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

Significance of 5-S-Cysteinyldopa as a Marker for Melanoma

Melanoma is one of the most lethal and malignant cancers and its incidence is increasing worldwide, and Japan is not an exception. Although there are numerous therapeutic options for melanoma, the prognosis is still poor once it has metastasized. The main concern after removal of a primary melanoma is whether it has metastasized, and early detection of metastatic melanoma would be effective in improving the prognosis of patients. Thus, it is very important to identify reliable methods to detect metastases as early as possible. Although many prognostic biomarkers (mainly for metastases) of melanoma have been reported, there are very few effective for an early diagnosis. Serum and urinary biomarkers for melanoma diagnosis have especially received great interest because of the relative ease of sample collection and handling. Several serum and urinary biomarkers appear to have significant potential both as prognostic indicators and as targets for future therapeutic methods, but still there are no efficient serum and urinary biomarkers for early detection, accurate diagnosis and prognosis, efficient monitoring of the disease and reliable prediction of survival and recurrence. Levels of 5-S-cysteinyldopa (5SCD) in the serum or urine as biomarkers of melanoma have been found to be significantly elevated earlier and to reflect melanoma progression better than physical examinations, laboratory tests and imaging techniques, such as scintigraphy and echography. With recent developments in the treatment of melanoma, studies reporting combinations of 5SCD levels and new applications for the treatment of melanoma are gradually increasing. This review summarizes the usefulness of 5SCD, the most widely used and well-known melanoma marker in the serum and urine, compares 5SCD and other useful markers, and finally its application to other fields.

Sunlight, melanogenesis and radicals in the skin

Melanocytes are cells of neural crest origin residing at the dermal-epidermal juncture. They produce specialized organelles called melanosomes within which the biochemical processes of melanization occurs. UV radiation is capable of inducing melanogenesis and, during the biosynthesis of melanins, several of the putative precursors "leak out" of the melanosome and can be detected in the skin, serum and urine of individuals undergoing active melanogenesis. Most notable are the cysteinyldopas (formed by nucleophilic addition of cysteine to dopaquinone) and several dihydroxyindoles (formed by intramolecular cyclization of dopaquinone). These catechols often are methylated in the melanocyte to afford a mixture of the monomethoxy derivatives and, in some cases, the dimethoxy species. Recent investigations in our laboratories have demonstrated that the cysteinyldopas, dihydroxyindoles, and their various methylated derivatives are photochemically unstable. Irradiation with biologically relevant ultraviolet radiation (i.e. wavelengths greater than 300 nm) results in the rapid destruction of the precursors/metabolites and the production of a variety of free radical species. The photochemistry and potential photobiological significance of melanogenic intermediates is discussed.