Cannabinoid Receptor 2 Compounds In The Attenuation Of Breast Cancer Cell

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Cannabinoids have been well established as mediators of tumor cell proliferation in several cancer models. The activity of cannabinoid receptor 1 (CB1) agonists as well as cannabinoid receptor 2 (CB2) agonists have been extensively studied over the last decade, though their mechanisms of action have yet to be defined in the context of attenuating tumor proliferation. CB1 is abundant in the central nervous system with a low level of expression in the periphery, while CB2 exists primarily on cells of the immune system. Due to the lack of neuronal expression of CB2 receptors, compounds acting at CB2 receptors do not produce the psychotropic effects associated with CB1 receptor compounds. Although CB1 and CB2 compounds have yielded similar antiproliferative results in some tumor cells in vitro, CB2 receptors are markedly upregulated in many tumor cell lines for unknown reasons. Therefore, we focused on compounds selective for the CB2 receptor, including the CB2 selective agonists JWH-015 and AM1241. We show here that CB2 agonists and antagonists alike attenuate the proliferation of mouse and human breast cancer cells in a concentration dependent manner. CB2 agonist induced breast cancer anti-proliferation is not blocked by pretreatment with pertussis toxin, the CB1 cannabinoid receptor antagonist SR141716 , or the transient receptor potential cation channel subfamily V member 1 (TRPV1) antagonist capsazepine. The CB1 and CB2 receptors are classified as G-protein coupled receptors (GPCRs) that are generally linked to Gai or Gaq. Agonists and antagonists of G protein coupled receptors are typically defined based on their Ga mediated effect on intracellular cAMP levels. This method of classification is not entirely effective: it ignores the possibility of differential effects on alternative kinases and the bg subunit activity. The anti-proliferative activity of both JWH-015 and SR144528 may be explained by alternative receptor coupling pathways, changes in constitutive activity, or activity at a separate receptor. Here, we show a dose and time dependent decrease in phosphorylated ERK in cells treated with either JWH-015 (CB2 agonist) or SR144528 (CB2 antagonist). Together, these data along with the absence of a pertussis toxin effect suggest that the CB2 compounds are acting in a non-Gai coupled manner, and are attenuating a pro-survival pathway. Further studies are necessary to identify the binding partner responsible for the antiproliferative effects of CB2 compounds. We advance the idea that CB2 receptors on breast cancer cells constitutively activate the MAP/ERK pro-survival pathway and that by preventing constituitive activity of the CB2 receptor, CB2 compounds downregulate phosphorylation of the MAPK/ERK pathway to promote apoptosis of breast cancer cells.

Source: Abstract P1-11-23: Cannabinoid Receptor 2 Compounds in the Attenuation of Breast Cancer Cell Proliferation: Mechanisms of Action -- Hanlon et al. 70 (1024): P1-11-23 -- Cancer Research