Glutathione levels were measured in 30 human lung cancer lines. Lower levels were detected in cell lines derived from small cell lung cancer specimens compared to non-small cell lines (mean 42 vs. 130 nmol mg-1 protein, P = 0.005). However, no difference were detected between cell lines derived from previously untreated patients, compared to those derived from patients who had received chemotherapy. Non-small cell lines were found to have increased activity of 4 detoxification enzymes compared to small cell lines, although these differences did not reach statistical significance: glutathione transferase activity (69 vs. 36 units, P = 0.137), glutathione reductase (139 vs. 82 units, P = 0.05), gamma-glutamyl transpeptidase (9.39 vs. 3.03 units, P = 0.072) and superoxide dismutase (20 vs. 13.6 units, P = 0.137). As the cell lines exhibit a similar chemosensitivity pattern to that observed in clinical practice, these differences in glutathione and detoxification enzyme levels may prove to be important indicators of intrinsic drug resistance often seen in patients with non-small cell lung cancer.

The first postirradiation division of synchronized S3 HeLa cells was studied using both continuous and fractionated irradiation treatments. Synchronized HeLa cells continuously irradiated at a dose rate of 37 rad/hr eventually accumulate in mitosis. If the continous irradiation is stopped before the cells enter G2 or even after they have progressed for a limited time into the G2 arrest that develops, very little subsequent accumulation of cells in mitosis occurs. If they progress for a longer time into the G2 arrest, then some mitotic accumulation does occur after the irradiation is stopped. When synchronized cells were allowed to progress through G1 and S before the irradiation was started, very little cell division occurred during subsequent continuous irradiation and extensive mitotic accumulation was observed. Thus, for continous irradiation of HeLa cells, the dose received by a cell during G2 or a G2 delay apparently determines whether it will be able to divide if it reaches mitosis. Arguing against ...

A technique for visualizing "interphase chromosomes" was applied to nuclei of the angio-spermous plant, Ornithogalum virens (2 n = 6), and the male mammal, Muntiacus munjak (2 n = 7), in an attempt to correlate the numbers of "chromosomes" visible during interphase with the respective diploid chromosome numbers. The alterations in chromosome structure observed during G1, S, and G2 periods were comparable to those previously reported in Allium cepa and Chinese hamster (CHO line) cells [33], but for technical reasons it was only possible to make accurate counts of interphase chromosomes in the G1 nuclei of O. virens. In addition, from our observations of interphase chromosomes that were pulse-labelled with tritiated thymidine and a parallel study of premature chromosome condensation (PCC) using pulse-labelled M.muntjak cells, we conclude that, although chromatin decondensation may be required for DNA synthesis, extreme chromatin decondensation can occur in the absence of DNA synthesis. Generally a morphological description of alterations in chromatin during interphase only roughly parallels the G1, S, and G2 phases defined by autoradiography following incorporation of tritiated thymidine. We suggest that both methods are valid through different ways of describing interphase.

The variation in heat and/or X-ray response of 7 mammalian cell lines treated under identical culture conditions and experimental procedures was examined. Large differences in thermal response at 42.5 and 45.5° (dose-modifying factors of greater than 10) were observed among the cell lines, and the order of heat sensitivity for the 7 cell lines was similar but not identical at 42.5 and 45.5°. However, classification of thermal sensitivity at 42.5° depended on the time of heating, since thermal tolerance developed at different survival levels after 3 to 4 hr of heating for pig kidney, muntjac, Chinese hamster (V79 and CHO), and HeLa cells, whereas no thermal tolerance and only a transitory thermal tolerance were observed for mouse LP59 and rat kangaroo cells, respectively. Also, Chinese hamster ovary cells were more heat sensitive when cultured in McCoy9s Medium 5a containing 10% calf serum plus 5% fetal calf serum than when cultured in F12 medium containing 10% fetal calf serum. Small variations in the X-ray dose response of the seven mammalian cell lines (dose-modifying factors of less than 1.5) were observed. The X-ray response was enhanced by thermal treatment at 42.5° for 1 hr preceding irradiation, and there was a positive correlation between the degree of thermal enhancement and cellular thermal sensitivity at 42.5°. However, there was no correlation between differences in heat sensitivity and differences in radiosensitivity. Also, no apparent correlation between heat and/or X-ray response and cell chromosome number, DNA content, cell volume, and cell population doubling time could be found. However, heat sensitivity could, in general, be related to the body temperature of the species from which the cell line was derived.

