Low Potential of Basimglurant to Be Involved in Drug-Drug Interactions: Influence of Non-Michaelis-Menten P450 Kinetics on Fraction Metabolized

Enzyme Kinetics of Oxidative Metabolism-Cytochromes P450

The cytochrome P450 enzymes (CYPs) are the most important enzymes in the oxidative metabolism of hydrophobic drugs and other foreign compounds (xenobiotics). The versatility of these enzymes results in some unusual kinetic properties, stemming from the simultaneous interaction of multiple substrates with the CYP active site. Often, the CYPs display kinetics that deviate from standard hyperbolic saturation or inhibition kinetics. Non-Michaelis-Menten or "atypical" saturation kinetics include sigmoidal, biphasic, and substrate inhibition kinetics (see Chapter 2 ). Interactions between substrates include competitive inhibition, noncompetitive inhibition, mixed inhibition, partial inhibition, activation, and activation followed by inhibition (see Chapters 4 and 6 ). Models and equations that can result in these kinetic profiles will be presented and discussed.

Detailed In Vitro Pharmacological Characterization of Clinically Tested Negative Allosteric Modulators of the Metabotropic Glutamate Receptor 5

Negative allosteric modulation of the metabotropic glutamate 5 (mGlu5) receptor has emerged as a potential strategy for the treatment of neurologic disorders. Despite the success in preclinical studies, many mGlu5 negative allosteric modulators (NAMs) that have reached clinical trials failed due to lack of efficacy. In this study, we provide a detailed in vitro pharmacological characterization of nine clinically and preclinically tested NAMs. We evaluated inhibition of l-glutamate-induced signaling with Ca2+ mobilization, inositol monophosphate (IP1) accumulation, extracellular signal-regulated kinase 1/2 (ERK1/2) phosphorylation, and real-time receptor internalization assays on rat mGlu5 expressed in HEK293A cells. Moreover, we determined association rates (kon) and dissociation rates (koff), as well as NAM affinities with [3H]methoxy-PEPy binding experiments. kon and koff values varied greatly between the nine NAMs (34- and 139-fold, respectively) resulting in long receptor residence times (>400 min) for basimglurant and mavoglurant, medium residence times (10-30 min) for AZD2066, remeglurant, and (RS)-remeglurant, and low residence times (<10 mins) for dipraglurant, F169521, F1699611, and STX107. We found that all NAMs inhibited l-glutamate-induced mGlu5 receptor internalization, generally with a similar potency to IP1 accumulation and ERK1/2 phosphorylation, whereas Ca2+ mobilization was less potently inhibited. Operational model of allosterism analyses revealed that dipraglurant and (RS)-remeglurant were biased toward (affinity) receptor internalization and away (cooperativity) from the ERK1/2 phosphorylation pathway, respectively. Our study is the first to measure mGlu5 NAM binding kinetics and negative allosteric modulation of mGlu5 receptor internalization and adds significant new knowledge about the molecular pharmacology of a diverse range of clinically relevant NAMs. SIGNIFICANCE STATEMENT: The metabotropic glutamate 5 (mGlu5) receptor is important in many brain functions and implicated in several neurological pathologies. Negative allosteric modulators (NAMs) have shown promising results in preclinical models but have so far failed in human clinical trials. Here we provide the most comprehensive and comparative molecular pharmacological study to date of nine preclinically/clinically tested NAMs at the mGlu5 receptor, which is also the first study to measure ligand binding kinetics and negative allosteric modulation of mGlu5 receptor internalization.

Small-Molecule Ligands that Bind the RET Receptor Activate Neuroprotective Signals Independent of but Modulated by Coreceptor GFRα1

Glial cell line-derived neurotrophic factor (GDNF) binds the GFRα1 receptor, and the GDNF-GFRα1 complex binds to and activates the transmembrane RET tyrosine kinase to signal through intracellular Akt/Erk pathways. To dissect the GDNF-GFRα1-RET signaling complex, agents that bind and activate RET directly and independently of GFRα1 expression are valuable tools. In a focused naphthalenesulfonic acid library from the National Cancer Institute database, we identified small molecules that are genuine ligands binding to the RET extracellular domain. These ligands activate RET tyrosine kinase and afford trophic signals irrespective of GFRα1 coexpression. However, RET activation by these ligands is constrained by GFRα1, likely via an allosteric mechanism that can be overcome by increasing RET ligand concentration. In a mouse model of retinitis pigmentosa, monotherapy with a small-molecule RET agonist activates survival signals and reduces neuronal death significantly better than GDNF, suggesting therapeutic potential. SIGNIFICANCE STATEMENT: A genuine ligand of RET receptor ectodomain was identified, which acts as an agonist. Binding and agonism are independent of a coreceptor glial cell line-derived neurotrophic factor family receptor α, which is required by the natural growth factor glial cell line-derived neurotrophic factor, and are selective for cells expressing RET. The lead agent protects neurons from death in vivo. This work validates RET receptor as a druggable therapeutic target and provides for potential leads to evaluate in neurodegenerative states. We also report problems that arise when screening chemical libraries.

Population Pharmacokinetic and Exposure-dizziness Modeling for a Metabotropic Glutamate Receptor Subtype 5 Negative Allosteric Modulator in Major Depressive Disorder Patients

Dizziness, the most frequently observed adverse event in patients with major depressive disorder, was observed with basimglurant, a selective, orally active metabotropic glutamate receptor subtype 5 negative allosteric modulator. The potential relationship between dizziness and basimglurant exposure was explored. The pharmacokinetics of basimglurant was characterized with nonlinear mixed effects modeling using data from 288 trial participants enrolled in five clinical trials. The pharmacokinetics of basimglurant after daily oral administration of a modified release formulation was best described by a two-compartment disposition model with a transit compartment, lag time for the absorption, and first-order elimination. The largest covariate effects were the effect of smoking and male gender on apparent clearance followed by the effect of body weight on distribution volumes. Clearance was twofold higher in smokers and 40% higher in males. A logistic regression model showed a statistically significant correlation between basimglurant C_max and incidence of dizziness. An increased risk of dizziness is predicted with increasing doses.