Frequency of radiation-induced micronuclei in neuronal cells does not correlate with clonogenic survival

It is generally assumed that radiation-induced micronuclei (MN) in cytokine sis-blocked cells are an expression of cellular radiosensitivity, Therefore , radiosensitive cells should have a high frequency of MN and radioresistan t cells should show lower levels. We have irradiated cells of a panel of 13 neuronal cell lines of widely differing radiosensitivity [human neuroblast omas: N2 alpha, SHSY5Y, SK-N-SH, KELLY and SK-N-BE(2c); murine neuroblastom as: OP-6 and OP-27; human glioblastomas: G120, G60, G28, G112, G44 and G62] and compared their radiation response using the micronucleus and standard clonogenic assays. It was found that micronucleus frequency was much higher in some of the radioresistant cell lines (N2 alpha, G28, G120 and G44; SF2 greater than or equal to 0.60). These cell lines showed a high frequency o f more than 0.32 MN per gray of Co-60 gamma radiation per binucleated cell. On the other hand, the more radiosensitive cell lines (OP-27 and SK-N-SH, SF2 less than or equal to 0.27) produced 0.08 +/- 0.01 and 0.04 +/- 0.01 MN per gray, respectively, OP-6, SK-N-BE(2c), G112, G62, G60 and KELLY cells constituted an intermediate group and displayed a micronucleus formation in dex between 0.10 and 0.24 MN per gray per binucleated cell. SHSY5Y cells sh owed no detectable formation of MN. In two groups [OP-6, SK-N-BE(2c), G112, G62, N2 alpha and G28 or G120, G60, OP-27 and SK-N-SH], the more resistant cell lines produced more MN per unit dose. Another group [OP-6, SK-N-BE(2c ), G112, G62, G44 and G120] showed no correlation between micronucleus form ation and radiosensitivity, We conclude that the relationship between cell survival and micronucleus formation is not straightforward and that it woul d be simplistic to translate micronucleus frequency into radiosensitivity, (C) 2000 by Radiation Research Society.