Optimization of 2-Amino-4,6-diarylpyrimidine-5-carbonitriles as Potent and Selective A1 Antagonists.

We herein document a large collection of 108 2-amino-4,6-disubstituted-pyrimidine derivatives as potent, structurally simple, and highly selective A1AR ligands. The most attractive ligands were confirmed as antagonists of the canonical cyclic adenosine monophosphate pathway, and some pharmacokinetic parameters were preliminarilly evaluated. The library, built through a reliable and efficient three-component reaction, comprehensively explored the chemical space allowing the identification of the most prominent features of the structure-activity and structure-selectivity relationships around this scaffold. These included the influence on the selectivity profile of the aromatic residues at positions R4 and R6 of the pyrimidine core but most importantly the prominent role to the unprecedented A1AR selectivity profile exerted by the methyl group introduced at the exocyclic amino group. The structure-activity relationship trends on both A1 and A2AARs were conveniently interpreted with rigorous free energy perturbation simulations, which started from the receptor-driven docking model that guided the design of these series.

Agomelatine and tianeptine antidepressant activity in mice behavioral despair tests is enhanced by DMPX, a selective adenosine A2A receptor antagonist, but not DPCPX, a selective adenosine A1 receptor antagonist.

BACKGROUND: Adenosine, an endogenous nucleoside, modulates the release of monoamines, e.g., noradrenaline, serotonin, and dopamine in the brain. Both nonselective and selective stimulation of adenosine receptors produce symptoms of depression in some animal models. Therefore, the main objective of our study was to assess the influence of a selective adenosine A1 receptor antagonist (DPCPX) and a selective adenosine A2A receptor antagonist (DMPX) on the activity of agomelatine and tianeptine. METHODS: The forced swim test (FST) and tail suspension test (TST) were performed to assess the effects of DPCPX and DMPX on the antidepressant-like activity of agomelatine and tianeptine. Drug serum and brain levels were analyzed using HPLC. RESULTS: Co-administration of agomelatine (20 mg/kg) or tianeptine (15 mg/kg) with DMPX (3 mg/kg), but not with DPCPX (1 mg/kg), significantly reduced the immobility time both in the FST and TST in mice. These effects were not associated with an enhancement in animals' spontaneous locomotor activity. The observed changes in the mouse behavior after concomitant injection of DMPX and the tested antidepressant agents were associated with elevated brain concentration of agomelatine and tianeptine. CONCLUSION: Our study shows a synergistic action of the selective A2A receptor antagonist and the studied antidepressant drugs, and a lack of such interaction in the case of the selective A1 receptor antagonist. The interaction between DMPX and agomelatine/tianeptine at least partly occurs in the pharmacokinetic phase. A combination of a selective A2A receptor antagonist and an antidepressant may be a new strategy for treating depression.

Design and synthesis of novel, potent and selective hypoxanthine analogs as adenosine A1 receptor antagonists and their biological evaluation.

Multipronged approach was used to synthesize a library of diverse C-8 cyclopentyl hypoxanthine analogs from a common intermediate III. Several potent and selective compounds were identified and evaluated for pharmacokinetic (PK) properties in Wistar rats. One of the compounds 14 with acceptable PK parameters was selected for testing in in vivo primary acute diuresis model. The compound demonstrated significant diuretic activity in this model.

PQ-69, a novel and selective adenosine A1 receptor antagonist with inverse agonist activity.

Potent and selective adenosine A1 receptor (A1AR) antagonists with favourable pharmacokinetic properties used as novel diuretics and antihypertensives are desirable. Thus, we designed and synthesized a series of novel 4-alkylamino substitution-2-arylpyrazolo[4,3-c]quinolin-3-one derivatives. The aim of the present study is to characterize the biological profiles of the optimized compound, PQ-69. In vitro binding assay revealed a K i value of 0.96 nM for PQ-69 in cloned hA1 receptor, which was 217-fold more selective compared with hA2A receptors and >1,000-fold selectivity for hA1 over hA3 receptor. The results obtained from [(35)S]-GTPγS binding and cAMP concentration assays indicated that PQ-69 might be an A1AR antagonist with inverse agonist activity. In addition, PQ-69 displayed highly inhibitory activities on isolated guinea pig contraction (pA2 value of 8.99) induced by an A1AR agonist, 2-chloro-N6-cyclopentyl adenosine. Systemic administration of PQ-69 (0.03, 0.3, 3 mg/kg) increased urine flow and sodium excretion in normal rats. Furthermore, PQ-69 displayed better metabolic stability in vitro and longer terminal elimination half-life (t 1/2) in vivo compared with 1,3-dipropyl-8-cyclopentylxanthine. These findings suggest that PQ-69 exhibits potent antagonist effects on A1AR in vitro, ex vivo and in vivo, it might be a useful research tool for investigating A1AR function, and it could be developed as a potential therapeutic agent.

