Nepicastat (SYN-117) HCl

Nepicastat (SYN-117) HCl is a potent and selective inhibitor of dopamine-β-hydroxylase with IC50 values of 8.5 and 9.0 nM in bovine and human, respectively [1].

Dopamine-β-hydroxylase is an enzyme involved in the synthesis of small-molecule membrane-bound neurotransmitters. Dopamine-β-hydroxylase catalyses the synthesis of noradrenaline [1].

Nepicastat (SYN-117) HCl is a potent and selective dopamine-β-hydroxylase inhibitor. (R)-Nepicastat exhibited 2-3 fold less potent than nepicastat [1].

In beagle dogs and spontaneously hypertensive rats, nepicastat reduced noradrenaline in a dose-dependent way and increased dopamine and dopamine/noradrenaline ratio in cerebral cortex, left ventricle and the artery. In beagle dogs, nepicastat (2 mg/kg) significantly reduced noradrenaline by 52% and increased dopamine by 646% and dopamine/noradrenaline ratio in plasma [1]. In pithed spontaneously hypertensive rats, nepicastat inhibited the pressor and positive chronotropic due to preganglionic sympathetic nerve stimulation. In spontaneously hypertensive rats, nepicastat (3 mg/kg) exhibited antihypertensive effects and reduced renal vascular resistance by 38% [2]. In rats, nepicastat significantly increased extracellular dopamine accumulation induced by cocaine and amphetamine in the medial prefrontal cortex [3].

References:
[1].  Stanley WC, Li B, Bonhaus DW, et al. Catecholamine modulatory effects of nepicastat (RS-25560-197), a novel, potent and selective inhibitor of dopamine-beta-hydroxylase. Br J Pharmacol, 1997, 121(8): 1803-1809.
[2].  Stanley WC, Lee K, Johnson LG, et al. Cardiovascular effects of nepicastat (RS-25560-197), a novel dopamine beta-hydroxylase inhibitor. J Cardiovasc Pharmacol, 1998, 31(6): 963-970.
[3].  Devoto P, Flore G, Saba P, et al. The dopamine beta-hydroxylase inhibitor nepicastat increases dopamine release and potentiates psychostimulant-induced dopamine release in the prefrontal cortex. Addict Biol, 2014, 19(4): 612-622.

Dopamine beta-hydroxylase inhibitors enhance the discriminative stimulus effects of cocaine in rats.[Pubmed:24068832]

J Pharmacol Exp Ther. 2013 Dec;347(3):564-73.

Inhibitors of dopamine beta-hydroxylase (DBH), the enzyme that converts dopamine (DA) to norepinephrine (NE) in noradrenergic cells, have shown promise for the treatment of cocaine abuse disorders. However, the mechanisms underlying the beneficial effects of these compounds have not been fully elucidated. We used the drug discrimination paradigm to determine the impact of DBH inhibitors on the interoceptive stimulus properties of cocaine. Sprague-Dawley rats were trained to discriminate cocaine (5.6 mg/kg) from saline using a multicomponent, food-reinforced discrimination procedure. On test days, subjects were pretreated with the nonselective DBH inhibitor disulfiram (0-100.0 mg/kg i.p.) or the selective DBH inhibitor nepicastat (0-56.0 mg/kg i.p.) 2 hours prior to a test session either alone or in combination with cumulatively administered cocaine (0-5.6 mg/kg i.p.). Neither disulfiram nor nepicastat substituted for the cocaine stimulus when tested up to doses that nonspecifically reduced responding. However, in combination studies, pretreatment with either disulfiram or nepicastat produced leftward shifts in the cocaine dose-response function and also conferred cocaine-like stimulus effects to the selective NE transporter inhibitor, reboxetine (0.3-5.6 mg/kg i.p.). These results indicate that pharmacological inhibition of DBH does not produce cocaine-like interoceptive stimulus effects alone, but functionally enhances the interoceptive stimulus effects of cocaine, possibly due to facilitated increases in DA released from noradrenergic terminals. These findings suggest that DBH inhibitors have low abuse liability and provide support to clinical reports that some subjective effects produced by cocaine, particularly aversive effects, are enhanced after DBH inhibition.

Effects of dopamine beta-hydroxylase inhibition with nepicastat on the progression of left ventricular dysfunction and remodeling in dogs with chronic heart failure.[Pubmed:11034950]

Circulation. 2000 Oct 17;102(16):1990-5.

