Growth arrest of solid human neuroblastoma xenografts in nude rats by natural IgM from healthy humans.

Neuroblastoma (NB) is the most common extracranial solid neoplasm of infancy and is associated with very poor prognosis in patients with advanced disease. Current therapeutic regimens of advanced NB which combine surgical resection with radiation therapy and/or chemotherapy brought some improvements, but in a significant number of patients, a cure remains elusive. Normal human serum of healthy adults contains natural IgM antibodies that are cytotoxic for human NB cells. In this study, we evaluated the anti-NB activity of these natural IgM antibodies in nude rats bearing solid human NB tumors. A single intravenous (i.v.) injection of purified cytotoxic IgM led to uptake of IgM into the tumors with massive perivascular complement activation and accumulation of neutrophil granulocytes after 24 hours. Five consecutive i.v. injections of purified cytotoxic IgM into NB-bearing animals resulted in complete growth arrest of even large and established solid tumors which lasted for several weeks after discontinuation of the injections, whereas tumors of control animals continued to grow exponentially during the observation period. These studies suggest that natural anti-NB IgM may have a potential as a novel therapeutic modality in the treatment of human NB.

Collaborating to Compete: Blood Profiling Atlas in Cancer (BloodPAC) Consortium.

The cancer community understands the value of blood profiling measurements in assessing and monitoring cancer. We describe an effort among academic, government, biotechnology, diagnostic, and pharmaceutical companies called the Blood Profiling Atlas in Cancer (BloodPAC) Project. BloodPAC will aggregate, make freely available, and harmonize for further analyses, raw datasets, relevant associated clinical data (e.g., clinical diagnosis, treatment history, and outcomes), and sample preparation and handling protocols to accelerate the development of blood profiling assays.

Participation in a clinical trial influences the future management of patients with gastro-oesophageal reflux disease in general practice.

BACKGROUND: The long-term effects of participation in trials has not been reported. A randomized-controlled trial (the ONE study) reported on the management of gastro-oesophageal reflux disease with esomeprazole in primary care, testing on-demand treatment vs. treatment courses. AIM: To evaluate the impact of participation in a trial on General Practitioners management and patient behaviour. METHODS: Management of gastro-oesophageal reflux disease was compared between General Practitioners who participated in ONE (ONE-GPs) and a random sample of General Practitioners who did not participate in ONE (Other-GPs). Symptom presentation and satisfaction with treatment was compared between patients who had participated in ONE (ONE-patients) and patients who had not (Other-patients). RESULTS: ONE-GPs prescribed on-demand treatment with proton-pump inhibitors to 47% of the patients, Other-GPs to 27%. ONE-patients consulted for significantly less symptoms compared with Other-patients. ONE-patients reported significantly higher patient satisfaction compared with Other-patients. ONE-patients used 98 doses during 6 months whereas Other-patients used 76 doses. CONCLUSIONS: Participation in a clinical trial influenced both doctors and patients. Treatment modalities introduced by the trial were used in daily practice by the General Practitioners. Patients who had participated in the trial consulted for less symptoms and used more medication, compared with patients who did not participate.

Relationship between serum concentrations of the growth factor pleiotrophin and pleiotrophin-positive tumors.

BACKGROUND: Growth factors produced by tumor cells are essential for tumor expansion and may be useful in monitoring tumor progression or therapeutic efficacy if the factors are released into the circulation. In this study, we measured serum levels of pleiotrophin, a secreted heparin-binding growth and angiogenesis factor, in mice bearing human tumor xenografts to determine whether these levels reflected overall tumor burden, and we examined the relationship between tumor expression of pleiotrophin and serum levels of this factor in patients with cancer. METHODS: Pleiotrophin in serum from mice and humans was measured by use of a highly sensitive enzyme-linked immunosorbent assay. For the clinical studies, serum specimens were obtained from 193 patients with various cancers of the gastrointestinal tract and from 28 healthy control subjects. In a subset of 64 cancer patients, serum levels of pleiotrophin were measured at the time of surgery, and tumor expression of this factor was detected immunohistochemically. All P values are two-sided. RESULTS: In mice, serum pleiotrophin levels were found to increase as a function of tumor size. In humans, elevated serum pleiotrophin levels were found in patients with pancreatic cancer (n = 41; P<.0001) and colon cancer (n = 65; P = .0079) but not in patients with stomach cancer (n = 87; P =.42). A statistically significant positive association was found between elevated levels of pleiotrophin in serum drawn at the time of surgery and expression of this factor by tumors (P<.0001). In both mice and humans, serum pleiotrophin levels dropped after successful tumor removal. CONCLUSIONS: Elevated serum pleiotrophin levels can indicate the presence of tumors expressing this factor. Monitoring serum levels of pleiotrophin may prove useful in determining the pharmacologic efficacy of cytotoxic or anti-pleiotrophin therapy.

