Ⅲ-3. Radiochemistry & Nuclear Chemistry

RIKEN Accel. Prog. Rep. 48 (2015)

Production of platinum radiotracer for Gamma-Ray Emission Imaging
S. Komoto,*1 M. Munekane,*1 T. Fukuchi,*2 H. Haba,*3 K. Higashikawa,*1 M. Ueda,*1 S. Motomura,*2 and S. Enomoto*1,*2
Platinum drugs such as cis-diammine dichloro
platinum(Ⅱ) (cisplatin) have been used for a long time as afirst-choice drug for several types of tumors. The efficacyof these types of drugs has been certainly approved
however the disadvantages are the strong toxic side effects
including nephrotoxicity, nausea, and neurotoxicity. Theseside effects are considered as dose-limitation factors.
Further, in treatment, the tumor gradually develops
resistance to these drugs. There are some mechanisms ofresistance such as “Decreased uptake” and “Increasedefflux.” 1)
To investigate potential side effects and drug efficacy, weare developing noninvasive and quantitative distribution
analysis methods that can determine the concentration ofplatinum drugs in normal tissues/organs and tumors. We
have propose using a new nuclear medicine imaging
technology called GREI (Gamma-Ray Emission Imaging),
to visualize the distribution of platinum drugs labeled withplatinum radionuclides. GREI comprises a Compton camera
composed of two planar germanium (Ge) detectors
developed in our laboratory.2) GREI has a wide detectableenergy range (200-2000 keV) which is different from theconventional imaging modalities, namely single photon
emission computed tomography (SPECT) and positronemission tomography (PET). Next, a variety of nuclides thatwere difficult to image can now be used because of GREI.
For the GREI experiment, platinum radionuclides withoptimum half-lives and emitting γ-rays are required. Someuseful radionuclides for the GREI are listed in Table 1. In
this study, we investigated the production of radio-platinum
nuclides that are suitable for GREI experiments via thenatOs(α,xn) reactions.
For the radio-platinum production, we used metallic natOs
powder (chemical purity: 99.99 %) as the target material.
Approximately 500 mg of osmium powder was pressed by
3 t at 1 min, and molded into a pellet (φ 15 mm). The pellet
was covered with a 10-μm Al foil (chemical purity:99.999%). The osmium target was irradiated by the 30-MeV
α-beam supplied by RIKEN AVF cyclotron for 1.5 h. The
beam intensity was 1 particle μA. The γ-ray spectrum of theirradiated target is shown in Fig. 1. This spectrum showsthat 189Pt and 191Pt were produced, and fewer quantities ofother impurities such as radio-osmium and radio-iridium
were produced. After the irradiation, the following
separation steps were performed to remove the targetosmium from the radio-platinum as reported by M. Bonardi,et al.3) First, for removing osmium, the irradiated target wasdissolved in 10 mL conc. HNO3 and heated at the 200 ℃.
Graduate school of Medicine, Dentistry, and Pharmaceutical Sciences,Okayama University*2
RIKEN Center for Life Science Technologies*3
RIKEN Nishina Center*1

In this step, osmium was distilled and trapped in 4.7 N
NaOH. After almost all of the liquid was evaporated,
another 10 mL of conc. HNO3 was added and heated until
dryness was achieved. After this step, the process of adding
5 mL of conc. HCl and drying up was repeated thrice. The
reaction vessel was washed with 5 mL of 3 M HCl and thesolution containing radio-platinum was transferred to a vial.
After the chemical separation, the radioactivities of 189Pt
and 191Pt were 0.48 and 1.0 MBq, respectively, and thechemical yield was over 90 %.
GREI can detect γ-rays of various energies that areemitted from 189Pt and 191Pt. This allows us to use both ofthese radio-platinum as radio tracers for imaging. In future,
we will synthesize cisplatin with radio-platinum, administerit to a tumor-bearing mouse, and perform imagingexperiments.
Table. 1. Useful platinum radionuclides for GREI.

Fig. 1. Gamma-ray spectrum of produced nuclides in
irradiated target.
References

1) S. Motomura et al.: J. Anal. At. Spectrom. 28 (6), 934 (2013).
2) M. Kartalou et al.: Mutat. Res.-Fund. Mol. M. 478.1, 23 (2001).
3) M. Bonardi et al.: J. Radioanal. Nucl. Chem. 236.1-2, 159,
(1998).

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