Rapid assay for cell age response to radiation by electronic volume flow cell sorting

Flow cytometry in radiation research: past, present and future

Flow cytometry is an invaluable technique in research and clinical laboratories. The technique has been applied extensively to many areas of radiation research at both the experimental and clinical level. In the past few years, there has been a significant increase in the capabilities of modern flow cytometers to undertake multicolor analysis in a user-friendly manner. The developments in cytometric technology are being matched by the rapid development of new reagents, new fluorochromes and new platforms such as bead arrays. These developments are facilitating many new applications in both basic and clinical research that have relevance for many fields of biology, including radiation research. This review provides a historical overview of the application of flow cytometry to radiobiology and an update on how technology and reagents have changed and cites examples of new applications relevant to radiation researchers. In addition, some entirely new flow instrumentation is currently under development that has significant potential for applications in radiation research.

Cell cycle dependence of epidermal growth factor induced radiosensitization

The effect of epidermal growth factor on the radiation response of two human squamous carcinoma cell lines, A431 (from vulva) and SiHa (from cervix), was examined. In both lines, cells in S phase were more radioresistant than cells in other cell cycle phases. Epidermal growth factor present after irradiation enhanced the radiation response of A431 cells in different cell cycle phases, whereas no effect was seen for SiHa cells. The enhancement was maximum with 10 ng/ml epidermal growth factor and was associated mainly with a reduction in the shoulder region of the cell survival curve. The ratio between the n values of the control and epidermal growth factor treated total cell population, G1, S, and G2M cells is 2.2, 4.1, 1.7, and 2.2, respectively. Epidermal growth factor reduced plating efficiency by about 50% for A431 cells in different cell cycle phases whereas a slight increase in plating efficiency was seen for SiHa cells. The present results indicate that epidermal growth factor related radiosensitization is dependent on both cell line and cell cycle.

Variation in radiation sensitivity during the cell cycle of two human squamous cell carcinomas

Changes in the radiation age response are described in two cell lines derived from human squamous cell carcinomas. A radioresistant tumor cell line, JSQ-3, has a DO of 240 cGy and is polyploid with a DNA content of 2.68. A relatively radiosensitive tumor cell line, SCC-61, has a DO of 126 cGy and has a DNA index of 1.16. Tumor cells were separated and synchronized by centrifugal elutriation; flow cytometry was used to determine cell-cycle parameters and relative synchrony. The radioresistant cell line, JSQ-3B, was found to have twice the number of cells in S-phase than the more sensitive cell line (28% and 13% for JSQ-3B and SCC-61B, respectively). Both cell lines, despite differences in intrinsic radiosensitivity, were most resistant during S-phase (DOs of 258 and 157 cGy for JSQ-3B and SCC-61B, respectively) and were maximally sensitive during G1 (DOs of 193 and 95 cGy for JSQ-3B and SCC-61B, respectively). Clinical implications of our findings are discussed.

Automated selective dissociation of cells from different regions of multicellular spheroids

In this report we describe a new apparatus which has been developed for the automated selective dissociation of multicellular spheroids into fractions of viable cells from different locations in the spheroid. This device is based on the exposure of spheroids to a 0.25% solution of trypsin under carefully controlled conditions, such that the cells are released from the outer spheroid surface in successive layers. Study of the spheroid size, number of cells per spheroid, and sections through the spheroid with increasing exposure to trypsin demonstrate the effectiveness of this technique. The technique has been successfully used on spheroids from five different cell lines over a wide range of spheroid diameters. We also present data detailing the effect of varying the dissociation temperature, the mixing speed, the trypsin concentration, and the number of spheroids being dissociated. The new apparatus has several advantages over previous selective dissociation methods and other techniques for isolating cells from different regions in spheroids, including: a) precise control over dissociation conditions, improving reproducibility; b) short time to recover cell fractions; c) ability to isolate large numbers of cells from many different spheroid locations; d) use of common, inexpensive laboratory equipment; and e) easy adaptability to new cell lines or various spheroid sizes. Applications of this method are demonstrated, including the measurement of nutrient consumption rates, regrowth kinetics, and radiation survivals of cells from different spheroid regions.

Sensitivity to X-irradiation in relation to cell size of CHO cells synchronized in early G1

A population of line CHO Chinese hamster cells was synchronized by mitotic selection and allowed to enter early G1, after which the largest and smallest cells in the population were sorted, irradiated, and their viability determined. Despite sizeable differences in volume, metabolic capability and cell cycle progression rates, an equivalent level of survival was obtained for the two populations, indicating that the factors responsible for the volume, metabolic and progression heterogeneity do not contribute greatly to radiation sensitivity.