Induction and Repair of DNA and Chromosome Damage by Neocarzinostatin in Quiescent Normal Human Fibroblasts

In an attempt to understand better the molecular basis of chromosome aberration formation, neocarzinostatin (NCS)-induced damage and repair were compared at the chromosome and DNA levels. Chromosome damage and repair in quiescent normal human fibroblasts (PA2 and DET 550) were assayed by the premature chromosome condensation technique in which the G1 prematurely condensed chromosomes are condensed and easily enumerated. DNA damage was monitored by neutral DNA elution. NCS induced chromosome breaks directly in the G1 cells; thus, its clastogenic action does not require passage of cells through S phase. The dose-response curve for NCS-induced damage suggested a two-hit-type event in the formation of chromosome breaks. The half-time of chromosome repair was approximately 4.5 hr, and all but one of the chromosome breaks were repaired by 46 hr. Neither 1-β-D-arabinofuranosylcytosine nor cycloheximide blocked the repair of either DNA or chromosome damage induced by NCS in quiescent human cells.