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Title: CB1 and CB2 receptors are novel molecular targets for Tamoxifen and 4OH-Tamoxifen

Highlights: •Tamoxifen produces cytotoxicity via estrogen-receptor (ER) independent mechanisms. •Tamoxifen binds to CB1 and CB2 cannabinoid receptors and acts as an inverse agonist. •CB1 and CB2 receptors are novel molecular targets for Tamoxifen. •ER-independent effects for Tamoxifen may be mediated via CB1 and/or CB2 receptors. -- Abstract: Tamoxifen (Tam) is classified as a selective estrogen receptor modulator (SERM) and is used for treatment of patients with ER-positive breast cancer. However, it has been shown that Tam and its cytochrome P450-generated metabolite 4-hydroxy-Tam (4OH-Tam) also exhibit cytotoxic effects in ER-negative breast cancer cells. These observations suggest that Tam and 4OH-Tam can produce cytotoxicity via estrogen receptor (ER)-independent mechanism(s) of action. The molecular targets responsible for the ER-independent effects of Tam and its derivatives are poorly understood. Interestingly, similar to Tam and 4OH-Tam, cannabinoids have also been shown to exhibit anti-proliferative and apoptotic effects in ER-negative breast cancer cells, and estrogen can regulate expression levels of cannabinoid receptors (CBRs). Therefore, this study investigated whether CBRs might serve as novel molecular targets for Tam and 4OH-Tam. We report that both compounds bind to CB1 and CB2Rs with moderate affinity (0.9–3 μM). Furthermore, Tam and 4OH-Tam exhibit inverse activity at CB1 and CB2Rs inmore » membrane preparations, reducing basal G-protein activity. Tam and 4OH-Tam also act as CB1/CB2R-inverse agonists to regulate the downstream intracellular effector adenylyl cyclase in intact cells, producing concentration-dependent increases in intracellular cAMP. These results suggest that CBRs are molecular targets for Tam and 4OH-Tam and may contribute to the ER-independent cytotoxic effects reported for these drugs. Importantly, these findings also indicate that Tam and 4OH-Tam might be used as structural scaffolds for development of novel, efficacious, non-toxic cancer drugs acting via CB1 and/or CB2Rs.« less
Authors:
 [1] ; ; ; ;  [2] ; ;  [1] ;  [2]
  1. Department of Pharmacology and Toxicology, College of Medicine, University of Arkansas for Medical Sciences, 4301 W. Markham, Little Rock, AR 72205 (United States)
  2. Department of Biochemistry and Molecular Biology, College of Medicine, University of Arkansas for Medical Sciences, 4301 W. Markham, Little Rock, AR 72205 (United States)
Publication Date:
OSTI Identifier:
22242189
Resource Type:
Journal Article
Resource Relation:
Journal Name: Biochemical and Biophysical Research Communications; Journal Volume: 441; Journal Issue: 2; Other Information: Copyright (c) 2013 Elsevier Science B.V., Amsterdam, The Netherlands, All rights reserved.; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
60 APPLIED LIFE SCIENCES; AMP; DRUGS; ESTROGENS; GTP-ASES; GUANOSINE; HAMSTERS; MAMMARY GLANDS; NEOPLASMS; OVARIES; PHENOL; RECEPTORS; TAMOXIFEN; TOXICITY