Potent catechol-O-methyltransferase Inhibitor Research Articles

The inhibition of catechol O-methyltransferase and monoamine oxidase by tetralone and indanone derivatives substituted with the nitrocatechol moiety

The enzymes, catechol O-methyltransferase (COMT) and monoamine oxidase (MAO) are important drug targets, and inhibitors of these enzymes are established therapy for symptomatic Parkinson’s disease (PD). COMT inhibitors enhance the bioavailability of levodopa to the brain, and therefore are combined with levodopa for the treatment of motor fluctuations in PD. Inhibitors of the MAO-B isoform, in turn, are used as monotherapy or in conjunction with levodopa in PD, and function by reducing the central degradation of dopamine. It has been reported that 1-tetralone and 1-indanone derivatives are potent and specific inhibitors of MAO-B, while compounds containing the nitrocatechol moiety (e.g. tolcapone and entacapone) are often potent COMT inhibitors. The present study attempted to discover compounds that exhibit dual COMT and MAO-B inhibition by synthesizing series of 1-tetralone, 1-indanone and related derivatives substituted with the nitrocatechol moiety. These compounds are structurally related to series of nitrocatechol derivatives of chalcone that have recently been investigated as potential dual COMT/MAO inhibitors. The results show that 4-chromanone derivative (7) is the most promising dual inhibitor with IC50 values of 0.57 and 7.26 μM for COMT and MAO-B, respectively, followed by 1-tetralone derivative (4d) with IC50 values of 0.42 and 7.83 μM for COMT and MAO-B, respectively. Based on their potent inhibition of COMT, it may be concluded that nitrocatechol compounds investigated in this study are appropriate for peripheral COMT inhibition, which represents an important strategy in the treatment of PD.

Tissue and interspecies comparison of catechol-O-methyltransferase mediated catalysis of 6-O-methylation of esculetin to scopoletin and its inhibition by entacapone and tolcapone

Catechol-O-methyltransferase (COMT) methylates both endogenous and exogenous catechol compounds to inactive and safe metabolites. We first optimised conditions for a convenient and sensitive continuous fluorescence-based 6-O-methylation assay of esculetin, which we used for investigating the COMT activity in human, mouse, rat, dog, rabbit, and sheep liver cytosols and microsomes and in ten different rat tissues. Furthermore, we compared the inhibition potencies and mechanisms of two clinically used COMT inhibitors, entacapone and tolcapone, in these species. In most tissues, the COMT activity was at least three times higher in cytosol than in microsomes. In the rat, the highest COMT activity was found in the liver, followed by kidney, ileum, thymus, spleen, lung, pancreas, heart, brain, and finally, skeletal muscle. Entacapone and tolcapone were characterised as highly potent mixed type tight-binding inhibitors. The competitive inhibition type dominated over the uncompetitive inhibition with entacapone, whereas uncompetitive inhibition dominated with tolcapone. Rats, dogs, pigs, and sheep are high COMT activity species, in contrast to humans, mice, and rabbits; COMT activity is highest in the liver. Both entacapone and tolcapone are potent COMT inhibitors, but their inhibition mechanisms differ.

Evaluation of nitrocatechol chalcone and pyrazoline derivatives as inhibitors of catechol-O-methyltransferase and monoamine oxidase

Literature reports that chalcones inhibit the monoamine oxidase (MAO) enzymes, mostly with specificity for the MAO-B isoform, while nitrocatechol compounds are established inhibitors of catechol–O-methyltransferase (COMT). Based on this, nitrocatechol derivatives of chalcone have been proposed to represent dual-target-directed compounds that may inhibit both MAO-B and COMT. Both these enzymes play key roles in the metabolism of dopamine and levodopa, and inhibitors are thus relevant to the treatment of Parkinson’s disease. The present study expands on the discovery of dual MAO-B/COMT inhibitors by synthesising additional nitrocatechol derivatives of chalcones which include heterocyclic derivatives, and converting them to the corresponding pyrazoline derivatives. The newly synthesised chalcone and pyrazoline compounds were evaluated as inhibitors of human MAO and rat COMT, and the inhibition potencies were expressed as IC50 values. A pyrazoline derivative, compound 8b, was the most potent COMT inhibitor with an IC50 value of 0.048 μM. This is more potent than the reference COMT inhibitor, entacapone, which has an IC50 value of 0.23 μM. The results indicated that the pyrazoline derivatives (IC50 = 0.048–0.21 µM) are more potent COMT inhibitors than the chalcones (IC50 = 0.14–0.29 µM). Unfortunately, the chalcone and pyrazoline derivatives were weak MAO inhibitors with IC50 values > 41.4 µM. This study concludes that the nitrocatechol derivatives investigated here are promising COMT inhibitors, while not being suitable as MAO inhibitors. Using molecular docking, potential binding modes and interactions of selected inhibitors with COMT are proposed.

