International Journal of Applied Radiation and Isotopes. Vol. 29, pp. 549 555 Pergamon Press Ltd.. 1978. Printed in Great Britain
The Importance of the Chemical State of 99mTc Radiopharmaceuticals" an Effective Tumor Imaging Form ofl,99mTCBleomycin AKIRA YOKOYAMA,* YOSHIAKI TERAUCHL KAZUKO HORIUCHI, SYUZO OKUMURA, YOSHIHIRO SAITO and HISASHI TANAKA Faculty of Pharmaceutical Sciences, Kyoto University, Japan and TERUO ODORI, RIKUSHI MORITA, T O R U M O R I and K A N J I T O R I Z U K A Department of Nuclear Medicine and Radiology, Kyoto University School of Medicine, Japan
(Received 16 November 1977) 99"Tc-labeled bleomycin (99mTc-BLM)has been introduced as a tumor-imaging agent. Nevertheless, this complex has been misjudged and its value for clinical use has received no proper evaluation. Various 99mTcrBLM species labeled with °9"Tc in different chemical states are produced depending upon the labeling conditions such as the concentrations of BLM and SnCl2, pH and reaction time. As a consequence, their biological behavior is found to be markedly affected by the state of 99mTc m the labeled compound administered. Detailed studies of the labeling reactions lead us to conclude that of the complexes tested, a 99mTc-BLMcomplex in which tetravalent 99mTc is coordinated through three nitrogen atoms of BLM, is considered to be a valuable one for clinical use. This 99mTcspecies is chemically the most stable and a rapid clearance from blood is obtained; yielding a high tumor-blood ratio of 99n'Tc activity after injection into tumor-bearing mice. A selective labeling method for this 99'nTc complex is described. BLEOMYCIN (BLM) complexes with various radioactive metal ions such as 67Ga, 57C0, ~l~In, 197Hg, 2°3Pb, 64Cui 59Fe and 99mTc have been reported as scintigraphic agents for the visualization of tumors."~ Among these metal complexes, the use of 99mTc-BLM should be emphasized because of the valuable physical character of 99mTc for human use, such as low radiation dose rate and low energy deposition, The preparation of 99"q'c-BLM has already been reported by MoRt, ~2~LIN c3) and Rvo, t41 nevertheless, its clinical value has received no proper evaluation. Preliminary experiments on 99mTc-BLM in our laboratory showed that various products with 99mTc in different chemical states were present depending upon slight changes in the labeling conditions. Difficulties in obtaining reproducible in vivo distribution data appeared to be closely related to 99mTc chemical state variability. Reduced 99mTc species may be coordinated with a ligand in various hydrolyzed states to form different kinds of complexes such as the "mononuclear", "dinuclear', "trinuclear" and so-called "polynuclear" complexes. ¢~ (In this paper, these complexes are abbreviated as Monomer, Low Polymer and High Polymer complexes.) In fact, the formation of these complexes was detected frequently in labeling reac* For reprints contact: A. Yokoyama, Faculty of Pharmaceutical Sciences, Kyoto University, Shimoadachi-cho, Yoshida, Sakyo-ku, Kyoto, Japan 606. 549
tions of 99'nTcO,, with penicillamine,161 KTS,tTl HIDA, ~s~ DOPA ~9~and ascorbic acid ,Ol in the presence of SnCIz. At the same time, these chemical states were assumed to be closely related to their biological behavior. The chemical character of 99roTe complexes such as chemical stability, molecular weight, and the charge have been mentioned as important factors affecting their biological behavior. Ii ~ Actually, there are many problems in relating the chemical state of the labeling compound to its biological behavior. However, we could determine that the chemical stability of the labeling compound is a critical factor in the biological evaluation of 99mTc-HIDA~12~ and 99mTc-penicillamine.~6~ A first approach to a selective preparation of the most chemically stable 99mTc-BLM complex is investigated. Its biological behavior is analyzed and shown to be the 99mTc-BLM complex with considerable promise for clinical use. METHODOLOGY
Materials and analytical methods Bleomycin was kindly supplied by Nihon Kayaku Co., as a sterile lyophilized powder. Its chemical form is a chloro or 1/2 sulfate of BLM-A2 and BLM-B2 (2:1 ratio), as shown in Fig. 1. The 9°mTcO~ generator was obtained from MaUinckrodt Inc. (St. Louis,
Akira Yokoyama et al.