The ability of S3 HeLa cells to divide during continuous irradiation was studied using time-lapse cinemicrography. Cells were initially synchronized by mitotic selection, and the irradiation was started 2 hr later. For dose rates of approximately 35 rad/hr very few cells were able to divide during 60 hr of continuous irradiation, but many accumulated for prolonged periods in a rounded configuration. Parallel studies in which cells were harvested and fixed for microscopic examination showed that most of the rounded cells seen in the time-lapse films must have been cells which entered mitosis, attempting to divide, and not cells rounding and dying from an interphase configuration. After 50 to 60 hr of continuous irradiation the frequency of cells with micronuclei increased sharply. Mitotic accumulation during continuous irradiation was similar in some respects to that seen in the presence of colcemide.

With the use of two mammalian cell lines (L5178Y and V79), a comparison was made of the efficiency of cell killing by gamma rays and beta particles from tritiated water and incorporated tritiated thymidine. For the latter, cells were incubated with tritiated thymidine for one generation (unifilar labeling) or for four generations (bifilar labeling). To prevent cell division during exposures, irradiations were carried out with cells held in the frozen state or, in one case, at 5$sup 0$C. There was no significant difference in cell killing efficiency for unifilar or bifilar modes of tritiated thymidine incorporation. In the frozen state an increase in D$sub 0$ was observed for all modes of irradiation, but an apparent increase in killing efficiency was observed for irradiations following incorporation of tritiated thymidine relative to that observed for irradiations with gamma rays. For cells irradiated at 5$sup 0$C, the efficiency of cell killing by beta particles from tritiated water or incorporated tritiated thymidine was not appreciably different, but both were more efficient than gamma irradiation delivered under similar conditions. For killing of V79 cells at 5$sup 0$C, and at a dose rate of 20 rad/hr, the relative biological effectiveness (RBE) of tritium beta particles relativemore » to cobalt-60 gamma rays was estimated to be approximately 1.7 to 1.9. (auth)« less

During prolonged hypoxia, a progressive change occurs in the radiosensitivity of cultured mammalian cells. An attempt was made to determine whether this could be explained on the basis of a progressive change in the life cycle or age distribution of cells during hypoxia. Cell population growth kinetics and the cell life cycle were studied by two conventional methods of analysis. Both indicated an appreciable heterogeneity in the cell populations with regard to the ability of individual cells to negotiate their life cycle during hypoxia. This heterogeneity was confirmed by studying the development of individual microcolonies under hypoxia. From this study, the following conclusions were reached regarding changes which occurred during hypoxia: (1) the growth rate was decreased and the life cycle lengthened; (2) the overall proportion of cells in DNA synthesis decreased with time; (3) on average, a disproportionate lengthening of the G1 phase of the life cycle was implicated; and (4) these changes were accompanied by a decrease in the shoulder and an increase in the D0 for the cell survival curve following irradiation with 60Co γ rays. Changes in the radiation response for reasons other than changes in the life cycle or age distribution could not be ruled out.

The life cycle and survival of synchronized HeLa and Chinese hamster cells were examined during continuous irradiation at dose rates of 38 or 90 rads per hour. The results indicate that over a given range of dose rates, life-cycle-related factors can play a significant role in what is commonly referred to as the dose-rate effect. Dose rates of 38 rads per hour for HeLa cells, and 90 rads per hour for V79 Chinese hamster cells essentially prevented cell division. Continuous irradiation had no effect on the progress of cells through G1 or S, but produced a G2 delay and prevented cell division. If the continuous irradiation was started just before mitosis, cell division was also prevented. Continuous irradiation at 38 rads per hour had no measurable effect on the life cycle or division of V79 cells during three successive generations.