JNJ-40255293, a novel adenosine A2A/A1 antagonist with efficacy in preclinical models of Parkinson's disease.

Adenosine A2A antagonists are believed to have therapeutic potential in the treatment of Parkinson's disease (PD). We have characterized the dual adenosine A2A/A1 receptor antagonist JNJ-40255293 (2-amino-8-[2-(4-morpholinyl)ethoxy]-4-phenyl-5H-indeno[1,2-d]pyrimidin-5-one). JNJ-40255293 was a high-affinity (7.5 nM) antagonist at the human A2A receptor with 7-fold in vitro selectivity versus the human A1 receptor. A similar A2A:A1 selectivity was seen in vivo (ED50's of 0.21 and 2.1 mg/kg p.o. for occupancy of rat brain A2A and A1 receptors, respectively). The plasma EC50 for occupancy of rat brain A2A receptors was 13 ng/mL. In sleep-wake encephalographic (EEG) studies, JNJ-40255293 dose-dependently enhanced a consolidated waking associated with a subsequent delayed compensatory sleep (minimum effective dose: 0.63 mg/kg p.o.). As measured by microdialysis, JNJ-40255293 did not affect dopamine and noradrenaline release in the prefrontal cortex and the striatum. However, it was able to reverse effects (catalepsy, hypolocomotion, and conditioned avoidance impairment in rats; hypolocomotion in mice) produced by the dopamine D2 antagonist haloperidol. The compound also potentiated the agitation induced by the dopamine agonist apomorphine. JNJ-40255293 also reversed hypolocomotion produced by the dopamine-depleting agent reserpine and potentiated the effects of l-dihydroxyphenylalanine (L-DOPA) in rats with unilateral 6-hydroxydopamine-induced lesions of the nigro-striatal pathway, an animal model of Parkinson's disease. Extrapolating from the rat receptor occupancy dose-response curve, the occupancy required to produce these various effects in rats was generally in the range of 60-90%. The findings support the continued research and development of A2A antagonists as potential treatments for PD.

Expression, pharmacology and functional activity of adenosine A1 receptors in genetic models of Huntington's disease.

Adenosine A1 receptor (A1R) stimulation exerts beneficial effects in response to various insults to the brain and, although it was found neuroprotective in a lesional model of Huntington's disease (HD), the features of this receptor in genetic models of HD have never been explored. In the present study we characterized the expression, affinity and functional effects of A1Rs in R6/2 mice (the most widely used transgenic model of HD) and in a cellular model of HD. Binding studies revealed that the density of A1Rs was significantly reduced in the cortex and the striatum of R6/2 mice compared to age-matched wild-type (WT), while receptor affinity was unchanged. The selective A1R agonist cyclopentyladenosine (CPA, 300nM) was significantly more effective in reducing synaptic transmission in corticostriatal slices from symptomatic R6/2 than in age-matched WT mice. Such an effect was due to a stronger inhibition of glutamate release from the pre-synaptic terminal. The different functional activities of A1Rs in HD mice were associated also to a different intracellular signaling pathway involved in the synaptic effect of CPA. In fact, while the PKA pathway was involved in both genotypes, p38 MAPK inhibitor SB203580 partially prevented synaptic effects of CPA in R6/2, but not in WT, mice; moreover, CPA differently modulated the phosphorylation status of p38 in the two genotypes. In vitro studies confirmed a different behavior of A1Rs in HD: CPA (100 nM for 5h) modulated cell viability in STHdh(Q111/Q111) (mhttHD cells), without affecting the viability of STHdh(Q7/Q7) (wthtt cells). This effect was prevented by the application of SB203580. Our results demonstrate that in the presence of the HD mutation A1Rs undergo profound changes in terms of expression, pharmacology and functional activity. These changes have to be taken in due account when considering A1Rs as a potential therapeutic target for this disease.

