Roger J. Berry

Effects of some Metabolic Inhibitors on X-ray Dose-response Curves for the Survival of Mammalian Cells in vitro, and on Early Recovery between Fractionated X-ray Doses

The rapid (0–8 hour) recovery from sub-lethal X-ray damage in HeLa S-3oxf cells in vitro is neither delayed nor reduced in magnitude by incubating the cells in media containing high concentrations of 2–4 Dinitrophenol, which deprives the cells of a major energy source by uncoupling oxidative phosphorylation. In fact, cells surviving 100 μg/ml. concentrations of DNP showed somewhat increased recovery between fractionated X-ray doses. 5-Fluorouracil in high concentrations sensitises the cells to single X-ray exposures, but the steeper dose-response curve retains a marked shoulder and no significant modification of the two-dose recovery curve is seen even with drug concentrations that are high enough to reduce cell survival drastically on their own. The antibiotics Puromycin and Cycloheximide, although inhibiting protein synthesis and sensitising cells to the effects of single doses of X rays, do not decrease early recovery even when the drug under study is added to the cell cultures as much as 20 hours prio...

RADIOSENSITIVITY AND THE OXYGEN EFFECT FOR MAMMALIAN CELLS CULTURED IN VITRO IN STATIONARY PHASE.

Abstract HeLa cells grown in medium 199 supplemented with 15 per cent human serum show increased radiosensitivity when irradiated in unfed confluent culture (“stationary phase”), compared with their response when irradiated during exponential growth (“log. phase”). In addition, a biphasic dose-response curve for stationary phase cells irradiated, under hypoxic conditions indicates that the oxygen enhancement ratio (OER) is reduced from circa 3·0 to circa 1·8 for a significant proportion of the cells. Thus, up to doses (if 500–600 rads, greater depopulation occurred in hypoxic stationary phase cells than in aerobic, exponentially growing cells. However, the same cells grown in human serum-supplemented medium F10 showed increased radiosensitivity in confluent culture but an unaltered OER. By contrast, Chinese hamster cells grown in confluent culture with or without medium changes showed no significant changes in the slope or shoulder of their dose-survival curves compared with those irradiated during expone...

QUANTITATIVE STUDIES OF RADIATION EFFECTS ON CELL REPRODUCTIVE CAPACITY IN A MAMMALIAN TRANSPLANTABLE TUMOR SYSTEM IN VIVO

The transplantability of leukemic ascites cells from mice bearing the transplanted lymphocytic leukemia P-358 was utilized as a measure of cell reproductive capacity. The response of mammalian cells to ionizing radiation appears to be similar in vivo and in vitro. The system is relatively free of host-immunity factors and has been used to study the effects of oxygenation and anoxia, the effects of dose fractionation and aspects of cellular recovery, and changes in radiation response induced by pharmacological agents. (auth)

DEMONSTRATION OF A CYTOTOXIC AGENT IN GAMMA-IRRADIATED CARBOHYDRATE SOLUTIONS

SummaryIrradiated carbohydrate solutions have been found to be toxic to mammalian cells in vitro. For 1 per cent solutions of dextrose or fructose added to the growth medium the effect is maximal after a dose of ∼ 105 rads. The toxic product, once formed, is heat-stable and persists after the heavy irradiation needed for sterilization for more than 6 months. Autoclaved dextrose and fructose solutions also show some cytotoxicity, but this is less pronounced in aged solutions.

Quantitative Studies of Relationships between Tumor Cell Ploidy and Dose Response to Ionizing Radiation in Vivo: Modification of Radiation Response in a Previously Irradiated Tumor

ggradiation was demonstrated in vivo between two closely related murine lymphocytic leukemias, one diploid and the other tetraploid. Dose-response curves were determined under oxygenated and anoxic conditions; in either condition the slopes of the dose-response curves were similar, but the extrapolation number for the tetraploid tumor exceeded that for the diploid tumor by a factor of approximately 2. A tumor line of diploid origin was subjected to 1000 rads of x irradiation at each of fifty sequential passages in vivo with 10/ sup 6/ tumor cells transplanted at each passage to minimize the chance of selection from small numbers of surviving celis. During the fifty irradiated passages, this tumor line was noted to have altered radiation response with a greater proportion of tumor cells surviving any given radiation dose, increased nucleic acid content per cell was seen, and tetraploid and aneuploid cells appeared in the population. The application of these findings to the acquired radioresistance reported by radiotherapists in the treatment of human cancer is discussed. (auth)

