Toxicity, radiation sensitivity modification, and combined drug effects of ascorbic acid with misonidazole in vivo on FSaII murine fibrosarcomas.

Ascorbic acid (ASC) has been shown to radioprotect nonmalignant tissue and to enhance the effects of misonidazole (MISO) on hypoxic cells in vitro. Since ASC is minimally toxic, it is an interesting candidate for improving the radiotherapeutic gain factor in vivo. The in vivo radiomodifying effects of ASC on a C3H/fSed murine fibrosarcoma (FSaII), on normal skin, and on bone marrow were determined with the use of the tumor growth delay and TCD50 (i.e., radiation dose required to control 50% of treated tumors for a minimum of 120 days) assays and the RD50 (i.e., dose required to cause a peak skin reaction of 2 in 50% of treated hind limbs) and LD50 (i.e., whole-body radiation lethal dose) assays, respectively. ASC was buffered to pH 7.35 and delivered ip at a dose of 4.5 mg g-1 body weight. ASC did not modify tumor growth delay induced by radiation or the TCD50 [87.1 Gy (control) vs. 85.6 Gy (ASC)]. Normal tissues, however, were radioprotected by ASC. RD50 values for 2+ acute skin reactions were 46.4 and 55.7 Gy for control and ASC-treated subjects, respectively; LD50 (30 days) values were 7.2 and 8.5 Gy. The enhancement ratios for skin and bone marrow were 1.20 and 1.18, and 95% confidence limits were (1.07 ... 1.34) and (1.14 ... 1.23), respectively. The therapeutic gain factor was 1.22 calculated as the ratio of the TCD50 and the reference normal tissue (RD50 or LD50). When ASC and MISO were combined, ASC reduced the in vivo radiosensitizing effects of MISO.