Synthesis and biological evaluation of novel potent dual acting ribose modified N6-substitued adenosine derivatives

Adenosine receptors (ARs) belong to the G protein-coupled receptor (GPCR) family, and can be subdivided into four subtypes A1, A2A, A2B and A3. A1 and A3 receptor subtypes couple to Gi-proteins, mediating the inhibition of adenylyl cyclase and a decrease in cAMP levels, whereas A2A and A2B receptors activate adenylyl cyclase and increase cAMP levels via the stimulatory Gs-proteins [1]. In the last two decades many selective ligands for a certain AR subtype have been developed and some are in clinical use. More recently the concept of multitarget drugs has emerged as strategy to potentiate efficacy (either additively or synergistically) and/or to reduce side effects. The dual-acting ligands of ARs may have considerable promise as novel approaches to treat pathological conditions e.g. ischemic conditions, asthma, inflammatory diseases and glaucoma. Our recent work discovered the first dual A1AR agonists and A3AR antagonists [2] by combining a 5’-C-ethyl-tetrazolyl moiety and an appropriate N6-substitution in adenosine derivatives. In order to better understand the role of the substituent in N6 position, a series of novel 5’-C-2-ethyl-tetrazolyl-N6-substituted adenosine derivatives were synthesized and assayed at all human adenosine receptor subtypes. The results of this study will be discussed. [1] B.B. Fredholm, A.P. IJzerman, K.A. Jacobson, J. Linden and C. Muller Pharmacol. Rev. 63 (2011) 1−34. [2] R. Petrelli, I. Torquati, S. Kachler, L. Luongo, S. Maione, P. Franchetti, M. Grifantini, E. Novellino, A. Lavecchia, K.-N. Klotz and L. Cappellacci J. Med. Chem. 58 (2015) 2560-2566

Novel dual acting 5’-C-ethyl-tetrazolyl-N6-substituted adenosine derivatives: synthesis and biological evaluation

Adenosine receptors (ARs) are members of the G protein-coupled receptors superfamily (GPCRs). They can be subdivided into four subtypes A1, A2A, A2B and A3. Over the past two decades, many synthetic ligands have been developed that selectively bind to a determined receptor subtype along with different functional profiles: partial or full agonists and antagonists. Potent and selective ligands of a certain AR subtype are in advanced clinical trials. Recent findings indicated that some compounds might act through two different subtypes of a receptor family, with both pathways leading to beneficial effects. A dual A2B and A3 AR antagonist was developed by Novartis as an antiasthmatic agent, while GlaxoSmithKline has investigated a dual A2A agonist and A3 antagonist as anti-inflammatory agent. Dual A2A agonists and A3 antagonists that might be advantageous for asthma or other inflammatory diseases, have been also reported [1]. Our recent work discovered the first dual acting A1AR agonists and A3AR antagonists [2] potentially useful in the treatment of some pathological conditions such as glaucoma and epilepsy. We found that the combination of 5’- C-ethyl-tetrazolyl moiety with the appropriate N6-substitution in adenosine derivatives improved affinity for both A1 and A3AR. A methyl- group at the N6 position of the 5′-C-2- ethyl-2H-tetrazolyl-adenosine derivatives was beneficial for high binding affinity at the A3, whereas a cyclopentyl-, endo-(±)-norbornyl- or 2-fluoro-4-chlorobenzyl-group conferred subnanomolar affinity for A1. Unexpectedly, the 5′-C-2-ethyl-2H-tetrazolyl-adenosine and the corresponding 2-chloro-adenosine showed high affinities for A1 and A3 and also for A2A, resulting in potent but non selective ligands. In order to better explore the influence of N6- substitution on AR affinity and selectivity of this class of AR ligands, novel 5’-C-2-ethyl- tetrazolyl-N6-substituted adenosine derivatives were synthesized and assayed at all human adenosine receptor subtypes. The results of these studies will be discussed. [1] Hou X, Majik MS, Kim K, Pyee Y, Lee Y, Alexander V, Chung H-J et al. J. Med. Chem. 2012, 55, 342. [2] Petrelli R, Lavecchia A, Luongo L, Maione S, Klotz KN, Cappellacci L et al J. Med. Chem. 2015, 58, 2560. This work was supported by the Italian MIUR fund (PRIN2009, prot. no. 200928EEX4_004 to P.R.)

