Radioimmunoscintigraphy Research Articles

Preparation and preclinical characterization of 111In-DTPA-Anti-MUC1 as a radioimmunoconjugate for diagnosis of breast cancer by single-photon emission computed tomography.

Targeting MUC1 antigens which are overexpressed in 80% of breast cancers can be widely used in the field of radioimmunoscintigraphy (RIS) of breast cancer. The aim of this study was to develop a new diagnostic labeled compound for breast cancer RIS. In this study, an efficient indirect labeling method of PR81 with Indium-111 was developed and preliminary preclinical qualifications were reported. 111In-DTPA-PR81 was prepared and its radiochemical purity and stabilities in human serum and in phosphate-buffered saline (PBS) buffer were surveyed. Furthermore, cellular studies including complex reactivity, binding specificity, cell toxicity, etc., were examined. Finally, biodistribution and scintigraphy of the complex were studied in normal and tumoral animals. Statistical analyses were performed using SPSS 10.0. 111In-DTPA-PR81 was prepared with a radiochemical purity of >99% at optimized conditions. Stability studies showed the radiochemical purity of >90% in PBS buffer after 96 h, while the stability in human serum showed decrement to 81% after 96 h. Reactivity of the complex with MUC1 was significantly (P < 0.005) higher than bovine serum albumin (BSA) (about 7-8 times), even though BSA concentration was about twice the MUC1. The binding specificity of the complex to the MUC1 antigen was confirmed by means of immunoreactivity assay. Cell toxicity examination showed no significant lethal effect of the radiolabeled compound on the cells. Biodistribution studies of the complex in normal rats were consistent with the biodistribution of antibodies and high accumulation was observed in the tissues expressing MUC1 antigen. The results of 111In-DTPA-PR81 scintigraphy in tumoral female BALB/c mice at 24 and 48 h after injection showed an increasement of the accumulation in the tumor site. 111In-DTPA-PR81 can be considered as a potential agent for imaging of the MUC1 +breast tumors.

Antibody-Based Imaging of HER-2: Moving into the Clinic

Human epidermal growth factor receptor-2 (HER-2) mediates a number of important cellular activities, and is up-regulated in a diverse set of cancer cell lines, especially breast cancer. Accordingly, HER-2 has been regarded as a common drug target in cancer therapy. Antibodies can serve as ideal candidates for targeted tumor imaging and drug delivery, due to their inherent affinity and specificity. Advanced by the development of a wide variety of imaging techniques, antibody-based imaging of HER-2 can allow for early detection and localization of tumors, as well as monitoring of drug delivery and tissue's response to drug treatment. In this review article, antibody-based imaging of HER-2 are summarized and discussed, with an emphasis on the involved imaging methods.

Salvage Radiotherapy After Postprostatectomy Biochemical Failure: Does Pretreatment Radioimmunoscintigraphy Help Select Patients with Locally Confined Disease?

Radioimmunoscintigraphy (RIS) has the potential to demonstrate early recurrences after prostatectomy and might be useful in selecting patients for salvage radiotherapy (RT). A total of 82 patients with adenocarcinoma of the prostate were treated with salvage RT between 1988 and 2005, for an elevated prostate-specific antigen (PSA) level after prostatectomy. Of the 82 patients, 32% had Gleason score 6 or less disease, 54% Gleason score 7 disease, 70% had Stage pT3 disease, 55% had positive margins, and 5% had pathologic lymph node involvement. The median pre-RT PSA level was 0.63 ng/mL. Of the 82 patients, 47 (57%) had a pre-RT RIS (ProstaScint) scan, which was used for both patient selection and target delineation. The RT regimen was a median dose of 66 Gy to the prostate bed. Also, 64% received androgen deprivation therapy. Biochemical failure was defined as a PSA level >0.1 ng/mL and increasing. Patients with a pre-RT RIS scan had a lower preoperative PSA level (p = 0.0240) and shorter follow-up (p = 0.0221) than those without RIS. With a median follow-up of 44 months, the biochemical control rate was 56% at 3 years and 48% at 5 years. Margin status was the only factor associated with biochemical control on univariate (p = 0.0055) and multivariate (p = 0.0044) analysis. Patients who had prostate bed-only uptake on RIS (n = 38) did not have improved outcomes, with biochemical control rates of 51% at 3 years and 40% at 5 years. Patients treated with salvage RT had modest responses. Patients who were selected for treatment with RIS did not have better biochemical outcomes. Our results indicated that patients with positive margins were most likely to benefit from salvage RT.

