Radioimmunodetection of colorectal cancer

Pretargeting: A Path Forward for Radioimmunotherapy

Pretargeted radioimmunodiagnosis and radioimmunotherapy aim to efficiently combine antitumor antibodies and medicinal radioisotopes for high-contrast imaging and high-therapeutic-index (TI) tumor targeting, respectively. As opposed to conventional radioimmunoconjugates, pretargeted approaches separate the tumor-targeting step from the payload step, thereby amplifying tumor uptake while reducing normal-tissue exposure. Alongside contrast and TI, critical parameters include antibody immunogenicity and specificity, availability of radioisotopes, and ease of use in the clinic. Each of the steps can be optimized separately; as modular systems, they can find broad applications irrespective of tumor target, tumor type, or radioisotopes. Although this versatility presents enormous opportunity, pretargeting is complex and presents unique challenges for clinical translation and optimal use in patients. The purpose of this article is to provide a brief historical perspective on the origins and development of pretargeting strategies in nuclear medicine, emphasizing 2 protein delivery systems that have been extensively evaluated (i.e., biotin-streptavidin and hapten-bispecific monoclonal antibodies), as well as radiohaptens and radioisotopes. We also highlight recent innovations, including pretargeting with bioorthogonal chemistry and novel protein vectors (such as self-assembling and disassembling proteins and Affibody molecules). We caution the reader that this is by no means a comprehensive review of the past 3 decades of pretargeted radioimmunodiagnosis and pretargeted radioimmunotherapy. But we do aim to highlight major developmental milestones and to identify benchmarks for success with regard to TI and toxicity in preclinical models and clinically. We believe this approach will lead to the identification of key obstacles to clinical success, revive interest in the utility of radiotheranostics applications, and guide development of the next generation of pretargeted theranostics.

Tumor Radioimmunolocalization in a Murine System using Monoclonal Antibodies

Tumor localization was obtained in a murine system by use of 131I-labeled monoclonal antibodies, both of IgG and IgM class. The A6 IgG2 monoclonal antibody (which recognizes the gp70 of MuLV) and the B3 IgM monoclonal antibody (which recognizes a proteic structure widely exposed on chemically induced tumors), which both manifest an in vitro cytotoxic activity for various types of murine lymphomas, were injected in tumor-bearing (B6 × BALB/c)F1 mice and B6 mice, respectively, at the dose of 1 μg per mouse. The radioactivity count demonstrated an optimal tumor accumulation of the radiolabeled monoclonal antibodies 96 h after iodine injection, although an initial accumulation was already present 48 h after injection. The scanning detection was less sensitive, since at 48 h no tumor localization was possible. In the experiments with the A6 antibody, the presence of the gp70 in the circulating form, demonstrated by the detection of immunocomplexes in kidney and spleen of tumor-bearing mice injected with the A6, did not prevent radioactivity accumulation in the tumor. This accumulation was found to increase with tumor size only up to 1 g of tumor weight, then a decreased binding index was observed, whereas in the kidney the accumulation was progressive and paralleled the increase in tumor weight.

Antibody to human α-fetoprotein inhibits cell growth of human hepatocellular carcinoma cells by resuscitating the PTEN molecule: in vitro experiments

It has been proposed that α-fetoprotein (AFP) is a new member of the intracellular signaling molecule family of the phosphoinositide 3-kinase (PI3K)/AKT signaling pathway via interaction with the phosphatase and tensin homolog (PTEN). In this study, the effects of anti-human AFP antibody on the functions of PTEN were examined using an AFP-producing human hepatoma cell line. The antibody caused significant inhibition of cell growth, compared to a normal IgG control, with the accumulation of intracellular immune complexes followed by significant reduction of cytosolic functional AFP. Decrease in the amount of AKT phosphorylated on serine (S) 473 indicated that PI3K/AKT signaling was suppressed in the cells. S380-phosphorylated PTEN increased markedly by the second day after antibody treatment, with slight but significant increase in the PTEN protein level. Since phosphorylation at S380 is critical for PTEN stability, the increase in S380-phosphorylated PTEN indicated maintenance of the number of PTEN molecules and the related potential to control PI3K/AKT signaling. p53 protein (P53) significantly, but slightly increased during antibody treatment, because PTEN expression increased the stability and function of P53 via both molecular interactions. P53 phosphorylated at S20 or at S392 dramatically increased, suggesting an increase in the stability, accumulation and activation of P53. Glucose transporter 1 (GLUT1) increased immediately after antibody treatment, pointing to a deficiency of glucose in the cells. Immunofluorescence cytology revealed that antibody-treatment re-distributed GLUT1 molecules throughout the cytoplasm with a reduction of their patchy localization on the cell surface. This suggested that translocation of GLUT1 depends on the PI3K/AKT pathway, in particular on PTEN expression. Antibody therapy targeted at AFP-producing tumor cells showed an inhibitory effect on the PI3K/AKT pathway via the liberation, restoration and functional stabilization of PTEN. PTEN simultaneously induced both P53 activation and intracellular translocation of GLUT1, since these are closely associated with PTEN.

