Early IGF-1 receptor inhibition in mice mimics preterm human brain disorders and reveals a therapeutic target.

Besides recent advances in neonatal care, preterm newborns still develop sex-biased behavioral alterations. Preterms fail to receive placental insulin-like growth factor-1 (IGF-1), a major fetal growth hormone in utero, and low IGF-1 serum levels correlate with preterm poor neurodevelopmental outcomes. Here, we mimicked IGF-1 deficiency of preterm newborns in mice by perinatal administration of an IGF-1 receptor antagonist. This resulted in sex-biased brain microstructural, functional, and behavioral alterations, resembling those of ex-preterm children, which we characterized performing parallel mouse/human behavioral tests. Pharmacological enhancement of GABAergic tonic inhibition by the U.S. Food and Drug Administration-approved drug ganaxolone rescued functional/behavioral alterations in mice. Establishing an unprecedented mouse model of prematurity, our work dissects the mechanisms at the core of abnormal behaviors and identifies a readily translatable therapeutic strategy for preterm brain disorders.

Preclinical Development of the Na-K-2Cl Co-transporter-1 (NKCC1) Inhibitor ARN23746 for the Treatment of Neurodevelopmental Disorders.

Alterations in the expression of the Cl- importer Na-K-2Cl co-transporter-1 (NKCC1) and the exporter K-Cl co-transporter 2 (KCC2) lead to impaired intracellular chloride concentration in neurons and imbalanced excitation/inhibition in the brain. These alterations have been observed in several neurological disorders (e.g., Down syndrome and autism). Recently, we have reported the discovery of the selective NKCC1 inhibitor "compound ARN23746" for the treatment of Down syndrome and autism in mouse models. Here, we report on an extensive preclinical characterization of ARN23746 toward its development as a clinical candidate. ARN23746 shows an overall excellent metabolism profile and good brain penetration. Moreover, ARN23746 is effective in rescuing cognitive impairment in Down syndrome mice upon per os administration, in line with oral treatment of neurodevelopmental disorders. Notably, ARN23746 does not present signs of toxicity or diuresis even if administered up to 50 times the effective dose. These results further support ARN23746 as a solid candidate for clinical trial-enabling studies.

A rat model of a focal mosaic expression of PCDH19 replicates human brain developmental abnormalities and behaviours.

Protocadherin 19 gene-related epilepsy or protocadherin 19 clustering epilepsy is an infantile-onset epilepsy syndrome characterized by psychiatric (including autism-related), sensory, and cognitive impairment of varying degrees. Protocadherin 19 clustering epilepsy is caused by X-linked protocadherin 19 protein loss of function. Due to random X-chromosome inactivation, protocadherin 19 clustering epilepsy-affected females present a mosaic population of healthy and protocadherin 19-mutant cells. Unfortunately, to date, no current mouse model can fully recapitulate both the brain histological and behavioural deficits present in people with protocadherin 19 clustering epilepsy. Thus, the search for a proper understanding of the disease and possible future treatment is hampered. By inducing a focal mosaicism of protocadherin 19 expression using in utero electroporation in rats, we found here that protocadherin 19 signalling in specific brain areas is implicated in neuronal migration, heat-induced epileptic seizures, core/comorbid behaviours related to autism and cognitive function.

Pharmacological tools to target NKCC1 in brain disorders.

The chloride importer NKCC1 and the chloride exporter KCC2 are key regulators of neuronal chloride concentration. A defective NKCC1/KCC2 expression ratio is associated with several brain disorders. Preclinical/clinical studies have shown that NKCC1 inhibition by the United States FDA-approved diuretic bumetanide is a potential therapeutic strategy in preclinical/clinical studies of multiple neurological conditions. However, bumetanide has poor brain penetration and causes unwanted diuresis by inhibiting NKCC2 in the kidney. To overcome these issues, a growing number of studies have reported more brain-penetrating and/or selective bumetanide prodrugs, analogs, and new molecular entities. Here, we review the evidence for NKCC1 pharmacological inhibition as an effective strategy to manage neurological disorders. We also discuss the advantages and limitations of bumetanide repurposing and the benefits and risks of new NKCC1 inhibitors as therapeutic agents for brain disorders.

Design, Synthesis, In Vitro and In Vivo Characterization of Selective NKCC1 Inhibitors for the Treatment of Core Symptoms in Down Syndrome.

