Use of the non-peptidic Nerve Growth Factor mimetic MT2 to activate TrkA and TrkB receptors: a therapeutic tool in Multiple Sclerosis

MT2 is a novel Nerve Growth Factor peptidomimetic, able to exert its effects binding the Tropomyosin receptor kinase A (TrkA) and B (TrkB), the high affinity receptor for Nerve Growth Factor (NGF) and Brain-derived neurotrophic factor (BDNF). These latter molecules are part of neurotrophins family, and they have been tested in pharmacology for their trophic function: despite this, their polypeptide nature forced to use very invasive way of administration, making them virtually impossible to use for therapeutic purposes. Unlike them, MT2 is a non-peptidic smaller molecule with an optimal pharmacokinetic that showed to be effective in activating the MAPK/ERK pathway. Through this pathway, MT2 demonstrated to trigger an anti-apoptotic signal both in in vitro model of Alzheimer's disease (AD) based on NGF deprivation of rat hippocampal neurons (Scarpi D et al. 2012) and in in vivo experimental models of acute global ischemia in gerbils, where it prevented death of hippocampal neurons. Considering this, our aim was to understand if MT2 could be a pharmaceutical tool for inflammatory insult in central nervous system (CNS) exploiting appropriate models. First, we set up an in vitro spinal cord organotypic culture during an induced inflammatory stress by a pro-inflammatory cytokines cocktail: in this model we proved that MT2 is able keep unchanged any synaptic alterations. This effect seems to be mediated by the activation of classical NGF neurotrophic pathways kinases-driven, triggered by the bound of MT2 with TrkA and TrkB. These positive results were entirely due to an effect on CNS cells, because the absence of immune system mediators in this model. These positive results led us to investigate whether MT2 could limit inflammatory events in central nervous system (CNS), setting up Experimental Autoimmune Encephalomyelites (EAE) MOG35-55-induced experiments. We treated animals during acute and chronic stages of disease: MT2 demonstrated to give beneficial effects treating animals at early stage of disease, limiting the classical hallmarks of disease. In fact, MT2-treated animals showed significant lower clinical signs in vivo and less presence of infiltrates and demyelinated areas in spinal cord, as demonstrated by ex vivo experiments. These effects resulted to be in charge of TrkA pathway activation. Moreover, we investigated if such effects could involve immune system cells, carrying on treatment on preclinical phase of EAE: ex vivo experiments results showed a significant lower production of IFN-γ by T-cells isolated from lymph nodes of treated animals, compared to controls, attesting a potent anti-inflammatory effect on immune system cells to MT2. Last, we tested the possible beneficial effect of MT2 in limiting demyelination and promoting the remyelination in in vivo Cuprizone model. The drug demonstrated its inability in counteracting a non-immune cells-driven insult: toxic event in demyelination were not limited and, even, the peptidomimetic showed to worsen myelin conditions during the remyelinating phase of this model. Considering everything in the whole, MT2 showed a neuroprotective its ability in narrowing the pro-inflammatory events on several neuroinflammatory models. The drug demonstrated to act both on immune system and on CNS cells, influencing the classical neurotrophic pathway activation. Despite this, it showed an adverse effect on toxic demyelination model, demonstrating that double specificity for TrkA and TrkB in absence of immune system involvement could possibly a harmful feature.