In Vitro and In Vivo Tumor Models for Studies of Distribution of Radiolabelled Monoclonal Antibodies and Fragments

Colon carcinoma multicellular spheroids were incubated in vitro with radiolabeled MAbs. The more rapid penetration of fragments as compared to intact MAbs was clearly demonstrated. For the study of antibody localization in tumors in vivo, the model of nude mice with ligated kidneys was used. Although very artificial, this model allowed to demonstrate that, without urinary excretion, Fab fragments accumulated more rapidly into the tumor than intact MAbs and disappeared faster from the blood. This difference was less striking for F(ab’)2 fragments. In the liver a decreased accumulation of both types of fragments as compared to intact MAbs was observed. Concerning radioimmunotherapy we think that Fab fragments are not useful because of their too short half-life in the circulation and in tumor and because they will probably be too toxic for the kidneys. Intact MAbs and F(ab’)2 fragments have each their advantages. Intact MAbs show highest tumor accumulation in mice without ligated kidney, however, they remain mostly on the periphery of tumor nodules, as shown by autoradiography. F(ab’)2 fragments have been found to penetrate deeper into the tumor and to accumulate less in the liver. It might be therefore an advantage to combine intact MAbs with F(ab’)2 fragments, so that in the tumor two different regions could be attacked whereas in normal tissues toxicity could be distributed to different organs such as to the liver with intact MAbs and to the kidney with F(ab’)2 fragments.

Radiolabeled MDA2, an oxidation-specific, monoclonal antibody, identifies native atherosclerotic lesions in vivo

BACKGROUND

Oxidatively modified low-density lipoprotein (LDL) is present in atherosclerotic but not normal arteries and plays a crucial role in the pathogenesis and adverse consequences of atherosclerotic lesions. We previously generated a series of monoclonal antibodies (MoAb) against oxidation-specific neo-epitopes formed during the oxidative modification of LDL. MDA2, a prototype MoAb, recognizes malondialdehyde-lysine epitopes (eg, in malondi-aldehyde-modified LDL) within atherosclerotic lesions. We describe the in vivo characteristics of MDA2 and initial noninvasive imaging studies of atherosclerosis in rabbits.

METHODS

To assess the in vivo specificity of MDA2 for atherosclerotic lesions, iodine 125-MDA2 was intravenously injected into 7 LDL-receptor deficient Watanabe heritable hyperlipidemic (WHHL) and 2 normal New Zealand white (NZW) rabbits, and the aortic plaque uptake was evaluated 24 hours later. 125I-Halb, an isotype-matched irrelevant MoAb that binds to human albumin, was injected into 5 WHHL and 2 NZW rabbits as a control. Aortic autoradiography was performed, and the mean uptake of MoAbs was measured as the percent injected dose per gram aortic tissue. Gamma camera imaging was then carried out in 7 WHHL rabbits and 2 NZW rabbits with 99mTc-MDA2. Imaging was carried out at 10 minutes and at 12 or 24 hours. Malondialdehyde-LDL was then injected to clear the blood pool signal, and final images were obtained 2 hours later.

RESULTS

Mean uptake of 125I-MDA2 in the entire aorta was 17.4-fold higher in WHHL than in NZW aortas (P < .001), and 2.8-fold higher than 125I-Halb in WHHL aortas. 125I-MDA2 also had higher specificity for lesioned areas than 125I-Halb (plaque/normal ratio 6.3 vs 2.9, P < .001). Autoradiograph of aortas of 125I-MDA2-injected WHHL rabbits revealed uptake in lipid-stained lesions with absence of signal in adjacent normal arterial tissue. Immunostaining of WHHL lesions, which accumulated MDA2 as noted on autoradiography, revealed that uptake was highest in areas with abundant foam cells and in lipid-rich necrotic core areas. Autoradiograph of aortas from NZW rabbits injected with 125I-MDA2 did not yield any visible signal. Planar gamma camera in vivo scintigraphy revealed a visible signal in 4/7 WHHL rabbits, which was confirmed by aortic Sudan staining.

CONCLUSION

Radiolabeled MDA2 shows excellent in vivo uptake and specificity for atherosclerotic lesions containing abundant oxidation-specific epitopes. The in vivo imaging studies suggest that noninvasive imaging of oxidation-rich atherosclerotic lesions with radiolabeled MDA2 may be feasible in human beings with optimization of the imaging methods.

Radioimmunotherapy of relapsed B-cell lymphoma with yttrium 90 anti-idiotype monoclonal antibodies

Tumor-specific anti-idiotype (anti-Id) monoclonal antibodies (MoAbs) to B-cell lymphomas have been administered to patients, resulting in significant clinical responses. However, clinical responses have been limited by the emergence of Id-negative lymphoma. To overcome the problem of tumor heterogeneity, we conducted a pilot evaluation of the safety and effectiveness of yttrium 90 (90Y)-labeled anti-Id and shared Id (sId) MoAbs in non-Hodgkin's B-cell lymphoma. Nine patients with relapsed B-cell lymphoma in whom tumor was successfully targeted with 111In-labeled anti-Id MoAb were treated with 90Y-labeled anti-Id MoAb. A total of 19 courses (one to four per patient) were administered using 1,000 to 2,320 mg unlabeled clearing MoAb and 10 to 54 mCi 90Y MoAb per patient. Two of nine patients had a complete response, one a partial response, three stable disease, and three disease progression. Time to progression varied from 1 to 12 months. Toxicities were predominately hematologic, and only one patient developed infection and required transfusion. At progression, three of five assessable patients had Id-positive lymphoma and two had Id-negative lymphoma. Human antimouse antibodies (HAMA) did not develop in the patients after treatment. 90Y anti-Id MoAbs demonstrated excellent in vivo stability, produced significantly tumor regression in three of nine patients, exhibited acceptable toxicities, and elicited no HAMA formation. Further investigation of repetitive, low-dose 90Y anti-Id and MoAb therapy is warranted; however, the advantages of a pan B MoAb may prove the latter to be the agent of choice for the radio immunotherapy of B-cell lymphoma.

