99Tcm-labelled anti-CEA monoclonal antibody for tumour immunoscintigraphy: first clinical results

An improved method of direct labeling monoclonal antibodies with 99mTc

An improved method of direct labeling MAbs with 99mTc is described. Two murine monoclonal antibodies, designated Lym-1 and B72.3, have been successfully labeled with 99mTc in 0.1 M borate buffer at pH 9.3. The choice of buffer and pH was essential for obtaining a radiolabeling yield greater than or equal to 98%. In vitro studies demonstrated that the radiolabeled antibodies were stable and retained their immunoreactivity. Imaging and biodistribution studies using Raji and LS174T human tumor-bearing nude mice demonstrated a significant tumor uptake at 24-h post-injection of 99mTc-labeled MAbs. This improved labeling method showed better stability than those of previously published methods and resulted in significant improvement in the uptake of antibody in tumor. External images at 24 h post-injection revealed clearly visible tumors demonstrating the benefit of this method for tumor immunoscintigraphy.

Immunoscintigraphic localization of renal tumours in an extracorporeal perfusion model with a monoclonal antibody against gamma-glutamyltransferase

Monoclonal antibody 138H11 against human gamma-glutamyltransferase has been shown to react immunohistochemically with 98% of all tested clear-cell type and chromophilic renal cell carcinomas, but not with renal chromophobic carcinomas, Duct-Bellini carcinomas or oncocytomas. In normal kidney the target epitopes of mAb 138H11 are located in the luminal brush-border membrane of proximal tubule cells, whereas in renal carcinomas the epitopes are found surrounding the whole tumour cells. These results form the basis of the present immunoscintigraphic study designed to evaluate mAb 138H11 in an extracorporeal perfusion model. Immediately after nephrectomy, human tumour-bearing kidneys were perfused with 99mTc-labelled mAb 138H11 in Euro-Collins solution. High specific uptake in 4/4 renal clear cell carcinomas could be demonstrated by planar immunoscintigraphy and single-photon-emission computed tomography, "regions of interest" investigation and immunohistochemistry. In contrast, a perfused oncocytoma showed up as an unlabelled lesion. The results indicate a possible use for mAb 138H11 in immunoscintigraphy or even therapy, provided high tumour uptake can be confirmed in patients.

Generation of bispecific monoclonal antibodies for two phase radioimmunotherapy

A two phase radioimmunotherapy based on bispecific MAbs in which one arm recognises a tumour antigen and the other a radiolabelled chelate, may prove more effective in the treatment of carcinomas than currently available immunotherapies. To establish this system we first showed that penetration into human carcinoma xenografts as well as long term retention of intact MAb outside the carcinoma cells can be obtained. Epitope saturation was not obtained however, despite the large MAb doses injected i.v. for 10 days. We then generated hybridomas producing high avidity anti-metal chelate MAbs (anti-DTPA-Y). These hybridomas were fused with hybridomas producing MAbs against CEA or GIT-mucin, and stable bispecific MAb producing quadromas were obtained. For the anti-GIT-mucin x anti-chelate MAb a purification procedure based on double anti-idiotype affinity chromatography was shown to result in greater than 95% pure bispecific immunoreactive MAb. Comparative in vivo stability studies profiled DTPA-Y as the chelate of choice for in vivo application.

Immunoscintigraphy using different methods of applying a 99mTc labeled monoclonal anti-CEA-antibody in the staging of patients with liver metastases before partial hepatectomy

It was the aim of this study to determine the value of portal-venous (p.v.), intra-arterial (i.a.) or intravenous (i.v.) IS in the detection of liver metastases. Immediately after angiography and i.a. CT (20 patients) or p.v. CT (6 patients), 0.7-1.2 GBq of the 99mTc labeled anti-CEA MoAb were injected via the i.a. catheter, and in 10 patients i.v. Planar scanning was performed. Using IS in the detection of liver metastases a total sensitivity of 61% was established. However, IS was still found to be the decisive method of excluding extrahepatic tumor deposits.

