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

The Use of Monoclonal Antibodies for Radioscintigraphic Detection of Cancer

Beginning with Ehrlich's original “magic bullet” concept of 1904, the pioneering human trials in the late 1970s of Goldenberg and Mach using polyclonal antibodies, and the Nobel Prize-winning work of Kohler and Milstein in 1975 for developing monoclonal antibody (MAb) technology, there has been much interest in the use of antibodies for detecting and treating cancer. Although not the revolutionary breakthrough that was initially hoped for, marked progress has been made. The Food and Drug Administration (FDA) has recently approved the intact murine IgG, 111-indium CYT-103 (satumomoab, Oncoscint™ Cytogen, Princeton, NJ) for clinical use in detecting colorectal and ovarian cancer. However, the agent has been approved for only a single, one-time use, because patients developed an immune response (human anti-mouse antibody, or HAMA) that alters MAb biodistribution and may limit the clinical effectiveness of this agent when repeat studies are performed. Other MAbs reacting with a variety of antigens and targeting numerous tumors, including breast, lung, prostate, and melanomas, are currently undergoing large-scale clinical trials. To reduce induction of immune responses, many of the agents use immunoglobulin fragments [Fab, or F(ab)2] labeled with the short-lived isotope 99m-technetium used for most routine nuclear medicine diagnostic testing. Future developments will use even smaller fragments such as single chain antibodies or custom synthesized molecular recognition units (small peptides containing only the specific antigen combining site). Presented herein is an overview of the past results and an assessment of the current status of radioimmunoscintigraphy for various neoplasms.

Monoclonal antibodies in the treatment of malignancy: basic concepts and recent developments

Antibodies have long been considered to be potential anticancer agents because of their specificity for cell-membrane antigens. Applications of hybridoma and recombinant DNA technology have led to the production of unlimited quantities of clinical-grade murine, chimeric, and humanized monoclonal antibodies for clinical use. Whole antibodies may produce anticancer effects in conjunction with the immune system by interaction with complement proteins and/or effector cells via the Fc portion of the antibody molecule. Antibodies may also neutralize circulating ligands or block cell membrane receptors and thus interrupt ligand/receptor interactions and signal transduction that are associated with proliferative or anti-apoptotic effects. The anti-idiotype network cascade provides a rationale for antibodies as vaccine therapy. Antibodies may also serve as the guiding or targeting system for other cytotoxic pharmaceutical products such as (i) radiolabeled antibodies for radioimmunodetection and radioimmunotherapy; (ii) immunotoxins; (iii) chemotherapy/antibody conjugates; (iv) cytokine/antibody conjugates; and (v) immune cell/antibody conjugates. After years of anticipation, as of late 1999 there were four monoclonal antibodies that had been approved by the U.S. Food and Drug Administration based on activity against human malignancy, all of which are in widespread clinical use. Several other products are in various stages of clinical trial testing. Monoclonal antibodies have joined interferon-alpha, interleukin-2 (IL-2), and various hematopoietic growth factors as well-established components of biological therapy, the fourth modality of cancer treatment.

Results of immunoscintigraphy using a cocktail of radiolabeled monoclonal antibodies in the detection of colorectal cancer

BACKGROUND

External immunoscintigraphy using a single monoclonal antibody has been employed successfully to localize primary, recurrent, and occult colorectal carcinoma. This prospective study investigated the accuracy and sensitivity of external immunoscintigraphy when the combination or "cocktail" of radiolabeled monoclonal antibodies, CYT-103 (an IgG1a) and CYT-372 (an IgG2b) directed against TAG-72 and CEA, respectively, is given to patients with known or suspected colorectal cancer.

METHODS

Eleven patients enrolled in this open label phase I/II study underwent preoperative external immunoscintigraphy after intravenous cocktail administration of two indium 111-labeled monoclonal antibodies (MoAb), CYT103 and CYT372. Antibody dose ranged from 0.2 mg (five patients) to 1.0 mg (six patients), each antibody radiolabeled with 2.5 mCi of indium 111, delivering a total dose of 5 mCi per patient. Planar and SPECT images were performed 2 to 5 days postinjection. Suspected lesions were surgically resected within 2 weeks of injection.

RESULTS

A total of 23 lesions (sites) were identified in the eleven patients, 19 of which were confirmed by pathology (hematoxylin and eosin [H&E]). Cocktail immunoscintigrams identified 16 of the 19 confirmed lesions. Computed tomography (CT) scan detected 9 of the 19 lesions. The sensitivities of cocktail immunoscintigraphy and CT scan for the detection of colorectal cancer were 84% and 64%, respectively. The positive predictive value for immunoscintigraphy was 94%. The antibody scans detected six occult, previously unsuspected lesions. Cocktail immunoscintigraphy changed the surgical management in four of the 11 (36%) patients.

CONCLUSIONS

The combination of In 111 CYT-103 and CYT-372 improved the sensitivity of external immunoscintigraphy for the detection of colorectal cancer compared to that obtained with a single MoAb imaging. Cocktail antibody imaging may enhance the staging and management of patients with cancers of colon and rectum.

Diagnostic and therapeutic applications of monoclonal antibodies in colorectal cancer

PURPOSE

The study contained herein was undertaken to review and summarize the current literature on diagnostic and therapeutic applications of monoclonal antibodies in colorectal cancer.