550
0
NH2
N
The Importance of the Chemical State of 99mTc Radiopharmaceuticals" an Effective Tumor Imaging Form ofl,99mTCBleomycin AKIRA YOKOYAMA,* YOSHIAKI TERAUCHL KAZUKO HORIUCHI, SYUZO OKUMURA, YOSHIHIRO SAITO and HISASHI TANAKA Faculty of Pharmaceutical Sciences, Kyoto University, Japan and TERUO ODORI, RIKUSHI MORITA, T O R U M O R I and K A N J I T O R I Z U K A Department of Nuclear Medicine and Radiology, Kyoto University School of Medicine, Japan
(Received 16 November 1977) 99"Tc-labeled bleomycin (99mTc-BLM)has been introduced as a tumor-imaging agent. Nevertheless, this complex has been misjudged and its value for clinical use has received no proper evaluation. Various 99mTcrBLM species labeled with °9"Tc in different chemical states are produced depending upon the labeling conditions such as the concentrations of BLM and SnCl2, pH and reaction time. As a consequence, their biological behavior is found to be markedly affected by the state of 99mTc m the labeled compound administered. Detailed studies of the labeling reactions lead us to conclude that of the complexes tested, a 99mTc-BLMcomplex in which tetravalent 99mTc is coordinated through three nitrogen atoms of BLM, is considered to be a valuable one for clinical use. This 99mTcspecies is chemically the most stable and a rapid clearance from blood is obtained; yielding a high tumor-blood ratio of 99n'Tc activity after injection into tumor-bearing mice. A selective labeling method for this 99'nTc complex is described. BLEOMYCIN (BLM) complexes with various radioactive metal ions such as 67Ga, 57C0, ~l~In, 197Hg, 2°3Pb, 64Cui 59Fe and 99mTc have been reported as scintigraphic agents for the visualization of tumors."~ Among these metal complexes, the use of 99mTc-BLM should be emphasized because of the valuable physical character of 99mTc for human use, such as low radiation dose rate and low energy deposition, The preparation of 99"q'c-BLM has already been reported by MoRt, ~2~LIN c3) and Rvo, t41 nevertheless, its clinical value has received no proper evaluation. Preliminary experiments on 99mTc-BLM in our laboratory showed that various products with 99mTc in different chemical states were present depending upon slight changes in the labeling conditions. Difficulties in obtaining reproducible in vivo distribution data appeared to be closely related to 99mTc chemical state variability. Reduced 99mTc species may be coordinated with a ligand in various hydrolyzed states to form different kinds of complexes such as the "mononuclear", "dinuclear', "trinuclear" and so-called "polynuclear" complexes. ¢~ (In this paper, these complexes are abbreviated as Monomer, Low Polymer and High Polymer complexes.) In fact, the formation of these complexes was detected frequently in labeling reac* For reprints contact: A. Yokoyama, Faculty of Pharmaceutical Sciences, Kyoto University, Shimoadachi-cho, Yoshida, Sakyo-ku, Kyoto, Japan 606. 549
tions of 99'nTcO,, with penicillamine,161 KTS,tTl HIDA, ~s~ DOPA ~9~and ascorbic acid ,Ol in the presence of SnCIz. At the same time, these chemical states were assumed to be closely related to their biological behavior. The chemical character of 99roTe complexes such as chemical stability, molecular weight, and the charge have been mentioned as important factors affecting their biological behavior. Ii ~ Actually, there are many problems in relating the chemical state of the labeling compound to its biological behavior. However, we could determine that the chemical stability of the labeling compound is a critical factor in the biological evaluation of 99mTc-HIDA~12~ and 99mTc-penicillamine.~6~ A first approach to a selective preparation of the most chemically stable 99mTc-BLM complex is investigated. Its biological behavior is analyzed and shown to be the 99mTc-BLM complex with considerable promise for clinical use. METHODOLOGY
Materials and analytical methods Bleomycin was kindly supplied by Nihon Kayaku Co., as a sterile lyophilized powder. Its chemical form is a chloro or 1/2 sulfate of BLM-A2 and BLM-B2 (2:1 ratio), as shown in Fig. 1. The 9°mTcO~ generator was obtained from MaUinckrodt Inc. (St. Louis,
Akira Yokoyama et al.
550
0
NH2
N
