An alternative assay system for the detection of transforming genes

We have developed an alternative assay system based on DNA mediated gene transfer (DMGT) for the detection of functional transforming genes which we find more sensitive and reliable than other assay systems. This approach involves selecting in tissue culture for cells which are expressing a drug-resistance marker co-transferred with the tumour DNA thus isolating the small number of cells which have taken up and are expressing exogenously added DNA. The ability of transformed cells present in this drug-resistant cell population to form tumours in athymic (nu/nu) nude mice was then used to assay for transforming genes. Using NIH3T3 and Rat 2 cells as recipients, tumours produced after DMGT with DNA from non-tumorgenic cells were only very rarely observed. Tumour induction was observed using DNA from a biopsy of a human ovary carcinoma and a spontaneous murine lung carcinoma. Two human retinoblastoma cell lines were negative for tumour induction. The transforming gene from the ovarian carcinoma was identified as c-K-ras2.