Milameline (CI-979/RU35926): a muscarinic receptor agonist with cognition-activating properties: biochemical and in vivo characterization.

Milameline (E-1,2,5,6-tetrahydro-1-methyl-3-pyridinecarboxaldehyde, O-methyloxime monohydrochloride, CI-979, PD129409, RU35926) was characterized in vitro and evaluated for effects on central and peripheral cholinergic activity in rats and rhesus monkeys. In muscarinic binding studies, milameline displayed nanomolar affinity with an agonist ligand and micromolar affinity with antagonist ligands, with approximately equal affinities determined at the five subtypes of human muscarinic receptors (hM(1)-hM(5)) with whole cells or membranes from stably transfected Chinese hamster ovary (CHO) cells. On binding, milameline stimulated phosphatidylinositol hydrolysis in hM(1) and hM(3) CHO cells and inhibited forskolin-activated cAMP accumulation in hM(2) and hM(4) CHO cells. Additionally, it decreased K(+)-stimulated release of [(3)H]acetylcholine from rat cortical slices. Responses were not caused by the inhibition of acetylcholinesterase, and there was no significant binding to approximately 30 other neurotransmitter binding sites. In rats, milameline decreased spontaneous and scopolamine-induced swimming activity, improved water-maze performance of animals impaired by basal forebrain lesions, increased cortical blood flow, decreased core body temperature, and increased gastrointestinal motility. Electroencephalogram activity in both rats and monkeys was characterized by a predominance of low-voltage desynchronized activity consistent with an increase in arousal. Milameline also reversed a scopolamine-induced impairment of attention on a continuous-performance task in monkeys. Thus, milameline possesses a pharmacological profile consistent with that of a partial muscarinic agonist, with central cholinergic actions being produced in rats and monkeys at doses slightly lower than those stimulating peripheral cholinergic receptors.

PD 90780, a non peptide inhibitor of nerve growth factor's binding to the P75 NGF receptor.

Nerve growth factor is a peptide that supports the survival and differentiation of discrete neuronal populations in the peripheral and central nervous systems. NGF binds to both trkA, a tyrosine kinase receptor, and to the p75 nerve growth factor receptor, a protein lacking a consensus signalling sequence. We have identified a substituted pyrazoloquinazolinone, PD 90780, which inhibits binding of nerve growth factor to the p75 receptor. This inhibition of binding occurs due to PD 90780 binding to nerve growth factor, not to the p75 receptor. This compound may be useful in identifying the region(s) of nerve growth factor involved in binding to the p75 receptor and in clarifying the role of p75 receptor in the actions of the neurotrophins.

Kynurenic acid derivatives inhibit the binding of nerve growth factor (NGF) to the low-affinity p75 NGF receptor.

The ability of a series of substituted kynurenic acids, thienopyridinonecarboxylic acids, and related compounds to inhibit the binding of nerve growth factor (NGF) to the p75 NGF receptor (NGFR) was evaluated in a radioligand binding assay that utilized a biotinylated derivative of the extracellular domain of p75 NGFR (p75ext) fixed to streptavidin-coated plastic wells. Two compounds, 6-aminokynurenic acid (5h) and the 3-methyl ester of 4,7-dihydro-2-methyl-7-oxothieno[3,2-b]pyridine-3,5-dicarboxylic acid (16), were found to inhibit the binding of [125I]NGF to p75ext with IC50 values in the low micromolar range. Other amino-substituted kynurenic acids also possessed activity at slightly higher concentrations. Several structural features seem to be essential, including the carboxylic acid, a polar group on the benzene ring (or thiophene ring, in the case of analogues of 16), and the C-4 carbonyl group in the pyridinone ring. These compounds were also found to inhibit the binding of [125I]NGF to its receptors in membranes from PC12 cells (which express p75 as well as trka receptors for NGF) and DG44-CHO cells (transfected with full length p75 NGFR). The available data for 5h and 16 do not allow the determination of whether the effects of these compounds are mediated by their interaction with NGF or the NGF receptors.