荒野 泰

The persistent localization of radioactivity in the kidney after administration of In-111-DTPA-D-Phe(1)-octreotide impairs the diagnostic accuracy of this radiopharmaceutical. To better understand the mechanisms responsible for the renal radioactivity levels of In-111-DTPA-D-Phe(1)-octreotide, the renal metabolism of this compound was compared with In-111-DTPA-L-Phe(1)-octreotide, where the N-terminal D-phenylalanine was replaced with L-phenylalanine to facilitate metabolism. DTPA-D-Phe(1)-octreotide and DTPA-L-Phe(1)-octreotide were synthesized by solid-phase methods. Both In-111-DTPA-conjugated octreotide analogues were prepared with radiochemical yields of over 96%, and both remained stable after a 3 h incubation in murine serum at 37 degrees C. When injected into mice, the two In-111-DTPA-conjugated octreotide analogues showed similar radioactivity elimination rates from the blood and accumulation in the kidney with about 60% injected radioactivity being excreted in the urine by 24 h postinjection. Over 85% of the radioactivity in the urine existed as intact peptides for both analogues. Despite the similar renal radioactivity levels, significant differences were observed in the radiolabeled species remaining in the kidney between the two; while In-111-DTPA-L-Phe(1)-octreotide was rapidly metabolized to the final radiometabolite, In-111-DTPA-L-Phe, the metabolic rate of In-111-DTPA-D-Phe(1)-octreotide was so slow that various intermediate radiolabeled species were observed. However, both In-111-DTFA-D-Phe and In-111-DTPA-L-Phe remained in the lysosomal compartment of the renal cells as the final radiometabolites for long periods. These findings indicated that although the metabolic stability of In-111-DTPA-D-Phe(1)-octreotide in the renal cells may be partially involved, the slow elimination rate of the radiometabolite derived from In-111-DTPA-D-Phe(1)-octreotide from the lysosomal compartment of renal cells would be predominantly attributable to the persistent renal radioactivity levels of In-111-DTPA-D-Phe(1)-octreotide.

Radioiodinated biocytin derivatives are potentially useful for multi-step tumour targeting using the avidin-biotin system. We synthesized a radioiodinated biocytin derivative and evaluated its properties in vivo. We labelled biocytin with I-125 by coupling biocytin to radioiodinated N-succinimidyl 3-(tri-n-butyl-stannyl) benzoate, and assessed its binding to avidin and its biodistribution in normal and tumour-bearing mite. When the synthesized biocytin was incubated with immobilized avidin, more than 94% of the radioactivity was bound. However, after 2 h incubation in serum, only 40% of the radioactivity was bound to the avidin. The iodinated biocytin derivative was characteristically taken up by the liver and the kidneys when injected intravenously into mice. In mice bearing an intraperitoneal tumour xenograft,I-125-biocytin and In-111-biotin were co-injected intraperitoneally 4 h after the intraperitoneal administration of avidin, which accumulated in the intraperitoneal tumours. At 2 and 24 h, the tumour uptake of I-125-biocytin was 8.2 and 3.8% ID/g respectively, whereas that of In-111-biotin was 20.0 and 18.7% ID/g respectively. When radioiodinated, biocytin retains its binding capacity to avidin, and it localizes well with high tumour-to-normal tissue ratios early post-injection using the two-step method, but compared to In-111-biotin it is unstable. We conclude that the stability of the product in serum needs to be improved prior to in-vivo applications. ((C) 1998 Lippincott Williams & Wilkins).

