MLi-2, a Potent, Selective, and Centrally Active Compound for Exploring the Therapeutic Potential and Safety of LRRK2 Kinase Inhibition.

Mutations in the leucine-rich repeat kinase 2 (LRRK2) gene are the most common genetic cause of familial and sporadic Parkinson's disease (PD). That the most prevalent mutation, G2019S, leads to increased kinase activity has led to a concerted effort to identify LRRK2 kinase inhibitors as a potential disease-modifying therapy for PD. An internal medicinal chemistry effort identified several potent and highly selective compounds with favorable drug-like properties. Here, we characterize the pharmacological properties of cis-2,6-dimethyl-4-(6-(5-(1-methylcyclopropoxy)-1H-indazol-3-yl)pyrimidin-4-yl)morpholine (MLi-2), a structurally novel, highly potent, and selective LRRK2 kinase inhibitor with central nervous system activity. MLi-2 exhibits exceptional potency in a purified LRRK2 kinase assay in vitro (IC50 = 0.76 nM), a cellular assay monitoring dephosphorylation of LRRK2 pSer935 LRRK2 (IC50 = 1.4 nM), and a radioligand competition binding assay (IC50 = 3.4 nM). MLi-2 has greater than 295-fold selectivity for over 300 kinases in addition to a diverse panel of receptors and ion channels. Acute oral and subchronic dosing in MLi-2 mice resulted in dose-dependent central and peripheral target inhibition over a 24-hour period as measured by dephosphorylation of pSer935 LRRK2. Treatment of MitoPark mice with MLi-2 was well tolerated over a 15-week period at brain and plasma exposures >100× the in vivo plasma IC50 for LRRK2 kinase inhibition as measured by pSer935 dephosphorylation. Morphologic changes in the lung, consistent with enlarged type II pneumocytes, were observed in MLi-2-treated MitoPark mice. These data demonstrate the suitability of MLi-2 as a compound to explore LRRK2 biology in cellular and animal models.

Structure based evolution of a novel series of positive modulators of the AMPA receptor.

Starting from compound 1, we utilized biostructural data to successfully evolve an existing series into a new chemotype with a promising overall profile, exemplified by 19.

A novel series of positive modulators of the AMPA receptor: discovery and structure based hit-to-lead studies.

Starting from an HTS derived hit 1, application of biostructural data facilitated rapid optimization to lead 22, a novel AMPA receptor modulator. This is the first demonstration of how structure based drug design can be exploited in an optimization program for a glutamate receptor.

A novel series of positive modulators of the AMPA receptor: structure-based lead optimization.

Starting from lead compound 1, we demonstrate how X-ray structural data can be used to understand SAR and expediently optimize bioavailability in a novel series of AMPA receptor modulators, furnishing 5 with improved bioavailability and robust in vivo activity.

Antiglucocorticoids, neurogenesis and depression.

Recent evidence suggests that antiglucocorticoids, like conventional antidepressants, may recover depressive symptoms by boosting hippocampal neurogenesis. Here, we explore several possible antiglucocorticoid-based antidepressive therapeutic strategies. Firstly, we review specific glucocorticoid receptor/antagonist interactions. Secondly, we discuss a potential new therapeutic target, doublecortin-like kinase, which regulates glucocorticoid signaling in neuronal progenitor cells.

Discovery of a 3-(4-Pyrimidinyl) Indazole (MLi-2), an Orally Available and Selective Leucine-Rich Repeat Kinase 2 (LRRK2) Inhibitor that Reduces Brain Kinase Activity.

Leucine-rich repeat kinase 2 (LRRK2) is a large, multidomain protein which contains a kinase domain and GTPase domain among other regions. Individuals possessing gain of function mutations in the kinase domain such as the most prevalent G2019S mutation have been associated with an increased risk for the development of Parkinson's disease (PD). Given this genetic validation for inhibition of LRRK2 kinase activity as a potential means of affecting disease progression, our team set out to develop LRRK2 inhibitors to test this hypothesis. A high throughput screen of our compound collection afforded a number of promising indazole leads which were truncated in order to identify a minimum pharmacophore. Further optimization of these indazoles led to the development of MLi-2 (1): a potent, highly selective, orally available, brain-penetrant inhibitor of LRRK2.

Recent advances in positive allosteric modulators of the AMPA receptor.

The alpha-amino-3-hydroxy-5-methyl-4-isoxazole-propioic acid (AMPA) subtype of glutamate receptors mediate fast excitatory neurotransmission throughout the mammalian nervous system and participate in the forms of synaptic plasticity that are considered to underlie learning and memory. Positive allosteric modulators of these receptors are the subject of much investigation because of their emerging therapeutic potential for a range of psychiatric and neurological disorders such as schizophrenia and Alzheimer's disease. This review focuses on the most recent developments in preclinical and clinical research on novel classes of AMPA receptor positive modulators and highlights how the application of biostructural studies has increased our understanding of the biophysical effects produced by these drugs.

Development of a novel high-throughput assay for the investigation of GlyT-1b neurotransmitter transporter function.

