Virus particles and murine leukemia virus complement-fixing antigen in neoplastic and nonneoplastic cell lines.

Twenty-seven lines of murine tissue cultures derived from 12 different cell pools and grown on various media were examined with the electron microscope for morphologically detectable virus particles. They were also tested for complement-fixing mouse leukemia virus antigens and for recoverable virus. A 100-percent correlation between results obtained by these two methods is reported. An additional 19 lines from 8 different cell pools were examined for either virus particles or complement-fixing antigens. All lines were assayed for neoplastic transformation. Seven cell pools gave rise to lines showing evidence of contamination with leukemia virus. Since most of these lines had also undergone "spontaneous" neoplastic transformation in vitro, this virus cannot be excluded as a possible cause of the neoplastic change, or of influencing it. The remaining cell pools gave rise to lines with no evidence of contamination with leukemia virus;but most of these lines also underwent similar transformation. These results suggest that "spontaneous" neoplastic transformation can occur in the absence of detectable mouse leukemia virus.

Neoplastic transformation of human epidermal keratinocytes by AD12-SV40 and Kirsten sarcoma viruses.

Recent investigations have begun to dissect the number and nature of genetic alterations associated with cancer cells. In the present study, primary human epidermal keratinocytes acquired indefinite life-span in culture but did not undergo malignant conversion in response to infection with a hybrid of adenovirus 12 and simian virus 40. Addition of Kirsten murine sarcoma virus, which contains a K-ras oncogene, to these cells induced morphological alterations associated with the acquisition of neoplastic properties. These findings demonstrate the malignant transformation of human primary epithelial cells in culture and support a multiple-step process for neoplastic conversion.

Carrier detection in xeroderma pigmentosum.

We were able to detect clinically normal carriers of xeroderma pigmentosum (XP) genes with coded samples of either peripheral blood lymphocytes or skin fibroblasts, using a cytogenetic assay shown previously to detect individuals with cancer-prone genetic disorders. Metaphase cells of phytohemagglutinin-stimulated T-lymphocytes from eight individuals who are obligate heterozygotes for XP were compared with those from nine normal controls at 1.3, 2.3, and 3.3 h after x-irradiation (58 R) during the G2 phase of the cell cycle. Lymphocytes from the XP heterozygotes had twofold higher frequencies of chromatid breaks or chromatid gaps than normal (P less than 10(-5)) when fixed at 2.3 or 3.3 h after irradiation. Lymphocytes from six XP homozygotes had frequencies of breaks and gaps threefold higher than normal. Skin fibroblasts from an additional obligate XP heterozygote, when fixed approximately 2 h after x-irradiation (68 R), had a twofold higher frequency of chromatid breaks and a fourfold higher frequency of gaps than fibroblasts from a normal control. This frequency of aberrations in cells from the XP heterozygote was approximately half that observed in the XP homozygote. The elevated frequencies of chromatid breaks and gaps after G2 phase x-irradiation may provide the basis of a test for identifying carriers of the XP gene(s) within known XP families.

Retinoid protection against x-ray-induced chromatid damage in human peripheral blood lymphocytes.

Oral administration of isotretinoin (13-cis retinoic acid) was shown previously (Kraemer, K. H., J. J. DiGiovanna, A. N. Moshell, R. E. Tarone, and G. L. Peck. 1988. N. Engl. J. Med. 318:1633-1637) to reduce the frequency of skin cancers in xeroderma pigmentosum (XP) patients. The mechanism of protection was unclear. In the present study, x-ray-induced chromatid damage in PHA-stimulated blood lymphocytes from five XP patients receiving isotretinoin was approximately half that in blood samples from the same patients before or subsequent to treatment. The x-ray-induced chromatid damage in blood lymphocytes from a normal control was reduced significantly by cocultivation with blood or plasma from an XP patient receiving isotretinoin or by addition of 10(-6) M isotretinoin to cultures 1 h before x-irradiation. A similar reduction in x-ray-induced chromatid damage was reported previously by adding to the culture medium, mannitol, a scavenger of the free hydroxyl radical, or catalase, which decomposes hydrogen peroxide; both of these products are generated during ionizing radiation. The present observations suggest that isotretinoin acts as a scavenger of such radiation products, thereby providing protection against x-ray-induced chromatid damage.

Neoplastic transformation of mouse and hamster cells in vitro with and without polyoma virus.

