New (99m)Tc(CO)(3) mannosylated dextran bearing S-derivatized cysteine chelator for sentinel lymph node detection

The aim of the present study is to synthesize new mannosylated dextran derivative that can be labeled with Tc-99m for potential use in sentinel lymph node detection (SLND). The compound was designed to have a dextran with molecular weight of 10 kDa as a backbone, mannose for binding to mannose receptors of the lymph node and S-derivatized cysteine as a suitable chelator for labeling with [(99m)Tc(H(2)O)(3)(CO)(3)](+) precursor. Reaction of allyl bromide with dextran (MW 11800) yielded the intermediate allyl-dextran (1) with about 40% coupling. Addition of cysteine to allyl-dextran resulted in the S-derivatized cysteine, compound DC15 (2). The final product DCM20 (3) was obtained in good yield after in situ hydrolysis and activation of cyanomethyl tetraacetyl-1-thio-d-mannopyranoside and coupling to DC15. All derivatives were purified by ultrafiltration and characterized by NMR. DC15 and DCM20 were quantitatively labeled with (99m)Tc (>95% radiochemical purity) using the fac-[(99m)Tc(OH(2))(3)(CO)(3)](+) precursor and ligand concentration of 1.5 × 10(-6) M at neutral pH. Both (99m)Tc-labeled compounds (99m)Tc(CO)(3)-DC15 (6) and (99m)Tc(CO)(3)-DCM20 (7) remained stable after 6 h incubation at 37 °C in the presence of excess histidine or cysteine, as well as even after 20-fold dilution and incubation for 24 h at room temperature. The characterization of the compounds 6 and 7 was performed by comparing their HPLC radiochromatograms with those of their rhenium surrogates Re(CO)(3)-DC15 (4) and Re(CO)(3)-DCM20 (5) respectively that were prepared using the precursor [NEt(4)](2)fac-[ReBr(3)(CO)(3)] and characterized by IR and NMR spectroscopy. When injected subcutaneously from the foot pad of mice, (99m)Tc-labeled mannosylated dextran (7) showed accumulation in the popliteal lymph node (SLN in this model) higher than that of non-mannosylated analogue (6) and the (99m)Tc-phytate serving as standard. Compound 7 also exhibited lower radioactivity levels at the injection site compared to (99m)Tc-phytate. The SPECT/CT studies in mice confirmed that 7 accumulated in the popliteal lymph node allowing its clear visualization. The present findings demonstrate that compound 7 ((99m)Tc(CO)(3)-DCM20) is promising and merits further evaluation as a radiopharmaceutical for sentinel lymph node detection.

[Intractable pneumothorax for pleuritis carcinomatosis effectively treated with bronchial embolization: report of a case]

A 57-year-old female was admitted with compliant of cough and body weight loss. Chest X-ray and thoracic computed tomography (CT) scan revealed a collapsed lung and pleural effusion. We diagnosed a pleulitis carcinomatosis. After right chest tube drainage was performed, she developed right intractable pneumothorax. It was occluded endobronchially by the placement of vascular embolization coils and histoacryl. This method is thought to be an effective treatment for intractable pneumothorax patients in endstage of lung cancer.

A novel radiopharmaceutical for detection of malignant melanoma, based on melanin formation: 3-iodo-4-hydroxyphenyl-L-cysteine

The aim of this study was to develop a new artificial amino acid radiopharmaceutical labelled with radioiodine for detection of malignant melanoma, based on melanin formation. By considering the affinity for tyrosinase, a starting enzyme on the branching point to melanin biosynthesis, 3-[125I]iodo-4-hydroxyphenyl-L-cysteine (125I-L-PC) was synthesized and evaluated biologically. Labelling of 125I-L-PC using the chloramine-T method was carried out conveniently and efficiently in a short period of time, with high specific activity. In a biodistribution study, 125I-L-PC showed a low accumulation in normal tissue and relative retention in B16 melanoma. A high contrast image of peripheral tumour was obtained during autoradiography. During an in vitro accumulation study, inhibition of 125I-L-PC with a tyrosinase inhibitor suggested interaction of this tracer with tyrosinase. It indicates that the uptake mechanism of 125I-L-PC to melanoma tissue was dependent on high tyrosinase activity in melanoma cells. Thus, 125I-L-PC appears to be a promising radioiodinated amino acid radiopharmaceutical for imaging malignant melanoma in relation to melanin formation, namely specific metabolism with high tyrosinase activity.

A new 68Ge/68Ga generator system using an organic polymer containing N-methylglucamine groups as adsorbent for 68Ge

A macroporous styrene-divinylbenzene copolymer containing N-methylglucamine groups was selected for a new 68Ge/68Ga generator system. This resin packed into a column effectively adsorbed the parent nuclide 68Ge. The daughter 68Ga was eluted from the resin with a solution of a low-affinity gallium chelating ligand such as citric or phosphoric acid. The 68Ge leakage was less than 0.0004% of the 68Ge adsorbed on the resin. By simple mixing of transferrin and desferoxamine conjugated HSA and IgG with the eluate from the column, 68Ga-labeling was completed in high yield.

Altering pharmacokinetics of radiolabeled antibodies by the interposition of metabolizable linkages. Metabolizable linkers and pharmacokinetics of monoclonal antibodies

Monoclonal antibodies, their fragments and low molecular weight oncophilic molecules such as synthetic somatostatin derivatives have been used to deliver radioactivity to target cells for both diagnostic and therapeutic purposes. Clinical studies demonstrated high abilities of the radiolabeled antibodies and peptides for nuclear medicine applications. However, high and persistent localization of radioactivity was observed in the liver or kidney especially when these molecules are labeled with metallic radionuclides, which reduce diagnostic accuracy and compromise therapeutic effectiveness. Thus, radiolabeled antibodies and peptides would become much more useful in both targeted imaging and radiotherapy if the undesirable radioactivity localization can be diminished. As a means to reduce the undesirable radioactivity, interposition of a metabolizable linkage between an antibody and a radiolabel was proposed to generate radiolabeled small molecules of urinary excretion from the parental antibody by enzymatic cleavage of the linkage. In this paper, after indicating the rationale behind the radiopharmaceutical design, a significant role played by the interposition of the metabolizable linkage in altering pharmacokinetics of radiolabeled antibodies is described from a variety of studies so far reported with an emphasis being laid on the importance of radiometabolite-based design of metabolizable linkages.

Antiproliferative activity induced by the somatostatin analogue, TT-232, in human pancreatic cancer cells

Somatostatin analogues have been developed as antiproliferative agents, but their administration as general antitumour agents is limited, mainly because of the wide distribution of somatostatin receptors throughout the human body. TT-232, a new somatostatin structural analogue, was reported to have tumour-selective antiproliferative activity without an antisecretory action. We examined whether TT-232 had antiproliferative activity in human pancreatic cancer cell lines, and compared its antiproliferative activity with that of RC-160 and other TT-232 derivatives. TT-232 inhibited the growth of all of the cell lines used in this study and induced apoptotic cell death. RC-160 showed no such growth inhibition. TT-232 also inhibited tumour formation in a xenograft model. A competitive binding assay was performed using the cell membrane fraction and 111In-DTPA-TT-232 in order to show the existence of a specific binding site on the cells. A specific binding site was detected in MIAPaCa-2 cells. It has been shown that the activation of protein tyrosine phosphatase (PTPase) is one of the main intracellular pathways responsible for somatostatinergic inhibition of cell growth. We found a significant PTPase stimulation after TT-232 administration using an immunoblot analysis assessing the level of protein tyrosine phosphorylation, and also a direct measurement of the PTPase activity. We also demonstrated that PTPase stimulation by TT-232 was involved in its antiproliferative activity as this activity was reversed by the addition of sodium orthovanadate, a PTPase inhibitor. Our results indicate that TT-232 could be a potentially useful therapeutic agent if these data are translated into clinical practice.

