Nalidixic acid and oxolinic acid reversibly suppress 3‐methylcholanthrene‐induced cell transformation of BALB/3T3 mouse cells

The effects of nalidixic acid (Nal) and oxolinic acid (Oxl), synthetic antibacterial compounds that inhibit bacterial DNA gyrase, on 3‐methylcholanthrene (MC)‐induced transformation of BALB/3T3 mouse cells were investigated. Exposure of the cells to Nal or Oxl for 2 weeks at any time during 4 weeks of incubation following MC treatment suppressed MC‐induced transformation. Nal and Oxl also suppressed the enhancement of transformation by 12‐O‐tetradecanoylphorbol‐13‐acetate (TPA) initiated by MC. The suppression of transformation by Nal was released by exposure of the cells to TPA after removal of Nal. Since the suppressive effects of Nal and Oxl on transformation were time‐related, they may be due to epigenetic changes.