Repair of potentially lethal damage after single injection or continuous infusion of bleomycin

The repair of potentially lethal damage after administration of bleomycin by a single injection or by continuous infusion was studied in vivo. Experimental tumors were the fifth generation isotransplants of a squamous cell carcinoma which arose spontaneously in a C3Hf/He female mouse. Bleomycin was administered intraperitoneally by a single injection or by 24-hr continuous infusion. Cell survival was assayed by TD50 method. Dose-survival curve after a single injection exhibited a biphasic or upward concave curve. Surviving fraction increased rapidly if tumors were left in situ after treatment and reached a plateau at 5 hr, indicating that tumor cells were able to repair the potentially lethal damage induced by bleomycin. Dose-survival curve after continuous infusion was also biphasic, but had a small shoulder. The repair of potentially lethal damage was slight, if any, when tumors remained in situ for 6 hr after the end of 24-hr continuous infusion. This indicates that potentially lethal damage was being repaired during drug infusion.