in the same signaling pathway as CB₁ in male mice. To clarify the mechanisms behind the sex differences, we used ovariectomized (OVX) female mice with estradiol benzoate (EB) replacement. In the OVX female mice, we showed that Rim-alone and EB-alone, but not Rim-and-EB-combined, facilitated the low-dose cocaine CPP memory. Moreover, 4-hydroxytamoxifen (4-OHT), an estrogen receptor (ER) antagonist, blocked Rim's and EB's facilitating effect. Finally, 2-methyl-6-(phenylethynyl)pyridine (MPEP), an mGluR5 antagonist, partially blocked EB's facilitating effect. In sum, we identified sex-specific effects of Rim on cocaine-induced CPP memory and the respective signaling pathways: mGluR5-CB₁ for male mice and ER-mGluR5-CB₁ for female mice. These findings may have merits for the development of sex-specific treatment for cocaine addiction.

Chelation-Tamoxifen Conjugates for Imaging of Estrogen Receptors

Background: The differential diagnosis of estrogen receptor-positive (ER+) pathway-activated systems by using a labeled antiestrogen helps to select the patients for optimal response to endocrine therapy and to discontinue the treatment when resistance occurs. The authors' purpose was to synthesize chelator-tamoxifen conjugates for imaging ER (+) diseases. Materials and Methods: A hydroxypropyl linker was incorporated between either cyclam or cyclam diacetic acid and tamoxifen analog to produce SC-05-L-1 (Z-1-(1,4,8,11-tetraazacyclotetradecan-1-yl)-3-((5-(4-(2-(diethylamino)ethoxy) phenyl) -4,5-diphenylpent-4-en-1-yl)oxy)propan-2-ol) and SC-05-N-1 (Z-2,2'-(4-(3-((5-(4-(2-(diethylamino)ethoxy)phenyl)-4,5-diphenylpent-4-en-1-yl)oxy)-2-hydroxy-propyl) -1,4,8,11-tetraazacyclotetradecane-1,8-diyl)diacetic acid), respectively. In vitro cell uptake and cell/media ratios of ^99mTc-SC-05-L-1 and ^99mTc- SC-05-N-1 in ER (+) ovarian cancer cells (TOV-112D and OVCAR3) were performed. To ascertain the specificity of cell uptake, the cell uptake was blocked with estrone. In vivo ^99mTc-SC-05-L-1 or ^99mTc-SC-05-N-1 single-photon emission computed tomography/computed tomography was conducted in tumor-bearing rodents and compared to ¹⁸F-fluoro-2-deoxy-d-glucose (¹⁸F-FDG) positron emission tomography/magnetic resonance imaging (a reference technology). Results: The radiochemical purities of ^99mTc-SC-05-L-1 and ^99mTc-SC-05-N-1 were greater than 99% (n = 10). ^99mTc-SC-05-L-1 had higher cell/media ratios than ^99mTc-SC-05-N-1 in OVCAR-3 ER (+) cells. The cell uptake of ^99mTc-SC-05-L-1 was blocked 80% by estrone indicating an ER-mediated process occurred. ^99mTc-SC-05-N-1 was further selected for in vivo imaging studies due to higher maximum tolerated dose and superior water solubility than ^99mTc-SC-05-L-1. ^99mTc-SC-05-N-1 showed higher tumor uptake and tumor/muscle count density ratios than ¹⁸F-FDG in tumor-bearing rodents. Conclusion: ^99mTc-SC-05-N-1 showed better differential diagnosis of ovarian tumors than ¹⁸F-FDG, indicating great promising in chelator-tamoxifen conjugate for ER pathway-directed systems imaging.

Unveiling the mechanism of action behind the anti-cancer properties of cannabinoids in ER+ breast cancer cells: Impact on aromatase and steroid receptors