Immunoscintigraphy of colorectal carcinoma with an anti-CEA monoclonal antibody: a critical review

An anti-CEA monoclonal antibody (FO23C5), belonging to the IgG1a class, was used to perform several preclinical and clinical studies on radioimmunoscintigraphy (RIS) in patients with colorectal carcinoma. Preliminary screening on different tissues showed high specificity of this antibody for gastric and colorectal carcinomas. A pilot study on 51 patients with 64 localizations of colorectal carcinoma was realized, followed by a multicenter validation study in which, among 509 patients bearing CEA secreting tumors, 254 patients had primary or relapsed colorectal tumors. High sensitivity and specificity values were obtained by these studies and many "unsuspected" localizations were recorded. In order to better define the clinical utility of this approach, a prospective trial was run on 59 patients previously submitted to surgery for colorectal carcinoma and with suspected local relapses. A comparative evaluation of RIS, CT scan, US and MRI was performed. RIS and MRI have the highest value of accuracy (86%) followed by CT scan (68%) and US (54%). No adverse reactions were noticed in any of the patients examined.

Progress in research on ligands, nuclides and techniques for labeling monoclonal antibodies

This paper reviews the current methods for radiolabelling monoclonal antibodies with particular emphasis on radiometals useful for radioimmunoscintigraphy. The discussion, however, is equally applicable to therapeutic radionuclides. The advantages and the pitfalls of the various techniques are critically evaluated. Both direct labeling methods, as well as indirect methods using the bifunctional chelating agent approach, are covered. Recent work on the development and synthesis of new and more specific chelating agents, including the approach of utilizing rigid polyaminocarboxylates, is described. Preliminary promising results with these newer generation chelating agents are presented.

Diagnostic evaluation of 111In and 99mTc radiolabelled monoclonal antibodies in ovarian and colorectal cancer: correlations with surgery

The results of radioimmunoscintigraphy, RIS, in colorectal and gynaecological cancers were related to the surgical findings and the analysis of the surgical specimens. The improvement in the accuracy of RIS with the progression from 111In through 123I to 99mTc as radiolabel is demonstrated. The convenience, low cost and low radiation dose of 99mTc-labelled antibodies brings the technique of RIS into routine use in the management of patients with these cancers.

Radiopharmaceuticals: state of the art

In the past four years most of the effort in radiopharmaceutical chemistry has been devoted to compounds for positron emission tomography, but widespread use of this technique is still compromised by its high cost. On the other hand, steady progress has also been made in the development of technetium-99m-labelled radiopharmaceuticals. A variety of 99mTc-labelled agents is now available or in clinical evaluation for the study of brain perfusion (99mTc-labelled HMPAO, ECD, MRP20), myocardial perfusion (99mTc-labelled MIBI, teboroxime and phosphines) and renal function (99mTc-MAG3, 99mTc-L,L-EC). Different direct reduction methods and indirect conjugation methods have been developed to label antibodies or their fragments efficiently with 99mTc with preservation of immunoreactivity. However, the strict requirements of the regulatory authorities with respect to purification and quality of these preparations limit their use drastically in clinical practice. Radiopharmaceuticals labelled with beta-emitting radionuclides for radioimmunotherapy and palliative treatment of skeletal metastases are receiving increasing interest. Numerous agents are now available for imaging inflammation, but more clinical experience is required to determine which of them is the most appropriate. The growing importance of radiolabelled receptor-imaging agents is apparent from the commercial availability of the first such compound in Europe.