Selective killing of human bladder cancer cells by combined treatment with A and B chain ricin antibody conjugates.

The monoclonal antibody 486P 3-12-1 raised against transitional bladder carcinoma cells was coupled to either the ricin A or B chain. The toxicity of A chain conjugates could be enhanced by addition of either free ricin B chain or by ricin B chain coupled to 486P 3-12-1 or to antibodies conjugated to ricin B and directed against the mouse monoclonal antibody. Using a two-step procedure where the A and B chains of ricin were delivered separately, the appropriate target cells 486P and 647V were killed, while the pancreatic cell line QGP-1 was not affected. The efficiency of killing by immunotoxin was independent whether free or coupled B chain was used, but B chain was essential for mediating the toxicity of the A chain. The two-step procedure enhances the selectivity of immunotoxin treatment by reducing nonspecific toxicity. Such a procedure could be applicable in vivo by direct administration to the bladder cavity.

A novel metastatic animal model reflecting the clinical appearance of human neuroblastoma: growth arrest of orthotopic tumors by natural, cytotoxic human immunoglobulin M antibodies.

Neuroblastoma (NB), the most common extracranial solid tumor in childhood is associated with poor prognosis in patients with advanced tumor stages. Natural human cytotoxic anti-NB IgM antibodies present in the serum of healthy humans are discussed as a potential novel immunotherapeutic regimen against human NB because these antibodies have been shown to affect growth arrest of solid s.c. xenografts of human NB in nude rats. Subcutaneously induced tumors, however, exhibit a different growth pattern compared with the typical growth pattern of NB tumors in humans. Therefore, we developed in this study a novel metastatic tumor model in nude rats that reflects the clinical appearance of human NB and used this model to study the therapeutic efficacy of human anti-NB IgM. Intra-aortal injection of human NB cells in nude rats resulted in the development of large invasive adrenal gland tumors and micrometastases in the liver and bones. Apparently, adrenal glands provide most favorable growth conditions for human NB cells, as documented by the preferential and rapid growth of NB cells in this location. We studied three different treatment protocols of natural human anti-NB IgM. Anti-NB IgM completely inhibited tumor formation and metastases when injected simultaneously with human LAN-1 NB cells (P < 0.05). When antibody treatment was started 6 days after tumor cell injection (i.e., micrometastatic stage), tumor growth was inhibited by 90% (P < 0.05). An anti-NB IgM therapy directed against established tumors (14 days after tumor cell injection) shrank adrenal gland tumors by 90% (P < 0.05). Analysis of the tumors revealed both complement activation and an induction of apoptosis as two independent mechanisms of antitumor function. This study strongly suggests human anti-NB IgM antibodies as new agents for the therapy of neuroblastoma.

Pleiotrophin can be rate-limiting for pancreatic cancer cell growth.

Pancreatic cancer is one of the most aggressive malignant tumors, with an overall survival rate of 2%. The identification of growth factors that contribute to the malignant phenotype can help to identify new targets for therapy. In this study, we analyzed the growth factor pleiotrophin (PTN) that was originally described as a developmentally regulated cytokine during early embryogenesis. More recently, PTN was found to be overexpressed in a variety of neuroectodermal tumors and described as an essential angiogenic growth factor in choriocarcinoma and melanoma, promoting metastatic growth. Recently, we discovered high expression levels of PTN in patients with gastrointestinal malignancies, particularly in those patients with pancreatic cancer. However, it is not known whether PTN is a contributor to the growth of pancreatic cancer or is only a bystander. We used ribozymes to deplete PTN mRNA from Colo357 pancreatic cancer cells and studied the resulting phenotype. The reduction of PTN resulted in a decrease in the proliferation rate, soft agar colony formation, and tumor growth in animals. Supplementation of cells with PTN partially reversed the ribozyme effect. The autocrine function of PTN was confirmed by using PTN-binding antibodies that inhibited the proliferation rate by 50% in Colo357 cells but also in a different pancreatic cancer cell line, Panc89. Our study identifies PTN as a new and essential growth factor for pancreatic cancer. Due to the restricted expression pattern of PTN in adults, PTN is suggested as a target for pancreatic cancer therapy.

