Effects of a novel mGlu₂/₃ receptor agonist prodrug, LY2140023 monohydrate, on central monoamine turnover as determined in human and rat cerebrospinal fluid

Rationale: Accumulating evidence suggests that the primary symptoms of schizophrenia may be associated with altered central glutamate transmission. LY2140023 monohydrate is the methionine prodrug of the selective mGlu(2/3) receptor agonist LY404039 and is currently being assessed for the treatment of schizophrenia.

Objective: The objective of this study was to evaluate the central pharmacological activity of LY2140023 monohydrate in preclinical and clinical studies.

Methods: Effects on neurotransmitter/metabolite concentrations were assessed in male rats following single oral doses of LY2140023 monohydrate (microdiasylates from the prefrontal cortex), single intraperitoneal injection of LY404039 [cerebrospinal fluid (CSF)], or LY2140023 monohydrate dosed once daily for 7 days (CSF). A clinical study in 16 healthy subjects assessed the effects of LY2140023 monohydrate 40 mg orally twice daily for 14 days in lumbar CSF.

Results: Rat studies: Acute dosing with LY2140023 monohydrate resulted in significant dose-dependent increases in extracellular concentrations of dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA), but not 5-hydroxyindoleacetic acid (5-HIAA), in the prefrontal cortex. LY2140023 monohydrate dosing for 7 days elevated the concentrations of HVA in CSF, while acutely dosed LY404039 increased the concentrations of DOPAC, HVA, and methoxy-hydroxyphenylglycol (MHPG), but not 5-HIAA. Clinical study: Significant increases were seen for DOPAC, HVA, 5-HIAA, and MHPG in the CSF of subjects receiving LY2140023 monohydrate, but not placebo.

Conclusions: LY2140023 monohydrate and/or LY404039 dosing potently affected dopamine turnover and also significantly affected serotonin turnover in the human and rat central nervous systems. The measurement of biogenic amine metabolites such as DOPAC and HVA may serve as useful biomarkers of LY2140023 monohydrate and/or LY404039 central pharmacodynamic activity.