Antibody-based immunological therapies.

Clinical research in the area of antibody-based tumor-targeted therapy has been driven for many years by the prospect of identifying cell surface antigens with sufficient restrictive tissue expression patterns to allow for the selective and specific accumulation of antibody in tumor tissue. Few, if any, such antibody-antigen systems have been identified which can effectively deliver a large fraction of an administered therapeutic agent to metastatic cancer. Despite this limitation, however, a greater understanding of the biological and physiological principles of tumor-targeted therapy has resulted in successful antibody-based therapy of lymphoma, colon cancer and breast cancer in recent clinical trials.

Phase I and imaging trial of indium 111-labeled anti-epidermal growth factor receptor monoclonal antibody 225 in patients with squamous cell lung carcinoma.

Murine monoclonal antibody (MAb) 225 (IgG1) against the epidermal growth factor (EGF) receptor competitively blocks EGF binding and inhibits EGF-induced activation of receptor tyrosine kinase and cell proliferation. The effect of MAb 225 was studied in a phase I trial in patients with inoperable squamous cell carcinoma of the lung, which invariably expresses high levels of EGF receptors. Groups of three patients received total doses of MAb 225 ranging from 1 mg to 300 mg. Except at the lowest dose, each infusion included 4 mg of indium 111 (111In)-labeled MAb 225. No toxicity was observed. Tumors were imaged in all patients who received doses of 20 mg or greater. Presumed metastases greater than or equal to 1 cm in diameter were imaged with doses of 40 mg or greater. Single-photon-emission-computed tomography could be carried out at the 120-mg and 300-mg doses and significantly improved tumor visualization. All patients produced anti-murine antibodies. We conclude that treatment with an MAb that inhibits EGF receptor function is safe at the doses and schedule studied. 111In-labeled MAb images squamous cell lung carcinoma; tumor uptake of the labeled MAb is dose dependent. Further studies are warranted to explore the potential therapeutic efficacy of anti-EGF receptor MAbs and other agents that act in a comparable manner.

Radiolocalization of monoclonal antibodies in hepatic metastases from human colon cancer in congenitally athymic mice.

Intrasplenic injection of the HT-29 LMM metastatic human colon cancer line reproducibly results in hepatic metastasis formation in congenitally athymic mice. HT-29-15, a murine monoclonal antibody (mAb) of the IgG1 class reactive with the HT-29 LMM line, and BL-3, an isotype-matched control antibody, were labeled with 125I. Labeled mAbs were injected i.v. in mice with hepatic metastases, and animals were sacrificed on days 3, 5, and 7. Specific mAb uptake by tumor was significantly greater than nonspecific mAb uptake, as evidenced by specific/nonspecific tumor/blood ratios (radiolocalization indices) of 3.47/1-25.6/1. Relative mAb uptake was greater by the hepatic tumors than by the splenic tumors from day 3 to day 7, although this was significant (P less than 0.05) only on day 7 (5.12 +/- 2.97 versus 1.79 +/- 0.71). Tumor/uninvolved tissue ratios were also significantly greater (P less than 0.05) for the hepatic metastases than for the splenic tumors on day 7 (12.23 +/- 3.85 versus 6.63 +/- 2.63). This murine hepatic metastasis model appears useful for evaluation of localization of mAbs to hepatic metastases from human colon carcinoma.

Radioimmunodetection of hepatic metastases from human colon cancer in nude mice with a gamma-detecting probe.

The utility of a gamma detecting probe (GDP) in the detection of experimental hepatic metastases in nude mice using radiolabeled monoclonal antibody (mAb) was assessed. Twelve mice with established hepatic metastases from the HT-29 LMM cell line, 5 mice with s.c. tumors in the left flank and 6 non-tumor-bearing control mice were given i.v. injections of 40 microCi/4 micrograms of 125I-labeled mAb HT-29-15. Six tumor-bearing mice were given i.v. injections of an isotype-matched control mAb (BL-3). Using the GDP, measurements were obtained daily over the region of the heart, the region of the liver (i.e., the right flank), and the s.c. tumor when applicable. Intraoperative measurements were obtained at laparotomy on days 5 and 7. Subsequently, the metastases, normal liver, and blood were resected and the radioactivity/g tissue was measured in a gamma well counter. External right flank/heart ratios were significantly higher in the tumor-bearing group than in controls. External measurements allowed detection of small tumors weighing only 161 +/- 87 (SD) mg and occupying 11.5 +/- 4% of the entire liver weight. Metastases counted intraoperatively with the GDP measured 1 to 7 mm in greatest diameter. The mean metastasis/heart GDP ratio was 1.7 +/- 0.4:1. Tumors weighing as little as 51 +/- 42 mg could be identified. These experimental results confirm the usefulness of the GDP for the detection of small hepatic metastases from colon cancer and illustrate important features of probe measurement of radiolabeled mAb uptake.

