Debra J. Post-Munson

Targeting acute ischemic stroke with a calcium-sensitive opener of maxi-K potassium channels

During ischemic stroke, neurons at risk are exposed to pathologically high levels of intracellular calcium (Ca++), initiating a fatal biochemical cascade. To protect these neurons, we have developed openers of large-conductance, Ca++-activated (maxi-K or BK) potassium channels, thereby augmenting an endogenous mechanism for regulating Ca++ entry and membrane potential. The novel fluoro-oxindoles BMS-204352 and racemic compound 1 are potent, effective and uniquely Ca++-sensitive openers of maxi-K channels. In rat models of permanent large-vessel stroke, BMS-204352 provided significant levels of cortical neuroprotection when administered two hours after the onset of occlusion, but had no effects on blood pressure or cerebral blood flow. This novel approach may restrict Ca++ entry in neurons at risk while having minimal side effects.

The synthesis and characterization of BMS-204352 (MaxiPost) and related 3-fluorooxindoles as openers of maxi-K potassium channels

3-Aryl-3-fluorooxindoles can be efficiently synthesized in two steps by the addition of an aryl Grignard to an isatin, followed by treatment with DAST. Oxindole 1 (BMS-204352; MaxiPost) can be isolated using chiral HPLC or prepared by employing chiral resolution. Cloned maxi-K channels are opened by 1, which demonstrates a brain/plasma ratio >9 in rats.

Reduced bicuculline response and GABAA agonist binding in aged rat hippocampus

Extracellular field recordings from CA1 pyramidal cells in the rat hippocampal slice preparation were used to examine the effects of age on gamma-aminobutyric acid (GABA)-mediated recurrent inhibition. The actions of bicuculline (1-100 microM), a GABAA antagonist, were assessed in slices from young (1-3 months) and aged (26 months) Fischer 344 rats. Pre-drug population spike amplitudes were smaller in slices from aged rats. Bicuculline increased population spike amplitudes in slices from both age groups, but slices from young rats were more sensitive to the antagonist. Bicuculline also produced multiple population spikes in slices from both age groups, however the increase in population spike burst durations was much greater in slices from young rats than in slices from aged rats. Agonist radiolabeled GABAA binding site density was significantly decreased in hippocampal tissue from aged rats. Our results suggest there is a reduction in GABAergic inhibition in hippocampal slices from aged rats, possibly mediated by a decrease in GABAA receptors.

Synthesis and excitatory amino acid pharmacology of some novel quinoxalinediones

Abstract The synthesis and amino acid pharmacology of twelve N-substituted quinoxalinediones is reported. In particular, compounds 4a and 4b show significant antagonism at both the AMPA and glycine-site NMDA receptors. The functional antagonism of 4a has been demonstrated.

Discovery of a novel series of quinolone α7 nicotinic acetylcholine receptor agonists

High throughput screening led to the identification of a novel series of quinolone α7 nicotinic acetylcholine receptor (nAChR) agonists. Optimization of an HTS hit (1) led to 4-phenyl-1-(quinuclidin-3-ylmethyl)quinolin-2(1H)-one, which was found to be potent and selective. Poor brain penetrance in this series was attributed to transporter-mediated efflux, which was in turn due to high pKa. A novel 4-fluoroquinuclidine significantly lowered the pKa of the quinuclidine moiety, reducing efflux as measured by a Caco-2 assay.

Development of New Benzenesulfonamides As Potent and Selective Nav1.7 Inhibitors for the Treatment of Pain

By taking advantage of certain features in piperidine 4, we developed a novel series of cyclohexylamine- and piperidine-based benzenesulfonamides as potent and selective Nav1.7 inhibitors. However, compound 24, one of the early analogs, failed to reduce phase 2 flinching in the mouse formalin test even at a dose of 100 mpk PO due to insufficient dorsal root ganglion (DRG) exposure attributed to poor membrane permeability. Two analogs with improved membrane permeability showed much increased DRG concentrations at doses of 30 mpk PO, but, confoundingly, only one of these was effective in the formalin test. More data are needed to understand the disconnect between efficacy and exposure relationships.

Effects of BMS-902483, an α7 nicotinic acetylcholine receptor partial agonist, on cognition and sensory gating in relation to receptor occupancy in rodents.

