A comparison of markers of human fibroblast transformation induced by chemical carcinogen treatment or by transfection of an origin-defective SV40-containing plasmid.

We have investigated the sensitivity to oncogenic transformation by an origin-defective SV40-containing plasmid, '8-16' (ori-SV40), of skin fibroblasts from normal individuals (NF), and from patients with 2 hereditary diseases characterized by an increased cancer risk, Bloom's syndrome (BS) and Fanconi's anemia (FA). It was hypothesized that perhaps these cells had already undergone some stage, or stages, of the progression to neoplasia, and that as a consequence of these changes, one could observe differential expression of characteristics of the transformed phenotype in these cells compared to normal, or perhaps they would behave differently in vivo. The data showed that FA cells and NF possessed comparable sensitivities to transformation by ori-SV40 DNA transfection, as measured either by focus formation above a confluent monolayer, or anchorage-independent growth. The BS cells, on the other hand, were 5-10 times less sensitive to this method of transformation, and further, the transformed phenotype was unstable. The resistance of BS cells to transformation by the 8-16 plasmid may be a reflection of their inherent genetic instability which affects stable integration and expression of the transfected plasmid DNA, since no differences in initial uptake of transfected DNA were observed between the various cell strains. Immortality and tumorigenicity were not readily demonstrated in this ori-SV40 transformation model. The results are discussed in relationship to the characteristics of the transformed phenotype of chemically treated normal human fibroblasts. SV40, an agent known to transform human cells, can be cast in a positive control role with respect to the appropriateness of the assays, the frequency of appearance of various markers, immortality and tumorigenicity. The tumorigenicity results are further compared to results obtained during the establishment of a wide range of fresh human tumor biopsies as xenograft lines in athymic nude mice, with particular emphasis on the sarcoma data.