The Role of Indium-111 Radioimmunoscintigraphy in Post-Radical Retropubic Prostatectomy Management of Prostate Cancer Patients

Indium-111 radioimmunoscintigraphy (RIS) has an increasing role in the treatment of prostate cancer and is most commonly performed at this disease site using labeled monoclonal antibody against prostate-specific membrane antigen. There are many limitations of RIS, including low spatial resolution, low diagnostic yield and limited availability. Despite these limitations, the efficacy of RIS has been demonstrated in many clinical studies, including multi-institutional investigations. The highest sensitivity and specificity of RIS appears to be in the post-radical retropubic prostatectomy (post-RRP) setting. RIS has recently been explored for its role in clinical radiotherapy decision-making, and was found to have a significant impact in selecting patients for radiotherapy and for the general radiotherapy treatment volume definition. RIS has also recently been explored for its role in radiotherapy planning and was found to impact clinical target volume design. However, manual editing of the RIS volume is still necessary when projected into the radiotherapy-planning scan, as there is often overlap in the RIS-defined uptake regions with normal structures (rectum, bladder and symphysis bone marrow). The impact of RIS on biochemical control has been explored, with studies in this area yielding conflicting results. It appears that the maximum impact of RIS is possible when areas of labeled antibody uptake regions are co-registered with the radiotherapy-planning computed tomography scan. The larger RIS-guided target volumes do not appear to be prohibitive in increasing radiotherapy-related toxicity. Future directions of the use of RIS for post-RRP prostate cancer are discussed.

Differential diagnosis of adnexal masses: risk of malignancy index, ultrasonography, magnetic resonance imaging, and radioimmunoscintigraphy

A risk of malignancy index (RMI), based on menopausal status, ultrasound (US) findings, and serum CA125, has previously been described and validated in the primary evaluation of women with adnexal masses and is widely used in selective referral of women from local cancer units to specialized cancer centers. Additional imaging modalities could be useful for further characterization of adnexal masses in this group of women. A prospective cohort study was conducted of 196 women with an adnexal mass referred to a teaching hospital for diagnosis and management. Follow-up data was obtained for 180 women; 119 women had benign and 61 women malignant adnexal masses. The sensitivity and specificity of specialist US, magnetic resonance imaging (MRI), radioimmunoscintigraphy (RS), and the RMI were determined. We identified a subgroup of women with RMI values of 25-1000 where the value of further specialist imaging was evaluated. Sensitivity and specificity for specialist US were 100% and 57%, for MRI 92% and 86%, and for RS 76% and 87%, respectively. Analysis of 123 patients managed sequentially, using RMI cutoff values of > or =25 and <1000 and then US and MRI provided a sensitivity of 94% and a specificity of 90%. Using this RMI cutoff followed by specialist US and MRI, as opposed to the traditional RMI cutoff value of 250, can increase the proportion of patients with cancer appropriately referred in to a cancer center, with no change in the proportion of patients with benign disease being managed in a local unit.