A monoclonal antibody-cobra venom factor conjugate increases the tumor-specific uptake of a 99mTc-labeled anti-carcinoembryonic antigen antibody by a two-step approach.

Monoclonal antibodies (mabs) have considerable potential for specific cancer treatment. However, due to the antigen heterogeneity and especially the low uptake in solid tumors, mabs have not been used successfully in most clinical trials to date. This study investigates the effects of a mab-cobra venom factor (CVF) conjugate in vitro and in vivo in an orthotopic pancreatic cancer model using nude rats. CVF, a nontoxic glycoprotein from cobra venom, permanently activates the alternative pathway of complement. Coupled to a mab with tumor-binding properties, the complement activation can be targeted to the tumor tissue. We studied the activity of a mab CA19-9-CVF conjugate with the human pancreatic cancer cells PancTu I. PancTu I cells express the complement resistance factors CD46, CD55, and CD59, as we demonstrated by immunostaining, an observation that may explain the lack of cytotoxicity of the CA19-9-CVF conjugate. However, using ELISA, Western blot, and immunostaining, we showed that CA19-9-CVF activates the complement cascade, including the release of the anaphylatoxin C3a, a mediator of an inflammatory reaction. The in vivo studies of CA19-9-CVF-treated nude rats showed an increased tumor infiltration by natural killer cells and macrophages. The tumor uptake of 99Tc-labeled anti-carcinoembryonic antigen antibody was increased approximately 2-fold in rats pretreated with 70 micrograms of CA19-9-CVF, compared to animals that received an equimolar mixture of noncoupled mab and CVF. This study indicates the value of mab-CVF conjugates in adjuvant immunotherapy. mab-CVF conjugates might be useful in pretargeting approaches by increasing the uptake of a therapeutic mab.

Comparative analysis of bone marrow and venous blood isolates from gastrointestinal cancer patients for the detection of disseminated tumor cells using reverse transcription PCR.

We investigated 141 bone marrow and 104 venous blood isolates from gastrointestinal cancer patients with a cytokeratin (CK) 20-specific nested reverse transcription PCR for the detection of disseminated tumor cells at time of primary tumor resection. In colorectal cancer patients, 20 of 65 (31%) bone marrow and 9 of 52 (17%) venous blood isolates yielded a CK 20 mRNA-positive result in a stage-dependent manner. The detection rates for gastric cancer patients were 11 of 49 (22%) and 5 of 30 (17%) for bone marrow and venous blood, respectively. In pancreatic cancer patients, positive signals were found in advanced tumor stage. A duplex PCR system improved the feasibility of the test. After analyzing 70 sets of bone marrow and venous blood isolates from colorectal, gastric, and pancreatic cancer patients, we observed a higher detection rate in bone marrow isolates. Survival of patients with CK 20 mRNA-positive findings was significantly shorter than that of negatively tested patients.

Expression of a truncated 100 kDa HER2 splice variant acts as an endogenous inhibitor of tumour cell proliferation.

Overexpression of the HER2 (neu/c-erbB-2) oncogene frequently coincides with an aggressive clinical course of certain human adenocarcinomas. Expression and secretion of aberrant HER2 splice variants has been reported in various cell lines and tissues and can interfere with the oncogenic HER2 activity. Here we demonstrate, using two different approaches, that expression of a truncated 100 kDa HER2 variant which encodes the extracellular domain of HER2 (HER-ECD) inhibits growth factor-mediated tumour cell proliferation. A HER2-ECD cDNA encoding the truncated variant was overexpressed in MCF7 breast cancer cells. HER2-ECD overexpression decreased spontaneous proliferation of MCF7 cells as well as heregulin-mediated soft agar colony formation. Concomitantly, heregulin-induced phosphorylation of HER4 as well as downstream activation of p44/p42 MAP-kinases was decreased. To confirm these data, ribozymes were targeted to the 3'-untranslated region of the 2.3 kb HER2-ECD mRNA which is spontaneously expressed in MKN7 gastric cancer cells. HER2-ECD-targeted ribozymes downregulated HER2-ECD expression and enhanced EGF-mediated soft agar colony formation of MKN7 cells. In parallel, EGF-induced activation of p44/p42 MAP-kinases and activation of c-Fos expression were increased in ribozyme-transfected MKN7 cells. Finally, in RT-PCR we found a trend towards a progressive loss of 2.3 kb HER2-ECD mRNA expression in more advanced gastric tumours. These data show that the HER2-ECD variant inhibits growth factor-mediated tumour cell proliferation suggesting an important role during the progression of human cancer.