Reduced striatal adenosine A2A receptor levels define a molecular subgroup in schizophrenia.

Schizophrenia (SZ) is a mental disorder of unknown origin. Some scientific evidence seems to indicate that SZ is not a single disease entity, since there are patient groups with clear symptomatic, course and biomarker differences. SZ is characterized by a hyperdopaminergic state related to high dopamine D2 receptor activity. It has also been proposed that there is a hypoadenosynergic state. Adenosine is a nucleoside widely distributed in the organism with neuromodulative and neuroprotective activity in the central nervous system. In the brain, the most abundant adenosine receptors are A1R and A2AR. In the present report, we characterize the presence of both receptors in human postmortem putamens of patients suffering SZ with real time TaqMan PCR, western blotting and radioligand binding assay. We show that A1R levels remain unchanged with respect to age-matched controls, whereas nearly fifty percent of patients have reduced A2AR, at the transcriptional and translational levels. Moreover, we describe how DNA methylation plays a role in the pathological A2AR levels with the bisulfite-sequencing technique. In fact, an increase in 5-methylcytosine percentage in the 5' UTR region of ADORA2A was found in those SZ patients with reduced A2AR levels. Interestingly, there was a relationship between the A2A/ß-actin ratio and motor disturbances as assessed with some items of the PANSS, AIMS and SAS scales. Therefore, there may be a subgroup of SZ patients with reduced striatal A2AR levels accompanied by an altered motor phenotype.

Simultaneous pharmacokinetic model for rolofylline and both M1-trans and M1-cis metabolites.

Rolofylline is a potent, selective adenosine A1 receptor antagonist that was under development for the treatment of patients with acute congestive heart failure and renal impairment. Rolofylline is metabolized primarily to the pharmacologically active M1-trans and M1-cis metabolites (metabolites) by cytochrome P450 (CYP) 3A4. The aim of this investigation was to provide a pharmacokinetic (PK) model for rolofylline and metabolites following intravenous administration to healthy volunteers. Data included for this investigation came from a randomized, double-blind, dose-escalation trial in four groups of healthy volunteers (N=36) where single doses of rolofylline, spanning 1 to 60 mg ,were infused over 1-2 h. The rolofylline and metabolite data were analyzed simultaneously using NONMEM. The simultaneous PK model comprised, in part, a two-compartment linear PK model for rolofylline, with estimates of clearance and volume of distribution at steady-state of 24.4 L/h and 239 L, respectively. In addition, the final PK model contained provisions for both conversion of rolofylline to metabolites and stereochemical conversion of M1-trans to M1-cis. Accordingly, the final model captured known aspects of rolofylline metabolism and was capable of simultaneously describing the PK of rolofylline and metabolites in healthy volunteers.

Genetic inactivation of the adenosine A(2A) receptor exacerbates brain damage in mice with experimental autoimmune encephalomyelitis.

Studies with multiple sclerosis patients and animal models of experimental autoimmune encephalomyelitis (EAE) implicate adenosine and adenosine receptors in modulation of neuroinflammation and brain injury. Although the involvement of the A(1) receptor has been recently demonstrated, the role of the adenosine A(2A) receptor (A(2A)R) in development of EAE pathology is largely unknown. Using mice with genetic inactivation of the A(2A) receptor, we provide direct evidence that loss of the A(2A)R exacerbates EAE pathology in mice. Compared with wild-type mice, A(2A)R knockout mice injected with myelin oligodendroglia glycoprotein peptide had a higher incidence of EAE and exhibited higher neurological deficit scores and greater decrease in body weight. A(2A)R knockout mice displayed increased inflammatory cell infiltration and enhanced microglial cell activation in cortex, brainstem, and spinal cord. In addition, demyelination and axonal damage in brainstem were exacerbated, levels of Th1 cytokines increased, and Th2 cytokines decreased. Collectively, these findings suggest that extracellular adenosine acting at A(2A)Rs triggers an important neuroprotective mechanism. Thus, the A(2A) receptor is a potential target for therapeutic approaches to multiple sclerosis.