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.

Development of a PC12 Cell Based Assay for Screening Catechol-O-methyltransferase Inhibitors.

The male rat adrenal pheochromocytoma cell-derived PC12 cell line can synthesize and release catecholamine neurotransmitters, and it has been widely used as a model system in cell biology and toxicology research. Catechol-O-methyltransferase (COMT) is involved in the inactivation of the catecholamine neurotransmitters, and it is particularly important for the regulation of dopamine. In this study, we explored the feasibility of using PC12 cells as an in vitro drug screening platform to compare the activity of multiple COMT inhibitors. Incubation of PC12 cells with tolcapone, a highly potent and selective COMT inhibitor, increased the concentrations of dopamine and its metabolite 3,4-dihydroxyphenylacetic acid (DOPAC) while reducing the metabolites 3-methoxytyramine (3-MT) and homovanillic acid (HVA) in the cell culture medium. LIBD-3, a novel, non-nitrocatechol COMT inhibitor, produced similar effects compared to tolcapone. LIBD-4, a less potent inhibitor, exhibited the expected right-shift in functional inhibition in the assay. These results match the known in vivo effects of COMT inhibition in rodents. Together, these data support the continued use of PC12 cells as an in vitro screen that bridges cell-free enzyme assays and more costly in vivo assays.

Management of Fluctuating Parkinson’s Disease: From Science to Clinical Wisdom

This symposium took place at the 4th Congress of the European Academy of Neurology (EAN) 2018 in Lisbon, Portugal, and focussed on the effective management of fluctuating Parkinson’s disease (PD). Prof Poewe introduced the topic by explaining how response fluctuations, including wearing-off, remain a key priority in the effective management of PD. Wearing-off fluctuations are often categorised as motor or non-motor, but the reality is that patients are frequently affected by both, with a significant impact on daily activities and quality of life. Prof Stocchi went on to explain that management strategies include adjunct therapies with catechol-O-methyl transferase (COMT) inhibitors, monoamine oxidase (MAO)-B inhibitors, and dopamine agonists. Clinical experience shows that within a few years most patients will be receiving a cocktail of these drugs to manage PD symptoms. Although many antiparkinsonian drug classes have overlapping indications, they have distinct mechanisms of action that can complement each other. Opicapone is a third generation, highly potent and effective COMT inhibitor that received European Union (EU) market approval in 2016 as an adjunct to levodopa for PD patients experiencing response fluctuations. While the efficacy and safety of once-daily opicapone have been proven in clinical studies, Prof Ebersbach gave an overview of real-life data from his own clinics, which show that the benefits of opicapone can be observed within 3 days of treatment initiation. The final presentation from Dr Morgante considered the management of non-motor symptoms in PD. Classically, these non-motor symptoms have been managed as non-urgent symptoms but are now recognised as a significant source of disability. It is vital for clinicians to recognise that many of these symptoms respond to treatment.

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.

Inhibition of human catechol-O-methyltransferase-mediated dopamine O-methylation by daphnetin and its Phase II metabolites

1. Finding and developing inhibitors of catechol-O-methyltransferase (COMT) from natural products is highly recommended. Daphnetin, a naturally occurring catechol from the family thymelaeaceae, has a chemical structure similar to several potent COMT inhibitors reported previously. Here the potential of daphnetin and its Phase II metabolites as inhibitors of COMT was investigated with human liver cytosol (HLC).2. Daphnetin and its methylated metabolite (8-O-methyldaphnetin) were found to inhibit COMT-mediated dopamine O-methylation in a dose-dependent manner. The IC50 values for daphnetin (0.51∼0.53 μM) and 8-O-methyldaphnetin (22.5∼24.3 μM) were little affected by changes in HLC concentrations. Further kinetic analysis showed the differences in inhibition type and parameters (Ki) between daphnetin (competitive, 0.37 μM) and 8-O-methyldaphnetin (noncompetitive, 25.7 μM). Other metabolites, including glucuronidated and sulfated species, showed negligible inhibition against COMT. By using in vitro–in vivo extrapolation (IV-IVE), a 24.3-fold increase in the exposure of the COMT substrates was predicted when they are co-administrated with daphnetin.3. With high COMT-inhibiting activity, daphnetin could serve as a lead compound for the design and development of new COMT inhibitors. Also, much attention should be paid to the clinical impact of combination of daphnetin and herbal preparations containing daphnetin with the drugs primarily cleared by COMT.