Diagnostic efficacy and safety of 99mTc-Labeled monoclonal antibody ior c5 in patients with colorectal and anal carcinomas: Final report clinical trial phase I/II

Monoclonal antibody (mAb) ior c5 is an IgG1, which recognizes a glycoprotein tumor specific antigen IOR C2 over expressed in the surface of colon and ovarian cancer cells. The aim of the present work was to evaluate the diagnostic efficacy of the 99mTc-labeled mAb ior c5 for the detection of colorectal tumors, its metastases and recurrences. Methods: Eighty six patients with colorectal or anal cancer, mean age 57 +/- 13 yrs, were involved in a phase I/II multicentric, open clinical trial to assess the ability of Radioimmunoscintigraphy (RIS) with 99mTc- mAb ior c5 to detect those tumors. 74 patients received 1 mg of c5 labeled with 1480-1850 MBq to determinate diagnosis efficacy and safety of murine mAb by intravenously (i.v) bolus injection (group 1). In order to evaluate pharmacokinetic, bio distribution and dosimetry of this radiolabel molecule, 12 patients received 3 mg of labeled ior c5. Planar anterior and posterior images of the lesion sites and suspected metastases were acquired at 2, 4 and 18-24 hours after injection using a matrix size 128 x128 and 500 Kcounts per view. SPECT were scanned at 5 hr post-injection, using a 360° circular orbit with 64 images. HAMA response was measured in serum at 2, 4, 8 and 12 week post-administration. Results: Labeling efficiency was (97.8 ± 0.6) %. No adverse reactions or side effects were observed. Overall sensitivity, specificity, accuracy, positive and negative predictive values of the immunoscintigraphy were 95.80%, 100%, 96.51%, 100.0% and 82.35%, respectively. Unknown metastases were detected in 37 of 86 cases (43.02%). No HAMA response was found. Conclusions: Immunoscintigraphy with 99mTc -labeled mAb ior c5 could be a useful procedure for the diagnosis and follow-up of the patients with colorectal tumors, its metastasis and recurrences.

Postprostatectomy Target-Normal Structure Overlap Volume Differences Using Computed Tomography and Radioimmunoscintigraphy Images for Radiotherapy Treatment Planning

The purpose of this study was to analyze regions of uptake in normal structures on postprostatectomy radioimmunoscintigraphy (RIS) images by evaluating differences in the overlap volumes of prostate fossa clinical target volume (CTV) and planning target volume (PTV) using correlative computed tomography (CT) images. The electronic records of 13 patients who received external beam radiotherapy postprostatectomy and who underwent a vessel-based RIS/CT registration were reviewed. For each patient, the RIS-defined CTV (CTV(RIS)) was compared (in terms of the overlap volume with the surrounding bladder, rectum, pubic symphysis, and penile bulb) with the CT-defined CTV(pre) before this registration and also with CTV(post) (the final target volume used for treatment). Similar analyses were done for PTV(RIS), PTV(pre), and PTV(post) defined in each case to be the corresponding CTV + 1-cm margin. CTV(RIS) overlapped significantly more with the bladder, rectum, and symphysis, but not with the penile bulb, than did either the CTV(pre) or CTV(post). However, the corresponding PTV analyses revealed no significant differences between any of the overlap volumes of any of the PTVs with the bladder, rectum, and penile bulb, but did reveal a significant difference between the PTV(RIS) and PTV(post) overlap volumes with the symphysis compared with PTV(pre) overlap volumes with the symphysis. On RIS images, there appear to be areas of uptake in the bladder, rectum, and pubic symphysis but not the penile bulb; however, the dosimetric consequences of this uptake for radiation treatment planning are minimal on the bladder, rectum, and penile bulb, but require segmentation for dose reduction to the pubic symphysis.

Post-Prostatectomy Target-Normal Structure Overlap Volumes using Computed Tomography and Radioimmunoscintigraphy Images for Radiotherapy Treatment Planning

Purpose/Objective: To analyze regions of uptake on post-prostatectomy (post-RRP) radioimmunoscintigraphy (RIS) images by evaluating the differences in the overlap volumes of prostate fossa clinical target volume (CTV) and planning target volume (PTV) with surrounding critical structures using computed tomography (CT) images and RIS images.

