A new mouse tumor model system (RIF-1) for comparison of end-point studies.

A new tumor model system (RIF-1) was developed that is very suitable for studies in which clonogenic survival is compared with growth delay and control probability following various forms of treatment. The tumor was a radiation-induced sarcoma in the inbred female C3H/Km mouse. It had a low median tumor dose, had a satisfactory plating efficiency direct from in vivo to in vitro, was nonimmunogenic or minimally immunogenic, and metastasized only at a relatively advanced stage of growth. The cell line grew either as a monolayer on plastic dishes, as tumor spheroids in spinner culture, as lung nodules following injection of a single-cell suspension into the tail veins of syngeneic mice, or as a solid tumor. Both diploid and tetraploid clonogenic cells were found in monolayer cultures of the RIF-1 line.

The effect of treatment in fractionated schedules with the combination of X-irradiation and six cytotoxic drugs on the RIF-1 tumor and normal mouse skin.

RIF-1 tumors, implanted syngeneically in the gastrocnemius muscles of the right hind legs of C3H/Km mice, were treated either with X ray alone, drug alone, or drug and X ray combined. The drugs tested were bleomycin, BCNU, cis-diamminedichloro platinum, adriamycin, cyclophosphamide, and actinomycin-D. All drugs were administered either in the maximum tolerated dose or a dose that causes minimal tumor growth delay. Both drugs and X rays were administered either as a single dose or in five daily fractions. In addition to the single modality controls, seven different schedules of combined modalities were tested. Tumors were measured periodically after treatment in order that the day at which each tumor reached 4 times its initial cross-sectional area, i.e., its size at the time of treatment, could be determined. The effect of treatment on tumors was based upon excess growth delay (GD), i.e., T400% (treated)-T400% (untreated control). Treatment effects for the same combined modality schedules were also determined for normal skin, using the early skin reaction as an endpoint. Dose effect factors (DEF) were computed for all combined modality schedules and were based upon calculated radiation dose equivalents. We also calculated supra-additivity ratios, SRI and SRII, therapeutic gain factors and adjusted therapeutic gain factors. The only drugs to produce significant supra-additivity with X rays were cis-Pt and cyclo. Maximum supra-additivity for cis-Pt was afforded by divided doses of the drug (5 X 2.4 mg/kg/day) given immediately before X ray (5 X 1000 rad/day) on 5 consecutive days, although 3 other schedules also produced significant supra-additivity. Maximum supra-additivity for cyclo was seen for a single dose of 100 mg/kg followed 1 day later by a course of 5 daily X ray doses (5 X 1000 rad/day), and at least one other schedule produced almost as great an effect.