RESULTS

Limitations of traditional imaging techniques have encouraged development of targeted imaging strategies using radiolabeled monoclonal antibodies. Diagnostic immunoscintigraphy can detect lesions not identified by conventional imaging modalities, although it has not proven useful in the management of primary colorectal cancers and in hepatic metastases. Immunoscintigraphy shows promise in cases of local recurrence and rising carcinoembryonic antigen values; however, the impact of immunoscintigraphy on clinical outcomes and cost-effectiveness remains unproven. Radioimmunoguided surgery has been advocated as a method of more accurately detecting tumor extension and accomplishing radical resection. The technique remains controversial, and its use is not widespread. With respect to therapeutic applications, immunotherapy has most often been investigated in the setting of advanced stage disease. Results in this setting have been poor. In contrast, adjuvant immunotherapy after resection of Dukes C carcinoma has achieved convincing results, with improvements in survival comparable with that of adjuvant chemotherapy. Adjuvant trials are now under way to examine the effectiveness of monoclonal antibodies in the postoperative treatment of early-stage (II) tumors and the combination of monoclonal antibodies and chemotherapy in advanced-stage (III) tumors. Bispecific antibodies, or immunoconjugates with cytokines or toxins, represent additional areas of interest and future investigations.

CONCLUSIONS

At present, immunoscintigraphy is not sufficient to determine, by itself, resectability of colorectal tumor and has limited usefulness in select cases of recurrent cancer and possibly in cases of rising carcinoembryonic antigen values. Immunotherapy with monoclonal antibodies as a postoperative adjuvant treatment shows promise and is currently being investigated in national trials.

Trials and tribulations: oncological antibody imaging comes to the fore

At the present time, there are three radiolabeled antibodies that have been approved by the US Food and Drug Administration (FDA) for imaging of cancer, a fourth commercially sponsored product recommended for approval (as of 10/29/96, cap romab pendetide (ProstaScint; Cytogen Corp., Princeton, NJ) was upgraded from recommended for approval to approved), and several additional agents in FDA-monitored trials. The majority of antibodies studied to date have been whole or fragmented murine monoclonals whereas the first of the human and humanized immunoglobulins are now entering clinical trials. While no antibody has behaved as a perfect imaging agent, they have consistently been shown to contribute to diagnosis, complementing and often exceeding the diagnostic ability of conventional modalities. Many promising new trends in antibody imaging, relating to the radiolabeled immunoglobulin, its route and manner of administration, and mode of detection, are under development. Because of the requisite several-year delay inherent in the (FDA) testing process, there is a lag before the most-promising of these innovations will achieve (FDA) approval and be incorporated into routine imaging studies. In spite of this effective performance, as "new kid on the block," radioimmunoscintigraphy may have often been expected to perform in an unrealistic manner, considering the great variation in biological behavior of primary and metastatic cancer and the consequent limitation of all diagnostic tests. Nonetheless, because radioimmunoscintigraphy identifies antigens on a cellular level, differing fundamentally from anatomic imaging modalities such as computed tomography and ultrasound which identify gross morphological changes, it has potential to impact significantly on patient care. With adequate resources focused on radioimmunoscintigraphy, this technology will continue to emerge as an important and unique diagnostic tool in the care of cancer patients, with demonstrable clinical efficacy and cost effectiveness.

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.

Immunoscintigraphy with a new indium-111-labeled monoclonal antibody (MAb 1A3) in patients with colorectal cancer

PURPOSE

This study was designed to evaluate a new anticolorectal carcinoma monoclonal antibody (1A3), conjugated with the bifunctional chelating agent N,N'-bis(2-hydroxybenzyl)1(4-bromoacetamidobenzyl)1,2-ethylenediam ine-N,N'- diacetic acid and labeled with indium-111, in a Phase I/II study involving 38 patients with localized or advanced colorectal cancer.

METHODS

Patients were injected with indium-111-N,N'-bis(2-hydroxybenzyl) 1(4-bromoacetamidobenzyl)1,2-ethylenediamine-N,N'-diacetic acid-monoclonal antibody 1A3 (1-50 mg, 1-5 mCi) and imaged at two or three sessions one to five days later. Scintigraphic findings were compared with radiologic, pathologic, surgical, and other clinical findings to assess the accuracy of radioimmunoscintigraphy.

RESULTS

At least one known tumor site was clearly defined by planar scintigraphy in 29 (76 percent) patients. Increased radioactivity was seen in 40 of 63 known tumor sites (37/43 abdominal-pelvic, 3/15 hepatic, and 0/5 pulmonary sites) without any apparent dose-related effects. Nineteen previously undetected sites were considered positive by imaging, and, of these, six were biopsy-proven tumor sites, four were probable tumor sites, three were definitely false positive sites, and six were probable false positive sites. Radioimmunoscintigraphy detected proven tumor in 15 of 16 patients with negative or equivocal computed tomography results. Of of the 28 patients with rectosigmoid cancer, 25 (89 percent) had positive studies with 34 of 47 tumor sites showing definite uptake on the scintigrams. This included 3 of 9 hepatic metastases. The only adverse reaction occurred in one patient who developed transient hives. Human anti-mouse antibody responses occurred in approximately one-half of the patients injected with doses of 10 or 50 mg.

CONCLUSION

This study shows that radioimmunoscintigraphy with this indium-111-labeled monoclonal antibody is safe, it can detect most nonhepatic abdominal-pelvic tumors with a positive predictive value of 83 (44/53) percent, and it should prove to be useful, particularly in the diagnosis of recurrent rectal carcinoma.