Skip to main page content
U.S. flag

An official website of the United States government

Dot gov

The .gov means it’s official.
Federal government websites often end in .gov or .mil. Before sharing sensitive information, make sure you’re on a federal government site.

Https

The site is secure.
The https:// ensures that you are connecting to the official website and that any information you provide is encrypted and transmitted securely.

Access keys NCBI Homepage MyNCBI Homepage Main Content Main Navigation
. 2015 Nov 19:5:16802.
doi: 10.1038/srep16802.

The accumulation mechanism of the hypoxia imaging probe "FMISO" by imaging mass spectrometry: possible involvement of low-molecular metabolites

Yukiko Masaki  1 , Yoichi Shimizu  2   3 , Takeshi Yoshioka  1 , Yukari Tanaka  4 , Ken-Ichi Nishijima  2   5 , Songji Zhao  5 , Kenichi Higashino  1 , Shingo Sakamoto  4 , Yoshito Numata  1 , Yoshitaka Yamaguchi  4 , Nagara Tamaki  5 , Yuji Kuge  2   5
Affiliations

The accumulation mechanism of the hypoxia imaging probe "FMISO" by imaging mass spectrometry: possible involvement of low-molecular metabolites

Yukiko Masaki et al. Sci Rep. .

Abstract

(18)F-fluoromisonidazole (FMISO) has been widely used as a hypoxia imaging probe for diagnostic positron emission tomography (PET). FMISO is believed to accumulate in hypoxic cells via covalent binding with macromolecules after reduction of its nitro group. However, its detailed accumulation mechanism remains unknown. Therefore, we investigated the chemical forms of FMISO and their distributions in tumours using imaging mass spectrometry (IMS), which visualises spatial distribution of chemical compositions based on molecular masses in tissue sections. Our radiochemical analysis revealed that most of the radioactivity in tumours existed as low-molecular-weight compounds with unknown chemical formulas, unlike observations made with conventional views, suggesting that the radioactivity distribution primarily reflected that of these unknown substances. The IMS analysis indicated that FMISO and its reductive metabolites were nonspecifically distributed in the tumour in patterns not corresponding to the radioactivity distribution. Our IMS search found an unknown low-molecular-weight metabolite whose distribution pattern corresponded to that of both the radioactivity and the hypoxia marker pimonidazole. This metabolite was identified as the glutathione conjugate of amino-FMISO. We showed that the glutathione conjugate of amino-FMISO is involved in FMISO accumulation in hypoxic tumour tissues, in addition to the conventional mechanism of FMISO covalent binding to macromolecules.

PubMed Disclaimer

Conflict of interest statement

Prof. Yuji Kuge has grant support from Shionogi & Co., Ltd. The other authors declare no competing financial interests.

Figures

Figure 1
Figure 1. Proposed mechanism of reduction and accumulation of FMISO in hypoxic tissue regions.
Figure 2
Figure 2. Distribution of radioactivity in tumours derived from 18F-FMISO injected mice.
(A) Distribution of radioactivity from 18F-FMISO between a fraction covalently bound to macromolecules and a low-molecular-weight fraction. Data are means ± s.d. (n = 3). (B) Radio-HPLC chromatogram of the low-molecular-weight fraction of FMISO. (C,D) Autoradiograph (ARG) of tissue sections without (C) and with (D) washing. Scale bar represents 1 mm. (E) Immunohistochemical staining for pimonidazole. Scale bar represents 1 mm.
Figure 3
Figure 3. Representative mass spectrometric images of FMISO and amino-FMISO, ARG and pimonidazole staining in mouse tumour 4 h after administration of 18F-FMISO. Scale bar represents 1 mm.
(A) Mass spectrometric images of m/z 190->m/z 174.0673 representing FMISO. (B) Mass spectrometric images of m/z 160.088 representing amino-FMISO. (C) ARG image showing total radioactivity. (D) Immunohistochemical staining for pimonidazole.
Figure 4
Figure 4. Representative mass spectrometric images of low-molecular-weight FMISO metabolites, ARG and pimonidazole staining in mouse tumour 4 h after administration of 18F-FMISO. Scale bar represents 1 mm.
(A) Mass spectrometric images of m/z 174.067 representing nitroso-FMISO (a reductive intermediates of FMISO, see Fig. 1). (B) Mass spectrometric images of m/z 176.083 representing hydroxylamino-FMISO (a reductive intermediates of FMISO, see Fig. 1). (C) Mass spectrometric images of m/z 465.157 representing glutathione conjugate of amino-FMISO. (D) ARG showing total radioactivity. (E) Immunohistochemical staining for pimonidazole.
Figure 5
Figure 5. Validation of the glutathione conjugate of amino-FMISO in mouse tumour by isotope pattern and MS/MS analysis.
(A) Structure and predicted MS/MS pattern of glutathione conjugate of amino-FMISO. (B) Isotope pattern of glutathione conjugate of amino-FMISO. (C) Fragmentation pattern from MS/MS analysis of m/z 465.157 in mouse tumour
Figure 6
Figure 6. Proposed mechanism of metabolism and tissue accumulation of FMISO in tumour hypoxic regions revealed from this study.
See this image and copyright information in PMC

References

    1. Wilson W. R. & Hay M. P. Targeting hypoxia in cancer therapy. Nat. Rev. Cancer. 11, 393–410 (2011). - PubMed
    1. Horsman M. R., Mortensen L. S., Petersen J. B., Busk M. & Overgaard J. Imaging hypoxia to improve radiotherapy outcome. Nat. Rev. Clin. Oncol. 9, 674–687 (2012). - PubMed
    1. Krohn K. A., Link J. M. & Mason R. P. Molecular imaging of hypoxia. J. Nucl. Med. 49 Suppl 2, 129S–148S (2008). - PubMed
    1. Weissleder R. & Pittet M. J. Imaging in the era of molecular oncology. Nature. 452, 580–589 (2008). - PMC - PubMed
    1. Nunn A., Linder K. & Strauss H. W. Nitroimidazoles and imaging hypoxia. Eur. J. Nucl. Med. 22, 265–280 (1995). - PubMed

Publication types