Rapid fluorometric detection of drug resistant tumour cells.

Abstract

A rapid estimation of mutation frequency in tumours would be invaluable in cancer management. Considerable evidence suggests that drug resistance in tumours frequently arises as a consequence of spontaneous somatic mutation (Goldie & Coldman, 1979) and therefore the mutation rate of a tumour will be an index of the potential to develop drug resistance. Previous studies have compared the mutation rates of cell lines using cloning assays. Cifone & Fidler (1981) reported a higher mutation rate in metastatic variant of UV-2237 fibrosarcoma cells than in a clone of the same cell line with lower metastatic potential. Warren et al. (1981) reported that fibroblasts from patients with Bloom syndrome, which predisposes individuals to various cancers, had a 10-15 fold higher mutation rate than did fibroblasts from normal individuals. These findings have been important in correlating malignant capacity with genetic instability, but unfortunately, the techniques used have limited general application since few human tumour cells will form colonies on plastic. An alternative assay, soft agar cloning, has also been used for the determination of mutation rates in a variety of mammalian cell lines, including Chinese hamster ovary cells (Li & Shimizu, 1983) and the L5178Y mouse lymphoma cell line (Irr & Snee, 1982). Again, the low cloning efficiency of human tumour cells in soft agar (Hamburger et al., 1978) and the fact that this method selects only mutant cells which clone in agar limits the use of this assay to determine mutation frequency in human tumours. This latter source of error might bias the estimation of the mutation rate in favour of more malignant cells, which generally have higher cloning efficiencies (Elmore et al., 1983). Morley et al. (1983) and Albertini et al. (1982) have reported a limiting dilution technique for the measurement of mutation frequency in human lymphocytes. Culture conditions have been optimised for peripheral blood lymphocytes and a cloning efficiency of 20-60% has been obtained. Problems have been encountered, however, in studies of cultured lymphoblast lines with variable