Discovery of Indazoles as Potent, Orally Active Dual Neurokinin 1 Receptor Antagonists and Serotonin Transporter Inhibitors for the Treatment of Depression.

Combination studies of neurokinin 1 (NK1) receptor antagonists and serotonin-selective reuptake inhibitors (SSRIs) have shown promise in preclinical models of depression. Such a combination may offer important advantages over the current standard of care. Herein we describe the discovery and optimization of an indazole-based chemotype to provide a series of potent dual NK1 receptor antagonists/serotonin transporter (SERT) inhibitors to overcome issues of ion channel blockade. This effort culminated in the identification of compound 9, an analogue that demonstrated favorable oral bioavailability, excellent brain uptake, and robust in vivo efficacy in a validated depression model. Over the course of this work, a novel heterocycle-directed asymmetric hydrogenation was developed to facilitate installation of the key stereogenic center.

NK1 receptor antagonism lowers occupancy requirement for antidepressant-like effects of SSRIs in the gerbil forced swim test.

The known interactions between the serotonergic and neurokinin systems suggest that serotonin reuptake inhibitor (SSRIs) efficacy may be improved by neurokinin-1 receptor (NK1R) antagonism. In the current studies combination of a subeffective dose of an SSRI (0.3 mg/kg fluoxetine or 0.03 mg/kg citalopram) with a subeffective dose of an NK1R antagonist (0.3 mg/kg aprepitant or 1 mg/kg CP-122,721) produced efficacy in the gerbil forced swim test (FST). Serotonin transporter (SERT) occupancy produced by 1 mg/kg fluoxetine (lowest efficacious dose) was 52 ± 5% and was reduced to 29 ± 4% at 0.3 mg/kg, a dose that was efficacious in combination with 0.3 mg/kg aprepitant or 1 mg/kg CP-122,721; the corresponding NK1R occupancies were 79 ± 4% and 61 ± 4% for aprepitant and CP-122,721, respectively. For citalopram, SERT occupancy at the lowest efficacious dose (0.1 mg/kg) was 50 ± 4% and was reduced to 20 ± 5% at 0.03 mg/kg, a dose that was efficacious when combined with aprepitant (0.3 mg/kg). Aprepitant (10 mg/kg) augmented the serotonin elevation produced by fluoxetine (1 or 10 mg/kg) in the gerbil prefrontal cortex; i.e. NK1R antagonism can modulate serotonin responses. A novel orally-available dual-acting NK1R antagonist/SERT inhibitor BMS-795176 is described; gerbil Ki = 1.4 and 1 nM at NK1R and SERT, respectively. BMS-795176 was efficacious in the gerbil FST; efficacy was observed with 35 ± 3% SERT occupancy and 73 ± 3% NK1R occupancy. The interaction between NK1R antagonism and SERT inhibition to lower the SERT occupancy required for antidepressant-like efficacy suggests that BMS-795176 has the potential to improve efficacy with a reduction in SSRI-associated side effects.

Design, optimization, and in vivo evaluation of a series of pyridine derivatives with dual NK1 antagonism and SERT inhibition for the treatment of depression.

A series of substituted pyridines, ether linked to a phenylpiperidine core were optimized for dual NK(1)/SERT affinity. Optimization based on NK(1)/SERT binding affinities, and minimization of off-target ion channel activity lead to the discovery of compound 44. In vivo evaluation of 44 in the gerbil forced swim test (a depression model), and ex-vivo NK(1)/SERT receptor occupancy data support the potential of a dual acting compound for the treatment of depression.

Behavioral and pharmacological validation of the gerbil forced-swim test: effects of neurokinin-1 receptor antagonists.

Several studies have suggested that neurokinin-1 (NK1) receptor antagonists may have therapeutic potential as novel antidepressant drugs. To test these compounds preclinically, gerbils have become one of the preferred species in that they demonstrate close NK1 receptor homology with humans and bind NK1 antagonists with higher affinity than rats and mice. The intent of the present study was to determine whether the forced-swim test (FST), one of the most commonly used animal tests of antidepressant-like activity, could be adapted for use with the gerbil. Critical factors in the establishment of this assay included swim tank diameter, weight, and sex of the animals tested. Pharmacological validation of the FST using standard antidepressant compounds (eg fluoxetine, paroxetine, desipramine) resulted in decreased immobility time during the test, indicative of an antidepressant-like effect. Similar to results reported for the rat and mouse FST, the antipsychotic drug haloperidol increased immobility, whereas the psychostimulant, amphetamine decreased immobility, and anxiolytic drugs (eg buspirone) had no effect. Investigation into the locomotor effects of all compounds tested was consistent with previous reports in other species, with the exception of paroxetine, which produced hyperactivity at therapeutically effective doses in gerbils. In addition to standard antidepressants, NK1 antagonists (L-733060, MK-869, and CP-122721) all reduced immobility in the gerbil FST without affecting locomotor activity. Overall, these results suggest that the gerbil is an ideal species for use in the FST, and that this paradigm may have predictive validity for identifying novel antidepressant compounds.

Fluorine substitution can block CYP3A4 metabolism-dependent inhibition: identification of (S)-N-[1-(4-fluoro-3- morpholin-4-ylphenyl)ethyl]-3- (4-fluorophenyl)acrylamide as an orally bioavailable KCNQ2 opener devoid of CYP3A4 metabolism-dependent inhibition.

The formation of a reactive intermediate was found to be responsible for CYP3A4 metabolism-dependent inhibition (MDI) observed with (S)-N-[1-(3-morpholin-4-ylphenyl)ethyl]-3-phenyl-acrylamide (1). Structure-3A4 MDI relationship studies culminated in the discovery of a difluoro analogue, (S)-N-[1-(4-fluoro-3-morpholin-4-ylphenyl)ethyl]-3-(4-fluoro-phenyl)acrylamide (2), as an orally bioavailable KCNQ2 opener free of CYP3A4 MDI.

(S)-N-[1-(3-morpholin-4-ylphenyl)ethyl]- 3-phenylacrylamide: an orally bioavailable KCNQ2 opener with significant activity in a cortical spreading depression model of migraine.

(S)-N-[1-(3-Morpholin-4-ylphenyl)ethyl]-3-phenylacrylamide (2) was synthesized as an orally bioavailable KCNQ2 potassium channel opener. In a rat model of migraine, 2 demonstrated significant oral activity in reducing the total number of cortical spreading depressions induced by potassium chloride.