Department of Chemistry & Biochemistry Seminar
Friday, April 15th, 2011
Characterization of GPR35 and GPR55 – Putative Cannabinoid
Receptors?
Dr. Mary E. Abood
Associate Professor of Anatomy and Cell Biology
Center for Substance Abuse Research
Temple University School of Medicine
Host: Dr. Patricia Reggio
Two cannabinoid receptor subtypes, CB1 and CB2, have been identified, but the
complex pharmacological properties of exogenous cannabinoids and endocannabinoids
are not fully explained by their signaling. GPR55 binds a subset of CB1/CB2 ligands
and consequently has been proposed as a cannabinoid receptor. This designation,
however, is controversial as a result of recent studies, including ones where
lysophosphatidylinositol (LPI) is identified as a GPR55 agonist. Using a beta-arrestin
green fluorescent protein biosensor as a direct readout of GPR55 activation and
phosphorylation of ERK1/2 kinase as a secondary readout we have characterized
cannabinoid ligands both as agonists and antagonists. In addition, from a β-arrestin,
high-throughput, high-content screen of 300,000 compounds run in collaboration with
the Molecular Libraries Probe Production Centers Network initiative (PubChem AID1965
and AID2079), we have now identified potent GPR55 selective agonists and
antagonists. Our findings suggest that while GPR55 shares some common ligands with
CB1 and CB2, GPR55 selective ligands have been identified and will aid in defining the
biological role of this receptor.
GPR35 is closely related to GPR55, but turns out to be unresponsive to all cannabinoid
ligands that we have tested. In collaboration with Larry Barak and Marc Caron at Duke
University, we screened a human GPR35 receptor U2OS cell line (UGPR35β) with the
Prestwick Chemical library of 1120 small molecules, 90% being marketed drugs and
10% bioactive alkaloids or related substances. This library was chosen as it presents
the greatest possible degree of drug-likeliness. One high potency hit, oxantel pamoate,
was obtained from this library. We next tested pyrantel pamoate and pamoic acid (4[(3-carboxy-2-hydroxynaphthalen-1-yl)methyl]-3-hydroxynaphthalene-2-carboxylic acid),
also called embonic or pamoic acid, and found that the active compound at GPR35 is
pamoic acid, with nanamolar potency. Pamoic acid (as well as zaprinast and kynurenic
acid, known agonists at GPR35), induced β-arrestin recruitment, receptor internalization
and ERK1/2 activation. Pamoic acid inhibited acetic-acid induced writhing in mice, an in
vivo correlate of antinociception, suggesting that GPR35 could be an important drug
target. Pamoic acid is used to obtain long-acting formulations of numerous drugs, Our
results demonstrate an unexpected biological function for pamoic acid and open
potential new uses for a common drug adjuvant.
1:00 p.m. Sullivan Science Building * Wachovia Lecture Hall (Room 201)
Refreshments will be served in the lobby immediately following the seminar.