Serological analysis of human anti-human antibody responses in colon cancer patients treated with repeated doses of humanized monoclonal antibody A33.

Mouse monoclonal antibody A33 (mAb A33) recognizes a M(r) 43,000 cell surface glycoprotein (designated A33) expressed in human colonic epithelium and colon cancer but absent from most other normal tissues. In patients, mAb A33 localizes with high specificity to colon cancer and is retained for up to 6 weeks in the cancer but cleared rapidly from normal colon (5-6 days). As a carrier of (125)I or (131)I, mAb A33 has shown antitumor activity. Induction of strong human anti-mouse antibody (immunoglobulin; HAMA) responses in patients, however, limits the use of the murine mAb A33 to very few injections. A humanized version of this antibody (huAb A33) has been prepared for Phase I and II clinical studies in patients with colon cancer. In those studies, immunogenicity of huAb A33 has been monitored using a novel, highly sensitive BIACORE method, which allows measurement of human anti-human antibodies (HAHAs) without the use of secondary reagents. We found that 63% (26 of 41) of the patients treated with repeated doses of huAb A33 developed HAHAs against a conformational antigenic determinant located in the V(L) and V(H) regions of huAb A33. Detailed serological analysis showed two distinct types of HAHAs. HAHA of type I (49% of patients) was characterized by an early onset with peak HAHA levels after 2 weeks of treatment, which declined with ongoing huAb A33 treatment. HAHA of type II (17% of patients) was characterized by a typically later onset of HAHA than in type I and by progressively increasing HAHA levels with each subsequent huAb A33 administration. Colon cancer patients with type I HAHAs did not develop infusion-related adverse events. In contrast, HAHA of type II was indicative of infusion-related adverse events. By using this new method, we were able to distinguish these two types of HAHAs in patients while on antibody treatment, allowing patients to be removed from study prior to the onset of severe infusion-related adverse events.

Enhanced antitumor activity of combination radioimmunotherapy (131I-labeled monoclonal antibody A33) with chemotherapy (fluorouracil).

Monoclonal antibody (mAb) A33 reacts with an antigen expressed by >95% of colon cancer and normal colon epithelial cells. An earlier Phase I trial of 131I-labeled mAb A33 (131I-mAb A33) demonstrated bone marrow suppression as the dose-limiting toxicity, and although modest antitumor effects were seen, no normal colon toxicity was observed. In this study, a nude mouse model was used to test whether combinations of low-dose 131I-mAb A33 (0.1 mCi) and chemotherapy [5-fluorouracil (5-FU) or 5-FU + leucovorin, doxorubicin, or carmustine] enhance the antitumor effects, compared to 131I-mAb A33 alone or either drug regimen alone. 5-FU was administered either at 30 mg/kg/day for 5 days or at 75 mg/kg/day on days 1 and 5. In assessing the reduction in tumor volumes over the first 28 days of the experiment, 5-FU treatment (with or without leucovorin) in combination with 131I-mAb A33 showed a statistically significant additive antitumor effect compared to 131I-mAb A33 alone or to chemotherapy alone. When long-term survival was used as an end point, 38% of the mice treated with 5-FU and 131I-mAb A33 were disease free at 276 days compared to none from any other group, suggesting a synergistic effect. These data indicate that Phase II clinical trials combining radiolabeled antibody therapy with 5-FU-based treatments are warranted.

Immunization of colorectal cancer patients with modified ovine submaxillary gland mucin and adjuvants induces IgM and IgG antibodies to sialylated Tn.