Several cell lines were examined under different culture conditions in an effort to find one that would not undergo "spontaneous" neoplastic transformation but could be transformed by polyoma virus. With such a cell line, large numbers of neoplastic and non-neoplastic cultures might be obtained for comparative studies. Four cell lines derived from different tissues of 2 strains of mice and all 8 lines of cells from 5 different pools of hamster embryo cells underwent spontaneous neoplastic transformation without polyoma virus. However, certain of these lines might be useful, since neoplastic conversion occurred only after prolonged culture. Fairly reproducible neoplastic transformations could be induced by polyoma virus with high multiplicities of infection and rather drastic treatment of cells, including trypsinization. Although it has been postulated that normal Syrian hamster embryo cells have a finite lifespan in vitro, we found that under our culture conditions, continuously growing, non-neoplastic cell lines could be routinely established.

Interaction of BCG-activated macrophages with neoplastic and nonneoplastic cell lines in vitro : quantitation of the cytotoxic reaction by release of tritiated thymidine from prelabeled target cells.

Peritoneal cells from mice infected ip with Mycobacterium bovis, strain BCG, were cytotoxic to syngeneic tumor cells in vitro. Cytotoxicity was estimated by measurement of release of tritiated-thymidine (3-H-TDR) from prelabeled target cells. The cell responsible for tumor cytotoxicity was the macrophage. Macrophages from uninfected mice or from oil-, starch-, or thioglycollate-induced peritoneal exudates had little effect on labeled tumor monolayers. Tumoricidal macrophages were present at 3-7 days and persisted through 6 weeks after a single BCG injection. Two neoplastic/nonneoplastic cell-line pairs, all four of the cell lines derived from a cloned syngeneic embryo cell line, were used as target cells for BCG-activated macrophages. Both tumor cell lines released significantly more 3-H-TDR than did the two nonneoplastic lines. In a mixed neoplastic/nonneoplastic target cell population, BCG-activated macrophages selectively destroyed the neoplastic cells; nonneoplastic cells were not affected as "innocent bystanders".

Ruthenium red-staining coat of paired neoplastic and nonneoplastic mouse cell lines in cluture.

The ruthenium red-staining coat (RRSC) of a pair of neoplastic and nonneoplastic cell lines derived from a common pool of mouse embryo cells was examined by electron microscopy. The object was to establish whether a thickening of RRSC is associated with "spontaneous" neoplastic transformation of cells in culture. Ruthenium red has an affinity for acid mucopolysaccharides of the cell coat. Differences in thickness of RRSC between cells of these neoplastic and nonneoplastic lines were negligible.

Approaches to enhance proliferation of human epidermal keratinocytes in mass culture.

Because of interest in mechanisms of carcinogenesis in human epithelial cells, quantitative procedures were developed for the mass culture of human epidermal keratinocytes in the absence of feeder cells. Several approaches were used to enhance proliferation since target cells are considered most susceptible to transformation if they are treated with carcinogenic agents during DNA synthesis. Mass cultures of enzymatically dispersed human foreskin were initiated in collagen-coated flasks containing medium NCTC 168 with 10% Chelex 100-treated horse serum. Under these conditions, human keratinocytes required a higher calcium ion concentration ([Ca2+]) than that reported for suspensions plated at low cell density. Neither the cohesiveness of the epidermal sheet nor continued proliferation was maintained by 0.15 mM Ca2+; 0.3 mM Ca2+ maintained these properties in primary culture only. A concentration of 1.0 mM Ca2+ provided the highest cell yield for prolonged growth as determined by the enumeration of cell nuclei isolated by citric acid. Reproducibility of successful initiation was achieved by inoculation of cells into a medium designed for clonal growth followed by culture in medium NCTC 168. Thus the balance of nutrients and electrolytes must be adjusted to satisfy the requirements of a dynamically expanding keratinocyte population.

Search for "indicators" of neoplastic conversion in vitro.

