Objective       To determine the effect of hypoxia on tumor formation and survival time in tumor-bearing C57 mice implanted with glioma GL261 cells.       Methods       Cultured glioma GL261 cells were transduced to express luciferase under blasticidin selection (5 μg/mL) to produce GL261-Luc cells. Then SPF C57 mice (n=42

female

6 weeks old

weighing 17.5±2.3 g) implanted with GL261-Luc cells in the brain were randomized into 2 groups equally

fed under hypoxia condition (10% O

2

)

or normoxia (21% O

2

). The tumor growth was observed by bioluminescence imaging (bli) in the days 7

14 and 21 after injection (n=6 per group). The remaining tumor-bearing mice (n=15 per group) were observed for their survival within 30 d

and then the results were analyzed by Kaplan-Meier curve. HE staining was used to observe the tumor formation for those dead mice and survived mice within 30 d.       Results       Bioluminescence imaging showed that obvious tumor masses were developed in hypoxia-treated group

whereas no tumor was formed under normoxia. Measuring viral activity in the brain tumor cells indicated that the hypoxia-treated group had stronger capacity in tumor formation than the normoxia group (P0.05). The survival time of mice in hypoxia group was 22.5 d

significantly lower than that of normoxia group (P0.01). Gross and morphological observation found that there were 18 tumor masses in the mice of hypoxia group

but only 2 in the other group. Immunohistochemical staining showed that glial fibrillary acidic protein (GFAP) was highly expressed in the tumor masses.       Conclusion       Hypoxia promotes tumor formation and declines survival rate in glioma-bearing mice

when compared with the tumor-bearing mice living under normoxia

which indicating hypoxia improves malignancy in the implanted tumor.