Evaluation of a nude mouse tumor model using beta-galactosidase-expressing melanoma cells

We developed and evaluated an in vivo athymic nude mouse model for tumor growth, angiogenesis, metastasis, and antineoplastic drug development. Melanoma cell lines expressing beta-galactosidase encoded by the Escherichia coli lac Z gene have been created by infecting an immortal murine melanocyte cell line with a recombinant retrovirus expressing the v-Ha-ras oncogene and lac Z to generate the MRB (melanoma, ras, beta-galactosidase) cell lines. The amelanotic, phorbol ester-independent, transformed melanoma cell lines developed tumors rapidly when injected subcutaneously into nude mice, as well as experimental lung metastases when injected i.v. into the tail vein. beta-galactosidase-expressing subcutaneous tumors and lung metastases stained blue with X-gal. The melanomas produced in nude mice have been characterized by using various histochemical and immunohistochemical staining methods to detect melanoma- and endothelial-cell-specific markers to determine the extent of neovascularization in MRB nude mouse tumors. Optimal staining of endothelial cells involved in tumor angiogenesis was observed by using ADPase activity and antiangiotensin-converting enzyme antibody staining. Attempts at indirect quantification of metastatic tumor cell number within the lung by either beta-galactosidase enzymatic activity or ELISA immunoreactivity were unsuccessful. However, the MRB cell lines should be useful in screening for and studying the mechanisms of action of antineoplastic, antimetastatic, and angiostatic drugs in vivo in athymic nude mice.