Radiation response of cells from human tumor biopsies as assessed by a dye exclusion technique: a possible predictive assay

Differential Staining Cytotoxicity assay: a review

Differential Staining Cytotoxicity (DiSC) assay is the prototype for a closely related family of assays based on the concept of total cell kill, or, in other words, cell death occurring in the entire population of tumor cells. It is probably the most versatile of the cell-death end points, in that it (1) can be applied to both solid and hematologic neoplasms, (2) can be applied to specimens in which it is not possible to obtain a pure population of highly enriched tumor cells, and (3) can be applied to a wide variety of drugs, ranging from traditional cytotoxic agents to biological response modifiers with activity mediated through tumor-infiltrating effector cells, to "targeted" kinase inhibitors, and to antivascular agents, such as bevacizumab and pazopanib. The basic principles of the assay are to culture three-dimensional fresh tumor cell clusters in anchorage-independent conditions. At the conclusion of the culture period, Fast Green dye is added to the microwells, the contents of which are then sedimented onto permanent Cytospin centrifuge slides and then counterstained with hematoxylin-eosin or Wright-Giemsa. "Living" cells stain with the cytologic stain in question and can be identified as either normal or neoplastic, based on standard morphologic criteria. "Dead" cells stain blue-green. Nonviable endothelial cells appear as strikingly hyperchromatic, blue-black, and often refractile objects, which may be readily distinguished from other types of dead cells. This assay has been biologically and clinically validated in a number of ways, as described in this chapter.

Thein VitroRadiosensitivity of Lymphocytes from Chronic Lymphocytic Leukaemia Using the Differential Staining Cytotoxicity (DiSC) Assay. I—Investigation of the Method

A tumour sensitivity assay, the differential staining cytotoxicity (DiSC) assay, which has been shown to have potential in predicting tumour response to cytotoxic drugs, has been developed to investigate the radiosensitivity of peripheral blood lymphocytes isolated from patients with chronic lymphocytic leukaemia (CLL). The method involved irradiating isolated lymphocytes (0.64-20.48 Gy at 8 x 10(5) cells/ml) and incubating for 4 days. Subsequent radiation-induced cell kill was assessed by differential staining of dead and live cells and calculation of tumour cell viability. Factors affecting assay success rate and in vitro radioresponse were investigated. Results were shown to be reproducible both when repeat assays were performed on the same specimen on the same day, and on different specimens from the same patient after intervening periods of time. Greater than 1 day transit time (whole blood) or storage (separated cells in medium) was found to be detrimental to assay success, but pH of the medium (either pH 7.3 or 8) had little effect. An increased incubation period (from 4 to 7 days) slightly reduced cell survival, but the underlying radioresponsiveness of the cells did not change.

Fibroblasts from ataxia telangiectasia (AT) and AT heterozygotes show an enhanced level of residual DNA double-strand breaks after low dose-rate gamma-irradiation as assayed by pulsed field gel electrophoresis

Skin fibroblasts from ataxia telangiectasia (AT) patients, obligate AT heterozygotes (ATH) and normal individuals were studied for colony-forming ability and repair of DNA double-strand breaks (dsb) after gamma-irradiation. AT cells were three to four times more radiosensitive than normal cells at high and low dose-rate exposures; ATH cells, however, showed a marginally increased radiosensitivity after high dose-rate gamma-irradiation and an intermediate response after low dose-rate exposure. The repair of DNA dsb was studied by pulsed field gel electrophoresis. After high dose-rate gamma-irradiation the repair time constant (t1/2) was around 1 h for normal, ATH and AT cells. After low dose-rate gamma-irradiation the fraction of residual dsb was 1.4% for normal, 2.1% for ATH and 5.2% for AT cells, demonstrating a deficiency in the repair of a small fraction of dsb in AT. Thus the fraction of residual dsb after low dose-rate exposure was not only four times higher in AT than in normal cells, but was also significantly increased in ATH compared to normal cells.