Effect of molecular charges on renal uptake of 111In-DTPA-conjugated peptides

The effect of molecular charges on renal accumulation of 111In-DTPA-labeled low molecular weight (LMW) peptides was investigated using 111In-DTPA-octreotide derivatives as models to design radiolabeled peptides that are taken up less by renal cells. The N-terminal D-phenylalanine (Phe) of 111In-DTPA-D-Phe(1)-octreotide was replaced with L-aspartic acid (Asp), L-lysine (Lys), L-methionine (Met) or L-Phe. Cellulose acetate electrophoresis indicated that both 111In-DTPA-L-Phe(1)-octreotide and 111In-DTPA-L-Met(1)-octreotide showed similar net charges, whereas 111In-DTPA-L-alphaLys(1)-octreotide and 111In-DTPA-L-Asp(1)-octreotide had more positive and negative charges, respectively, at pH values similar to those in blood and glomerular filtrate. When injected into mice, significant differences were observed in the renal radioactivity levels. 111In-DTPA-L-alphaLys(1)-octreotide showed the highest radioactivity levels from 10 min to 6 h postinjection, whereas the lowest radioactivity levels were observed with 111In-DTPA-L-Asp(1)-octreotide at all the postinjection intervals. These findings indicated that the replacement of only one amino acid in 111In-DTPA-D-Phe(1)-octreotide significantly altered net molecular charges of the resulting peptides and that the net charges of the 111In-DTPA-octreotide derivatives significantly affected their renal uptake. Thus, an increase of negative charges in peptide molecules may constitute a strategy for designing 111In-DTPA-conjugated LMW peptides with low renal radioactivity levels.

Significance of (111)In-DTPA chelate in renal radioactivity levels of (111)In-DTPA-conjugated peptides

Metabolic studies of (111)In-DTPA-labeled polypeptides and peptides showed that the radiolabeled (poly)peptides generated (111)In-DTPA-adducts of amino acid that possess long residence times in the lysosomal compartment of the tissues where (poly)peptides accumulated. However, a recent study suggested that metal-chelate-methionine (Met) might possess in vivo behaviors different from metal-chelate adducts of other amino acids. In this study, to elucidate whether some biological characteristics of Met may accelerate the renal elimination rate of (111)In-DTPA-adduct of Met into urine, (111)In-DTPA-Met(1)-octreotide was synthesized and the renal handling of (111)In-DTPA-Met was investigated using (111)In-DTPA-L-Phe(1)-octreotide (Phe represents phenylalanine), which was reported previously, as a reference. Both (111)In-DTPA-conjugated octreotide analogs were stable against 3-h incubation in murine serum at 37 degrees C. Both (111)In-DTPA-octreotide analogs also showed rapid clearance of the radioactivity from the blood and similar accumulation of the radioactivity in the kidney. No significant differences were observed in the renal radioactivity levels from 10 min to 24 h postinjection between the two. Metabolic studies indicated that (111)In-DTPA-Met(1)-octreotide and (111)In-DTPA-L-Phe(1)-octreotide generated (111)In-DTPA-adducts of Met and Phe, respectively, as the final radiometabolites at similar rates. These findings suggested that the long residence times of the radioactivity in tissues after administration of (111)In-DTPA-labeled peptides and polypeptides would be attributed to inherent characteristics of (111)In-DTPA chelate.

(99m)Tc-HYNIC-derivatized ternary ligand complexes for (99m)Tc-labeled polypeptides with low in vivo protein binding

6-Hydrazinopyridine-3-carboxylic acid (HYNIC) is a representative agent used to prepare technetium-99m ((99m)Tc)-labeled polypeptides with tricine as a coligand. However, (99m)Tc-HYNIC-labeled polypeptides show delayed elimination rates of the radioactivity not only from the blood but also from nontarget tissues such as the liver and kidney. In this study, a preformed chelate of tetrafluorophenol (TFP) active ester of [(99m)Tc](HYNIC)(tricine)(benzoylpyridine: BP) ternary complex was synthesized to prepare (99m)Tc-labeled polypeptides with higher stability against exchange reactions with proteins in plasma and lysosomes using the Fab fragment of a monoclonal antibody and galactosyl-neoglycoalbumin (NGA) as model polypeptides. When incubated in plasma, [(99m)Tc](HYNIC-Fab)(tricine)(BP) showed significant reduction of the radioactivity in high molecular weight fractions compared with [(99m)Tc](HYNIC-Fab)(tricine)(2.) When injected into mice, [(99m)Tc](HYNIC-NGA)(tricine)(BP) was metabolized to [(99m)Tc](HYNIC-lysine)(tricine)(BP) in the liver with no radioactivity detected in protein-bound fractions in contrast to the observations with [(99m)Tc](HYNIC-NGA)(tricine)(2.) In addition, [(99m)Tc](HYNIC-NGA)(tricine)(BP) showed significantly faster elimination rates of the radioactivity from the liver as compared with [(99m)Tc](HYNIC-NGA)(tricine)(2.) Similar results were observed with (99m)Tc-labeled Fab fragments where [(99m)Tc](HYNIC-Fab)(tricine)(BP) exhibited significantly faster elimination rates of the radioactivity not only from the blood but also from the kidney. These findings indicated that conjugation of [(99m)Tc](HYNIC)(tricine)(BP) ternary ligand complex to polypeptides accelerated elimination rates of the radioactivity from the blood and nontarget tissues due to low binding of the [(99m)Tc](HYNIC)(tricine)(BP) complex with proteins in the blood and in the lysosomes. Such characteristics would render the TFP active ester of [(99m)Tc](HYNIC)(tricine)(BP) complex attractive as a radiolabeling reagent for targeted imaging.

Renal metabolism of 3'-iodohippuryl N(epsilon)-maleoyl-L-lysine (HML)-conjugated Fab fragments

Renal localization of radiolabeled antibody fragments constitutes a problem in targeted imaging and radiotherapy. Recently, we reported use of a novel radioiodination reagent, 3'-[131I]iodohippuryl N(epsilon)-maleoyl-L-lysine (HML), that liberates m-iodohippuric acid before antibody fragments are incorporated into renal cells. In mice, HML-conjugated Fab demonstrated low renal radioactivity levels from early postinjection times. In this study, renal metabolism of HML-conjugated Fab fragments prepared by different thiolation chemistries and by direct radioiodination were investigated to determine the mechanisms responsible for the low renal radioactivity levels. Fab fragments were thiolated by 2-iminothiolane modification or by reduction of disulfide bonds in the Fab fragments, followed by conjugation with radioiodinated HML to prepare [131I]HML-IT-Fab and [125I]HML-Fab, respectively. In biodistribution studies in mice, both [131I]HML-IT-Fab and [125I]HML-Fab demonstrated significantly lower renal radioactivity levels than those of [125I]Fab. In subcellular distribution studies, [125I]Fab showed migration of radioactivity from the membrane to the lysosomal fraction of the renal cells from 10 to 30 min postinjection. On the other hand, the majority of the radioactivity was detected only in the membrane fraction at the same time points after injection of both [131I]HML-IT-Fab and [125I]HML-Fab. In metabolic studies, while [125I]Fab remained intact at 10 min postinjection, both HML-conjugated Fab fragments generated m-iodohippuric acid as a radiometabolite at the same postinjection time. [131I]HML-IT-Fab registered two radiometabolites (intact [131I]HML-IT-Fab and m-iodohippuric acid), whereas additional radiometabolites were observed with [125I]HML-Fab. This suggested that metabolism of both HML-conjugated Fab fragments would occur in the membrane fractions of the renal cells. The findings of this study reinforced our previous hypothesis that radiochemical design of antibody fragments that liberate radiometabolites that are excreted into the urine by the action of brush border enzymes would constitute a useful strategy to reduce renal radioactivity levels from early postinjection times.

