Imaging of colon carcinoma with 111-indium-labeled anti-CEA monoclonal antibodies (Indacea) prior to surgery

In Vitro Characterization of 177Lu-DOTA-M5A Anti-Carcinoembryonic Antigen Humanized Antibody and HSP90 Inhibition for Potentiated Radioimmunotherapy of Colorectal Cancer

Carcinoembryonic antigen (CEA) is an antigen that is highly expressed in colorectal cancers and widely used as a tumor marker. ¹³¹I and ⁹⁰Y-radiolabeled anti-CEA monoclonal antibodies (mAbs) have previously been assessed for radioimmunotherapy in early clinical trials with promising results. Moreover, the heat shock protein 90 inhibitor onalespib has previously demonstrated radiotherapy potentiation effects in vivo. In the present study, a ¹⁷⁷Lu-radiolabeled anti-CEA hT84.66-M5A mAb (M5A) conjugate was developed and the potential therapeutic effects of ¹⁷⁷Lu-DOTA-M5A and/or onalespib were investigated. The ¹⁷⁷Lu radiolabeling of M5A was first optimized and characterized. Binding specificity and affinity of the conjugate were then evaluated in a panel of gastrointestinal cancer cell lines. The effects on spheroid growth and cell viability, as well as molecular effects from treatments, were then assessed in several three-dimensional (3D) multicellular colorectal cancer spheroid models. Stable and reproducible radiolabeling was obtained, with labeling yields above 92%, and stability was retained at least 48 h post-radiolabeling. Antigen-specific binding of the radiolabeled conjugate was demonstrated on all CEA-positive cell lines. Dose-dependent therapeutic effects of both ¹⁷⁷Lu-DOTA-M5A and onalespib were demonstrated in the spheroid models. Moreover, effects were potentiated in several dose combinations, where spheroid sizes and viabilities were significantly decreased compared to the corresponding monotherapies. For example, the combination treatment with 350 nM onalespib and 20 kBq ¹⁷⁷Lu-DOTA-M5A resulted in 2.5 and 2.3 times smaller spheroids at the experimental endpoint than the corresponding monotreatments in the SNU1544 spheroid model. Synergistic effects were demonstrated in several of the more effective combinations. Molecular assessments validated the therapy results and displayed increased apoptosis in several combination treatments. In conclusion, the combination therapy of anti-CEA ¹⁷⁷Lu-DOTA-M5A and onalespib showed enhanced therapeutic effects over the individual monotherapies for the potential treatment of colorectal cancer. Further in vitro and in vivo studies are warranted to confirm the current study findings.

Pilot Trial Evaluating an 123I-Labeled 80-Kilodalton Engineered Anticarcinoembryonic Antigen Antibody Fragment (cT84.66 Minibody) in Patients with Colorectal Cancer

Purpose: The chimeric T84.66 (cT84.66) minibody is a novel engineered antibody construct (VL-linker-VH-CH3; 80 kDa) that demonstrates bivalent and high affinity (4 × 1010 m−1) binding to carcinoembryonic antigen (CEA). The variable regions (VL and VH) assemble to form the antigen-combining sites, and the protein forms dimers through self-association of the CH3 domains. In animal models, the minibody demonstrated high tumor uptake, approaching that of some intact antibodies, substantially faster clearance than intact chimeric T84.66, and superior tumor-to-blood ratios compared with the cT84.66 F(ab′)2 fragment, making it attractive for further evaluation as an imaging and therapy agent. The purpose of this pilot clinical study was to determine whether 123I-cT84.66 minibody demonstrated tumor targeting and was well tolerated as well as to begin to evaluate its biodistribution, pharmacokinetics, and immunogenicity in patients with colorectal cancer.

Experimental Design: Ten patients with biopsy-proven colorectal cancer (6 newly diagnosed, 1 pelvic recurrence, 3 limited metastatic disease) were entered on this study. Each received 5–10 mCi (1 mg) of 123I-labeled minibody i.v. followed by serial nuclear scans and blood and urine sampling over the next 48–72 h. Surgery was performed immediately after the last nuclear scan.

