Ultraviolet radiation-induced neoplastic transformation of normal human cells, in vitro

Comparative stages of expression of human squamous carcinoma cells and carcinogen transformed keratinocytes

The mouse monoclonal antibody OSU 22-3 was prepared using cells from a squamous cell carcinoma (SCC) as an immunogen. This antibody reacts with an antigen found on squamous cell carcinomas but does not react with normal keratinocytes. This antibody and two antibodies that react with normal keratinocytes were used as markers of malignant and normal phenotypes. These markers were used to evaluate several spontaneous and carcinogen initiated SCC tumors and to identify the expression of an antigen associated with a malignant phenotype. A variety of subpopulations in carcinogen initiated tumors and spontaneous SCC tumors were noted. The subpopulations that reacted only with MoAb OSU 22-3 exhibited features of anchorage independent growth and cellular invasiveness, and formed progressively growing tumors in nude mice. Other SCC spontaneous tumor cell subpopulations reacted with the antibodies associated with normal keratinocytes. These cells did not proliferate in vitro and did not form tumors in the nude mouse. There were other carcinogen transformed cells which reacted with MoAb OSU 22-3 but not with the antibodies associated with normal keratinocytes. These cells exhibited anchorage independent growth and cellular invasiveness but did not form tumors in nude mice. We conclude from this work that human SCC tumors contain multiple cell populations. These cell populations have varied growth properties and express surface antigens that may indicate their malignant vigor. Carcinogen transformed keratinocytes do exhibit some of the characteristics of SCC tumor phenotypes but not the property of malignant progressively growing cells on a routine and consistent basis. This feature is transiently and inconsistently expressed in a surrogate host by populations prepared from spontaneous SSC tumors.

Benzamide prevention of ultraviolet radiation-induced transformation as measured by anchorage-independent growth and the absence of correlation with thymidine dimer formation and DNA repair

Synchronized human fibroblasts were exposed in early S phase to increasing doses of ultraviolet (UV) irradiation in the presence and absence of an antitransforming drug, benzamide. Cellular survival, initial thymidine dimer formation and its repair, and cellular phenotypic transformation were simultaneously monitored in the presence and absence of 1 mM externally added benzamide that reaches 8 to 15 microM intracellular levels. Cellular transformation as measured by an expression of anchorage-independent growth was inhibited by nontoxic doses of benzamide. Antitransforming action of benzamide is confined to low intracellular drug concentrations, which in the case of benzamide is in the 4-9 microM range. Because of the lack of effect of benzamide on the formation of UV-induced thymidine dimers and the specific repair of these dimers, these results suggest that the processes of thymidine dimer formation and its repair are not involved in the mode of action of benzamide that influences the expression of a transformed phenotype with low malignant vigor.

Towards an understanding of the malignant transformation of diploid human fibroblasts

This paper reviews the major reports of the spontaneous or carcinogen-induced transformation of human fibroblasts to the malignant state, to infinite lifespan, or to anchorage independence. In some cases, the transformed cells and the parent cell with which the work began were made available to us to be tested to determine whether the cells shared common isozymes, HLA antigens, restriction-fragment length polymorphisms, marker chromosomes, etc., as one would expect. When we examined the normal fibroblastic cell line KD for these markers, and the transformed HuT cell lines developed from it by Kakunaga (Proc. Natl. Acad. Sci. (U.S.A.), 75, 1334, 1978) for these markers, we found marked differences, indicating that KD cells and HuT cells are derived from different individuals. When we applied these techniques to the 3 human fibroblast cell lines transformed by Namba to acquire infinite lifespan in culture (Gann, 27, 221, 1981), it became clear that KSMT-6 was derived from the parent cell, KMS-6, but that both cell lines CT-1 and SUSM-1 were derived from the same parental cell line, AD387. Similar studies with other sets of cell lines are also reported. In the light of these studies, it appears that there is no example of the malignant transformation of human fibroblasts by carcinogen treatment. However, neoplastic transformation and transformation to infinite lifespan by carcinogen treatment have been achieved by a number of workers. We speculate as to how malignant transformation might be obtained by carcinogen treatment.

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.

