Low molecular weight, non-peptidic agonists of TrkA receptor with NGF-mimetic activity

Abstract

Exploitation of the biologic activity of neurotrophins is desirable for medical purposes, but their protein nature intrinsically bears adverse pharmacokinetic properties. Here, we report synthesis and biologic characterization of a novel class of low molecular weight, non-peptidic compounds with NGF (nerve growth factor)-mimetic properties. MT2, a representative compound, bound to Trk (tropomyosin kinase receptor)A chain on NGF-sensitive cells, as well as in cell-free assays, at nanomolar concentrations and induced TrkA autophosphorylation and receptor-mediated internalization. MT2 binding involved at least two amino-acid residues within TrkA molecule. Like NGF, MT2 increased phosphorylation of extracellular signal-regulated kinase1/2 and Akt proteins and production of MKP-1 phosphatase (dual specificity phosphatase 1), modulated p38 mitogen-activated protein kinase activation, sustained survival of serum-starved PC12 or RDG cells, and promoted their differentiation. However, the intensity of such responses was heterogenous, as the ability of maintaining survival was equally possessed by NGF and MT2, whereas the induction of differentiation was expressed at definitely lower levels by the mimetic. Analysis of TrkA autophosphorylation patterns induced by MT2 revealed a strong tyrosine (Tyr)490 and a limited Tyr785 and Tyr674/675 activation, findings coherent with the observed functional divarication. Consistently, in an NGF-deprived rat hippocampal neuronal model of Alzheimer Disease, MT2 could correct the biochemical abnormalities and sustain cell survival. Thus, NGF mimetics may reveal interesting investigational tools in neurobiology, as well as promising drug candidates.

Original Nerve Growth Factor Mimetic Dipeptide GK-2 Restores Impaired Cognitive Functions in Rat Models of Alzheimer’s Disease

“…Another low-molecular-weight non-peptide mimetic of NGF known as MT2, which is also a TrkA-receptor agonist, exhibits neuroprotective and antiamyloidogenic activity in cellular AD models at a concentration of 5–30 μmol/ml [44]. …”

Neurotropin promotes NGF signaling through interaction of GM1 ganglioside with Trk neurotrophin receptor in PC12 cells

“…However, their therapeutic application has been largely limited because of their poor pharmacological properties, such as low stability in serum, restricted penetration across blood-brain barrier, minimal diffusion in central nervous system and, more importantly, the pleiotropic actions triggered by their ability to bind multiple receptors (Longo and Massa, 2013 for review). In order to overcome such disadvantages of native neurotrophins, substantial efforts have been made to discover small molecules mimicking NGF actions with a better pharmacokinetics and receptor selectivity (Lee and Chao, 2001;Jang et al, 2007;Yamada et al, 2008;Scarpi et al, 2012). Most of these compounds act as robust Trk agonists that induce Trk signals even in the absence of NGF.…”

The p75 neurotrophin receptor: at the crossroad of neural repair and death

“…The precise pharmacological mechanisms of protection are under investigation but may include facilitation of Akt signaling and inhibition of proNGF binding. The ability to selectively modify specific neurotrophin actions with small ligands is also seen with the experimental TrkA ligand, MT2, which has been shown to influence the TrkA tyrosine phosphorylation pattern, resulting in NGF-like pro-survival activity with significantly less effect on differentiation (Scarpi et al, 2012). Although these efforts are still in relatively early stages of development they provide strong proof of concept that small molecules targeted to specific domains of the p75 NTR can exert fine control over neurotrophin receptor signaling.…”