Metal Radionuclides Research Articles

Imaging with radiolabeled antisense oligonucleotides for the detection of intracellular messenger RNA and cardiovascular disease

Most of the research efforts in nuclear medicine in the last two decades have focused on the development of radioactive ligands for the detection of extracellular antigens expressed on the membrane surface such as tumor markers, somatostatin receptors on tumor cells, or receptors that are more readily accessible than cytosolic or nuclear receptors. However, these general concepts of radiolabeling methods for these ligands have helped us significantly to embark on the next phase of development of gamma-emitting singlestranted ASON probes for studying gene activation. Previous studies have demonstrated the nuclease-sensitivity of ASON probes. Further modifications of phosphodiester backbone, ribose, and nucleotide subunits have identified derivatives with improved potency, desirable pharmacokinetics, and reduced toxicity. Encouraged by in vitro and in vivo inhibition studies, the oligonucleotides have been radiolabeled with nonmetallic and metallic radionuclides of I-123, In-111, and Tc-99m and demonstrated their use in imaging specific mRNA of oncogenes, c-myc, erb-b2, and telomerase present in breast tumors in the mouse model. Noninvasive imaging of mRNA of heat shock protein (HSP-70) has been shown in a pig model during an ischemic episode of cardiopulmonary bypass. The radiochemists have developed ASON probes for positron emission tomography imaging labeled whereby they were with carbon 11 and fluorine 18. The radiolabeled antisense probes may provide a novel method to image the amplified oncogenes in atherosclerotic plaques and heat shock genes in myocardial stress. The standard methods of radiolabeling and novel methods of charge neutralization may enhance the intracellular delivery for imaging a variety of activated genes in cardiovascular diseases.

Targeted Delivery of Radiolabeled Imaging and Therapeutic Agents: Bifunctional Radiopharmaceuticals

Clinical application of radioactive diagnostic and therapeutic agents constitutes one of the great advances in noninvasive medicine, nuclear medicine. The radioactive agents used in the nuclear medical field are called "radiopharmaceuticals," and are required to exhibit high and specific localization of radioactivity into target tissue. Among radionuclides used in radiopharmaceuticals, radiometals such as 99mTc and (111)In have received much attention because of their nuclear physical characteristics and widespread availability. However, since these metallic elements are not constituents of bioactive molecules, they cannot simply replace common constituent atoms in biologically interesting compounds. Thus, demand for biospecific radiopharmaceuticals constitutes a great challenge in rational design of biologically active molecules labeled with metallic radionuclides, and evolves into a generation of bifunctional radiopharmaceuticals. Molecules contain both a biologically active site and a chelating group for binding the metallic radionuclide in which attachment of a chelating group does not affect the inherent biospecificity of the mother compound. This paper describes recent progress in research of macro- and small-molecular bifunctional radiopharmaceuticals for targeted diagnosis and therapy.

Elimination of Free Radionuclide by a Chelating Agent Improves Tumor-to-Nontumor Ratios Following Radioimmunotargeting with Antibody Labeled with 67Ga

To circumvent radionuclide accumulation in nontarget tissues when employing metallic radionuclides for radioimmunoscintigraphy or radioimmunotherapy, we have investigated the effect of the chelating agent deferroxamine (DFO) on the biodistribution of 67Ga following its administration attached to intact monoclonal antibody MAb35 and its F(ab′) 2 fragment. Following administration of 67Ga-labeled MAb35, DFO accelerated whole-body elimination of 67Ga and reduced its accumulation in several normal tissues, including liver, spleen and kidney. No reduction in tumor accumulation of 67Ga was observed. Following administration of 67Ga-labeled F(ab′) 2 fragment, kidney accumulation was higher than with the intact antibody (29% and 4% ID/g, respectively) and blood levels lower (0.69% and 5% ID/g, respectively). Again, no alteration in tumor accumulation of 67Ga was seen following DFO, although liver, kidney and blood levels were reduced and whole-body elimination accelerated.

Synthesis of new aza-thiophosphinate ligands

A series of new tetradentate, acyclic ligands incorporating thiophosphinate functionalities has been synthesised with regard to the potential application of their complexes with metal radionuclides for diagnostic imaging.

Development of labelled somatostatin and its analogues for the diagnosis and treatment of tumors

For recent years, the labeling and application of Somatostatin and Its Analogues have been becoming more and more important in the both diagnosis and treatment of a variety of tumors, especially the neuroendocrine tumors. This paper's goals are to deal with the chemical aspects of the radiolabeling of somatostatin and its analogues. It reviews the selected radionuclides and bifunctional chelating agents may be used in the labeling of Somatostatin and its analogues with metal radionuclides. The prospects of application of the Labelled Somatostatin and its analogues are comparatively assessed.