Pharmacokinetics of an indium-labeled IgG monoclonal antibody over a prolonged period

This study was directed toward determining the pharmacokinetic fate of an IgG2a monoclonal antibody (MoAb). The 96.5 anti-melanoma MoAb was labeled with indium-111 and indium-114m and administered to BALB/c mice. The mice receiving 111In MoAb were sacrificed at 4 and 72 h, while those receiving 114mIn 96.5 MoAb (50-day physical half-life) were sacrificed at 4 h and 3, 15, and 30 days. Multiple tissues were counted against a standard of the injectate and the data expressed as percent injected dose per organ and percent total dose excreted in the urine and feces. The 111In- and 114mIn-labeled MoAbs had nearly identical distribution through 72 h. Over the 30-day period 25% of the 114mIn label was excreted in the urine and 50% eliminated in the feces. All of the tissues studied showed a decrease in 114mIn in the 30-day period. We conclude that the metabolic products of indium-labeled MoAbs, the indium itself, or a combination of both are eliminated from the tissues over a period of several weeks and do not accumulate to a significant extent in any single site.

Pharmacokinetics of 111In-labelled monoclonal antibody ZCE-025 and fragments in tumour-bearing mice

Radiolabelled anti-tumour antibodies, their fragments and derivatives hold promise for imaging and therapeutics in oncology. A better understanding of the pharmacokinetics of these entities is therefore important for clinical applications and management. In the present study, the in vivo behaviour of 111Indium-labelled monoclonal anti-CEA antibody ZCE-025 and its F(ab')2 and Fab' fragments and a Fab' derivative are compared in the nude mouse-human tumour model. The object of the derivative was to improve the tumour uptake of the fragment yet reduce its high renal uptake while continuing to achieve desirable kinetics in the normal tissues. Uptake of the derivative in the tumour was comparable to that of the intact antibody and exceeded that of the underivatized fragments. Moreover, uptake in non-target tissues was lower with the derivative than with the intact entity. The renal uptake of the derivative was dramatically lower than for the fragments. The modelling data strongly suggest that the derivatives will be advantageous for clinical use compared with the underivatized whole antibodies or their fragments.

Human anti-mouse antibody response in cancer patients following single low-dose injections of radiolabeled murine monoclonal antibodies

We examined the human anti-mouse antibody (HAMA) response in 61 cancer patients following a single, diagnostic injection of any one of ten 111In conjugated murine monoclonal antibodies. Between 1 and 22 mg of antibody containing 1-5 mCi 111In was administered. The populations studied included 30 patients with colorectal carcinoma (four different antibodies), 22 with malignant melanoma (four antibodies), and nine with prostate cancer (two antibodies). Forty-one percent of the patients developed HAMA within 14 days. Three patients (5%) developed an IgM response, five patients (8%) developed an IgG response, and 17 patients (28%) developed both IgM and IgG. Only 27% of the patients with colon cancer developed HAMA, compared to 55% of the melanoma patients and 56% of the prostate cancer patients. There were no correlations among injected dose, various clinical parameters, and HAMA response. There were variations in the HAMA response to different monoclonal antibodies, but population samples were too small to infer significance. Most of the HAMA responses had a significant proportion of idiotypic or isotypic specificity. Only 1/6 patients who were HAMA negative after the first infusion developed HAMA following subsequent infusions of the same monoclonal antibody. Our data demonstrate that a significant percent of cancer patients develop HAMA following a single, low-dose injection of a radiolabeled monoclonal antibody for diagnostic purposes. This may have important implications for the future therapeutic use of monoclonal antibodies in such patients.

Chromatofocusing studies involving a monoclonal Fab'

Isoelectric focusing (IEF) of the Fab' derivative of murine monoclonal antibody ZCE-025 is known to detect at least six bands having isoelectric points (pI) ranging from 5.4 to 7.8. Chromatofocusing was employed to separate these bands. Electrophoresis of the starting materials under nonreducing conditions indicated all of the materials to migrate as Fab'. The electrophoresis of urine samples obtained from Balb/c and nude mice 8 hr after the i.v. injection of the various 125I bands revealed the low pI bands to migrate approximately as a 125I-Fab'. The higher pI band activity was located in lower molecular weight regions. Serum samples taken at 8 hr postinjection from the above mice revealed a series of what appeared to be high molecular weight complexes and some low molecular weight species. Biodistribution studies in comparison Balb/c mice and nude mice revealed that the low pI 125I-Fab' bands gave an organ and tumor uptake at 8 hr very similar to Fab', while the high pI 125I-Fab' bands were rapidly excreted into the urine and feces and did not concentrate in the tumor. The data suggest that the population of molecules making up the Fab' of this antibody is heterogeneous and variably stable. Theoretically, some of the entities observed could be counter productive to successful radioimmunoimaging. It is also possible that some of the labeled molecules are associating in vivo with endogenous proteins that might, in some Mabs, affect the biodistribution of the radiopharmaceutical.

