ENHANCEMENT OF RADIATION EFFECT BY GINKGO-BILOBA EXTRACT IN C3H MOUSEFIBROSARCOMA

Background and purpose: Ginkgo biloba leaf extract (GEE) is known to i ncrease peripheral blood circulation. The hypothesis that GEE may be a ble to enhance radiosensitivity of tumor by improving tumor blood flow and thus decreasing hypoxic fraction was tested. Materials and method s: Fibrosarcoma (FSaII) growing in C3H mouse leg muscle was used as a tumor model. GEE was given i.p. 1 h before irradiation with or without priming dose given 1 day earlier. Effect on tumor and normal tissue r adiation reaction was investigated. Results: Tumor growth delay by rad iation was more elongated after two doses (1-day interval) of GEE than after a single dose. Radiation dose for 3-day tumor growth delay was decreased from 12.45 (10.97-13.93) Gy to 6.06 (3.89-8.22) Gy by two do ses of GEE [enhancement ratio=2.06 (1.32-2.79)]. Hypoxic cell fraction was 10.6% (6.3-18.2%) for control, 7.2% (3.8-14.0%) after a single do se (P=0.18) and 2.7% (1.5-5.0%) after two doses (P <0.001). Radiation effect on normal tissue, estimated by acute skin reaction and jejunal crypt assay, was not affected by GEE. Conclusion: Ginkgo biloba extrac t enhances radiation effect on tumor without increasing acute normal t issue radiation damage in this model system probably by increasing tum or blood flow and further investigation for this possible radiosensiti zer is needed.