Plasma protein binding of (99m)Tc-labeled hydrazino nicotinamide derivatized polypeptides and peptides

6-Hydrazinopyridine-3-carboxylic acid (HYNIC) constitutes one of the most attractive reagents to prepare (99m)Tc-labeled polypeptides and peptides of various molecular weights in combination with two tricine molecules as coligands. Indeed, (99m)Tc-HYNIC-conjugated IgG showed biodistribution of radioactivity similar to that of (111)In-DTPA-conjugated IgG. However, recent studies indicated significant plasma protein binding when the (99m)Tc labeling procedure was expanded to low molecular weight peptides. In this study, pharmacokinetics of (99m)Tc-HYNIC-conjugated IgG, Fab and RC160 using tricine were compared with their radioiodinated counterparts to evaluate this (99m)Tc-labeling method. In mice, [(99m)Tc](HYNIC-IgG)(tricine)(2) and [(99m)Tc](HYNIC-Fab)(tricine)(2) showed persistent localization of radioactivity in tissues when compared with their (125)I-labeled counterparts. [(99m)Tc](HYNIC-IgG)(tricine)(2) eliminated from the blood at a rate similar to that of (125)I-labeled IgG, while [(99m)Tc](HYNIC-Fab)(tricine)(2) showed significantly slower clearance of the radioactivity than (125)I-labeled Fab. On size-exclusion HPLC analyses, little changes were observed in radiochromatograms after incubation of [(99m)Tc](HYNIC-IgG)(tricine)(2) in murine plasma. However, [(99m)Tc](HYNIC-Fab)(tricine)(2) and [(99m)Tc](HYNIC-RC160)(tricine)(2) demonstrated significant increases in the radioactivity in higher molecular weight fractions in plasma. Formation of higher molecular weight species was reduced when [(99m)Tc](HYNIC-RC160)(tricine)(2) was stabilized with nicotinic acid (NIC) to generate [(99m)Tc](HYNIC-RC160)(tricine)(NIC). [(99m)Tc](HYNIC-RC160)(tricine)(NIC) also demonstrated significantly faster clearance of the radioactivity from the blood than [(99m)Tc](HYNIC-RC160)(tricine)(2). These findings suggested that one of the tricine coligands in (99m)Tc-HYNIC-labeled (poly)peptides would be replaced with plasma proteins to generate higher molecular weight species that exhibit slow blood clearance. In addition, the molecular sizes of parental peptides played an important role in the progression of the exchange reaction of one of the tricine coligands with plasma proteins.

The integrity of the disulfide bond in a cyclic somatostatin analog during 99mTc complexation reactions

Recent development of a variety of thiol-free chelating agents has facilitated the design of 99mTc-labeled somatostatin analogs suitable for receptor imaging of somatostatin-positive tumors. However, it remains ambiguous whether the disulfide bonds in cyclic peptides are stable during 99mTc complexation reactions, and contradictory results have been reported regarding the integrity of disulfide bonds in cyclic somatostatin analogs. To estimate the stability of the disulfide bond in a synthetic somatostatin analog at low peptide concentrations, [125I]I-RC-160, in which radioiodine was incorporated into the 3-Tyr residue, was synthesized and the integrity of the disulfide bond of the peptide was investigated in the presence of reducing agents such as ascorbic acid, dithionite, and stannous ions. The disulfide bond in [125I]I-RC-160 remained stable in the presence of ascorbic acid in boiling water. The disulfide bond was also stable when treated with stannous ions at concentrations sufficient to reduce 99mTc for complexation with a thiol-free chelating agent, bis(hydroxamamide) analog when the 99mTc complexation reaction was performed at room temperature. However, the disulfide bond of [125I]I-RC-160 was slightly cleaved in the presence of a small amount of stannous ions when the reaction was performed in boiling water. Treatment of [125I]I-RC-160 with dithionite in boiling water markedly reduced the disulfide bond of the parental peptide. These findings indicated that synthetic somatostatin analogs may be labeled with 99mTc with stannous ions as the reducing agent without impairing their structure after conjugation of thiol-free chelating agents that provide 99mTc chelates under mild reaction conditions.

A novel immunoscintigraphy technique using metabolizable linker with angiotensin II treatment

Immunoscintigraphy is a tumour imaging technique that can have specificity, but high background radioactivity makes it difficult to obtain tumour imaging soon after the injection of radioconjugate. The aim of this study is to see whether clear tumour images can be obtained soon after injection of a radiolabelled reagent using a new linker with antibody fragments (Fab), in conditions of induced hypertension in mice. Fab fragments of a murine monoclonal antibody against human osteosarcoma were labelled with radioiodinated 3′-iodohippuryl N-ɛ-maleoyl-L-lysine (HML) and were injected intravenously to tumour-bearing mice. Angiotensin II was administered for 4 h before and for 1 h after the injection of radiolabelled Fab. Kidney uptake of ¹²⁵I-labelled-HML-Fab was much lower than that of ¹²⁵I-labelled-Fab radioiodinated by the chloramine-T method, and the radioactivity of tumour was increased approximately two-fold by angiotensin II treatment at 3 h after injection, indicating high tumour-to-normal tissue ratios. A clear tumour image was obtained with ¹³¹I-labelled-HML-Fab at 3 h post-injection. The use of HML as a radiolabelling reagent, combined with angiotensin II treatment, efficiently improved tumour targeting and enabled the imaging of tumours. These results suggest the feasibility of PET scan using antibody fragment labelled with ¹⁸F-fluorine substitute for radioiodine. © 1999 Cancer Research Campaign

Intracellular metabolic fate of radioactivity after injection of technetium-99m-labeled hydrazino nicotinamide derivatized proteins

Hydrazino nicotinate (HYNIC) has been shown to produce technetium-99m (99mTc)-labeled proteins and peptides of high stability with high specific activities. However, persistent localization of radioactivity was observed in nontarget tissues such as the liver and kidney after administration of [99mTc]HYNIC-labeled proteins and peptides, which compromises the diagnostic accuracy of the radiopharmaceuticals. Since lysosomes are the principal sites of intracellular catabolism of proteins and peptides, 99mTc-HYNIC-labeled galactosyl-neoglycoalbumin (NGA) was prepared using tricine as a co-ligand to investigate the fate of the radiolabel after lysosomal proteolysis in hepatocytes. When injected into mice, over 90% of the injected radioactivity was accumulated in the liver after 10 min injection. At 24 h postinjection, ca. 40% of the injected radioactivity still remained in liver lysosomes. Size-exclusion HPLC analyses of liver homogenates at 24 h postinjection showed a broad radioactivity peak ranging from molecular masses of 0.5-50 kDa. RP-HPLC analyses of liver homogenates suggested the presence of multiple radiolabeled species. However, most of the radioactivity migrated to lower molecular weight fractions on size-exclusion HPLC after treatment of the liver homogenates with sodium triphenylphosphine-3-monosulfonate (TPPMS). The TPPMS-treated liver homogenates showed a major peak at a retention time similar to that of [[99mTc](HYNIC-lysine)(tricine)(TPPMS)] on RP-HPLC. Similar results were obtained with urine and fecal samples. These findings suggested that the chemical bonding between 99mTc and HYNIC remains stable in the lysosomes and following excretion from the body. The persistent localization of radioactivity in the liver could be attributed to the slow elimination rate of the final radiometabolite, [[99mTc](HYNIC-lysine)(tricine)2], from lysosomes, and subsequent dissociation of one of the tricine co-ligands in the low pH environment of the lysosomes in the absence of excess co-ligands, followed by binding proteins present in the organelles. The findings in this study also suggested that the development of appropriate co-ligands capable of preserving stable bonding with the Tc center is essential to reduce the residence time of radioactivity in nontarget tissues after administration of [99mTc]HYNIC-labeled proteins and peptides.