Results: Tumor imaging was observed with 123I-labeled minibody in seven of the eight patients who did not receive neoadjuvant therapy before surgery. Two patients received neoadjuvant radiation and chemotherapy, which significantly reduced tumor size before surgery and minibody infusion. At surgery, no tumor was detected in one patient and only a 2-mm focus was seen in the second patient. 123I-labeled minibody tumor targeting was not seen in either of these pretreated patients. Mean serum residence time of the minibody was 29.8 h (range, 10.9–65.4 h). No drug-related adverse reactions were observed. All 10 patients were evaluated for immune responses to the minibody, with no significant responses observed.

Conclusion: This pilot study represents one of the first clinical efforts to evaluate an engineered intermediate-molecular-mass radiolabeled antibody construct directed against CEA. cT84.66 minibody demonstrates tumor targeting to colorectal cancer and a faster clearance in comparison with intact antibodies, making it appropriate for further evaluation as an imaging and therapy agent. The mean residence time of the minibody in patients is longer than predicted from murine models. We therefore plan to further evaluate its biodistribution and pharmacokinetic properties with minibody labeled with a longer-lived radionuclide, such as 111In.

Fusion proteins of B7.1 and a carcinoembryonic antigen (CEA)-specific antibody fragment opsonize CEA-expressing tumor cells and coactivate T-cell immunity

Genetic engineering can be used to generate antigen-specific molecules for improved tumor immunotherapy. We have constructed genes coding for fusion proteins consisting of a high-affinity antibody single-chain antibody fragment (scFv) specific for the human carcinoembryonic antigen (CEA) and the costimulation domain of the murine B7.1 molecule (mB7.1) linked to the antibody moiety by an IgG3 peptide linker. The hybrid genes were constructed in 2 orientations, one with the scFv located N-terminal to mB7.1 and one vice versa. Soluble proteins were expressed by CHO cells, purified using anti-idiotype-affinity chromatography and characterized by tumor-cell binding and costimulation activity. When tumor cells expressing CEA on the cell membrane were opsonized with the CEA-specific costimulators, both fusion proteins specifically stimulated murine T-cell preparations to proliferate in a similar manner. Our data suggest that "costimulation coating" of tumor cells may be a suitable approach for activation of a sustained cellular antitumor response. It also provides the opportunity to increase tumor immunogenicity using easily generated soluble fusion proteins that advantageously link biological functions of both the humoral and the cellular arm of the specific immune system.

Imaging of recurrent intestinal carcinoma with indium-111-labeled anti-carcinoembryonic antigen monoclonal antibody CEA102

CEA102 is a mouse immunoglobulin G1 monoclonal antibody (mAb) that detects an epitope of carcinoembryonic antigen (CEA). The biodistribution and imaging characteristics of indium-111-labeled (111-In)-mAb CEA102 were studied in 1 primary and 9 extrahepatic recurrent intestinal carcinoma patients. Evaluation included antibody pharmacokinetics and assessment of antibody distribution in surgical specimens, in comparison with whole body imaging using a gamma camera, and imaging with single photon emission computed tomography. Selective mAb CEA102 localization to tumor tissue was demonstrated in 7 patients with tumors over 2 cm in size, and the external images correlated well with the results of surgical inspection, pathological examination, and tissue radioactivity measurements. Tumor:serum ratios ranged from 0.20:1 to 3.22:1, and serial biodistribution study of "regions of interest" also demonstrated a high radioactivity in the tumor. These results indicated the potential exploitability of the 111-In-labeled mAb CEA102 in radioimmunodetection of primary and extrahepatic recurrence of CEA-positive intestinal carcinomas.

