Highly potent dual acting A1 and A3 adenosine receptor ligands: synthesis, binding, functional assays and analgesic effects in mice

Adenosine (Ado) is a purine nucleoside endowed with many different physiological and pathological functions. Many studies support the fact that Ado acts as a neurotrasmitter and neuromodulator, and as an endogenous agonist on adenosine receptors (ARs). ARs belong to the superfamily of G-protein- coupled receptors (GPCRs) and are represented by four subtypes: A1, A2A, A2B, and A3 ARs (1). They are found in almost all kind of tissue: central nervous system (CNS), peripheral neurons, cardiovascular system, respiratory tract and immune system (2). Due to the wide distribution of ARs throughout the body, there is a substantial possibility that Ado ligands will have unwanted effects in non target tissues. One way to overcome adverse effects is the use of multitarget drugs (3). A multitarget drug may display an improved therapeutic efficacy compared to a highly selective one. In fact, multitarget activities may potentiate the effect of treatment either additively or synergistically. Moreover, a multitarget drug has the advantage of following only one pharmacokinetic and metabolic pattern, thus overcoming the limits of combination therapy. Substitutions at both purine and sugar moiety of adenosine results on AR ligands endowed with different affinity and selectivity at the four AR subtypes (4). Potent and highly selective A1AR agonists have been previously obtained by replacement of the 5’-hydroxyl group with a chlorine atom in N6-substituted-adenosine derivatives (5). 5’-Chloro-5’-deoxy-N6-(±)-(endo-norborn-2-yl)- adenosine (5’Cl5’d-(±)-ENBA) showed analgesic effects in mice without affecting cardiovascular and motor functions (6). Combining a 5’-C-ethyltetrazol-2-yl group with the appropriate N6-substitution in adenosine derivatives led to an increased affinity versus both hA1AR and hA3AR, reaching subnanomolar values, while remaining agonists at hA1 and antagonists at hA3AR (7). In this work a new series of 5’-C-ethyltetrazol-2-yl-N6-substituted adenosine derivatives were synthesized and studied both in vitro in binding and functional assays and in vivo in a mouse model of pain. Through an in silico receptor-driven approach, the molecular bases of the hA1- and hA3AR recognition and activation of this series of 5’-C-ethyl-tetrazolyl derivatives were explained. References: 1. Fredholm, B. B.; IJzerman, A. P.; Jacobson, K. A.; Linden, J.; Muller, C. Pharmacol. Rev. 2011, 63, 1-34. 2. Jacobson, K. A.; Muller, C. E. Neuropharmacology 2016, 104, 31-49. 3. Anighoro, A.; Bajorath, J.; Rastelli, G. J. Med. Chem. 2014, 57, 7874-7887. 4. Petrelli, R.; Grifantini, M.; Cappellacci, L. Curr. Med. Chem. 2016, 23, 3118-3135. 5. Franchetti, P.; Cappellacci, L.; Vita, P.; Petrelli, R.; Lavecchia, A.; Kachler, S.; Klotz, K.-N.; Marabese, I.; Luongo, L.; Maione, S.; Grifantini, M. J. Med. Chem. 2009, 52, 2393-2406. 6. Luongo, L.; Petrelli, R.; Gatta, L.; Giordano, C.; Guida, F.; Vita, P.; Franchetti, P.; Grifantini, M.; De Novellis, V.; Cappellacci, L.; Maione, S. Molecules 2012, 17, 13712-13726. 7. Petrelli, R.; Torquati, I.; Kachler, S.; Luongo, L.; Maione, S.; Franchetti, P.; Grifantini, M.; Novellino, E.; Lavecchia, A.; Klotz, K.- N.; Cappellacci, L. J. Med. Chem. 2015, 58, 2560-2566.