Induction of tumor growth and lung metastasis by a cDNA cloned from an aflatoxin B₁-induced rat liver cancer cell line

Abstract

Previously we isolated a cancer cell line AFB-1 from a hepatocellular carcinoma that had been induced by aflatoxin B₁ in a male Fischer 344 rat. In the present study, we constructed the subtracted cDNA libraries between mRNAs from AFB-1 and rat normal liver cell line BL9, and identified a 650 bp cDNA which hybridized with mRNA of AFB-1 but not with that of BL9 in Northern blot analysis. We transfected the 650 bp cDNA/vector recombinant into AFB-1 and BL9, and then inoculated either transfected cells or parental cells at 1×10⁷ cells/rat subcutaneously at the dorsal region of syngenic rats. The transfection of AFB-1 with the 650 bp cDNA/vector recombinant increased the incidence of subcutaneous tumor growth (14 of 14 in male rats inoculated with transfected AFB-1 versus 8 of 13 in those with parental AFB-1, P<0.02) and that of lung metastasis (9 of 14 in male rats inoculated with transfected AFB-1 versus 0 of 13 in those with parental AFB-1, P<0.001). The transfection of the 650 bp cDNA/vector recombinant transformed normal liver cell line BL9 into cancer cells i.e. the transfected BL9 formed subcutaneous tumor nodules in 9 of 10 male rats and in all 10 female rats and formed metastatic foci in the lungs in 6 of 10 female rats. This is the first instance where a cDNA from a subtracted cDNA library not only enhanced subcutaneous tumor growth and lung metastasis of cancer cells but also induced those activities in normal cells.