Metabolism of N-Acylated-Dopamine

N-oleoyl-dopamine (OLDA) is a novel lipid derivative of dopamine. Its biological action includes the interaction with dopamine and the transient receptor potential vanilloid (TRPV1) receptors. It seems to be synthesized in a dopamine-like manner, but there has been no information on its degradation. The aim of the study was, therefore, to determine whether OLDA metabolism proceeds the way dopamine proper does. We addressed the issue by examining the occurrence of O-methylation of exogenously supplemented OLDA via catechol-O-methyltransferase (COMT) under in vitro, ex vivo, and in vivo conditions using rat brain tissue. The results show that OLDA was methylated by COMT in all conditions studied, yielding the O-methylated derivative. The methylation was reversed by tolcapone, a potent COMT inhibitor, in a dose-dependent manner. We conclude that OLDA enters the metabolic pathway of dopamine. Methylation of OLDA may enhance its bioactive properties, such as the ability to interact with TRPV1 receptors.

Abstract 4242: Clinically used nitrocatechols and EGCG synergistically inhibit lung cancer cells in vitro

Abstract Polyphenols are likely to be responsible for the anticancer effects of green tea, with (−)-epigallocatechin-3-gallate (EGCG) the most well-studied. EGCG reduces lung cancer cell viability effectively in vitro, yet it is methylated by catechol-O-methyl transferase (COMT), limiting its effectiveness in inhibiting cancer cell growth. The nitrocatechol drugs entacapone and tolcapone are potent inhibitors of COMT and are used to mitigate effects of Parkinson's disease. Here, we investigated the synergistic effects of entacapone/tolcapone and EGCG in human (H1299) and murine (CL-13) cell lines. The IC50s of entacapone, tolcapone, and EGCG were 76.8, 29.3, and 174.9 μM, respectively in H1299 cells, and 50.7, 19.7, and 181.5 μM, respectively in CL-13 cells following treatment for 72 h. The IC50s were dramatically reduced when entacapone and tolcapone were used in combination with EGCG. The interactions were determined to be synergistic using isobolographic analysis. Inhibition of COMT-mediated methylation of EGCG by entacapone and tolcapone was also measured by LC-MS over 30 min and the IC50 values were 10 and 20 μM, respectively. The anticancer effects of the nitrocatechols and EGCG were also evaluated in pathways of apoptosis (TUNEL) and cell cycle (flow cytometry). In conclusion, the combination of EGCG and entacapone or tolcapone has greater lung cancer growth inhibitory activity than treatment with any of the single compounds. The mechanistic basis for this synergy is likely due in part to COMT inhibition, yet other mechanisms are also likely to play a role. Funded by NIH grant AT004678. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 4242. doi:10.1158/1538-7445.AM2011-4242

Role of tolcapone in the treatment of Parkinson’s disease

For decades, the cornerstone of treatment for Parkinson’s disease (PD) has been levodopa, which provides a smooth clinical response early in the course of disease. However, many PD patients develop motor complications on long-term levodopa therapy. Catechol-O-methyltransferase (COMT) is a selective and widely distributed enzyme involved in the catabolism of levodopa. Tolcapone and entacapone are selective and potent COMT inhibitors that slow the metabolism of levodopa, thus prolonging its effects. While both drugs act peripherally, tolcapone also inhibits COMT in the CNS. Tolcapone has been shown to be an effective adjunct in the treatment of PD in Phase II and III clinical trials, improving motor fluctuations and reducing levodopa requirements. Rare reports of severe hepatotoxicity, however, limited tolcapone’s implementation in the treatment of PD. A reappraisal of the data for tolcapone treatment in PD has found that this risk is very small if proper hepatic monitoring guidelines are followed. This article reviews the pharmacology and clinical data on tolcapone, with particular focus on drug safety and the future role of tolcapone therapy in the treatment of PD.