The glycine transporter (GlyT-1b) is a Na(+)/Cl(-)-dependent electrogenic transporter which mediates the rapid re-uptake of glycine from the synaptic cleft. Based on its tissue distribution, GlyT-1 has been suggested to co-localise with the NMDA receptor where it may modulate the concentration of glycine at its co-agonist binding site. This data has led to GlyT-1 inhibitors being proposed as targets for disorders such as schizophrenia and cognitive dysfunction. Radiolabelled uptake assays (e.g. [(3)H]glycine) have been traditionally used in compound screening to identify glycine transporter inhibitors. While such an assay format is useful for testing limited numbers of compounds, the identification of novel glycine uptake inhibitors requires a functional assay compatible with high-throughput screening (HTS) of large compound libraries. Here, the authors present the development of a novel homogenous cell-based assay using the FLIPR membrane potential blue dye (Molecular Devices) and FLEXstation. Pharmacological data for the GlyT-1 inhibitors Org 24598 and ALX 5407 obtained using this novel electrogenic assay correlated well with the conventional [(3)H]-glycine uptake assay format. Furthermore, the assay has been successfully miniaturised using FLIPR(3) and therefore has the potential to be used for high-throughput screening.

Phosphoproteomics reveals that Parkinson's disease kinase LRRK2 regulates a subset of Rab GTPases.

Mutations in Park8, encoding for the multidomain Leucine-rich repeat kinase 2 (LRRK2) protein, comprise the predominant genetic cause of Parkinson's disease (PD). G2019S, the most common amino acid substitution activates the kinase two- to threefold. This has motivated the development of LRRK2 kinase inhibitors; however, poor consensus on physiological LRRK2 substrates has hampered clinical development of such therapeutics. We employ a combination of phosphoproteomics, genetics, and pharmacology to unambiguously identify a subset of Rab GTPases as key LRRK2 substrates. LRRK2 directly phosphorylates these both in vivo and in vitro on an evolutionary conserved residue in the switch II domain. Pathogenic LRRK2 variants mapping to different functional domains increase phosphorylation of Rabs and this strongly decreases their affinity to regulatory proteins including Rab GDP dissociation inhibitors (GDIs). Our findings uncover a key class of bona-fide LRRK2 substrates and a novel regulatory mechanism of Rabs that connects them to PD.

Comparison of alterations in c-fos and Egr-1 (zif268) expression throughout the rat brain following acute administration of different classes of antidepressant compounds.

The majority of immediate-early gene (IEG) studies focus on a few key brain regions associated with the class of psychoactive compound being studied. Recently, using a meta-analysis of the c-fos literature, we demonstrated the utility of c-fos profiling to classify such compounds. The present study examined acute delivery of a range of antidepressant classes; fluoxetine, imipramine, LiCl, and mirtazapine. The dual aims were to study the IEG profiles of these varying classes of antidepressants throughout the rat brain and to compare the utility of c-fos or Egr-1 as IEGs to classify clinically efficacious antidepressants. All antidepressants increased c-fos mRNA in the central amygdala, as previously shown, while c-fos was also increased in the anterior insular cortex and significantly decreased within the septum. Although acute antidepressant administration altered c-fos expression in a number of brain regions, Egr-1 expression was only significantly altered in the central amygdala, suggesting that Egr-1 may not be as useful a marker to investigate acute antidepressant treatment. The fact that these drugs, including the previously unclassified antidepressant mirtazapine, share a number of common loci of activation, which are implicated by human and animal studies in depression, adds further support to the use of IEG mapping to classify psychoactive compounds.

The relationship between glycine transporter 1 occupancy and the effects of the glycine transporter 1 inhibitor RG1678 or ORG25935 on object retrieval performance in scopolamine impaired rhesus monkey.

Reduced NMDA receptor functioning is hypothesized to underlie the cognitive and negative symptoms associated with schizophrenia. However, because direct activation of the NMDA receptor is accompanied by neurotoxicity, mechanisms that activate the glycine co-agonist site on the NMDA receptor could carry greater therapeutic potential. In the current study, the effects of two glycine transporter 1 (GlyT1) inhibitors, RG1678 and ORG25935, were characterized in the object-retrieval detour (ORD) task in scopolamine-impaired rhesus monkeys and, using positron emission tomography (PET), the GlyT1 occupancy to efficacy relationship of each compound was established. Scopolamine exerted a significant decrease in accuracy in the ORD task. Lower doses of RG1678 (0.3 and 1.0 mg/kg, p.o.) significantly attenuated the impact of scopolamine, whereas the highest dose tested (1.8 mg/kg) did not. The predicted GlyT1 occupancies of RG1678 at the effective doses were ~10 and 30 %. ORG25935 (0.1, 0.3, and 1 mg/kg, p.o.) also significantly attenuated the impact of scopolamine on the ORD task, whereas 3 mg/kg did not. The predicted GlyT1 occupancies of ORG25935 at the effective doses ranged from 16 to 80 %. These data suggest that GlyT1 inhibitors have the potential to improve performance on prefrontal cortex-dependent tests such as the ORD task, but that efficacy is lost when higher occupancies are achieved. Importantly, recent Ph2B data published by Roche suggests that low but not high doses of RG1678 improved negative symptoms in patients with schizophrenia, highlighting the potential translational nature of the current preclinical findings.