Identification of Cell Surface Straight Chain Poly-N-Acetyl-Lactosamine Bearing Protein Ligands for VH4-34-Encoded Natural IgM Antibodies.

B cell binding and cytotoxicity by human VH4-34-encoded Abs of the IgM isotype has been well documented. A VH4-34-IgM has recently shown a favorable early response in a phase 1 trial for treatment of B cell acute lymphoblastic leukemia. Although its B cell ligand has been identified as straight chain poly-N-acetyl-lactosamine (SC-PNAL), the carrier of the sugar moiety has not been identified. Using nanoelectrospray ionization mass spectrometry, we identify the metabolic activation related protein complex of CD147-CD98 as a major carrier of poly-N-acetyl-lactosamine (SC-PNAL) on human pre-B cell line Nalm-6. Previous studies have suggested CD45 as the SC-PNAL carrier for VH4-34-encoded IgG Abs. Because Nalm-6 is CD45 negative, human peripheral blood B lymphocytes and human B cell line, Reh, with high CD45 expression, were examined for SC-PNAL carrier proteins. Western blot analysis shows that the CD147-98 complex is indeed immunoprecipitated by VH4-34-encoded IgMs from human peripheral blood B lymphocytes and human B cell lines, Reh, OCI-Ly8, and Nalm-6. However, CD45 is immunoprecipitated only from peripheral B lymphocytes, but not from Reh despite the high expression of CD45. These results suggest that human B cells retain SC-PNAL on the CD147-98 complex, but modulate the sugar moiety on CD45. Because the carbohydrate moiety may act as a selecting Ag for VH4-34 autoantibody repertoire, its differential expression on proteins may provide a clue to the intricate atypical regulation of the VH4-34 gene.

IgG Subclasses and Isotypes of VH4-34 Encoded Antibodies.

VH4-34 gene encoded autoantibodies are elevated in systemic lupus erythematosus (SLE) and in other diseases associated with B-cell hyperproliferation/dysfunction. One of the autoantigens recognized by VH4-34-encoded antibodies are branched/linear poly N-acetyl lactosamine chains. Since the anti-carbohydrate response in humans is dominated by the IgG2 subclass, here we tested whether VH4-34 encoded IgG showed similar subclass segregation. Serum samples from SLE, infectious mononucleosis, nasopharyngeal carcinoma and hepatitis-C were analyzed. Levels of VH4-34-encoded IgM and IgA isotypes were also tested. VH4-34-IgM and IgA were elevated in all four clinical conditions. VH4-34-IgG was detected in the IgG1 and IgG3 subclass but not in the IgG2 and IgG4 subclass. Interestingly, VH4-34-IgG3 was also detected in serum samples of normal healthy adults. These observations are discussed in context of the VH4-34 gene regulation. VH4-34 repertoire development is of interest since it is the only human VH gene profoundly overrepresented in the naïve repertoire but counter-selected for antibody secretion. VH4-34 B-cell could thus become a unique tool to inspect germinal center independent/dependent pathways of subclass and isotype-specific antibody secretion.

Phase I trial of a novel human monoclonal antibody mAb216 in patients with relapsed or refractory B-cell acute lymphoblastic leukemia.

