Gangliosides of human melanoma: GM2 and tumorigenicity

An increased synthesis of the ganglioside GM2 has been reported on transformed murine cells, human fetal tissues, and transformed melanocytes. This study was designed to investigate whether any correlation existed between GM2 expression and the tumorigenicity of human melanoma. Ten established human melanoma cell lines, 5 rich in GM2 (group A) and 5 poor in GM2 (group B), were selected on the basis of previous ganglioside analysis of 28 melanoma cell lines. Six athymic nude mice per cell line were given an sc injection of 10(6) human melanoma cells/mouse. Tumors were measured every 2-4 days. By day 36 after the injection, 28 of 30 mice (93%) in group A developed medium to large tumors, but only 1 of 30 (3%) in group B developed a small tumor (P less than .005). The correlation of GM2 content of individual melanomas with tumor growth rate also was very high. GM2 content was expressed as nanomoles per gram wet weight of each melanoma. The area under the log values of tumor growth curves from day 0 to day 36, which represented tumor growth rate, tumor size, and latent period, was proportional to GM2 content, with a correlation coefficient of 0.927 and with P less than .001. The same log relationship when tested with other gangliosides, GM3, GD3, and GD2, was not statistically significant. These results, combined with the fact that variations in GM2 content do not affect in vitro growth of human melanoma cells, suggest that GM2 expression may be directly related to the dedifferentiation or the tumorigenicity of human melanoma.