Ferenc Soti

Initial Phase 2 Trial of a Nicotinic Agonist in Schizophrenia

OBJECTIVEnNicotinic acetylcholine receptors are possible therapeutic targets for schizophrenia, as shown by neurobiological and molecular evidence for deficiencies in expression of alpha(7)-nicotinic receptors. Patients heavy smoking suggests attempted self-medication through this mechanism. The agent 3-(2,4-dimethoxybenzylidene) anabaseine (DMXB-A) is a partial alpha(7)-nicotinic agonist and can be taken orally. A phase 1 trial showed evidence for cognitive enhancement in schizophrenia.nnnMETHODnThirty-one subjects with schizophrenia received DMXB-A at two different doses and placebo for periods of 4 weeks in a three-arm, two-site, double-blind, crossover phase 2 trial. The MATRICS Consensus Cognitive Battery assessed cognitive effects, and the Scale for the Assessment of Negative Symptoms (SANS) and Brief Psychiatric Rating Scale (BPRS) assessed clinical effects. Subjects continued their current antipsychotic drug during the trial and were nonsmokers.nnnRESULTSnThere were no significant differences in the MATRICS cognitive measures between DMXB-A and placebo over the three treatment arms, but the patients experienced significant improvement at the higher DMXB-A dose on the SANS total score and nearly significant improvement on the BPRS total score. Improvement was most notable on the SANS anhedonia and alogia subscales. Examination of the first treatment arm showed effects of DMXB-A on the attention/vigilance and working memory MATRICS domains, compared to baseline. Five subjects developed mild tremor, and nearly half had mild nausea while taking DMXB-A.nnnCONCLUSIONnDMXB-A, a nicotinic agonist that activates alpha(7)-nicotinic receptors, improved clinical ratings of negative symptoms that are generally resistant to treatment with dopamine antagonist antipsychotic drugs. The clinical utility of this treatment is not yet determined.

Effects of an Alpha 7-Nicotinic Agonist on Default Network Activity in Schizophrenia

BACKGROUNDn3-(2,4-dimethoxybenzylidene)-anabaseine (DMXB-A) is a partial agonist at α7 nicotinic acetylcholine receptors that has been evaluated clinically for treatment of schizophrenia. This study examined the effects of DMXB-A on default network activity as a biomarker for drug effects on pathologic brain function associated with schizophrenia.nnnMETHODSnPlacebo and two doses of DMXB-A were administered in a random, double-blind crossover design during a Phase 2 study of DMXB-A. Functional magnetic resonance imaging was performed on 16 nonsmoking patients with schizophrenia while they performed a simple eye movement task. Independent component analysis was used to identify the default network component. Default network changes were evaluated in the context of a polymorphism in CHRNA7, the α7-nicotinic acetylcholine receptor subunit gene, which was previously found to be associated with schizophrenia.nnnRESULTSnCompared with placebo, both 150 and 75 mg twice daily DMXB-A altered default network activity, including a reduction in posterior cingulate, inferior parietal cortex, and medial frontal gyrus activity and an increase in precuneus activity. The most robust difference, posterior cingulate activity reduction, was affected by CHRNA7 genotype.nnnCONCLUSIONSnThe observed DMXB-A-related changes are consistent with improved default network function in schizophrenia. Pharmacogenetic analysis indicates mediation of the effect through the α7-nicotinic receptor. These results further implicate nicotinic cholinergic dysfunction in the disease and suggest that default network activity may be a useful indicator of biological effects of novel therapeutic agents.

Activation and desensitization of nicotinic alpha7-type acetylcholine receptors by benzylidene anabaseines and nicotine.