Radioimmunoscintigraphy of advanced gastrointestinal carcinomas employing I-131 labeled CEA-79 monoclonal antibody

CEA-79 is a murine IgG2a type monoclonal antibody (MoAb) generated using purified CEA from culture supernatants of a human colon cancer cell line, LS174T. The association constant and immunoreactivity of the I-131 labeled CEA-79 ranged from 2.0 to 3.2 x 10(9) l/mole, and from 54 to 74%, respectively. The purpose of this study was to evaluate the feasibility of radioimmunoscintigraphy employing MoAb CEA-79 in patients with advanced gastrointestinal carcinomas. Two mgs of MoAb CEA-79 was labeled with 111 MBq (3 mCi) of I-131, and infused intravenously in 6 stomach cancer and 16 colon cancer patients. Out of 6 patients with stomach cancer, immunoscintigraphy was able to detect the tumors in 4 cases. However, immunoscintigraphy found out tumors in all patients with colon cancer. Moreover, 1 patient with stomach cancer and 2 patients with colon cancer showed increased uptake of MoAb in the tumor lesions despite normal serum levels of CEA. We could conclude that this antibody has a potential as a new imaging agent for the diagnosis of gastrointestinal carcinoma.

Variations in radioimmunoscintigraphic detection of tumor showed by five monoclonal antibodies to carcinoembryonic antigen

Radioimmunoscintigraphy using mouse monoclonal antibodies to various parts of a carcinoembryonic antigen (CEA) molecule was performed. Four radiolabeled antibodies (F4-82, 28A, F3-30, F33-104) were injected into tumor transplanted nude mice to compare the accumulation of these antibodies in tumors. The four antibodies were accumulated selectively in CEA- producing tumors. The tumor visualization correlated with the tumor/blood radioactivity ratio, whereas the tumor/blood radioactivity ratio did not correlate with the in vitro percent binding to tumor cells or the in vivo percent injected dose in CEA-producing tumors. Among the four antibodies, F33-104 showed the highest tumor/blood radioactivity ratio and the best image quality in any CEA-producing tumor. These results suggest that the antibody which has a high tumor/blood ratio rather than high total tumor uptake may be useful for radioimmunoscintigraphy.

Radioimmunolocalization of colorectal carcinoma. A correlation among RIL results, surgical findings, serum tumor marker levels and the presence of CEA and CA 19.9 in tumor tissue: the experience of the Hospital de la Santa Creu i Sant Pau

We report a prospective study in two groups of colorectal cancer patients carried out by radio-immunolocalization (RIL) with F(ab') fragments of monoclonal antibodies against CEA and CA 19.9 labeled with 131-I. Twenty-two patients were studied before radical surgery and 12 patients after initial surgery, when progressive increase in CEA was registered. Scintigraphic images obtained in vivo in RIL studies were compared with scintigraphic images of the corresponding surgical specimens. Results were compared with known serum marker levels and with the presence and localization of markers in the excised specimens. RIL images correctly identified 13 of 23 (52%) primary tumors, with only one false positive image. Scintigraphy of surgical specimens correlated with RIL findings in 14 of 19 cases (74%). Four specimens which showed antibody uptake had not been visualized preoperatively in the RIL study. Two of them were retrovesical and were obscured by residual activity in the bladder. Nine of 13 (64%) patients with at least one elevated tumor marker were imaged. Staining pattern or intensity of antigen staining in the specimens did not correlate with RIL findings. Recurrent disease was confirmed by laparotomy or other exploration in 10 of the 12 patients with progressive CEA elevation during follow-up. Spontaneous normalization of CEA levels was observed in the remaining 2 patients. RIL studies were positive in 7 of the 10 patients with confirmed recurrent disease. Of the 3 false negative patients 2 had liver metastases and one developed clinical lung, bone and adrenal metastases 11 months later. No false positive studies were observed in this group.(ABSTRACT TRUNCATED AT 250 WORDS)

