Oncogenesis by interspecific interaction of malignant murine and non-malignant hamster cells in vitro

A clone of Cloudman S91 murine melanoma was fused in vitro with non-malignant hamster cheek pouch cells by means of lysolecithin, and the putative hybrid progeny cells, HCP-MM, were found to be highly malignant in hamster, but not in appropriate mice. A malignant clone of HCP-MM cells was shown to have hamster species-specific surface antigens (as demonstrated by immunofluorescence and the cytotoxic antibody) and hamster-like lactate dehydrogenase and NAD-dependent malate dehydrogenase isoenzyme profiles. Nevertheless, chromosomes similar to those of both murine and hamster parental cells could be distinguished in cells of this malignant clone and in hamster tumor grafts by the method of trypsin-Giemsa banding. A majority of the murine chromosomes, however, appeared to be lost. This study indicates that a murine melanoma previously found untransplantable in hamsters could produce a highly malignant and lethal tumor for hamsters after being mixed in vitro with non-malignant hamster cells, in the presence of a fusing chemical. It is not as yet certain whether the production of transformed cells in vitro and of highly malignant tumors in the hamster (both with predominantly hamster properties) required heterosynkarion formation between the murine melanoma and hamster cheek pouch cells. Nevertheless, our results suggest that the presence of the murine melanoma, and possibly the interaction of its genome with non-malignant hamster cells, was implicated in this process.