Nicotinic receptor activation is inextricably linked to desensitization. This duality affects our ability to develop useful therapeutics targeting nicotinic acetylcholine receptor (nAChR). Nicotine and some α7-selective experimental partial agonists produce a transient activation of α7 receptors followed by a period of prolonged residual inhibition or desensitization (RID). The object of the present study was to determine whether RID was primarily due to prolonged desensitization or due to channel block. To make this determination, we used agents that varied significantly in their production of RID and two α7-selective positive allosteric modulators (PAMs): 5-hydroxyindole (5HI), a type 1 PAM that does not prevent desensitization; and 1-(5-chloro-2,4-dimethoxy-phenyl)-3-(5-methyl-isoxanol-3-yl)-urea (PNU-120596), a type 2 PAM that reactivates desensitized receptors. The RID-producing compounds nicotine and 3-(2,4-dimethoxybenzylidene)anabaseine (diMeOBA) could obscure the potentiating effects of 5HI. However, through the use of nicotine, diMeOBA, and the RID-negative compound 3-(2,4-dihydroxybenzylidene)anabaseine (diOHBA) in combination with PNU-120596, we confirmed that diMeOBA produces short-lived channel block of α7 but that RID is because of the induction of a desensitized state that is stable in the absence of PNU-120596 and activated in the presence of PNU-120596. In contrast, diOHBA produced channel block but only readily reversible desensitization, whereas nicotine produced desensitization that could be converted into activation by PNU-120596 but no demonstrable channel block. Steady-state currents through receptors that would otherwise be desensitized could also be produced by the application of PNU-120596 in the presence of a physiologically relevant concentration of choline (60 μM), which may be significant for the therapeutic development of type 2 PAMs.

Functional Magnetic Resonance Imaging of Effects of a Nicotinic Agonist in Schizophrenia

3-(2,4-Dimethoxybenzylidene)-anabaseine (DMXB-A) is a partial agonist at α7-nicotinic acetylcholine receptors and is now in early clinical development for treatment of deficits in neurocognition and sensory gating in schizophrenia. During its initial phase 2 test, functional magnetic resonance imaging (fMRI) studies were conducted to determine whether the drug had its intended effect on hippocampal inhibitory interneurons. Increased hemodynamic activity in the hippocampus in schizophrenia is found during many tasks, including smooth pursuit eye movements, and may reflect inhibitory dysfunction. Placebo and two doses of drug were administered in a random, double-blind crossover design. After the morning drug/placebo ingestion, subjects underwent fMRI while performing a smooth pursuit eye movement task. Data were analyzed from 16 nonsmoking patients, including 7 women and 9 men. The 150-mg dose of DMXB-A, compared with placebo, diminished the activity of the hippocampus during pursuit eye movements, but the 75-mg dose was ineffective. The effect at the 150-mg dose was negatively correlated with plasma drug levels. The findings are consistent with the previously established function of α7-nicotinic receptors on inhibitory interneurons in the hippocampus and with genetic evidence for deficits in these receptors in schizophrenia. Imaging of drug response is useful in planning future clinical tests of this compound and other nicotinic agonists for schizophrenia.

Hydrogen Bonding and Tautomerism in Anils of Salicylaldehydes and Related Compounds. A Study of Deuterium Isotope Effects on13C Chemical Shifts

Deuterium‐induced chemical shift differences on the 13C (DIS) are reported for a series of Schiff bases of salicylaldehydes, 1‐(phenyliminomethyl)naphthalen‐2‐ol and 4‐chloro‐1,7‐phenanthrolin‐10‐ol. Provided that corrections for the hydrogen donor atom and diamagnetic effects of the surrounding groups are made, plots of logarithms of two bond DIS vs. the chemical shift of the exchangeable proton are linear for compounds in which tautomeric equilibria are absent or strongly displaced in favor of one form. Molecules with comparably populated tautomers in fast exchange fall off this correlation. By this method, anils of salicylaldehydes were found to exist as hydroxy forms with localized hydrogen bonds while 1‐(phenyliminomethyl)naphthalen‐2‐ol and 4‐chloro‐1,7‐phenanthrolin‐10‐ol were found to be tautomeric mixtures dominated by the hydroxy forms. DIS also revealed that 4‐chlor‐1,7‐phenanthrolin‐10‐ol exists in solution as an aggregate of two molecules.

Inhibition of barnacle larval settlement and crustacean toxicity of some hoplonemertine pyridyl alkaloids.