Detection of occult tumor using indium 111-labeled anticarcinoembryonic antigen antibodies

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.

Alterations in an indium-111 Fab' under conditions of utilization

This study was conducted to investigate alterations that occur in an indium/111 Fab' of a monoclonal antibody following its in vivo administration. Patients were infused with 111In-Fab' of the monoclonal antibody ZCE-025. Serum and urine specimens were collected from these patients. Starting materials, serum, urine and controls samples were studied by electrophoresis. Animal distribution studies were performed in normal Balb/c mice and, in some cases, nude mice bearing a carcinoembryonic antigen (CEA)/producing human colon tumour since the antibody targets CEA. The studies indicated that the molecule circulated almost totally intact for at least 4 h and to a considerable extent for 24 h, with some evidence for in vivo fragmentation by 24 h. Evidence was also obtained suggesting the formation of a high molecular weight species in some patients. Shortly after infusion, some of the 111In in the urine appeared as the intact Fab', but within hours the majority migrated electro-phoretically as low molecular weight species. We conclude that while the majority of the 111In-Fab' of this particular antibody remains intact and immunoreactive following its administration, the molecule is structurally changed to some degree shortly after its infusion into humans. Since each monoclonal antibody is unique, the degree and rapidity of degradation of its Fab' in vivo could vary markedly from the above and possibly adversely effect its utility as a radiopharmaceutical.

"CORT-EX:" a program for quantitative analysis of brain SPECT data

A program was developed to extract from brain SPECT data global as well as regional concentrations of a radiopharmaceutical while allowing for improved subjective evaluation of its distribution. This program was used to process the data obtained from 17 normal subjects, 20 min, 2 hr, and 4 hr after the injection of iodine-labeled iodoamphetamines. The mean absolute cortical uptake at these three time periods was 0.921 (+/- 0.185), 0.803 (+/- 0.107), and 0.748 (+/- 0.103) in arbitrary units (+/- s.d.), respectively. The regional distribution of the tracer became more uniform with time due to an uneven washout rate. The cerebellum was noted to have a very high variability in its uptake and a high washout rate, making it unsuitable as an internal standard for relative quantification. Finally, a repeat study was performed on 10 subjects. No significant difference could be demonstrated in the mean uptake of the group at 2 and 4 hr, however the difference observed in the 20 min uptake values was significant at the p = 0.05 level.

Effect of acetylation on monoclonal antibody ZCE-025 Fab': distribution in normal and tumor-bearing mice

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.

Radioimmunotherapy of human B-cell lymphoma with 90Y-conjugated antiidiotype monoclonal antibody

We report the first case of 90Y-conjugated monoclonal antibody (MoAb) administration for human radioimmunotherapy. Ten mCi 90Y-labeled antiidiotype (anti-Id) MoAb were administered to a patient with B-cell lymphoma whose tumor successfully imaged with 111In-labeled anti-Id MoAb. No significant toxicities were observed. More than 2 g of unlabeled anti-Id MoAb were administered while clearing the circulating IgM idiotype prior to administration of the 90Y-MoAb. Transient partial regression of disease was observed. Serial fine needle aspirations of a malignant lymph node documented in vivo anti-Id penetration into a site that did not image by radioimmunoscintigraphy. The radiosensitivity of B-cell lymphoma, the tumor specificity of anti-Id, the antitumor activity of anti-Id alone, and the safe administration of 10 mCi 90Y-labeled anti-Id MoAb in this report suggest further investigation of this radioimmunoconjugate for therapy of B-cell lymphoma is warranted.

Distribution of radiolabeled human and mouse monoclonal IgM antibodies in murine models

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.

Scintigraphy with In-111-labeled monoclonal antitumor antibodies: kinetics, biodistribution, and tumor detection

The purpose of this study was to evaluate and compare the kinetics, biodistribution, and tumor-depicting properties of three intact indium-111-labeled murine monoclonal antibodies (MoAb) and to determine if use of In-111-labeled F(ab')2 fragments of one of them had advantages over its intact counterpart for immunoscintigraphy. Ten patients with prostate cancer were studied with an anti-prostatic acid phosphatase MoAb (PAY-276), with a resultant tumor detection rate of 15%. Twenty-eight patients with melanoma were studied with ZME-018, a MoAb that targets the KD-240 melanoma antigen. Forty-three percent of the known lesions were detected. Forty patients with carcinoembryonic antigen (CEA)-producing tumors were studied, 24 with intact ZCE-025, and anti-CEA MoAb, and 16 with its F(ab')2 fragment. With use of intact ZCE-025, 34% of known lesions were detected versus 83% with its F(ab')2 fragment. The distribution of each MoAb appears unique unto itself with regard to kinetics, normal tissue distribution, and response to MoAb mass.

Clinical efficacy of intravenous morphine administration in hepatobiliary imaging for acute cholecystitis

The most urgent diagnosis addressed by cholescintigraphy is acute cholecystitis. By administering low-dose intravenous morphine sulfate to patients undergoing cholescintigraphy (who demonstrate visualization of both the common bile duct and intestine and nonvisualization of the gallbladder), the time required to complete the study has been reduced to a maximum of 90 minutes. One hundred twenty-eight patients underwent cholescintigraphy for clinically suspected acute cholecystitis. Forty patients received intravenous morphine sulfate during the procedure. In patients who received morphine sulfate during the examination, the sensitivity of cholescintigraphy for the diagnosis of acute cholecystitis was 100%; the specificity was 85%.