Effect of glycogenolytic agents on glycogen synthase activity in polymorphonuclear leukocytes. Evidence for a Ca2+-mediated regulation of glycogen synthase activity.

Human polymorphonuclear leukocytes were found to respond to the beta-receptor activators, adrenalin and isoproterenol, with a rapid transient increase in cyclic AMP, activation of cyclic AMP-dependent protein kinase, phosphorylase kinase, deactivation of glycogen synthase and glycogen breakdown. This response was unaffected by the presence of 10 mM EGTA. Incubation of leukocytes with phorbol myristate acetate, which stimulates the hexose monophosphate shunt by a Ca2+ mediated mechanism, resulted in activation of phosphorylase without affecting cyclic AMP-dependent protein kinase or phosphorylase kinase activity, thus indicating a Ca2+-mediated activation of phosphorylase. This was, however, unaffected by EGTA. Prolonged incubation with phorbol myristate acetate was found to result in a parallel activation of phosphorylase and glycogen synthase secondary to a pronounced depletion of cellular glycogen. Addition of glucose to polymorphonuclear leukocytes resulted in total conversion of phosphorylase a to the b form and activation of glycogen synthase, however, when EGTA was included, the response to glucose was greatly amplified, thus indicating the synthase conversion is regulated by Ca2+ sensitive mechanisms which do not involve phosphorylase kinase. Addition of adrenalin to cells previously activated by glucose resulted in an increase in the concentration of cyclic AMP and activation of cyclic AMP-dependent protein kinase but deactivation of synthase was not effectuated under these conditions.

Dephosphorylation of glycogen synthase from human polymorphonuclear leukocytes.

Leukocyte glycogen synthase (UDPglucose:glycogen 4-alpha-d-glucosyltransferase, EC 2.4.1.11) was phosphorylated to about one P1/synthase subunit by either the cAMP-dependent protein kinase or the cAMP-dependent synthase kinase. The relationship between dephosphorylation and the increase in the ratio of independence was investigated by analysis of the release of 32P-labelled phosphopeptides from the trypsin-sensitive and the trypsin-insensitive regions. The trypsin-insensitive region was predominantly dephosphorylated and a close correlation between dephosphorylation of a phosphopeptide in the trypsin-insensitive region and activation of glycogen synthase is reported for the enzyme phosphorylated in both ways.

Purification and properties of protein kinase C from bovine polymorphonuclear leucocytes.

A calcium-activated, phospholipid-dependent protein kinase (protein kinase C) was purified to near homogeneity from bovine polymorphonuclear leucocytes. The purified enzyme had a specific activity of 10 000 U/mg protein and on SDS gelelectrophoresis the Mr was 88 000. The enzyme activity was almost totally dependent upon phosphatidylserine and could be strongly activated by Ca2+ concentrations in the micromolar range. At lower concentrations of calcium (less than 1 X 10(-7) M) the enzyme was only activated by the simultaneous presence of phosphatidylserine and diolein. Phorbol 12-myristate 13-acetate mimicked the effect of diolein and partially activated the enzyme. Protein kinase C activity and the phorbolester binding protein co-purified throughout all the purification steps.

Ca2+ and phorbol ester activation of protein kinase C at intracellular Ca2+ concentrations and the effect of TMB-8.

A calcium-activated, phospholipid-dependent protein kinase (protein kinase C) was purified to near homogeneity from human polymorphonuclear leukocytes and shown to be identical to bovine protein kinase C. The Ca2+ activation of the enzyme was studied and the Ca2+ concentrations required to activate the enzyme were compared to free cytosolic Ca2+ concentrations in resting and activated polymorphonuclear leukocytes. The free calcium concentrations in the cytosol and in the enzyme assay mixture were determined using the calcium indicator quin 2. The enzyme activity was almost totally dependent upon phosphatidylserine and could be strongly activated by Ca2+ concentrations in the micromolar range, but was not activated by phosphatidylserine at Ca2+ concentrations corresponding to the intracellular free Ca2+ concentration under resting conditions. However, at similar Ca2+ concentrations (less than 2.5 X 10(-7) M) the enzyme was highly activated by phorbol 12-myristate 13-acetate (PMA) or diolein in the presence of phosphatidylserine. It was demonstrated that PMA stimulation of human polymorphonuclear leukocytes did not induce any increase in the level of the intracellular free calcium concentration. It was concluded that PMA activation of protein kinase C occurred independently of a rise in the intracellular Ca2+ concentration. K0.5 (half-maximal activation) for the PMA activation of purified protein kinase C was shown to be equivalent to the K0.5 for PMA stimulation of superoxide (O-2) production in human polymorphonuclear leukocytes, suggesting that protein kinase C is involved in activation of the NADPH oxidase. The presumed intracellular Ca2+ antagonist TMB-8 inhibited the PMA-induced superoxide production, but neither by an intracellular Ca2+ antagonism nor by a direct inhibition of protein kinase C activity.