Hoplonemertines are carnivorous marine worms, which prey upon crustaceans and annelids. They paralyze their prey by injecting alkaloids with a stylet-bearing proboscis. The dermis of these animals also secretes alkaloids to repel predators. Besides affecting central and peripheral nervous system nicotinic receptors, some pyridyl alkaloids also activate certain chemoreceptor neurons in crustacean walking legs, which sense environmental chemicals. Anabaseine (2-[3-pyridyl]-3,4,5,6-tetrahydropyridyl) and 2,3-bipyridyl (2,3-BP) are two nemertine alkaloids, which potently paralyze crustaceans. Anabaseine is an agonist of vertebrate as well as invertebrate nicotinic receptors. While 2,3-BP is non-toxic to mice, it is toxic to crustaceans. We tested a variety of nemertine pyridyl alkaloids for inhibition of barnacle (Balanus amphitrite) larval settlement and for crustacean toxicity in order to determine whether toxicity could be dissociated from inhibition of larval settlement. We prepared eight C-methylated 2,3-BP isomers to determine where substitution is permitted without loss of activity. Anti-settlement and toxicity activities were not always related. For instance, 4-methyl-2,3-BP displayed only 3% of the crayfish paralytic activity of 2,3-BP, but inhibited settlement almost 2-fold more effectively. Two other isomers displaying exceptional anti-settlement activity were the 4- and 5-methyl-2,3-BPs; these also displayed high crustacean toxicity. Nemertelline inhibited barnacle settlement at concentrations similar to 2,3-BP but was 136-fold less toxic when injected into crayfish. Thus, certain bipyridyls and tetrapyridyls may be useful anti-fouling additives.

Positive modulation of alpha7 nAChR responses in rat hippocampal interneurons to full agonists and the alpha7-selective partial agonists, 4OH-GTS-21 and S 24795

One approach for the identification of therapeutic agents for Alzheimers disease has focused on the research of α7 nAChR-selective agonists such as the partial agonists 3-(4-hydroxy,2-methoxybenzylidene)anabaseine (4OH-GTS-21) and, more recently, 2-[2-(4-bromophenyl)-2-oxoethyl]-1-methyl pyridinium (S 24795). An alternative approach for targeting α7 nAChR has been the development of positive modulators for this receptor. In this study we examined the interactions between full or partial agonists and positive modulators of α7 nAChRs in situ in brain tissue. Three positive modulators were used, 5-hydroxyindole (5-HI), 1-(5-chloro-2,4-dimethoxy-phenyl)-3-(5-methyl-isoxanol-3-yl)-urea (PNU-120596), and genistein. Whole-cell recordings were performed in stratum radiatum interneurons from rat brain slices. Hippocampal interneurons were stimulated by ACh, choline, S 24795, or 4OH-GTS-21, before and after bath perfusion with the positive modulators. 5-HI was not effective at potentiating 200 μM 4OH-GTS-21-evoked responses, however 5-HI induced a sustained potentiation of responses evoked by 30 μM 4OH-GTS-21. When 1 mM ACh and 200 μM 4OH-GTS-21 were applied alternately α7-mediated responses to both agonists were reduced, suggesting that high concentration of 4OH-GTS-21 produces residual inhibition or desensitization and that 5-HI is not effective at overcoming receptor desensitization. Similar results were obtained with α7 receptors expressed in Xenopus oocytes. Interestingly, responses evoked by S 24795 were potentiated by 5-HI but not by genistein. Additionally, PNU-120596 was able to potentiate α7-mediated responses, regardless of the nature of the agonist. We demonstrated that the potentiation of α7 nAChR response would depend on the nature and the effective concentration of the agonist involved and its particular interaction with the positive modulator.

Redox targeting of LY231617, an antioxidant with potential use in the treatment of brain damage

Abstract Several brain-targeting chemical delivery systems (CDS) based on a dihydropyridine ⇌ pyridinium salt-type targetor were synthesized and evaluated for LY231617 (1), a di-tert-butylated phenolic amine antioxidant with potential use in the treatment of brain injuries. The dihydropyridine moiety was chemically attached to the amine (by either amide or various substituted carbamate linkages) or to the phenolic hydroxyl (by carboxylic ester linkage) functionalities of LY231617. In vitro stability and in vivo tissue distribution studies (in the rat) were performed with the novel derivatives. The results indicated that a simple amide-type CDS demonstrated efficient delivery of LY231617-targetor conjugate to the CNS. This derivative which contains the intact pharmacophore might possess intrinsic pharmacological antioxidant activity. Favorable in vitro properties suggested that a substituted carbamate-type CDS might be a better delivery modality for LY231617.