Intracellular chloride concentration [Cl-]i is defective in several neurological disorders. In neurons, [Cl-]i is mainly regulated by the action of the Na+-K+-Cl- importer NKCC1 and the K+-Cl- exporter KCC2. Recently, we have reported the discovery of ARN23746 as the lead candidate of a novel class of selective inhibitors of NKCC1. Importantly, ARN23746 is able to rescue core symptoms of Down syndrome (DS) and autism in mouse models. Here, we describe the discovery and extensive characterization of this chemical class of selective NKCC1 inhibitors, with focus on ARN23746 and other promising derivatives. In particular, we present compound 40 (ARN24092) as a backup/follow-up lead with in vivo efficacy in a mouse model of DS. These results further strengthen the potential of this new class of compounds for the treatment of core symptoms of brain disorders characterized by the defective NKCC1/KCC2 expression ratio.

Discovery of a Small Molecule Drug Candidate for Selective NKCC1 Inhibition in Brain Disorders.

Aberrant expression ratio of Cl- transporters, NKCC1 and KCC2, is implicated in several brain conditions. NKCC1 inhibition by the FDA-approved diuretic drug, bumetanide, rescues core symptoms in rodent models and/or clinical trials with patients. However, bumetanide has a strong diuretic effect due to inhibition of the kidney Cl- transporter NKCC2, creating critical drug compliance issues and health concerns. Here, we report the discovery of a new chemical class of selective NKCC1 inhibitors and the lead drug candidate ARN23746. ARN23746 restores the physiological intracellular Cl- in murine Down syndrome neuronal cultures, has excellent solubility and metabolic stability, and displays no issues with off-target activity in vitro. ARN23746 recovers core symptoms in mouse models of Down syndrome and autism, with no diuretic effect, nor overt toxicity upon chronic treatment in adulthood. ARN23746 is ready for advanced preclinical/manufacturing studies toward the first sustainable therapeutics for the neurological conditions characterized by impaired Cl- homeostasis.

Rescuing Over-activated Microglia Restores Cognitive Performance in Juvenile Animals of the Dp(16) Mouse Model of Down Syndrome.

Microglia are brain-resident immune cells and regulate mechanisms essential for cognitive functions. Down syndrome (DS), the most frequent cause of genetic intellectual disability, is caused by a supernumerary chromosome 21, containing also genes related to the immune system. In the hippocampus of the Dp(16) mouse model of DS and DS individuals, we found activated microglia, as assessed by their morphology; activation markers; and, for DS mice, electrophysiological profile. Accordingly, we found increased pro-inflammatory cytokine levels and altered interferon signaling in Dp(16) hippocampi. DS mice also showed decreased spine density and activity of hippocampal neurons and hippocampus-dependent cognitive behavioral deficits. Depletion of defective microglia or treatment with a commonly used anti-inflammatory drug rescued the neuronal spine and activity impairments and cognitive deficits in juvenile Dp(16) mice. Our results suggest an involvement of microglia in Dp(16)-mouse cognitive deficits and identify a new potential therapeutic approach for cognitive disabilities in DS individuals.

In vivo methods for acute modulation of gene expression in the central nervous system.

Accurate and timely expression of specific genes guarantees the healthy development and function of the brain. Indeed, variations in the correct amount or timing of gene expression lead to improper development and/or pathological conditions. Almost forty years after the first successful gene transfection in in vitro cell cultures, it is currently possible to regulate gene expression in an area-specific manner at any step of central nervous system development and in adulthood in experimental animals in vivo, even overcoming the very poor accessibility of the brain. Here, we will review the diverse approaches for acute gene transfer in vivo, highlighting their advantages and disadvantages with respect to the efficiency and specificity of transfection as well as to brain accessibility. In particular, we will present well-established chemical, physical and virus-based approaches suitable for different animal models, pointing out their current and future possible applications in basic and translational research as well as in gene therapy.

APache Is an AP2-Interacting Protein Involved in Synaptic Vesicle Trafficking and Neuronal Development.

Synaptic transmission is critically dependent on synaptic vesicle (SV) recycling. Although the precise mechanisms of SV retrieval are still debated, it is widely accepted that a fundamental role is played by clathrin-mediated endocytosis, a form of endocytosis that capitalizes on the clathrin/adaptor protein complex 2 (AP2) coat and several accessory factors. Here, we show that the previously uncharacterized protein KIAA1107, predicted by bioinformatics analysis to be involved in the SV cycle, is an AP2-interacting clathrin-endocytosis protein (APache). We found that APache is highly enriched in the CNS and is associated with clathrin-coated vesicles via interaction with AP2. APache-silenced neurons exhibit a severe impairment of maturation at early developmental stages, reduced SV density, enlarged endosome-like structures, and defects in synaptic transmission, consistent with an impaired clathrin/AP2-mediated SV recycling. Our data implicate APache as an actor in the complex regulation of SV trafficking, neuronal development, and synaptic plasticity.