Structure activity relationships biochemical metabolic and m

Structure–activity relationships [23], [24], [25], [26], biochemical [24], [25], [26], [27], [28], [29], [30], [31], metabolic [19], [27], [28], [29], [30], [31], and molecular [32] investigations have demonstrated that the substrate specificity, as well as other characteristics of T. gondii adenosine kinase, differs significantly from those of the human enzyme, and have established the enzyme as an excellent potential chemotherapeutic target for the treatment of toxoplasmosis [19], [20]. It was also demonstrated that 6-benzylthioinosine, among other 6-substituted purine nucleoside analogues, is a substrate for the parasite, but not human adenosine kinase [19], [23], [27], [28], [29]. Furthermore, 6-benzylthioinosine was shown to be metabolized preferentially to the nucleotide level and becomes selectively toxic to T. gondii, but not their host, thereby acting as a subversive substrate [19], [23], [27], [28], [29]. Therefore, modification of the chemical structure of 6-benzylthioinosine could further potentiate its anti-toxoplasmic efficacy. We have previously synthesized 6-benzylthioinosine analogues with various substitutions at their purine ring which increased the binding affinities of these analogues to T. gondii adenosine kinase [24], [25] as well as their efficacy as anti-toxoplasmic agents [29], [31]. As a part of our continuing effort to develop potential anti-toxoplasmic agents, we turned our attention to carbocyclic nucleosides, wherein an oxygen panx of the ribose ring is replaced by a methylene group. An advantage of the carbocyclic nucleosides is metabolic stability due to the absence of a typical glycosidic bond [33], [34]. The carbocyclic nucleosides also have considerable effects on ring conformation and lipophilicity which may improve the therapeutic potency of carbocyclic nucleosides [33], [34]. Specifically, we wanted to explore the structural effect of carbasugar moiety on the efficacy of 6-benzylthioinosine analogues. In the present study we report the testing of newly synthesized carbocyclic 6-benzylthioinosine analogues, with various substitutions at their phenyl ring as anti-toxoplasmic agents in cell culture.
Materials and methods
Results and discussion
Acknowledgments This research was supported by the U.S. Public Health Service Grant AI-52838 from the National Institute of Health. We thank Mudar Al Safarjalani, P.E. for the computer programming and estimations of the IC50 values, and Marion Kirk for Mass spectrometry analyses. The mass spectrometer was purchased by Grant S10RR13795 and UAB Health Services Foundation General Endowment Fund.
Introduction The endogenous purine nucleoside, adenosine (ADO) interacts with specific extracellular G-protein coupled cell-surface receptors identified as A1, A2A, A2B, and A3, to serve as an extracellular signalling molecule in a variety of tissues including the kidney (Hasko and Pacher, 2008, Roberts et al., 2014). ADO receptors are widely distributed in renal tissue and play a broad regulatory role including modulation of local blood flow, glomerular filtration, and urine flow (McCoy et al., 1993). Additionally, local and circulating levels of ADO are elevated and its receptors up-regulated in renal tissue following local injury and/or disease-related pathology such as diabetic nephropathy (DN) (Pawelczyk et al., 2005, Quezada et al., 2013). Compelling evidence has accumulated linking ADO modulation to renal protection, with the A2A receptor as the primary effector (Hasko and Pacher, 2008, Ferenbach and Hughes, 2011, Quezada et al., 2013). Renal injury was exacerbated by knocking out A2A receptor in mouse models of unilateral ureter obstruction (UUO), ischemia-reperfusion and DN (Awad et al., 2006, Li et al., 2012, Xiao et al., 2013a, Xiao et al., 2013b). Pharmacologically, administration of nonselective ADO receptor or A2A receptor selective agonists diminished pathological events in a spectrum of rodent renal models of renal disease and dysfunction, including streptozotocin (STZ)-induced DN, puromycin aminonucleoside (PAN)-induced podocyte injury, anti-glomerular basement membrane (GBM) serum induced glomerulonephritis and UUO-induced renal fibrosis (Awad et al., 2006, Awad et al., 2008, Garcia et al., 2008, Ferenbach and Hughes, 2011, Garcia et al., 2011, Xiao et al., 2013a, Xiao et al., 2013b). In addition, an A2A receptor agonist had been advanced into Phase 1 safety tolerability studies in patients with stage 3 or 4 chronic kidney disease (CKD) (Ananthasubramaniam et al., 2012). However, therapeutic application of these drugs may be hindered by the occurrence of serious cardiovascular adverse events (Gordi et al., 2007), especially as cardiovascular complications are common in patients with CKD.