Problems associated with radioimmunodetection and possibilities for future solutions

It is the opinion of the authors that the molecule of the future for radioimmunodetection (and hopefully radioimmunotherapy and delivery of drugs) will have the following characteristics: It will be an altered fragment, rather than an intact molecule or fragment. It will be small, perhaps 60,000 molecular weight, yet remain in the vascular compartment for a comparatively long period of time, then be eliminated via the kidney. It will be of human origin or a murine molecule altered to mask its immunogenic properties. It will be 111In- or 99mTc-labeled or bifunctionally chelated to another metal ion. It will target a cell surface antigen, but one that does not circulate. It will be used in combination with derivatives of other MoAbs that target other antigens on the cell. It would be a hapten-type device that follows the administration of a "bifunctional MoAb." Whatever the final molecule, it will be administered to a patient who has been "prepped" with an antigen-enhancing substance or one that "unmasks" a gene and allows a repressed marker to be expressed by the tumor cell to which the MoAb was developed. It may be a MoAb that attaches to a white cell, which then chemotactically seeks the tumor that has been previously induced to produce a substance that the white cell recognizes.

False-negative bone image with radiographically evident osteoblastic lesions in prostatic carcinoma

A unique case of documented prostatic carcinoma with radiographically evident osteoblastic lesions and a false-negative bone image is presented.

In vitro and in vivo tumor models for studies of distribution of radiolabelled monoclonal antibodies and fragments

Colon carcinoma multicellular spheroids were incubated in vitro with radiolabelled MAbs. The more rapid penetration of fragments as compared to intact MAbs was clearly demonstrated. For the study of antibody localization in tumors in vivo, the model of nude mice with ligated kidneys was used. Although very artificial, this model allowed to demonstrate that, without urinary excretion, Fab fragments accumulated more rapidly into the tumor than intact MAbs and disappeared faster from the blood. This difference was less striking for F(ab')2 fragments. In the liver a decreased accumulation of both types of fragments as compared to intact MAbs was observed. Concerning radioimmunotherapy we think that Fab fragments are not useful because of their too short half-life in the circulation and in tumor and because they will probably be too toxic for the kidneys. Intact MAbs and F(ab')2 fragments have each their advantages. Intact MAbs show highest tumor accumulation in mice without ligated kidney, however, they remain mostly on the periphery of tumor nodules, as shown by autoradiography. F(ab')2 fragments have been found to penetrate deeper into the tumor and to accumulate less in the liver. It might be therefore an advantage to combine intact MAbs with F(ab')2 fragments, so that in the tumor two different regions could be attacked whereas in normal tissues toxicity could be distributed to different organs such as to the liver with intact MAbs and to the kidney with F(ab')2 fragments.

Continuous infusion of T101 monoclonal antibody in chronic lymphocytic leukemia and cutaneous T-cell lymphoma

We report results of 24-h continuous infusions of murine monoclonal antibody T101 in six patients with chronic lymphocytic leukemia (CLL), and 10 with cutaneous T-cell lymphoma (CTCL), at doses of 10, 50, 100, or 500 mg. Similar side-effects were seen in CLL and CTCL, including direct toxic effects of therapy, such as fever, sweats, and chilling, and a 30% frequency of allergic manifestations. In vivo binding of T101 to target cells in blood, skin, lymph nodes, tumor masses, and bone marrow was demonstrated. Antigenic modulation occurred rapidly in all cases, and persisted throughout the infusion period. Peak serum T101 levels for equivalent doses were somewhat higher, and persisted longer in CTCL, perhaps because of differences in the number of circulating target cells. Antimouse antibodies were demonstrated in 5 of 10 CTCL vs. 0 of 6 CLL patients. In all five cases, there was a substantial component of T101 specificity in the antimouse response. Brief objective clinical responses were observed in 4 of 10 CTCL and 2 of 6 CLL patients. Acute anti-tumor effects of T101 were substantially more dramatic in CTCL than CLL, but appeared limited by antigenic modulation and the emergence of antimouse antibodies. In view of the in vivo binding and modulation, more durable anti-tumor effects may be achievable with cytotoxic immunoconjugates of this monoclonal antibody.

Tissue distribution and serum kinetics of T101 monoclonal antibody during passive anti-cancer therapy

We have administered fifty-six 24 hr infusions of the anti-human T-cell monoclonal antibody T101 to 10 patients with cutaneous T-cell lymphoma (CTCL) and 6 patients with chronic lymphocytic leukemia (CLL) in doses of 10, 50, 100, 150, and 500 mg. The larger doses of T101 resulted in higher, more persistent serum T101 concentrations, and CTCL patients generally developed higher serum T101 levels than CLL patients given equivalent doses. The presence of host anti-mIgG antibodies prior to infusion was associated with decreased serum concentrations of T101. Treatments that demonstrated measurable serum T101 levels were also associated with in vivo T101 binding and cytodestruction of circulating target cells. Immunofluorescence analysis of bone marrow and lymph node biopsies in CLL, and skin biopsies in CTCL, suggested that T101 had reached extravascular tumor sites. Infusion of 111In-conjugated T101 showed uptake in the liver, spleen, lymph nodes, and (in CTCL) skin infiltrates. Our data demonstrate the tissue distribution of T101 and suggest that immunoconjugates of T101 with toxins, drugs, or radioisotopes may result in better therapeutic responses.

