Fig. 1

The hypoxia-sensing human breast cancer xenograft model. a, b MDA-MB-231 cells stably expressing the HRE-EGPF reporter gene are implanted either orthotopically in mammary fat pads (a) or ectopically in the hind back (b) of female athymic mice. Hypoxic regions are visualized by immunostaining of the Hypoxyprobe (red). Expression of the hypoxia reporter gene is shown by fluorescence of enhanced green fluorescent protein (EGFP). Nuclei are counterstained with Hoechst 33342. c The hypoxic populations from the MDA-MB-231/HRE-EGFP and MCF7/HRE-EGFP xenografts, respectively, are analyzed by fluorescence-activated cell sorting. d Microarray analysis shows that expression of a panel of commonly observed hypoxia-induced genes is significantly upregulated in the EGFP⁺ cells freshly isolated from the MDA-MB-231/HRE-EGFP xenografts, compared to the EGFP⁻ cells from the same xenografts (n = 3; analysis of variance, p < 0.05). SSC, side scatter