Preladenant

Preladenant is a high selective antagonist of adenosine A2A receptor with Ki value of 1.1 nM [1].
Parkinson's Disease is characterized by the loss of dopaminergic neuronal projection. The patients with PD lost the capability to control their muscles. As an antagonist of adenosine A2A receptor, preladenant is a non-dopaminergic drug developed for the treatment of PD. This compound showed potency in Phase II clinical trials but failed in Phase III trials and so was discontinued. Preladenant is a methoxyethoxy derivative of the previously discovered A2A receptor antagonist SCH 58261 and has much higher selectivity for A2A receptors over A1 receptors [1 and 2].
Preladenant was obtained through modifying the phenethyl side chain of SCH 58261. It exerted higher binding affinity for both rat and human A2A receptors with Ki values of 2.5 and 1.1 nM, respectively. Preladenant also showed more than 1000-fold higher selectivity for A2A receptors over other adenosine receptors. The Ki values of preladenant for A1, A3 and A2B receptors are all above 1000 nM. Besides that, preladenant showed no significant affinity for a panel of 59 other enzymes, receptors and ion channels. In the cell assays, preladenant also inhibited the activity of both human and rat adenylate cyclase stimulated by CGS 21680 (an agonist of A2A receptor) with Kb values of 1.3 and 0.7 nM, respectively [1].
Preladenant also showed efficacies in animal models. In cynomolgus monkeys treated with MPTP, administration of preladenant at dose of both 1 and 3 mg/kg resulted in parkinsonian scores reduction. In a Dunnets post hoc test, the combination treatment of preladenant and L-Dopa significantly increased the locomotor activity by 80%. Besides that, preladenant was found to have anti- catalepsy effects and dose of 0.3 mg/kg and significantly reduce the hypolocomotion caused by CGS-21680 at dose of 0.1 mg/kg in rats models [2 and 3].
References:
[1] Neustadt B R, Hao J, Lindo N, et al. Potent, selective, and orally active adenosine A 2A receptor antagonists: arylpiperazine derivatives of pyrazolo [4, 3-e]-1, 2, 4-triazolo [1, 5-c] pyrimidines. Bioorganic & medicinal chemistry letters, 2007, 17(5): 1376-1380.
[2] Hodgson R A, Bedard P J, Varty G B, et al. Preladenant, a selective A 2A receptor antagonist, is active in primate models of movement disorders. Experimental neurology, 2010, 225(2): 384-390.
[3] Hodgson R A, Bertorelli R, Varty G B, et al. Characterization of the potent and highly selective A2A receptor antagonists preladenant and SCH 412348 [7-[2-[4-2, 4-difluorophenyl]-1-piperazinyl] ethyl]-2-(2-furanyl)-7H-pyrazolo [4, 3-e][1, 2, 4] triazolo [1, 5-c] pyrimidin-5-amine] in rodent models of movement disorders and depression. Journal of Pharmacology and Experimental Therapeutics, 2009, 330(1): 294-303.