Technetium-99m-labeled medium-chain fatty acid analogues metabolized by beta-oxidation: radiopharmaceutical for assessing liver function

External imaging of energy production activity of living cells with 99mTc-labeled compounds is a challenging task requiring good design of 99mTc-radiopharmaceuticals. On the basis of our recent findings that 11C- and 123I-labeled medium-chain fatty acids are useful for measuring beta-oxidation activity of hepatocytes, we focused on development of 99mTc-labeled medium-chain fatty acid analogues that reflect beta-oxidation activity of the liver. In the present study, monoamine-monoamide dithiol (MAMA) ligand and triamido thiol (MAG) ligand were chosen as chelating groups because of the stability and size of their complexes with 99mTc and their ease of synthesis. Each ligand was attached to the omega-position of hexanoic acid (MAMA-HA and MAG-HA, respectively). In biodistribution studies, [99mTc]MAMA-HA showed high initial accumulation in the liver followed by clearance of the radioactivity in the urine. Analysis of the urine revealed [99mTc]MAMA-BA as the sole radiometabolite. Furthermore, when [99mTc]MAMA-HA was incubated with living liver slices, generation of [99mTc]MAMA-BA was observed. However, [99mTc]MAMA-HA remained intact when the compound was incubated with liver slices in the presence of 2-bromooctanoate, an inhibitor of beta-oxidation. The findings in this study indicated that [99mTc]MAMA-HA was metabolized by beta-oxidation after incorporation into the liver. On the other hand, poor hepatic accumulation was observed after administration of [99mTc]MAG-HA.

Species difference in radioactivity elimination from liver parenchymal cells after injection of radiolabeled proteins

To elucidate the cause for the different levels of hepatic radioactivity among mammals after injection of protein radiopharmaceuticals, the metabolism of radiolabeled proteins and the fate of their radiometabolites in the parenchymal cells of rat liver were investigated and compared with those of mice. We used galactosyl-neoglycoalbumin (NGA) as a carrier protein, and NGA was labeled with 111In via 1-(4-isothiocyanatobenzyl)ethylenediaminetetraacetic acid (SCN-Bz-EDTA) or 1-[p-(5-maleimidopentyl)aminobenzyl]ethylenediaminetetraacetic acid (EMCS-Bz-EDTA) and with 125I via direct iodination. All radiolabeled NGAs exhibited rapid accumulation in liver parenchymal cells after intravenous injection into rats. Radioactivity was eliminated following NGA-125I injection at similar rates from rat and mouse liver. In contrast, both 111In-labeled NGAs demonstrated much slower elimination of radioactivity in rat when compared with mouse liver. Analyses of radioactivity in bile and liver indicated that both SCN-Bz-EDTA and EMCS-Bz-EDTA rendered mono-amino acid adducts as the final radiometabolites, which were generated in rat liver within 1 h postinjection. Subcellular distribution studies suggested that these radiometabolites were copurified with lysosome in rat liver. Because similar results were observed in mice previously, the difference between rats and mice in radioactivity elimination from liver parenchymal cells would be predominantly attributable to the different efflux rate of the 111In-labeled metabolites from the lysosome between these species. Such differences in the efflux rates of radiometabolites from the lysosome among mammals may also account for the different hepatic radioactivity levels of radiolabeled proteins between animal and clinical studies.

A novel immunoscintigraphy technique using metabolizable linker with angiotensin II treatment

Immunoscintigraphy is a tumour imaging technique that can have specificity, but high background radioactivity makes it difficult to obtain tumour imaging soon after the injection of radioconjugate. The aim of this study is to see whether clear tumour images can be obtained soon after injection of a radiolabelled reagent using a new linker with antibody fragments (Fab), in conditions of induced hypertension in mice. Fab fragments of a murine monoclonal antibody against human osteosarcoma were labelled with radioiodinated 3'-iodohippuryl N-epsilon-maleoyl-L-lysine (HML) and were injected intravenously to tumour-bearing mice. Angiotensin II was administered for 4 h before and for 1 h after the injection of radiolabelled Fab. Kidney uptake of 125I-labelled-HML-Fab was much lower than that of 125I-labelled-Fab radioiodinated by the chloramine-T method, and the radioactivity of tumour was increased approximately two-fold by angiotensin II treatment at 3 h after injection, indicating high tumour-to-normal tissue ratios. A clear tumour image was obtained with 131I-labelled-HML-Fab at 3 h post-injection. The use of HML as a radiolabelling reagent, combined with angiotensin II treatment, efficiently improved tumour targeting and enabled the imaging of tumours. These results suggest the feasibility of PET scan using antibody fragment labelled with 18F-fluorine substitute for radioiodine.

A case report of gastric carcinosarcoma with rhabdomyosarcomatous and neuroendocrinal differentiation

We report herein an unusual gastric carcinosarcoma with rhabdomyosarcomatous and neuroendocrinal differentiation in a 63-year-old Japanese male. The tumor was a pedunculated large polypoid tumor (7 x 6.5 x 3.5 cm) located in the pylorus. Histologically, it invaded to the subserosa and was composed of both adenocarcinomatous and sarcomatous components. Adenocarcinomatous foci generally showed tubular to solid patterns and occupied the parts facing the gastric lumen, while the sarcomatous components showed a generally irregular and solid arrangement. There were transitions between the sarcomatous and carcinoma elements. In addition, carcinoma cells with a cord-like or trabecular arrangement similar to that seen in endocrine carcinoma expressed chromogranin A, and were mainly observed in an intermediate area between the adenocarcinomatous and sarcomatous foci. The sarcomatous areas were mainly composed of spindle cells and occasionally contained a sarcomatous component showing rhabdomyosarcomatous differentiation. This is an interesting case to consider how the variety of cell type appeared in such a type of tumor in the stomach.

Metabolic properties of normal and mutant mannan-binding proteins in mouse plasma

Human mannan-binding protein (MBP) is a serum lectin involved in innate immunity. MBP activates the complement pathway through its interaction with mannose-rich carbohydrates on various microorganisms and a common opsonic defect has been shown to be associated with a low serum concentration of MBP. This low serum concentration is closely associated with a single base mutation in codon 52, 54 or 57 of the human MBP gene, which results in a change of Arg52 to Cys, Gly54 to Asp, or Gly57 to Gln, respectively, in the collagen-like region of the molecule and prevents the formation of higher oligomers. However, the mechanism underlying the low serum concentration in such patients is completely unknown. The levels of protein synthesis and secretion of the normal and mutant MBPs seem to be similar according to our previous in vitro results. In this study, we examined the plasma clearance of the normal and mutant human (Gly54Asp) MBPs in mice, and found that the half-life of the mutant MBP is about half that of the normal MBP, explaining in part the difference in the plasma levels between the two types of MBP.

The relationship of glycosylation and isoelectric point with tumor accumulation of avidin

Radiolabeled avidin markedly accumulated in intraperitoneal tumors and was cleared rapidly from circulation when given intraperitoneally. This study investigated the mechanisms of the tumor localization of avidin.

METHODS

Avidin was deglycosylated through endoglycosydase-H digestion and/or neutralized by acetylation of its lysine amino acids with acetic acid N-hydroxysuccinimide ester. Avidin and modified avidins were analyzed using sodium dodecylsulfate-polyacrylamide gel electrophoresis (SDS/PAGE) and isoelectric focusing. A tumor model was established by intraperitoneal injection of human colon cancer cells, LS180, in nude mice. Avidin and modified avidins were labeled with 111In using diethyleneamine pentaacetic acid-biotin and were administered intraperitoneally into the tumor-bearing mice. The biodistribution of radioactivity was examined 2 and 24 h postinjection.

RESULTS

Deglycosylated avidins revealed a major band of smaller molecules on SDS/PAGE. The isoelectric point of neutralized avidins was reduced to less than 5, whereas that of unneutralized avidins was more than 9.5. Biodistribution study demonstrated that liver uptake was decreased by deglycosylation and kidney accumulation was decreased by neutralization, respectively. The blood clearance was remarkably slowed by combined modification of deglycosylation and neutralization. The tumor uptake of radioactivity was reduced by either deglycosylation or neutralization and was further decreased with combined modification.

CONCLUSION

Both high glycosylation and positive charge of avidin contributed to its accumulation in tumor. This study may facilitate development of a new vehicle for the delivery of therapeutic agents to intraperitoneal tumors.