Abstract The &agr;7 nicotinic acetylcholine receptor is thought to play an important role in human cognition. Here we describe the in vivo effects of BMS‐902483, a selective potent &agr;7 nicotinic acetylcholine receptor partial agonist, in relationship to &agr;7 nicotinic acetylcholine receptor occupancy. BMS‐902483 has low nanomolar affinity for rat and human &agr;7 nicotinic acetylcholine receptors and elicits currents in cells expressing human or rat &agr;7 nicotinic acetylcholine receptors that are about 60% of the maximal acetylcholine response. BMS‐902483 improved 24 h novel object recognition memory in mice with a minimal effective dose (MED) of 0.1 mg/kg and reversed MK‐801‐induced deficits in a rat attentional set‐shifting model of executive function with an MED of 3 mg/kg. Enhancement of novel object recognition was blocked by the silent &agr;7 nicotinic acetylcholine receptor agonist, NS6740, demonstrating that activity of BMS‐902483 was mediated by &agr;7 nicotinic acetylcholine receptors. BMS‐902483 also reversed ketamine‐induced deficits in auditory gating in rats, and enhanced ex vivo hippocampal long‐term potentiation examined 24 h after dosing in mice. Results from an ex vivo brain homogenate binding assay showed that &agr;7 receptor occupancy ranged from 64% (novel object recognition) to ˜90% (set shift and gating) at the MED for behavioral and sensory processing effects of BMS‐902483.

A functional NaV1.7-NavAb chimera with a reconstituted high affinity ProTx-II binding site

The NaV1.7 voltage-gated sodium channel is implicated in human pain perception by genetics. Rare gain of function mutations in NaV1.7 lead to spontaneous pain in humans whereas loss of function mutations results in congenital insensitivity to pain. Hence, agents that specifically modulate the function of NaV1.7 have the potential to yield novel therapeutics to treat pain. The complexity of the channel and the challenges to generate recombinant cell lines with high NaV1.7 expression have led to a surrogate target strategy approach employing chimeras with the bacterial channel NaVAb. In this report we describe the design, synthesis, purification, and characterization of a chimera containing part of the voltage sensor domain 2 (VSD2) of NaV1.7. Importantly, this chimera, DII S1–S4, forms functional sodium channels and is potently inhibited by the NaV1.7 VSD2 targeted peptide toxin ProTx-II. Further, we show by [125I]ProTx-II binding and surface plasmon resonance that the purified DII S1–S4 protein retains high affinity ProTx-II binding in detergent. We employed the purified DII S1–S4 protein to create a scintillation proximity assay suitable for high-throughput screening. The creation of a NaV1.7-NaVAb chimera with the VSD2 toxin binding site provides an important tool for the identification of novel NaV1.7 inhibitors and for structural studies to understand the toxin-channel interaction.

BMS-933043, a Selective α7 nAChR Partial Agonist for the Treatment of Cognitive Deficits Associated with Schizophrenia

The therapeutic treatment of negative symptoms and cognitive dysfunction associated with schizophrenia is a significant unmet medical need. Preclinical literature indicates that α7 neuronal nicotinic acetylcholine (nACh) receptor agonists may provide an effective approach to treating cognitive dysfunction in schizophrenia. We report herein the discovery and evaluation of 1c (BMS-933043), a novel and potent α7 nACh receptor partial agonist with high selectivity against other nicotinic acetylcholine receptor subtypes (>100-fold) and the 5-HT3A receptor (>300-fold). In vivo activity was demonstrated in a preclinical model of cognitive impairment, mouse novel object recognition. BMS-933043 has completed Phase I clinical trials.

B-973, a novel piperazine positive allosteric modulator of the α7 nicotinic acetylcholine receptor

Abstract The alpha7 (&agr;7) nicotinic acetylcholine receptor is a therapeutic target for cognitive disorders. Here we describe 3‐(3,4‐difluorophenyl)‐N‐(1‐(6‐(4‐(pyridin‐2‐yl)piperazin‐1‐yl)pyrazin‐2‐yl)ethyl)propanamide (B‐973), a novel piperazine‐containing molecule that acts as a positive allosteric modulator of the &agr;7 receptor. We characterize the action of B‐973 on the &agr;7 receptor using electrophysiology and radioligand binding. At 0.1 mM acetylcholine, 1 &mgr;M B‐973 potentiated peak acetylcholine‐induced currents 6‐fold relative to maximal acetylcholine (3 mM) and slowed channel desensitization, resulting in a 6900‐fold increase in charge transfer. The EC50 of B‐973 was approximately 0.3 &mgr;M at acetylcholine concentrations ranging from 0.03 to 3 mM. At a concentration of 1 &mgr;M, B‐973 shifted the acetylcholine EC50 of peak currents from 0.30 mM in control to 0.007 mM. B‐973 slowed channel deactivation upon acetylcholine removal (&tgr;=50 s) and increased the affinity of the &agr;7 agonist [3H]A‐585539. In the absence of exogenously added acetylcholine, application of B‐973 at concentrations >1 &mgr;M induced large methyllycaconitine‐sensitive currents, suggesting B‐973 can function as an Ago‐PAM at high concentrations. B‐973 will be a useful probe for investigating the biological consequences of increasing &agr;7 receptor activity through allosteric modulation. Graphical abstract Figure. No caption available.