Radiation exposure inside reinforced concrete buildings at Nagasaki.

In this study, the radiation doses to occupants of two reinforced concrete buildings at Nagasaki, who survived the immediate effects of the nuclear weapon detonation, are determined using state-of-the-art radiation transport techniques. The radiation doses at all locations in the buildings are calculated using the Three-Dimensional Oak Ridge Discrete Ordinates Radiation Transport Code which was constructed especially for this task. This code represents a new and unique capability that has been previously reported. This study resulted in case-by-case lists of doses to occupants and an uncertainty analysis. These data have been used in a companion study as the basis for determining a new value of the dose producing a 50% risk of fatality.

Pharmacokinetics of an indium-111-labeled monoclonal antibody in cancer patients.

We have evaluated the pharmacokinetics in patients of a monoclonal antibody (19-9) F(ab')2 fragment coupled with DTPA and labeled with 111In. In addition to imaging and organ uptake determinations, serum and urine samples were analyzed to help determine the in vivo behavior of the label. Using a competitive binding assay, the immunoreactivity of the coupled fragment was found to be indistinguishable from that of the unmodified fragment. The absence of radiocolloids in the injectate was confirmed as was the in vivo stability of the attached DTPA groups. By a variety of techniques, we show that the only significant source of label instability was transcomplexation to circulating transferrin. About 9% per day of label exposed to transferrin (about 1-2% of the injected dose) dissociated with slight bone marrow accumulation. Following i.v. administration, serum activity levels fell rapidly (T 1/2 alpha 2 hr, T 1/2 beta 19 hr). Whole-body clearance of the label was slow (T 1/2 160 hr) and may be attributed entirely to urinary excretion (0.26% of the injected dose per hour). Organ accumulation was greatest in the liver and persisted after rapidly attaining high values (20% of the injected dose). A total of 14 cancer patients were studied, nine with identifiable sites of metastatic disease from colorectal [8], pancreatic [2], ovarian [3], or small cell lung [1] primaries. Eight of the 12 sites of documented tumor were visualized by external imaging (67%) most distinctly at 48-72 hr postadministration.

Optimum conditions for labeling of DTPA-coupled antibodies with technetium-99m.

The covalent attachment of strong chelating groups such as DTPA to IgG antibodies may simplify the labeling of these proteins with 99mTc and may improve the stability of the label. Accordingly, we have investigated the labeling of DTPA-coupled antibodies by determining the effect of DTPA:tin molar ratio, pH, and DTPA concentration. We have determined that the optimum conditions are a molar ratio of 1:1.5, a pH of 4, a DTPA concentration as high as possible, and an antibody concentration as low as possible. Using these conditions, a DTPA-coupled antibody was labeled with 99mTc and its stability in 37 degrees C serum compared with that of the uncoupled antibody labeled in the identical fashion. High performance liquid chromatographic analysis of the incubates showed that the coupled antibody lost its label slowly compared to the uncoupled antibody. Both labeled antibodies were also administered to normal mice along with 111In-labeled coupled antibody as a further control. Biodistribution results obtained at 1 hr and 20 hr confirm the increased stability of the label in the case of the coupled antibody and provide evidence for redistribution of the 99mTc following catabolism at sites of localization. To obtain the above results, however, it was necessary to attach an average of two to five DTPA groups per antibody molecule. Furthermore, it was not possible to reduce to negligible levels nonspecific binding of 99mTc to the antibody.

The preparation of DTPA-coupled antibodies radiolabeled with metallic radionuclides: an improved method.

Isotopes of iodine are often employed as radiolabels for antibodies used in radioimmunodetection studies in which tumor localization is determined by external imaging. Because of drawbacks associated with the use of these isotopes, alternative labeling methods have been considered; such as covalently attaching strong chelators so that the coupled protein may be radiolabeled with metallic radionuclides by chelation. We have developed a method of coupling the strong chelator diethylenetriaminepentaacetic acid (DTPA) which is simple, efficient, and superior to reported methods. Using the cyclic anhydride, coupling to IgG antibody is about 75% efficient and is completed in less than 1 min at neutral pH. Because the concentration of hydrolytic products is small, the coupled protein is rapidly purified for use or storage. Labeling of the protein is also accomplished rapidly and the labeled product has been shown to be stable both in vitro and in vivo.

Radioactive labeling of antibody: a simple and efficient method.

A simple and efficient method of covalently coupling the strong chelator diethylenetriaminepentaacetic acid to proteins was developed for radiolabeling immunoglobulin G antibodies. After being coupled and labeled with indium-111, a monoclonal antibody to carcinoembryonic antigen retained its ability to bind to its antigen in vitro and in vivo. In nude mice with a human colorectal xenograft, 41 percent of the injected radioactivity became localized in each gram of xenograft at 24 hours compared with 9 percent for control antibody and 19 percent for radioiodinated antibody to carcinoembryonic antigen.

Evaluation of the viability of In-111-labeled DTPA coupled to fibrinogen.

In earlier work, DTPA has been covalently coupled to albumin via the cyclic anhydride of DTPA. Using fibrinogen, we have studied the effect of such coupling on protein viability by both an in vitro and an in vivo assay. Clotting time remained identical to that of the native protein whether the anhydride-to-protein molar ratio was 1:1 or 5:1. In vivo studies were done in dogs, with human fibrinogen labeled with 1-125 and In-111. Throughout 130 hr, blood clearances for the two tracers agreed whether with 1:1 or 5:1 coupling. In a dog model with a thrombogenic catheter, the clot-to-blood ratios for the two radiotracers agreed within experimental error. Finally, 1:1-coupled canine fibrinogen, labeled with In-111, was administered to dogs with a catheter in a jugular vein, and scintigrams at 24 hr clearly showed clotting along the length of the catheter. We conclude that fibrinogen, coupled to DTPA, retains its viability, behaving like radioiodinated fibrinogen in vivo, and In-111 labeled fibrinogen looks promising as a clinical diagnostic agent.

The preparation and labeling of DTPA-coupled albumin.

A new method has been developed for the coupling of diethylenetriaminepentaacetic acid (DTPA) to proteins using the cyclic anhydride of DTPA. The anhydride, prepared by a simple one-step synthesis, is added as the solid to the solid protein. Coupling is completed in minutes at room temperature following the addition of aqueous pH 7 buffer. The coupling has been characterized by the use of exhaustive dialysis, gel chromatography, and u.v. spectrophotometry. Under optimal conditions of anhydride: protein molar ratio and protein concentration, up to 70% of the DTPA groups may be coupled to protein. Essentially all free DTPA may be removed from DTPA-coupled albumin preparations by a single passage through a 20-cm gel filtration column. Biodistributions in normal mice at 45 min obtained for 111In-albumin showed 33 +/- 1% injected dose per gram in blood compared to 35 +/- 3% for 125I-albumin. Results for all tissue samples are in agreement within two standard deviations. The simplicity with which albumin has been coupled with DTPA by this method contrasts sharply with existing methods and is an attractive area of research for the labeling of a variety of proteins with a variety of metallic radionuclides.