Quantitative Relationships between Radiation Dose and the Reproductive Capacity of Tumor Cells in a Mammalian System in Vivo1

The ability to grow mammalian cells in clonal culture provided the first direct method for measuring the destruction of the reproductive capacity of the cell by ionizing radiation (1). The first system for similarly studying the reproductive capacity of tumor cells in the intact mammalian host was provided by the elegant work of Hewitt and Wilson (2–5). By dividing the number of tumor cells from unirradiated leukemic donor mice necessary to produce tumor “takes” in 50 per cent of recipient mice of the same strain, by the number of tumor cells from irradiated donor animals needed to produce similar 50 per cent “takes,” they obtained the “surviving fraction,” i.e., the percentage of cells remaining capable of unlimited reproduction after a given dose of radiation. The results reported by Hewitt and Wilson were in close agreement with those obtained in vitro and suggested that the reproductive integrity of many mammalian cells, regardless of species, and of normal or malignant origin, showed strikingly simil...

The Effect of Radiation Ionization Density (LET) upon the Reproductive Capacity of Mammalian Tumour Cells Irradiated and assayed in vivo

The response of mammalian tumour cells to ionizing radiation has been studied in vivo using the transplantability of leukaemic ascites cells as a measure of cell reproductive capacity. Dose-response curves are presented under both oxygenated and anoxic conditions for X rays, 60Co γ, fission-spectrum fast neutrons, 14 MeV monoenergetic neutrons, and for irradiation with both the plateau and Bragg-peak regions of beams of 340 MeV protons and 380 MeV α particles. The significance of changes with LET in D0 (37 per cent dose) slope and extrapolation number of the dose-response curves are discussed and additional evidence is presented of correlation between the ability of cells to show recovery with fractionated irradiation and dose-response extrapolation numbers greater than unity. Considerations for the use of high LET (densely-ionizing) radiations in radiotherapy of human cancer are discussed.

ON THE SHAPE OF X-RAY DOSE-RESPONSE CURVES FOR THE REPRODUCTIVE SURVIVAL OF MAMMALIAN CELLS

In clonal cell culture experiments, not only the absolute survival to a given X- or γ-radiation dose, but also the shape of the dose-response curve for cell reproductive capacity in vitro can be altered by changes in the growth medium six days after irradiation. Comparisons are drawn between clonal survival in vitro and results obtained using transplantable tumour assays in vivo, and implications for the formulation of model systems are discussed.

Fast neutron irradiation and the relationship of radiation dose and mammalian tumor cell reproductive capacity.

The dose-response relationship for neutron irradiation of a quantitative in vivo mouse tumor cell system was determined and compared with the dose- response relationship for x irradiation performed under both anoxic and oxygenated conditions. Values of n = l.0 and D/sub 37/. = 85 rads were obtained for fission-spectrum fast neutron irradiation as compared with n = 1.6 and D/sub 37/ = 365 rads for x irradiation under anoxic conditions and n = l.6 and D/su b 37/ = I60 rads for x irradiation under oxygenated conditions. The cell system employed conforms in its radiobiological behavior with other mammalian cell culture systems and constitutes a useful test system for the study of cell radiobiological phenomena. The same or greater degree of apparent radiosensitivity was attained by direct neutron irradiation of cells in the anoxic state as was attained by x irradiation in the oxygenated state. Radiosensitivity cannot be defined in terms of a single RBE ratio but only in terms of the complete dose-response relationship or in respect to the parameters, n and D/sub 37/, which describe this relationship, (auth)

Survival of mammalian cells exposed to x rays at ultra-high dose-rates.

Abstract X irradiation delivered in single, nanosecond-length pulses, so that the instantaneous dose-rate exceeded 7 × 1010 rads/second, was less effective in abolishing the subsequent reproductive capacity of HeLa and Chinese hamster cells in vitro than was irradiation delivered at lower dose-rates. It was felt that this was not due to the production of transient intracellular hypoxia during the radiation pulse in these mammalian cells, and an alternative hypothesis is proposed to explain these results. Possible applications of ultra-high dose-rate irradiation in radiotherapy are discussed.