Synthesis and Biological Evaluation of Potent Bisubstrate Inhibitors of the Enzyme CatecholO-Methyltransferase (COMT) Lacking a Nitro Group

Inhibition of the enzyme catechol O-methyltransferase (COMT) represents a viable strategy for regulation of the catabolism of catecholamine neurotransmitters or their precursors, and is of considerable interest in the therapy of Parkinson's disease. Herein, we report the development of a new generation of potent bisubstrate inhibitors of COMT derived from nitro-substituted ligand 1 (Ki = 28 nM, Table 1), which achieve high biological activity despite the lack of a NO2 substituent on the catechol moiety. Their synthesis takes advantage of a convergent approach, in which a series of functionalized catechol intermediates is prepared (Schemes 2–7) and coupled to a common adenosine-derived allylic amine building block (Scheme 8). Biological activities of the newly synthesized inhibitors, determined by in vitro enzymatic assay and kinetic studies, clearly demonstrate that high inhibitory potency of the bisubstrate inhibitors is not correlated with the pKa of the catechol OH groups. Aromatic residues, connected to the catechol via a biaryl-type linkage, were found to maximally benefit from additional favorable hydrophobic interactions with the enzyme and thus to be preferred replacements of the NO2 group in 1. A competitive kinetic inhibition mechanism (Fig. 2) with respect to the cofactor binding site was confirmed in all cases, supporting a bisubstrate inhibition mode for inhibitors 2–19.

Catechol-O-methyltransferase inhibition in erythrocytes and liver by BIA 3-202 (1-[3,4-dibydroxy-5-nitrophenyl]-2-phenyl-ethanone).

The present study evaluated the relationship between the degree of catechol-O-methyltransferase (COMT) inhibition in erythrocytes and liver by BIA 3-202 (1-[3,4-dihydroxy-5-nitrophenyl]-2-phenyl-ethanone) and determined its effects upon the O-methylation of L-DOPA in rats orally treated with L-DOPA plus benserazide. The soluble form of COMT (S-COMT) in erythrocytes was endowed with the same affinity as liver S-COMT for the substrate adrenaline. BIA 3-202 inhibited erythrocytes and liver S-COMT with ED50's of 1.9 (0.7, 3.1) and 1.9 (0.5, 3.2) (95% confidence limits) mg kg(-1), respectively. BIA 3-202 reduced the L-DOPA-induced rise of 3-O-methyl-L-DOPA in the peripheral circulation, striatal dialysate levels and striatum, and increased dopamine striatal levels. In BIA 3-202-treated rats the increase in L-DOPA in peripheral blood and striatal dialysates was significantly greater than in vehicle-treated rats. It is concluded that S-COMT activity in erythrocytes may provide important information on the pharmacodynamic profile of COMT inhibitors. The novel COMT inhibitor BIA 3-202 is a potent COMT inhibitor that enhances the availability of L-DOPA to the brain by reducing its O-methylation, which may prove beneficial in patients with Parkinson's disease treated with L-DOPA.

Kinetic inhibitory profile of BIA 3-202, a novel fast tight-binding, reversible and competitive catechol- O-methyltransferase inhibitor

The present study reports the kinetic inhibitory profile of 1-[3,4-dihydroxy-5-nitrophenyl]-2-phenyl-ethanone (BIA 3-202), a novel inhibitor of soluble catechol- O-methyltransferase (COMT) in rat liver. After an oral single dose (30 mg kg −1), there was a time-dependent recovery of enzyme activity from 98±2% inhibition at 30 min to total recovery at 24 h after treatment. The inhibitory effect produced by BIA 3-202 on soluble COMT was reversible after gel filtration of the samples. BIA 3-202 acted as a fast inhibitor of rat liver soluble COMT, interacting immediately with the enzyme after mixing. No differences were observed in the metanephrine formation rates (in nmol mg protein −1 min −1) obtained without and with a 60-min preincubation with 30 nM of BIA 3-202 (1.30±0.02 and 1.35±0.03, respectively). The tight-binding nature of the inhibition produced by BIA 3-202 was evaluated by performing an Ackermann–Potter plot. The true K i for BIA 3-202, derived from the nonlinear regression analysis, was 0.19±0.02 nM. In substrate competition studies, an increase in the concentration of adrenaline resulted in a linear increase in IC 50 values for BIA 3-202. In conclusion, BIA 3-202 behaves as a reversible, potent and fast tight-binding COMT inhibitor that acts competitively at the substrate binding site of rat liver soluble COMT.

Clinical pharmacology, therapeutic use and potential of COMT inhibitors in Parkinson's disease.

