THE RADIOSENSITIVITY OF HUMAN-MALIGNANT MELANOMAS EVALUATED BY CYTOKINESIS-BLOCK MICRONUCLEUS ASSAY

Cytokinesis-block micronucleus assay (CB-MNA) was applied for comparis on of radiation sensitivity of 25 human malignant melanomas in primary culture. Cells obtained from tumor specimens were irradiated (0-4.Gy) on dishes, incubated with cytochalasin B (2 mu g/ml) to block cytokin esis, stained in situ and micronuclei (MN) scored in binucleate cells (BNC). Proportions of BNC in nonirradiated controls after fixed time o f incubation (96 h) ranged from 2.3 to 38% indicating great difference s (C.V. = 74%) in proliferative activity among tumors evaluated. No co rrelation was observed between proliferative activity and susceptibili ty of cells to induction of MN by radiation. The great inter-tumor het erogeneity was observed in respect of radiation sensitivity expressed either as normalized (Net) frequency (Fq) of BNC with MN or as number of MN per BNC. Both endpoints differed widely at 2 Gy and 4 Gy as well (Net FqBNC with MN = 0.28-25.4% or 1.5-45% and MN/BNC = 0.004-0.309 o r 0.013-0.593 respectively at 2 Gy and 4 Gy) with coefficients of vari ation ranging from 44 to 57%. Extreme difference in MN frequency was a lso observed between one primary tumor and its metastasis indicating i ntra-tumor heterogeneity. Our results suggest that CB-MNA may contribu te some clinically useful information for discriminating tumors that w ill eventually respond to radiotherapy and those that win probably not . However, studies aimed at comparison of MN induction in vitro with c linical radioresponsiveness of malignant melanomas are urgently requir ed.