480 In vitro radiosensitivity of head and neck tumour cells and fibroblasts assessed from single biopsies

Abstract

The assumed selective growth of tumour cells in the soft agar clonogenic assay has formed the basis for its use to test in vitro sensitivity of tumours. However, studies in our laboratory have shown that also normal skin fibroblasts grow in soft agar. The present study was initiated to quantify the contaminating growth of fibroblasts in the enriched modified Courtenay-Mills soft agar assay, and to investigate ways to overcome this problem. A new colony filter-technique including immunohistochemical identification was developed, and 88–100% of the colonies obtained from 13 head and neck tumours were 5B5 Fibroblast Antibody positive, whereas 0–25% of the colonies were Cytokeratin AE1-3 positive. Thus, the present technique identifies tumour and fibroblast colonies, respectively, and it can measure the in vitro radiosensitivity of both tumour cells and fibroblasts. The parameter normally reported, the overall Surviving Fraction at 2 Gy (SF 2 ), based on the number of colonies in agar, was significantly correlated to SF 2 of fibroblasts (SF 2 F), but not to SF 2 of tumour cells (SF 2 T). The overall SF 2 was significantly different from SF 2 T in half of the examined patients. The SF 2 T was not correlated to SF 2 F. Thus, it is necessary to make a routine correction for fibro blast contamination, when studying tumour cell radiosensitivity. If this is done, the possibility of estimating both tumour cell and fibroblast radiosensitivities from a single biopsy is of interest in future clinical studies on predictive assays.