Systematic investigation into interaction of ionizing radiation and doxorubicin in the Dunning R3327G prostatic adenocarcinoma model.

The interaction of doxorubicin and radiation has been systematically studied in the Dunning R3327G prostatic adenocarcinoma, the preeminent animal model for human prostatic cancer. Subcutaneous tumors (produced by injection of 10(7) cells) were treated when about 1 cm3 in volume (19-22 days postimplant). Each modality was used at 1 of 3 dose levels; 2, 4, and 9 mg/kg for doxorubicin; and 5, 15, and 25 Gy for radiation. Single treatment with each agent was combined, in both sequences and five delay times (0.5, 12, 24, 48, and 120 hr) between agents. Growth of individual tumors was fit to a quadratic exponential growth model which was solved for the growth delay and growth rate at twice initial volume. Analysis of variance identified significant interactions for doxorubicin and radiation (due to drug toxicity), sequence and delay, and sequence and radiation, in addition to the four factors individually. The effect on the tumor of combined doxorubicin and radiation is basically additive. Sequence and delay are important in overall tumor control.