Pharmacokinetics of 111In-labeled OC-125 antibody in cancer patients compared with the 19-9 antibody

We recently reported on the pharmacokinetics in 14 cancer patients of the 19-9 antibody radiolabeled with 111In. We have now repeated this investigation in 18 cancer patients using the OC-125 antibody, in part to compare the in vivo behavior of two murine monoclonal antibodies of the same subclass administered as the F(ab\u27)2 fragments, by the same route and at the same dose. As in the earlier investigation, 1 mg of fragments was infused i.v., and organ quantitation was obtained for up to 72 h along with frequent blood and urine samples for chromatographic evaluation. Analysis of urine showed that activity clearance by this route amounted to 0.29%/h and consisted of labeled DTPA only in early samples and metabolic products thereafter. Analysis of serum samples often showed the presence of a high-molecular-weight species appearing within 24 h. This species is probably due to antibody binding to circulating antigen, although the percentage of circulating activity present as this species did not correlate well with circulating antigen levels. As before, organ accumulation was greatest in the liver, although levels were significantly reduced (12% compared to 20% of administered dose at 24 h, P less than 0.01). Plasma clearance was also significantly different: whereas the label in the case of the OC-125 antibody showed one-compartment clearance kinetics and remained in the plasma compartment, in the 19-9 case the label diffused to a second, unidentified compartment

Pharmacokinetics in patients of an anti-carcinoembryonic antigen antibody radiolabeled with indium-111 using a novel diethylenetriamine pentaacetic acid chelator

The pharmacokinetics of the C110 anti-carcinoembryonic antigen antibody radiolabeled with 111In via a novel benzylisothiocyanate derivative of diethylenetriamine pentaacetic acid have been determined in 12 patients. The chelator was attached to the protein via a thiourea bond and in such a way that all 5 carboxymethyl arms were presumably able to participate in chelation. Patients with known or suspected colorectal carcinoma received between 5 and 20 mg of the IgG antibody labeled with 5 mCi of 111In. Individual organ radioactivity levels were quantitated, and serum and urine samples were analyzed, principally by size exclusion high-performance liquid chromatography (HPLC). Total urinary excretion averaged 0.18% of the injected dose/h with large patient to patient variation. At early times postadministration (less than 8 h) the predominant radiolabeled species in urine was free diethylenetriamine pentaacetic acid most probably administered as a small radiocontaminant in the injectate. Thereafter, radioactivity in urine was primarily present as a low molecular weight catabolic product. Analysis of serum by size exclusion HPLC occasionally showed 3 radioactivity peaks, 2 of which are due to circulating immune complexes and labeled antibody. The third peak is of low molecular weight and is due to one or more products of antibody catabolism. Transchelation of 111In to circulating transferrin was observed but at modest levels. Quantitation of organ radioactivity showed that 18 +/- 4 (SD)% of the injected dose was in the liver at 1 day postadministration and 1.4 +/- 1.1 and 1.2 +/- 0.9% was in the spleen and in both kidneys, respectively, at this time. The mean half-life for clearance of total injected radioactivity was fitted to a single exponential and was found to be 34 h (SD, 14 h; N = 13) and that for antibody alone, assessed by size exclusion HPLC analysis of serum samples, was calculated to be 22 h (SD, 8 h; N = 10). Neither of these values nor organ radioactivity levels were affected by antibody-loading dose

Antisense and nuclear medicine

Despite many uncertainties concerning mechanism, synthetic single-strand antisense deoxyribonucleic acids (DNAs) are now in clinical trials for the chemotherapy of viral infections such as human immunodeficiency virus (HIV) and human papilloma virus; several cancers, including follicular lymphoma and acute myelogenous leukemia; inflammatory processes such as Crohn\u27s disease and rheumatoid arthritis and in allergic disorders. There are approximately 10 trials, and early results are generally encouraging. Therefore, the expectation is that antisense DNAs will be important to future chemotherapy. The question considered here is whether antisense DNAs will also be important to future nuclear medicine imaging. While efforts toward developing antisense imaging are comparatively nonexistent thus far, investigations into the mechanisms of cellular transport and localization and the development of a second generation of antisense DNAs have occurred largely within the antisense chemotherapy industry. Fortunately, many of the properties of DNA for antisense imaging, such as high in vivo stability and adequate cell membrane transport, are the same as those for antisense chemotherapy. Unfortunately, interests diverge in the case of several other key properties. For example, rapid localization and clearance kinetics of the radiolabel and prolonged retention in the target are requirements unique to nuclear medicine. No doubt the development of antisense imaging will continue to benefit from improvements in the antisense chemotherapy industry. However, a considerable effort will be required to optimize this approach for imaging (and radiotherapy). The potential of specifically targeting virtually any disease or normal tissue should make this effort worthwhile

