Eumelanin-related indolic compounds in the urine of treated melanoma patients

A method was developed for the quantitation of six eumelanin-related indolic compounds in urine. The procedure employs methane ionization of the hexafluoroisopropyl and/or pentafluoropropionyl derivatives of 5,6-dihydroxyindole, 5-hydroxy-6-methoxyindole, 6-hydroxy-5-methoxyindole, 5-hydroxy-6-methoxyindolyl-2-carboxylic acid, 6-hydroxy-5-methoxyindolyl-2-carboxylic acid and 5,6-dimethoxyindolyl-2-carboxylic acid together with their deuterated analogues, and selected ion-monitoring. Deuterated analogues are added as internal standards to enzymatically hydrolysed urine before diethyl ether extraction. The method was used for monitoring urinary excretion in patients with malignant melanoma treated with cytostatics. In several cases, a decrease of the excretion of the eumelanin-related substances was recorded after the therapy. The usefulness of the individual indolic compounds for such follow-up studies is discussed.