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, IgG 1) 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.

Hydrochemical modelling of the retention and transport of metallic radionuclides in the soils of an upland catchment

The CHemistry of the Uplands Model (CHUM) describes the transport of chemicals through upland catchments with acid, organic-rich soils, by a combination of sub-models for equilibrium soil chemistry, hydrology, weathering, and nitrogen cycling. CHUM was used to simulate the retention and transport of metallic radionuclides (Co, Sr, Cs, UO 2, U(IV), Th, Am), in the soils of a small catchment in Cumbria, UK, for 2 years after their atmospheric deposition in a single hypothetical precipitation event. Export of radionuclides to streamwater is calculated to occur most readily following deposition of the dissolved elements at high water saturation of the catchment, when little incoming rainwater is required to make up the small moisture deficit of the organic surface horizon, and solutes can move to greater depths in the soil profile. Deposition when the catchment is drier, or of particulate radionuclides, leads to stronger retention. Radionuclide retention or transport depends on the strength of chemical interaction with the solid phases of the different soil horizons; this varies among the elements, and also with oxidation state, U(IV) species being more strongly retained than UO 2. For purely organic soils, the least strongly retained radionuclide is Cs, but the presence in the mineral soil horizon of small amounts of clay mineral with high selectivity towards Cs can markedly increase with high selectivity towards Cs can markedly increase its retention. For the actinides, binding by dissolved organic matter is important; for example, the rate of transport of Th to the stream is increased by more than two orders of magnitude by complexation with dissolved fulvic acid. The model assumptions suggest that, in the longer term, losses from the catchment of Co, Sr and Cs would take place on a time-scale of decades, whereas the actinides would be much more persistent.

Preparation and preclinical evaluation of humanised A33 immunoconjugates for radioimmunotherapy.

A humanised IgG1/k version of A33 (hA33) has been constructed and expressed with yields up to 700 mg l-1 in mouse myeloma NS0 cells in suspension culture. The equilibrium dissociation constant of hA33 (KD = 1.3 nM) was shown to be equivalent to that of the murine antibody in a cell-binding assay. hA33 labelled with yttrium-90 using the macrocyclic chelator 12N4 (DOTA) was shown to localise very effectively to human colon tumour xenografts in nude mice, with tumour levels increasing as blood concentration fell up to 144 h. A Fab' variant of hA33 with a single hinge thiol group to facilitate chemical cross-linking has also been constructed and expressed with yields of 500 mg l-1. Trimaleimide cross-linkers have been used to produce a trivalent Fab fragment (hA33 TFM) that binds antigen on tumour cells with greater avidity than hA33 IgG. Cross-linkers incorporating 12N4 or 9N3 macrocycles have been used to produce hA33 TFM labelled stably and site specifically with yttrium-90 or indium-111 respectively. These molecules have been used to demonstrate that hA33 TFM is cleared more rapidly than hA33 IgG from the circulation of animals but does not lead to accumulation of these metallic radionuclides in the kidney. 90Y-labelled hA33 TFM therefore appears to be the optimal form of the antibody for radioimmunotherapy of colorectal carcinoma.

A newly designed radioimmuno-conjugate releasing a hippurate-like radiometal chelate for enhanced target/non-target radioactivity

Target-to-non-target ratio of radioactivity can be enhanced by the injection of monoclonal antibodies (MoAbs) labeled with metallic radionuclides, if some modality to accelerate the urinary excretion of radioactivity accumulated in non-target tissues could be introduced. In this study, a radioimmunoconjugate chemically designed to release a hippurate-like radiometal chelate was synthesized and tested in vivo. A 67Ga chelate of succinyldeferoxamine (SDF) was conjugated with a MoAb against osteogenic sarcoma (OST7, IgG 1) through an ester bond using a new metabolizable MESS linker, N-[[4-(maleimidoethoxy)succinyl]oxy]succinimide ( 67Ga-DFO-MESS-OST7). When injected into normal mice, 67Ga-DFO-MESS-OST7 exhibited faster clearance of radioactivity from circulation with less accumulation in the liver, kidney and spleen than those observed with 67Ga-DFO-EMCS-OST7, which was prepared under identical conditions to 67Ga-DFO-MESS-OST7 except for using a non-metabolizable linker holding no ester bond to release 67Ga-SDF. Size exclusion HPLC analysis of the liver homogenate obtained from mice 24 h after injection of 67Ga-DFO-MESS-OST7 indicated that all the radioactivity was eluted in the high molecular weight fraction with most of it being present as the 67Ga-DFO-MESS-OST7 fraction. Reverse-phase HPLC analysis of urine sample from the same mice showed a single radioactivity peak at the same retention time as that of 67Ga-SDF. In athymic mice bearing osteogenic sarcoma, 67Ga-DFO-MESS-OST7 exhibited higher tumor-to-blood and tumor-to-organ ratio of radioactivity when compared with 67Ga-DFO-EMCS-OST7. These results indicated that 67Ga-DFO-MESS-OST7 achieved enhanced target-to-non-target ratio of the radioactivity, due to preferential cleavage of the ester bond in non-target tissues, followed by rapid urinary excretion of the resulting chelate (probably as 67Ga-SDF). These results also suggest that the present design would become an applicable modality for enhancing the target-to-non-target ratio of radioactivity by MoAbs.