Membrane-associated protein kinases in phorbol ester-activated human polymorphonuclear leukocytes.

Membrane-associated protein kinases in human polymorphonuclear leukocytes were studied. In unstimulated polymorphonuclear leukocytes the protein kinase C was predominantly present in the cytosol but in phorbol 12-myristate 13-acetate- (PMA-) activated cells a time and dose-dependent translocation of the kinase to the particulate fraction occurred. Two new protein kinase activities also appeared in the particulate fraction upon PMA activation. The one had a Mr of 40,000 and its activity was independent of phospholipids. The other (Mr 90,000) as partially activated by phospholipids, but separated from protein kinase C on DEAE-cellulose chromatography.

Specific detection of carcinoembryonic antigen-expressing tumor cells in bone marrow aspirates by polymerase chain reaction.

PURPOSE: To establish a sensitive assay for the specific detection of carcinoembryonic antigen (CEA)-expressing tumor cells in the bone marrow of patients with colorectal cancer and other CEA-positive carcinomas. PATIENTS AND METHODS: A CEA-specific nested reverse transcriptase (RT) polymerase chain reaction (PCR) assay was developed and optimized using limiting dilutions of a CEA-positive cancer cell line mixed with normal bone marrow cell specimens. The optimized test was then used to examine bone marrow samples obtained from 15 patients with abdominal carcinomas (colorectal, n = 10; pancreatic, n = 3; gastric, n = 2) and six patients with breast cancer. Specificity was assessed by examination of 56 negative controls (malignant hematologic disease, n = 28; nonmalignant disease conditions, n = 5; healthy bone marrow donors, n = 8; normal peripheral-blood samples, n = 15). For 11 patients with abdominal carcinomas, immunostaining evaluations were performed using an anti-CEA and an anticytokeratin antibody, and the results compared with the nested PCR assay. RESULTS: In the sensitivity calibration system, single CEA-expressing tumor cells were detected in 2 to 5 x 10(7) normal bone marrow cells. All 56 control samples failed to amplify. This demonstrates that mRNAs coding for highly homologous CEA-related antigens expressed by various lineages of blood cells do not interfere. Bone marrow samples from 10 of 15 patients with abdominal cancers and four of six breast cancer patients scored positive, indicating micrometastatic bone disease. Four of 11 samples from the gastrointestinal cancer patients were found to be positive by the PCR method, but were negative with the immunocytology method. CONCLUSION: Since approximately 30% of the colorectal carcinoma patients that score negative in immunocytology staining of bone marrow samples have been reported to relapse, earlier diagnosis of the presence of malignant cells is needed. Our result that samples scoring positive in the described CEA-specific PCR test remained negative by two immunostaining methods suggests a higher sensitivity. We conclude that PCR amplification of CEA mRNA may lead to an earlier diagnosis of micrometastatic bone disease in patients with CEA-expressing carcinomas.

Disseminated tumor cells in pancreatic cancer patients detected by immunocytology: a new prognostic factor.

Using an immunocytological approach, we previously showed that disseminated cancer cells are frequently found in peritoneal cavity and bone marrow samples of gastrointestinal and pancreatic cancer patients. Recently, we demonstrated that the detection of isolated tumor cells could serve as a new prognostic factor in gastric and colorectal cancer. Thus far, no conclusive data concerning the clinical implication of minimal residual disease in pancreatic cancer exist. In this study, we investigated peritoneal lavage and bone marrow samples of 80 pancreatic cancer patients to determine the predictive value of immunocytologically detected disseminated tumor cells. Therefore, immunocytological findings were correlated with the clinical follow-up data (median observation time, 10.7 months; range, 2-61 months), and the findings in peritoneal cavity and bone marrow samples were compared. Fifty-two % of the patients showed minimal residual disease at least in one compartment (39% positive lavage and 38% positive bone marrow samples). The detection rate of isolated tumor cells increased in parallel to the tumor stage. The presence of tumor cells in the peritoneal cavity significantly correlated with the survival time of the patients (P = 0.0035). In bone marrow samples, a strong trend was seen (P = 0.06). The evaluation of both compartments increased the number of positive patients and resulted in a highly significant correlation: all patients who were positive in at least one compartment died within 18 months, whereas negative patients showed a 5-year survival rate of 30% (P<0.0001). We recommend immunocytological investigation of peritoneal cavity and bone marrow samples as a new prognostic marker in pancreatic cancer patients.

