K562. A human cellular system capable of undergoing in vitro differentiation: measurement of genotoxic parameters useful for cytotoxicity evaluation

By Sapora, O. - Maggi, A. - Maione, B. - Pazzaglia, S. - Tabocchini, M.A.

The initial damage produced by ionising radiation and its subsequent repair have been studied in a cellular system. K562 cells are used which are capable of undergoing in vitro pseudoerythroid differentiation in the presence of 2 mM butyric acid. The level of initial damage is similar in actively growing and 48-hour differentiated cells, while it is lower by a factor of two in cells irradiated after exposure to the inducer for 72 hours. In differentiated cells, the kinetics of repair measured up to 60 minutes is slower than that in actively growing cells. These findings suggest that the genome of actively proliferating cells is not only more susceptible to radiation-induced damage, but also more accessible to repair enzymes than the more compact genome of differentiated cells. Repair after a longer time interval has also been investigated. After 24 hours of repair, the amount of residual damage is higher in actively proliferating cells than in differentiated ones. However, in proliferating cells, DNA synthesis can interfere with repair of the lesions or vice versa, while in differentiated cells, due to the lack of proliferation, damage occurring in nontranscribing genes can presumably be sustained for longer periods without biological consequences. A method to evaluate the relative sensitivity of non-duplicating differentiated cells is proposed. It is based on measurement of the residual damage, detected after 24 hours of repair, and on the assumption that a relationship exists between unrepaired DNA damage (residual damage) and the ability of the cell to survive.