In-vivo evaluation of indium-111-diethylenetriaminepentaacetic acid-labelling for determining the sites and rates of protein catabolism in mice

Pharmacokinetic analyses of protein pharmaceuticals are of prime importance for their clinical application. Because many proteins have pharmacological activity at low concentrations, radiolabelling of proteins is widely used to identify the sites and determine the rates of protein catabolism in-vivo due to the high sensitivity of detection of radioactivity. Recently, a metallic radionuclide, (111)In, has been used to trace the pharmacokinetics of proteins of interest after conjugation of the proteins with diethylenetriaminepentaacetic acid (DTPA). In this study, galactosyl-neoglycoalbumin (NGA) was reacted with the cyclic dianhydride of DTPA and labelled with (111)In to estimate the validity of this radiolabelling procedure for pharmacokinetic analyses. For comparison, we also evaluated direct radioiodination, because directly-radioiodinated proteins are widely used to assess the pharmacokinetics of proteins of interest. The hepatic radioactivity profile after intravenous injection of [131I]NGA or [(111)In]DTPA-NGA into mice was analysed pharmacokinetically, and the first-order rate constant representing the elimination of the respective radiometabolite from hepatic parenchymal cells was determined. The results indicated that direct radioiodination is inappropriate for pursuing the pharmacokinetics of the proteins, because of rapid elimination of the radioactivity from the sites of protein catabolism. These findings also implied that the [(111)In]DTPA label could be used to identify the catabolic sites and determine the rates of catabolism of proteins with relatively short biological half-lives, although characterization of radiolabelled species at the sites of accumulation would be required for accurate determination of the catabolic sites of proteins.

Bis(hydroxamamide)-based bifunctional chelating agent for 99mTc labeling of polypeptides

To develop chelating molecules that provide 99mTc-labeled polypeptides of high in vivo stability and high specific activities under mild reaction conditions, an asymmetrical bis(benzohydroxamamide) compound with an amine group, 4'-aminomethyl-N,N'-trimethylenedibenzohydroxamamide [NH2-C3(BHam)2], was designed and synthesized. The amine residue of NH2-C3(BHam)2 was converted to a maleimide group by reaction with N-succinimidyl-6-maleimidohexanoate, and the conjugation product was coupled to thiol groups of a monoclonal antibody against osteogenic sarcoma (OST7, IgG1) pretreated with 2-iminothiolane to prepare C3(BHam)2-OST7. 99mTc radiolabeling of C3(BHam)2-OST7 was performed by the exchange reaction with [99mTc]glucoheptonate. [99mTc]C3(BHam)2-OST7 was further characterized using directly radioiodinated OST7 ([125I]OST7) and [111In]labeled OST7 with 1-[4-[(5-maleimidopentyl)amidobenzyl]ethylenediamine-N,N, N'N'-tetraacetic acid (EMCS-Bz-EDTA) as references. [99mTc]C3(BHam)2-OST7 was obtained with radiochemical yields of over 94% at protein concentrations as low as 0.2 mg/mL at room temperature for 1 h. [99mTc]C3(BHam)2-OST7 remained stable after incubation in freshly prepared murine plasma and in the presence of cysteine. Similar binding affinities to tumor cells were observed between [99mTc]C3(BHam)2-OST7 and [125I]OST7. When injected into normal mice, [99mTc]C3(BHam)2-OST7 exhibited radioactivity levels in the blood similar to [111In]-EMCS-Bz-EDTA-OST7 up to 24 h postinjection with significantly faster elimination rate of the radioactivity from the liver. In nude mice bearing osteogenic sarcoma, no significant differences were observed in the radioactivity levels in the blood and the tumor between [99mTc]C3(BHam)2-OST7 and [125I]OST7 at 24 h postinjection. These findings indicated that C3(BHam)2 provided 99mTc chelate of high stability at low concentrations even when conjugated to an intact antibody. Such characteristics render bis(hydroxamamide) compounds useful as chelating molecules for preparation of 99mTc-labeled polypeptides.

Chemical design of radiolabeled antibody fragments for low renal radioactivity levels

The renal uptake of radiolabeled antibody fragments presents a problem in targeted imaging and therapy. We hypothesized that the renal radioactivity levels of radiolabeled antibody fragments could be reduced if radiolabeled compounds of urinary excretion were released from glomerularly filtered antibody fragments before they were incorporated into renal cells by the action of brush border enzymes, present on the lumen of renal tubules. 3'-[131I]Iodohippuryl N(epsilon)-maleoyl-L-lysine ([131I]HML) was conjugated with a thiolated Fab fragment because the glycyl-lysine sequence in HML is a substrate for a brush border enzyme and metaiodohippuric acid is released by cleavage of the linkage. Fab fragments were also radiolabeled by direct radioiodination (125I-Fab) or by conjugation with meta-[125I]-iodohippuric acid via an amide bond [N-(5-maleimidopentyl) 3'-iodohippuric acid amide ([125I]MPH-Fab)] or an ester bond [maleimidoethy 3'-iodohippurate ([125I]MIH-Fab)] by procedures similar to those used for [131I]HML-Fab. In biodistribution experiments in mice, [131I]HML-Fab demonstrated markedly low renal radioactivity levels with kidney:blood ratios of radioactivity of 1 from 10 min to 1 h due to rapid release of meta-[131I]iodohippuric acid. [125]MIH-Fab and 1251-Fab reached their peak ratios of 3.8 and 7.3 at 1 h, respectively, and [125I]MPH-Fab showed the maximum ratio of 16.8 at 6 h. In subcellular distribution studies, both [125I]MIH-Fab and 125I-Fab showed migration of radioactivity from the membrane to the lysosomal fraction of the renal cells from 10 to 30 min postinjection, whereas the majority of the radioactivity was detected only in the membrane fraction after administration of [131I]HML-Fab at both time points. In nude mice, [131I]HML-Fab showed one-quarter of the renal radioactivity of simultaneously administered 125I-Fab without impairing the target radioactivity levels 3 h after injection. These findings indicated that HML is a useful reagent for targeted imaging and therapy using antibody fragments as vehicles. These findings also suggested that the radiochemical design of radiolabeled antibody fragments that liberate radiometabolites of urinary excretion from antibody fragments by the action of brush border enzymes may constitute a new strategy for reducing the renal radioactivity levels of antibody fragments.

Strategies to reduce renal radioactivity levels of antibody fragments

Antibody fragments such as Fab and single-chain Fv fragments possess many advantages over intact antibodies as vehicles to deliver radioactivity for diagnostic and therapeutic applications. However, radiolabled antibody fragments exhibited high and persistent localization of the radioactivity in the kidney, which compromises diagnostic accuracy and therapeutic effectiveness. Recent studies indicated that the persistent localization of renal radioactivity would be originated from the re-absorption of glomerularly-filtered radiolabeled antibody fragments, followed by the retention of the radiometabolites generated after degradation in the lysosomal compartment of the renal cells. Two major approaches have been performed to reduce the renal radioactivity levels of antibody fragments. One is to block the reabsorption of radiolabeled antibody fragments themselves at the proximal tubular cells from the luminal fluid by administration of basic amino acids such as L-lysine. The other approach is to decrease the residence time of the radiometabolites within the lysosomal compartments of the renal cells by introducing a cleavable linkage between antibody fragments and radiometabolites of rapid urinary excretion. Another approach to reduce renal radioactivity levels of antibody fragments may be to release radiolabeled compound of urinary excretion from glomerularly-filtered antibody fragments before they are reabsorbed into the renal cells by the action of brush border enzymes present on the lumen of the renal proximal cells. In this paper, recent studies of the three approaches to reduce the renal radioactivity levels of antibody fragments are briefly reviewed.