Labeling biomolecules with radiorhenium: a review of the bifunctional chelators

For radiotherapy, biomolecules such as intact antibodies, antibody fragments, peptides, DNAs and other oligomers have all been labeled with radiorhenium ((186)Re and (188)Re). Three different approaches have been employed that may be referred to as direct, indirect and integral labeling. Direct labeling applies to proteins and involves the initial reduction of endogenous disulfide bridges to provide chelation sites. Indirect labeling can apply to most biomolecules and involves the initial attachment of an exogenous chelator. Finally, integral labeling is a special case applying only to small molecules in which the metallic radionuclide serves to link two parts of a biomolecule together in forming the labeled complex. While the number of varieties for the direct and integral radiolabeling approaches is rather limited, a fairly large and diverse number of chelators have been reported in the case of indirect labeling. Our objective herein is to provide an overview of the various chelators that have been used in the indirect labeling of biomolecules with radiorhenium, including details on the labeling procedures, the stability of the radiolabel and, where possible, the influence of the label on biological properties

A Brief Review of Chelators for Radiolabeling Oligomers

The chemical modification of oligomers such as DNA, PNA, MORF, LNA to attach radionuclides for nuclear imaging and radiotherapy applications has become a field rich in innovation as older methods are improved and new methods are introduced. This review intends to provide a brief overview of several chelators currently in use for the labeling of oligomers with metallic radionuclides such as 99mTc, 111In and 188Re. While DNA and its analogs have been radiolabeled with important radionuclides of nonmetals such as 32P, 35S, 14C, 18F and 125I, the labeling methods for these isotopes involve covalent chemistry that is quite distinct from the coordinate-covalent chelation chemistry described herein. In this review, we provide a summary of the several chelators that have been covalently conjugated to oligomers for the purpose of radiolabeling with metallic radionuclides by chelation and including details on the conjugation, the choice of radionuclides and labeling methods

Localization of infection using streptavidin and biotin: an alternative to nonspecific polyclonal immunoglobulin

Since favorable images of infection are obtained with radio-labeled nonspecific IgG, streptavidin has been considered as an alternative protein in this investigation. The advantage of streptavidin is that once localized it may be targeted with radiolabeled biotin. Studies were conducted in a mouse model with an Escherichia coli infection in one thigh. Indium-111-labeled streptavidin showed equivalent localization to the infection as that obtained with 111In-labeled polyclonal nonspecific IgG, however blood levels with streptavidin were lower at all time points; consequently, target-to-blood ratios were improved. Pretargeting with unlabeled streptavidin followed 3 hr later with 111In-labeled biotin showed equivalent localization in the target and reduced activity in all organs sampled. As such, infected thigh-to-normal thigh ratios were improved 3-fold for pretargeting versus either labeled IgG or streptavidin. Improvements in infected thigh-to-liver and blood ratios were greater than 8-fold. Only in the case of kidneys was the ratio unimproved. In conclusion, we have shown that by preadministration of unlabeled streptavidin followed by labeled biotin, infectious lesions in a mouse model may be imaged earlier with lower background levels relative to the administration of labeled nonspecific IgG

An experimental and theoretical evaluation of the influence of pretargeting antibody on the tumor accumulation of effector