Breast cancer is the leading cause of cancer-related death in women worldwide. In the last years, cannabinoids have gained attention in the clinical setting and clinical trials with cannabinoid-based preparations are underway. However, contradictory anti-tumour properties have also been reported. Thus, the elucidation of the molecular mechanisms behind their anti-tumour efficacy is crucial to better understand its therapeutic potential. Considering this, our work aims to clarify the molecular mechanisms underlying the anti-cancer properties of the endocannabinoid anandamide (AEA) and of the phytocannabinoids, cannabidiol (CBD) and Δ⁹-tetrahydrocannabinol (THC), in estrogen receptor-positive (ER⁺) breast cancer cells that overexpress aromatase (MCF-7aro). Their in vitro effects on cell proliferation, cell death and activity/expression of aromatase, ERα, ERβ and AR were investigated. Our results demonstrated that cannabinoids disrupted MCF-7aro cell cycle progression. Unlike AEA and THC that induced apoptosis, CBD triggered autophagy to promote apoptotic cell death. Interestingly, all cannabinoids reduced aromatase and ERα expression levels in cells. On the other hand, AEA and CBD not only exhibited high anti-aromatase activity but also induced up-regulation of ERβ. Therefore, all cannabinoids, albeit by different actions, target aromatase and ERs, impairing, in that way, the growth of ER⁺ breast cancer cells, which is dependent on estrogen signalling. As aromatase and ERs are key targets for ER⁺ breast cancer treatment, cannabinoids can be considered as potential and attractive therapeutic compounds for this type of cancer, being CBD the most promising one. Thus, from an in vitro perspective, this work may contribute to the growing mass of evidence of cannabinoids and cannabinoids-based medicines as potential anti-cancer drugs.

Sex differences and the endocannabinoid system in pain

Cannabis use has been increasing in recent years, particularly among women, and one of the most common uses of cannabis for medical purposes is pain relief. Pain conditions and response to analgesics have been demonstrated to be influenced by sex, and evidence is emerging that this is also true with cannabinoid-mediated analgesia. In this review we evaluate the preclinical evidence supporting sex differences in cannabinoid pharmacology, as well as emerging evidence from human studies, both clinical and observational. Numerous animal studies have reported sex differences in the antinociceptive response to natural and synthetic cannabinoids that may correlate to sex differences in expression, and function, of endocannabinoid system components. Female rodents have generally been found to be more sensitive to the effects of Δ⁹-THC. This finding is likely a function of both pharmacokinetic and pharmacodynamics factors including differences in metabolism, differences in cannabinoid receptor expression, and influence of ovarian hormones including estradiol and progesterone. Preclinical evidence supporting direct interactions between sex hormones and the endocannabinoid system may translate to sex differences in response to cannabis and cannabinoid use in men and women. Further research into the role of sex in endocannabinoid system function is critical as we gain a deeper understanding of the impact of the endocannabinoid system in various disease states, including chronic pain.

Pharmacokinetic comparison of two bazedoxifene acetate 20 mg tablet formulations in healthy Korean male volunteers

Bazedoxifene, used as bazedoxifene acetate, is a selective estrogen receptor modulator that selectively affects the uterus, breast tissue, bone metabolism, and lipid metabolism by antagonizing or enhancing estrogens in the estrogen receptor in the tissue. This study was conducted as an open, randomized, two-period, two-treatment, crossover design to compare the pharmacokinetic (PK) characteristics and tolerability of two bazedoxifene tablets when administered to 50 healthy Korean male volunteers. Enrolled subjects were randomly allocated to 2 sequences of a single oral administration of a test drug and a reference drug, or vice versa with a 14-day washout period between the two doses. Serial blood samples were collected over 96 h for PK analysis. Plasma concentration of bazedoxifene was assayed using liquid chromatography-tandem spectrometry mass. Forty-five participants completed the study with no clinically relevant safety issues. The peak concentrations (C_max, mean ± strandard deviation) of reference drug and test drug were 3.191 ± 1.080 and 3.231 ± 1.346 ng/mL, respectively, and the areas under the plasma concentration‐time curve from 0 to the last measurable concentration (AUC_last) were 44.697 ± 21.168 ng∙h/mL and 45.902 ± 23.130 ng∙h/mL, respectively. The geometric mean ratios of test drug to reference drug and their 90% confidence intervals for C_max and AUC_last were 0.9913 (0.8828–1.1132) and 1.0106 (0.9345–1.0929), respectively. The incidence of adverse events between the two formulations was similar. The present study showed that PK and tolerability of two bazedoxifene tablet formulations were comparable when administered to healthy Korean male volunteers.

Cannabinoid Receptor Type 2: A Possible Target in SARS-CoV-2 (CoV-19) Infection?

