Imaging of HIF-1-Active Tumor Hypoxia Using a Protein Effectively Delivered to and Specifically Stabilized in HIF-1-Active Tumor Cells

doi:10.2967/jnumed.108.061119

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Basic Science Investigation

Imaging of HIF-1-Active Tumor Hypoxia Using a Protein Effectively Delivered to and Specifically Stabilized in HIF-1-Active Tumor Cells

Takashi Kudo¹, Masashi Ueda¹^,2, Yuji Kuge¹, Takahiro Mukai³, Shotaro Tanaka⁴, Maki Masutani¹, Yasushi Kiyono²^,5, Shinae Kizaka-Kondoh⁴, Masahiro Hiraoka⁴ and Hideo Saji¹

¹ Department of Patho-Functional Bioanalysis, Graduate School of Pharmaceutical Sciences, Kyoto University, Kyoto, Japan; ² Radioisotopes Research Laboratory, Faculty of Medicine, Kyoto University Hospital, Kyoto University, Kyoto, Japan; ³ Department of Biomolecular Recognition Chemistry, Graduate School of Pharmaceutical Sciences, Kyushu University, Fukuoka, Japan; ⁴ Department of Radiation Oncology and Image-Applied Therapy, Kyoto University Graduate School of Medicine, Kyoto University, Kyoto, Japan; and ⁵ Biomedical Imaging Research Center, University of Fukui, Fukui, Japan

Correspondence: For correspondence or reprints contact: Hideo Saji, Department of Patho-Functional Bioanalysis, Graduate School of Pharmaceutical Sciences, Kyoto University, 46-29 Yoshida-Shimo-Adachi-cho, Sakyo-ku, Kyoto 606-8501, Japan. E-mail: hsaji{at}pharm.kyoto-u.ac.jp

Hypoxia-inducible factor-1 (HIF-1) plays an important role inmalignant tumor progression and in the development of resistanceto radiotherapy. We designed a novel fusion protein (PTD-ODD-SAV[POS]) consisting of a protein transduction domain (PTD), streptavidin(SAV), and a portion of the oxygen-dependent degradation domain(ODD) of HIF-1 ${alpha}$ that confers the same oxygen-dependent regulationas HIF-1 ${alpha}$ on POS. (3-^123/125I-iodobenzoyl)norbiotinamide (^123/125I-IBB)was conjugated to the SAV moiety of POS to synthesize ^123/125I-IBB-labeledPOS (^123/125I-IPOS). The purpose of this study was to evaluatethe feasibility of ¹²³I-IPOS as an imaging probe for HIF-1-activetumor hypoxia. Methods: After a 24-h incubation of ¹²⁵I-IPOSwith various tumor cell lines under either normoxic (20% O₂)or hypoxic (0.1% O₂) conditions, the intracellular radioactivitywas investigated. Then, the biodistribution of ^123/125I-IPOSwas examined with tumor-implanted mice, and an in vivo imagingstudy was performed. The tumoral accumulation of ¹²⁵I-IPOS wascompared with HIF-1 activity using the mice carrying tumorswith the HIF-1-dependent luciferase reporter gene. Furthermore,the intratumoral localization of ¹²⁵I-IPOS was examined by theautoradiographic study, and then the same slide was subjectedto immunostaining for pimonidazole, which is the hypoxic marker.Results: The ratios of radioactivity in hypoxic cells to thatin normoxic cells were more than 2. These results indicate incorporationof ¹²⁵I-IPOS into these cells and degradation of ¹²⁵I-IPOS bynormoxic tumor cells. In the biodistribution study, ¹²⁵I-IPOSaccumulated in the tumor (1.4 ± 0.3 percentage injecteddose per gram) 24 h after administration. At that time, ¹²⁵I-IPOSshowed high tumor-to-blood and tumor-to-muscle ratios (5.1 ±0.3 and 14.0 ± 3.9, respectively). The tumors were clearlyvisualized by in vivo imaging 24 h after ¹²³I-IPOS injection(tumor-to-muscle ratio was 9.6). The tumoral accumulation of¹²⁵I-IPOS correlated with HIF-1 activity (R = 0.71, P < 0.05),and its intratumoral distribution coincided with the hypoxicregions. Conclusion: ¹²³I-IPOS is a potential probe for theimaging of HIF-1 activity in tumors. Given the role of HIF-1in tumor biology, its detection may be considered an indicatorof aggressive cancer phenotypes.

Key Words: molecular imaging • oncology • radiopharmaceuticals • hypoxia-inducible factor-1 (HIF-1) • tumor hypoxia • oxygen-dependent degradation (ODD) • protein transduction domain (PTD)

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