Characterization of RO4583298 as a novel potent, dual antagonist with in vivo activity at tachykinin NK₁ and NK₃ receptors.

<bold>Background and Purpose: </bold>Clinical results of osanetant and talnetant (selective-NK₃ antagonists) indicate that blocking the NK₃ receptor could be beneficial for the treatment of schizophrenia. The objective of this study was to characterize the in vitro and in vivo properties of a novel dual NK₁/NK₃ antagonist, RO4583298 (2-phenyl-N-(pyridin-3-yl)-N-methylisobutyramide derivative).<bold>Experimental Approach: </bold>RO4583298 in vitro pharmacology was investigated using radioligand binding ([³H]-SP, [³H]-osanetant, [³H]-senktide), [³H]-inositol-phosphate accumulation Schild analysis (SP- or [MePhe⁷]-NKB-induced) and electrophysiological studies in guinea-pig substantia nigra pars compacta (SNpc). The in vivo activity of RO4583298 was assessed using reversal of GR73632-induced foot tapping in gerbils (GFT; NK₁) and senktide-induced tail whips in mice (MTW; NK₃).<bold>Key Results: </bold>RO4583298 has a high-affinity for NK₁ (human and gerbil) and NK₃ (human, cynomolgus monkey, gerbil and guinea-pig) receptors and behaves as a pseudo-irreversible antagonist. Unusually it binds with high-affinity to mouse and rat NK₃, yet with a partial non-competitive mode of antagonism. In guinea-pig SNpc, RO4583298 inhibited the senktide-induced potentiation of spontaneous activity of dopaminergic neurones with an apparent non-competitive mechanism of action. RO4583298 (p.o.) robustly blocked the GFT response, and inhibited the MTW.<bold>Conclusions and Implications: </bold>RO4583298 is a high-affinity, non-competitive, long-acting in vivo NK₁/NK₃ antagonist; hence providing a useful in vitro and in vivo pharmacological tool to investigate the roles of NK₁ and NK₃ receptors in psychiatric disorders. [ABSTRACT FROM AUTHOR]