Design and characterization of optimized adenosine A2A/A1 receptor antagonists for the treatment of Parkinson's disease.

The design and characterization of two, dual adenosine A(2A)/A(1) receptor antagonists in several animal models of Parkinson's disease is described. Compound 1 was previously reported as a potential treatment for Parkinson's disease. Further characterization of 1 revealed that it was metabolized to reactive intermediates that caused the genotoxicity of 1 in the Ames and mouse lymphoma L51784 assays. The identification of the metabolites enabled the preparation of two optimized compounds 13 and 14 that were devoid of the metabolic liabilities associated with 1. Compounds 13 and 14 are potent dual A(2A)/A(1) receptor antagonists that have excellent activity, after oral administration, across a number of animal models of Parkinson's disease including mouse and rat models of haloperidol-induced catalepsy, mouse and rat models of reserpine-induced akinesia, and the rat 6-hydroxydopamine (6-OHDA) lesion model of drug-induced rotation.

Pharmacokinetics of oral tonapofylline and its acyl-glucuronide metabolite in patients with mild and moderate hepatic impairment.

The objective of the study was to evaluate the effect of hepatic impairment on the pharmacokinetics of tonapofylline. Patients with mild or moderate hepatic impairment were enrolled in parallel with demographically matched healthy subjects. All study participants received a single 75-mg oral tonapofylline capsule. The pharmacokinetic parameters for both tonapofylline and its active metabolite, acyl-glucuronide (tonapofylline-AG), were affected by hepatic impairment significantly (P < .1) except for time to peak plasma concentration (t(max)), terminal half-life (t(½)), and apparent volume of distribution based on the terminal phase (Vdz/F). In the mild group, peak plasma concentration (C(max)), area under the time-concentration curve from time 0 to 48 hours postdose (AUC(48 h)), and from time 0 to infinity (AU(Cinf)) of tonapofylline modestly increased as compared with the control healthy subjects (GMR 1.62, 1.57, and 1.53, respectively). The extent of increase of these parameters for tonapofylline-AG was more profound than tonapofylline with geometric mean ratio (GMR) ranging from 2.02 to 2.08. Moderate hepatic impairment was also associated with modest increases of C(max), AUC(48 h), and AUC(inf) of tonapofylline (GMR 1.41, 1.98, and 2.08, respectively). Similar to the mild group, the increase of these parameters were higher for tonapofylline-AG with GMR ranging from 2.80 to 3.86. Single oral 75-mg tonapofylline was safe and well tolerated in patients with mild or moderate hepatic impairment.

Pharmacokinetics and pharmacodynamics of tonapofylline in subjects with severe renal impairment and in elderly subjects.

OBJECTIVE: The study was conducted to characterize the pharmacokinetics and pharmacodynamics of tonapofylline in subjects with severe renal impairment and in elderly subjects. METHOD: Subjects with severe renal impairment were matched demographically with healthy subjects. Elderly subjects with normal renal function for their ages were also enrolled. All subjects (n = 8 per group) received a single intravenous administration of tonapofylline at 1 mg/kg. RESULTS: The pharmacokinetics of tonapofylline was not significantly different in subjects with severe renal impairment, or in elderly subjects, as compared to healthy subjects. Among all pharmacokinetic parameters, the only statistically significant difference was observed for Cmax between the healthy and the severe renal impairment groups, which was 21% and considered clinically insignificant. Pharmacodynamic assessment demonstrated the natriuretic effects of tonapofylline across groups, with little accompanying kaliuresis. No change in renal function occurred after single dose of tonapofylline, despite substantial increases in excretion of urinary sodium. Single 1 mg/kg intravenous administration of tonapofylline was generally safe. CONCLUSION: The pharmacokinetics of tonapofylline in subjects with severe renal impairment and elderly subjects with normal renal function for age is similar to that in healthy subjects. It has been demonstrated in all groups that tonapofylline has natriuretic effects and is able to maintain renal function, which can be beneficial to patients with congestive heart failure.