BACKGROUND: This phase I trial was conducted to determine the safety and pharmacokinetics of monoclonal antibody 216, a human monoclonal Immunoglobulin M antibody targeting a linear B-cell lactosamine antigen, administered alone and in combination with vincristine in patients with relapsed or refractory B-cell acute lymphoblastic leukemia, and to preliminarily assess tumor targeting and efficacy. DESIGN AND METHODS: Three cohorts of patients received escalating doses of monoclonal antibody 216 administered as an intravenous infusion. In the case of poor response to the first dose of monoclonal antibody 216 alone, defined as less than 75% reduction in peripheral blood blast count, a second dose of the antibody with vincristine was given between days 4 and 7. Responses were assessed weekly until day 35. Serum concentration of monoclonal antibody 216 was measured before and after infusion. Monoclonal antibody 216 targeting was determined with an anti-idiotypic antibody to monoclonal antibody 216 and preliminary efficacy was analyzed by changes in peripheral blood blasts. RESULTS: Thirteen patients were enrolled. One episode of grade 3 epistaxis was the only dose-limiting toxicity observed. All patients showed a poor response to the first monoclonal antibody 216 infusion with a decrease in peripheral blasts from 6-65% in 9 patients. In 8 patients, addition of vincristine to monoclonal antibody 216 resulted in an average reduction of the peripheral blasts of 81%. One patient without peripheral blasts achieved a hypoplastic marrow without evidence of leukemia after one infusion of monoclonal antibody 216 and monoclonal antibody 216/vincristine each. Monoclonal antibody 216 was detected on peripheral blasts in all patients. CONCLUSIONS: Treatment with monoclonal antibody 216 in combination with vincristine is feasible and well tolerated in patients with relapsed or refractory B-cell acute lymphoblastic leukemia. Binding of monoclonal antibody 216 to leukemic blasts was efficient, and favorable early responses were observed.

Taxol-oligoarginine conjugates overcome drug resistance in-vitro in human ovarian carcinoma.

OBJECTIVE: Multidrug resistance is the major cause of failure of many chemotherapeutic agents. While resistance can arise from several factors, it is often dominated by drug efflux mediated by P-glycoprotein (P-gp), a membrane-bound polysubstrate export pump expressed at high levels in resistant cells. While co-administration of pump inhibitors and a drug could suppress efflux, this two-drug strategy has not yet advanced to therapy. We recently demonstrated that the reversible attachment of a guanidinium-rich molecular transporter, polyarginine, to a drug provides a conjugate that overcomes efflux-based resistance in cells and animals. This study is to determine whether this strategy for overcoming resistance is effective against human disease. METHODS: Tumor samples from ovarian cancer patients, both malignant ascites cells and dissociated solid tumor cells, were exposed to Taxol-oligoarginine conjugates designed to release free drug only after cell entry. Cell viability was determined via propidium-iodide uptake by flow cytometry. To analyze bystander effect, toxicity of the drug conjugates was also tested on peripheral blood leucocytes. RESULTS: Human ovarian carcinoma specimens resistant to Taxol in vitro demonstrated increased sensitivity to killing by all Taxol-transporter conjugates tested. These studies also show that the drug conjugates were not significantly more toxic to normal human peripheral blood leukocytes than Taxol. CONCLUSIONS: These studies with human tumor indicate that oligoarginine conjugates of known drugs can be used to overcome the efflux-based resistance to the drug, providing a strategy that could improve the treatment outcomes of patients with efflux-based drug-resistance.

Ovarian carcinoma glyco-antigen targeted by human IgM antibody.

Epithelial Ovarian Cancer (EOC) cells expression of a novel carbohydrate antigen was defined using a human VH4-34 encoded IgM monoclonal antibody (mAb216). MAb216 binds to a poly N-acetyllactosamine epitope expressed on B cells and kills normal and malignant B cells in vitro and in vivo. EOC patient ascites and EOC cell lines were used to study the anti tumor effect of mAb216. Various assays were used to characterize the epitope and demonstrate antibody-mediated binding and cytotoxicity in EOC. Drug and antibody combination effects were determined by calculating the combination index values using the Chou and Talalay method. MAb216 displays direct antibody mediated cytotoxicity on a population of human EOC tumor and ascites samples and EOC cell lines, which express high amounts of poly N-acetyllactosamine epitope, carried by CD147/CD98. Eighty four percent of patient samples, including platin resistant, had a tumor population that bound the monoclonal antibody. The binding pattern of mAb216 and mechanism of cytotoxicity was similar to that seen on normal and malignant B cells with unique general membrane disruption and "pore" formation. In vitro incubation with mAb216 and cisplatin enhanced killing of OVCAR3 cell line. In EOC cell lines percent cytotoxicity correlated with percent expression of epitope. Although in vitro data shows specific EOC cytotoxicity, for possible treatment of EOC MAb216 would need to be evaluated in a clinical trial with or without chemotherapy.