Metal compounds in therapy and diagnosis.

There is increasing interest in the use of metal-containing compounds in medicine. This review describes several therapeutic applications, such as the use of platinum complexes in cancer chemotherapy, gold compounds in the treatment of arthritis, gallium in hypercalcemia, bismuth in anti-ulcer medication, and sodium nitroprusside in hypertension. The use of metal radionuclides in diagnosis and radiotherapy and the role of paramagnetic metal complexes as contrast agents in magnetic resonance imaging are also discussed.

Studies on the preparation of186ReDTPA complexes using low specific activity186Re for antibody labeling

186Re is considered as “Therapy” Isotope and can be used in radioimmunotherapy. The radiation characteristics of this isotope are ideal for therapy. Generally metallic radionuclides are labeled to antibodies through bifunctional chelating agents, such as DTPA (diethylenetetraaminepentaacetic acid). A study has been carried out on the complexation of DTPA with186Re using low specific activity186Re. This was carried out to evaluate various parameters which are involved in the complex formation including methods of processing of raw material186Re. Stannous chloride was used as the reducing agent for the reduction of rhenium. Different labeling conditions such as pH, time, temperature and concentration of reducing agent were all studied for complex formation. The complex was characterized by paper electrophoresis, paper chromatography and gel column chromatography.

Metabolic fate of engineered antibody by labeling with Metallic Radionuclides of Indium-111 and Technetium-99M

Journal Article Metabolic fate of engineered antibody by labeling with Metallic Radionuclides of Indium-111 and Technetium-99M Get access M.K. Dewanjee, M.K. Dewanjee University of Miami School of Medicine, Departments of Radiology and Oncology, Miami, FL 33101, U.S.A. Search for other works by this author on: Oxford Academic PubMed Google Scholar S. Glenn, S. Glenn University of Miami School of Medicine, Departments of Radiology and Oncology, Miami, FL 33101, U.S.A. Search for other works by this author on: Oxford Academic PubMed Google Scholar R. Vargas-Cuba, R. Vargas-Cuba University of Miami School of Medicine, Departments of Radiology and Oncology, Miami, FL 33101, U.S.A. Search for other works by this author on: Oxford Academic PubMed Google Scholar A.N. Serafini, A.N. Serafini University of Miami School of Medicine, Departments of Radiology and Oncology, Miami, FL 33101, U.S.A. Search for other works by this author on: Oxford Academic PubMed Google Scholar G.N. Sfakianakis G.N. Sfakianakis University of Miami School of Medicine, Departments of Radiology and Oncology, Miami, FL 33101, U.S.A. Search for other works by this author on: Oxford Academic PubMed Google Scholar Protein Engineering, Design and Selection, Volume 6, Issue Supplement, 1993, Page 12, https://doi.org/10.1093/protein/6.Supplement.12-a Published: 01 January 1993

Synthesis and structure of N1‐e‐benzo‐4,7,13,16,21,26‐hexaoxa‐1,10‐diazabicyclo[8.8.8]hexacos‐23‐yl‐N2‐phenylthiourea. Derivative of a bifunctional complexing agent

AbstractA cryptand with an aminobenzo group 4,7,13,16,21,24‐hexaoxa‐5,6‐(4′‐aminobenzo)‐1,10‐diazabicyclo‐[8.8.8]hexacosane, has been synthesized as a bifunctional complexing intermediate for investigation of the labeling of proteins with metal radionuclides. This amine, although unstable, can be prepared as the stable stannic salt. The free base was converted to the corresponding phenylthiourea by 1) reaction with phenyliso‐thiocyanate and 2) conversion to its isothiocyanate followed by reaction with aniline. The thiourea structure was confirmed by X‐ray crystallographic analysis.