Tn and sialylated Tn (sTn) are blood group-related epitopes expressed on mucins of colon carcinoma and other epithelial tumors and are, therefore, potential targets for immunological control. We have immunized 20 colorectal cancer patients at high risk for recurrence with a vaccine consisting of partially desialylated ovine submaxillary gland mucin (modified OSM) which contains both Tn and sTn determinants. Six patients were treated with modified OSM alone (group 1), eight patients were treated with modified OSM and the immunological adjuvant DETOX (group 2), and six patients were treated with modified OSM and Bacillus Calmette-Guérin (group 3). Pre- and postvaccination sera were tested by enzyme-linked immunosorbent assay and dot blot immune stains for antibodies reactive with modified OSM. Antibody titers increased in 4 of 8 patients immunized with modified OSM and DETOX, in 5 of 6 patients immunized with modified OSM and B. Calmette-Guérin, and in 0 of 6 patients receiving modified OSM without adjuvant. The specificity of induced IgM and IgG antibodies was confirmed by demonstrating reactivity with OSM, bovine submaxillary mucin, and synthetic glycoconjugates sTn-human serum albumin (HSA) and Tn-HSA in enzyme-linked immunosorbent assay and immune stains. Median IgM pre-postvaccination reciprocal titers were 20/80 for Tn-HSA and 10/320 for sTn-HSA. Low level IgG antibody titers against sTn-HSA were detected after vaccination in 7 patients. Toxicity was limited to inflammatory skin reactions at the site of vaccination resulting from the adjuvants. No inflammatory infiltrates were seen in the skin when the modified OSM vaccine was administered in the absence of an immunological adjuvant. These results demonstrate that sTn and Tn can be recognized by the human immune system and that vaccines containing these structures can be administered safely with immunological adjuvants. Attempts to augment the immunogenicity of these carbohydrate antigens by covalent attachment to immunogenic carrier proteins and the use of more potent immunological adjuvants are now being pursued.

Specific localization, gamma camera imaging, and intracellular trafficking of radiolabelled chimeric anti-G(D3) ganglioside monoclonal antibody KM871 in SK-MEL-28 melanoma xenografts.

The chimeric monoclonal antibody KM871, directed against the G(D3) antigen, is under evaluation for its potential to target melanoma. To facilitate the in vivo evaluation of biodistribution properties and measurement of pharmacokinetics, KM871 was radiolabeled with (125)I via tyrosine residues and with (111)In via the bifunctional metal ion chelator C-functionalized trans-cyclohexyl diethylenetriaminepentaacetic acid (CHX-A"-DTPA) to lysine residues. Using antigen-positive SK-MEL-28 melanoma cells, immunoreactivities of 42 and 40% cell binding were obtained, respectively, for the two radioconjugates. Binding was enhanced in the presence of added unlabeled antibody. A humanized A33 antibody was similarly labeled with the two isotopes and used as a control. To determine and compare in vivo biodistribution characteristics of KM871 radiolabeled with (111)In or (125)I, mixtures of the radioconjugates were injected i.v. into BALB/c nude mice bearing G(D3)-positive-SK-MEL-28 melanoma xenografts. Gamma camera images were acquired; groups of five mice were sacrificed at various time intervals, and tumors, blood, and tissues were analyzed. (111)In-labeled CHX-A"-DTPA-KM871 showed a maximum tumor uptake of 41.9 +/- 7.0% injected dose/g at 72 h with prolonged retention over a 15-day period. The tumor:blood ratio was 3:1 by 72 h, and higher ratios were observed at later time points. No abnormal accumulation of (111)In-labeled conjugate was found in normal tissues. In contrast, there was little accumulation of (125)I-labeled KM871 in the same tumors. The specificity of antibody localization was confirmed by the low tumor uptake values for radiolabeled control antibody. Gamma camera imaging demonstrated excellent uptake of (111)In-labeled CHX-A"-DTPA-KM871 in the xenografts. Chromatographic analyses of xenograft cytosolic extracts demonstrated tumor internalization and catabolism of radiolabeled KM871 with the formation of small molecular weight metabolites. Laser scanning confocal microscopy demonstrated that the majority of intracellular KM871 is localized to lysosomes. Despite the catabolism of the radioconjugate, a dose-dependent increase in KM871 tumor localization was shown through immunohistochemical examination of xenograft biopsies. This study demonstrates for the first time the in vivo localization of a radiolabeled anti-G(D3) monoclonal antibody to G(D3)-expressing xenografts using gamma camera scanning techniques and tumor cell internalization of KM871 tagged with a green fluorescent dye, Alexa Fluor 488, through confocal microscopy. KM871 has potential for targeting tumors in patients with melanoma.

Quantitative analysis of antibody localization in human metastatic colon cancer: a phase I study of monoclonal antibody A33.