Clinical pharmacokinetics of tonapofylline: evaluation of dose proportionality, oral bioavailability, and gender and food effects in healthy human subjects.

Tonapofylline is an antagonist of adenosine A1 receptor being developed for heart failure. In the present studies, pharmacokinetic characteristics, including dose proportionality, bioavailability, and effects of gender and food, were evaluated in healthy subjects receiving single-dose tonapofylline (0.2-375 mg) in a parallel or crossover design. Following oral administration, tonapofylline concentrations mostly peaked within 3 hours and declined over time in a multiple phasic manner. Based on a power model, dose proportionality of peak concentration (C(max)), area under the time-concentration curve for all values (AUC(all)), and area under the time-concentration curve to infinity (AUC(inf)) was concluded in a clinical setting. The bioavailability of tonapofylline was 81.2% (90% confidence interval, 70.6%-93.5%). Following intravenous administration, the steady-state volume of distribution of tonapofylline was estimated to be 756 mL/kg. The total clearance of tonapofylline was low (64.8 mL/h/kg), approximately 5% of hepatic blood flow. The terminal half-life was variable within groups and ranged from 11.2 to 24.2 hours across the dose range. Female subjects showed significantly higher C(max), AUC(all), and AUC(inf) than male subjects (P < .05). Food decreased C(max) by approximately 39%, whereas it did not appear to affect AUC(all) and AUC(inf). The intersubject variability of the pharmacokinetic parameters of tonapofylline was generally less than 30%. In these studies, a single dose of tonapofylline was safe and well tolerated.

Effects of BG9928, an adenosine A1 receptor antagonist, in patients with congestive heart failure.

Previous studies suggest that adenosine A1 receptor antagonists may promote natriuresis without deleterious effects on renal function. This study evaluated renal and hemodynamic effects as well as safety, pharmacokinetics, and tolerability of BG9928, a selective adenosine A1-receptor antagonist, in patients with heart failure. In this multicenter, randomized, double-blind, placebo-controlled, dose-escalation study, 33 patients received a single dose of BG9928 (0.03, 0.3, 1.0, or 3.0 mg/kg) or placebo intravenously. Change from baseline in urinary sodium excretion for the 8-hour postdose interval was greater for all dosing groups versus placebo. The 0.03-mg/kg and 0.3-mg/kg groups had significant reductions in body weight versus placebo (-0.8 kg, -1.1 kg, 0.3 kg, respectively; P < 005). No changes in creatinine clearance or hemodynamic parameters were observed among any of the BG9928 groups versus placebo. However, pulmonary capillary wedge pressure tended to decrease and correlated with weight loss. Across the range of doses studied, pharmacokinetic parameters were linear and predictable. One patient who received the highest dose (3.0 mg/kg) developed seizures, and no further patients received that dose. Single intravenous BG9928 doses of up to 1.0 mg/kg were well tolerated and increased sodium excretion without worsening renal function. Further studies are needed to determine the clinical benefit of adenosine A1 receptor antagonism.

In vivo characterization of a dual adenosine A2A/A1 receptor antagonist in animal models of Parkinson's disease.

The in vivo characterization of a dual adenosine A(2A)/A(1) receptor antagonist in several animal models of Parkinson's disease is described. Discovery and scale-up syntheses of compound 1 are described in detail, highlighting optimization steps that increased the overall yield of 1 from 10.0% to 30.5%. Compound 1 is a potent A(2A)/A(1) receptor antagonist in vitro (A(2A) K(i) = 4.1 nM; A(1) K(i) = 17.0 nM) that has excellent activity, after oral administration, across a number of animal models of Parkinson's disease including mouse and rat models of haloperidol-induced catalepsy, mouse model of reserpine-induced akinesia, rat 6-hydroxydopamine (6-OHDA) lesion model of drug-induced rotation, and MPTP-treated non-human primate model.

Identification and optimization of substituted 5-aminopyrazoles as potent and selective adenosine A1 receptor antagonists.

Potent and selective adenosine A(1) receptor antagonists were disclosed. SAR and pharmacological profile of selected compounds were discussed.