Abstract
This study characterizes the receptor binding and functional effects of CVT-3619 [2-{6-[((1R,2R)-2-hydroxycyclopentyl)-amino]purin-9-yl}(4S,5S,2R,3R)-5-[(2-fluorophenylthio)methyl]-oxolane-3,4-diol], a novel N6-5′ -substituted adenosine analog and A1 -adenosine receptor (A AdoR) agonist, on rat epididymal and inguinal adipocytes and on the isolated heart and compares these effects with those caused by the full agonist N6 -cyclopentyladenosine (CPA). In addition, the hypothesis that adipocyte A1AdoR are a heterogeneous population with regard to their affinities for ligands was tested. CVT-3619 was 10–100-fold selective for A1AdoR versus other AdoR and bound to adipocyte membranes with high (KH = 14 nM) and low (K = 5.4 μM) affinities. CVT-3619 reduced cyclic AMP content and release of nonesterified fatty acids from epididymal adipocytes with IC50 values of 6 and 44 nM, respectively. CVT-3619 was a partial agonist relative to CPA to reduce lipolysis in epididymal and inguinal adipocytes. CVT-3619 did not change atrial rate in rat heart and caused a small (6-ms) prolongation of the stimu-lus-to-His bundle interval without causing atrioventricular block in guinea pig heart (effects mediated by A1AdoR), whereas CPA caused atrioventricular block and near cessation of atrial electrical activity. CVT-3619 increased coronary conductance (effect mediated by A2AAdoR) only at concentrations ≥10 μM. Rat epididymal adipocyte A1AdoR had similar affinities for the antagonist 8-cyclopentyl-1,3-dipropylxanthine in the presence of three dissimilar A AdoR agonists (2-chloro-N6 -cyclopentyladenosine, N6 -sulfophenyladenosine, and N-5′ -ethylcarboxamidoadenosine) as determined by Schild analysis. It was concluded that rat epididymal adipocyte A1AdoR are a homogeneous receptor population with regard to affinities for ligands and that CVT-3619 is a partial agonist with selectivity for A1AdoR and inhibition of lipolysis.
Footnotes
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This project was supported in part by Grant 56747 from National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health (J.C.S.).
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doi:10.1124/jpet.105.099119.
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ABBREVIATIONS: A1AdoR, A1-adenosine receptor(s); ADA, adenosine deaminase; BSA, bovine serum albumin; CCPA, 2-chloro-N6 -cyclopentyladenosine; HEK, human embryonic kidney; CPA, N6 -cyclopentyladenosine; CPX, 8-cyclopentyl-1,3-dipropylxanthine; CVT-3619, 2-{6-[((1R,2R)-2-hydroxycyclopentyl)amino]purin-9-yl}(4S,5S,2R,3R)-5-[(2-fluorophenylthio)methyl]oxolane-3,4-diol; EHNA, erythro-9-(2-hydroxy-3-nonyl)-adenine; KRH, Krebs-Ringer-HEPES; MRE3008F20, 5N-(4-methoxyphenylcarbamoyl)amino-8-propyl-2-(2-furyl)pyrazolo[4,3-e]-1,2,4-triazolo[1,5-c]pyrimidine; NECA, 5′-N-ethylcarboxamidoadenosine; NEFA, nonesterified fatty acid; S-H, stimulus to His bundle; SPA, N6-sulfophenyladenosine; TE, Tris-EDTA; ZM241385, 4-(2-[7-amino-2-(2-furyl)[1,2,4]triazolo[2,3-a][1,3,5]triazin-5-ylamino]ethyl)phenol; CHO, Chinese hamster ovary; PCR, polymerase chain reaction.
- Received November 25, 2005.
- Accepted January 9, 2006.
- The American Society for Pharmacology and Experimental Therapeutics