1-[(3-Fluoro-4-pyridinyl)amino]-3-methyl-1(H)-indol-5-yl methyl carbamate (P10358) is a potent, reversible acetylcholinesterase inhibitor that produces central cholinergic stimulation after oral and parental administration in rats and mice. P10358 is a 2.5 times more potent acetylcholinesterase inhibitor than THA in vitro (IC50 = 0.10 +/- 0.02 microM vs. IC50 = 0.25 +/- 0.03 microM). It also inhibits butyrylcholinesterase activity as potently as THA (IC50 = 0.08 +/- 0.05 microM vs. IC50 = 0.07 +/- 0.01 microM). Ex vivo, P10358 (0.2 - 20 mg/kg, p.o.) produced dose-dependent inhibition of brain acetylcholinesterase activity. At 10 and 20 mg/ kg, it produced profound and long-lasting hypothermia in mice. P10358 enhanced performance in rats in a step-down passive avoidance task (0.62 and 1.25 mg/kg) and in a social recognition paradigm (0.32, 0.64 and 1.25 mg/kg) in mice. It reversed scopolamine-induced deficits in the Morris Water maze in rats (1.25 and 2.5 mg/kg) and a higher dose elevated striatal homovanillic acid levels. These behavioral and biochemical effects are consistent with central cholinergic stimulation. Hemodynamic studies in the rat demonstrated a 16-fold separation between behaviorally active doses (1.25 mg/kg) and those that elevated arterial pressure (20 mg/kg). Lethality in rats occurred at an oral dose of 80 mg/kg, but not at lower doses. Chemically, P10358 is an N-aminoindole and may not have the hepatotoxic liability associated with aminoacridine structure of tacrine. P10358 had weak affinity (>10 microM) at a variety of aminergic and peptidergic receptors and uptake carriers. These properties suggest that P10358 may be a safe and promising symptomatic treatment for Alzheimer's disease.
Acetylcholinesterase (AChE) inhibitors from several chemical classes have been tested for the symptomatic treatment of Alzheimer's disease; however, the therapeutic success of these compounds has been limited. Recently, another AChE inhibitor, galanthamine hydrobromide (GAL), has shown increased clinical efficacy and safety. Using biochemical, behavioral and pharmacokinetic analyses, this report compares GAL with two of its analogs, 6-O-acetyl-6-O-demethylgalanthamine hydrochloride (P11012) and 6-O-demethyl-6-O[(adamantan-1-yl)-carbonyl]galanthamine hydrochloride (P11149), for their therapeutic potential. P11012 and P11149 were found to be potent, competitive and selective inhibitors of AChE, demonstrating central cholinergic activity, behavioral efficacy and safety. P11012 and P11149, though pharmacokinetic analyses, were shown to act as pro-drugs, yielding significant levels of 6-O-demethylgalanthamine. In vitro, 6-O-demethylgalanthamine was 10- to 20-fold more potent than GAL as an inhibitor of AChE, and it demonstrated greater selectivity for inhibition of AChE vs. butyrylcholinesterase. Like GAL, both P11012 and P11149 showed central cholinergic activity biochemically, by significantly inhibiting rat brain AChE; physiologically, by causing hypothermia; and behaviorally, by attenuating scopolamine-induced deficits in passive avoidance. In addition, GAL, P11012 and P11149 enhanced step-down passive avoidance, another measure of behavioral efficacy. By comparing efficacious doses with primary overt effects, P11012 and P11149 had better oral therapeutic indices than GAL. Oral pharmacokinetic analyses of GAL, P11012 and P11149 revealed differences. Although P11012 and P11149 exhibited similar area under the curve values, 191149 had slower, lower and more sustained concentration maximum levels. P11012 and GAL rapidly reached their concentration maximums, but GAL, in brain had the highest area under the curve and concentration maximum. Because of its composite profile, including duration of action, oral therapeutic index and pharmacokinetics, P11149 is considered the better therapeutic candidate for the treatment of Alzheimer's disease.
4-Amino-3-pyridyl carbamates (2a-c) were synthesized as potential acetylcholinesterase inhibitors and acetylcholine releasers on the basis of the reported activity of the analogous N-(4-amino-3-pyridyl)-N',N'-dimethylurea (1). Although 4-amino-3-pyridyl N,N-dimethylcarbamate (2b) showed good cholinesterase inhibition [concentration that elicited a 50% reduction in the maximal enzyme response (IC50) was 13.4 microM], it had no effect on the stimulated release of [3H]acetylcholine from rat striatal slices. 4-[[(Dimethylamino)methylene]amino]-3-pyridyl N,N-dimethylcarbamate (7a), an intermediate in the synthesis of 2b, demonstrated surprisingly good cholinesterase inhibition (IC50 was 9.4 microM) but showed no activity as a release. A precursor to 7a, N-(3-hydroxy-4-pyridyl)-N',N'-dimethylformamidine (6a), showed some activity in release but was not an esterase inhibitor, whereas the precursor to 6a, 4-amino-3-pyridinol (5a), was a potent releaser. A new synthesis of 5a, based on an ortho-directed lithiation strategy, is also reported.