A33 is a mouse immunoglobulin G2a (IgG2a) monoclonal antibody (mAb) that detects a heat-stable, protease- and neuraminidase-resistant epitope. The antigen is homogeneously expressed by virtually all colon cancers and in the colon mucosa but not other epithelial tissues. The biodistribution and imaging characteristics of iodine-131 (131I)-mAbA33 were studied in colorectal carcinoma patients with hepatic metastases. Antibody labeled with 2 to 5 mCi of 131I was administered intravenously (IV) 7 to 8 days before surgery at five dose levels, ranging from 0.2 mg to 50 mg, with three or more patients entered at each dose level. In addition, three patients received 2 mg 131I-mAbTA99 (an isotype-matched control mAb) together with 125I-mAbA33. Evaluation included whole-body imaging with a gamma camera, technetium-99 (99mTc)-human serum albumin blood pool scans, liver/spleen scans, abdominal computed tomographic (CT) scans, hepatic arteriograms, antibody pharmacokinetics, and assessment of antibody distribution in biopsied malignant and normal tissues. Selective mAbA33 localization to tumor tissue was demonstrated in 19 of 20 patients, and external imaging correlated with surgical inspection, pathologic examination, and tissue radioactivity. One week after antibody administration, tumor:liver ratios ranged from 6.9:1 to 100:1 and tumor:serum ratios from 4.1:1 to 25.2:1. 99mTc-albumin blood pool studies showed that liver metastases were hypovascular, emphasizing the selective localization of mAbA33 despite poor tumor-blood flow. Control mAbTA99 studies showed mAbA33 localization was antigen-specific; tumor:liver ratios were 2.3- to 45-fold higher for specific antibody. In metastatic lesions, radioisotope was localized primarily in the viable periphery; however, even the necrotic tumor core concentrated specific antibody. External imaging showed isotope visualization in some patients' large bowel; whether this represents specific antibody uptake or gastric iodine secretion is unclear.

Phase I/II study of iodine 131-labeled monoclonal antibody A33 in patients with advanced colon cancer.

PURPOSE: A phase I/II study was designed to determine the maximum-tolerated dose (MTD) of iodine 131-labeled monoclonal antibody (mAb) A33 (131I-mAb A33) administered intravenously, its limiting organ toxicity, and its radioisotope retention in tumors, and to develop preliminary evidence of antitumor activity. PATIENTS AND METHODS: Patients (N = 23) with colorectal cancer who had failed to respond to conventional chemotherapy but had not received prior radiotherapy were treated with escalating doses of 131I-mAb A33. Three or more patients were entered at each dose level, starting at 30 mCi/m2, with increments of 15 mCi/m2 to a maximal dose of 90 mCi/m2. Radiolabeling was performed to maintain a specific activity of 30 mCi/m2/4 mg mAb A33 (projected maximum, 15 mCi/mg). Patients were under strict isolation precautions until whole-body radiation levels decreased to less than 5 mrem/h at 1 m. Serial radioimmunoscintigrams were performed in some cases for up to 3 weeks after 131I-mAb A33 administration. RESULTS: All 20 patients with radiologic evidence of disease showed localization of radioisotope to sites of disease. Two patients with elevated carcinoembryonic antigen (CEA) levels and negative radiologic tests did not have positive antibody scans. One patient with a small-bowel cancer also had a negative antibody scan. The major toxicity was hematologic and was more pronounced in patients with compromised bone marrow due to prior chemotherapy. Of five patients who received 78 to 84 mCi/m2 131I-mAb A33, one had grade 3 and one grade 4 toxicity; of six patients treated with 86 to 94 mCi/m2 131I-mAb A33, two had grade 4 and one grade 1 toxicity. The MTD was determined to be 75 mCi/m2 in these heavily pretreated patients. Although the isotope showed variable uptake in the normal bowel, gastrointestinal symptoms were mild (n = 8) or absent. No major responses were observed; however, three patients had evidence of mixed responses, and CEA levels decreased in two patients without clinical or radiologic measurable disease. Immunoreactivity of radiolabeled mAb A33 decreased at the highest dose levels in preparations in which specific activity exceeded 18 mCi/mg. CONCLUSION: The A33 antigen appears to be a promising target for radioimmunotherapy of colon cancer. The modest antitumor activity of 131I-mAb A33 in heavily pretreated patients is encouraging because of its lack of toxicity in the bowel, the only antigen-positive normal tissue.

