Localization by hand-held gamma probe of tumor labeled with antibody "cocktail"

124I-HuCC49deltaCH2 for TAG-72 antigen-directed positron emission tomography (PET) imaging of LS174T colon adenocarcinoma tumor implants in xenograft mice: preliminary results

Background

¹⁸F-fluorodeoxyglucose positron emission tomography (¹⁸F-FDG-PET) is widely used in diagnostic cancer imaging. However, the use of ¹⁸F-FDG in PET-based imaging is limited by its specificity and sensitivity. In contrast, anti-TAG (tumor associated glycoprotein)-72 monoclonal antibodies are highly specific for binding to a variety of adenocarcinomas, including colorectal cancer. The aim of this preliminary study was to evaluate a complimentary determining region (CDR)-grafted humanized C_H2-domain-deleted anti-TAG-72 monoclonal antibody (HuCC49deltaC_H2), radiolabeled with iodine-124 (¹²⁴I), as an antigen-directed and cancer-specific targeting agent for PET-based imaging.

Methods

HuCC49deltaC_H2 was radiolabeled with ¹²⁴I. Subcutaneous tumor implants of LS174T colon adenocarcinoma cells, which express TAG-72 antigen, were grown on athymic Nu/Nu nude mice as the xenograft model. Intravascular (i.v.) and intraperitoneal (i.p.) administration of ¹²⁴I-HuCC49deltaC_H2 was then evaluated in this xenograft mouse model at various time points from approximately 1 hour to 24 hours after injection using microPET imaging. This was compared to i.v. injection of ¹⁸F-FDG in the same xenograft mouse model using microPET imaging at 50 minutes after injection.

Results

At approximately 1 hour after i.v. injection, ¹²⁴I-HuCC49deltaC_H2 was distributed within the systemic circulation, while at approximately 1 hour after i.p. injection, ¹²⁴I-HuCC49deltaC_H2 was distributed within the peritoneal cavity. At time points from 18 hours to 24 hours after i.v. and i.p. injection, ¹²⁴I-HuCC49deltaC_H2 demonstrated a significantly increased level of specific localization to LS174T tumor implants (p = 0.001) when compared to the 1 hour images. In contrast, approximately 50 minutes after i.v. injection, ¹⁸F-FDG failed to demonstrate any increased level of specific localization to a LS174T tumor implant, but showed the propensity toward more nonspecific uptake within the heart, Harderian glands of the bony orbits of the eyes, brown fat of the posterior neck, kidneys, and bladder.

Conclusions

On microPET imaging, ¹²⁴I-HuCC49deltaC_H2 demonstrates an increased level of specific localization to tumor implants of LS174T colon adenocarcinoma cells in the xenograft mouse model on delayed imaging, while ¹⁸F-FDG failed to demonstrate this. The antigen-directed and cancer-specific ¹²⁴I-radiolabled anti-TAG-72 monoclonal antibody conjugate, ¹²⁴I-HuCC49deltaC_H2, holds future potential for use in human clinical trials for preoperative, intraoperative, and postoperative PET-based imaging strategies, including fused-modality PET-based imaging platforms.

A comprehensive overview of radioguided surgery using gamma detection probe technology

The concept of radioguided surgery, which was first developed some 60 years ago, involves the use of a radiation detection probe system for the intraoperative detection of radionuclides. The use of gamma detection probe technology in radioguided surgery has tremendously expanded and has evolved into what is now considered an established discipline within the practice of surgery, revolutionizing the surgical management of many malignancies, including breast cancer, melanoma, and colorectal cancer, as well as the surgical management of parathyroid disease. The impact of radioguided surgery on the surgical management of cancer patients includes providing vital and real-time information to the surgeon regarding the location and extent of disease, as well as regarding the assessment of surgical resection margins. Additionally, it has allowed the surgeon to minimize the surgical invasiveness of many diagnostic and therapeutic procedures, while still maintaining maximum benefit to the cancer patient. In the current review, we have attempted to comprehensively evaluate the history, technical aspects, and clinical applications of radioguided surgery using gamma detection probe technology.

Radioimmunodetection: technical problems and methods of improvement

Radioimmunodetection (RAID) is a technique which uses radiolabelled antibodies to visualize tumours, taking advantage of antigens preferentially expressed by malignant tissue. Gamma radiation emitted by radioisotopes can be detected using an external gamma camera (RAID), or intraoperatively with a hand-held Geiger counter (radioimmunoguided surgery, RIGS). RAID has significant inherent problems. Many have been overcome as a result of nearly 50 years of research, and others still remain as obstacles precluding the routine use of the technique. This article summarizes the technical limitations of RAID and outlines the relative successes of the methods evolved to overcome them.