Spontaneous in vitro malignant transformation in a xeroderma pigmentosum fibroblast line

This paper deals with a spontaneous malignant transformation in one of our XP fibroblast lines. This cell line, designated XP29MA, was derived from a 14-year-old boy who did not show skin tumors or precancerous alterations either at the time of clinical examination or when the biopsy was taken. We have compared the following features in both the malignant and the benign cell line from which the malignant line developed: tumor formation in nude mice, repair capacity, cytogenetic status, light and electron microscopic characteristics. The benign cell line XP29MA had a doubling time of 4.3 d, did not form tumors in nude mice, showed a very low repair capacity (as determined by colony-forming ability, unscheduled DNA synthesis and alkaline elution) but exhibited a normal cytogenetic and ultrastructural status. In contrast, the transformed cell line XP29MAmal grew three times faster, formed colonies in methyl cellulose, gave rise to fibrosarcomas in nude mice, showed a drastically higher repair capacity, and was characterized by an extreme genetic imbalance, resulting from numerical and structural chromosome alterations of Nos. 1, 3, 4, 8, 12, 16, 17, 18, 20 and 21. Ultrastructural examination revealed fusiform and polygonal cells, the latter exhibiting large indented nuclei, vesicular dilatations of the endoplasmatic reticulum and numerous lysosomes. The higher repair capacity in XP29MAmal cells is tentatively explained in terms of reversion, enhancement of post-replication repair and/or expression of SOS-type functions.

A comparison of expression of neoplastic potential of carcinogen-transformed human fibroblasts in nude mice and in chick embryonic skin

Human foreskin fibroblasts transformed by representative chemicals from five different classes of chemical carcinogens, some requiring enzymatic activation and direct acting carcinogens, produced cell populations that exhibited anchorage-independent growth and expression of neoplastic potential in either nude mice or chick-embryonic skin (CES). There is a high degree of correlation between tumor incidence and invasiveness of CES. The unique feature of CES is the rapidity of expression of cellular neoplasia and interpretation of the simulated tumor in 4 d as a simulated fibrosarcoma. This method represents a system that can be used to evaluate human carcinogens in vitro in 6 to 10 wk.

Frequency of UV-induced neoplastic transformation of diploid human fibroblasts is higher in xeroderma pigmentosum cells than in normal cells

If neoplastic transformation of diploid human cells results from carcinogen-induced mutations, cells deficient in excision repair of UV-induced DNA damage should be significantly more sensitive to transformation by UV light than normal cells. We tested this hypothesis by irradiating fibroblasts from a xeroderma pigmentosum patient (XP7BE, complementation group D) with low doses of Uv light (254 nm) and cells from a normal person with much higher doses and comparing the frequency of transformation to anchorage independence. Both sets of cells exhibited a dose-dependent increase in transformation which corresponded to a dose-dependent decrease in survival. At doses that caused equal cell killing, the frequency of anchorage-independent cells was approximately equal. Colonies of XP7BE and normal cells isolated from agar, propagated, and injected into X-irradiated athymic mice produced fibrosarcomas in 100% of the animals. Normal cells irradiated shortly before the onset of DNA synthesis exhibited a high frequency of anchorage-independent cells; cells irradiated in early G1 showed no increase over background. These results agree with those we observed for UV induction of 6-thioguanine-resistant mutants in these cells and support the hypothesis that anchorage independence results from mutations induced by DNA replication on a damaged template.

Characterization of human cells transformed by chemical and physical carcinogens in vitro

Several different classes of chemical carcinogens induced the transformation of human fibroblasts grown in vitro. Characteristics of the events that occur from time of treatment through the expression of neoplastic transformation are presented. The S-phase appeared to be the portion of the cell cycle most vulnerable to insult. Staging of the cells by blocking them in G1 before releasing them to proceed through scheduled DNA synthesis (S) was required to induce reproducible transformation. Compounds such as insulin were added to the cells upon release from the block to sensitize the cells to the carcinogen that was added during S. Growth of the transformed cells as distinct from nontransformed cells was promoted by growth in medium supplemented with 8X nonessential amino acids. Carcinogen-treated cells in the early stage of transformation exhibited abnormal colony morphology and were able to grow at 41 degrees C, in air atmosphere, and in medium supplemented with only 1% serum. In addition, the transformed cells were insensitive to KB cell lysate and exhibited density independent, as well as anchorage independent, growth (i.e., growth in 0.33% agar). Cells that grew in soft agar also produced undifferentiated mesenchymal tumors in preirradiated nude mice.