In treating tumors by pretargeting, the antitumor antibody and the cytotoxic effector (e.g., toxins and radioactivity) are separately administered. Therefore, pretargeting is more complicated with many variables. We are conducting studies to understand the influence of each variable using a novel recognition pair of mutually complementary phosphorodiamidate morpholino oligomers (MORF/cMORF). Earlier we developed a semi-empirical model capable of accurately predicting the behavior of a radiolabeled cMORF effector with variations in dosages and timing. We have now extended the model to predict the effector behavior, in particular, its maximum percent tumor accumulation (MPTA) in mice pretargeted with three different MORF-conjugated antibodies (MN14, B72.3, and CC49). The MN14 and the CC49 target different antigens in the same tumor, whereas the CC49 and the B72.3 target the same antigen but with very different tumor accumulation. By comparing the pretargeting results of these three antibodies with our prediction, we confirmed that the MPTA of the radiolabeled cMORF effector in the LS174T tumor is independent of the antibodies. In conclusion, the MPTA cannot be improved through the use of different pretargeting antibodies, although different antibodies may improve the maximum absolute tumor accumulation, the heterogeneity, and/or the tumor-to-normal tissue ratios of the effector. This conclusion will apply equally well to effectors carrying a fluorescent probe, an anticancer agent, or a radioactive imaging agent

Pretargeting with Amplification Using Polymeric Peptide Nucleic Acid

One goal of this investigation was to develop a polymer conjugated with multiple copies of peptide nucleic acid (PNA) and with pharmacokinetic properties suitable for applications in vivo. The second goal was to establish whether the multiple copies of PNA on the polymer could be targeted by hybridization in vitro and in vivo with 99mTc-labeled complementary PNA (cPNA). If successful, this approach could then be considered in further investigations as an alternative to existing pretargeting approaches because of the potential for signal amplification in the target. A 80 KDa poly(methyl vinyl ether-alt-maleic acid) (PA) polymer was conjugated with multiple copies of PNA and with multiple copies of poly(ethylene glycol) (PEG) by reacting the NHS derivative of PA with the amine derivatives of PNA and PEG. Using 99mTc-MAG3-cPNA, targeting of PNA-PA-PEG was studied in vitro and in vivo in inflammation and tumor mouse models, in both cases relying upon nonspecific diffusion for localization. In addition, cPNA-avidin was considered as a clearing agent with biotinylated PNA-PAPEG. About 80 PNAs could be conjugated to PA provided that about 200 PEGs were also conjugated to raise the aqueous solubility of the PNA-PA-PEG polymer lowered by the addition of the PNAs. About 70% of the PNAs on this polymer in vitro either in solution or attached to beads could be successfully targeted with 99mTc-cPNA. In both the inflammation and tumor mouse models, between 35 and 60% of these PNAs could be targeted in the lesions. The advantage of amplification was evident when less favorable results were obtained with PNA-PA-PEG conjugated with only six PNAs. We conclude that amplification can be achieved in vivo using polymers of PNA followed by radiolabeled complementary PNA and that the application of pretargeting using polymers of PNA for amplification can improve localization

Early results in the irrational design of new bifunctional chelators

BACKGROUND: The development of a simple route for the synthesis of the N-hydroxysuccinimide (NHS) ester of S-acetyl-protected mercaptoacetyltriglycine (MAG3) has opened the possibility of preparing novel bifunctional N3S chelators for technetium-99m (99mTc) and other radionuclides. In particular, the synthesis may be applied to a vast number of tripeptides in place of triglycine, to provide a library of bifunctional N3S chelators, each with unique properties related to the particular amino acid residues within each tripeptide. METHODS: The authors have synthesized by this simple route the NHS esters of four N3S chelators by reacting NHS-S-acetylthioglycolic acid with ala-gly-gly, phe-gly-gly, pro-gly-gly, and ser-ser-ser, in addition to gly-gly-gly. Each bifunctional chelator was conjugated to biocytin as a model primary amine and radiolabeled with 99mTc. The properties of the four chelators were compared with MAG3 with respect to the stability of the label in saline and serum, the extent of serum protein binding, and the instability to cysteine challenge. RESULTS: A range of values was observed. Labeled mercaptoacetyltriserine showed stability towards transchelation to cysteine similar to that of MAG3 as well as lower serum protein binding; labeled mercaptoacetylalanyldiglycine showed slightly higher serum protein binding than labeled MAG3 but greater stability to cysteine challenge. CONCLUSIONS: The authors concluded that this simple synthesis and evaluation scheme may be used to prepare and screen a large library of bifunctional chelators for those with useful properties