Tumor size: effect on monoclonal antibody uptake in tumor models

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.

Toxicities and side effects associated with intravenous infusions of murine monoclonal antibodies

Toxicity was assessed during and following 186 infusions of various murine monoclonal antibodies (MoAbs) in 82 patients afflicted with 10 different malignancies. Doses ranged from 0.5 to 500 mg per infusion and were administered over 0.25-24 h. Reactions of varying degrees were noted in 27 patients (33%) during or following 57 (31%) infusions. For antibodies that reacted with circulating cells, toxicity was seen in 20/82 of the first infusions compared with 0/55 for patients receiving antibodies that did not react with circulating cells. A 25% decrease in white blood cells (WBC) was associated with side effects in 40/66 courses whereas only 9/81 courses were associated with any sort of toxicity when the WBC decreased by less than 25%. Fevers, rigors, chills, and diaphoresis were observed in 21-23% of patients, but only in association with removal of circulating cells that bound the antibody. Presumed hypersensitivity reactions, including urticaria, pruritus, bronchospasm, and anaphylaxis occurred in 15 patients (18%). The two episodes of bronchospasm and single episode of anaphylaxis occurred in patients treated more than once, at least 2 weeks after a previous treatment. There was no clear relationship between dose or rate of infusion and toxicity for these antibodies. We conclude that murine MoAbs can be given with an acceptable frequency of serious allergic reactions and that the biologic effects of specific antibody-antigen reactions may be a more significant source of toxicity for such antibodies.

The advantages and limits of indium-111 labeling of antibodies. Experimental studies and clinical applications

Radiolabeling of antibodies with In-111 has now been accomplished to the point that it is highly reproducible, achieves excellent labeling efficiency, and does not damage the antibody. Use of In-111 for radioimmunodetection is advantageous because of the excellent imaging characteristics of the In-111, moderate radiation dose, ease of labeling, and appropriate half-life. The liabilities of the In-111 method include slightly greater cost of the radionuclide, slow clearance of background sites, and a shelf life requiring it to be ordered on a weekly basis. When all characteristics of the radionuclide are taken into account, it appears to be superior to I-131 for radioimmunoimaging. A controlled study using iodinated and Indium labeled antibodies in the same group of patients needs to be done to accurately access how well the two function for tumor detection.

In vivo kinetics of radiolabeled monoclonal anti-CEA antibodies in animal models

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.

Athymic mouse model of a human T-cell tumor

Because of the large number of different immunoconjugates which can be produced from monoclonal antibody-directed anti-cancer therapy, it would be useful to have in vivo tumor models to compare such preparations. Although historically human leukemias-lymphomas have been difficult to establish in athymic mice we have succeeded in establishing human T-cell tumors from primary MOLT-4 cultures in 290 of 353 animals and have successfully transferred tumors in 42 of 45 animals during ten serial passages. The potential utility of this model for testing immunoconjugates of murine monoclonal antibody T101 have been confirmed by: (a) in all 148 tumors sampled including all passaged tumors the human T-cell antigen, T65, was expressed in a manner identical to that of cultured cells; (b) 111In-T101 was concentrated preferentially in the tumor; and (c) T101 injected by both the i.p. and i.v. routes bound to tumor and induced antigenic modulation to the same extent as that observed previously in vitro and in human studies.

Radioimmunodetection of melanoma utilizing In-111 96.5 monoclonal antibody: a preliminary report

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.

Carcinoembryonic antigen production, secretion, and kinetics in BALB/c mice and a nude mouse-human tumor model

Carcinoembryonic antigen (CEA) is currently being used as a target antigen in the radioimmunodetection of cancer. Circulating CEA may adversely affect the outcome of such studies by formation of intravascular immune complexes. The following studies were undertaken to expand our knowledge of the production, secretion, and pharmacokinetics of CEA, since these factors should have a direct bearing on the serum levels of CEA encountered in radioimmunodetection. The production of CEA was assessed in nude mice given implants of the T-380 CEA secreting human colon tumor. Serum CEA rose linearly as the tumors enlarged; however, the concentration of CEA per g of extracted tumor remained constant throughout the weight range studied. The secretory rate of the T-380 tumor was determined by surgically removing all blood flow to the liver and gastrointestinal tract of the nude mouse model. This procedure removes the known sites of CEA degradation. Serum CEA levels rose progressively following surgery, the values being directly related to the tumor size. The secretory rate was also proportional to tumor size but was a constant 13.8 +/- 3.6 (S.D.) ng/g tumor/hr when expressed on a per g tumor basis. To determine if the serum levels of CEA observed in patients could be due to unique differences in the clearance rates of each patient's CEA, serum from three patients with CEA levels of 2150, 709, and 58 ng/ml was administered i.v. to groups of mice at the original and diluted concentrations. The kinetics of all samples followed a single exponential clearance pattern with a half-time of about 2.5 hr. This was dramatically different from the kinetics of tumor-extracted CEA which exhibited a multiexponential pattern, the first component having a half-time of 3 min. These data suggest that CEA secreted by a tumor is in some way different from that adhering to the tumor. If the secreted CEA truly has a monoexponential clearance with a fixed rate as the experiments suggest, the absolute values of serum CEA are either entirely a function of the tumor secretory rate, or else the product having the short half-time is not measured in serum samples obtained from patients.

