7362
S. Kimura et al. / Bioorg. Med. Chem. Lett. 21 (2011) 7359–7362
and not because of simple hydrolysis. The selective accumulation
of 99mTc radioactivity in hypoxic cells is attributed to the phys-
iochemical properties of the reduced metabolite of 99mTc-SD32.
These results are encouraging for further in vivo SPECT imaging
and continued exploration of 99mTc-labeled probes based on this
molecular design.
Acknowledgments
The authors would like to thank Professor Hideo Saji, PhD at
Kyoto University for providing FM3A cells and Professor Hideko
Nagasawa, PhD at Gifu Pharmaceutical University for measuring
the high resolution mass spectrometry. This research was sup-
ported in part by the Health and Labor Sciences Research Grants
for Third Term Comprehensive 10-year Strategy for Cancer Con-
trol, the Grant-in-Aid for Cancer Research (21-5) from the Minis-
try of Health, Labor and Welfare and the Grant-in-Aid for
Scientific Research on Innovative Areas ‘Integrative Research on
Cancer Microenvironment Network’ (No. 23112525) from the
Ministry of Education, Culture, Sports, Science and Technology.
Figure 5. LC/MS analysis (a) Re-SD32 incubated with NADPH for 2 h (control);
(b–e) Re-SD32 incubated with nitroreductase and NADPH for 0.1, 5, 15, and
120 min, respectively.
(shown in Fig. S2) provided further information on the structure of
the metabolites. The ion peak corresponding to new UV peak at
1.4 min in Figure 5 showed negative ions of high intensity at
m/z = 460/462 that is identical to the value of the debenzylated
metabolite, Re-MAG3. Furthermore, two other ion peaks with high
intensity were found in the mass chromatogram. These peaks were
not detected in UV chromatogram. One peak at 9.8 min showed
m/z = 579/581, and the other at 8.0 min showed m/z = 581/583.
These molecular weights are consistent with that of nitroso and
hydroxylamine derivatives of Re-SD32, respectively, and these
products were presumed to be the reduction intermediates of Re-
SD32. The existence of these intermediates as well as Re-MAG3
indicated that the conversion of Re-SD32 to Re-MAG3 proceeded
via these intermediates. Thus, it was suggested that Re- and 99mTc-
SD32 were subject to stepwise reduction to produce the correspond-
ing carboxylic acids as shown in previous report16 and they were not
formed by simple hydrolysis.
Supplementary data
Supplementary data associated with this article can be found, in
References and notes
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