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

Paul L. Prather,Shengyu Mu,Lance N. Benson,Amal M. Shoeib,Lee Ann MacMillan-Crow

doi:10.3390/ijms23063049

Paul L. Prather, Shengyu Mu + Show 3 more

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https://doi.org/10.3390/ijms23063049

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Abstract

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 Gi/Go-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.

Highlights

Cancer is the second most common cause of death following heart disease in the US and it is estimated that over 600,000 patients in the U.S will die of cancer in 2021 [1]
Radioligand binding screens were first used to determine whether cannabinoid receptors (CBRs) were expressed in mouse (C6-glioma), rat (PC-12), and human (HeLa, PC-3 and DU-145) cancer cell lines (Figure 1)
TRPV3 and TRPV4 ligands N-oleoyl-valine [42] and HC-067047 [43], respectively, did produce 15 ± 2.7 and 22 ± 3.8% displacement, these results would predict very low μM affinity for the expressed non-canonical receptors, which is inconsistent with the high nM affinity these ligands are known to exhibit for Transient Receptor Potential (TRP) channels [38–43]. These results suggest that non-canonical cannabinoid receptors expressed in DU-145 cells are not TRP channels

Summary

Introduction

Cancer is the second most common cause of death following heart disease in the US and it is estimated that over 600,000 patients in the U.S will die of cancer in 2021 [1]. Most malignancies, including prostate cancer, pheochromocytoma, and glioma, are often treated with a combination of chemotherapeutic agents and radiotherapy [2–4]. Such multiagent chemotherapeutic regimens represent the predominant treatment of many cancers, this approach is often associated with severe side effects, subsequent co-morbidities, and complications [4–6]. Docetaxel is a mainstay chemotherapeutic agent employed to manage prostate cancer; its use results in a host of adverse events, such as muscle weakness, GI distress, neuropathies, fluid retention, and pneumonitis [7,8]. Radiotherapy used to treat prostate cancer, glioma, and pheochromocytoma is associated with severe side effects, including deterioration of neurocognitive functions, endocrine dysfunction, insomnia, and fatigue [3,5,9]. Alternative therapeutic options are needed that efficaciously inhibit tumor growth, while resulting in fewer of the deleterious adverse effects that often accompany current multi-regimen chemotherapy and radiotherapy associated with treatment of most cancers

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