Distribution, Kinetics and Immunoscintigraphy of 131-I Labelled Intact Antifibrinogen-fibrin Antibody (AbFbg) and its F(ab')2 Fragment

131-I-labelled anti fibrin-fibrinogen antibody (AbFbg) was compared with its F(ab')2 fragment in distribution studies and by immunoscintigraphy with a view to tumour visualization in tumour bearing rats. The distribution studies indicated that the intact antibody is more concentrated in tumour tissue than the F(ab')2 fragment. By 168h after injection, when tumour-to-tissue ratios were highest in the majority of tissues, the tumour concentration of intact antibody was 3 to 4 times that of the F(ab')2 fragment. The intact antibody is more suitable than the F(ab')2 fragment for tumour imaging especially in the abdominal region where the highest tumour-to tissue ratios were obtained with intact antibody in liver, spleen, intestines and kidneys.

Radiolabeling of monoclonal antibody against carcinoembryonic antigen with 88Y and biodistribution studies

The biodistribution of the 202 monoclonal antibody against CEA labeled with 88Y by the bicyclic DTPA anhydride method was studied in normal Balb/c mice. The in vitro binding to 1 X 10(7) CO112, LS174T and WiDR colon cancer cells was 21.0, 27.3 and 18.8%, respectively. The binding to an equal number of KM-3 leukemia cells and normal human lymphocytes was 8.9 and 3.2%, respectively. Liver, spleen, kidney and blood were the tissues that showed the highest uptake of radiolabeled antibody in vivo.

Monoclonal antibodies in the treatment of cancer

Potential uses of monoclonal antibodies in anti-cancer treatment include passive serotherapy, radioisotope conjugates, toxin-linked conjugates, and chemotherapy-monoclonal antibody conjugates. The bases for these applications have been founded in research with heterologous antisera, and in some cases with monoclonal antibodies in animal tumor models. Human trials with passive serotherapy have already begun in both hematopoietic and solid tumor malignancies. Promising results have been reported in cutaneous T cell lymphoma with anti-T cell monoclonal antibody, and in nodular lymphoma with anti-idiotype monoclonal antibody. Radioisotope conjugate work appears promising for imaging in both animals and humans, and this work will lay the foundation for possible therapeutic application of radio-immunotherapy. Toxin-linked conjugates are promising in vitro and may have application in autologous bone marrow transplantation. Research with chemotherapy conjugates is also underway. Preliminary results suggest that murine monoclonal antibodies will be well tolerated clinically except in the setting of circulating cells which bear the target antigen, where rapid infusions may be associated with intolerable side effects. In certain diseases, production of endogenous anti-mouse antibodies may also limit application. Advances in the technology for human-human hybridoma production may help solve some of these problems.

Radioimmunodetection of cancer using antibodies to alpha-fetoprotein and carcinoembryonic antigen

This study reports the use of radiolabeled antibody to AFP and CEA for the detection and localization of AFP- or CEA-producing tumors. Thirty-one patients received 131I-labeled anti-AFP or anti-CEA antibodies. Photoscans were taken at 24 and 48 hours after injection of radioantibodies. In three of six patients with CEA-producing tumors, radioimmunodetection with anti-CEA antibody showed positive scans. In AFP-producing tumors, 7 of 15 patients had positive findings on immunoscintigraphy using polyclonal anti-AFP antibody, and two of nine patients had positive findings when monoclonal antibodies were used. Analysis of radioantibody in the blood after injection showed both complex and free antibody with immunoreactivity in the circulation, and smaller complexes were seen to form after administration of monoclonal antibodies.

The detection and evaluation of human tumor metastases

Many biochemical indices are purported to have clinical utility in the detection and management of neoplasia. Experience gained during the past decade tends to indicate their having a more important role in the detection and monitoring of metastases than of the primary lesion. From this present review of some of the commoner human tumours, it is concluded that such marker substances are important adjuncts in the management of germ cell and certain endocrine and endocrine-related tumours. The carcinoembryonic antigen (CEA) provides a marker for many gastrointestinal cancers, but there are no presently available substances with clinical usefulness for either breast or lung neoplasms. Alternative approaches to the detection of metastases are also presented. The particular use of antibody probes at an immunohistochemical level has been claimed to be able to detect micrometastastic disease in bone marrow or tumour-related monoclonal antibody probes may have application to other cancers in the future.