Binding of a human monoclonal antithyroglobulin antibody to cultured human thyroid cancer cells

To develop a new method of radioimmunodetection for thyroid cancer, we tested the binding ability of a human antithyroglobulin monoclonal antibody, VB5, to primary culture of human thyroid cancer cells. VB5 was able to immunostain cytoplasmic thyroglobulin (Tg) in the acetone-fixed cancer cells when used in a labeled streptavidin-biotin method but not in a conventional indirect immunoperoxidase technique. The antibody was readily labeled with I-125 in the standard chloramin-T method, and showed specific binding to the antigen on cultured malignant thyrocytes displaceable with non-labeled VB5 or with excess Tg antigen. Although these initial results in vitro are encouraging, the observed low specific binding (about 1% at room temperature) to intact cells with a single monoclonal antibody seems insufficient to conduct any in vivo immunolocalization experiments in animals. To obtain more binding, we would need a cocktail of several monoclonal antibodies to different epitopes, and also fragmentation of antibody molecules to penetrate into cytoplasm.

Radioimmunoguided surgery and colorectal cancer

Radioimmunoguided surgery is a technique that aims to delineate the extent of epithelial neoplasms (primary/recurrent) and their spread (local, regional, and distant) which are not adequately visualized by conventional imaging techniques. The target lesion binds radiolabelled, tumour-associated monoclonal antibodies which are administered in the days before surgery and which bind to the target lesion. The radiotracer is detected intraoperatively using a hand-held gamma detecting probe. This identifies the extent of the tumour, involvement of lymph nodes or other organs and may allow a more complete surgical clearance of the tumour. This article provides a basic understanding of the RIGS (radioimmunoguided surgery) technique, the monoclonal antibodies which are used and outlines the advantages and limitations of this technique.

Avidin-biotin system in radioimmunoguided surgery for colorectal cancer. Advantages and limits

PURPOSE

Radiolabeled monoclonal antibodies (MAbs) have been reported to allow tumor intraoperative detection by means of a gamma-detecting probe. The technology is called the Radioimmunoguided Surgery (RIGS) system. The main inconveniences of the method are 1) the long interval needed for clearance of unattached MAbs from the patient's body, between the injection of the MAb and surgery, and 2) the low sensitivity of current MAbs used in detecting small tumors. We describe a new method to overcome these inconveniences using biotinylated MAbs and avidin in order to obtain a rapid blood clearance of the radiolabeled MAbs both anticarcinoembryonic antigen and antitumor-associated glycoprotein-72 MAbs.

METHODS

Twenty patients with primary and recurrent colorectal cancer have been enrolled in the study; 125I-biotinylated MAbs FO23C5 (anticarcinoembryonic antigen) and B72.3 (antitumor-associated glycoprotein-72) followed by cold avidin were injected in 13 patients and 7 patients, respectively.

RESULTS

A decrease of 94 +/- 3 percent of circulating radioactivity was achieved in 3 to 5 days. Patients underwent surgery approximately seven days after MAb injections rather than after four weeks. Tumors were localized in 14/20 (70 percent) patients (true positive), 2 (10 percent) were false negative, and 4 (20 percent) were true negative. The overall sensitivity level in early-stage primary cancers was 37 percent when related to the presence of disease and 75 percent when related to antigenic expression. The sensitivity for more advanced cancer and for recurrences was 100 percent. Moreover, the in vivo tumor targeting of biotinylated MAb was demonstrated in frozen tumor section by direct streptoavidin-peroxidase staining.

CONCLUSIONS

The avidin-biotin system may enhance applicability and effectiveness of radioimmunoguided surgery (RIGS).

Impact of Radioimmunoguided Surgery

Radioimmunoguided surgery (RIGS) is a technique employed to locate tumor deposits with the aid of intravenously injected, tumor-specific, radiolabeled monoclonal antibodies and a small gamma detecting device. The gamma detecting probe (GDP) is a small, portable unit which has the capacity to be used intraoperatively to survey the entire peritoneal surface for increased radioactivity indicative of targeted tumor tissue during abdominal exploration for colorectal cancer. Trials in humans have demonstrated the ability of this system to locate clinically nonpalpable tumor deposits in patients undergoing carcinoembryonic antigen second-look laparotomies. This feature may be of value in improving the definition of tumor location and extent as well as allowing a more thorough resection of tumor-bearing tissue to be performed and hopefully improving overall patient survival.

Gamma-detecting probe and autoradiographic studies of radiolabeled antibody B72.3 in CX-1 colon xenografts

Nude mice bearing CX-1 colon tumors were injected with 50 microCi 125I-labeled monoclonal antibody (MAb) B72.3. Radioactivity in tumors was studied with the gamma detecting probe (GDP) on days 1, 3, 7, and 10 after MAb injection. On each day, two mice were sacrificed and sections were examined with autoradiography (ARG), immunoperoxidase methods (IMP), and routine stains. Mean probe counts showed increasing tumor to background ratios and ARG demonstrated a progressive increase in radionuclide in the tumors. The distribution of 125I was primarily around the vascular spaces on day 1, but by day 3 and progressively it appeared in tumor gland lumina and necrotic areas. A regional correlation was shown between radionuclide in vascular spaces and its sequestration in tumor elements.