The evaluation of 186Re-labeled antibodies using N 2S 4 chelate in vitro and in vivo using tumor-bearing nude mice

We have recently described a method for radiolabeling monoclonal antibodies, with metallic radionuclides using a new chelating agent N 2S 3. Using this chelate the monoclonal antibodies Lym-1 and B72.3 were labeled with 186Re and their biological integrity was evaluated in vitro and in vivo. 186Re-labeled antibodies using N 2S 4 methodology were found to be stable in human serum and retained their immunoreactivity. Intravenous administration of 0.5 mCi 186Re-labeled antibodies resulted in partial or complete regression of tumor tissue in mice.

Synthesis and preliminary evaluation of a new chelate N 2S 4 for use in labeling proteins with metallic radionuclides

The successful attachment of various metallic radionuclides such as 99mTc to monoclonal antibodies for targeting tumor tissue in vivo depends upon the development and use of suitable bifunctional chelating agents. We have successfully synthesized a new N 2S 4 (compound 4) chelate. This chelate forms a stable complex with 99mTc and is capable of coupling to different proteins. The N 2S 4 compound is quite stable if kept as a hydrochloride salt and is coupled to antibody under neutral conditions with better than 95% efficiency without the loss of immunoreactivity.

Implementation of macrocycle conjugated antibodies for tumour-targetting

Abstract

Endotoxin testing with limulus amoebocyte lysate (ETLAL) in radiopharmaceuticals containing chelated metallic radionuclides (RPMETRN) and chelating agents (CA)

Endotoxin testing with limulus amoebocyte lysate (ETLAL) in radiopharmaceuticals containing chelated metallic radionuclides (RPMETRN) and chelating agents (CA)

Metallothionein: a bifunctional chelator for the radiolabeling of biologically active molecules.

Cysteine-rich metallothionein has been shown to bind as many as seven TcO3+ cores in TcO (Cys) units which adopt square-base pyramidal geometry. The Tc atoms in 99mTc,Zn-MT and 99mTc,Zn-MT-MAb species formed in the exchange reaction with the labile 99mTcO (glucoheptonate) complex are stable to oxidation and transchelation in vivo. The kinetics of labeling with the carrier-free radionuclide 99mTc are diffusion-limited at MT concentrations below 10(-5) M. Zinc-MT-MAb conjugates can be efficiently radiolabeled at concentrations greater than or equal to 10(-5) M. The conjugation of MT to tumor specific MAb's has been accomplished with the preservation of the in vivo tumor targeting capability of the MAb and the excellent metal-binding properties of MT. The success achieved in this research demonstrates the potential of metallothionein as a carrier of medically useful metallic radionuclides in labeling of important biologically active molecules.

Labeling of monoclonal antibodies with a 67Ga-phenolic aminocarboxylic acid chelate. Part I. Chemistry and labeling technique.

As a chelating agent for labeling antibodies (Abs) with metallic radionuclides, a propionic acid substituted ethylenediamine N,N'-di-[(o-hydroxyphenyl) acetic acid] (P-EDDHA), which tightly complexes 67Ga, was synthesized. The 67Ga-P-EDDHA chelate was coupled in aqueous solution to IgG at a molar ratio of 1:1 via carbodiimide. The average coupling yield was 15%. A specific activity of 4 mCi/mg IgG could be obtained with commercially supplied 67Ga. In vitro stability was evaluated in human serum at 37 degrees C and showed a half-life of about 120 h for the release of 67Ga from the labeled Ab during the initial phase of incubation. This in vitro halflife is similar to that measured for 111In-DTPA labeled Abs. Because of the high stability of the 67Ga-P-EDDHA chelate, the in vivo formation of radioactive labeled transferrin by transchelation, as described for 111In-DTPA labeled Abs, should, however, be reduced by this labeling technique.

Label stability in serum of four radionuclides on DTPA-coupled antibodies—An evaluation

Although DTPA forms strong chelates with many metals, the harsh chemical environment of the serum may nevertheless dissociate metallic radionuclides from DTPA attached to proteins. We have investigated the stability in 37 °C serum of 111In, 99mTc, 90Y and 153Gd chelated to DTPA-coupled antibodies. Stability was evaluated primarily by affinity chromatography and HPLC analysis of serum incubates; however, the stability of 111In was determined in vivo in patient studies. Analysis of patient urine showed no evidence for dissociation of DTPA from antibody whereas analysis of serum demonstrated exchange rates of 111In to transferrin of about 9%/day. When labeled by the described method, 99mTc on DTPA coupled antibodies shows instability in serum but superior stability than 99mTc on antibodies without the attached DTPA. Both 90Y and 153Gd dissociate in serum at rates which are comparable to that of 111In.