BACKGROUND: Inhibition of dopamine beta-hydroxylase (DBH) results in a decrease in norepinephrine synthesis. The present study was a randomized, blinded, placebo-controlled investigation of the long-term effects of therapy with the DBH inhibitor nepicastat (NCT) on the progression of left ventricular (LV) dysfunction and remodeling in dogs with chronic heart failure (HF). METHODS AND RESULTS: Moderate HF (LV ejection fraction [LVEF] 30% to 40%) was produced in 30 dogs by intracoronary microembolization. Dogs were randomized to low-dose NCT (0.5 mg/kg twice daily, n=7) (L-NCT), high-dose NCT (2 mg/kg twice daily, n=7) (H-NCT), L-NCT plus enalapril (10 mg twice daily, n=8) (L-NCT+ENA), or placebo (PL, n=8). Transmyocardial (coronary sinus-arterial) plasma norepinephrine (tNEPI), LVEF, end-systolic volume, and end-diastolic volume were measured before and 3 months after initiating therapy. tNEPI levels were higher in PL compared with NL (86+/-20 versus 13+/-14 pg/mL, P:<0.01). L-NCT alone and L-NCT+ENA reduced tNEPI toward normal (28+/-4 and 39+/-17 pg/mL respectively), whereas HD-NCT reduced tNEPI to below normal levels (3+/-10 pg/mL). In PL dogs, LVEF decreased but was unchanged with L-NCT and increased with L-NCT+ENA. L-NCT and L-NCT+ENA prevented progressive LV remodeling, as evidenced by lack of ongoing increase in end-diastolic volume and end-systolic volume, whereas H-NCT did not CONCLUSIONS: In dogs with HF, therapy with L-NCT prevented progressive LV dysfunction and remodeling. The addition of ENA to L-NCT afforded a greater increase in LV systolic function. NCT at doses that normalize tNEPI may be useful in the treatment of chronic HF.

Catecholamine modulatory effects of nepicastat (RS-25560-197), a novel, potent and selective inhibitor of dopamine-beta-hydroxylase.[Pubmed:9283721]

Br J Pharmacol. 1997 Aug;121(8):1803-9.

1. Inhibitory modulation of sympathetic nerve function may have a favourable impact on the progression of congestive heart failure. Nepicastat is a novel inhibitor of dopamine-beta-hydroxylase, the enzyme which catalyses the conversion of dopamine to noradrenaline in sympathetic nerves. The in vitro pharmacology and in vivo catecholamine modulatory effects of nepicastat were investigated in the present study. 2. Nepicastat produced concentration-dependent inhibition of bovine (IC50 = 8.5 +/- 0.8 nM) and human (IC50 = 9.0 +/- 0.8 nM) dopamine-beta-hydroxylase. The corresponding R-enantiomer (RS-25560-198) was approximately 2-3 fold less potent than nepicastat. Nepicastat had negligible affinity (> 10 microM) for twelve other enzymes and thirteen neurotransmitter receptors. 3. Administration of nepicastat to spontaneously hypertensive rats (SHRs) (three consecutive doses of either 3, 10, 30 or 100 mg kg-1, p.o.; 12 h apart) or beagle dogs (0.05, 0.5, 1.5 or 5 mg kg-1, p.o.; b.i.d., for 5 days) produced dose-dependent decreases in noradrenaline content, increases in dopamine content and increases in dopamine/noradrenaline ratio in the artery (mesenteric or renal), left ventricle and cerebral cortex. At the highest dose studied, the decreases in tissue noadrenaline were 47%, 35% and 42% (in SHRs) and 88%, 91% and 96% (in dogs) in the artery, left ventricle and cerebral cortex, respectively. When tested at 30 mg kg-1, p.o., in SHRs, nepicastat produced significantly greater changes in noradrenaline and dopamine content, as compared to the R-enantiomer (RS-25560-198), in the mesenteric artery and left ventricle. 4. Administration of nepicastat (2 mg kg-1, b.i.d, p.o.) to beagle dogs for 15 days produced significant decreases in plasma concentrations of noradrenaline and increases in plasma concentrations of dopamine and dopamine/noradrenaline ratio. The peak reduction (52%) in plasma concentration of noradrenaline and the peak increase (646%) in plasma concentration of dopamine were observed on day-6 and day-7 of dosing, respectively. 5. The findings of this study suggest that nepicastat is a potent, selective and orally active inhibitor of dopamine-beta-hydroxylase which produces gradual modulation of the sympathetic nervous system by inhibiting the biosynthesis of noradrenaline. This drug may, therefore, be of value in the treatment of cardiovascular disorders associated with over-activation of the sympathetic nervous system, such as congestive heart failure.

Nepicastat hydrochloride (SYN-117 hydrochloride) is a selective, potent, and orally active inhibitor of dopamine-beta-hydroxylase. Nepicastat hydrochloride produces concentration-dependent inhibition of bovine (IC50=8.5 nM) and human (IC50=9 nM) dopamine-beta-hydroxylase. Nepicastat hydrochloride can cross the blood-brain barrier (BBB).

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