Increased tumor localization by monoclonal antibody A7 after F(ab')2 fragmentation in athymic nude mice bearing human pancreatic carcinomas

Much recent research has been directed toward the use of monoclonal antibodies (MoAbs) for the immunodetection of solid tumors. In pancreatic cancer, conventional immunoscintigraphy using intact MoAbs remains disappointing. In this study, 125I-labeled F(ab')2 fragments produced by pepsin digestion of MoAb A7 were injected intravenously into nude mice bearing human pancreatic cancer, HPC-YS, xenografts that have previously been shown to react specifically with MoAb A7. The tumor tissue/blood ratio of 125I-labeled F(ab')2 fragments of MoAb A7 increased with time and was much higher than those for normal tissues. Moreover, the tumor tissue/blood ratio of 125I-labeled F(ab')2 fragments was greater than that of intact MoAb A7, although the F(ab')2 accumulation was less than that of intact MoAb A7 in the tumor. These results suggest that F(ab')2 fragments of MoAb A7 may be suitable carriers of radionuclides for immunodetection of human pancreatic cancer.

Immunoscintigraphy in primary colorectal cancer

Immunoscintigraphy is an experimental diagnostic nuclear medicine imaging technique that targets tumor sites with radiolabeled antibodies reactive with tumor-associated antigens. Primary tumors, regional lymph node metastases, and distant metastases have been imaged in patients with colorectal cancer, and United States Food and Drug Administration (FDA) approval of a commercial preparation of radiolabeled murine monoclonal antibodies for diagnostic use in such patients is expected soon. Immunoscintigraphy is complementary to computed tomography (CT) scanning in the evaluation of the abdomen and pelvis in patients with colorectal cancer, and it has the additional capability of serial whole body imaging for detection of distant metastases. However, the clinical utility of immunoscintigraphy is being investigated, and its precise diagnostic role in patients with primary colorectal cancer has not been adequately defined. The management of selected patients at increased risk of regional or distant spread of tumor likely would benefit from detection of occult disease and a change in clinical staging, but the routine use of immunoscintigraphy in the preoperative evaluation of patients with primary colorectal cancer is more problematic. More studies are required to determine whether it should be used to stage all patients before operation or merely be reserved for selected patients at increased risk for metastatic disease.

Autoradiographic analysis of radiolabeled anti-carcinoembryonic antigen monoclonal antibody CEA102 in colorectal cancer using computed radiography

Anti-carcinoembryonic antigen monoclonal antibody (MAb) CEA102 was produced by immunization with purified CEA and the specific accumulation of radiolabeled CEA102 in colorectal cancers was investigated by autoradiography of surgical specimens using Fuji Computed Radiography (FCR). Five patients with colorectal cancer were injected intravenously with 131I-labeled intact CEA102 or its F(ab')2. Primary tumor and liver metastases were successfully detected by external scanning with a gamma camera in 4 cases. Autoradiographic study of the surgical specimens using FCR showed predominant localization of 131I-labeled CEA102 in primary tumors and liver metastases in all cases. Even a small liver metastasis (0.5 cm) was clearly visualized in the autoradiogram by FCR. The pixel distribution curves of the density of the respective tissues in the autoradiograms by FCR showed the heterogeneity of the distribution of administered radiolabeled MAb in individual tumors, but the density of the tumors was higher than that of the normal tissues. In the quantitative distribution analysis of CEA102, the uptake of the primary tumor (mean 1.10%ID/kg) was ten-fold greater than that of the normal colon mucosa (mean 0.10%ID/kg). These results revealed that the application of MAb has great potential in radioimmunodetection as well as in antibody-directed therapy.

Preoperative imaging of colorectal cancers. Targeting the epithelial membrane antigen with a radiation-labeled monoclonal antibody

