High background activity produces imaging problems when scanning with antibodies. The following work is directed towards reducing this background. The murine monoclonal antibody (MAb) CHA-255 selectively binds 111In-nitrobenzyl EDTA, a molecule referred to as a 'hapten'. Balb/c mice studies indicate that if the antibody is administered prior to the hapten, it predictably modifies the biodistribution and pharmacokinetics of the hapten. The pharmacokinetics for the hapten were proportional to antibody dose and inversely proportional to the time interval between injection of the antibody and the hapten. A hybrid MAb was produced by the enzymatic digestion of CHA-255 and ZCE-025, an anti-carcinoembryonic antigen (CEA) MAb, followed by joining of the two via a thioether linkage. The result was a F(ab')2 with affinity for both CEA and the hapten. The pharmacokinetics of the hapten were again dependent upon the kinetics and distribution of the hybrid antibody. Data in tumour models are also presented for 111In-nitrobenzyl EDTA and 111In-thioureabenzyl EDTA (TUBE), a newer hapten. The data indicate that the antibody-hapten system is capable of targetting tumour quickly while normal tissue rapidly becomes depleted of radioactivity. We conclude that the hapten-antibody technique shows some advantages over directly labelled MAb as a targetting system.

Even with the advancement of radiologic techniques, metastatic cancers can still be difficult to detect. In this study, 48 patients suspected of having occult metastases were studied by radioimmunodetection following the administration of 92.5 to 181.3 MBq of indium 111-labeled monoclonal anticarcinoembryonic antigen antibody. All but seven patients were thought to have metastatic colorectal carcinoma. In the majority of cases, physical examinations and computed tomographic scans had failed to detect a lesion. At least one lesion that was later proved to exist was detected in 34 of the 50 studies performed on these patients. Seven of eight patients with normal radioimmunodetection scans remain free of disease. One hundred one sites were detected overall; 60 were considered true-positive sites and 27 false-positive sites. Fourteen sites remained in question. Nineteen false-negative sites occurred. Radioimmunoimaging appears valuable for the detection of occult cancer where standard, noninterventional techniques have failed to detect the suspected disease.

Studies were performed to determine in vitro and in vivo effects of acetylation on Fab' fragments of ZCE-025, a monoclonal anti-CEA antibody. Isoelectric focusing revealed a drop in isoelectric point of 1.7 pI units following acetylation. Biodistribution studies of acetylated and nonacetylated [111In]Fab' were performed in normal BALB/c mice and in nude mice bearing the T-380 CEA-producing human colon tumor. The acetylated fragments remained in the vascular compartment longer and had significantly diminished renal uptake of 111In compared to controls. While acetylation itself effected a 50% drop in immunoreactivity, tumor uptake of the acetylated and nonacetylated 111In-labeled Fab' fragments was comparable, with the exception of one data point, through 72 h.

Detection of specific tumor sites was studied with scintigraphy and radiolabeled human IgM monoclonal antibodies (MoAbs). Ten patients with metastatic breast cancer received an infusion of one of three indium-111-labeled anti-breast carcinoma MoAbs. The time of infusion ranged from 30 minutes to 2 hours. Three patients received YBB-190 at total doses of 2, 4.25, or 11 mg, four patients received YBM-209 at total doses of 1 mg (n = 1) or 20 mg (n = 3), and three patients each received 22 mg of YBY-088. Imaging was performed immediately after infusion and at 4, 24, 48, 72, 120, and 144 hours. Many presumed sites of metastatic disease were imaged in three of the four patients who received 20 mg of YBM-209 and in two of the three patients who received YBY-088. Tumor was not detected in any of the patients who received YBB-190, in the patient who received a 1-mg dose of YBM-209, or in the patient who received YBY-088 and in whom a biopsy of tumor tissue failed to demonstrate target antigen. The authors conclude that In-111-labeled human IgM MoAbs can target human breast cancer, but antigen expression and antibody dose determine successful immunoscintigraphy.

The distribution and kinetics of six human and one murine monoclonal IgM antibodies (MoAb) were studied in BALB/c mice. Labeling was with 111In, 75Se, and 125I. The monomers and pentamers of certain MoAbs were studied. Human distribution studies were also performed. The serum containing [111In]MoAb was obtained from one of the patients 24 hr after administration and injected into mice which were then killed and assayed for 111In distribution. In general, the [75Se] and [111In]MoAbs had distribution and kinetic patterns that were similar while the 125I-labeled MoAbs dehalogenated after 4 hr. Monomers and pentamers had highly similar distributions suggesting that the distribution of IgMs may be based on factors other than molecular size. The murine IgM showed a somewhat different distribution in mice than did human IgMs. Serum from the patient containing [111In]MoAb had a distribution in mice similar to that of the patient with high liver and gastrointestinal uptake. The human imaging indicates that it is possible to target tumor with human IgM MoAbs, but significant problems remain in regard to their clinical use.