When peripheral decarboxylation is blocked by carbidopa or benserazide, the main metabolic pathway of levodopa is O-methylation by catechol-O-methyltransferase (COMT). Entacapone and tolcapone are new potent, selective and reversible nitrocatechol-type COMT inhibitors. Animal studies have demonstrated that entacapone mainly has a peripheral effect whereas tolcapone also inhibits O-methylation in the brain. In human volunteers, both entacapone and tolcapone dose-dependently inhibit the COMT activity in erythrocytes, improve the bioavailability and decrease the elimination of levodopa, and inhibit the formation of 3-O-methyldopa (3-OMD). Entacapone is administered with every scheduled dose of levodopa whereas tolcapone is administered 3 times daily. The different administration regimens for these agents are based on their different pharmacokinetic and pharmacodynamic profiles. Both entacapone and tolcapone enhance and extend the therapeutic effect of levodopa in patients with advanced and fluctuating Parkinson's disease. They prolong the duration of levodopa effect. Clinical studies show that they increase the daily ON time by an average 1 to 3 hours, improve the activities of daily living and allow daily levodopa dosage to be decreased. Correspondingly, they significantly reduce the daily OFF time. No comparative studies between entacapone and tolcapone have been performed. Tolcapone also appears to have a beneficial effect in patients with nonfluctuating Parkinson's disease. The main adverse effects of the COMT inhibitors are related to their dopaminergic and gastrointestinal effects. Enhancement of dopaminergic activity may cause an initial worsening of levodopa-induced adverse effects, such as dyskinesia, nausea, vomiting, orthostatic hypotension, sleep disorders and hallucinations. Levodopa dose adjustment is recommended to avoid these events. Tolcapone is associated with diarrhoea in about 16 to 18% of patients and entacapone in less than 10% of patients. Diarrhoea has led to discontinuation in 5 to 6% of patients treated with tolcapone and in 2.5% of those treated with entacapone. Urine discoloration to dark yellow or orange is related to the colour of COMT inhibitors and their metabolites. Elevated liver transaminase levels are reported in 1 to 3% of patients treated with tolcapone but very rarely, if at all, in patients treated with entacapone. The descriptions of acute, fatal fulminant hepatitis and potentially fatal neurological reactions, such as neuroleptic malignant syndrome and rhabdomyolysis, in association with tolcapone led to the suspension of its marketing authorisation in the European Community and Canada. In many other countries, the use of tolcapone is restricted to patients who are not responding satisfactorily to other therapies. Regular monitoring of liver enzymes is required if tolcapone is used. No such adverse reactions have so far been described for entacapone and no laboratory monitoring has been proposed. COMT inhibitors added to levodopa therapy are beneficial, particularly in patients with fluctuating disease. They may be combined with other antiparkinsonian drugs, such as dopamine agonists, selegiline and anticholinergics without adverse interactions. They provide a new treatment possibility in patients with Parkinson's disease who have problems with their present levodopa therapy.

Interventions to achieve tonic exposure to levodopa: delaying or preventing the onset of motor complications.

Variations in levodopa delivery and subsequent dopamine exposure may lead to motor fluctuations and dyskinesias in patients with Parkinson's disease, as the therapeutic window for levodopa narrows with disease progression. Long-term exposure to the oscillations in levodopa-derived dopamine also is suggested to cause postsynaptic changes within the dopaminergic system, leading to further reductions in the drug's efficacy. The need to extend the actions of levodopa led to the development of the catechol-O-methyltransferase (COMT) inhibitors, which are the newest agents introduced to manage the symptoms of Parkinson's disease. Entacapone and tolcapone are two potent, selective, and reversible COMT inhibitors that effectively augment levodopa's pharmacokinetics by increasing area under the plasma concentration versus time curve and plasma elimination half-life without significantly affecting peak levodopa concentrations. This enhanced pharmacokinetic effect results in marked improvements in patients' clinical response. In patients experiencing end-of-dose wearing-off, the addition of either entacapone or tolcapone led to improvements in "on" time, "off" time, and the Unified Parkinson's Disease Rating Scale scoring system, even though many patients already were receiving optimum dosages of various other antiparkinsonian drugs. In patients with stable responses to long-term levodopa, addition of tolcapone significantly reduced the onset of motor fluctuations. These data, combined with the potential for delaying the onset of motor fluctuations, suggest that COMT inhibition may enhance levodopa's short- and long-term efficacy.