Antibody targeting in metastatic colon cancer: a phase I study of monoclonal antibody F19 against a cell-surface protein of reactive tumor stromal fibroblasts.

PURPOSE: To define the toxicity, imaging, and biodistribution characteristics of iodine 131-labeled monoclonal antibody F19 (131I-mAbF19). MAbF19 recognizes the fibroblast activation protein (FAP), a cell-surface glycoprotein not present in most normal tissues, but abundantly expressed by reactive stromal fibroblasts of epithelial cancers, including more than 95% of primary and metastatic colorectal carcinomas. PATIENTS AND METHODS: 131I-mAbF19 was administered intravenously to 17 patients with hepatic metastases from colorectal carcinoma who were scheduled for resection of localized metastases or insertion of hepatic artery catheter for regional chemotherapy. Seven to 8 days before surgery, patients received 131I-mAbF19 at three dose levels, with at least four patients entered at each level. RESULTS: No toxicity associated with intravenous 131I-mAbF19 administration was observed. Tumor images were obtained on planar and single-photon emission tomography (SPECT) scans in 15 of 17 patients with hepatic metastases, tumor-infiltrated portal lymph nodes, and/or recurrent pelvic disease. The smallest lesion visualized was 1 cm in diameter. The optimal time for tumor imaging was 3 to 5 days after 131I-mAbF19 administration. The use of image registration techniques allowed precise anatomic localization of 131I-mAbF19 accumulation. Immunohistochemical analysis of biopsy tissues showed expression of FAP in the tumor stroma (but not in normal liver) in all patients studied and confirmed that the FAP-positive tumor stromal fibroblasts were interposed between the tumor capillaries and the malignant colon epithelial cells. At the time of surgery, tumor-to-liver ratios up to 21:1 and tumor-to-serum ratios up to 9:1 were obtained. The fraction of the injected 131I-mAbF19 dose per gram tumor (%ID/g tumor) localized to hepatic metastases at the time of surgery ranged from 0.001% to 0.016%. CONCLUSION: The FAP tumor fibroblast antigen is highly expressed in primary and metastatic colorectal carcinomas and shows limited expression in normal adult tissues. This highly selective expression pattern allows imaging of colorectal carcinoma lesions as small as 1 cm in diameter on 131I-mAbF19 scans. Because of the consistent presence of FAP in the stroma of epithelial cancers and the accessibility of FAP-positive tumor stromal fibroblasts to circulating monoclonal antibodies (mAbs), this study suggests possible diagnostic and therapeutic applications of humanized mAbF19 and mAbF19 constructs with novel immune and nonimmune effector functions.

Clinical pharmacology of recombinant human tumor necrosis factor in patients with advanced cancer.

Twenty-six patients with advanced cancer refractory to standard therapy were treated with recombinant human tumor necrosis factor (rTNF) in a study aimed at determining the toxicity and tolerance of rTNF and at seeking evidence of antitumor activity. The study design involved two treatments per week for 4 weeks with alternating subcutaneous and intravenous (IV) administration, and weekly dose escalation through four levels in each patient. The dose range was 1 to 200 micrograms/m2 for IV bolus injection, and 5 to 250 micrograms/m2 for subcutaneous injection. Thirteen patients completed the full course. Early discontinuation of treatment was related to rTNF toxicity in seven cases. The major side effects were rigors, fever, headache, fatigue, and hypotension. Acute changes in granulocyte, lymphocyte, and monocyte counts, changes in serum zinc levels and plasma cortisol levels consistent with an acute phase response, and inflammation at the site of subcutaneous injection were also seen. At doses of 125 to 250 micrograms/m2, inflammation at the subcutaneous injection site was unacceptably severe. Minor changes were seen in hemostatic parameters. Hypotension was corrected by fluid administration and did not require treatment with vasopressors. Initial serum concentrations of rTNF were measured at five minutes after IV administration and were found to range from 2.5 ng/mL after a dose of 35 micrograms/m2 to 80 ng/mL after a dose of 200 micrograms/m2. The half-life of rTNF in the blood was 20 minutes. A decrease in lymph node size was observed in a patient with B cell lymphoma.

Phase I/II study of iodine 125-labeled monoclonal antibody A33 in patients with advanced colon cancer.