NOVEL 5'-C-ETHYL-TETRAZOLYL-N6-SUBSTITUTED-ADENOSINE DERIVATIVES: SYNTHESIS AND BIOLOGICAL EVALUATION

Adenosine is an endogenous purine ribonucleoside implicated in the control of the function of many tissues and organs. It exerts a protective action throughout all organs of the body and plays an important role not only in the pathophysiological processes, but also in the modulation of normal processes. Adenosine exerts its effects by interacting with specific G-protein coupled receptors, classified in 4 subtypes: A1, A2A, A2B and A3 (1). A1 adenosine receptor (A1AR) is widely distributed throughout the brain but also in the heart, aorta, liver kidney, bladder and eye. A1AR agonists have shown neuro- and cardioprotective effects, but their clinical use is hampered by severe cardiovascular side effects. A3AR are expressed in multiple organs and at low levels in the CNS. A3AR agonists are in clinical trials for the treatment of cancer and inflammatory diseases, and recent preclinical studies reported their analgesic effects in chronic neuropathic pain (2). Our previous work showed that potent dual A1AR agonists and A3AR antagonists have been obtained combining a 5'-C-ethyl-tetrazolyl moiety and an appropriate N6-substitution in adenosine derivatives (3). A dual A1 agonist and A3 antagonist might be useful in the treatment of glaucoma and other diseases, and might have advantages respect to the combination of two drugs. In order to study the influence of N6-substitution on affinity and selectivity at ARs, a novel series of 5'-C-2-ethyl-tetrazolyl-N6-substituted adenosine derivatives were synthesized and assayed at all human adenosine receptor subtypes. The results of this study will be discussed. (1) Fredholm, B.B.; Ijzerman, A.P.; Jacobson, K:A., Linden, J.; Muller, C.E. International Union of Basic and Clinical Pharmacology. LXXXI. Nomenclature and calssification of adenosine receptors - an update. Pharmacol. Rev. 2011, 63, 1-34. (2) Little, J.W.; Ford, A.; Symons-Liguori, A.M.; Chen, Z.; Janes, K.; Doyle, T.; Xie, J.; Luongo,, L.; Tosh, D.K.; Maione, S.; Bannister, K.; Dickenson, A.; Vandrah, T.W.; Porreca, F.; Jacobson, K.A.; Salvemini, D. Endogenous adenosine A3 receptor activation selectively alleviates persistent pain states. Brain 2015, 138, 28-35 (3) Petrelli, R.; Torquati, I.; Kachler, S.; Luongo, L.; Maione, S.; Franchetti, P.; Grifantini, M.; Novellino, E.; Lavecchia, A.; Klotz, K.-N-; Cappellacci, L. 5′‑C‑Ethyl-tetrazolyl‑N6‑Substituted Adenosine and 2‑Chloroadenosine Derivatives as Highly Potent Dual Acting A1 Adenosine Receptor Agonists and A3 Adenosine Receptor Antagonists. J. Med. Chem. 2015, 58, 2560-2566

Design, Synthesis, and Anticancer Activity of Novel Pyridyl and Aryl Hydrazones

Cancer is continuing to be a major health issue and despite the recent improvements in the chemotherapeutic management of some type of cancers, the therapeutic effectiveness toward the majority of solid tumors is relatively low. Half of all cancer patients fail to respond to chemotherapy and ultimately die for the disease progression. Recently, combination chemotherapy has improved dramatically the clinical outcomes of cancer patients. Even so, current treatments often do not completely release patients of their cancers and cancer cells can become resistant to various anticancer agents. Thus, the continued commitment to the arduous task of discovering new antineoplastic therapeutic agents remains critically important. The pronounced antineoplastic efficacy of hydrazones has been widely attributed to their inhibition of the mammalian enzyme Ribonucleotide Reductase (RNR), a key enzyme in DNA synthesis and cell growth control [1]. The enzyme is composed of a complex of two subunits, named R1 and R2. The R1 subunit contains the active site, while the R2 subunit contains a diferric-tyrosyl radical cofactor. Potent inhibitors interfering with the R2 subunit include the R-(N)-heterocyclic carboxaldehyde thiosemicarbazones (TSCs, such as Triapine) and the 2-acylpyridine-R-(N)-hetarylhydrazones. Currently, Triapine is in phase II clinical trial for cancer treatment, even though causes neutropenia, hypoxia and methaemoglobinemia. Following these observations, a range of chelators have been developed with improved iron chelation efficacy, lipophilicity and anti-cancer activity. Among these ligands are those of the hydrazone and thiosemicarbazone classes that demonstrate better efficacy than Triapine (e.g. Desforrioxamine, DFO or 2-pyridylketone 4,4-dimethyl-3-thiosemicarbazone, Dp44mT). From SAR studies of these compounds, it has been deducted that an N*-N*-S* or N*-N*-N* structural motif is essential for RNR inhibition [2]. As a logical continuation, we have synthesized a series of pyridyl and aryl hydrazones as potential RNR inhibitors. In addition, compounds containing a carbon-nitrogen C=N double bond (e.g. hydrazones, acyl hydrazones) present the very attractive feature of being double dynamic entities capable of undergoing both configurational and constitutional changes, as well as metal-ion coordination. The configuration of these compounds has been assigned according to the literature and was established to be E by means of 2D-1H-NMR spectroscopy. The antiproliferative activity of the novel pyridyl and aryl hydazones against a panel of human tumor cell lines will be presented. 1. Aye, Y.; Li, M.; Long, M.J.; Weiss, R.S. Ribonucleotide reductase and cancer: biological mechanisms and targeted therapies. Oncogene, 2014, 6, 155-163. 2. Shao J, Liu X, Zhu L, Yen Y Targeting ribonucleotide reductase for cancer therapy. Expert Opin Ther Targets. 2013, 12, 1423-1437