Radiolabeling of monoclonal antibody B43.13 with rhenium-188 for immunoradiotherapy.

In this study we report a novel method for direct radiolabeling of monoclonal antibody B43.13 (MAb-B43.13) with 188Re and have evaluated the product's radiochemical, biochemical, immunochemical and selected biological properties. 188Re-MAb-B43.13 was readily prepared by the addition of generator produced perrhenate to a preformulated antibody vial after an optimal amount of supplemental stannous ion, in the form of stannous tartrate, was added. The final radiolabeled product retained its biochemical purity (as determined by size-exclusion HPLC and R/NR-SDS-PAGE), its immunoreactivity (as determined by immunoassay) and presented with a typical stability (in the presence of serum and cysteine) and biodistribution (in tumored mice) profile. The evaluation of the product for immunoradiotherapy of ovarian cancer in a clinical setting requires further studies.

Preparation and protein conjugation of a divinyl sulphone derivatized bifunctional chelating agent.

A new bifunctional chelating agent with a novel linking arm, 2-[p-¿N-benzyl-N-(2-vinylsulfoethyl)¿- (aminobenzyl)¿-1,3-propane-diamine-N,N,N',N'-tetraacetic acid (VS-PDTA) was synthesized and was conjugated to protein for the purpose of attaching radiometals to monoclonal antibodies (MAbs). The effect of various parameters such as ligand concentration, protein concentration, pH, temperature and reaction period on the conjugation have been examined using chromatographic (SE and TLC) analysis after labeling with 111In. The parameters and chemical variables studied have significant effects on the efficiency and rate of protein conjugation.

Synthesis and evaluation of a new bifunctional chelating agent for the preparation of radioimmunoconjugates.

The conjugation of radiometals to monoclonal antibodies results in agents for radioimmunoimaging and other medical applications. Due to remarkable ability to form stable metal complexes with a great number of metal ions in different oxidation states, polyaminocarboxylate chelates are useful tools for this purpose. Bifunctional chelators that can hold radiometals with high stability under physiological conditions are essential to avoid radiation damage to non-target organs. We have synthesized a new bifunctional chelate 2-(p-aminobenzyl)-1,3-propylenediamine-N,N,N',N'-tetraacetic acid by a simple method and studied the rate of loss of radioactivity from the radiolabeled (111In, 90Y) chelates to serum proteins in human serum at 37 degrees C. The relative stability constant of this new bifunctional chelate was found to be very similar to the underivated form. This chelate was conjugated to murine monoclonal antibody (B43) and immunoreactivity of the conjugated was determined by competitive binding analysis, which showed no significant change in its immunological activity. Biodistribution of the 111In radioconjugate was examined in conventional Balb/c and tumor-bearing (-OVCAR-3) athymic Balb/c mice.

Radioiodinated 1-(2-fluoro-4-iodo-2,4-dideoxy-beta-L-xylopyranosyl)-2-nitroimidazole: a novel probe for the noninvasive assessment of tumor hypoxia.

1-(2-Fluoro-4-iodo-2,4-dideoxy-beta-L-xylopyranosyl)-2-nitroimidazole (FIAZP) has been synthesized and labeled with radioiodine (125I). Radioiodinated FIAZP is one of a series of sugar-coupled 2-nitroimidazoles developed in our laboratory as probes for noninvasive scintigraphic assessment of tumor hypoxia. An in vivo biodistribution study with [125I]FIAZP in the murine BALB/c EMT-6 tumor model showed a tumor-to-blood ratio of 6, 24 h after injection, with 0.5% of the injected dose present per gram of tumor. These values are several times higher than the respective ratios and distribution values in any of the organs, with the exception of liver. Radioactivity from tissues other than tumor and liver declined with time, following the decline of blood radioactivity. Rapid whole-body elimination of radioactivity was observed (> 96% in 24 h). The thyroid showed little uptake of radioactivity, indicating minimal in vivo deiodination. 1-(2-Fluoro-4-iodo-2,4-dideoxy-beta-L-xylopranosyl)-2-nitroimidazo le appears to undergo hypoxia-dependent binding in tumor tissue at levels comparable to those of other sugar-coupled 2-nitroimidazoles. The potential for imaging with this compound is discussed.

Radioiodinated azomycin pyranoside (IAZP): a novel non-invasive marker for the assessment of tumor hypoxia.

1-(4-Iodo-4-deoxy-beta-L-xylopyranosyl)-2-nitroimidazole (Iodoazomycin Pyranoside; IAZP) was synthesized, labelled with radioiodine(123I, 125I) and evaluated for non-invasive assessment of tumor hypoxia. A biodistribution study with Balb/c mice bearing EMT-6 tumors showed a tumor-to-blood ratio of 13.9, representing 0.5 percent of injected dose per gram of tissue, at 24 hours post injection. This ratio is the highest for any 2-nitro-imidazole reported to date in this tumor model. Rapid elimination of radioactivity from the whole-body was noted (greater than 97% in 24 hours) and thyroid radioactivity at 24 hours was much lower than with other analogues of this series. No toxicity was observed in Balb/c mice at a dose 100 times higher than the anticipated human dose required for scintigraphic imaging. Planar, whole-body gamma scintigraphic images in the murine Balb/c EMT-6 tumor model clearly delineated tumor tissue at 24 hours post injection. These observations suggest that IAZP may be a suitable agent for non-invasive, clinical assessment of tumor hypoxia.

Radioiodinated 1-(5-iodo-5-deoxy-beta-D-arabinofuranosyl)-2-nitroimidazole (iodoazomycin arabinoside: IAZA): a novel marker of tissue hypoxia.

1-(5-Iodo-5-deoxy-beta-D-arabinofuranosyl)-2-nitroimidazole (IAZA) has been synthesised and labeled with 125I. Radioiodinated IAZA was shown to undergo hypoxia-dependent binding in EMT-6 cells in vitro and to have an initial binding rate of 284 pmole/10(6) cells/hr at a substrate concentration of 30 microM. This binding rate is more than three times that of the reference compound, misonidazole (89 pmole/10(6) cells/hr). The elevated binding rate was accompanied by in vitro cytotoxicity 30-40 times greater than that observed for misonidazole. Whole-body elimination and biodistribution studies in BALB/c mice bearing implanted, subcutaneous EMT-6 tumors showed a rapid excretion (greater than 98% in 24 hr) with moderate tissue levels which, in general, declined as a function of blood clearance. Tumor-to-blood ratios of 4.6 (4 hr) and 8.7 (8 hr), with respective tumor uptake values of 2.08% and 1.22% ID/g of tissue, form a rational basis for evaluation of this and related 2-nitroimidazole analogs as radiopharmaceuticals suitable for scintigraphic evaluation of tissue (tumor) hypoxia.