PURPOSE: A phase I/II study was designed to determine the maximum-tolerated dose (MTD) of iodine 125-labeled monoclonal antibody A33 (125I-mAb A33), its limiting organ toxicity, and the uptake and retention of radioactivity in tumor lesions. PATIENTS AND METHODS: Patients (N = 21) with advanced chemotherapy-resistant colon cancer who had not received prior radiotherapy were treated with a single 125I-mAb A33 dose. 125I doses were escalated from 50 to 350 mCi/m2 in 50-mCi/m2 increments. Radioimmunoscintigrams were performed for up to 6 weeks after 125I-mAb A33 administration. RESULTS: All 20 patients with radiologic evidence of disease showed localization of 125I to sites of disease. Twelve of 14 patients, who underwent imaging studies 4 to 6 weeks after antibody administration, had sufficient isotope retention in tumor lesions to make external imaging possible. No major toxicity was observed, except in one patient with prior exposure to mitomycin who developed transient grade 3 thrombocytopenia. Although the isotope showed variable uptake in the normal bowel, gastrointestinal symptoms were mild or absent, and in no case did stools become guaiac-positive. The MTD was not reached at 125I doses up to 350 mCi/m2. However, cytotoxicity assays demonstrated that patients treated with the highest dose had sufficiently high serum levels of 125I-mAb A33 to lyse colon cancer cells in vitro. Among 21 patients, carcinoembryonic antigen (CEA) levels returned to normal in one patient and decreased by 35% and 23%, respectively, in two patients; one additional patient had a mixed response on computed tomography. Additional, significant responses were observed in those patients treated with chemotherapy [carmustine [BCNU], vincristine, flourouracil, and streptozocin [BOF-Strep]) after completion of the 125I-mAb A33 study. CONCLUSION: Low-energy emission radioimmunotherapy with doses of up to 350 mCi/m2 of 125I-mAb A33 did not cause bowel or bone marrow toxicity. The modest antitumor activity in these heavily pretreated patients is encouraging because of lack of toxicity at the doses studied. The long radioactivity retention in tumors suggests that isotopes with a long half-life may have a therapeutic advantage, based on calculated dose delivery to tumor versus normal tissue. Due to the low bone marrow dose, further 125I trials with humanized mAb A33 are warranted, and controlled studies must be conducted to evaluate the combination of radioimmunotherapy and chemotherapy.

Antibody localization in human renal cell carcinoma: a phase I study of monoclonal antibody G250.

PURPOSE: To define the imaging and biodistribution characteristics of iodine 131-labeled monoclonal antibody (mAb) G250 (131I-mAbG250), which recognizes a cell-surface antigen expressed by human renal cell carcinoma (RCC). PATIENTS AND METHODS: G250 is a cell-surface antigen recognized by mAbG250 expressed by RCC but not detected in normal kidney. Clear-cell RCC, the most frequent form of RCC, shows homogeneous expression of G250, whereas non-clear-cell RCC and cancers derived from other organs generally do not express G250. Expression in normal tissues is highly restricted and limited to large bile ducts and gastric epithelium. 131I-mAbG250 was administered intravenously (IV) to 16 patients with RCC 7 to 8 days before surgery at five dose levels, with at least three patients entered at each dose level. RESULTS: Clear tumor images were observed in 12 patients with G250-positive tumors and in one of three patients with G250-negative tumors. Imaged lesions in the peritoneal cavity were confirmed at surgery. The smallest lesion visualized was 8 mm in diameter. The specificity of 131I-mAbG250 localization to tumor tissue was established by radioactivity measurements, autoradiography, and immunohistochemistry of biopsied tissues, and technetium 99-human serum albumin blood-flow studies. The fraction of the injected 131I-mAbG250 dose per gram tumor (%ID/g tumor) localized in G250-positive tumors showed a broad range, but reached levels as high as 0.02% to 0.12%. CONCLUSION: 131I-mAbG250 localized specifically to G250 antigen-positive RCC and seems to have considerable potential as an imaging agent in RCC patients. 131I-mAbG250 uptake in the tumors, relative as well as absolute, are among the highest reported for tumor biopsies obtained 8 days after IV mAb administration. Based on the specific localization and high accumulation, mAb G250 may have therapeutic potential.

Phase I/II radioimmunotherapy trial with iodine-131-labeled monoclonal antibody G250 in metastatic renal cell carcinoma.