Radioimmunoscintigraphy of Breast Tumor Xenografts in Mouse Model by 99mTc Direct Radiolabeling of a Monoclonal Antibody PR81

Introduction: The radioimmunoscintigraphy (RIS) has found widespread clinical applications in tumor diagnosis. Human epithelial mucin, MUC1, is commonly over expressed in adenocarcinoma including 80% of breast cancers and represents a useful target for RIS. The PR81 is a new murine anti-MUC1 monoclonal antibody that was found to react with the membrane extracts of several human breast cancerous tissues and the cell surface of some MUC1 positive cell lines. In this study, a direct method which is very simple, rapid and efficient for the labeling of this MAb with 99mTc, particularly suitable for the development of a ‘kit’, was developed. The quality control of new radiopharmaceutical and immunoscintigraphy studies in BALB/c mice bearing breast tumor xenografts were also performed. Materials and Methods: The Ab reduction was performed with 2-mercaptoethanol (2-ME) at a molar ratio of 2000:1 (2-ME:MAb) and reduced Ab was labeled with 99mTc via methylene diphosphonate (MDP) as a transchelator. The labeling efficiency was determined by ITLC. The amount of radiocolloids was measured by cellulose nitrate electrophoresis. The stability of the labeled product was checked in fresh human serum by gel filtration chromatography (FPLC) over 24 hrs. The integrity of the labeled MAb was checked by the means of SDS-PAGE. Cell-binding assay was used to test the binding ability of 99mTc-PR81 to MCF7 cells. Biodistribution was studied in normal BALB/c mice at 4 and 24 hrs post-injection. The tumor imaging was performed in female BALB/c mice with breast tumor xenografts 24 hrs after the new complex injection. Results: The labeling efficiency was 94.2%±2.3 and radiocolloids were 2.5%±1.7. In vitro stability was 70%±5.7 in fresh human serum over 24 hrs. There was no significant Ab fragmentation due to the labeling procedure. Both the labeled and unlabeled PR81 were able to compete for binding to MCF7 cells. The biodistribution studies in normal BALB/c mice showed that there was no important accumulation in any organ. The immunoscintigraphy studies demonstrated definite localization of the preparation at the site of tumors with high sensitivity. Discussion and Conclusion: The results show that by using the Schwarz method of radiolabeling MAb PR81, a labeling yield higher than 90% with high stability of the complex in human serum can be obtained. These findings demonstrated that the new radiopharmaceutical can be considered as a promising candidate for imaging of human breast cancer.

Radioimmunoscintigraphy for post-prostatectomy radiotherapy: Analysis of toxicity and biochemical control

4660 Background: To evaluate the role of radioimmunoscintigraphy (RIS) directed against prostate specific membrane antigen (PSMA) [ProstaScint] in influencing post-radical retropubic prostatectomy (RRP) radiotherapy (RT) toxicity and biochemical failure-free survival (BFFS). Methods: The records of 107 consecutive post-RRP patients who underwent RT were reviewed. The group for whom no RIS scan was obtained (Group A, n=54, mean follow-up (FU) 26.7 months) was identified, as was the group for whom RIS was obtained (Group B, n=53, mean FU 21.3 months). Group B was comprised of those who had a RIS/computed tomography (CT) correlation to aid in treatment planning (Subgroup B1, n=40) and those who did not (Subgroup B2, n=13). The acute and late gastrointestinal (GI) and genitourinary (GU) toxicity were reviewed. BFFS curves were constructed, using two successive PSA rises after a nadir to a value > 0.2 ng/mL as the definition of failure. Results: No significant differences in late toxicity were observed between any Group/Subgroup. However, acute GI toxicity was higher for Group B vs A (p=0.026), and acute GU toxicity was higher in Subgroup B2 vs B1 (p=0.050). Most toxicity was Grade 1 or Grade 2; only 1 case of Grade 3 toxicity and no cases of Grade 4 or Grade 5 toxicity were seen. 3-year BFFS was higher for Group B vs A (80.7 vs 75.5%) and for Subgroup B1 vs Subgroup B2 (84.5 vs 71.6%). On multivariate analysis of patient (age, race), surgical (stage, grade, margin status, extracapsular extension, seminal vesicle invasion, post-RRP PSA nadir, post-RRP PSA max, and RRP to RT interval), and treatment (hormone therapy, RT dose, RT technique, RIS scan, and RIS/CT correlation) factors on BFFS, only RIS/CT correlation (p=0.042) reached significance. Conclusions: A BFFS advantage was observed in patients for whom RIS was obtained; however, this advantage only reached significance for the population in which RIS/CT correlation was used to guide RT target definition. The improved PSA control using RIS was achieved with a small increase in acute toxicity, but with no observed change in late toxicity. These findings can serve as the basis for prospective studies in this area. No significant financial relationships to disclose.

