Effect of hypoxia on lung cancer cell proliferation and cell progression in vitro and hypoxia-pretreatment on tumor growth in mice. A549 cells were cultured in 0.5% hypoxia for 7 days and then harvested for cell proliferation assay and cell cycle progression analysis. In addition, the harvested cancer cells were inoculated into nude mice subcutaneously. After 21 days, the animals were sacrificed and the tumors were collected. (A) Cell growth assay and (B) cell cycle progression analysis in vitro (n = 9 for each group); (C) Tumor growth and (D) Tumor weight in mice. n = 7 for each group.