J. Warren Beach

Desensitization of nicotinic acetylcholine receptors as a strategy for drug development

The specific pharmacological response evoked by a nicotinic acetylcholine receptor (nAChR) agonist is governed by the anatomical distribution and expression of each receptor subtype and by the stoichiometry of subunits comprising each subtype. Contributing to this complexity is the ability of agonists that bind to the orthosteric site of the receptor to alter the affinity state of the receptor and induce desensitization and the observation that, at low doses, some nAChR antagonists evoke agonist-like nicotinic responses. Brain concentrations of nicotine rarely increase to the low-mid micromolar concentrations that have been reported to evoke direct agonist-like responses, such as calcium influx or neurotransmitter release. Low microgram per kilogram doses of nicotine administered to humans or to nonhuman primates to improve cognition and working memory probably result only in low nanomolar brain concentrations—more in line with the ability of nicotine to induce receptor desensitization. Here we review data illustrating that nicotine, its major metabolite cotinine, and two novel analogs of choline, JWB1-84-1 [2-(4-(pyridin-3-ylmethyl)piperazin-1-yl)ethanol] and JAY2-22-33, JWB1-84-1 [2-(methyl(pyridine-3-ylmethyl)amino)-ethanol], improve working memory in macaques. The effectiveness of these four compounds in the task was linearly related to their effectiveness in producing desensitization of the pressor response to ganglionic stimulation evoked by a nAChR agonist in rats. Only nicotine evoked an agonist-like action (increased resting blood pressure). Therefore, it is possible to develop new chemical entities that have the ability to desensitize nAChRs without an antecedent agonist action. Because these “silent desensitizers” are probably acting allosterically, an additional degree of subtype specificity could be attained.

Chemotherapeutic agents for human immunodeficiency virus infection: mechanism of action, pharmacokinetics, metabolism, and adverse reactions

Since the mid-1980s, four new nucleoside reverse transcriptase (RT) inhibitors (zalcitabine, didanosine, stavudine, and lamivudine), two nonnucleoside RT inhibitors (nevirapine and delavirdine), and four new protease inhibitors (saquinavir, ritonavir, indinavir, and nelfinavir) have been approved by the US Food and Drug Administration for the treatment of patients with acquired immunodeficiency syndrome. The driving force behind the development of these new agents has been the increasing need for more potent agents with reduced or modified toxicity profiles. The purpose of this article is to review the absorption, distribution, metabolism, elimination, toxicities, adverse reactions, and mechanism of action of the currently available drugs.

Potent anti-HIV and anti-HBV activities of (-)-L-β-dioxolane-C and (+)-L-β-dioxolane-T and their asymmetric syntheses

Abstract The asymmetric synthesis of (+)- L -β-dioxolane-T and (−)- L -β-dioxolane-C were accomplished starting from 1,6-anhydro- L -β-gulopyranose, and their anti-HIV and anti-HBV activities were evaluated in human PBM cell, CEM cells and 2.2.15 cells, respectively.

Asymmetric synthesis of enantiomerically pure (-)-(1'R,4'R)-dioxolane-thymine and its anti-HIV activity

Abstract An asymmetric synthesis leading to the enantiomerically pure dioxolane-T has been achieved and its crystal structure has been determined and compared to the previously reported racemate. (−)-(1′R,4′R )-Dioxolane-T was found to have potent and selective anti-HIV activity in primary human lymphocytes.

An efficient total synthesis of 3′-azido-3′-deoxythymidine (AZT) and 3′-azido-2′,3′-dideoxyuridine (AZDDU, CS-87) from D-mannitol

Abstract An efficient stereoselective total synthesis of 3′-azido-3′-deoxythymidine (AZT) and 3′-azido-2′,3′-dideoxyuridine (AZDDU, CS-87) from readily available and inexpensive starting material, D -mannitol has been achieved.

Dopamine transporter-mediated cytotoxicity of β-carbolinium derivatives related to Parkinson's disease: relationship to transporter-dependent uptake

Endogenous or exogenous β‐carboline (βC) derivatives structurally related to the selective dopaminergic neurotoxin 1‐methyl‐4‐phenyl‐1,2,3,6‐tetrahydropyridine (MPTP) and its active metabolite 1‐methyl‐4‐phenylpyridinium (MPP+) may contribute to dopaminergic neurodegeneration in Parkinsons disease (PD). We addressed the importance of the dopamine transporter (DAT) for selective dopaminergic toxicity by testing the differential cytotoxicity and cellular uptake of 12 βCs in human embryonic kidney HEK‐293 cells ectopically expressing the DAT gene. Cell death was measured using [4,5‐Dimethylthiazol‐2‐yl]‐2,5‐diphenyltetrazolium bromide (MTT) and trypan blue exclusion assays, and uptake by a fluorescence‐based uptake assay. All βCs and MPP+ showed general cytotoxicity in parental HEK‐293 cells after 72 h with half‐maximal toxic concentrations (TC50 values) in the upper micromolar range. Besides MPP+, only 2[N]‐methylated compounds showed enhanced cytotoxicity in DAT expressing HEK‐293 cells with 1.3‐ to 4.5‐fold reduction of TC50 values compared with parental cell line. The rank order of selectivity was: MPP+ >> 2[N],9[N]‐dimethyl‐harminium > 2[N]‐methyl‐harminium > 2[N],9[N]‐dimethyl‐harmanium = 2[N]‐methyl‐norharmanium > 2[N]‐methyl‐harmanium > 2[N],9[N]‐dimethyl‐norharminium. Consistently, only 2[N]‐methylated βCs were transported into the cell through the DAT with up to five times greater Km and 12–220 times smaller Vmax values compared with dopamine and MPP+. There was a weak relation of DAT‐mediated selectivity with the affinity of βCs at the DAT (Km), but not with Vmax. Our data suggest that DAT‐mediated cellular uptake of 2[N]‐methylated βCs represents a potential mechanism for selective toxicity towards dopaminergic neurons and may be relevant for the pathogenesis of Parkinsons disease.