Controlled ribozyme targeting demonstrates an antiapoptotic effect of carcinoembryonic antigen in HT29 colon cancer cells.

PURPOSE: Clinical studies suggest that carcinoembryonic antigen (CEA) is associated with metastatic progression of colon cancer. However, the biological function of CEA is not well understood. We have established an approach that allows studying of CEA function within the intact pathophysiological context of human colon cancer cells. EXPERIMENTAL DESIGN: We expressed CEA-targeted ribozymes under control of a tet-off promoter system in human HT29 colon cancer cells. This approach allows regulation of CEA levels on the mRNA and protein level by 50% and enables screening analysis of CEA-mediated changes of gene expression by cDNA microarray analysis. RESULTS: Comprehensive analysis of 273 genes revealed that CEA affects expression of various groups of cancer-related genes, in particular cell cycle and apoptotic genes. Although cell cycle gene expression showed a balanced bidirectional dysregulation, apoptotic genes were unidirectionally down-regulated by CEA. In parallel phenotypic studies, CEA did not affect cell cycle or proliferation rate. However, CEA significantly protected HT29 cells from undergoing apoptosis under various conditions, including confluent growth, UV light, IFN-gamma treatment, and treatment with 5-fluorouracil. CONCLUSIONS: Our study suggests that CEA has an important regulatory role in apoptosis, and we propose that CEA is a survival factor for colon cancer cells.

Membrane-associated protein kinase C activity in superoxide-producing human polymorphonuclear leukocytes.

Protein kinase C activity was studied in superoxide-producing human polymorphonuclear leukocytes. Using equivalent cell concentrations, superoxide production and particulate fraction-associated protein kinase C activity increased in parallel in phorbol 12-myristate 13-acetate (PMA), oleoyl-acetyl-glycerol (OAG), opsonized zymosan, and A23187-activated leukocytes. Also, an increase in particulate fraction-associated phospholipid-independent kinase activity was observed upon stimulation with these activators. In contrast, in formyl-methionyl-leucine-phenylalanine (FMLP)-activated cells the increase in superoxide production was only accompanied by an increase in particulate fraction-associated protein kinase C activity if the cells were pretreated with cytochalasin B. Purified protein kinase C activity was stimulated by OAG and PMA, whereas no stimulation was observed using A23187 or opsonized zymosan. It is suggested that the activation induced in human neutrophils by PMA, OAG, opsonized zymosan, and A23187 involves a tight membrane association of phospholipid-dependent and -independent protein kinase activity. This contrasts to FMLP-activated neutrophils, in which a membrane-bound form is only observed after pretreatment with cytochalasin B.

Complement killing of human neuroblastoma cells: a cytotoxic monoclonal antibody and its F(ab')2-cobra venom factor conjugate are equally cytotoxic.

Only a few monoclonal antibodies mediate complement lysis of tumor cells, but for several antibodies it has been demonstrated that a complement-activating function can be introduced by covalent coupling of cobra venom factor (CVF), a non-toxic glycoprotein which is a structural and functional homologue of human complement component C3. In this study we compared the efficacy of complement killing of human neuroblastoma cells by the complement-activating monoclonal antibody 3F8 directed against the GD2 ganglioside antigen with that of its F(ab')2-CVF conjugate. At equal numbers bound per cell the 3F8 antibody and the 3F8 F(ab')2-CVF conjugate were found to be equally cytotoxic in the presence of complement from several species including human. Maximal killing reached up to 98%. The kinetics of killing and the bivalent metal requirement confirmed that the cytotoxic activity of the 3F8 antibody is mediated via the classical pathway and that of the 3F8 F(ab')2-CVF conjugate via the alternative pathway. To achieve a comparable degree of killing, an approximately eight-fold higher concentration of the 3F8 F(ab')2-CVF conjugate was required which appears to be a consequence of the approximately eight-fold lower binding activity of the 3F8 F(ab')2-CVF conjugate compared to the intact 3F8 antibody. Our data suggest that the coupling of CVF to non-cytotoxic antibodies allows the generation of conjugates with a cytotoxic activity similar to that of inherently cytotoxic antibodies.