N-Terminal Domains in Mouse and Human 5-Hydroxytryptamine3A Receptors Confer Partial Agonist and Antagonist Properties to Benzylidene Analogs of Anabaseine

The present study tested the hypothesis that mouse and human 5-hydroxytryptamine3A (5-HT3A) receptors may be differentially modulated by benzylidene analogs of anabaseine (BA) and that these analogs may be useful in assessing residues involved in receptor gating. Mouse and human wild-type and mouse and human chimeric 5-HT3A receptors expressed in Xenopus oocytes were evaluated with the two-electrode voltage clamp technique. Our previous studies demonstrated that 3-(2,4-dimethoxybenzylidene)-anabaseine (DMXBA) is an antagonist at the mouse wild-type 5-HT3A receptor, but that its metabolites 3-(2-hydroxy, 4-methoxybenzylidene)-anabaseine (2-OHMBA), 3-(2-methoxy, 4-hydroxybenzylidene)-anabaseine (4-OHMBA), and 3-(2,4-dihydroxybenzylidene)-anabaseine (2,4-DiOHBA) are partial agonists (J Pharmacol Exp Ther, 299: 1112–1117, 2001). In the human wild-type (HWT) 5-HT3A receptor, none of the BA compounds possessed partial agonist activity. BA compounds antagonized 1.5 μM 5-HT-mediated (EC50) responses in the HWT 5-HT3A receptor with a rank order of potency (IC50 in μM) of 2-OHMBA (1.5 ± 0.1) > DMXBA (3.1 ± 0.2) > 4-OHMBA (7.4 ± 0.5) > 2,4-DiOHBA (12.8 ± 0.7). In mouse receptor chimeras containing N-terminal human receptor orthologs, 2-OHMBA inhibited 5-HT-mediated (EC50) currents with IC50 values of 2.0 ± 0.08 and 3.0 ± 0.13 μM, respectively. In human receptor chimeras containing N-terminal mouse receptor orthologs, 2-OHMBA displayed partial agonist activities with EC50 values of 1.3 ± 0.15 and 5.0 ± 0.4 μM; efficacies were 43 and 57%, respectively. Thus, amino acids present in the distal one-third of the N terminus of mouse and human 5-HT3A receptors are necessary and sufficient to confer partial agonist or antagonist properties of 2-OHMBA.

A computational study of the binding of 3-(arylidene) anabaseines to two major brain nicotinic acetylcholine receptors and to the acetylcholine binding protein

Nicotinic acetylcholine receptors (nAChRs) have become targets for drug development in recent years. 3-(2,4-dimethoxybenzylidene)-anabaseine (DMXBA), which selectively stimulates the alpha7 nAChR, has been shown to alleviate some cognitive deficits associated with schizophrenia. In this paper we report an analysis of the interactions between 47 arylidene-anabaseines (including 45 benzylidene-anabaseines) and rat brain alpha7 and alpha4beta2 nicotinic acetylcholine receptors, using three different modeling techniques, namely 2D-QSAR, 3D-QSAR and molecular docking to the Aplysia californica acetylcholine binding protein (AChBP), a water soluble, homomeric nAChR surrogate receptor with a known crystal structure. Our investigation indicates the importance of: (1) the nitrogen atom of the tetrahydropyridyl (THP) ring for hydrogen bond formation; (2) pi-pi interactions between the aromatic rings of the ligands and the nAChBP binding site; (3) molecular surface recognition expressed in terms of steric complimentarity. On the basis of the 3D-QSAR results, bulky substituents at positions 2 (and due to the rotational freedom also at position 6) and 4 of the benzylidene moiety, with highly electronegative atoms projecting approximately 3-3.5A away from the benzylidene ring at position 4 seem optimal for enhancing binding affinity to the alpha7 nAChR.