ASSESSMENT OF THE PROLIFERATIVE ACTIVITY AND RADIOSENSITIVITY OF HUMAN TUMORS USING THE CYTOKINESIS-BLOCK MICRONUCLEUS ASSAY

We established an in vitro cytokinesis-block micronucleus assay of hum an tumours for estimation of the proportion of cells undergoing mitosi s (the dividing fraction, DF), the time for the number of nuclei to do uble and the radiosensitivity in terms of the micronucleus frequency, based on a concept described previously. Under certain conditions, the nuclear number doubling time (NNDT) was considered to represent the p otential doubling time. Tumour specimens obtained at surgery were disa ggregated into single-cell suspensions and were directly cultured in t he presence of cytochalasin B with or without irradiation. At various intervals, the percentage of multinucleate cells (the plateau value re presented the DF), the average number of nuclei per cell and the numbe r of micronuclei in binucleate cells were determined. DF and NNDT valu es were obtained in 58 of the 73 tumours investigated, and the micronu lceus frequency was obtained in 54 of these 58 tumours. The DF ranged from 4.1% to 71% and the NNDT ranged from 3.1 to 83 days. A DF greater than or equal to 20% was associated with a higher recurrence rate in patients undergoing curative operation. A correlation was found betwee n the NNDT and the lime to relapse in patients with recurrent disease. The average number of micronuclei per binucleate cell at 2 Gy of irra diation (after subtraction of the value at 0 Gy) ranged from 0.052 to 0.35. Tumours which produced more micronuclei after irradiation showed a better response to radiotherapy. This assay can be readily performe d on human tumours and appears to have promise as a predictive assay f or radiation therapy.