In-111-leukocyte scintigraphy for detection of infection associated with peritoneal dialysis catheters

In-111-labeled leukocytes were administered to 13 patients on continuous ambulatory peritoneal dialysis in order to locate catheter-associated infections. Using a marker to indicate the catheter exit site, infections of the catheter tunnel were correctly identified prior to surgery in 4 patients with relapsing peritonitis and infections of the exit site were diagnosed in 5 out of 7 patients. There were no false positives or negatives as documented by surgery or follow-up. The authors conclude that In-111-leukocyte scintigraphy appears to be accurate in diagnosing peritoneal infections of the dialysis catheter tunnel.

Lack of radioimmunodetection and complications associated with monoclonal anticarcinoembryonic antigen antibody cross-reactivity with an antigen on circulating cells

Characterization of several high-affinity murine monoclonal anticarcinoembryonic antigen (CEA) antibodies suggested good specificity except for cross-reactivity with an antigen on granulocytes and erythrocytes which was different from the previously described normal cross-reacting antigen of granulocytes. In vivo studies in athymic mice using an indium conjugate of an anti-CEA monoclonal antibody (MoAb) revealed excellent specific uptake in colorectal carcinoma xenografts. Studies were conducted in humans to determine the limitations produced by the cross-reactivity with granulocytes and erythrocytes. Patients with metastatic colorectal cancer received 3 to 6 mg of anti-CEA MoAb over 10 min or 2 hr. In five of six trials, the MoAb infusion was associated with a 40 to 90% decrease in circulating granulocytes and systemic toxicity including fever, rigors, and emesis. One patient had no change in cell count and had no toxicity. Radionuclide scans with 111In-anti-CEA MoAb showed marked uptake in the spleen when cells were eliminated, and in the liver, especially when pretreatment CEA levels were high. Metastatic tumor sites failed to concentrate the isotope. This study emphasizes the potential limitations for radioimmunodetection and/or radioimmunotherapy imposed by reactivity with circulating cells, and suggests that certain toxic reactions associated with MoAb infusions are related to destruction of circulating cells rather than allergic reactions to mouse protein. It also emphasizes how variables such as dose and binding affinity of antibody, radioisotope used, and assessment at different observation points can obscure lack of antibody specificity.

Single photon emission computed tomograms of the liver: normal vascular intrahepatic structures

Because of the high target-to-background contrast obtained with single photon emission computed tomography (SPECT), normal intrahepatic vessels approximately 2 cm in diameter may appear as distinct focal defects in tomographic sections throughout the liver even though normal vessels rarely cause such defects on planar images. To assess this problem, five subjects without evidence of liver disease underwent tomography of the liver with Tc-99m sulfur colloid (TSC) and on a separate occasion tomography of the intrahepatic blood pool with Tc-99m autologous red blood cells (RBC). In each case, well demarcated defects were obvious in contiguous TSC liver tomograms in various planes. Direct comparison with RBC tomograms showed that all of these defects corresponded to intrahepatic veins, typically the right portal vein, its posterior branch, and the left portal vein. Knowledge of the intrahepatic vascular anatomy in a variety of tomographic planes, with examination of each defect in multiple orthogonal planes is necessary to avoid false positive interpretations. In some instances a study with RBC may also be required for more conclusive evaluation of defects seen on TSC liver tomograms.

Stability, characterization, and kinetics of 111In-labeled monoclonal antitumor antibodies in normal animals and nude mouse-human tumor models

Monoclonal antibodies (MoAbs) against carcinoembryonic antigen were successfully radiolabeled with 111In, and the radiopharmaceutical was characterized in vitro and in normal and tumor-bearing mice. The 111In-MoAb proved to be stable in vitro and in vivo under normal conditions, although instability could be induced in vitro with large quantities of iron-free transferrin. Animal distribution studies with 111In-MoAb demonstrated tumor localization superior to 67Ga and pharmacokinetics that were highly similar to those of endogenously labeled 75Se-MoAb. The 111In-MoAb followed first-order kinetics and fit a two-compartmental model when studied in nude mice bearing human colon tumors known to express carcinoembryonic antigen. Significant quantities of radiolabel appeared in tissues other than tumor, with liver and skin having the highest concentrations. Sufficient tumor/background ratios were formed for scanning purposes. The data indicate that 111In-MoAb may prove to be effective as a radiopharmaceutical for tumor imaging.

The effect of certain variables on the tumor and tissue distribution of tracers: VI. False-carrier effect, Part III, Fe

Previous work has shown that Fe3+, when administered in the proper dose and time sequence, increases the tumor uptake of gallium-67 (67Ga) while decreasing its uptake by normal tissues. The purpose of this series of experiments was to examine further the postulate that the false carrier effect is mediated at the cellular as well as the vascular level, determine the lowest concentration of ionic Fe3+ that will induce near maximum tumor/background ratios (T/Bkg), determine the best technique for its administration, and decide whether Benadryl and dexamethasone could be used to offset side effects of the Fe3+ without altering tumor and tissue kinetics. Fe3+ altered tissue levels of 67Ga prior to changes in the blood. The threshold for initiation of the false-carrier effect varied to some extent from one organ to another. Tumor uptake of 67Ga was either enhanced or unaltered at 4 hours after injection; 0.3 mg Fe3+/kg administered 0.5 hour before and 2 hours after the 67Ga enhanced 4-hour T/Bkg by a factor of about ten. Twenty-four-hour ratios were improved (to a lesser extent than 4-hour), but decreased concentrations of 67Ga occurred in the tumor. Dexamethasone and Benadryl did not alter the outcome of the experiment. This technique should be useful for imaging with gallium-68 and the PET camera.

