[The future of methotrexate therapy and other folate inhibitors].

Because of its good effectiveness and tolerability, methotrexate (MTX) has been the most important DMARD for the treatment of rheumatoid arthritis (RA) worldwide for many years. Thus the treatment of this disease is strongly based on the principle of folate inhibition. Recent years have brought new insights into the pharmacology and mechanisms of action of MTX. As a result, it now appears possible to further develop folate inhibitors to increase effectiveness and specificity. Polyglutamation of the drug, a metabolic step which appears to play a role both in terms of therapeutic effects and hepatic side effects, might be a possible starting point. Moreover, methods of targeted drug delivery intended to increase drug accumulation at the site of inflammation can increase the effectiveness of treatment and reduce toxicity. Albumin-coupled and liposomally-conjugated MTX, both of which inhibit inflammation in animal models more potently than MTX, are undergoing preclinical evaluation. It was recognized that activated synovial macrophages upregulate folate receptor ß (FR-ß) expression and that MTX can become active by this pathway. This finding makes it possible to develop new FR-ß-specific folate inhibitors with specificity for this pathophysiologically important cell population.