Colon-specific antigen-p (CSAp). II. Further characterization in colorectal and pancreatic cancer

The physicochemical and immunological characteristics of colon-specific antigen-p (CSAp) in plasma and in colorectal and pancreatic tumors were investigated. CSAp in the plasma of a rectal cancer patient and in a colonic carcinoma xenografted in hamsters (GW-39 tumor) appeared to have similar chromatographic properties, being of a molecular size of 4 million or more. The activities of CSAp in both plasma and tumor were similarly destroyed by treatment with a thiol reagent. Finally, identical immunological reactions in radioimmunoassay and gel diffusion tests were obtained between the CSAp's in patient plasma and in GW-39 tumor tissue. Also CSAp in human pancreatic cancers xenografted in nude mice showed a precipitin line of complete identity with CSAp extracted from GW-39 human colonic carcinoma transplants. Thus, the CSAp's found in colorectal cancer patient plasma, in colonic carcinoma, and in pancreatic cancer tissues appear to be immunologically identical.

Human chorionic gonadotropin radioantibodies in the radioimmunodetection of cancer and for disclosure of occult metastases

Radioimmunodetection (RaID) of tumors containing human chorionic gonadotropin (hCG; choriogonadotropin) was evaluated in 25 patients by injecting 131I-labeled goat antibody IgG against hCG and performing total-body photoscans with a gamma scintillation camera 24 and 48 hr later. All 10 testicular cancer patients with proven tumor sites had positive RaID results, whereas three cases without known tumor were negative. Four patients with hydatidiform mole and one with degenerative products of conception showed positive RaID results consistent with elevated serum hCG titers. Two putatively false-positive results were obtained in patients with lung or ovarian cancer, whereas a false-negative metastasis to the liver of a patient with lung cancer and an elevated serum hCG titer was observed. Of 14 tumor sites found by RaID in 10 testicular cancer patients, 4 were revealed by RaID prior to any other detection method used and provided a lead time to definitive diagnosis by other measures of a few days to greater than 1 yr. Although a number of patients had high serum hCG levels, even exceeding 3 microgram/ml, the xenogeneic antibody was capable of localizing in tumor. No adverse effects were noted in any of the patients studied. Thus, hCG RaID appears to be a safe and effective method of detecting and locating hCG-producing tumors and has been found to disclose occult testicular cancers.

Clinical radioimmunodetection of cancer with radioactive antibodies to human chorionic gonadotropin

Injection of iodine-131-labeled goat immunoglobulin G antibody to human chorionic gonadotropin (hCG) into patients with hCG-secreting trophoblastic and germinal tumors permitted tumor detection and location by external gamma-ray scintigraphy. Excision of one of the metastatic tumors located by this method indicated a tumor/nontumor ration of 39.29. The method appears to offer a new clinical tool for precisely locating hCG-producing tumors in the body, even when tumor identification by other clinical methods has failed.

Clinical studies on the radioimmunodetection of tumors containing alpha-fetoprotein

This study reports the use of radiolabeled antibodies to alpha-fetoprotein for the detection and localization of hepatocellular and germ cell carcinomas. Twelve patients with histories of histologically-confirmed neoplasia received a total dose between 1.0 and 4.4 mCi of 131I-labeled goat IgG prepared against human alpha-fetoprotein. Total-body photoscans were taken with a gamma scintillation camera at various intervals after injection of the radioactive antibody. Computer subtraction of radioactive technetium background images from the antibody 131I scans permitted the visualization of all tumor sites known to be present in 4 patients with either primary hepatocellular cancer or metastatic germ cell carcinoma of the testis. In contrast to the results with the specific antibody, radioactive normal goat IgG given to one of these patients with metastatic embryonal carcinoma of the testis failed to show equivalent localization. Among 8 patients with diverse neoplasms not believed to contain alpha-fetoprotein, 5 of 19 tumor sites showed radioactive antibody accretion, although significantly less than in the patients with liver or testicular cancer. Circulating antigen levels of up to 15,000 ng per milliliter did not prevent successful tumor imaging after intravenous injection of the radioantibody. This investigation indicates that alpha-fetoprotein-containing tumors can be detected and localized in vivo by the method of radioimmunodetection.