Isolation and characterization of highly radioresistant malignant hamster fibroblasts that survive acute gamma irradiation with 20 Gy.

To study the acquired radioresistance of tumor cells, a model system of two cell lines, Djungarian hamster fibroblasts (DH-TK-) and their radioresistant progeny, was established. The progeny of irradiated cells were isolated by treating the parental cell monolayer with a single dose of 20 Gy (PIC-20). The genetic and morphological features, clonogenic ability, radiosensitivity, cell growth kinetics, ability to grow in methylcellulose, and tumorigenicity of these cell lines were compared. The plating efficiency of PIC-20 cells exceeded that of DH-TK- cells. The progeny of irradiated cells were more radioresistant than parental cells. The average D0 for PIC-20 cells was 7.4 +/- 0.2 Gy, which is three times higher than that for parental cells (2.5 +/- 0.1 Gy). Progeny cell survival in methylcellulose after irradiation with a dose of 10 Gy was 15 times higher than that of DH-TK- cells. In contrast to parental cells, the progeny of irradiated cells showed fast and effective repopulation after irradiation with doses of 12.5 and 15 Gy. The tumor formation ability of irradiated progeny cells was higher than that of parental cells; after 15 Gy irradiation, PIC-20 cells produced tumors as large as unirradiated progeny of irradiated cells, whereas the tumor development of DH-TK- cells diminished by 70%. High radioresistance of progeny of irradiated cells was reproduced during the long period of cultivation (more than 80 passages). The stability of the radioresistant phenotype of PIC-20 cells allows us to investigate the possible mechanisms of acquired tumor radioresistance.

Loss of p53 in craf-induced transgenic lung adenoma leads to tumor acceleration and phenotypic switch.

One of the most frequent malignancies in humans is lung adenocarcinoma.To develop novel diagnostic and therapeutic approaches for the management of this disease, animal models are required. We have used transgenic mice with lung-targeted expression of the CRaf kinase to evaluate genes altered frequently in human lung adenocarcinoma for their effect on tumor progression. Here we report that loss of p53 dramatically accelerates tumor development and induces a phenotypic switch in the target cell from cuboid to a nonciliated columnar morphology. Coexpression of lung epithelial cell markers surfactant protein C and Clara cell antigen suggests that tumor cell dedifferentiation could be involved in this process. The effect of p53 is specific, because loss of one of its target genes, p21(CIP1/WAF1), did not have this effect on cell phenotype although tumor latency was also reduced significantly. Neither loss of p53 nor p21 stimulated acquisition of the metastasis program beyond the stage of bronchiolar extension. This mouse model for pulmonary adenoma and adenocarcinoma should be very helpful for a better understanding of pathogenesis and treatment of this most deadly human cancer.