This Phase I/II radioimmunotherapy study was carried out to determine the maximum tolerated dose (MTD) and therapeutic potential of 131I-G250. Thirty-three patients with measurable metastatic renal cell carcinoma were treated. Groups of at least three patients received escalating amounts of 1311I (30, 45, 60, 75, and 90 mCi/m2) labeled to 10 mg of mouse monoclonal antibody G250, administered as a single i.v. infusion. Fifteen patients were studied at the MTD of activity. No patient had received prior significant radiotherapy; one had received prior G250. Whole-body scintigrams and single-photon emission computed tomography images were obtained in all patients. There was targeting of radioactivity to all known tumor sites that were > or =2 cm. Reversible liver function test abnormalities were observed in the majority of patients (27 of 33 patients). There was no correlation between the amount of 131I administered or hepatic absorbed radiation dose (median, 0.073 Gy/mCi) and the extent or nature of hepatic toxicity. Two of the first six patients at 90 mCi/m2 had grade > or =3 thrombocytopenia; the MTD was determined to be 90 mCi/m2 131I. Hematological toxicity was correlated with whole-body absorbed radiation dose. All patients developed human antimouse antibodies within 4 weeks posttherapy; retreatment was, therefore, not possible. Seventeen of 33 evaluable patients had stable disease. There were no major responses. On the basis of external imaging, 131I-labeled mouse monoclonal antibody G250 showed excellent localization to all tumors that were > or =2 cm. Seventeen of 33 patients had stable disease, with tumor shrinkage observed in two patients. Antibody immunogenicity restricted therapy to a single infusion. Studies with a nonimmunogenic G250 antibody are warranted.

Analysis of the fine specificities of 11 mouse monoclonal antibodies reactive with type 2 blood group determinants.

The specificity of 11 mouse monoclonal antibodies reacting selectively with type 2 blood group structures was analyzed in detail by studying their reactivities with a panel of standard glycolipids, glycolipids from erythrocytes and blood group glycoproteins. The antibodies reacted with monofucosyl type 2 H, difucosyl type 2 structures (Le gamma) or both; none of the antibodies reacted with type 1 (H, Lea, or Leb) structures. Only a small proportion of the antibodies were completely specific for either type 2H or Le gamma structures. None of the antibodies had identical patterns of reactivity and their specificities were individually distinct. Seven antibodies preferentially agglutinated O and A2 erythrocytes. Anti-Le gamma-specific antibodies, except mAb101, did not agglutinate erythrocytes or react with glycolipids from erythrocytes, indicating the absence of Le gamma structures in erythrocyte glycolipids. The ability of some antibodies to react with A erythrocytes was shown to be due to cross-reactivity of the antibodies with type 3 (repetitive) A structures. The study demonstrates that monoclonal anti-carbohydrate antibodies tend to react with a range of related, and even distantly related, structure in a pattern characteristic of each antibody and that very few antibodies have extremely restricted specificities.

Antibodies in the therapy of colon cancer.

Clinical research in antibody-based cancer therapy has been driven for many years by the prospect of identifying cell-surface antigens with sufficiently restrictive tissue expression patterns to allow the specific targeting of antibody to tumor tissue. Few if any such antibodies capable of targeting rapidly and efficiently to solid tumors have been identified. The main reasons for this are based on the inherent pharmacokinetics and physiology of IgG, the immunoglobulin G molecule. Factors that may limit targeting potential include accessibility of tumor antigen, and antibody affinity, molecular size, and metabolism. Immunoglobulins have evolved to optimally protect an organism from foreign invaders rather than to act as an efficient carrier molecule for therapeutic reagents. Despite these potential limitations, our growing understanding of the biologic and physiologic principles that underlie targeted therapy has led to the development of a generation of novel reagents and the first "positive" clinical trials. Recent strategies for therapeutic use of antibodies in colon cancer have focused on (I) unmodified mouse IgG; (2) immune globulin as carrier for targeted delivery of radioisotopes; toxins, and therapeutic molecules; (3) genetically engineered antibody constructs redesigned for specific uses; (4) humanized, nonimmunogenic IgG structures; and (5) novel antigen targets in tumors. Genetically engineered antibody constructs provide an exciting approach to address and subsequently overcome some of the problems identified for unmodified IgG. These new constructs should increase the dose fraction localized in tumors versus normal tissue and thereby improve the delivery capacity. In contrast, strategies such as immune-mediated cytotoxicity are less dependent on the quantitative difference between the antibody fraction localized in tumor and the nonlocalized fraction. Because antibodies, which direct host cytotoxic mechanisms, become activated in the tumor only when bound to antigen, one would not expect nonspecific toxic effects from nonlocalized antibody. The hypothesis that antibodies alone can destroy tumor tissue solely by directing immune cytotoxic mechanisms is just now being tested in clinical trials evaluating a new generation of humanized antibodies.