The epithelial membrane antigen (EMA) is expressed by the majority of colorectal cancers but has not previously been investigated as a target for radiation-labeled monoclonal antibodies (MoAb) in the imaging of patients with colorectal cancer. A rat IgG2a MoAb that recognizes EMA, ICR2, was labeled with Indium-111 (100 megabecquerel per milligram [MBq/mg]MoAb) using the bicyclic anhydride of the chelating agent diethylene triamine pentacetic acid (ccDTPA) and was administered intravenously to 22 patients known to have or thought to have colorectal cancer. Daily gamma camera imaging was performed for 3 days during the time between the administration of the radiation-labeled antibody and surgical procedure. At operation, the biopsies were done of the tumors and the normal colon, and the uptake of radiation-labeled MoAb was measured in a gamma well-counter. Immunocytochemistry for EMA expression also was done on resected tumors. Independent unblinded and blinded reporting was done on all scans. The sensitivity of 111In-ICR2 for detecting cancers preoperatively was 80% and 60%, respectively, on unblinded and blinded reporting, and the corresponding specificity 20% and 60%. The low unblinded specificity was attributable to a false-positive localization in severely dysplastic benign tumors (n = 2) and inflammatory tissue (n = 2). Liver metastases present in three patients were cold relative to normal liver. Lymph node metastases were localized in 1 of 6 patients preoperatively. The mean absolute uptake of 111In-ICR2 in tumor tissue was 7.75 +/- 3.77 x 10(-3) percent of injected dose per gram, and the ratio to normal colon was 2.10 +/- 0.92:1. On immunohistochemistry, EMA was expressed by 16 of the 17 primary cancers, both dysplastic adenomas, and all nodal metastatic deposits. EMA-negative tumors (1 cancer + 1 colonic lipoma) had negative antibody scans, and patients whose tumor was negative or only focally positive for EMA expression had lower tumor/normal colon ratios of radioactivity (1.30 +/- 0.26 versus 2.45 +/- 0.65, P = 0.005) on gamma well-counting of excised specimens. These results suggest a possible role for 111In-ICR2 in the detection of colorectal cancer and metastases but not its liver deposits.

Heterogeneity in antigenic expression and radiosensitivity in human colon carcinoma cell lines

A panel of human colon carcinoma cell lines were characterized regarding both antigenic heterogeneity and variations in radiosensitivity. Monoclonal antibodies were used to study the expression of carcinoembryonic antigen (CEA), gastrointestinal cancer antigen (GICA or CA 19-9) and carcinoma-associated antigen (CA-50). Radiosensitivity was studied with the clonogenic survival technique. Three cell lines, LS 174T, HCTC, and SW 1116 stained positive for all three antigens. HT-29 was positive for CA 19-9 and CA-50 whereas Caco-2 was positive for CEA and CA 19-9. The cell lines SW 620 and LIM 1215 only stained positive for one of the antigens, CA-50 and CEA, respectively. In nearly all positive cases the stainings were very heterogeneous with mixtures of positive and negative cells. One exception was the HCTC cells which stained homogeneously for the CA 19-9 and CA-50 antigens. The neuroendocrinelike COLO 320 cells were negative in all cases. The radiosensitivity varied strongly between the cell lines with Dq-values between 0.8 and 1.9, extrapolation numbers between 2.0 and 4.7, Do-values between 1.1 and 2.8. The surviving fraction at 2 Gy varied between 0.3 and 0.7 with HCTC as the most radiosensitive and HT-29 as the most radioresistant cell line. Thus, there were differences in antigenic expression and intrinsic radiosensitivity between the cell-lines and antigenic heterogeneities within each cell line. The analyzed panel of cell lines will be valuable in studies of dose-effect relations for monoclonal antibodies labeled with toxic radionuclides simulating both antigenic heterogeneity and variations in radiosensitivity.

Intraoperative localization of colorectal cancers using radiolabelled monoclonal antibodies