In late December 2019, a novel coronavirus (SARS-CoV-2 or CoV-19) appeared in Wuhan, China, causing a global pandemic. SARS-CoV-2 causes mild to severe respiratory tract inflammation, often developing into lung fibrosis with thrombosis in pulmonary small vessels and causing even death. COronaVIrus Disease (COVID-19) patients manifest exacerbated inflammatory and immune responses, cytokine storm, prevalence of pro-inflammatory M1 macrophages and increased levels of resident and circulating immune cells. Men show higher susceptibility to SARS-CoV-2 infection than women, likely due to estrogens production. The protective role of estrogens, as well as an immune-suppressive activity that limits the excessive inflammation, can be mediated by cannabinoid receptor type 2 (CB2). The role of this receptor in modulating inflammation and immune response is well documented in fact in several settings. The stimulation of CB2 receptors is known to limit the release of pro-inflammatory cytokines, shift the macrophage phenotype towards the anti-inflammatory M2 type and enhance the immune-modulating properties of mesenchymal stromal cells. For these reasons, we hypothesize that CB2 receptor can be a therapeutic target in COVID-19 pandemic emergency.

Cannabinoids and Hormone Receptor-Positive Breast Cancer Treatment

Breast cancer (BC) is the most common cancer in women worldwide. Approximately 70–80% of BCs express estrogen receptors (ER), which predict the response to endocrine therapy (ET), and are therefore hormone receptor-positive (HR+). Endogenous cannabinoids together with cannabinoid receptor 1 and 2 (CB1, CB2) constitute the basis of the endocannabinoid system. Interactions of cannabinoids with hypothalamic–pituitary–gonadal axis hormones are well documented, and two studies found a positive correlation between peak plasma endogenous cannabinoid anandamide with peak plasma 17β-estradiol, luteinizing hormone and follicle-stimulating hormone levels at ovulation in healthy premenopausal women. Do cannabinoids have an effect on HR+ BC? In this paper we review known and possible interactions between cannabinoids and specific HR+ BC treatments. In preclinical studies, CB1 and CB2 agonists (i.e., anandamide, THC) have been shown to inhibit the proliferation of ER positive BC cell lines. There is less evidence for antitumor cannabinoid action in HR+ BC in animal models and there are no clinical trials exploring the effects of cannabinoids on HR+ BC treatment outcomes. Two studies have shown that tamoxifen and several other selective estrogen receptor modulators (SERM) can act as inverse agonists on CB1 and CB2, an interaction with possible clinical consequences. In addition, cannabinoid action could interact with other commonly used endocrine and targeted therapies used in the treatment of HR+ BC.

Future Aspects for Cannabinoids in Breast Cancer Therapy

Cannabinoids (CBs) from Cannabis sativa provide relief for tumor-associated symptoms (including nausea, anorexia, and neuropathic pain) in the palliative treatment of cancer patients. Additionally, they may decelerate tumor progression in breast cancer patients. Indeed, the psychoactive delta-9-tetrahydrocannabinol (THC), non-psychoactive cannabidiol (CBD) and other CBs inhibited disease progression in breast cancer models. The effects of CBs on signaling pathways in cancer cells are conferred via G-protein coupled CB-receptors (CB-Rs), CB1-R and CB2-R, but also via other receptors, and in a receptor-independent way. THC is a partial agonist for CB1-R and CB2-R; CBD is an inverse agonist for both. In breast cancer, CB1-R expression is moderate, but CB2-R expression is high, which is related to tumor aggressiveness. CBs block cell cycle progression and cell growth and induce cancer cell apoptosis by inhibiting constitutive active pro-oncogenic signaling pathways, such as the extracellular-signal-regulated kinase pathway. They reduce angiogenesis and tumor metastasis in animal breast cancer models. CBs are not only active against estrogen receptor-positive, but also against estrogen-resistant breast cancer cells. In human epidermal growth factor receptor 2-positive and triple-negative breast cancer cells, blocking protein kinase B- and cyclooxygenase-2 signaling via CB2-R prevents tumor progression and metastasis. Furthermore, selective estrogen receptor modulators (SERMs), including tamoxifen, bind to CB-Rs; this process may contribute to the growth inhibitory effect of SERMs in cancer cells lacking the estrogen receptor. In summary, CBs are already administered to breast cancer patients at advanced stages of the disease, but they might also be effective at earlier stages to decelerate tumor progression.