Radioimmunodetection of colorectal carcinoma using technetium-99m-labeled Fab' fragments of the IMMU-4 anti-carcinoembryonic antigen monoclonal antibody

In vivo near-infrared fluorescence imaging of carcinoembryonic antigen-expressing tumor cells in mice

PURPOSE

To prospectively depict carcinoembryonic antigen (CEA)-expressing tumors in mice with a high-affinity probe consisting of a near-infrared (NIR) fluorochrome and the clinically used anti-CEA antibody fragment arcitumomab.

MATERIALS AND METHODS

This study was approved by the regional animal committee. By coupling a NIR fluorescent (NIRF) cyanine dye (DY-676) to a specific antibody fragment directed against CEA (arcitumomab) and a nonspecific IgG Fab fragment, a bio-optical high-affinity fluorescent probe (anti-CEA-DY-676) and a low-affinity fluorescent probe (FabIgG-DY-676) were designed. The dye-to-protein ratios were determined, and both probes were tested for NIRF imaging in vitro on CEA-expressing LS-174T human colonic adenocarcinoma cells and CEA-nonexpressing A-375 human melanoma cells by using a bio-optical NIR small-animal imager. In vivo data of xenografted LS-174T and A-375 tumors in mice (n = 10) were recorded and statistically analyzed (Student t test).

RESULTS

The dye-to-protein ratios were determined as 3.0-3.5 for both probes. In vitro experiments revealed the specific binding of the anti-CEA-DY-676 probe on CEA-expressing cells as compared with CEA-nonexpressing cells; the FabIgG-DY-676 probe showed a markedly lower binding affinity to cells. In vivo LS-174T tumors xenografted in all mice could be significantly distinguished from A-375 tumors with application of the anti-CEA-DY-676 but not with that of the FabIgG-DY-676 at different times (2-24 hours, P < .005) after intravenous injection of the probes. Semiquantitative analysis revealed maximal fluorescence signals of anti-CEA-DY-676 to CEA-expressing tumors about 8 hours after injection.

CONCLUSION

Findings of this study indicate the potential use of the high-affinity probe anti-CEA-DY-676 for specific NIRF imaging in in vivo tumor diagnosis.

Antibody-based diagnostic and therapeutic innovations for human cancer

As adjuvants, antibody-based diagnostic and therapeutic innovations can potentially decrease morbidity and mortality associated with many human malignancies. Current strategies employing genetically modified constructs may improve tumor penetration and increase versatility.

Radical surgery for extensive rectal cancer: is it worthwhile?

In a small proportion of patients with extensive primary or locally recurrent rectal cancer, disease remains confined to the pelvis for a prolonged period. Symptoms are highly prejudicial to quality of life and often refractory to treatment short of extirpative surgery. Cure requires en bloc excision of all involved pelvic viscera with tumor-free margins. The pelvic exenterations (PE) are the most radical operations for rectal cancer. PE carries a high risk of perioperative morbidity and mortality, and has profound functional, psychological, and psychosexual implications for patients. Careful preoperative counseling regarding surgical risks and the impact of PE on body function and image is indispensable; the patient's consent must be truly informed. Patients with major medical or psychiatric/emotional comorbidity and those who are mentally incompetent are not candidates. Tenesmus and central pelvic/perineal pain are amenable to PE whereas radicular pain is not; sciatica and lower extremity lymphedema portend unresectability. Extrapelvic disease should be excluded preoperatively. While invaded sacrum can be resected en bloc with involved viscera (sacropelvic exenteration), fixity of tumor to the pelvic sidewall(s) in nonirradiated patients almost invariably implies unresectability. Other contraindications to PE include invasion of the proximal (S1 or higher) lumbosacral spine or lumbosacral plexus/sciatic nerves, ureteric obstruction proximal to the ureterovesical junctions, and encasement of the external or common iliac vessels by tumor. PE for advanced primary rectal carcinoma yields 5-year survival of over 40%; when performed for recurrent disease, long-term salvage rates are not as high. While radical surgery is rarely indicated for palliation, PE in carefully selected (good performance status and life expectancy, complete excision of all gross disease) incurable patients results in abrogation of disabling symptoms and reasonable intervals of high-quality survival.

