Fig. 4: ATP-HIF-1α signaling promotes xenograft tumor chemoresistance in vivo.

A A model of xenograft experiment. In brief, six million stably transfected MDA-MB-231 cells (shNC, shHIF-1α) were inoculated orthotopically onto the mammary fat pad of 6-week-old female Balb/c mice, followed by apyrase or normal saline treatment after 2 weeks of inoculation. After the xenograft models successfully established, mice were randomly divided into different groups (with or without cisplatin) to investigate tumor growth and metastasis under cisplatin treatment. B Primary tumor size was measured (upper) and quantified every 5 days (lower). C Primary tumors and representative metastasis specimens were HE stained (left). Necrosis area ratios in primary tumor and numbers of metastatic lesions in lung and liver (yellow arrowheads) were quantified (right). D, E Expressions of HIF-1α and its target genes from inoculated tumor tissue were detected via qRT-PCR (D) and western blotting (E). F Expressions of HIF-1α and its target genes as well as Ki-67 and cleaved caspase-3 were immunohistochemistry (IHC) stained. In IHC staining analysis, data were calculated by Image Pro-Plus (IPP) (Media Cybernetics, Inc., Rockville, MD, USA). Error bars represent means ± SD from triplicates. Data are representative of at least three independent experiments. *p < 0.05, **p < 0.01, ***p < 0.001; ns, not significant.