Radiation detectors may allow the intraoperative localization of small cancer deposits following administration of radiolabelled tumour-associated antibodies. This technique was evaluated in 16 patients with colorectal tumours (14 cancers, one adenoma, one lipoma) with the 111In-labelled monoclonal antibody (MAb) ICR2 which recognizes the tumour-associated epithelial membrane antigen (EMA). At operation counting was carried out (3 x 20 s per site) using a hand-held radiation probe over the primary lesions and any palpable lymph nodes in the mesocolon. The tumour to normal colon (T/NC) ratio of counts recorded at operation was more than 1.5:1 in eight of the 14 patients with cancer (mean(s.d.), 1.54(0.41):1) and 0.91:1 and 1.06:1 respectively in the two patients with benign tumours. Node to normal colon ratios were higher in lymph nodes containing metastases. The uptake of radiolabelled antibody (T/NC ratio) was higher in EMA-expressing cancers than in those not expressing the target antigen (mean(s.d.), 2.45(0.65):1 versus 1.40(0.20):1, P = 0.019). An abdominal tumour model was also developed. Radioactively filled containers of 0.5-10 ml representing tumour deposits were suspended in a tank of 111In solution representing the background activity found in normal tissues. The ratio of radioactivity in the 'tumour' to that of background varied from 2:1 to 8:1. The 'tumour' was considered to be detectable if the mean counts recorded over the 'tumour' exceeded the mean of counts recorded over background by three standard deviations. At a ratio of 2:1 only 'tumours' greater than 5 ml could be detected with a sodium iodide probe and those over 10 ml could be detected with a cadmium telluride (CdTe) probe. At a ratio of 8:1, 'tumours' of 0.5 ml could be detected with either probe. At all ratios and counting periods the NaI probe was more sensitive than the CdTe.

A transition metal complex (Venus flytrap cluster) for radioimmunodetection and radioimmunotherapy

A novel transition metal complex, Venus flytrap cluster (VFC), is described for the preparation of radio-labeled antibodies. VFC contained 57Co, which was held tightly between the faces of two covalently bridged carborane ligands by cluster bonding of the metal with appropriate ligand orbitals. Anti-carcinoembryonic antigen monoclonal antibody T84.66 was conjugated to 57Co-VFC with full retention of immunological activity. Biodistribution studies in nude mice bearing carcinoembryonic antigen-producing tumors showed excellent tumor localization of 57Co-VFC-T84.66. The accumulation of radionuclide in normal liver was low and independent of dose, which may reflect the stability of the radionuclide complex. These results presage the use of VFC systems for binding transition metals that are clinically useful for radioimmunodiagnosis and radioimmunotherapy.

Localization of intraperitoneal xenografts of human colon cancer by radiolabeled anti-CEA antibodies

An intraperitoneal xenograft tumor model was developed in the nude mouse to represent advanced colorectal disease in the human patient. Intraperitoneal (ip) and subcutaneous (sc) tumor xenografts were successfully localized by indium 111-labeled anti-carcinoembryonic antigen monoclonal antibodies (Indacea) administered intravenously (IV) or intraperitoneally (IP). In the sc model, tumor uptake (% injected dose per g of tumor tissue--%ID/g) was significantly improved at 72 hours postinjection when Indacea was administered IP (44.01 +/- 1.94 vs. 33.74 +/- 0.87, P less than 0.005). In the ip model, tumor uptake at 72 hours was improved with IP Indacea (28.23 +/- 5.42 vs. 19.36 +/- 5.50, P less than 0.01) and the tumor to blood ratio was significantly improved for IP Indacea (17.83 +/- 2.95 vs. 8.45 +/- 1.38, P less than 0.01). Tumor mass was not a contributing factor in these differences. This study demonstrates that ip xenografts can be successfully imaged using radiolabeled antibodies and that the IP route of administration results in better tumor uptake of the antibody in ip lesions.

Impact of radiolabeled antibody imaging on management of colon cancer

One hundred patients with known or suspected colorectal cancer were studied by radioimmunoconjugate scintigraphy prior to operation. Study subjects received murine monoclonal anticarcinoembryonic antigen labeled with indium 111 (Indacea). Sensitivity of imaging was 76 percent for primary tumors, 44 percent for hepatic metastases, 38 percent for extrahepatic abdominal metastases, and 78 percent for extraabdominal metastases. Seventeen of 46 patients (37 percent) with known or suspected hepatic metastases and no evidence of extrahepatic disease by conventional imaging methods had extrahepatic metastases at exploratory surgery. Nine of the 17 patients had disease accurately predicted by the Indacea scanning. The management of each of these nine patients was, or could have been, modified by the scan findings and unnecessary surgery eliminated. A number of patients without post-operative disease had an unexplained increase in plasma carcinoembryonic antigen level due to production of human antimouse antibody. The addition of excess mouse immunoglobulin to the plasma prior to assay blocked this artifactual increase.