Structure-activity relationship of purine ribonucleosides for inhibition of hepatitis C virus RNA-dependent RNA polymerase.

As part of a continued effort to identify inhibitors of hepatitis C viral (HCV) replication, we report here the synthesis and evaluation of a series of nucleoside analogues and their corresponding triphosphates. Nucleosides were evaluated for their ability to inhibit HCV RNA replication in a cell-based, subgenomic replicon system, while nucleoside triphosphates were evaluated for their ability to inhibit in vitro RNA synthesis mediated by the HCV RNA-dependent RNA polymerase, NS5B. 2'-C-Methyladenosine and 2'-C-methylguanosine were identified as potent inhibitors of HCV RNA replication, and the corresponding triphosphates were found to be potent inhibitors of HCV NS5B-mediated RNA synthesis. The data generated in the cell-based assay demonstrated a fairly stringent structure-activity relationship around the active nucleosides. Increase in steric bulk beyond methyl on C2, change in the stereo- or regiochemistry of the methyl substituent, or change of identity of the heterobase beyond that of the endogenous adenine or guanine was found to lead to loss of inhibitory activity. The results highlight the importance of the ribo configuration 2'- and 3'-hydroxy pharmacophores for inhibition of HCV RNA replication in the cell-based assay and demonstrate that inclusion of the 2'-C-methylribonucleoside pharmacophore leads to increased resistance to adenosine deaminase and purine nucleoside phosphorylase mediated metabolism.

Structure-activity relationship of heterobase-modified 2'-C-methyl ribonucleosides as inhibitors of hepatitis C virus RNA replication.

Hepatitis C virus infection constitutes a significant health problem in need of more effective therapies. We have recently identified 2'-C-methyladenosine and 2'-C-methylguanosine as potent nucleoside inhibitors of HCV RNA replication in vitro. However, both of these compounds suffered from significant limitations. 2'-C-Methyladenosine was found to be susceptible to enzymatic conversions by adenosine deaminase and purine nucleoside phosphorylase, and it displayed limited oral bioavailability in the rat. 2'-C-Methylguanosine, on the other hand, was neither efficiently taken up in cells nor phosphorylated well. As part of an attempt to address these limitations, we now report upon the synthesis and evaluation of a series of heterobase-modified 2'-C-methyl ribonucleosides. The structure-activity relationship within this series of nucleosides reveals 4-amino-7-(2-C-methyl-beta-d-ribofuranosyl)-7H-pyrrolo[2,3-d]pyrimidine and 4-amino-5-fluoro-7-(2-C-methyl-beta-d-ribofuranosyl)-7H-pyrrolo[2,3-d]pyrimidine as potent and noncytotoxic inhibitors of HCV RNA replication. Both 4-amino-7-(2-C-methyl-beta-d-ribofuranosyl)-7H-pyrrolo[2,3-d]pyrimidine and 4-amino-5-fluoro-7-(2-C-methyl-beta-d-ribofuranosyl)-7H-pyrrolo[2,3-d]pyrimidine display improved enzymatic stability profiles as compared to that of 2'-C-methyladenosine. Consistent with these observations, the most potent compound, 4-amino-5-fluoro-7H-pyrrolo[2,3-d]pyrimidine ribonucleoside, is orally bioavailable in the rat. Together, the potency of the 2'-C-methyl-4-amino-pyrrolo[2,3-d]pyrimidine ribonucleosides and their improved pharmacokinetic properties relative to that of 2'-C-methyladenosine suggests that this class of compounds may have clinical utility.

B cell lymphoproliferative disorders and VH4-34 gene encoded antibodies.