Certain responses of mouse and hamster cells to polyoma virus were examined with respect to their specificity as "indicators" of neoplastic conversion in vitro. These responses included the development of transplantation antigens and changes in morphologic growth pattern, cytology, karyology, rates of proliferation, and glycolytic activities. Under limited conditions, i.e., in short-term, slow-growing cultures, the morphologic change in growth pattern and increases in glycolytic activity and proliferation rate induced by polyoma virus appeared to correlate with neoplastic conversion. However, in long-term or rapidly growing short-term cultures, similar morphologic patterns occurred in cells that subsequently tested as non-neoplastic. Also, such patterns could be induced by polyoma virus in cells already neoplastic. Cells that had undergone "spontaneous" neoplastic conversion frequently showed none of these morphologic features of virus-transformed cells. Prolonged culture of cells without added virus resulted in increased glycolytic activities and proliferation rates equivalent to those of virus-transformed cells. These changes occurred in at least one cell line long before evidence of neoplastic conversion. The cytologic changes in the virus-treated neoplastic cells were similar to those usually associated with neoplastic cells in vivo and may possibly serve as sensitive indicators of in vitro neoplastic conversion. From the observations of this study, the change in morphologic growth pattern is interpreted not as loss of "contact inhibition," but as a proliferative response accompanied by decreased adhesion of cells to the glass substrate.

Repair of chromosome damage induced by X-irradiation during G2 phase in a line of normal human fibroblasts and its malignant derivative.

A line of normal human skin fibroblasts (KD) differed from its malignant derivative (HUT-14) in the extent of cytogenetic damage induced by X-irradiation during G2 phase. Malignant cells had significantly more chromatid breaks and gaps after exposure to 25, 50, or 100 rad. On the assumption that each chromatid contains a single continuous DNA double helix, chromatid breaks would represent unrepaired DNA double-strand breaks; the gaps may represent single-strand breaks. Results from alkaline elution of cellular DNA immediately after irradiation showed that the normal and malignant cells in asynchronous population were equally sensitive to DNA single-strand breakage by X-irradiation. Caffeine or beta-cytosine arabinoside (ara-C), inhibitors of DNA repair, when added directly following G2 phase exposure, significantly increased the incidence of radiation-induced chromatid damage in the normal cells. In contrast, similar treatment of the malignant cells had little influence. Ara-C differed from caffeine in its effects; whereas both agents increased the frequency of chromatid breaks and gaps, only ara-C increased the frequency of gaps to the level observed in the irradiated malignant cells. Addition of catalase, which destroys H2O2, or mannitol, a scavenger of the derivative free hydroxyl radical (.OH), to the cultures of malignant cells before, during, and following irradiation significantly reduced the chromatid damage; and catalase prevented formation of chromatid gaps. The DNA damage induced by X-ray during G2 phase in the normal KD cells was apparently repaired by a caffeine- and ara-C-sensitive mechanism(s) that was deficient or absent in their malignant derivatives.

Role of photosensitization and oxygen in chromosome stability and "spontaneous" malignant transformation in culture.

Visible light and oxygen enhanced both chromosome instability and malignant transformation of mouse cells in culture. Nine cell lines were initiated from 8 pools of 10- to 13-day C3H embryos. Each cell line was divided into sublines, which were either maintained shielded from light or were exposed for 3 or 24 hours to fluorescent light (approximately 150 foot-candles) two or three times weekly. Cultures of the sublines were also maintained with either a gaseous phase of 0-1% oxygen or atmospheric (18%) oxygen. Each line was monitored for cytologic manifestations of malignant neoplastic transformation, and 8 lines were monitored for chromosome alterations. Seven lines were assayed for tumorigenicity by intraocular implantation into syngeneic hosts. Repeated light exposure and/or high oxygen increased the frequency of minute chromosomes, which result from chromatid breaks, and also increased the rate of shift from diploid to heteroploid state. Four cell lines showed no cytologic changes indicative of neoplastic change during the test period. Two of these were assayed in vivo and failed to grow as tumors. In the remaining 6 lines, cytologically neoplastic colonies appeared earlier or more abundantly in the light-exposed cultures and/or those gassed with high oxygen. In 3 of these lines, tumors developed only from the light-exposed cultures; in the other 2, tumor latency periods were significantly shorter in the cultures exposed to light or gassed with atmospheric oxygen.

Enhanced chromatid damage in blood lymphocytes after G2 phase x irradiation, a marker of the ataxia-telangiectasia gene.