Radioimmunoscintigraphy for post-prostatectomy radiotherapy: Analysis of toxicity and biochemical control

4660 Background: To evaluate the role of radioimmunoscintigraphy (RIS) directed against prostate specific membrane antigen (PSMA) [ProstaScint] in influencing post-radical retropubic prostatectomy (RRP) radiotherapy (RT) toxicity and biochemical failure-free survival (BFFS). Methods: The records of 107 consecutive post-RRP patients who underwent RT were reviewed. The group for whom no RIS scan was obtained (Group A, n=54, mean follow-up (FU) 26.7 months) was identified, as was the group for whom RIS was obtained (Group B, n=53, mean FU 21.3 months). Group B was comprised of those who had a RIS/computed tomography (CT) correlation to aid in treatment planning (Subgroup B1, n=40) and those who did not (Subgroup B2, n=13). The acute and late gastrointestinal (GI) and genitourinary (GU) toxicity were reviewed. BFFS curves were constructed, using two successive PSA rises after a nadir to a value > 0.2 ng/mL as the definition of failure. Results: No significant differences in late toxicity were observed between any Group/Subgroup. However, acute GI toxicity was higher for Group B vs A (p=0.026), and acute GU toxicity was higher in Subgroup B2 vs B1 (p=0.050). Most toxicity was Grade 1 or Grade 2; only 1 case of Grade 3 toxicity and no cases of Grade 4 or Grade 5 toxicity were seen. 3-year BFFS was higher for Group B vs A (80.7 vs 75.5%) and for Subgroup B1 vs Subgroup B2 (84.5 vs 71.6%). On multivariate analysis of patient (age, race), surgical (stage, grade, margin status, extracapsular extension, seminal vesicle invasion, post-RRP PSA nadir, post-RRP PSA max, and RRP to RT interval), and treatment (hormone therapy, RT dose, RT technique, RIS scan, and RIS/CT correlation) factors on BFFS, only RIS/CT correlation (p=0.042) reached significance. Conclusions: A BFFS advantage was observed in patients for whom RIS was obtained; however, this advantage only reached significance for the population in which RIS/CT correlation was used to guide RT target definition. The improved PSA control using RIS was achieved with a small increase in acute toxicity, but with no observed change in late toxicity. These findings can serve as the basis for prospective studies in this area. No significant financial relationships to disclose.

PET radioimmunoscintigraphy of renal cell cancer using 89Zr-labeled cG250 monoclonal antibody in nude rats.

