Biological Markers as Predictors of Radiosensitivity in Syngeneic Murine Tumors / 대한방사선종양학회지

PURPOSE: We investigated whether a relationship exists between tumor control dose 50 (TCD50) or tumor growth delay (TGD) and radiation induced apoptosis (RIA) in syngeneic murine tumors. Also we investigated the biological markers that can predict radiosensitivity in murine tumor system through analysis of relationship between TCD50, TGD, RIA and constitutive expression levels of the genetic products regulating RIA. MATERIALS AND METHODS: Syngeneic murine tumors such as ovarian adenocarcinoma, mammary carcinoma, squamous cell carcinoma, fibrosarcoma, hepatocarcinoma were used in this study. C3H/HeJ mice were bred and maintained in our specific pathogen free mouse colony and were 8~12 weeks old when used for the experiments. The tumors, growing in the right hind legs of mice, were analyzed for TCD50, TGD, and RIA at 8 mm in diameter. The tumors were also analyzed for the constitutive expression levels of p53, p21(WAF1/CIP1), BAX, Bcl-2, Bcl-x(L), Bcl-x(S), and p34. Correlation analysis was performed whether the level of RIA were correlated with TCD50 or TGD, and the constitutive expression levels of genetic products regulating RIA were correlated with TCD50, TGD, RIA. RESULTS: The level of RIA showed a significant positive correlation (R=0.922, p=0.026) with TGD, and showed a trend to correlation (R=-0.848), marginally significant correlation with TCD50 (p=0.070). It indicates that tumors that respond to radiation with high percentage of apoptosis were more radiosensitive. The constitutive expression levels of p21(WAF1/CIP1) and p34 showed a significant correlation either with TCD50 (R=0.893, p=0.041 and R=0.904, p=0.035) or with TGD (R=-0.922, p=0.026 and R=-0.890, p=0.043). The tumors with high constitutive expression levels of p21(WAF1/CIP1) or p34 were less radiosensitive than those with low expression. CONCLUSION: Radiosensitivity may be predicted with the level of RIA in murine tumors. The constitutive expression levels of p21(WAF1/CIP1) or p34 can be used as biological markers which predict the radiosensitivity.

Induction of Apoptosis and Expression of Apoptosis-related Gene Products in Response to Radiation in Murine Tumors / 대한치료방사선과학회지

PURPOSE: To analyze the involvement of apoptosis regulatory genes p53, p21waf1/cip1, bax and bcl-2 in induction of apoptosis by radiation in murine tumors. MATERIALS AND METHODS: The radiation-sensitive ovarian carcinoma OCa-I, and the radiation-resistant hepatocarcinoma HCa-I were used. Tumors, 8 mm in diameter, were irradiated with 25 Gy and at various times after irradiation, ranging from 1 to 48 h, were analyzed histologically for apoptosis and by western blot for alterations in the expression of these genes. The p53 status of the tumors were determined by the polymerase chain reaction-single strand conformation polymorphism assay. RESULTS: Both tumors were positive for wild-type p53. Radiation induced apoptosis in OCa-I but not in HCa-I. Apoptosis developed rapidly, peaked at 2 h after irradiation and returned to almost the background level at 48 h. In OCa-I radiation upregulated the expression of p53, p21waf1/cip1, and the bcl-2/bax ratio was decreased. In HCa-I radiation increased the expression of both p53 and p21waf1/cip1, although the increase of the latter was small. The bcl-2/bax ratio was greatly increased. In general the observed changes occurred within a few hours after irradiation, and either preceded or coincided with development of apoptosis. CONCLUSIONS: The development of apoptosis required upregulation of both p53 and p21waf1/cip1 as well as a decrease in bcl-2/bax ratio. In contrast, an increase in bcl-2/bax ratio prevented apoptosis in the presence of upregulated p53 and p21waf1/cip1. These findings indentified the involvement of multiple oncogenes in apoptosis regulation in vivo and demonstrate the complexity that may be associated with the use of a single oncogene assessment for predicting the outcome of cancer therapy with cytotoxic agents.