Limitations of renal function scanning in acute obstruction

This study was designed to determine if technetium-99m penicillamine (TPEN), could be used to predict recoverable function in dogs with acute obstruction. Renal accumulation of TPEN was measured in four control dogs, in four dogs with acute obstruction lasting 7-14 days, and in the same four dogs following a variable recovery period of 15-63 days. The relative renal uptake of TPEN in vivo showed good agreement with the relative uptake in vitro and both measurements correlated closely with the relative inulin clearances in the normal and in the post obstructed kidneys. The uptake of TPEN in the obstructed kidney following 7-14 days of obstruction averaged 6.8% of the total renal uptake. After relief of the obstruction and a variable recovery period the relative uptake of TPEN in the post obstructed kidney had increased to a mean of 29.5%. These results indicate that TPEN scans should not be used during acute obstruction to predict recoverable function. The observations noted in the study almost certainly apply to similar chelating agents such as dimercaptosuccinic acid (DMSA) and probably to other renal radiopharmaceuticals as well.

The effect of certain variables on the tumor and tissue distribution of tracers V: false carrier effect, II, Fe

The effect of Fe3+ citrate on carrier-free 67Ga and 59Fe kinetics was studied in a Buffalo rat-Morris 7777 hepatoma model. Two mg Fe3+ citrate/Kg were administered intravenously in a variety of time sequences, prior to and following the tracers, and the rats were killed at 4 or 24 hours. 67Ga concentrations could be increased in tumor and decreased in most normal tissues. Administering Fe3+ both one half hour before and 2 hours after the tracers produced 67Ga values equivalent to 72-hour carrier-free values after 4 hours, while simultaneously decreasing gut secretion and increasing urinary excretion. The 59Fe and 67Ga kinetics suggested that events at both vascular and cellular levels were responsible for these changes. This study demonstrated the potential utility of Fe3+ citrate for improving both conventional 67Ga and positron (68Ga) imaging of tumors.

The effect of certain variables on the tumor and tissue distribution of tracers. IV. False carriers: ferric citrate

The intravenous administration of Fe+3 -citrate (1.6 mg/kg body weight) was demonstrated to alter the concentration of carrier-free 67Ga and 54Mn in malignant and healthy tissues of the rat, Morris 7777 hepatoma model. When the Fe+3 was injected 2 hours before, simultaneously with, or 2 hours after 67Ga (and the rats sacrificed 4 hours after injection), the 67Ga in most normal tissues decreased, and the viable tumor concentrations increased by 135, 24, and 47%, respectively. Twenty-four hours after a simultaneous administration of Fe+3 and 67Ga, egress of 67Ga from the tumor was much less than from the healthy tissues. These changes resulted in significant improvements in viable tumor to background ratios, especially at 4 hours. These changes induced in the distribution of the two tracers by Fe+3 indicate that some kinetic characteristics are shared. This is discussed in the light of their response to carrier Ga and Mn. The use of Fe+3 shows promise as a means of improving tumor/background ratios for 68Ga and 52mMn, two short-lived positron emitters that can be used with positron scanners. Gallium-67 imaging may also be improved by these techniques. The Fe+3 increases excretion of 67Ga from the animal, and this could result in a lower radiation dose to a patient.

The effect of certain variables on the tumor and tissue distribution of tracers. III. Salicylates and vasoactive drugs

Attempts were made to increase the viable tumor concentration of 54Mn and 67Ga in a rat hepatoma model by administering rat angiotensin, tolazoline, and salicylates. Salicylates increased the tumor concentrations of 54Mn and improved 65Mn viable tumor/background ratios. 67Ga was not affected by the salicylates. The salicylate effect appeared to be mediated by intracellular mechanisms rather than alterations in plasma protein binding. Rat angiotensin slightly increased the concentrations of 67Ga in the tumors but not enough to suggest that it would be useful clinically. Tolazoline did not increase tumor uptake of the tracers.

The effect of parathyroid hormone on technetium-99m pyrophosphate distribution in rats

Sprague-Dawley rats were treated with varying quantities of parathyroid hormone for 1--3 days, then sacrificed at periods ranging from 1--6 h after administration of 99mTc-pyrophosphate. Very little increase in bone accumulation of tracer occurred with this treatment. A small, but obvious decrease occurred in the blood levels of 99mTc-pyrophosphate and a smaller and less consistent decrease was affected in the muscle levels of the radiopharmaceutical. The overall result was an improvement in the bone/blood and bone/muscle ratios. It is suggested that the basis of the "supernormal" bone scan of hyperparathyroidism is achieved by this mechanism and that the increased bone uptake of other ions in response to parathyroid hormone is not shared by 99mTc-pyrophosphate.

The effect of certain variables on the tumor and tissue distribution of tracers. II. Carrier effect: rapidity of onset and concentrations necessary for initiation and maximum response

The smallest quantity of carrier Ga and Mn necessary to initiate and maximize a carrier effect was studied in the Morris 7777 rat hepatoma model. The quantity needed for a maximum response did not appear to adversely effect the rats. Not all tissues were equally affected at the same plasma concentrations. If carrier Ga was administered 2 hours following 67Ga injection and the rats sacrificed 30 minutes later, a dramatic change occurred in background activity, which was more pronounced in healthy than malignant tissues. Early viable and nonviable tumor/background ratios were improved by this technique. The data suggest that the use of carrier Ga and Mn might improve early lesion/background ratios in patients. This could be of use if tumor imaging were undertaken with 68Ga or 52mMn with positron detector systems.