With the introduction of positron-emitting radionuclides with half-lifes in days, such as 89Zr and 124I, radioimmunoscintigraphy (RIS) with positron-emitter-labeled monoclonal antibodies (moAbs) becomes feasible. RIS, using positron emission tomography (immuno-PET), combines the specific localization of an antibody with the high resolution of a PET camera. In the present study, scintigraphic tumor imaging using chimeric moAb G250 labeled with 89Zr (immuno-PET) or 111In (RIS), and [18F]FDG-(PET) was explored in rats with s.c. renal cell carcinoma (RCC) tumors. Nude rats (6-8 rats per group) with s.c. SK-RC-52 tumors were i.v. injected with 4 MBq 111InDTPA-cG250, 20 MBq 89Zr-Df-cG250 or 4 MBq [18F]FDG. Planar 111In-DTPA-cG250 images were obtained 5 minutes, and 24, 48, and 72 hours postinjection (p.i.). 3D PET imaging was performed 5 minutes, and 24, 48, and 72 hours after a 89Zr-Df-cG250 injection and 1 hour after a [18F]FDG injection using a Siemens ECAT EXACT PET camera. Rats were killed after the last imaging session, and the uptake of the radiolabel in the dissected tissues was determined. Both radiolabeled antibody preparations were stable during 4 days of incubation in serum at 37 degrees C, and the immunoreactivity was preserved. Two (2) days after injection, s.c. tumors (100 mg) were clearly visualized, both with 89Zr-Df-cG250 and 111In-DTPA-cG250. Tumors were not visualized with [18F]FDG (uptake in tumor of 0.5 +/- 0.1 %ID/g, 1 hour p.i.). The biodistribution experiments showed an identical uptake in the tumor for both 89Zr-Df-cG250 and 111In-DTPA-cG250 at 3 days p.i. (5.0 +/- 2.4 and 4.9 +/- 2.9 %ID/g, respectively). Blood levels at 3 days p.i. were also identical (1.4 +/- 0.4 versus 1.7 +/- 0.7 %ID/g), and no significant differences were found in the biodistribution of normal tissues between the two radiolabeled cG250 preparations. The cG250 antibody can be stably labeled with the positron-emitter 89Zr, while preserving the immunoreactivity of the moAb. In this rat model, the in vivo biodistribution of 89Zr-Df-cG250 was identical to that of 111In-DTPA-cG250. Immuno-PET of RCC is feasible with 89Zr-cG250, and relatively small tumors could be visualized, even without a dedicated PET camera for small animals.

Radioimmunoscintigraphy (RIS) with Bectumomab (Tc99m Labeled IMMU-LL2, Lymphoscan®) in the Assessment of Recurrent Non-Hodgkin's Lymphoma (NHL)

The efficacy of a Tc99m-labeled anti-lymphoma antibody fragment, bectumomab [LymphoScan], was retrospectively examined in the staging of recurrent or newly diagnosed non-Hodgkin's lymphoma (NHL) [7 patients] and to assess targeting before radioimmunotherapy (RIT) [14 patients]. Performance was graded relative to conventional imaging. Tumors included 7 low-grade, 11 intermediate-grade, and 3 high-grade histologic subtypes. Computed x-ray tomography, radiogallium imaging, FDG-PET, and bone marrow biopsy defined 117 sites. Bectumomab revealed 56% of these sites. In 4 patients bectumomab uncovered five sites not evident by conventional imaging. In addition, it uncovered one site in the brain, an area not covered in the standard work-up of asymptomatic patients. Bectumomab imaging most often failed in central abdominal and thoracic locations, and excelled in revealing disease in the head and neck. Relative to Ga67 citrate imaging, the performance of bectumomab was variable, with no clear relation to anatomic location; there was better targeting of low and intermediate grade NHL. Radiogallium out-performed bectumomab imaging in 23 sites, 19 of which were in patients with high or intermediate-grade disease. Bectumomab was superior to radiogallium at six sites, five of which involved low-grade tumor. Bectumomab shows promise as a pre-RIT probe for targeting of B-cell NHL. It excelled at defining small volume, low-grade disease. However, as a purely diagnostic agent, its performance was variable.

New techniques for imaging colorectal cancer: the use of MRI, PET and radioimmunoscintigraphy for primary staging and follow-up.

Modern imaging techniques such as computed tomography (CT) and ultrasound (US) are in the majority of cases able to detect local and metastatic spread of malignancy. Increasingly, the requirement is for even more accurate pre-operative tumour staging to enable the use of new surgical techniques, neo-adjuvant therapies and, postoperatively, to enable detection of tumour recurrence on follow-up. Recent imaging research has focused on magnetic resonance imaging (MRI) for the detection of local tumour extension particularly for rectal tumours and on positron emission tomography (PET) and radioimmunoscintigraphy (RIS) for the detection of metastatic nodal and soft tissue disease. This article briefly describes these three imaging modalities and their role in primary staging, detection of hepatic metastases and local recurrence.