Recent developments in the radiolabeling of antibodies with iodine, indium, and technetium

The use of radiolabeled antibodies for tumor detection and therapy has provided some striking successes despite unfavorable tumor-to-normal tissue radioactivity ratios due, in part, to the accumulation of the label in normal tissues. One approach, which has been and is still under consideration to reduce unwanted background levels, is the improvement of ways in which radiolabels are attached to antibody, especially with the goal of increasing in vivo stability. Although these improvements have occurred throughout the history of this field, important developments have recently been reported in the labeling of antibodies with three radiolabels, namely radioiodine, 111In, and 99mTc. Thus, antibodies may now be labeled with radioisotopes of iodine in ways that minimize the extent of in vivo dehalogenation leading to thyroid, stomach, and gut radioactivity uptake. Newer and stronger chelates for 111In have been developed in the hope that their use would result in lower radioactivity levels in the liver. Finally, newer methods, both direct and indirect, for the attachment of 99mTc to antibodies have been developed and are now being clinically tested. Although these developments have taken place only recently and the in vivo behavior of labels attached in these ways have not yet been fully characterized, it is possible to make tentative conclusions regarding their impact. Thus, the use of stably radioiodinated antibodies appears to have resulted in modest improvements in patient images. In contrast, the use of stable chelates for labeling antibodies with 111In may have had no appreciable effect on liver radioactivity levels. The use of antibodies radiolabeled with 99mTc, especially via the newer direct labeling methods, are providing superior images in patients with low radioactivity levels in organs such as liver. However, it must still be established whether the short physical half-life of 99mTc lowers sensitivities and specificities of detection relative to other labels.

Multi-centre immunoscintigraphic study using indium-111-labelled CEA-specific and/or 19-9 monoclonal antibody F(ab')2 fragments

Six European nuclear medicine centres performed immunoscintigraphy first retrospectively in 34 patients using indium-111-labelled carcinoembryonic antigen (CEA)-specific and/or 19-9 F(ab')2 fragments. Results for sensitivity and specificity in tumour sites were 94% and 87%, respectively, for the pelvis and 73% and 100% for the extrahepatic abdomen. A second prospective series concerned 58 other patients previously operated on for colorectal adenocarcinoma (27 colon, 31 rectum). Two-thirds of these patients had a suspected recurrence signalled by an isolated rise in tumour markers, and 46 patients examined by immunoscintigraphy, X-ray computed tomography and ultrasonography were found to have a recurrence (a total of 62 tumour sites). Sensitivity and specificity with immunoscintigraphy were 90% and 97%, respectively, for the pelvis and 62% and 95% for the extrahepatic abdomen. For 29 patients injected with CEA-specific fragments, sensitivity was 90% and specificity 94% for the pelvis. For 25 patients injected with 19-9 fragments, pelvic sensitivity and specificity were 80% and 100%, respectively, whereas sensitivity for the extrahepatic abdomen was only 29% since several cases of peritoneal carcinosis were not visualized. In the prospective series, comparison of the three imaging techniques for all tumour sites (including liver and in 5 cases thorax) gave a sensitivity and specificity of 82% and 91%, respectively, for immunoscintigraphy, 52% and 95% for X-ray computed tomography and 59% and 100% for ultrasonography. These results thus confirm the advantage of using 111In-labelled CEA-specific or 19-9 to visualize and localize recurrences of colorectal cancer.

The development of new radiopharmaceuticals

The development of new radiopharmaceuticals is the basis of the continuing growth of nuclear medicine. Chemical interactions of electron clouds in their three-dimensional conformations bring together, in the process of molecular recognition, the reaction of antibody and antigen, receptor and ligand, enzyme and substrate, hormone and response site. This convergence enables the computer design of molecules such as ligands to fit computer-displayed conformational models showing active centres, positive and negative charges and other interactions. Indeed, given a particular molecule, a complementary binding structure can be devised. The hybridoma approach to monoclonal antibody production is being superceded by the bacterial bioengineer. The gene for the hypervariable region from the spleen cells of immunized mouse can be coupled with the myeloma gene. The polymerase chain reaction can duplicate the DNA a million times over in 20 min and the result transfected into a bacterial plasmid to produce the antibody. These scientific problems are soluble in principle and are being solved. However, so much damage to this developing biological field is being done by regulatory authorities that one must ask who should or can regulate the regulators. These problems have to be overcome in order to provide the new radiopharmaceuticals that are the food and wine of nuclear medicine.

