[Sigma-ligands for new therapeutic drugs]

Compounds that show their pharmacological actions via specific receptors are considered potential candidates for new drugs. Recently, several compounds that have specific binding sites and show certain pharmacological actions have been identified, but neither their binding sites, their endogenous substances, nor the functional role of the binding sites have been clarified. Regardless of the exact role of the binding sites of the compounds, research into the sites has opened up new areas of receptor investigation, and also new strategies for developing drugs. The sigma-ligand is one such kind of compound, and the existence of a binding site for the ligand was first postulated to account for the psychotomimetic effects of N-allylnormetazocine and related racemic benzomorphans. The binding site of the sigma-ligand is widely distributed in the central nervous system and peripheral systems. However, it still remain to be established whether sigma-ligand binding sites are to be referred to as "receptors". The classification of the ligands as agonists or antagonists at the sites and the heterogeneity and the functional role of the binding sites have not yet been clarified. Furthermore, the therapeutic targets have not been clearly determined. However, the sigma-ligands have high potential for developing new drugs. One of the possible targets of the sigma-ligands as new forms of drugs is schizophrenia. Recently, we identified two potent and highly selective sigma-ligands, FH-510 and NE-100. Together with the data on the binding properties and pharmacological actions of these compounds, the possibilities of the sigma-ligand as a new therapeutic drug were discussed.