An anti-angiogenic agent (TNP-470) inhibited reoxygenation during fractionated radiotherapy of murine mammary carcinoma

Purpose: Angio genesis is one of the important factors for tumor growth. Therefore, an angio genesis inhibitor might decelerate tumor repopulation and is expected to improve the tumor control rate in fractionated radiotherapy (RT). On the other hand, it might increase hypoxic fraction of tumors or inhibit tumor reoxygenation during fractionated RT. This study investigated the effects of an angio genesis inhibitor on fractionated RT. Materials and Methods: Animal-tumors were early generation iso transplants of mammary carcinoma in C3H/He mice. Tumor response was studied by tumor growth (TG) time and TCD-50 (50% tumor control dose) assays. Treatments were started when tumors on the right paw grew 4-5 mm in diameter. Radiation was locally given to tumors in air or under hypoxic condition. An angio genesis inhibitor, TNP-470, a synthetic analogue of fumagillin which is a natural product of Aspergillus fumigatus, has been reported to inhibit endothelial cell growth in vitro. TNP-470 was administered s.c. twice a week at a dose of 100mg/kg. In the TG time assay, fractionated RT was delivered daily for 5 days to a total dose of 10Gy (2Gy/fraction x 5). Two or four doses of TNP-470 were administered during and/or after fractionated RT. The time required for a tumor to reach 3-fold of initial tumor volume (TG time) was determined for each group. In the TCD-50 assay, a single or fractionated irradiation was given alone or in combination with TNP-470. Fractionated irradiation was delivered daily, five times per week, over two weeks (10 fractions). One dose of TNP-470 was administered 24 h prior to a single dose of irradiation, whereas four doses of TNP-470 were given during fractionated RT. Tumors were observed for recurrence once a week for 120 days following the end of RT. Results: The TG time for no treatment group, a group treated with fractionated RT alone, or two doses of TNP-470 alone was 5.3 days (95% confidence limits: 4.8-5.9), 15.6 days (15.1-16.1) or 7.8 days (7.1-8.5), respectively. Significant delay of tumor growth was observed by TNP-470 alone (100mg/kg x 2), indicating that TNP-470 alone has antitumor effect in vivo (p < 0.001). This antitumor effect of TNP-470 was not observed when this drug was given during fractionated RT. However, TNP-470 given after the end of fractionated RT showed significantly additional growth delay. The values of TCD-50 are as follows; TNP-470 given prior to RT did not alter hypoxic fraction of tumors significantly. TNP-470 administered during fractionated RT decreased radio curability of the tumors in air, although no difference in TCD50 was observed under hypoxic condition. It suggested that TNP-470 inhibited reoxygenation during 10-fraction RT. Conclusions: TNP-470 showed additional tumor growth delay in the TG time assay, only when it was given after the whole course of fractionated RT. In the TCD-50 assay, administration of TNP-470 during 10 fractions of RT decreased the local tumor control rate. These results suggest that reoxygenation during fractionated RT might be inhibited by TNP-470. When TNP-470 is combined with fractionated RT, administration after the end of RT is recommended