The VH4-34 represents an unusual Ig heavy chain variable region gene given that it is conserved and overexpressed despite its autoreactivity. Besides RBC 'I/i' recognition, a subset of VH4-34 encoded Igs bind and kill human B-lymphocytes via interaction with a cytoskeletally-associated ligand similar in structure to the cord RBC 'i' antigen. In vivo, secretion of VH4-34 gene encoded antibodies is minimal in healthy individuals. The turn on signal occurs in few clinical conditions such as, systemic lupus erythematosus, AIDS and infectious mononucleosis. Here we show that secretion of VH4-34 Abs is also switched on in hepatitis C and nasopharyngeal carcinoma; but not in diseases such as HPV-associated cervical carcinoma, multiple sclerosis and sarcoidosis. All syndromes with increased VH4-34 Igs appear to be associated with B cell hyperproliferation and B cell lymphotropic viruses, particularly EBV. The significance of the tightly controlled secretion of an autoreactive, conserved Ig gene is discussed.

Effects of human monoclonal antibody 216 on B-progenitor acute lymphoblastic leukemia in vitro.

BACKGROUND: Human monoclonal antibody (mAb) 216 is a naturally occurring IgM cytotoxic mAb that binds to a glycosylated epitope on the surface of B-lymphocytes. This study investigated if this mAb could bind and kill acute lymphoblastic leukemia (ALL) B-progenitor lymphoblasts in vitro. ALL cell lines were used to determine if combining mAb 216 with chemotherapeutic drugs would enhance killing and cell lines were used to measure cytotoxicity by mAb 216 with human complement. PROCEDURE: Expression of cell surface markers and mAb 216 epitope on fresh and banked ALL bone marrow samples was determined by flow cytometry. Fresh lymphoblasts were incubated for 20 hr with mAb 216 without complement to measure cytotoxicity. Cytotoxicity of ALL cell lines incubated with mAb 216 and vincristine (VCR) or human complement was determined using flow cytometry. RESULTS: Pre-B-ALL cells but not T-ALL cells are bound and killed by mAb 216. The combination of mAb 216 and VCR at sub-therapeutic levels demonstrated enhanced cytotoxicity beyond that observed for either agent alone. Incubation of mAb 216 with human complement increased cytotoxicity of ALL cell lines. CONCLUSION: This increased cytotoxicity with chemotherapy and the functional ability of mAb 216 to use multiple pathways to induce cell death identify mAb 216 as a potentially novel therapeutic tool in the treatment of B-progenitor ALL. Based on the results from this preclinical study, a Phase I clinical trial with mAb 216 for the treatment of patients with relapsed or refractory B-lineage ALL is ongoing.

VH4-34 encoded antibody in systemic lupus erythematosus: effect of isotype.

OBJECTIVE: To determine the clinical significance of elevated serum levels of VH4-34 encoded IgM and IgG antibodies with respect to the clinical characteristics of systemic lupus erythematosus (SLE). METHODS: VH4-34 encoded IgM and IgG immunoglobulin was measured in 95 patients with SLE by ELISA using antiidiotype monoclonal antibody (Mab) 9G4. SLE disease activity, severity, and damage were assessed by visual analog scales, Systemic Lupus Activity Measure, Lupus Severity of Disease Index, and Systemic Lupus International Collaborating Clinics/American College of Rheumatology Damage Index. Presence of VH4-34 encoded antibodies on patients' B lymphocytes was analyzed by flow cytometry using Mab 9G4. RESULTS: Fifty-two of 95 patients with SLE had elevated levels of VH4-34 encoded antibodies of IgG isotype; 17 patients with VH4-34 IgG had elevated VH4-34 of the IgM isotype. Forty-three of the 95 patients had normal levels of VH4-34 encoded antibodies. When disease severity was correlated to VH4-34 isotype, patients with circulating VH4-34 IgG but without IgM had significantly more severe disease compared to patients who had VH4-34 of both isotypes. Eighty-six percent of patients with SLE nephritis and 100% of those with central nervous system (CNS) lupus had VH4-34 IgG without IgM. In vivo, VH4-34 encoded antibodies were found to bind autologous B lymphocytes. CONCLUSION: Presence of VH4-34 IgG in the absence of VH4-34 IgM was the finding most strongly associated with severe SLE, nephritis, and CNS lupus, suggesting that isotype switching of VH4-34 encoded antibodies or loss of VH4-34 IgM encoded antibodies may influence the progression of disease in SLE.