Epidermal growth factor as a potential radiosensitizer in mouse xenograft model

Abstract

Introduction: The conventional principle of epidermal growth factor (EGF) – epidermal growth factor receptor (EGFR) interaction involves increased cell growth, proliferation and differentiation. However, previous experimental studies have shown the anti-tumor effect and the possibility of radiosensitizing effect of exogenous EGF. This study aimed to evaluate if EGF could enhance the radiation sensitivity in vivo. Methods: Balb/c-nu mice with A431 human epidermoid carcinoma were divided into five groups: group I (no treatment), group II (EGF for 6 days), group III (EGF for 20 days), group IV (radiotherapy (RT)), and group V (RT with concomitant EGF for 6 days) (n=8 for each group). EGF was given by intraperitoneal injection (5mg/ kg) once daily, and the total RT dose was 30 Gy with a fraction size of 5 Gy/ fx at 24-h intervals. For the group of RT+EGF, EGF was injected concomitantly with RT. Each treatment was started when the tumors reached a volume of about 200mm3, and the tumor volumes were measured every other day until day 23. The relative tumor volume (RTV) was calculated by dividing the tumor volumes at any time by the tumor volume at the start of treatment. Mice of group I-V were sacrificed on day 0, 12, 23 to obtain tumor and major organ tissues. Histologic examinations of tumor, liver, lung, and kidney tissues were performed from H&E staining, and immunohistochemistry (IHC) staining of caspase-3 was performed to assess EGF-induced apoptosis in tumor tissues. Results: Mice with EGF for 6 daysshowed decreased tumor growth in comparison with the control group. On day 13, the mean values of RTV for the group I and II were 9.06 and 7.23, respectively. However, the relative tumor volume approached to the level of the control group on day 23, and the differences over the duration of follow-up were not statistically significant (P = 0.550). In the group IV and V, differences in tumor volume were observed after the emergence of the 1st minimal value of tumor volume (0.92 ± 0.05 on day 9 for group IV

0.69 ± 0.11 on day 13 for group V). Both groups showed subsequent increases in tumor volumes, however, the slope of the tumor re-growth phase was higher in group IV than group V. The differences were statistically significant (P = 0.034). In contrast to the group II,decrease in tumor volume was maintained until the end of follow-upin mice with EGF for 20 days. On day 23, the mean values of relative tumor volume of group I, II, and III were 17.63, 16.48, and 10.64, respectively (P< 0.001). In IHC of cleaved caspase-3 antibody, EGF-treated mice of group II and III showed stronger staining results than the control group. Also in the group IV and V, the intensity of the immunostaining was higher in group V. There were no abnormal histologic findings in H&E slides of major organs, such as liver, lung, and kidney. Conclusions: The EGF-induced effect of tumor growth suppression was observed in A431 human epidermoid carcinoma of mouse xenograft model. Concomitant use of EGF induced tumor growth delay more, and it showed the potential as a radiosensitizer in the design of fractionated RT.