Reoxygenation in the RIF-1 tumor after chemotherapy.

The proportion of hypoxic cells in the RIF-1 tumor was observed for 24 hr after treatments with bleomycin, cisplatin, cyclophosphamide, and mitomycin C. The assays were based upon the paired survival curve method for determining the hypoxic fraction using irradiation of aerobic and artificially hypoxic tumors. It was observed that at 1/2 hr after bleomycin, hypoxic fraction was elevated but returned to baseline levels by 2 hr. Following cisplatin, hypoxic fraction did not rise above baseline. However, after cyclophosphamide, hypoxic fraction was elevated and did not return to baseline over the 24-hr observation period of this study. At 1/2 hr after mitomycin treatment, the hypoxic fraction was raised but within 1 hr returned to baseline. These results indicate that tumor reoxygenation varies after different drug treatments and that the determination of drug specificity for aerobic versus hypoxic cells may be strongly biased by the choice of the time after treatment for making the determination.