[en] Experiments with fractionated radiation doses, showed that cell transformation frequencies remained about the same for doses between 150 and 600 rad whether delivered by a single dose or by split exposures. At higher doses fractionation led to a reduction in the transformation frequency

[en] This paper examines the role of thyroid hormones in x-ray-induced neoplastic transformation of C3H/10 T 1/2 cells. In addition, the delineation of the time when transformation is sensitive to T3, the dependence of transformation on T3 concentration, and the involvement of protein synthesis are studied. The results indicate that thyroid hormone plays a key role in the initiation of x-ray-induced neoplastic transformation and that induction of protein synthesis may mediate this response

[en] We have shown that oncogenic transformation induced by x-rays or bleomycin and the enhancement of transformation by phorbol esters (TPA) can be inhibited by superoxide dismutase (SOD). SOD catalyzes the conversion of the superoxide radical (0₂^-) to H₂O₂ plus O₂, and H₂O₂ is removed by catalase. The present results suggest that SOD plays an inhibitory role in oncogenic transformation by inhibiting promotion. 33 references, 2 figures, 2 tables

[en] DNA damage and repair in human fibroblasts were investigated by a variety of standard techniques to ascertain whether antipain a protease inhibitor, has a discernible, direct effect on DNA. Antipain was also incubated with rat-liver microsomal S9 mix to determine whether it could be activated by mechanisms often observed with carcinogens. It was hoped that these experiments would aid in determining the mechanism of antipain in modifying cell transformation and the existence in mammalian cells of mechanisms analogous to the prokaryotic recA inducible system

[en] Techniques have recently been developed to identify and score quantitatively neoplastic transformation caused by x-rays in cultured cells derived from rodents. The present report describes for the first time the neoplastic transformation in vitro of human diploid cells by x-ray irradiation into cells which can progress in vitro into advanced stages of neoplastic development, namely, to form colonies in agar and give rise to tumors when injected into nude mice

[en] In an effort to evaluate membrane changes associated with neoplastic transformation of fibroblasts and epithelial cells by radiation and chemicals, alterations in membrane-associated (Na⁺ + K⁺)-ATPase and 5'-nucleotidase activities were investigated. Cell cultures consisted of normal and radiation transformed hamster embryo fibroblasts (HE) and mouse C3H 10T 1/2 fibroblasts, normal and chemically transformed adult rat liver epithelial cells (ARL), as well as hepatocarcinoma cells induced by the liver transformants. Transformed fibroblasts demonstrated a 1-2 fold increase in (Na⁺ + K⁺)-ATPase activity over the normal, while the transformed liver epithelial cells and carcinoma cells showed a 60% and 40% decrease in activity compared to the normal values, respectively. The 5'-nucleotidase activity was 2 to 3 times higher in the transformed fibroblasts

No abstract available

[en] One of the basic questions in radiation carcinogenesis has been whether ionizing radiation produces neoplasms directly by inducing heritable changes in a single cell or indirectly by activating a virus, or changing homeostatic mechanisms. The complexity of in vivo systems and the inordinate number of animals required for whole-body studies greatly hinder investigators who are trying to elucidate the mechanism(s) of radiation carcinogenesis. Our approach has been to use an in vitro system, in which cells are irradiated either in mass cultures or as cloned single cells. These cells are maintained in vitro under defined conditions before and after treatment and therefore are not subject to homeostatic mechanisms that could modify their behavior. In the work described here, we set out to study whether x-rays could directly induce a hereditary conversion of normal cells into neoplastic cells, a process referred to as transformation. Following the successful completion of this first stage, we attempted to characterize some of the conditions required for this transformation and to study the biologic properties of the cells. A logical extension of this work was to determine a dose-response relationship between absorbed dose and transformation and to investigate the ability of other types of ionizing radiation to produce this transformation

[en] Pregnant hamsters were exposed to 300 rad of x rays at 12 days of gestation and the embryos were removed 30 min later. Cell cultures were prepared and transformed cells were identified by altered morphology and growth patterns. Observations were made on chromosome number, fibrinolytic activity of transformed cells, release of macrophage inhibitory factor, the pattern of cellular lysosomal hydrolases, and the ganglioside content of cells. The transformed cells gave rise to tumors in syngeneic hamsters

[en] In recent years it has become evident from epidemiological and experimental data that a large number of environmental factors, including diet, play a role in modifying the incidence of cancer. Cell culture systems in which oncogenic transformation serves as an end point are powerful tools for evaluating these questions. Using such systems it has been shown recently that pyrolysis products from charred surfaces of broiled meat and fish can transform hamster embryo cells in vitro as well as produce tumors in the animal. Our studies in vitro have demonstrated the oncogenic potential of ionizing radiation in both hamster and human cells and have established in hamster cells the dose response relationship at doses ranging from 1 to 600 rad for x-rays and 0.1 to 150 rad for neutrons. The present work was aimed at evaluating whether there exists a cocarcinogenic interaction between a pyrolysis product and x-rays in their ability to transform hamster embryo cells in vitro. We have found that when cells are exposed to x-rays prior to treatment with the pyrolysis product there appears to be a synergistic interaction between the two agents in their ability to transform the cells