2-Thioether-5'-O-(1-thiotriphosphate)-adenosine derivatives: New insulin secretagogues acting through P2Y-receptors

P2-receptors (P2-Rs) repersent significant targets for novel drug development. P2-Rs were identified also on pancreatic B cells and are involved in insulin secretion. The aim of our study was to synthesize and evaluate pharmacologically the novel P2Y-R ligands, 2-thioether-5'-O-phosphorothioate adenosine derivatives, as potential insulin secretagogues. An efficient synthesis of these nucleosides and a facile method for separation of the chiral products is described. The enzymatic stability of the compounds towards pig-pancreas NTPDase was evaluated. The rate of hydrolysis of 2-hexylthio-5'-O-(1-thiotriphosphate)-adenosine (2-hexylthio-ATP-α-S) isomers by NTPDase was 28% that of ATP. The apparent affinity of the compounds to P2Y₁-R was determined by measurement of P2Y-receptor-promoted phospholipase C activity in turkey erythrocyte membranes. 2-RS-ATP-α-S derivatives were agonists, stimulating the production of inositol phosphates with K_0.5 values in the nM range. 2-RS-AMP-S derivatives were full agonists although 2 orders of magnitude less potent. All the compounds were more potent than ATP. The effect on insulin secretion and pancreatic flow rate was evaluated on isolated and perfused rat pancreas. A high increase, up to 500%, inglucose-induced insulin secretion was due to addition of 2-hexylthio-ATP-α-S in the nM concentration range, which represents 100-fold enhancement of activity relative to ATP. 2-Hexylthio-AMP-S was 2.5 orders of magnitude less effective. A high chemical hydrolytic stability was observed for 2-hexylthio-ATP-α-S. Hydrolysis of the phosphoester bond, which was the only detectable degrading reaction under the investigation conditions (pH 7.4, 37°C), was slow, with a half-life of 264 hours. Moreover, even at gastric juice conditions (pH 1.4, 37°C), hydrolysis of the terminal phosphate was the only detectable reaction, with a half-life of 1.75 hours. 2-Hexylthio-ATP-α-S isomers are enzymatically and chemically stable. These isomers are highly potent and effective insulin secretagogues, increasing, however, pancreatic vascula resistance.