An assay for ataxia-telangiectasia (A-T) heterozygotes, i.e., healthy carriers of the A-T gene(s), requiring only a small sample (3.5 mL) of peripheral blood, is described. Frequencies of chromatid aberrations in phytohemagglutinin-stimulated blood lymphocytes collected by demecolcine from 0.5 hour to 1.5 hours after x irradiation with 58 roentgens were twofold to threefold higher in A-T heterozygotes than in clinically normal controls and twofold to three-fold higher in A-T patients (homozygotes) than in A-T gene carriers. The persistence of chromatid breaks and gaps in lymphocytes following radiation-induced DNA damage during G2 suggests a deficiency or deficiencies in DNA repair that may be the defect at the molecular level that results in the enhanced radiosensitivity and cancer proneness characterizing A-T gene carriers and patients.

Test for malignant transformation of rat liver cells in culture: cytology, growth in soft agar, and production of plasminogen activator.

Three parameters were evaluated as diagnostic of the malignant potential of cultured rat liver epithelial cells: cytology, growth in soft agar, and production of extracellular plasminogen activator. A total of 22 tumorigenic and nontumorigenic cultures from 15 cell lines were sent coded from their originators to two different laboratories for the evaluation of these three parameters. Cytologic diagnosis and growth in soft agar were reliable means of determining the malignant potential of the cultured cells. However, the production of extracellular plasminogen activator showed little correlation with tumorigenicity. Of cytologic properties evaluated, the two that correlated best with malignant potential were increased cytoplasmic basophilia and and increased nuclear:cytoplasmic ratio.

Cytometric analysis of neoplastic transformation of vertebrate cell populations.

Two parameters of neoplastic transformation in spontaneously transforming fibroblasts were examined. One parameter, the predilection for rounding of cells at metaphase, was studied using time-lapse cinephotomicrography and fixed, stained preparations. Ten different cell lines were assayed, including established lines of hamster, rat, and mouse cells, and six rodent cultures of known neoplastic potential as determined by animal injection and tumor production. There was a close correlation between the assumption by cells of a spherical shape at metaphase and their ability to form tumors on injection in syngeneic hosts. The projected area of adherent cells 24 hr after plating over a coverglass was used to assay the transition of these rodent cell populations in culture from nonneoplastic to neoplastic. As the cell population became neoplastic, there was a significant decrease in the mean projected area of the cells. Furthermore, as the cell cultures became capable of producing tumors, the projected area profile of the population shifted proportionally to smaller area classes.

Morphology and serum dependence of cloned cell lines undergoing spontaneous malignant transformation in culture.

A number of morphological changes were found to correlate with the occurrence of spontaneous neoplastic transformation in sublines of five rigidly isolated clones of mouse embryo fibroblasts. These morphological changes included increased cytoplasmic basophilia, reduced spreading of cells on the substrate, increased nuclear:cytoplasmic ratio, greater heterogeneity in the size and shape of cells and nuclei, and more random orientation of cells. Because these changes were reproducible, occurring in some sublines of all five clones, they have been described and illustrated to serve as a guide for identifying spontaneous transformants among rodent fibroblasts in culture. Neoplastic transformation was determined by the growth of the cells as malignant neoplasms in syngeneic hosts. The spontaneous transformants, as compared with nonneoplastic fibroblasts derived from the same cell, showed similar saturation densities and serum dependence. Some clones had a higher transformation frequency than the parental line, which remained nonneoplastic for years. Thus, the capacity for continuous growth in vitro can be independent of malignant potential. The use of horse serum as supplement to the medium did not accelerate or increase the frequency of neoplastic transformation.

Colony morphology and growth in agarose as tests for spontaneous neoplastic transformation in vitro.

Adherent fibroblast-like cells from paired lines, one non-neoplastic and the other "spontaneously" transformed neoplastic, were compared in simultaneous in vivo and in vitro assays. The in vivo assay was the i.m. implantation of 10(6) or 10(7) cells in irradiated syngeneic animals, and the two in vitro assays were the evaluation of colony morphology on plastic and the enumeration of colony growth in semisolid agarose. The percentage of colonies diagnosed from their morphology as neoplastic correlated with tumorigenicity as follows: 100% always indicated a tumorigenic cell population with tumor latent periods from 6 to 230 days and tumor incidence from 40 to 100%; 0% always indicated a nontumorigenic cell population; 1 to 32% indicated either a tumorigenic cell line with long tumor latent period (218 days) with 70% tumor incidence or a nontumorigenic cell line. Growth in agarose, as measured by colony number and size, correlated with tumorigenicity as follows: nontumorigenic cell lines produced no colonies; tumorigenic cell lines produced colonies, but not always larger than 0.1 mm in diameter. The number of size or colonies did not correlate with the tumor latent period or tumor incidence. Therefore, both in vitro tests were reliable qualitative assays of spontaneous neoplastic transformation, but they did not correlate directly with the tumor incidence or mean tumor latent period. The relative success of the agarose assay emphasizes the importance of decreased anchorage dependence for progressive growth of injected cells as a malignant neoplasm in vivo.