Interposition of a metabolizable linkage has been performed to reduce the hepatic radioactivity levels of radiolabeled antibodies. To estimate the validity of this strategy, a radioiodination reagent (HML) that provides a stable attachment for m-iodohippuric acid with proteins in plasma while facilitating rapid and selective release of the compound after lysosomal proteolysis in the liver was conjugated with a monoclonal antibody (mAb) against osteogenic sarcoma (OST7, IgG(1)). Radiolabeled OST7 conjugates with a plasma-labile ester bond for releasing m-iodohippuric acid (MIH), plasma-stable amide bonds for releasing radiometabolites of hepatobiliary excretion (MPH), or slow elimination rates from hepatocytes ([In-111]EMCS-Bz-EDTA) were prepared with similar conjugation chemistry. The four radiolabeled OST7 conjugates were characterized both in vitro and in vivo. All the radiolabeled OST7 conjugates had similar radiochromatograms on size-exclusion HPLC and similar antigen binding affinities. While MIH-OST7 indicated accelerated clearance of radioactivity from the blood due to the release of m-iodohippurate, the rest of the three radiolabeled OST7 conjugates remained stable in serum incubation studies and had similar radioactivity elimination from the blood in vivo. When injected into normal mice, HML-OST7 demonstrated tissue-to-blood ratios of radioactivity similar to those of MIH-OST7 and significantly lower than those of the other two radiolabeled OST7 conjugates. In biodistribution studies in nude mice, both HML-OST7 and MIH-OST7 exhibited tumor-to-liver or tumor-to-intestine ratios of radioactivity higher than those of [In-111]EMCS-Bz-EDTA-OST7 or MPH-OST7, respectively. HML-OST7, MPH-OST7, and [In-111]EMCS-Bz-EDTA-OST7 indicated there were no changes in the radioactivity levels in the tumor between 24 and 48 h postinjection, whereas MIH-OST7 significantly decreased the radioactivity levels in the tumor at these time points. HML reduced the radioactivity levels in nontarget tissues without impairing the tumor radioactivity levels delivered by OST7. These findings indicated that the design of a radiolabeled mAb that is stable in plasma and liberates the radiometabolite of rapid urinary excretion constitutes an effective strategy for achieving target-selective radioactivity delivery.

Both N,N'-ethylene bis(benzohydroxamamide) [(C-2(BHam)(2))] and N,N'-propylene bis(benzohydroxamamide) [(C-3(BHam)(2))] were designed as new thiol-free chelating molecules for Tc-99m radiopharmaceuticals. Synthetic procedures using oxadiazoline intermediates were developed for C-2(BHam)(2) and C-3(BHam)(2). Both C-2(BHam)(2) and C-3(BHam)(2) formed Tc-99m complexes with high yields over a wide pH range (pH 3-12) at room temperature. Complexation yields of over 95% were achieved at ligand concentrations as low as 2.5 x 10(-6) M. Reversed-phase HPLC analyses indicated that both C-2(BHam)(2) and C-3(BHam)(2) formed Tc-99m complexes as single species with stabilities much higher than those of Tc-99m-BHam. Selective complex formation of Tc-99m with the two ligands was observed in the presence of human IgG. No decomposition with low protein binding were demonstrated when the two Tc-99m complexes were incubated in murine plasma. Although further structural studies are required, these findings implied that the Ham based tetradentate ligands would serve as new chelating molecules for Tc-99m radiopharmaceuticals. (C) 1998 Elsevier Science Inc.

(99m)Tc labeled galactosyl serum albumin (GSA) has been used clinically as a receptor-binding agent for the assessment of liver function. The aim of this study was to investigate the usefulness of (99M)Tc-GSA in intraperitoneal (i.p.) tumor imaging. A tumor model was established by i.p. inoculating nude mice with human ovarian cancer cell SHIN-3, or colon cancer cell LS180. Radiolabels were i.p. injected into the tumor-bearing mice and the biodistribution of radioactivity was examined. After administration, (99m)Tc-GSA rapidly accumulated in the tumor. The tumor uptake was 5.82-8.46 %ID/g from 30 min to 6 h after the injection. Radioactivity in the blood was very low, less than 0.3 %ID/g, resulting in high tumor-to-blood ratio. Tumors could be clearly seen by scintigraphic imaging. Accumulation of i.p.-injected (99M)Tc labeled human serum albumin (HSA) in i.p. tumors was similar to that of (99m)Tc-GSA, but radioactivity of (99m)Tc-HSA in the circulation was high, resulting in a significantly lower tumor-to-blood ratio. In conclusion, (99m)Tc-GSA, when i.p. injected, accumulated in i.p. tumors and cleared from circulation rapidly, which would make it useful for the imaging of i.p. tumors.