Renal metabolism of 111In-DTPA-D-Phe1-octreotide in vivo

The persistent localization of radioactivity in the kidney after administration of 111In-DTPA-D-Phe1-octreotide impairs the diagnostic accuracy of this radiopharmaceutical. To better understand the mechanisms responsible for the renal radioactivity levels of 111In-DTPA-D-Phe1-octreotide, the renal metabolism of this compound was compared with 111In-DTPA-L-Phe1-octreotide, where the N-terminal D-phenylalanine was replaced with L-phenylalanine to facilitate metabolism. DTPA-D-Phe1-octreotide and DTPA-L-Phe1-octreotide were synthesized by solid-phase methods. Both 111In-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 degreesC. When injected into mice, the two 111In-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 111In-DTPA-L-Phe1-octreotide was rapidly metabolized to the final radiometabolite, 111In-DTPA-L-Phe, the metabolic rate of 111In-DTPA-D-Phe1-octreotide was so slow that various intermediate radiolabeled species were observed. However, both 111In-DTPA-D-Phe and 111In-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 111In-DTPA-D-Phe1-octreotide in the renal cells may be partially involved, the slow elimination rate of the radiometabolite derived from 111In-DTPA-D-Phe1-octreotide from the lysosomal compartment of renal cells would be predominantly attributable to the persistent renal radioactivity levels of 111In-DTPA-D-Phe1-octreotide.

A radioiodinated biocytin derivative for in-vivo applications

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 125I 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 mice. 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 xeno-graft, 125I-biocytin and 111In-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 125I-biocytin was 8.2 and 3.8% ID/g respectively, whereas that of 111In-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 111In-biotin it is unstable. We conclude that the stability of the product in serum needs to be improved prior to in-vivo applications.

Assessment of the radiochemical design of antibodies with a metabolizable linkage for target-selective radioactivity delivery

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, IgG1). 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 ([111In]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 [111In]EMCS-Bz-EDTA-OST7 or MPH-OST7, respectively. HML-OST7, MPH-OST7, and [111In]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.

Imaging of intraperitoneal tumors with technetium-99m GSA

99mTc 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 99mTc-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 LS 180. Radiolabels were i.p. injected into the tumor-bearing mice and the biodistribution of radioactivity was examined. After administration, 99mTc-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 99mTc labeled human serum albumin (HSA) in i.p. tumors was similar to that of 99mTc-GSA, but radioactivity of 99mTc-HSA in the circulation was high, resulting in a significantly lower tumor-to-blood ratio. In conclusion, 99mTc-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.

Synthesis and evaluation of hydroxamamide-based tetradentate ligands as a new class of thiol-free chelating molecules for 99mTc radiopharmaceuticals

Both N,N'-ethylene bis(benzohydroxamamide) [(C2(BHam)2)] and N,N'-propylene bis(benzohydroxamamide) [(C3(BHam)2)] were designed as new thiol-free chelating molecules for 99mTc radiopharmaceuticals. Synthetic procedures using oxadiazoline intermediates were developed for C2(BHam)2 and C3(BHam)2. Both C2(BHam)2 and C3(BHam)2 formed 99mTc 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 C2(BHam)2 and C3(BHam)2 formed 99mTc complexes as single species with stabilities much higher than those of 99mTc-BHam. Selective complex formation of 99mTc with the two ligands was observed in the presence of human IgG. No decomposition with low protein binding were demonstrated when the two 99mTc 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 99mTc radiopharmaceuticals.

Avidin targeting of intraperitoneal tumor xenografts

BACKGROUND

Lectins (proteins that bind specific sugar molecules on glycoproteins and glycolipids) are expressed at various levels on the surface of tumor cells. Conjugation of cytotoxic agents to glycoproteins recognized by lectins could be useful in the treatment of tumors. Avidin (a highly glycosylated, positively charged protein found in egg white) contains terminal N-acetylglucosamine and mannose residues that bind to some lectins. In this study, we tested the ability of avidin, labeled through conjugation to radioactive biotin (a B vitamin), to target intraperitoneal tumors.

METHODS

Biotin was radioactively labeled with 111In. Four tumor models (one ovarian, one lung, and two colon) were established in nude mice by intraperitoneal injection of cultured cancer cells. The following two approaches were used in the intraperitoneal administration of avidin: 1) radioactive biotin-avidin conjugates were injected and 2) avidin was injected 1-24 hours before the injection of radioactive biotin (avidin pretargeting; avidin-biotin conjugates formed in vivo). The distribution of injected radioactivity in the tissues of treated animals was assessed.

RESULTS

Radiolabeled avidin localized highly and rapidly in the tumors. More than 50% of the administered dose of avidin-biotin conjugate accumulated per gram of tumor tissue 2 hours after injection; high tumor uptake of radioactivity was observed up to 24 hours after conjugate injection. In contrast, accumulation of radioactivity in normal tissues was low, yielding high tumor to nontumor ratios. With avidin pretargeting, accumulation of radioactivity in the liver, kidney, and spleen was reduced to a greater extent than that in the tumor, and tumor to nontumor ratios were increased.

CONCLUSIONS

Avidin may be a promising vehicle for the delivery of radioisotopes, drugs, toxins, or therapeutic genes to intraperitoneal tumors.

Pharmacokinetic models to evaluate radiolabeling reagents for protein radiopharmaceuticals

Pharmacokinetic models were constructed to further estimate the hepatic radioactivity levels derived from bifunctional chelating agents used for radiolabeling of proteins. Both galactosyl-neoglycoalbumin (NGA) and mannosyl-neoglycoalbumin (NMA) were labeled with (111)In using two benzyl-EDTA derivatives. Time-activity profiles for the liver with gallbladder, intestine, and blood after administration of (111)In-labeled NGAs in mice were simultaneously fitted to a multi-compartment model, and the first-order rate constants representing the disappearance from parenchymal cells were obtained. Similarly, a model composed of the blood and liver compartment was constructed, and the disappearance rate constants from nonparenchymal cells were calculated from the biodistribution studies following administrations of (111)In-labeled NMAs. Fitting curves showed good agreements with the experimental data. Each rate constant clearly distinguished the elimination rate of the respective radiometabolite from the liver cells. Thus, quantitative estimations of radiolabeling reagents were performed only by animal biodistribution studies, and the present pharmacokinetic analyses would be useful for screening of newly designed reagents for protein radiopharmaceuticals.

A novel radioiodination reagent for protein radiopharmaceuticals with L-lysine as a plasma-stable metabolizable linkage to liberate m-iodohippuric acid after lysosomal proteolysis

Radiochemical design of polypeptides using metabolizable linkages would be attractive to enhance target-selective localization of radioactivity for diagnostic and therapeutic nuclear medicine. However, while use of ester bonds as the linkage allows selective release of the designed radiometabolite from covalently conjugated polypeptides after lysosomal proteolysis in nontarget tissues, low plasma stability of ester bonds causes a decrease in radioactivity levels of the target. In pursuit of new metabolizable linkages that provide stable attachment of radiolabels with polypeptide in plasma while facilitating rapid and selective release of designed radiometabolites of rapid urinary excretion in lysosomes, a new radioiodination reagent with L-lysine as the metabolizable linkage to liberate m-iodohippuric acid (L-HML) was designed and synthesized. Stabilities of the metabolizable linkage in serum and cleavabilities of the linkage in lysosomal proteolysis in hepatic cells were investigated after conjugation of [131I]-L-HML with galactosyl-neoglycoalbumin (NGA). For comparison, a radioiodination reagent with an ester bond to release m-iodohippuric acid (MIH) was conjugated with NGA under similar conditions. When incubated in human serum, [131I]-L-HML-NGA liberated less than 3% of the initial radioactivity after 24 h, whereas [125I]MIH-NGA released more than 60% of its radioactivity during the same interval. In biodistribution studies, [131I]-L-HML-NGA demonstrated radioactivity elimination from murine liver at a rate and excretion route similar to [125I]MIH-NGA. Analyses of murine urine after injection of [131I]-L-HML-NGA indicated a single radioactivity peak at fractions identical to those of m-iodohippuric acid. Biodistribution studies of radioiodinated NGAs with D-lysine or cadaverine as the linkages demonstrated a delayed elimination rate from murine liver with significantly higher radioactivity being excreted in the feces at 24 h postinjection. Thus, L-HML is the first reagent that allows stable attachment of radiolabel with polypeptide in serum while facilitating selective release of a radiometabolite with rapid urinary excretion from covalently conjugated polypeptides after lysosomal proteolysis at a rate similar to that of ester bonds. Thus, L-HML is potentially useful for the radioiodination of polypeptides for diagnostic and therapeutic purposes.

