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Document<br />

Page 343<br />

14<br />

Structural Aspects in the Inhibitor <strong>Design</strong> of Catechol O-Methyltransferase<br />

Jukka Vidgren and Martti Ovaska<br />

Orion Corporation Orion Pharma, Espoo, Finland<br />

I. Introduction<br />

Catechol O-methyltransferase (COMT) plays an important role in the catabolic inactivation of<br />

catecholamines. It is present both in extracerebral tissues and in the central nervous system. During the<br />

last few years there has been a remarkable interest in COMT. Basic biochemical and molecular biology<br />

research has given detailed insights into the function and nature of the enzyme. The knowledge of the<br />

crystallographic structure has allowed researchers to analyze the molecular mechanism of the catalytic<br />

reaction and to accomplish the structure-<strong>based</strong> design of inhibitors. The development of potent and<br />

selective inhibitors has provided effective pharmacological tools to investigate the physiological role of<br />

the enzyme. The main clinical interest has been the possible application of COMT inhibitors as adjuncts<br />

in the L-dopa therapy of Parkinson's disease. Parkinson's disease is a dopamine deficiency disorder. The<br />

dopamine-producing neurons in striatum are destroyed. The medication strategy is to replenish the<br />

missing dopamine. L-Dopa, given together with a peripheral inhibitor of dopa decarboxylase (DDC), for<br />

example, carbidopa, is a standard therapy in Parkinson's disease. While dopamine does not penetrate<br />

into the brain, L-dopa penetrates the blood-brain barrier and is decarboxylated into dopamine in the<br />

brain. The half-life of L-dopa is short and in the presence of DDC inhibitor a large amount of the drug is<br />

eliminated <strong>by</strong> COMT. The COMT enzyme produces the metabolite 3-methoxytyrosine (3-OMD), which<br />

has no benefit in the treatment of Parkinson's disease, but has a long elimination half-life and may be<br />

harmful during chronical treatment. Also a gradual loss of the efficacy of L-dopa occurs during longterm<br />

medication. Since the early 1980s active<br />

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