Radioiodination of BODIPY and its application to a nuclear and optical dual functional labeling agent for proteins and peptides

Masahiro Ono,Hiroyuki Watanabe,Yuki Ikehata,Kohei Sano,Masashi Yoshimura,Ning Ding,Hideo Saji

doi:10.1038/s41598-017-03419-z

Abstract

In molecular imaging research, the development of multimodal imaging probes has recently attracted much attention. In the present study, we prepared radioiodinated BODIPY and applied it as a nuclear and optical dual functional labeling agent for proteins and peptides. We designed and synthesized [125I]BODIPY with a N-hydroxysuccinimide (NHS) ester, and evaluated its utility as a nuclear and fluorescent dual labeling agent for proteins and peptides. In the radioiodination reaction of BODIPY-NHS with [125I]NaI, [125I]BODIPY-NHS was obtained at a 48% radiochemical yield. When we carried out the conjugation reaction of [125I]BODIPY-NHS with bovine serum albumin (BSA) and RGD (Arg-Gly-Asp) peptide as a model protein and peptide, respectively, [125I]BODIPY-BSA and [125I]BODIPY-RGD peptide were successfully prepared at 98 and 82% radiochemical yields, respectively. Furthermore, we prepared [123I]BODIPY-trastuzumab by this conjugation reaction and successfully applied it to single photon emission computed tomography (SPECT) imaging studies using tumor-bearing mice, suggesting that radioiodinated BODIPY-NHS serves as a dual functional labeling agent for proteins and peptides. Since iodine has various radioisotopes that can be used for SPECT and positron emission tomography (PET) imaging, biological research, and radiotherapy, the radioiodinated BODIPY may be extensively applicable from basic to clinical research.

Highlights

The in vivo quantitative detection of the biodistribution of biologically active proteins and peptides plays an important role in a wide range of research in life science
We selected bovine serum albumin (BSA), RGD peptide, and trastuzumab as a model protein, peptide, and biologically active protein, respectively, to validate the basic concept for the development of new dual functional probes based on the radioiodinated BODIPY, and evaluated the feasibility of using [123/125I]BODIPY as a dual functional labeling agent for peptides and proteins
For the first time, we revealed that radioiodinated BODIPY can function as a new agent useful for the nuclear and optical dual functional labeling of various biologically active proteins and peptides

Summary

Results and Discussion

Most [125I]4-BSA was detected as a monomer of BSA together with a small amount of BSA dimer, and no marked radioactivity of [125I]4-BSA was found in a region where low-molecular-weight compounds were observed (Fig. 10) This means that the bonds between [125I]4 and BSA should be mainly formed by the covalent bonding of the NHS ester of [125I]4 with the amino groups of BSA. The radioactivity of [125I]4-trastuzumab was detected in a region where the intact trastuzumab was detected while no marked radioactivity was found in a region where low-molecular-weight compounds were detected (Fig. 13) This suggests that the NHS ester of [125I]4 may bind to the amino groups of trastuzumab via covalent bonds, to [125I]4-BSA. Since no marked radioactivity accumulation was observed in the thyroid (Fig. S1B), [123I]4 shows high stability against in vivo deiodination reactions even after conjugation with an antibody, suggesting that radioiodine may stably bind to the BODIPY scaffold in vivo. [123I]4-trastuzumab suggests the feasibility of RI/fluorescence dual imaging, in principle, by replacing it with the new BODIPY derivative with longer excitation and emission wavelengths effective for in vivo imaging

Conclusions

Author Contributions

Additional Information