Effects of Cytochrome P450 3A4 Induction and Inhibition on the Pharmacokinetics of BI 425809, a Novel Glycine Transporter 1 Inhibitor

Development of the novel GlyT1 inhibitor, iclepertin (BI 425809), for the treatment of cognitive impairment associated with schizophrenia

Schizophrenia is a psychiatric disorder characterised by symptoms in three domains: positive (e.g. delusions, hallucinations), negative (e.g. social withdrawal, lack of motivation) and cognitive (e.g. working memory and executive function impairment). Cognitive impairment associated with schizophrenia (CIAS) is a major burden for patients and negatively impacts many aspects of a patient's life. Antipsychotics are the standard-of-care treatment for schizophrenia but only address positive symptoms. So far there are no approved pharmacotherapies for the treatment of CIAS. Iclepertin (BI 425809) is a novel, potent and selective glycine transporter 1 (GlyT1) inhibitor, under development by Boehringer Ingelheim for the treatment of CIAS. Phase I studies have shown it to be safe and well tolerated in healthy volunteers, and central target engagement (inhibition of GlyT1) was achieved in a dose-dependent manner from 5 to 50 mg in healthy volunteers. A Phase II study has demonstrated that iclepertin is safe and well tolerated in patients with schizophrenia and improves cognition at doses of 10 mg and 25 mg. Phase III studies are ongoing to confirm these initial positive safety and efficacy findings with the 10 mg dose, and if successful, iclepertin could become the first approved pharmacotherapy used to treat CIAS.

Characterization of Divergent Metabolic Pathways in Elucidating an Unexpected, Slow-Forming, and Long Half-Life Major Metabolite of Iclepertin

PURPOSE

After single oral dosing of the glycine reuptake transporter (GlyT1) inhibitor, iclepertin (BI 425809), a single major circulating metabolite, M530a, was identified. However, upon multiple dosing, a second major metabolite, M232, was observed with exposure levels ~ twofold higher than M530a. Studies were conducted to characterize the metabolic pathways and enzymes responsible for formation of both major human metabolites.

METHODS

In vitro studies were conducted with human and recombinant enzyme sources and enzyme-selective inhibitors. The production of iclepertin metabolites was monitored by LC-MS/MS.

RESULTS

Iclepertin undergoes rapid oxidation to a putative carbinolamide that spontaneously opens to an aldehyde, M528, which then undergoes reduction by carbonyl reductase to the primary alcohol, M530a. However, the carbinolamide can also undergo a much slower oxidation by CYP3A to form an unstable imide metabolite, M526, that is subsequently hydrolyzed by a plasma amidase to form M232. This difference in rate of metabolism of the carbinolamine explains why high levels of the M232 metabolite were not observed in vitro and in single dose studies in humans, but were observed in longer-term multiple dose studies.

CONCLUSIONS

The long half-life iclepertin metabolite M232 is formed from a common carbinolamine intermediate, that is also a precursor of M530a. However, the formation of M232 occurs much more slowly, likely contributing to its extensive exposure in vivo. These results highlight the need to employ adequate clinical study sampling periods and rigorous characterization of unexpected metabolites, especially when such metabolites are categorized as major, thus requiring safety assessment.

Rational and Translational Implications of D-Amino Acids for Treatment-Resistant Schizophrenia: From Neurobiology to the Clinics

Schizophrenia has been conceptualized as a neurodevelopmental disorder with synaptic alterations and aberrant cortical–subcortical connections. Antipsychotics are the mainstay of schizophrenia treatment and nearly all share the common feature of dopamine D2 receptor occupancy, whereas glutamatergic abnormalities are not targeted by the presently available therapies. D-amino acids, acting as N-methyl-D-aspartate receptor (NMDAR) modulators, have emerged in the last few years as a potential augmentation strategy in those cases of schizophrenia that do not respond well to antipsychotics, a condition defined as treatment-resistant schizophrenia (TRS), affecting almost 30–40% of patients, and characterized by serious cognitive deficits and functional impairment. In the present systematic review, we address with a direct and reverse translational perspective the efficacy of D-amino acids, including D-serine, D-aspartate, and D-alanine, in poor responders. The impact of these molecules on the synaptic architecture is also considered in the light of dendritic spine changes reported in schizophrenia and antipsychotics’ effect on postsynaptic density proteins. Moreover, we describe compounds targeting D-amino acid oxidase and D-aspartate oxidase enzymes. Finally, other drugs acting at NMDAR and proxy of D-amino acids function, such as D-cycloserine, sarcosine, and glycine, are considered in the light of the clinical burden of TRS, together with other emerging molecules.