Radioimmunoscintigraphy for colorectal cancer: Current status and future prospects

Abstract Radioimmunoscintigraphy (RIS) as an imaging modality in oncology is in transition. In early experience with indium-111–labeled intact murine monoclonal antibodies (MoAbs) in colorectal cancer, RIS imaged hepatic metastases poorly and immunogenicity was frequent. Technetium-99m–labeled antibody fragments and human MoAbs provide significantly improved imaging efficacy, and lack of immune reactivity makes serial imaging possible. RIS is superior to computed tomography (CT) for detection of extrahepatic abdominal and pelvic colorectal carcinoma, and complements CT in imaging liver metastases. In surgical decision-making analyses, RIS improved the accuracy of predicting resectability and nonresectability as compared to CT. New MoAb moieties, manipulation of tumor cell antigen expression, and innovative tumor targeting strategies promise to bring RIS into the mainstream of diagnostic oncology, and, when used in conjunction with intraoperative gamma probes, may allow surgeons to localize and remove disease that can neither be visualized nor palpated. Copyright © 2002 by W.B. Saunders Company

Assessment of spread of primary rectal carcinoma with radioimmunoscintigraphy (RIS) using anti-CEA antibody (IMMU-4)

Assessment of spread of primary rectal carcinoma with radioimmunoscintigraphy (RIS) using anti-CEA antibody (IMMU-4)

Radioimmunoguided surgery of colorectal carcinoma with an 111In-labelled anti-TAG72 monoclonal antibody

Radioimmunoscintigraphy (RIS) and radioimmunoguided surgery (RIGS) were assessed for their usefulness in patients with colorectal carcinoma. Twenty-nine patients (18 primary tumours, 10 with a suspicion of recurrence and one colonic diverticulitis) were studied. Radioimmunoscintigraphy was performed 48 and 72 h after the injection of an anti-TAG72 monoclonal antibody (CYT-103) labelled with 111In. Radioimmunoguided surgery was performed between 72 and 96 h post-injection. During surgery, a systematic screening was performed with a hand-held gamma detecting probe and a surgical index (tumour-to-normal tissue) was obtained. There were statistically significant differences between counts in normal tissue versus tumour (P < 0.001) and RIGS was considered positive for the detection of tumour if the ratio between the counts in the area suspicious of tumour and the counts in the normal tissue was greater than 1.5. The overall sensitivity for RIS and RIGS was 71.4% (55.6% in primary tumours and 100% in recurrences) and 82.1% (83.3% in primary tumours and 80% in recurrences), respectively. Radioimmunoguided surgery changed the surgical procedure in two cases with small tumour deposits. Occult regional lymph node involvement in primary tumours was not found; therefore, RIGS, as a complementary technique to RIS, is particularly useful in recurrences and can help the surgeon in the resection of small tumour deposits which are difficult to localize.

A Thousand Points of Light or Just Dim Bulbs? Radiolabeled Antibodies and Colorectal Cancer Imaging

Radioimmunoscintigraphy (RIS) is coming into its own as an imaging modality in clinical oncology. Early experience with indium-III-labeled intact murine monoclonal antibodies (MoAbs) in colorectal cancer suggested that RIS images hepatic metastases poorly. Moreover, an antimurine immune response was frequently provoked, precluding multiple follow-up RIS studies in individual patients due to reticu-loendothelial sequestration of the radioimmunoconjugate before tumor targeting could occur. Recent trials of technetium-99m- labeled antibody fragments and human MoAbs have demonstrated significant improvement in imaging efficacy, and repeated or serial imaging is possible because of the absence of associated immunoge-nicity. RIS is demonstrably more sensitive than conventional diagnostic modalities (CDM) such as computed tomography (CT)for detection of extrahepatic abdominal and pelvic colorectal carcinoma and is complementary to CDM in imaging liver metastases. In a surgical decision-making analysis comparing CT, RIS (IMMU-4 99mTc-Fab′; CEA-Scan®), and CT plus RIS in patients with recurrent or metastatic colorectal cancer, CT plus RIS improved correct prediction of resectability by 40% and correct prediction of unresectability by 100% compared with CT alone. At the present time, RIS used in combination with CDM contributes an incremental improvement in diagnostic accuracy in colorectal cancer patients with known or suspected recurrent disease. Basic and clinical research currently in progress promises to yield agents and methods that provide rapid high-resolution imaging, high tumor-to-background ratios in all organs at risk for tumor recurrence or metastasis, negligible immuno genicity and toxicity, and a signficant further improvement in the accuracy of clinical decision making in oncology patients.

