The influence of efaproxiral on breast cancer xenograft hypoxia and HIF-1-alpha expression

10102 Background: Efaproxiral (E), a synthetic allosteric modifier of hemoglobin, has demonstrated clinical safety and efficacy as a radiosensitizer in patients with brain metastases from breast cancer. Although shown to enhance oxygenation in a murine mammary tumor, efaproxiral has not previously been tested in a human breast cancer xenograft. We studied changes in tumor oxygenation in a human xenograft and evaluated whether efaproxiral induces cell signaling events of potential therapeutic value. Methods: MDA-MB-468 breast cancer cells in matrigel were injected into the flank of nude mice. After tumors grew to 1–1.5 cm, animals were subjected to 1 of 3 treatments: ip saline +room air breathing (RA), ip saline + 50% oxygen breathing (O2), or ip efaproxiral (300 mg/kg) + 50% oxygen breathing (E+O2). Twenty minutes later the hypoxia marker, pimonidazole (pimo), was given, and 70 minutes later tumors were harvested for immunohistochemical study of hypoxia and hypoxia-inducible factor 1-alpha (HIF1-α) and RNA extraction to identify early changes in gene expression. Image analysis software was used to quantify observations. Results: Tumor hypoxia and HIF1-α staining were significantly decreased by efaproxiral (Table). HIF1-α staining did not entirely colocalize with pimo, implying different oxygen tension levels for HIF1-α ubiquitination and pimo reduction. Gene arrays indicated that after E+O2, expression of the hypoxia-induced DR1 transcription repressor was reduced compared with O2. Conclusions: The combination of E+O2 reduced hypoxia and HIF1-α expression in MDA-MB-468 human breast tumors in vivo, and an early effect on gene expression was reduced DR1. The results demonstrate an efaproxiral-mediated enhanced oxygenation of human hypoxic breast cancer. Furthermore, the efaproxiral-mediated down-regulation of HIF1-α suggests possible new opportunities in the clinical application of efaproxiral, notably as an adjuvant to systemic agents for which HIF1-α-mediated resistance limits efficacy. [Table: see text] [Table: see text]