Carbohydrate-derivatized immunoconjugate of the anti-(carcinoembryonic antigen) monoclonal antibody C46: immunohistological reactivity and pharmacokinetic comparison with a randomly derivatized C46 immunoconjugate

In this study, a site-specific glycyl-tyrosyl-(N-epsilon-diethylenetriaminepentaacetic acid)-lysine (GYK-DTPA) immunoconjugate of the anti-carcinoembryonic antigen monoclonal antibody C46 (C46-GYK-DTPA) was characterized by immunohistological and immunofluorescence methods for reactivity with normal and neoplastic human tissues. In addition, pharmacokinetic studies assessed the ability of C46-GYK-DTPA labeled with 111In to localize to and image human tumor xenografts in nude mice. The native antibody and the site-specific immunoconjugate exhibited similar patterns of reactivity with normal human tissues. C46 did not bind to the surface of normal human granulocytes, which indicates lack of reactivity with normal cross-reacting antigen. C46-GYK-DTPA reacted with 100% of the colon, breast and renal carcinomas examined and with two of three lung carcinomas, but did not react with any sarcomas, melanomas or lymphomas examined. Intravenously administered C46-GYK-DTPA-111In rapidly localized to and imaged LS174T human colon adenocarcinoma xenografts in nude mice, reaching maximal levels of about 25% of injected dose/g tumor within 1 day. No unusual localization to any non-tumor tissue or organ was seen; the level of radioactivity in the normal tissues and organs was at or below that in the blood. The accessible binding sites in 1 g tumors appeared to be saturated at an antibody dose between 100 micrograms and 1000 micrograms/mouse. Further, in a direct in vivo comparison, the site-specific conjugate C46-GYK-DTPA had more favorable pharmacokinetics and better tumor localization than a randomly derivatized C46 immunoconjugate (C46-DTPA). These findings suggest that the site-specific immunoconjugate C46-GYK-DTPA may be useful in the diagnosis and therapy of colon cancer and other adenocarcinomas expressing carcinoembryonic antigen.

Imaging of colorectal carcinoma with radiolabeled antibodies

Colorectal cancer has been the tumor type most frequently studied with radiolabeled antibodies. Among the various antibodies, a majority of patients with colorectal cancer have received xenogeneic polyclonal or monoclonal antibodies against carcino-embryonic antigen. This review summarizes the current status of colorectal cancer imaging with radiolabeled antibodies, ie, radioimmunodetection (RAID), and examines the published studies involving carcinoembryonic antigen (CEA) antibodies and 17-1A, 19-9, and B72.3, and other monoclonal antibodies. In order to better address the issue of the current and future clinical usefulness of this emerging technology, particular attention is given to the protocols, methods, and results of the published studies. Despite differences in study parameters, antibodies and forms, labels, administration routes and doses, and scanning instruments and methods, it has been found that (1) almost no adverse reactions have been evident; (2) antibody fragments are preferred over whole immunoglobulin G reagents because they achieve higher tumor-to-background ratios earlier, thus reducing or precluding the need for dual-isotope subtraction methods or long delays before imaging; (3) use of antibody fragments, including the monovalent Fab' form, permits imaging with short-lived radionuclides of excellent photon properties, such as 123I and 99mTc; (4) circulating antigens against which the imaging antibody is directed can complex with the injected antibody, but such complexes have not prevented successful RAID; (5) patients with high serum titers of the appropriate antigen target usually have higher rates of positive RAID; (6) patients who are seronegative for the tumor antigen being studied can have positive RAID findings, which can represent the detection of occult lesions; (7) single photon emission computed tomography appears to provide better image resolution than planar scanning; (8) regardless of the sensitivity reported in any particular study, almost all investigators have observed the disclosure of occult neoplasms by RAID; and (9) RAID, a more functional test of usually high specificity, can complement other radiological methods, such as computed tomography scans, which are limited to structural information.