Catechol-O-methyltransferase activity in rat brain primary neuronal and glial cell cultures and its inhibitation by novel drugs

To analyze the intracellular catechol-O-methyltransferase (COMT) activity in cultured cells, a substrate (dihydroxybenzoic acid) was added to the tissue culture plates and the product (vanillic acid) was anlayzed with reversed-phase HPLC with coulometric detection. The cultures, prepared from various regions of the brain, were immunohistochemically characterized. Basal COMT activites were similar in all glial cultures while in some neuron-enriched cultures the enzyme activity was lower. Preincubation with nitrocatechol COMR inhibitors, entacapone or tolcapone (30-300 nM), decreased COMT activity in all culture types with slightly different potencies. An atypical inhibitor of O-methylation, CGP 28104, had no oeffect on COMT activity in any of these cultures. In conclusion: 1) this method enables straight-forward analysis of a large number of COMT activity samples in cultured cells, 2) COMT activity is almost equally distributed throughout the brain, and 3) tolcapone was a more potent COMT inhibitor than entacapone in cultures containing glial cells.

A semiempirical study on inhibition of catechol O-methyltransferase by substituted catechols.

Catechol and endogenous catechol derivatives are readily methylated by catechol O-methyltransferase (COMT). In contrast, many catechol derivatives possessing electronegative substituents are potent COMT inhibitors. The X-ray structure of the active site of COMT suggests that the methylation involves a lysine as a general base. The lysine can activate one of the catecholic hydroxyl groups for a nucleophilic attack on the active methyl group of the coenzyme S-adenosyl-L-methionine (AdoMet). We studied the effect of dinitrosubstitution of the catecholic ring at the semiempirical PM3 level on the methylation reaction catalysed by COMT. The electronegative nitro groups make the ionized catechol hydroxyls less nucleophilic than the corresponding hydroxyl groups of the non-substituted catechol. As a consequence, dinitrocatechol is not methylated but is instead a potent COMT inhibitor. The implications of this mechanism to the design of COMT inhibitors are discussed.

Clinical Potential of Catechol-O-Methyltransferase (COMT) Inhibitors as Adjuvants in Parkinsonʼs Disease

A series of new and selective catechol-O-methyltransferase (COMT) inhibitors have been developed. Entacapone, nitecapone and to1capone are nitrocatechol- type agents that are potent COMT inhibitors in vitro and are active in vivo after oral administration. CGP 28014 is a pyridine derivative that is active only in vivo.In animal studies, these compounds inhibit effectively the O-methylation of levodopa, thus improving its bioavailability and brain penetration, and potentiating its behavioural effects. Entacapone and nitecapone have mainly peripheral effects, whereas to1capone and CGP 280 14 inhibit O-methylation also in the brain. In human volunteers, entacapone, nitecapone and tolcapone inhibit dose-dependently COMT activity of erythrocytes. COMT inhibitors also decrease the levels of COMT-dependent metabolites of adrenaline (epinephrine) and noradrenaline (norepinephrine) in plasma.Entacapone, to1capone and CGP 28014 improve the bioavailability of levodopa and inhibit the formation of 3-0-methyldopa in human volunteers. In initial clinical studies in patients with Parkinson's disease, both entacapone and tolcapone potentiated and prolonged the therapeutic effects of levodopa.

Dihydroxynitrobenzaldehydes and hydroxymethoxynitrobenzaldehydes: synthesis and biological activity as catechol-O-methyltransferase inhibitors.

A series of nitro derivatives of dihydroxy- and hydroxymethoxybenzaldehyde was synthesized and tested as potential inhibitors of partially purified pig liver catechol-O-methyltransferase (COMT). All the dihydroxynitrobenzaldehydes prepared were potent inhibitors of COMT, but only one hydroxymethoxynitrobenzaldehyde (3-hydroxy-4-methoxy-5-nitrobenzaldehyde) showed activity as a COMT inhibitor. Although previously reported data showed that the presence of electron-withdrawing substituents at position 5 seemed to be very important for activity as COMT inhibitor, our results suggest that the requirement necessary to enhance the activity of the dihydroxyni-trobenzaldehyde derivatives toward COMT is the presence of the nitro group in a position ortho with respect to one hydroxyl group. The assayed compounds showed a reversible inhibition of COMT, which was mixed for all the dihydroxynitro derivatives but noncompetitive for 3-hydroxy-4-methoxy-5-nitrobenzaldehyde when pyrocatechol was the variable substrate and uncompetitive in all the inhibitors with respect to S-adenosyl-L-methionine.