Conventional and high-yield synthesis of DTPA-conjugated peptides: application of a monoreactive DTPA to DTPA-D-Phe1-octreotide synthesis

Successful imaging of somatostatin receptor-positive tumors with 111In-DTPA-D-Phe1-octreotide has stimulated development of peptide radiopharmaceuticals using DTPA as the chelating agent. However, use of cyclic DTPA dianhydride (cDTPA) resulted in low synthetic yields of DTPA-peptide by either solution or solid-phase syntheses. This paper reports a novel high-yield synthetic procedure for DTPA-D-Phe1-octreotide that is applicable to other peptides of interest using a monoreactive DTPA derivative. A monoreactive DTPA that possesses one free terminal carboxylic acid along with four carboxylates protected with tert-butyl ester (mDTPA) was synthesized. Fmoc-Thr(tBu)-ol, prepared from Fmoc-Thr(tBu)-OH, was loaded onto 2-chlorotrityl chloride resin. After construction of the peptide chains by Fmoc chemistry, mDTPA was coupled to the alpha amine group of the peptide on the resin in the presence of 1,3-diisopropylcarbodiimide and 1-hydroxybenzotriazole. Treatment of the mDTPA-peptide-resin with trifluoroacetic acid-thioanisole removed the protecting groups and liberated [Cys(Acm)2,7]-octreotide-D-Phe1-DTPA from the resin. Iodine oxidation of the DTPA-peptide, followed by the reversed-phase HPLC purification, produced DTPA-D-Phe1-octreotide in overall 31.8% yield based on the starting Fmoc-Thr(tBu)-ol-resin. The final product gave a single peak on analytical HPLC, and amino acid analysis and mass spectrometry confirmed the integrity of the product. 111In radiolabeling of the product provided 111In-DTPA-D-Phe1-octreotide with > 95% radiochemical yield, as confirmed by analytical reversed-phase HPLC, TLC, and CAE. These finding indicated that use of mDTPA during solid-phase peptide synthesis greatly increased the synthetic yield of DTPA-D-Phe1-octreotide, due to the absence of nonselective reactions that are unavoidable when cDTPA is used. These results also suggested that mDTPA would be a versatile reagent to introduce DTPA with high yield into peptides of interest.

[Significance of 5'-deoxy-5-fluorouridine (5'-DFUR) administration before surgery for advanced gastric and colonic cancers--activity of pyrimidine nucleoside phosphorylase (PyNPase) and serum immunosuppressive acidic protein (IAP)]

We administered preoperatively 5'-deoxy-5-fluorouridine (5'-DFUR) for treatment of advanced gastric and colonic cancers, and measured pyrimidine nucleoside phosphorylase (PyNPase) in the excised tumor sample and serum immunosuppressive acidic protein (serum IAP), which is an index of the immunity of host-bearing cancer, while studying its direct antitumor effect and improved immunity. Patients with 24 advanced gastric cancers and 36 colonic cancers were randomly divided into a preoperatively administered group and a non-administered group. In the preoperatively administered group, 5'-DFUR (1,200 mg/day) was orally administered on preoperative days 7 approximately 14. After collecting samples (about 0.5 g) from adjacent normal tissues with tumor within 30 minutes after extirpation of tumor and freezing those less than -20 degrees C, the PyNPase level was measured as soon as possible. Moreever, serum IAP levels at pre-administration in the administered group and on admission in the non-administered group were measured. Those in the administered group were measured again on the operative day. No decreasing tendency of PyNPase was generally found in cases with gastric colonic cancers, and no significant difference in stage-II was not either. However, a decreasing tendency in tumor activity was found by pre-administration. Moreover, there was significant improvement in the serum IAP level in cases with gastric and colonic cancers by pre-operative administration of 5'-DFUR. This tendency was also found in advanced colonic cancer with Dukes-C by Dukes's classification. In conclusion, it was suggested that the pre-operative administration of 5'-DFUR for treatment of advanced gastric and colonic cancers has a favorable influence for prognosis because the tumor region was retarded by the high PyNPase activity according to the severity of tumors and elevating tendency of the immune response in host.

Assessment of radiochemical design of antibodies using an ester bond as the metabolizable linkage: evaluation of maleimidoethyl 3-(tri-n-butylstannyl)hippurate as a radioiodination reagent of antibodies for diagnostic and therapeutic applications

Reduction of radioactivity levels in nontarget tissues such as the liver and kidney constitutes a problem to be resolved in diagnostic and therapeutic applications of radiolabeled monoclonal antibodies (mAbs). A new radioiodination reagent with an ester bond to liberate m-iodohippuric acid from covalently conjugated proteins, maleimidoethyl 3-(tri-n-butylstannyl)hippurate (MIH), was recently developed. MIH liberated m-iodohippuric acid from galactosylneoglycoalbumin in murine liver, and the radiometabolite was rapidly eliminated from the liver into urine as an intact structure. In this study, intact IgG and Fab fragment of a mAb against osteogenic sarcoma were radioiodinated with MIH to further assess the applicability of MIH to radioimmunoimaging and therapy. For comparison, a mAb radioiodinated with N-succinimidyl iodobenzoate (SIB) and indium-111 (111In)-labeled mAbs with diethylenetriaminepentaacetic dianhydride (cDTPA) or 1-[4-[(5-maleimidopentyl)amino]benzyl]-ethylenediaminetetraacetic acid (EMCS-Bz-EDTA) were used. Size-exclusion HPLC analysis and cell binding assays indicated the preservation of both structure and antigen binding affinity of radioiodinated MIH-OST7 (IgG). In biodistribution studies in mice, [125I]MIH-OST7 (IgG) showed faster systemic clearance of radioactivity after 24 h postinjection than did [131I]SIB- and [111In]EMCS-Bz-EDTA-OST7 (IgG). [125I]MIH-OST7 (IgG) also exhibited much lower radioactivity levels in nontarget tissues such as the liver and kidney, with higher radioactivity levels in the blood up to 72 h postinjection when compared with [111In]cDTPA-OST7 (IgG). Radioactivity excreted from the mice was found in the urine as m-iodohippuric acid, following administration of [125I]MIH-OST7 (IgG). In athymic mice bearing osteogenic sarcoma, [131I]MIH-OST7 (IgG) indicated higher tumor-to-nontarget ratios of radioactivity at both 24 and 48 h postinjection than [125I]SIB-OST7 (IgG). Although both radioiodinated OST7s showed similar radioactivity levels in the target at 24 h postinjection, a small but significant decrease in the target radioactivity level was observed with [131I]MIH-OST7 (IgG) at 48 h postinjection. In addition, [131I]MIH-OST7 (Fab) showed very rapid cleavage of the ester bond both in vivo and in vitro. These findings indicated that while MIH may be a useful reagent for radioimmunoimaging using IgG, mAb, its application to smaller molecular weight mAbs and radioimmunotherapy would be hindered due to the labile characteristics of the ester bond in plasma. Thus, while the present study reinforced the usefulness of metabolizable linkages for reducing nontarget radioactivity levels, a development of plasma-stable metabolizable linkages is also warranted for radioimmunotherapy and for smaller molecular weight polypeptides.

