Radiation-Induced DNA Damage and Lethality in E. coli As Modified by the Antitumor Agent cis-Dichlorodiammineplatinum(II)

The antitumor drug, $cis\text{-}{\rm Pt}({\rm NH}_{3})_{2}{\rm Cl}_{2}$, has been tested on stationary phase cells of E. coli C for toxicity, radiation sensitization, and effect on radiation-induced thymine base residue release from cellular DNA. Sensitization in ${\rm N}_{2}\text{-saturated}$ suspensions is about 60% greater than that obtained in O2-saturated suspensions. Additionally, a small component of low-dose radiation sensitivity is observed for bacteria irradiated in the presence of sensitizing concentrations of the Pt complex under anoxic, but not oxic, conditions. When stationary phase cells which contain ^{3}{\rm H}\text{-thymine-labeled}$ DNA are irradiated and treated under conditions designed to inhibit enzyme action, various tritiated products are obtained from the cellular DNA. The product of highest yield has been identified as thymine, and more thymine is produced when oxygen is present during irradiation than when it is absent. When cells are irradiated in the presence of a sensitizing concentrations of the platinum drug, the thmine yield is reduced and shows little difference between oxic and anoxic conditions.