The melanoma malignum is one of the most malignant and often occurring skin tumors, which derives from melanin producing cells – melanocytes. Due to increased melanogenesis in melanoma cells, melanin formation could be used to targeted therapy of the tumor [1]. The increase of the pigment synthesis by melanoma cells results in arise of pheo- and eumelanin precursors (5-S-cysteinyldopa and indole derivatives) in blood and urine. These substances may be useful for therapy monitoring as tumor markers. The recognition of related to melanogenesis phenotype of melanoma cells could provide a possibility of appropriate selection of therapeutic agents.

The aim of our study was to characterize chemical structure of melanin isolated from the human melanoma malignum by two different enzymatic methods of Wilczek et al. [2] and Double et al. [3], with some modifications. Isolated pigment was thermally degraded in the presence of tetramethylammonium hydroxide (TMAH) and thermochemolysis products were analyzed by GC/MS.

Lipid products, especially fatty acids methyl esters and aliphatic and cyclic hydrocarbons were predominant among pyrolysis products of melanin isolated from melanoma malignum by the Wilczek method. In contrast, during thermochemolysis of melanin isolated from the tumor cells by the Double method, mainly eumelanin markers (pyrrole and its methyl derivatives, toluene, styrene and benzonitrile) and glycine and alanine methyl derivatives were obtained. The characteristic thermochemolysis products of pheomelanin (sulphur-containing heterocycles) were not observed. The presence of volatile, low-molecular weight compounds such as CO₂, CO, NH₃, H₂S, CH₃SH and SO₂ was confirmed by the analysis of selected mass ions.

Thermochemolysis technique may be useful not only for elucidation of the pigment structure, but it could be also applied to establish the relationship between melanin type and malignancy of melanoma malignum.

[1] Riley P.A., 2003, Melanogenesis and melanoma. Pigment Cell Res., 16, (5): 548-552.
[2] Wilczek A., Kondoh H., Mishima Y., 1996, Composition of mammalian. Pigment Cell Res., 9, (2): 63-67.
[3] Double K.L., Zecca L., Costi P., Mauer M., Griesinger C., Ito S., Ben-Shachar D., Bringmann G., Fariello R.G., Riederer P., Gerlach M., 2000, Structural characteristics of human substantia nigra neuromelanin and synthetic dopamine melanins. J. Neurochem., 75, (6): 2583-2589.1

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