The measurement of intrinsic cellular radiosensitivity in human tumours and normal tissues

Human tumour and normal cell radiosensitivity are thought to be important factors determining the response of tumour and normal tissues to radiotherapy, respectively. Clonogenic assays are the standard method for measuring radiosensitivity but they are of limited applicability for clinical use with fresh human tumours. The main aim of this work was to evaluate the Adhesive Tumour Cell Culture System (ATCCS), as a method for measuring the radiosensitivity of human tumours. A soft agar clonogenic assay, the modified Courtenay-Mills assay, was used as a standard to compare with the ATCCS. The demonstration that fibroblast contamination could occur with both assay methods led to the investigation of a new technique for removing unwanted fibroblasts from tumour cell suspensions and to the use of a multiwell assay for measuring fibroblast radiosensitivity. Established tumour cell lines were used to validate and optimise the ATCCS. Success rates with human tumour biopsy specimens were initially poor with both assay methods but further modifications led to success rates of ~70%. In a comparison of the modified Courtenay-Mills assay and the ATCCS there was close agreement between the measurements of surviving fraction at 2 Gy (SF2) for established tumour cell lines but with primary tumour cultures the SF2 values were significantly lower in the ATCCS. The main limitations of the ATCCS for clinical use were inter-experimental variability and fibroblast contamination. Using antibody-coated magnetic beads as a method for removing fibroblasts from tumour cell suspensions, some selectivity for fibroblasts was shown, but the specificity was too low for this method to be of value in its current form. The multiwell assay was found to be a satisfactory method for measuring fibroblast radiosensitivity although inter-experimental variability may limit its clinical use as a predictive test for normal tissue damage in patients.