Novel, non-nitrocatechol catechol-O-methyltransferase inhibitors modulate dopamine neurotransmission in the frontal cortex and improve cognitive flexibility.

RATIONALE: Cognitive impairment is a primary feature of many neuropsychiatric disorders and there is a need for new therapeutic options. Catechol-O-methyltransferase (COMT) inhibitors modulate cortical dopaminergic function and have been proposed as potential cognitive enhancers. Unfortunately, currently available COMT inhibitors are not good candidates due to either poor blood-brain barrier penetration or severe toxicity. OBJECTIVES: To address the need for safe, brain-penetrant COMT inhibitors, we tested multiple novel compounds in a set of preclinical in vivo efficacy assays in rats to determine their ability to inhibit COMT function and viability as potential clinical candidates. METHODS: We measured the change in concentration of dopamine (DA) metabolites in cerebrospinal fluid (CSF) from the cisterna magna and extracellular fluid (ECF) from the frontal cortex produced by our novel compounds. Additionally, we tested the effects of our brain-penetrant COMT inhibitors in an attentional set-shifting assay (ASST). We benchmarked the performance of the novel COMT inhibitors to the effects produced by the known COMT inhibitor tolcapone. RESULTS: We found that multiple COMT inhibitors, exemplified by LIBD-1 and LIBD-3, significantly modulated dopaminergic function measured as decreases in homovanillic acid (HVA) and increases in 3,4-Dihydroxyphenylacetic acid (DOPAC), two DA metabolites, in CSF and the frontal cortex. Additionally, we found that LIBD-1 significantly improved cognitive flexibility in the ASST, an effect previously reported following tolcapone administration. CONCLUSIONS: These results demonstrate that LIBD-1 is a novel COMT inhibitor with promising in vivo activity and the potential to serve as a new therapy for cognitive impairment.

Synthesis and Evaluation of Bicyclic Hydroxypyridones as Inhibitors of Catechol O-Methyltransferase.

A series of bicyclic pyridones were identified as potent inhibitors of catechol O-methyltransferase (COMT). Substituted benzyl groups attached to the basic nitrogen of the core scaffold gave the most potent inhibitors within this series. Rat pharmacokinetic studies showed medium to high levels of clearance for this series, but with high free fraction due to remarkably low levels of protein and tissue binding. In rat biomarker studies, levels of unbound drug exposure are seen in the brain, which exceed their respective IC50s, leading to changes in the levels of dopamine metabolites in a manner consistent with COMT inhibition.

Optimization of 8-Hydroxyquinolines as Inhibitors of Catechol O-Methyltransferase.

A series of 8-hydroxy quinolines were identified as potent inhibitors of catechol O-methyltransferase (COMT) with selectivity for the membrane-bound form of the enzyme. Small substituents at the 7-position of the quinoline were found to increase metabolic stability without sacrificing potency. Compounds with good pharmacokinetics and brain penetration were identified and demonstrated in vivo modulation of dopamine metabolites in the brain. An X-ray cocrystal structure of compound 21 in the S-COMT active site shows chelation of the active site magnesium similar to catechol-based inhibitors. These compounds should prove useful for treatment of many neurological and psychiatric conditions associated with compromised cortical dopamine signaling.

Exercise protects against chronic restraint stress-induced oxidative stress in the cortex and hippocampus.

Chronic stress induces high levels of reactive oxygen species, creating a neurotoxic environment. Because exercise protects against the neurodegenerative effects of oxidative stress, we investigated the protective effects of exercise against chronic restraint stress (CRS)-induced expression of the proapoptotic cortical B-cell associated X protein (Bax) and cyclooxegenase-2 (Cox-2) as well as microglial/macrophage proliferation and co-expression of Cox-2 in the cortex and hippocampus of mice. CRS induced a large, moderately significant increase in protein levels of Bax 1 h following stress. However, exercised mice had significantly lower cortical levels of Bax at both the 1 and 24 h time points. The level of Cox-2 protein was also significantly lower in the cortex of exercised mice. While no significant changes in microglia/macrophage proliferation were observed in either brain region, CRS induced significant increases of Cox-2 labeling on microglia/macrophages in both the hippocampus and cortex of stressed mice. In the cortex, stressed mice showed significantly greater numbers of Iba1/Cox-2 co-labeled cells than non-stressed mice; however, exercise alone did not induce any changes. In the hippocampus, CRS induced significantly greater numbers of Cox-2 labeled microglia/macrophages in stressed sedentary animals as compared to non-stressed controls. However, exercised mice were protected against these increases, as there was no significant difference in the numbers of Iba1/Cox-2 co-labeled cells between stressed and non-stressed exercised mice. Therefore, exercise protects against CRS-induced increases in levels of Bax in the cortex, and microglial/macrophage expression of Cox-2 in the hippocampus. Taken together, these data suggest that exercise may confer neuroprotection by acting to increase the resilience of the brain against CRS-induced oxidative stress.