Enhanced tumorigenicity, melanogenesis, and metastases of a human malignant melanoma after subdermal implantation in nude mice

Transplantation of human tumors into the organ or tissue of their origin (orthotopic transplantation) in nude mice can result in significant enhancement of tumor growth and metastases, compared with sc (ectopic) transplantation. Because melanocytes are normally found in the epidermal-dermal junction, intradermal inoculation of melanoma cells might be expected to improve their potential for malignant growth as xenografts. The purpose of our study was to examine this possibility. We found that because mouse epidermis and dermis are so thin, it was not possible to inject a bolus of tumor cells intradermally; instead the cells were actually deposited in the most superficial layer of the subcutis (i.e., subdermally). We evaluated the behavior of cells from a human melanoma cell line after sc or subdermal inoculation into National Institutes of Health Swiss athymic nude mice. The cells used were from (1) the predominantly amelanotic human malignant melanoma cell line MeWo, originally established from a melanotic lymph node metastasis, and (2) two MeWo variants resistant to wheat germ agglutinin (WGAr), which were selected for altered malignant capacities. Whereas 5 X 10(5) MeWo cells were required to achieve 100% tumor take with sc injection, only 2 x 10(4) cells were required with subdermal inoculation. Subdermal injection of the MeWo cells resulted in the development of highly melanotic and nonencapsulated primary tumors, which grew quickly into the dermis and epidermis and metastasized at high frequency to draining lymph nodes. In contrast, the tumors that developed after sc injection were found in the deepest layer of the subcutis and were predominantly amelanotic and encapsulated; they rarely metastasized to lymph nodes.(ABSTRACT TRUNCATED AT 250 WORDS)