In solid tumors, the distribution of oxygen pressure is not homogenous because of the uncontrolled tumor growth and immature blood vessels during angiogenesis, which generate a hypoxic microenvironment. Tumor hypoxia causes resistance to radiotherapy and chemotherapy, and malignant progression Hypoxia-inducible factor-1 (HIF-1) is a master transcriptional regulator for adaptation to hypoxia by inducing more than 100 genes, which are closely associated with malignant phenotype. Thus, HIF-1-active cells are hallmark of malignant tumors. We have been developing fusion protein probes specific to HIF-1-active microenvironment for imaging and targeting malignant tumors. We recently constructed a fusion protein POH, which consisted of Protein Transduction Domain (PTD), Oxygen-dependent Degradation Domain (ODD) and HaloTag. The PTD was a membrane-permeable peptide, which efficiently delivered fusion proteins into cells. The ODD was responsible for the oxygen-dependent regulation of the probe, which stabilized in a hypoxic environment and degraded immediately under normoxic conditions. In addition, HaloTag was used to covalently conjugate with its specific ligand labeled with near-infrared fluorescence (NIRF) dye. POH-NIRF was examined for its target-specificity and in vivo dynamic status by in vivo and ex vivo fluorescence imaging with IVIS-SPECTRUM. To visualize the targets in vivo, we used bioluminescence imaging of tumor cells, which stably retained a HIF-1-dependent luciferase reporter gene. POH-NIRF probes successfully imaged HIF-1-active regions defined by bioluminescence imaging in subcutaneously implanted human xenograft tumors and orthotopic pancreatic cancers 9 to 24 hrs after POH-NIRF injection. Furthermore, immunohistochemical analysis of tumor sections from the mice 6h after POH-NIRF injection revealed the regions imaged with POH-NIFR was overlapped with HIF-1α-positive regions, while the intracellular localization of POH-NIRF was in cytoplasm. Overall results demonstrated that POH-NIRF was a specific probe for HIF-1-active/hypoxic cells and suggested that a PTD-ODD probe would become a unique imaging probe for tumor malignancy.

Note: This abstract was not presented at the AACR 101st Annual Meeting 2010 because the presenter was unable to attend.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 5230.