We have infused 13 111In-labeled murine IgG monoclonal antibodies (MAb) into 73 patients who had been diagnosed as having 7 types of cancers, and 3 111In-labeled human MAb into 8 patients with breast cancer. To each patient, 1.5-5 mCi attached to a maximum of 1 mg MAb had been given in a total MAb dose of 0.5-500 mg. The most encouraging overall results have been obtained with anti-human T-cell MAb T101 (33 of 33 tumor sites imaged in 5 patients), antimelanoma MAb P96.5 (47 of 88 sites imaged in 21 patients), anti-prostate MAb PSA399 (14 of 21 sites imaged in 4 patients), and anti-colon MAb ZCE025 (16 of 26 sites imaged in 12 patients). Poor imaging results were related to lower doses, reactivity with circulating cells, and limited antigen expression in various tumor sites. The problems involved in radioimmunodetection included low extraction of MAb from the serum by the tumor that resulted in poor tumor uptake of the radiopharmaceutical, and high background activity in the liver, heart, spleen, and gastrointestinal tract that made imaging difficult in those areas. Heterogeneous antigen production leaves some tumor deposits without targets, and the immunogenicity of the MAb limits use of these agents repetitively in humans. Nevertheless, these early results are encouraging for their potential diagnostic and therapeutic applications.

Studies were performed to determine the effect of tumor size on the incorporation of radiolabeled monoclonal antitumor antibodies (MoAbs) into human tumors growing in nude mice. The colon tumors ranged in size from 0.03-1.6 g, the melanoma from 0.1 to 6.7 g, and the lymphoma from 0.06 to 10.2 g. Indium-111 was primarily used as the radiolabel, however, both 125I and 111In were used as tracers for the MoAb in one experiment. The per g radiopharmaceutical uptake by tumors was inversely proportional to tumor size when tumor specific MoAb was administered. This finding was independent of the radiolabel and was demonstrable when the mice bore two tumors of differing size. When the MoAb was not specific for the tumor, the data were less well defined and a statistically significant correlation with size did not occur. These data are strong evidence for a decrease in per g uptake of labeled tumor specific antibodies as tumors increase in size.

The murine 96.5 monoclonal antimelanoma antibody (MoAb) was labeled with In-111, and 1-20 mg were administered to 21 patients who had proved or suspected melanoma metastases. One patient was studied twice. In four patients, unlabeled 96.5 MoAb was administered prior to the radiopharmaceutical. All of the patients tolerated the procedure without toxicity regardless of the mass of MoAb administered. The scans were interpreted by two observers, one with full knowledge, the other with no knowledge of the cases. Increasing the MoAb mass or preinfusing unlabeled MoAb prior to the administration of In-111 MoAb resulted in a prolongation of the serum half time, and appeared to improve tumor detection. Lesions were best seen at 72 hours after infusion or later. In all patients who had metastatic disease, at least one tumor site was apparent. Fifty-six per cent of known lesions 1.5 cm or greater in size were detected by the physician who had knowledge of the cases when data from all doses were considered. There were eight lesions detected that were not suspected in the workup of the patient. When these are included, the detection rate rises to 61%. Forty-nine per cent were detected by the other physician. Subtraction techniques were not employed. Lesions were often better seen with single photon emission computed tomography than with planar imaging techniques. The 96.5 In-111 MoAb appears to have utility for the detection of metastatic melanoma. Further clinical evaluation of 96.5 In-111 MoAb is warranted.

Studies were performed to determine the effect of the radiolabel and circulating carcinoembryonic antigen (CEA) on the pharmacodynamics of monoclonal anti-CEA antibodies (MoAbs). The studies were performed in normal BALB/c mice and in nude mice bearing human colon tumors. Three different tumors were used, each of which produced CEA levels characteristic of that particular tumor's secretory rate. The CEJ-326 MoAb labeled with either 111In or 125I was used in all studies. Circulating CEA induced the removal of 125I and 111In MoAbs from the vascular compartment. Liver concentrations of 111In increased and 125I levels decreased as the CEA secretory rate of the tumor rose. This indicates that circulating CEA complexes form in the vascular compartment which, in an animal model, are removed by the liver and spleen. This results in decreased tumor uptake of the labeled MoAb. The iodinated MoAb complexes are dehalogenated while the 111In is retained by the liver. This dehalogenation may account for the relatively low liver activity observed in radioimmunoimaging with intact radioiodinated anti-CEA MoAbs, provided the CEA complexes are similarly removed from the vascular compartment by the human liver.

Gadolinium-DTPA complex (Gd-DTPA) is a potential clinical magnetic resonance (MR) contrast agent that enhances images primarily by decreasing spin-lattice relaxation time (T1) in tissues in which it localizes. This study was designed to determine the immediate tissue distribution of intravenously administered Gd-DTPA in selected organs of interest as a function of administered dose and tissue Gd-DTPA concentration. An intravenous bolus of Gd-DTPA with a tracer quantity of Gd-153 was administered to three groups of rabbits at the following doses: 0.01 mM/kg (n = 6); 0.05 mM/kg (n = 6); 0.10 mM/kg (n = 6). A control group received sham injections. Five minutes after Gd-DTPA was administered, all animals were killed; samples of serum, lung, heart, kidney, liver, and spleen were analyzed in a 0.25 T MR spectrometer to measure T1, and then in a gamma well counter to determine tissue concentration of Gd-DTPA. Tissue distribution (per cent dose/tissue weight in g) at five minutes after injection was proportionally constant over the range of doses given. Tissue concentration varied linearly with injected dose (r greater than 0.98 for all tissues). Relaxation rate (1/T1) varied linearly with injected dose and with tissue Gd-DTPA concentration (r greater than 0.97 for all tissues). The order of tissue relaxation rate response to a given dose was: kidney greater than serum greater than lung greater than heart greater than liver greater than spleen. We conclude that because of its extracellular distribution and linear relaxation rate versus concentration relationship, Gd-DTPA enhancement in MR images may be a good marker of relative organ perfusion.