Improved tumor targeting of rhenium-186-labeled anti-human high-m.w. melanoma-associated antigen monoclonal antibody 763.74 following purification with anti-idiotypic monoclonal antibody MK2-23.

Because of its high-energy beta emissions and imageable gamma emissions, 186Re represents an attractive isotope to radiolabel monoclonal antibodies (MAbs) recognizing human tumor-associated antigens (TAAs) for radioimmunoscintigraphy (RIS) and radioimmunotherapy (RIT) of patients with malignant diseases. Application of 186Re, however, is hindered by the frequent denaturation of MAbs following exposure to the strong reducing conditions employed in the labeling procedures. To overcome this problem, we have utilized a direct labeling procedure and combined it with affinity chromatography over columns of immobilized anti-idiotypic (anti-id) MAbs which recognize idiotopes in the antigen-combining site of the radiolabeled MAb. The validity of the procedure was demonstrated with the anti-high-m.w. melanoma-associated antigen (HMW-MAA) MAb 763.74 and its corresponding anti-id MAb MK2-23. Utilizing this approach, MAb 763.74 was labeled to specific activities of 2.8 +/- 0.6 mCi/mg with 186Re. Furthermore, its immunoreactivity, which was reduced to about 30% following labeling with 186Re, was improved to about 50% by affinity chromatography over columns of anti-id MAb MK2-23. The improvement in immunoreactivity of 186Re MAb 763.74 resulted in a significant (p < 0.05) increase in targeting to human melanoma tumors grown in nude mice and an increase in sensitivity of RIS. Our results suggest that direct labeling of anti-TAA MAb with 186Re coupled with purification over affinity columns of anti-id MAb may facilitate the application of 186Re to RIS and RIT.

Synthesis and evaluation of 99mTc/ 99Tc-MAG3-biotin conjugates for antibody pretargeting strategies

Four 99mTc-MAG3-biotin conjugates were synthesized to determine their potential use in antibody pretargeting strategies for radioimmunoscintigraphy (RIS). To use these 99mTc-MAG3-biotin conjugates as model compounds for 186Re-MAG3-biotin conjugates for radioimmunotherapy (RIT), nanomolar amounts of 99Tc were added as carrier to 99mTc. The biotin derivatives used for the preparation of the conjugates—biocytin, biotin hydrazide, biotinyl-piperazine, and biotinyl-diaminosuccinic acid—differed at the site that is regarded to be susceptible to hydrolysis by biotinidase present in human plasma. All four conjugates were produced with high radiochemical purity, were stable in PBS, and demonstrated full binding capacity to streptavidin. The 99mTc/ 99Tc-MAG3-labeled biotinyl-piperazine and biotinyl-diaminosuccinic acid conjugates were stable in mouse as well as human plasma, whereas the corresponding biocytin and biotin hydrazide conjugates were rapidly degraded. The biodistribution in nude mice at 30 min after injection was similar for all conjugates, and a rapid blood clearance and high intestinal excretion were both observed. It is concluded that the metabolic routing of a conjugate containing biotin and MAG3 is dominated by these two moieties. For this reason, MAG3-biotin conjugates do not seem suited for pretargeted RIT, for which quantitative and fast renal excretion is a prerequisite to minimize radiation toxicity. However, in a pretargeted RIS approach the 99mTc-MAG3-biotin conjugates might have potential.