Guanine inhibits the growth of human glioma and melanoma cell lines by interacting with GPR23

Roberta Garozzo; Mariachiara Zuccarini; Patricia Giuliani; Valentina Di Liberto; Giuseppa Mudò; Francesco Caciagli; Renata Ciccarelli; Francisco Ciruela; Patrizia Di Iorio; Daniele F Condorelli

doi:10.3389/fphar.2022.970891

Guanine inhibits the growth of human glioma and melanoma cell lines by interacting with GPR23

Front Pharmacol. 2022 Sep 19:13:970891. doi: 10.3389/fphar.2022.970891. eCollection 2022.

Authors

Affiliations

¹ Department of Biomedical and Biotechnological, Section of Medical Biochemistry, University of Catania, Catania, Italy.
² Department of Medical, Oral and Biotechnological Sciences, Section of Pharmacology and Toxicology, School of Medicine, University of Chieti-Pescara, Chieti, Italy.
³ Center for Advanced Studies and Technologies (CAST), University of Chieti-Pescara, Chieti, Italy.
⁴ Department of Biomedicine, Neuroscience and Advanced Diagnostic, University of Palermo, Palermo, Italy.
⁵ Pharmacology Unit, Department of Pathology and Experimental Therapeutics, Faculty of Medicine and Health Sciences, Institute of Neurosciences, University of Barcelona, Barcelona, Spain.
⁶ Neuropharmacology and Pain Group, Neuroscience Program, Institut d'Investigació Biomèdica de Bellvitge, IDIBELL, Barcelona, Spain.

Abstract

Guanine-based purines (GBPs) exert numerous biological effects at the central nervous system through putative membrane receptors, the existence of which is still elusive. To shed light on this question, we screened orphan and poorly characterized G protein-coupled receptors (GPRs), selecting those that showed a high purinoreceptor similarity and were expressed in glioma cells, where GBPs exerted a powerful antiproliferative effect. Of the GPRs chosen, only the silencing of GPR23, also known as lysophosphatidic acid (LPA) 4 receptor, counteracted GBP-induced growth inhibition in U87 cells. Guanine (GUA) was the most potent compound behind the GPR23-mediated effect, acting as the endpoint effector of GBP antiproliferative effects. Accordingly, cells stably expressing GPR23 showed increased sensitivity to GUA. Furthermore, while GPR23 expression was low in a hypoxanthine-guanine phosphoribosyl-transferase (HGPRT)-mutated melanoma cell line showing poor sensitivity to GBPs, and in HGPRT-silenced glioma cells, GPR23-induced expression in both cell types rescued GUA-mediated cell growth inhibition. Finally, binding experiments using [³H]-GUA and U87 cell membranes revealed the existence of a selective GUA binding (K_D = 29.44 ± 4.07 nM; Bmax 1.007 ± 0.035 pmol/mg prot) likely to GPR23. Overall, these data suggest GPR23 involvement in modulating responses to GUA in tumor cell lines, although further research needs to verify whether this receptor mediates other GUA effects.

Keywords: G protein-coupled receptor 23 (GPR23); antiproliferative effects; glioma cell lines; guanine (GUA); guanine-based purines (GBPs); lysophosphatidic acid (LPA); melanoma cell lines; purine nucleoside phosphorylase (PNP).