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-111-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 reticuloendothelial 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 immunogenicity. 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 immunogenicity and toxicity, and a significant further improvement in the accuracy of clinical decision making in oncology patients.

Probe-guided surgery for colorectal cancer

Anti-CEA-scintigraphy turned out to be very reliable in detecting primary and recurrent colorectal cancer, its overall accuracy being more than 90%. The intraoperative application of this technology should provide similar results when focussing at extrahepatic tumor deposits, for example in lymph nodes, thus allowing accurate staging of the underlying disease. To test this hypothesis we launched the following feasibility study the results of which are compared to those reported in the recent literature. We investigated 20 patients, six with rectum and 14 with colon cancer. 24 hours before surgery they were intravenously given 1 ml of a fab'-fragment-antibody to CEA, labeled with 25 mCi of 99mTc (CEA-Scan). During surgery the radioactivity in lymph glands regional to the tumors was measured and compared to the much lower activity in healthy nodes. For this we used a scintillation probe (C-Trak, Care Wise, Inc., Morgan Hill, CA). All lymph nodes of interest were then excised and submitted to frozen section pathology. In 7 out of 20 cases scintimetry led to an up-staging of the disease. In addition we found metastatic spread to lymph nodes that were basically not regional to the primary tumor (retroperitoneum, renal hilum etc.). Scintimetry can precisely identify even very small tumor deposits. So it leads to accurate staging while surgery is still ongoing. In a further step the concept of sentinel node diagnosis, which is right now being clinically evaluated, may some day be applied in colorectal surgical oncology.

Clinical imaging of cancer metastasis

Tumour imaging is an essential part of the practice of oncology, with a crucial role in screening programmes and in diagnosis and staging of established disease. Furthermore, the assessment of tumour size by imaging, usually with computer tomography (CT) scanning, is a key component in determining the tumour response to therapy both in clinical trials and in daily oncology practice. Techniques such as CT, ultrasound (US) and magnetic resonance imaging (MRI) provide high resolution anatomical images with detailed structural information. However, these imaging modalities yield limited functional information on the tumour tissues and often cannot distinguish residual disease from non-viable or necrotic tumour masses, nor can they detect minimal residual disease. In contrast, radiopharmaceutical imaging and, in particular, positron emission tomography (PET) can give some functional information about the underlying tissues. The possibility of refining these techniques and also the emergence of newer imaging modalities that can detect changes in cancers at the physiological, cellular or molecular levels, gives rise to the notion that these methods will have implications for drug development strategies and also future clinical management. In this review, we briefly discuss the current role of imaging in clinical practice, describe some of the advances in imaging modalities currently undergoing evaluation, and speculate on the future role of these techniques in developmental therapeutics programmes.

Effect of radioimmunoscintigraphy on the management of recurrent colorectal cancer

BACKGROUND

Radioimmunoscintigraphy (RIS) is being used increasingly as a new investigation in the diagnosis of recurrent colorectal cancer. This study assessed the efficacy of 99mTc-radiolabelled PR1A3 scanning in a cohort of patients with possible recurrent colorectal cancer and the effects of scan interpretation on subsequent clinical management.

METHODS

The scans and case notes of patients scanned over a 3-year period were reviewed.

RESULTS

Forty-seven scans in 40 patients were available for analysis. In 39 instances in which scan interpretation could be verified accurately, sensitivity for recurrent colorectal cancer was 22 of 23 (96 per cent), specificity for recurrent colorectal cancer was eight of 16 (50 per cent), positive predictive value for recurrence was 22 of 30 (73 per cent) and negative predictive value for recurrence was eight of nine (89 per cent). In 16 of the 40 patients, scan interpretation strengthened a management decision or altered management. This was beneficial to ten patients and possibly detrimental to six.

CONCLUSION

This study demonstrated that RIS is sensitive in the detection of recurrent colorectal cancer and benefited the patient in one-quarter of cases. For the majority of patients, accurate detection of recurrent disease cannot be followed by curative therapy, but there is an important subgroup of patients in whom RIS alters management beneficially. However, a randomized prospective study is needed to confirm this.

Progress in nuclear medicine imaging of cancers

Nuclear imaging is assuming an increasing role in the management of patients with cancer. A variety of new radiopharmaceuticals, several antibody or peptide based, as well as innovative uses of existing radiopharmaceuticals, mean that most nuclear medicine departments equipped with standard imaging devices can image the single photon imaging agents without difficulty.

