Development of an oxygen-sensitive degradable peptide probe for the imaging of hypoxia-inducible factor-1-active regions in tumors.

[Purpose]We aimed to develop a radiolabeled peptide probe for the imaging of hypoxia-inducible factor-1 (HIF-1)-active tumors. [Procedures]We synthesized the peptide probes that contain or lack an essential sequence of the oxygen-dependent degradation of HIF-1α in proteasomes ([123/125]I-DKOP30 or [125]I-mDKOP, respectively). The degradation of probes was evaluated in vitro using cell lysates containing proteasomes. In vivo biodistribution study, planar imaging, autoradiography, and comparison between probe accumulation and HIF-1 transcriptional activity were also performed. [Results]The [125]I-DKOP30 underwent degradation in a proteasome-dependent manner, while [125]I-mDKOP was not degraded. Biodistribution analysis showed [125]I-DKOP30 accumulation in tumors. The tumors were clearly visualized by in vivo imaging, and intratumoral distribution of [125]I-DKOP30 coincided with the HIF-1α-positive hypoxic regions. Tumoral accumulation of 125I-DKOP30 was significantly correlated with HIF-1-dependent luciferase bioluminescence, while that of [125]I-mDKOP was not. [Conclusion] [123]I-DKOP30 is a useful peptide probe for the imaging of HIF-1-active tumors

Rapid detection of hypoxia-inducible factor-1-active tumours: pretargeted imaging with a protein degrading in a mechanism similar to hypoxia-inducible factor-1alpha

PURPOSE: Hypoxia-inducible factor-1 (HIF-1) plays an important role in malignant tumour progression. For the imaging of HIF-1-active tumours, we previously developed a protein, POS, which is effectively delivered to and selectively stabilized in HIF-1-active cells, and a radioiodinated biotin derivative, (3-(123)I-iodobenzoyl)norbiotinamide ((123)I-IBB), which can bind to the streptavidin moiety of POS. In this study, we aimed to investigate the feasibility of the pretargeting method using POS and (123)I-IBB for rapid imaging of HIF-1-active tumours. METHODS: Tumour-implanted mice were pretargeted with POS. After 24 h, (125)I-IBB was administered and subsequently, the biodistribution of radioactivity was investigated at several time points. In vivo planar imaging, comparison between (125)I-IBB accumulation and HIF-1 transcriptional activity, and autoradiography were performed at 6 h after the administration of (125)I-IBB. The same sections that were used in autoradiographic analysis were subjected to HIF-1alpha immunohistochemistry. RESULTS: (125)I-IBB accumulation was observed in tumours of mice pretargeted with POS (1.6%ID/g at 6 h). This result is comparable to the data derived from (125)I-IBB-conjugated POS-treated mice (1.4%ID/g at 24 h). In vivo planar imaging provided clear tumour images. The tumoral accumulation of (125)I-IBB significantly correlated with HIF-1-dependent luciferase bioluminescence (R=0.84, p<0.01). The intratumoral distribution of (125)I-IBB was heterogeneous and was significantly correlated with HIF-1alpha-positive regions (R=0.58, p<0.0001). CONCLUSION: POS pretargeting with (123)I-IBB is a useful technique in the rapid imaging and detection of HIF-1-active regions in tumours

Evaluation of [125I]IPOS as a molecular imaging probe for hypoxia-inducible factor-1-active regions in a tumor: comparison among single-photon emission computed tomography/X-ray computed tomography imaging, autoradiography, and immunohistochemistry.

To image hypoxia-inducible factor-1 (HIF-1)-active tumors, we previously developed a chimeric protein probe ([(123/125) I]IPOS) that is degraded in the same manner as HIF-1α under normoxic conditions. In the present study, we aim to show that the accumulation of radioiodinated POS reflects the expression of HIF-1. In vivo single-photon emission computed tomography (SPECT)/X-ray CT (CT) imaging, autoradiography, and double-fluorescent immunostaining for HIF-1α and pimonidazole (PIMO) were carried out 24 h after the injection of [(125) I]IPOS. Tumor metabolite analysis was also carried out. A tumor was clearly visualized by multi-pinhole, high-resolution SPECT/CT imaging with [(125) I]IPOS. The obtained images were in accordance with the corresponding autoradiograms and with the results of ex vivo biodistribution. A metabolite analysis revealed that 77% of the radioactivity was eluted in the macromolecular fraction, suggesting that the radioactivity mainly existed as [(125) I]IPOS in the tumors. Immunohistochemistry revealed that the HIF-1α-positive areas and PIMO-positive areas were not always identical, only some of the regions were positive for both markers. The areas showing [(125) I]IPOS accumulation were positively and significantly correlated with the HIF-1α-positive areas (R = 0.75, P < 0.0001). The correlation coefficient between [(125) I]IPOS-accumulated areas and HIF-1α-positive areas was significantly greater than that between the [(125) I]IPOS-accumulated areas and the PIMO-positive areas (P < 0.01). These findings indicate that [(125) I]IPOS accumulation reflects HIF-1 expression. Thus, [(123/125) I]IPOS can serve as a useful probe for the molecular imaging of HIF-1-active tumors

PET imaging of hypoxia-inducible factor-1-active tumor cells with pretargeted oxygen-dependent degradable streptavidin and a novel [18]F-labeled biotin derivative.

: We aimed to evaluate the feasibility of using streptavidin–biotin-based pretargeting for positron emission tomography (PET) imaging of hypoxia-inducible factor (HIF)-1-active tumors. : We used POS, a genetically engineered form of streptavidin that selectively stabilizes in HIF-1-active cells, and (4-[18]F-fluorobenzoyl)norbiotinamide ([18]F-FBB), a radiolabeled biotin derivative, for performing a biodistribution study and for PET imaging. The tumoral [18]F-FBB accumulation was compared to the HIF-1-dependent luciferase bioluminescence and HIF-1α immunohistochemical signal. : [18]F-FBB accumulation was observed in POS-pretargeted tumors in mice (2.85 ± 0.55% injected dose per gram at 3 h), and clear PET images were obtained at the same time point. The tumoral [18]F-FBB accumulation positively correlated with luciferase bioluminescence (R = 0.72, P  : Pretargeting with POS and [18]F-FBB is an effective approach for PET imaging of HIF-1-active areas in tumors