Population density as a factor in the evolution of neoplastic cell lines.

The influence of population density in the progression from the nonneoplastic to the neoplastic state has been reassessed. Two twice-cloned, nonneoplastic mouse lines, NCTC 7914 and 7915, were transferred each 3 to 4 days at inoculum sizes selected to minimize or maximize cell-cell contact, 1 X 10(5) or 4 X 10(5) cells/T-15, respectively. As tested by in vivo assay, the regime designed to minimize cell-cell contact did not reproducibly delay transformation, and tumor production was observed in all lines, irrespective of inoculum size. Also, results of tumorigenesis assays correlated with blind evaluation of morphological and cytological alterations, growth in agarose, and susceptibility to killing by activated macrophages. Generally higher saturation densities were seen as a function of period in culture, and no significant differences in glucose utilization or lactic acid production were observed between nonneoplastic and neoplastic cell populations.

Chromosomal radiosensitivity of human tumor cells during the G2 cell cycle period.

Thirteen cell lines derived from human tumors of diverse tissue origin and histopathology were compared with 12 lines of normal skin fibroblasts with respect to chromatid damage induced by 25, 50, or 100 R of X-irradiation during the G2 period of the cell cycle. Only cells in metaphase were examined, and these had been irradiated 1.5 hr before fixation. When irradiated under identical conditions, the tumor cells showed significantly more chromatid breaks and gaps than did the normal cells at all doses tested. The data suggest that the increased G2 chromosomal radiosensitivity of the tumor cells is associated with deficient DNA repair during the G2-prophase period of the cell cycle.

Enhanced G2 chromatid radiosensitivity, an early stage in the neoplastic transformation of human epidermal keratinocytes in culture.

A deficiency in DNA repair, manifest as enhanced chromatid radiosensitivity during the G2 phase of the cell cycle, together with a proliferative stimulus such as that provided by active oncogenes may be necessary and sufficient for the malignant neoplastic transformation of human keratinocytes in culture. Normal epidermal keratinocytes established as continuous cell lines by transfection with pSV3-neo or infection with adeno 12-SV40 hybrid virus developed enhanced G2 chromatid radiosensitivity after 18 passages in culture. In contrast to cells from primary or secondary culture, these cells could be transformed to malignant neoplastic cells by infection with Kirsten murine sarcoma virus containing the Ki-ras oncogene or in one line by the chemical carcinogen, N-methyl-N'-nitro-N-nitrosoguanidine; both of these agents produced a marked proliferative response. Cytological heterogeneity and karyotypic instability characterized the cells during their progression to neoplasia. These results are interpreted in terms of a mechanism for neoplastic transformation.

Topography of nonneoplastic and neoplastic cells of common origin.

The possibility that neoplastic transformation may characteristically alter cell surface morphology prompted a comparison by scanning electron microscopy of nonneoplastic and tumorigenic cell lines from a single clone of mouse embryo cells. Among those studied by scanning electron microscopy, six lines of this clone proved nonneoplastic, and nine others underwent neoplastic transformation in culture, as evidenced by tumor production in vivo. Combined cinephotomicrography and scanning electron microscopy allowed the determination of postmitotic time and topography of individual cells without perturbing the cells or detectably altering their surface morphology; no pattern of morphological change as a function of postmitotic time was evident in either nonneoplastic or neoplastic cell populations. Accordingly, these cell populations could be compared under their usual conditions of attached asynchronous growth despite differences in proliferation rates. Cells of the neoplastic lines were characteristically less spread, and some lines displayed greater morphological variability than was evident among cells of nonneoplastic lines. However, most cells in all nine neoplastic lines and all six nonneoplastic lines were smooth surfaced. Thus, the exaggerated incidence of microvilli, ruffles, or blebs reported for established tumor-derived lines and most morphologically transformed lines did not prove a reliable criterion of neoplastic state for these cell lines of common origin grown under the same culture conditions.