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.

Tumor localization of anti-CEA single-chain Fvs: improved targeting by non-covalent dimers

BACKGROUND

Genetic engineering can produce novel antibody fragments with improved properties for applications such as tumor targeting in vivo.

OBJECTIVES

To produce stable monomeric (27 kDa) and dimeric (55 kDa) forms of a single-chain Fv (scFv) from the anti-carcinoembryonic antigen (anti-CEA) antibody T84.66, and assess the targeting and biodistribution properties in an animal model.

STUDY DESIGN

ScFv were constructed with either a 28 or 14 amino acid connecting peptide and expressed by secretion from E. coli. Following affinity purification, proteins were characterized by gel electrophoresis and mass spectrometry. Binding properties were assessed by size exclusion HPLC after incubation with antigen, and affinities determined by surface plasmon resonance. The shorter linker favored formation of dimers (and higher multimers) which showed unusual stability. ScFv were radiolabeled with 125I for tumor targeting and biodistribution studies of monomeric or dimeric forms were conducted in athymic mice bearing LS174T human colorectal carcinoma xenografts.

RESULTS

125I-scFv monomers and dimers targeted exhibited rapid clearance kinetics in tumor-bearing mice. Nevertheless, the anti-CEA scFvs targeted very well to xenografts, leading to high tumor: normal organ ratios (greater than 20:1 at 24 h) for both forms. Tumor localization of the non-covalent dimers was much higher than monomers, reaching 10-15% injected dose per gram at 1 h.

CONCLUSION

Non-covalent dimers of scFv (also known as diabodies) are stable, easy to produce and show excellent targeting as compared to monomeric scFv, probably due to increased mass and valency.

Radioimmunodetection of human cervical carcinoma xenograft by 111In-labeled monoclonal antibody MAb Cx-99

Radioimmunodetection (RAID) is more sensitive and specific than conventional diagnostic methods. In this study, a monoclonal antibody against cervical carcinoma antigen, MAb Cx-99, was labeled with 111Indium (111In). This immunoconjugate was intravenously injected into athymic nude mice bearing cervical squamous cell carcinoma (SCC) xenografts. The tissue distribution study showed that the xenograft tumor had higher binding activity than most other tissues after 48 h from injection, demonstrated by localization ratio of tumor of tissues (c.p.m./g) against blood (c.p.m./g). However, this localization ratio was also high in the liver, spleen and kidney. The imaging study by immunoscintigraphy also showed that the tumor and liver were distinct from other background tissues 2 days after injection. This preliminary study showed that 111In-labeled MAb Cx-99 may have potential for RAID of cervical cancer, especially for tumors in the pelvis.

Radiolabelled monoclonal antibodies in tumour imaging and therapy: out of fashion?

The initial enthusiasm for the development of diagnostic and therapeutic studies involving the use of monoclonal antibodies was replaced by scepticism as hopes remained unfulfilled. Against this background one needs to ask whether immunoscintigraphy (IS) serves clinical needs effectively and whether radioimmunotherapy (RIT) has a future. The current review considers these questions by reference to relevant studies. Taking colorectal cancer as an example, an appraisal is offered of the ability of IS to detect disease at an early stage and thereby to reduce mortality, and of the influence of the results of IS on patient management. It is concluded that in a limited number of cases of colorectal cancer and other solid tumors, IS will allow surgery to be performed at a stage where cure is still possible because of its ability to detect early recurrence. Turning to RIT, the results of studies in respect of various tumour types are reviewed, with due attention to reported toxicity. As regards colorectal cancer, no consistent therapeutic effects have been achieved, and myelotoxicity is typically the dose-limiting factor. Thus many questions remain to be answered, regarding antigens to be targeted, fractionation schedule, the use of "humanised" antibodies, choice of radionuclide and the use of intact immunoglobulins or fragments. These questions are considered. Overall it is concluded that the most promising application of RIT is as adjuvant therapy in patients with minimal residual disease, and a controlled multicentre trial is recommended. The development of more potent radio-immunoconjugates for therapeutic and ultimately diagnostic purposes will contribute to the improvement and development of IS by increasing its potential to influence prognosis.