ET-39 * REPEATED PHARMACOLOGICAL DOSES OF ASCORBATE PROTECTS TUMOURS FROM RADIATION DAMAGE IN AN INTRACRANIAL MOUSE GLIOMA MODEL

Abstract

High dose ascorbate is used as an anti-cancer treatment by complementary and alternative medicine. In the acidic, metal-rich tumour environment ascorbate acts as a pro-oxidant, generating free radicals and DNA damage, similar to ionising radiation. We showed that addition of high-dose ascorbate to radiation blocked repair of radiation-induced DNA damage in primary GBM cell lines, effectively radio-sensitising. We examined the effect of ascorbate and radiation on the murine glioma GL261 in vitro, and combined with intra-peritoneal ascorbate in an intra-cranial GL261 model. As previously seen, high dose ascorbate radio-sensitized GL261 cells in a clonogenicity assay. Tumour-bearing mice were treated with: 4.5Gy to the brain 8 days post-implantation; repeated high-dose ascorbate from day 8-45; both treatments; or no treatment. While radiation increased survival, intraperitoneal ascorbate alone had no effect. In contrast with in vitro data, tumour-bearing mice treated with radiation and daily ascorbate had poorer survival than those treated with radiation alone. Histological analysis of the tumours showed less necrosis and bleeding within tumours treated with both radiation and ascorbate, consistent with a radio-protective effect of ascorbate in vivo. While the mechanism of protection is not yet defined, this finding might have important clinical implications for combining high-dose ascorbate with radiation therapy.