Ester bonds have been used as metabolizable linkages to reduce radioactivity levels in non target tissues following the administration of antibodies labeled with metallic radionuclides. In this radio chemical design of antibodies, while the ester bonds should be cleaved rapidly in non-target tissues, high stability of the ester bonds in plasma is also required to preserve target radioactivity levels. To assess the structural requirements to stabilize the ester bond, a new benzyl EDTA derived bifunctional chelating agent with an ester bond, (1-[4-[4-(2-maleimidoethoxy)succinamido]benzyl]ethylenediamine-N,N,N',N' -tetraacetic acid MESS-Bz-EDTA), was developed, MESS-Bz-EDTA was coupled with a thiolated monoclonal antibody (OST7, IgG1) prepared by reducing its disulfide bonds to introduce the ester bond close and proximal to the antibody molecule. For comparison, 1-[4-(5-maleimidopentyl)aminobenzyl]ethylenediamine- N,N,N',N-tetraacetic acid (EMCS-Bz-EDTA) and meleimidoethyl 3-[131I]iodohippurate (MIH) was coupled to OST7 under the same conjunction chemistry. When incubated in 50% murine plasma or a buffered-solution of neutral pH, OST7-MESS-Bz-EDTA-111In rapidly released the radioactivity, and more than 95% of the initial radioactivity was liberated after a 24 h incubation in both solutions, due to a cleavage of the ester bond. On the other hand, only about 20% of the radioactivity was released from OST7-MIH-131I in both solutions during the same incubation period. In mice biodistribution studies, while a slightly faster radioactivity clearance from the blood with less radioactivity levels in the liver and kidneys was observed with OST7-MIH-131I than with OST7-EMCS-Bz-EDTA-111In, OST7-MESS-Bz-EDTA-111In indicated radioactivity clearance from the blood much faster than and almost comparable to that of OST7 MIH-131I and succinamidobenzyl-EDTA-111In, respectively. These findings as well as previous findings on radiolabeled antibodies with ester bonds suggested that while an introduction of an ester bond close to an antibody molecule stabilized the ester bond against esterase access, chemical structures of the linkages and radiolabels attached to the ester bonds play a significant role in the chemical stability of the ester bond. This may explain the different stability of the ester bonds in radioimmunoconjugates so far reported.

¹⁸⁶Re標識1-hydroxyethylidene-1, 1-diphosphonate (HEDP) は癌性疼痛緩和に有効と報告されている。日本原子力研究所が¹⁸⁶Reの試験製造を開始したことから, HEDPの¹⁸⁶Re標識条件, ¹⁸⁶Re-HEDPのマウス体内挙動を検討した。種々の標識パラメータの探求から, 副作用が問題となる以下のHEDP量で疼痛緩和に必要な放射能量の¹⁸⁶Re-HEDPを高い放射化学的収率で与えるキットを開発した。本キットで作製した¹⁸⁶Re-HEDPは^99mTc-HEDP, ^99mTc-HMDPと同等の骨集積を示し, 従来の報告にある¹⁸⁶Re-HEDPと同程度の疼痛緩和効果が本薬剤の投与で期待される。一方, 従来同様に生体内における¹⁸⁶Re-HEDPの分解が観察され, Reの化学的性質を考慮した新たな配位子の開発が要望される。

¹⁸⁶Re標識1-hydroxyethylidene-1, 1-diphosphonate (HEDP) は癌性疼痛緩和に有効と報告されている。日本原子力研究所が¹⁸⁶Reの試験製造を開始したことから, HEDPの¹⁸⁶Re標識条件, ¹⁸⁶Re-HEDPのマウス体内挙動を検討した。種々の標識パラメータの探求から, 副作用が問題となる以下のHEDP量で疼痛緩和に必要な放射能量の¹⁸⁶Re-HEDPを高い放射化学的収率で与えるキットを開発した。本キットで作製した¹⁸⁶Re-HEDPは^99mTc-HEDP, ^99mTc-HMDPと同等の骨集積を示し, 従来の報告にある¹⁸⁶Re-HEDPと同程度の疼痛緩和効果が本薬剤の投与で期待される。一方, 従来同様に生体内における¹⁸⁶Re-HEDPの分解が観察され, Reの化学的性質を考慮した新たな配位子の開発が要望される。