Identification of a New Series of Potent Adenosine A2A Receptor Antagonists Based on 4-Amino-5-carbonitrile Pyrimidine Template for the Treatment of Parkinson's Disease.

Adenosine receptor A2A antagonists have emerged as potential treatment for Parkinson's disease in the past decade. We have recently reported a series of adenosine receptor antagonists using heterocycles as bioisosteres for a potentially unstable acetamide. These compounds, while showing excellent potency and ligand efficiency, suffered from moderate cytochrome P450 inhibition and high clearance. Here we report a new series of adenosine receptor A2A antagonists based on a 4-amino-5-carbonitrile pyrimidine template. Compounds from this new template exhibit excellent potency and ligand efficiency with low cytochrome P450 inhibition. Although the clearance remains moderate to high, the leading compound, when dosed orally as low as 3 mg/kg, demonstrated excellent efficacy in the haloperidol induced catalepsy rat model for Parkinson's disease.

Substructure-based virtual screening for adenosine A2A receptor ligands.

A virtual ligand-based screening approach was designed and evaluated for the discovery of new A(2A) adenosine receptor (AR) ligands. For comparison and evaluation, the procedures from a recently published virtual screening study that used the A(2A) AR X-ray crystal structure for the target-based discovery of new A(2A) ligands were largely followed. Several screening models were constructed by deriving the distinguishing structural features from selected sets of A(2A) AR antagonists, so-called frequent substructure mining. The best model in statistical terms was subsequently applied to large-scale virtual screens of a commercial vendor library. This resulted in the selection of 36 candidates for acquisition and testing. Of the selected candidates, eight compounds significantly inhibited radioligand binding at A(2A) AR (>30%) at 10 µM, corresponding to a "hit rate" of 22%. This hit rate is quite similar to that of the referenced target-based virtual screening study, while both approaches yield new, non-overlapping sets of ligands.

Discovery of novel quinolinone adenosine A2B antagonists.

A novel series of quinolinone-based adenosine A(2B) receptor antagonists was identified via high throughput screening of an encoded combinatorial compound collection. Synthesis and assay of a series of analogs highlighted essential structural features of the initial hit. Optimization resulted in an A(2B) antagonist (2i) which exhibited potent activity in a cAMP accumulation assay (5.1 nM) and an IL-8 release assay (0.4 nM).

Preladenant, a novel adenosine A(2A) receptor antagonist for the potential treatment of parkinsonism and other disorders.

Adenosine A(2A) receptor antagonists exert antiparkinsonian effects in animal models and several drugs in this class are currently being assessed in clinical trials. Preladenant (SCH-420814) is an adenosine A(2A) receptor antagonist with a high affinity and very high selectivity for adenosine A(2A) receptors, which is being developed by Merck & Co Inc (following its acquisition of Schering-Plough Corp) for the potential treatment of Parkinson's disease. Preclinical studies in rodent and primate models of parkinsonism demonstrated that preladenant can reverse the motor impairments induced by dopamine depletion or antagonism. Phase I and II clinical trials indicated that preladenant was well tolerated. Moreover, preladenant met its major endpoints by reducing OFF time and increasing ON time in l-DOPA-treated patients with Parkinson's disease, without worsening dyskinesias. Therefore, preladenant may have considerable utility for the treatment of Parkinson's disease, as well as the parkinsonian side effects of dopamine D2 receptor antagonists. As research has suggested that adenosine A(2A) receptor antagonists are active in animal models of effort-based decision making, it is possible that preladenant could also be useful for treating energy-related symptoms, such as fatigue, psychomotor retardation and anergia in patients with parkinsonism or depression. At the time of publication, phase III clinical trials were recruiting patients with Parkinson's disease.