Neuroprotection by Small Molecule Activators of the Nerve Growth Factor Receptor

Abstract

There is a great deal of interest in neurotrophin therapy to prevent neuronal degeneration. However, the blood-brain barrier presents a major hurdle in the use of peptide therapeutics. The goal of this study was to identify small molecule, cellpermeable nerve growth factor (NGF) activators. Combinatorial libraries of asterriquinones (Ͼ300) and mono-indolyl-quinones (Ͼ60) were screened using a 96-well enzyme-linked immunosorbent assay that detects phosphorylated TrkA, the NGF receptor. The libraries were also screened for dose-dependent cytotoxicity. From these screens, we generated quantitative structure-activity relationship models for activity and toxicity, and then we selected two compounds, 2-(6-chloro-1H-indol-3-yl)-5-(2-cyclopropyl-1H-indol-3-yl)-3,6-dihydroxy-[1,4]benzoquinone (1H5) and 2,5-dimethoxy-3-(7-fluoro-1H-indol-3-yl)-[1,4]-benzoquinone (5E5), for further study based on high activity and low toxicity. Compound 1H5 (30 M) is an asterriquinone that is a moderate TrkA activator (50% the activity of 100 ng/ml NGF), and it shows little toxicity at concentrations up to 100 M. 1H5 can protect differentiated PC12 neurons from apoptotic cell death induced by NGF withdrawal. Compound 5E5 (30 M) is a mono-indolyl-quinone that is a very strong activator of TrkA (Ͼ200% the activity of 100 ng/ml NGF), and it is nontoxic at concentrations up to 10 M. Activation of TrkA can be detected at 1 M 5E5, and 3 to 10 M 5E5 activates TrkA and extracellular signal-regulated kinase as strongly as a maximal dose of NGF (100 ng/ml). A combination of a low dose of 5E5 (1 M) with a submaximal dose of NGF (10 ng/ml) promotes neuronal differentiation of PC12 cells. These compounds represent a new class of TrkA activators that could have potential utility in the treatment of neurodegenerative diseases.

Microarray Analysis of Hippocampal CA1 Neurons Implicates Early Endosomal Dysfunction During Alzheimer's Disease Progression

“…This relationship between Ab and neurotrophin receptor levels suggests that rab5-positive endosomal trafficking acts as a critical factor regulating cell survival. Taken together, the present results strongly implicate deregulation of early endosomal function as a causative factor for TrkB down regulation, suggesting a novel site for pharmacotherapeutic interventions via small molecule activators and/or TrkB transactivation (55–59). …”

Effects of minocycline on the expression of NGF and HSP70 and its neuroprotection role following intracerebral hemorrhage in rats

“…In contrast, signaling via p75NTR can activate pathways of cell death[20]. Therefore, the final effect of NGF is a balance between cell survival signal derived from the TrkA family and cell death signal from the p75NTR[21]. The effect of NGF may be related not only to a neuroprotective activity against apoptosis, but also to the formation of new neural pathways, as it is known that NGF has the ability to promote neural plasticity and axonal regeneration[22].…”

Small Molecule Activators of the TRK Receptors for Neuroprotection

“…In this assay, the original compound DAQ-B1 did not activate TrkB and our lead drug 5E5 activated to 74% the effect of BDNF. This is a little higher than the activation we measured by immunoblotting whole cell extracts (~40%) but may simply reflect the difference between the ELISA and western blot (1). Thirty-nine compounds had activity >25% BDNF.…”