[Protein- and peptide-derived radiopharmaceuticals]

Recent development of radiochemistry has provided various reagent that allow stable attachment of radiolabels to proteins in vivo. The advent of genetic and protein engineering have generated proteins and peptides with reduced or no immunogenicity or more favorable distribution characteristics. However, localization of radioactivity in nontarget tissues still constitutes a problem to be resolved for accurate diagnosis and effective therapy using the radiopharmaceuticals. Recent studies have indicated that radiometabolites after lysosomal proteolysis of proteins play a critical role in the radioactivity levels in nontarget tissues. Furthermore, radiochemical design of polypeptides that liberates radiometabolites of rapid urinary excretion after lysosomal proteolysis in nontarget tissues has facilitated rapid radioactivity elimination from nontarget tissues to urine. From these findings, we believe a new era of protein- and peptide-derived radiopharmaceuticals much more suitable for diagnostic and therapeutic applications will be opened soon.

Reassessment of diethylenetriaminepentaacetic acid (DTPA) as a chelating agent for indium-111 labeling of polypeptides using a newly synthesized monoreactive DTPA derivative

Previous studies on indium-111 (111In) labeling of polypeptides and peptides using cyclic diethylenetriaminepentaacetic dianhydride (cDTPA) as a bifunctional chelating agent (BCA) have indicated that DTPA might be a useful BCA for 111In labeling of polypeptides at high specific activities when DTPA can be incorporated without inducing intra- or intermolecular cross-linking. To investigate this hypothesis, a monoreactive DTPA derivative with a maleimide group as the peptide binding site (MDTPA) was designed and synthesized. A monoclonal antibody (OST7, IgG1) was used as a model polypeptide, and conjugation of MDTPA with OST7, 111In radiolabeling of MDTPA-OST7, and the stability of 111In-MDTPA-OST7 were investigated using cDTPA and benzyl-EDTA derivatives as references. SDS-PAGE analysis demonstrated that while cDTPA induced intramolecular cross-linking, no such undesirable side reactions were observed with MDTPA. MDTPA generated 111In-labeled OST7 with high radiochemical yields at higher specific activities than those produced using cDTPA and benzyl-EDTA derivatives as the BCAs. Incubation of each 111In-labeled OST7 in human serum indicated that MDTPA generated 111In-labeled OST7 of much higher and a little lower stability than those derived from cDTPA and benzyl-EDTA derivatives, respectively. These findings indicated that the low in vivo stability of cDTPA-conjugated antibody reported previously is not attributable to low stability of 111In-DTPA but to formation of intramolecular cross-linking during cDTPA conjugation reactions. The present study also indicated that MDTPA and its precursor, the tetra-tert-butyl derivative of DTPA, would be useful BCAs for 111In radiolabeling of polypeptides that have rapid blood clearance with high specific activities.

Stability of a metabolizable ester bond in radioimmunoconjugates

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 radiochemical 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.

Comparison of pleuropneumonectomy and limited surgery for lung cancer with pleural dissemination

The role of surgery in the management of lung cancer with pleural dissemination is controversial. We performed a retrospective analysis of our patients with lung cancer and pleural dissemination who were treated surgically. Between 1973 and 1993, 1,206 patients with lung cancer underwent pulmonary resection at Kanazawa University Hospital. Among them, 40 (3.3%) had pleural dissemination without pleural effusion. The 1-, 3-, and 5-year survival rates for 38 patients (except 2 patients undergoing exploratory thoracotomy alone) were 51.5%, 19.4%, and 19.4%, respectively. The 1-year survival rate in the 10 patients who underwent pleuropneumonectomy was only 20%, and 9 of these patients died within 18 months postoperatively (1 patient has survived for 25 months). In contrast, the 1-, 3-, and 5-year survival rates for the 14 patients who underwent resection of the primary tumor plus parietal pleurectomy were 85.1%, 35.5%, and 35.5%, respectively, a significantly better outcome (P < 0.01). Seven patients are still alive (the longest survival time is 65 months with the disease). The average survival time in the seven fatal cases was 18 months. In patients with lung cancer accompanied by pleural dissemination, it is quite possible that local excision plus pleurectomy will be justified.

Radiolabeled metabolites of proteins play a critical role in radioactivity elimination from the liver

We have recently reported that the behavior of radiolabeled metabolites in the liver appears to be responsible for the hepatic radioactivity levels after administration of protein radiopharmaceuticals. To better understand the role played by radiolabeled metabolites in hepatic radioactivity levels, two benzyl-EDTA derivatives rendering different radiolabeled metabolites, 1-(4-isothiocyanatobenzyl)ethylenediaminetetraacetic acid (SCN-Bz-EDTA) and 1-[p-(5-maleimidopentyl)aminobenzyl]ethylenediaminetetraacetic acid (ECMS-Bz-EDTA), were selected as bifunctional chelating agents (BCAs), and 111In labeling of galactosyl-neoglycoalbumin (NGA) and mannosyl-neoglycoalbumin (NMA) was performed. Biodistribution of radioactivity in mice and subcellular distribution of radioactivity in hepatocytes were then compared. After accumulation in hepatic parenchymal cells, NGA-EMCS-Bz-EDTA-111In rendered a faster elimination rate of radioactivity from the liver than NGA-SCN-Bz-EDTA-111In. Although each 111In-NMA exhibited a delayed elimination rate of radioactivity from the liver compared to the 111In-NGA counterpart, NMA-EMCS-Bz-EDTA-111In showed faster elimination rate of radioactivity than NMA-SCN-Bz-EDTA-111In. Analyses of radioactivity excreted in feces and urine and remaining in the liver indicated that both BCAs rendered mono-amino acid adducts as the major radiolabeled metabolites (cysteine-EMCS-Bz-EDTA-111In and lysine-SCN-Bz-EDTA-111In), which were generated in both cell types of the liver within 1 h postinjection. Subcellular distribution of radioactivity indicated that the radioactivity was copurified with lysosomes. These results demonstrate that although in vivo stability of radiometal chelates is essential, the biological properties of the radiolabeled metabolites generated after lysosomal proteolysis in hepatocytes play a critical role in radioactivity elimination from the liver.

[Two cases of chondrosacoma of rib]

Chondrosarcoma of rib origin is rare in Japan. We treated two cases of chondrosarcoma of rib origin. Case 1: A 68-year-old man with anterior chest wall mass and chest pain was underwent aspiration biopsy in Inami General Hospital. The histological examination showed Class V. Operation was done in our department and the histological diagnosis was chondrosarcoma. The tumor was 30 x 20 x 20 mm in size arising from the left fourth rib. The defect of bony chest wall was repaired with a double layer of Marlex mesh. His postoperative course was uneventful. Case 2: 66-year-old man noticed a tumor in left anterior part of the chest 7 months ago. He was underwent incisional biopsy and the histological diagnosis was chondrosarcoma. Radical resection was performed. The tumor was 70 x 50 x 50 mm in size arising from the left rib. His postoperative course was uneventful.

Results of surgical treatment of pulmonary metastases

From 1970 to 1993, 155 thoracotomies for metastatic lung tumors were performed on 113 patients in the Department of Surgery, Kanazawa University School of Medicine. Overall 30-day mortality amounted to 0.9% (1/113). The cumulative 3- and 5-year survival rates were 39.4% and 29.1%, respectively. The overall median survival was 24 months. The 5-year survival rate for carcinoma was 37.2% and for sarcoma it was 14.5% (P < 0.01). The other significant predictors of better long-term survival with metastatic lung tumors were solitary lesions, disease-free interval (DFI) > 24 months, and tumor size < or = 20 mm in diameter. There was no significant difference in survival based on the method of pulmonary resection. Repeat thoracotomy for recurrent metastases was performed in 27 patients, whose 5-year survival rate after the first lung resection was 35.5%. For bilateral pulmonary metastases, we recently performed simultaneous bilateral thoracotomy via median sternotomy on 25 patients and transsternal simultaneous bilateral thoracotomy on 8 patients. The latter procedure provides a wide operative field and better survival. We conclude that resection of metastatic lung tumors is safe and effective, and that repeat thoracotomy is warranted in selected patients with recurrent pulmonary metastases.