Wf-516

In vivo electrophysiological assessment of the putative antidepressant Wf-516 in the rat raphe dorsalis, locus coeruleus and hippocampus

Wf-516 is a potential novel antidepressant. It has high affinity for serotonin (5-hydroxytryptamine; 5-HT) transporters, 5-HT(1A) and 5-HT(2A) receptors. In the present study, the pharmacologic properties of Wf-516 were thus assessed using in vivo electrophysiology in the rat dorsal raphe nucleus (DRN), locus coeruleus (LC) and hippocampus. Glass microelectrodes were lowered into the DRN, LC or hippocampus, and neurons were recorded and tested using systemic or microiontophoretic injections of drugs. In the DRN, cumulative doses of 0.5 mg/kg of Wf-516 were injected intravenously and total inhibition of 5-HT neurons firing was obtained with 2.8 +/- 0.3 mg/kg. The administration of 1 mg/kg of Wf-516, which by itself did not induce a change in the firing of 5-HT neurons, markedly attenuated the inhibitory effect of the 5-HT(1A) autoreceptor agonist LSD, indicating that Wf-516 is a 5-HT(1A) autoreceptor antagonist. In the LC, 1 mg/kg of Wf-516 dampened the inhibitory effect of the preferential 5-HT(2A) agonist DOI on norepinephrine (NE) neurons, indicating that Wf-516 is also a 5-HT(2A) receptor antagonist. In the hippocampus, cumulative intravenous doses of Wf-516 significantly increased the recovery time of firing activity of CA(3) pyramidal neurons after 5-HT applications, indicating an inhibitory effect on 5-HT reuptake. Unlike the 5-HT(1A) antagonist WAY100635, Wf-516 did not block the inhibitory effect of microiontophoretic application of 5-HT, indicating that this drug is devoid of 5-HT(1A) receptor antagonistic activity in this postsynaptic structure. These properties of WF-516 define the transporter/receptorial profile of an antidepressant with superior effectiveness.

Presynaptic selectivity of a ligand for serotonin 1A receptors revealed by in vivo PET assays of rat brain

A novel investigational antidepressant with high affinity for the serotonin transporter and the serotonin 1A (5-HT(1A)) receptor, called Wf-516 (structural formula: (2S)-1-[4-(3,4-dichlorophenyl)piperidin-1-yl]-3-[2-(5-methyl-1,3,4-oxadiazol-2-yl)benzo[b]furan-4-yloxy]propan-2-ol monohydrochloride), has been found to exert a rapid therapeutic effect, although the mechanistic basis for this potential advantage remains undetermined. We comparatively investigated the pharmacokinetics and pharmacodynamics of Wf-516 and pindolol by positron emission tomographic (PET) and autoradiographic assays of rat brains in order to elucidate their molecular interactions with presynaptic and postsynaptic 5-HT(1A) receptors. In contrast to the full receptor occupancy by pindolol in PET measurements, the binding of Wf-516 to 5-HT(1A) receptors displayed limited capacity, with relatively high receptor occupancy being achieved in regions predominantly containing presynaptic receptors. This selectivity was further proven by PET scans of neurotoxicant-treated rats deficient in presynaptic 5-HT(1A) receptors. In addition, [(35)S]guanosine 5'-O-[γ-thio]triphosphate autoradiography indicated a partial agonistic ability of Wf-516 for 5-HT(1A) receptors. This finding has lent support to reports that diverse partial agonists for 5-HT(1A) receptors exert high sensitivity for presynaptic components. Thus, the present PET data suggest a relatively high capacity of presynaptic binding sites for partial agonists. Since our in vitro and ex vivo autoradiographies failed to illustrate these distinct features of Wf-516, in vivo PET imaging is considered to be, thus far, the sole method capable of pharmacokinetically demonstrating the unique actions of Wf-516 and similar new-generation antidepressants.

Utility of small-animal positron emission tomographic imaging of rats for preclinical development of drugs acting on the serotonin transporter

Visualization of neurotransmission components in living small animals using positron emission tomography (PET) has the potential of contributing to the preclinical development of neuroactive drugs, although it is yet to be examined whether quantitative animal PET data on candidate compounds can be extrapolated to humans. Here, we investigated the comparability of the occupancies of serotonin transporter (5-HTT) by therapeutic agents in rat PET studies with our predetermined data from ex- vivo animal experiments and clinical PET scans. Rats were treated with varying doses of fluvoxamine and a newly developed compound, (2S)-1-[4-(3,4-dichlorophenyl) piperidin-1-yl]-3-[2-(5-methyl-1,3,4-oxadiazol-2-yl)benzo[b]furan-4-yloxy]propan-2-ol monohydrochloride (Wf-516), and underwent PET scans with [11C]3-amino-4-(2-dimethylaminomethyl-phenylsulfanyl)-benzonitrile ([11C]DASB), a selective radioligand for in-vivo quantification of 5-HTT. PET images indicated a reduction of [11C]DASB binding to 5-HTT as a function of the doses and/or plasma concentrations of fluvoxamine and Wf-516. The doses of these drugs at half-maximal effect (15.2 mg/kg and 3.1 mg/kg, respectively), determined that using binding potentials for [11C]DASB, were comparable to those estimated by our previous ex-vivo measurements in rats (4.5 mg/kg and 1.1 mg/kg, respectively), as there was only a 3-fold difference between these results. Moreover, the plasma concentration of fluvoxamine needed for 50% occupancy of central 5-HTT (6.1 ng/ml) was almost equivalent to the value determined in human PET studies (4.6 ng/ml). These findings support the view that the conjunctive use of small-animal PET and [11C]DASB facilitates a quantitative comparison of in-development drugs targeting 5-HTT with established inhibitors and a predictive estimation of their plasma concentrations exerting therapeutic effects in humans.