An efficient synthesis of enantiomerically pure (+)-(2S,5R)-1-[2-(hydroxymethyl)-1,3-oxathiolan-5-yl]cytosine [(+)-BCH-189] from d-galactose

Abstract An efficient and short synthesis of enantiomerically pure (+)-BCH-189 has been accomplished from D-galactose via 1,6-thioanhydro-D-galactose.

The effects of JWB1-84-1 on memory-related task performance by amyloid Aβ transgenic mice and by young and aged monkeys

JWB1-84-1 is one of 50 tertiary amine analogs of choline synthesized with expectation that they would be high potency compounds for cytoprotection. As one of the more potent analogs in this regard, JWB1-84-1, a piperazine derivative, was selected for testing as a cognition-enhancing agent. The compound was evaluated for efficacy in Alzheimers disease transgenic mice (B6C3-Tg(APPswe, PSEN1dE9)85Dbo/J). A separate cohort of mice (AD Tg) were first subjected to a behavioral test battery in which the transgenic strain was compared with the wild-type strain. AD Tg mice were shown to exhibit specific deficits in the acquisition of a working memory (5-trial/session radial arm water maze, RAWM) task at a time when the animals exhibited maximal cerebral amyloid burden. JWB1-84-1 produced a dose-dependent decrease in the number of errors made by well trained AD-Tg mice the RAWM task that was maximal after the 20 microg/kg dose. Aged macaques (20-32 y) were trained to proficiency in their performance of a computer-assisted delayed matching-to-sample task. Vehicle (normal saline) or JWB1-84-1 (5-150 microg/kg, i.m.) was administered 10 min before the initiating of testing. On average, JWB1-84-1 treatment significantly improved task accuracy after all but the lowest dose. The maximal degree of improvement was attained after animals received the 100 microg/kg dose. The drugs effects were restricted primarily to Medium and Long delay trials - the most difficult portions of the task, which were improved by up to 18% above control. In young macaques JWB1-84-1 treatment also significantly reversed the decrements in task accuracy associated with the random presentation of a task distractor. Thus JWB1-84-1exhibits the potential for treating the cognitive symptoms associated with neurodegenerative diseases and attention deficit disorders. Its cytoprotective action might also work to slow the progression of Alzheimers disease.

Identification of brain proteins that interact with 2-methylnorharman: An analog of the parkinsonian-inducing toxin, MPP+

N-Methylated beta-carbolines, including 2-methylnorharman, are structural and functional analogs of the parkinsonian-inducing toxin, MPP+. We are investigating N-methylated beta-carbolines, including 2-methylnorharman, as possible etiologic factors in the pathogenesis of Parkinsons disease. The cellular targets of N-methylated beta-carboline-mediated cytotoxicity are unknown; therefore, we used the T7Select Phage Display System in a novel approach to identify brain proteins that bind to 2-methylnorharman. We incubated (biopanned) immobilized 2-methylnorharman with a phage display cDNA library that expressed a library of human brain proteins on the surface of bacteriophage T7. We washed off unbound phage, amplified the phage that were bound to 2-methylnorharman, and enriched for toxin-interacting phage by repeating the biopanning and amplification steps. The cDNA sequences from the toxin-interacting phage were used to derive the amino acid sequences of the phage-displayed proteins. Five of the six 2-methylnorharman-interacting proteins may have relevance to Parkinsons disease: alpha-tubulin, paraoxonase, dorfin, fatty acid binding protein, and platelet-activating factor acetylhydrolase. Dorfin has sequence homology with parkin, which is interesting because mutations in the parkin gene associate with early-onset Parkinsons disease. Our findings are the basis for future studies aimed at determining whether 2-methylnorharman affects the function of these specific proteins in vitro and in vivo.

Solubility of Guaifenesin in the Presence of Common Pharmaceutical Additives

The aqueous solubility of guaifenesin, a highly water‐soluble drug, in the presence of salts, sugars, and cosolvents was determined at 25°C and 40°C. The solubility of drug at both temperatures was reduced with increasing concentrations of salts and sugars. The extent of reduction in drug solubility was dependent on the type of salts and sugars used. The salting‐out coefficient of additives was calculated by plotting log‐linear solubility profiles of the drug against the concentrations of the additives. The solubility of guaifenesin, a neutral compound, was found to be higher at lower pH values, which could be due to hydrogen‐bonding effects. At 25°C, glycerin, PEG 300, and propylene glycol increased the solubility of drug at low solvent concentrations while the solubility was reduced at high concentrations. At 40°C, the solubility of drug was reduced at all concentrations of cosolvents. The thermodynamic events accompanying the solubility process were discussed to explain the solubility phenomena observed in the presence of additives. The reduced aqueous solubility of guaifenesin in the presence of additives greatly improved the entrapment of drug into controlled‐release wax microspheres.