The effect of certain variables on the tumor and tissue distribution of tracers. Part 1; Carrier

Buffalo rats bearing thigh-implanted strain-7777 Morris hepatomas were used as a model for studying the effect of carrier material on the body distribution, tumor uptake, excretion, and tumor-to-background ratios of 67Ga and 54Mn. An effort was also made to observe the changes in 67Ga and 54Mn concentrations induced by carrier in viable tumor and skeletal muscle, relative to their interstitial fluid space. This value is referred to as the Tissue Distribution Index. Carrier manipulation resulted in striking changes in the distribution of the two ions from the carrier-free state. The data also indicated a difference in the pharmacodynamics of 67Ga and 54Mn in malignant and healthy tissues which could be of importance to nuclear medicine and oncology.

Distributions of 137Cs, 201Tl, 203Hg, 203Pb and 57Co in a rat hepatoma model. Comparison with 67Ga

The distribution of carrier-free 203Pb-acetate, 203HgCl2, 57 CoCl2, 137CsCl and 201TlCl was investigated in rats bearing thigh-implanted Morris 7777 hepatomas. Viable and nonviable tumor tissue was collected in order to determine the relative affinities of the radiopharmaceuticals for these tissues. The animals were sacrificed at 4, 24, 48, 72 and 96 hrs following intravenous injection. Washout of the radioisotope from the viable tumor tissue was rapid, the maximum concentration being reached on or before 4 hrs following injection. In contrast, residual activity within the nonviable tumor tissue decreased much more slowly and in some cases even increased with time. Viable tumor-to-muscle and nonviable tumor-to-muscle ratios for 203Pb, 203Hg and 57Co were comparable to the analogous ratios reported for 67Ga. However, none of these isotopes approached 67Ga as a potential tumor imaging agent because the large ratios were the result of low muscle uptake rather than high tumor uptake. Blood clearance of 67Ga was faster than any of the five cations, while viable and nonviable tumor affinity for 67Ga was greater than for any of the radiopharmaceuticals studied.

Comparison of viable and nonviable tumor uptake of Sc-46, Mn-54, Zn-65, In-111 and Au-195 with Ga-67 citrate in a hepatoma model

The tissue distribution of Sc-46, Mn-54, Zn-65, In-111 and Au-195 were studied in a rat hepatoma model at various time intervals over a 96 h period. The tumor localizing properties of these isotopes were evaluated by examining their incorporation and clearance from viable and nonviable tumor tissue and determining the critical tissue ratios formed with blood and muscle. In general, the results showed greater uptake in viable than nonviable tumor tissue at early time periods (4-24 h). By 96 h, however, the activity remaining in the nonviable tumor tissue exceeded the quantity in viable tumor tissue. This trend was previously noted for Ga-67. When compared with Ga-67, only Mn-54 among the isotopes studied showed remarkably higher viable tumor/blood ratios (4-24 h, 45:1-83:1 respectively). Manganese-54 also showed highly significant accumulation in cardiac muscle with a heart/blood ratio at 4 h superior to comparable values previously reported for Cs-137 and Tl-201. It is suggested that tumor and heart imaging may be feasible utilizing radioactive manganese (Mn-51 or Mn-52) with the new positron imaging systems.

Tissue distribution studies with radioactive manganese: a potential agent for myocardial imaging

Manganese, a trace metal, is known to localize in mitochondria. Because mitochondria are abundant in heart muscle, the possible utility of radioactive manganese as a myocardial imaging agent was examined in 25 rats and six dogs. Myocardial uptake of Mn-54 in rats was found to exceed that of thallium-201; myocardium-to-blood ratios averaged 306:1 versus 48:1 for Tl-201. In the dog, uptake of Mn-54 by ischemic myocardium was reduced by 17-75% compared with normal myocardium. Thus, radioactive manganese appears promising as an intravenous myocardial imaging agent, and might be useful in studying the function of myocardial mitochondria by external imaging.

99mTc-thiomalic acid complex: a nonstannous chelate for renal scanning

Thiomalic acid (monomercaptosuccinic acid) has been labeled with 99mTc without the use of an intermediary reducing agent. Tissue distribution studies in rats following the injection of 99mTc-tagged thiomalic acid (99mTc-TMA) showed 40-48% of the injected dose in the kidneys. Renal incorporation of this compound was influenced by various parameters such a pH, quantity of thiomalic acid, heating time, and the preparation-injection interval. Scintigrams of a midline kidney slice showed that the 99mTc activity concentrated mainly in the renal cortex. As a proposed renal-imaging agent 99mTc-TMA compared favorably with 99mTc-Sn-dimercaptosuccinate and 99mTc-penicillamine regarding the precent incorporation into the kidney and was superior in this respect to 99mTc-Sn-glucoheptonate and 99mTc-Sn-diethylenetriamine pentaacetic acid. The 99mTc-TMA was also shown to be highly stable through 24 hr. The reagent can be made available in kit form and is easily combined with 99mTc in two steps. Finally, the absence of stannous ion in the 99mTc-TMA complex should avoid the problem of interference with other procedures involving pertechnetate 99mTco4- as the imaging agent.