Antipsychotic-like effects of a novel phosphodiesterase 10A inhibitor T-251 in rodents.

Phosphodiesterase 10A (PDE10A) is a dual-substrate PDE that hydrolyzes both cAMP and cGMP. PDE10A is selectively expressed in medium spiny neurons in the striatum, suggesting the potential of PDE10A inhibitors in the treatment of schizophrenia. This study presents the pharmacological profile of a novel PDE10A inhibitor, 2-[(E)-2-(7-fluoro-3-methylquinoxalin-2-yl)vinyl]-6-pyrrolidin-1-yl-N-(tetrahydro-2H-pyran-4-yl)pyrimidin-4-amine hydrochloride (T-251) in rodent models of schizophrenia. T-251 showed a potent inhibitory activity against human PDE10A (IC50 = 0.050 nmol/L) and showed high selectivity over other PDE families which have over 10,000-fold IC50 values. Oral administration of T-251 (0.1-1.0 mg/kg) increased cAMP and cGMP in the striatum in a dose-dependent manner. Oral administration of T-251 attenuated MK-801 induced hyperactivity (ED50 = 0.68 mg/kg) and suppressed conditioned avoidance response (ID50 = 0.87 mg/kg) in rats in a dose dependent manner. Furthermore, T-251 significantly attenuated MK-801 induced prepulse inhibition deficits and cognitive deficits in rats. Unlike haloperidol and olanzapine, T-251 (1.0-30 mg/kg) did not cause catalepsy in rats. Moreover, T-251 (0.6 and 6.0 mg/kg) did not increase plasma levels of prolactin at 1 h after administration, whereas haloperidol and olanzapine significantly increased them. The antipsychotic-like effects and cognitive enhancement of T-251 without catalepsy or plasma prolactin elevation observed in rats suggests that T-251 would be a novel antipsychotic with an improved side-effect profile.

Pharmacological characterization of T-2328, 2-fluoro-4'-methoxy-3'-[[[(2S,3S)-2-phenyl-3-piperidinyl]amino]methyl]-[1,1'-biphenyl]-4-carbonitrile dihydrochloride, as a brain-penetrating antagonist of tachykinin NK1 receptor.

The pharmacological properties of T-2328 were evaluated as an antagonist of the tachykinin neurokinin 1 (NK(1)) receptor. T-2328 inhibited the specific binding of [(3)H][Sar(9),Met(O(2))(11)]substance P to tachykinin NK(1) receptors in human lymphoblastic IM9 cells with K(i) of 0.08 nM. In the same assay, K(i) for aprepitant, a brain-penetrating NK(1) antagonist, was 1.3 nM. The antagonism of T-2328 is highly selective for the human NK(1) receptors since the affinities for human NK(2), NK(3) receptors, and 13 other kinds of receptors and ion channels were >1000-fold lower than for NK(1) receptors. Reduction in Bmax with no change in affinity suggests the non-competitive nature of T-2328 interaction with the NK(1) receptor. T-2328 (0.03-0.1 mg/kg, i.v.) and aprepitant (1 - 3 mg/kg, i.v.) significantly prevented the GR73632 (i.c.v.)-induced foot tapping response in gerbils. The potencies of T-2328 in both in vitro and in vivo studies were more than 10 times greater than those of aprepitant. I.v. administration of T-2328 (0.1-0.3 mg/kg) potently blocked both acute and delayed emetic responses induced by cisplatin (5 mg/kg, i.p.) in ferrets. It is concluded that T-2328 is a potent, centrally active NK(1) antagonist. T-2328 may have potential as a novel therapeutic agent for the treatment of chemotherapy-induced emesis.

Long-lasting anti-emetic effect of T-2328, a novel NK(1) antagonist.

The effect of T-2328 {2-fluoro-4'-methoxy-3'-[[[(2S,3S)-2-phenyl-3-piperidinyl]amino]methyl]-[1,1'-biphenyl]-4-carbonitrile dihydrochloride}, a novel tachykinin NK(1)-receptor antagonist, was examined on cisplatin-induced emesis in ferrets. Cisplatin induced acute emesis in 24 h and delayed emesis during 24 and 72 h, respectively. Ondansetron, a 5-HT(3) antagonist, almost completely blocked the acute emesis and transiently reduced the delayed emesis. In contrast, T-2328 elicited long-lasting anti-emetic effects on both acute and delayed phases by a single intravenous administration. Suppression of delayed emesis was not due to elimination of the acute phase because the delayed emesis was also suppressed by administration after the onset of delayed emesis. Persistent blockade of NK(1) receptors in the brain was demonstrated by inhibition of the NK(1) agonist-induced foot tapping response for over 24 h. An appreciable amount of T-2328 was present in the brain 32 and 72 h after the injection. The NK(1) agonist-induced contractions of isolated ileum in guinea pigs was antagonized with IC(50) values of 1.4 nM in an insurmountable manner. It is likely that T-2328 exerts the long-lasting anti-emetic effect by not only long-term presence in the brain but also its insurmountable inhibition of NK(1) receptors.