Increased yields of IgG2a- and IgG3-secreting hybridomas after fusion of B cells from mice with autoimmune diseases.

Hybridoma technology has made the production of antigen-specific monoclonal antibodies feasible and almost routine, but the production of certain biologically desirable antibody isotypes has remained difficult. Three strains of autoimmune mice (MRL/l, NZB, and BXSB) were compared to a normal strain (BALB/c), in fusions with a BALB/c myeloma (NS-1) in order to study the rescue of relevant isotypes with the desired antigenic specificities. Mice from these four strains were immunized with colon carcinoma cells, and the hybridoma supernatants from thirty fusions were analyzed for (1) reactivity with cell surface determinants on the immunizing cell line; and (2) Ig class and subclass isotypes. We found that compared to BALB/c mice, MRL/l mice produced greater numbers, and NZB and BXSB mice comparable numbers, of cell surface-reactive hybridoma clones per fusion. MRL/l mice produced the largest number and highest percentage of cell-surface reactive IgG2a (22.4%) and IgG3 (10.6%) producing clones, followed by NZB mice which produced predominantly IgG2a clones (12.3%). BXSB mice, which have latent autoimmune disease, showed no significant difference from normal BALB/c controls (IgG2a:0.7% and IgG3:1.9% vs. IgG2a:4.8% and IgG3:4.8%). The increase in IgG2a and IgG3 clones derived from MRL/l mice was age-dependent, correlating with the age at which abnormal proliferation of T cell and splenic enlargement occurs (2-4 months). We conclude that MRL/l mice are useful for generating monoclonal antibodies of the IgG2a or IgG3 isotype, provided fusions are performed at the time of maximal lymphoproliferation.

Some monoclonal antibody reagents (C219 and JSB-1) to P-glycoprotein contain antibodies to blood group A carbohydrate determinants: a problem of quality control for immunohistochemical analysis.

Monoclonal antibodies (MAb) C219 and JSB-1 have been used extensively in the analysis of P-glycoprotein expression in normal and malignant tissues. This study demonstrates that some commercial lots of these MAb, even those supplied as purified immunoglobulins, contain contaminating anti-A blood group antibodies. In both sources of reagent, the antibody was specific for a particular A structure, known as repetitive or Type 3 A. These observations may account for earlier studies showing polymorphic variation in P-glycoprotein expression in epithelial tissues and an apparent correlation with the A blood type of the donor. Such reactivity can be eliminated by absorption of anti-P-glycoprotein reagents with A erythrocytes. These data re-emphasize the importance of evaluating MAb samples for unsuspected contaminating antibodies.

Relative therapeutic efficacy of (125)I- and (131)I-labeled monoclonal antibody A33 in a human colon cancer xenograft.

UNLABELLED: A33, a monoclonal antibody that targets colon carcinomas, was labeled with (125)I or (131)I and the relative therapeutic efficacy of the 2 radiolabeled species was compared in a human colon cancer xenograft system. METHODS: Nude mice bearing human SW1222 colon carcinoma xenografts were administered escalating activities of (125)I-A33 (9.25-148 MBq) or (131)I-A33 (0.925-18.5 MBq), (125)I- and (131)I-labeled control antibodies, unlabeled antibody, or no antibody. The effects of treatment were assessed using the endpoints of tumor growth delay and cure. RESULTS: Tumor growth delay increased with administered activity for all radiolabeled antibodies. Approximately 4.5 times more activity was required for (125)I-A33 to produce therapeutic effects that were equivalent to those of (131)I-A33. This ratio was approximately 7 for a nonspecific, noninternalizing isotype-matched, radiolabeled control antibody. Unlabeled A33 antibody had no effect on tumor growth. Approximately 10 times more activity of (125)I-A33 produced toxicity similar to that of (131)I-A33, and this ratio fell to approximately 6 for radiolabeled control antibody. CONCLUSION: Treatment with (125)I-A33 resulted in a relative therapeutic gain of approximately 2 compared with (131)I-A33 in this experimental system.