leupeptins and Lymphoma--B-Cell

The proteasome, which plays a pivotal role in the control of many cell cycle-regulatory processes, has become the focus of new approaches to the treatment of cancer, including B-cell malignancies, and the first proteasome inhibitor, bortezomib (VELCADE; formerly PS-341), has entered clinical trials. The proteasome controls the stability of numerous proteins that regulate progression through the cell cycle and apoptosis, such as cyclins, cyclin-dependent kinases, tumor suppressors, and the nuclear factor-kB. By altering the stability or activity of these proteins, proteasome inhibitors sensitize malignant cells to apoptosis. Bortezomib is a dipeptidyl boronic acid proteasome inhibitor that effectively and specifically inhibits proteasome activity. In preclinical studies, bortezomib and other proteasome inhibitors have shown activity against a variety of B-cell malignancies, including multiple myeloma, diffuse large B-cell lymphoma, mantle cell lymphoma, and Hodgkin's lymphoma. These agents can induce apoptosis and sensitize tumor cells to radiation or chemotherapy. Based on these findings, phase I clinical trials were conducted with bortezomib in various solid and hematologic malignancies. In these studies, bortezomib was generally well tolerated with manageable toxicities. Phase II trials have been initiated for relapsed and refractory multiple myeloma, refractory chronic lymphocytic leukemia, and non-Hodgkin's lymphoma. Preliminary data from the multiple myeloma phase II study indicate that a significant number of patients responded to therapy or exhibited stable disease and that the drug had manageable toxicities. These findings, along with extensive preclinical data, suggest that bortezomib and other proteasome inhibitors may have far-reaching potential in the treatment of various cancers, including B-cell malignancies.

Topics: Acetylcysteine; Animals; Boronic Acids; Bortezomib; Cell Cycle Proteins; Clinical Trials as Topic; Drug Screening Assays, Antitumor; Enzymes; Gene Expression Regulation; Hodgkin Disease; Humans; Leukemia, B-Cell; Leupeptins; Lymphoma, B-Cell; Lymphoma, Large B-Cell, Diffuse; Lymphoma, Mantle-Cell; Mice; Multiple Myeloma; Neoplasm Proteins; NF-kappa B; Oncogene Proteins; Peptide Hydrolases; Protease Inhibitors; Proteasome Endopeptidase Complex; Pyrazines; Substrate Specificity; Transcription Factors; Treatment Outcome

Growing evidence suggests the Δ133p53α isoform may function as an oncogene. It is overexpressed in many tumors, stimulates pathways involved in tumor progression, and inhibits some activities of wild-type p53, including transactivation and apoptosis. We hypothesized that Δ133p53α would have an even more profound effect on p53 variants with weaker tumor-suppressor capability. We tested this using a mouse model heterozygous for a Δ133p53α-like isoform (Δ122p53) and a p53 mutant with weak tumor-suppressor function (mΔpro). The Δ122p53/mΔpro mice showed a unique survival curve with a wide range of survival times (92-495 days) which was much greater than mΔpro/- mice (range 120-250 days) and mice heterozygous for the Δ122p53 and p53 null alleles (Δ122p53/-, range 78-150 days), suggesting Δ122p53 increased the tumor-suppressor activity of mΔpro. Moreover, some of the mice that survived longest only developed benign tumors. In vitro analyses to investigate why some Δ122p53/mΔpro mice were protected from aggressive tumors revealed that Δ122p53 stabilized mΔpro and prolonged the response to DNA damage. Similar effects of Δ122p53 and Δ133p53α were observed on wild-type of full-length p53, but these did not result in improved biological responses. The data suggest that Δ122p53 (and Δ133p53α) could offer some protection against tumors by enhancing the p53 response to stress.

Topics: Animals; Antineoplastic Agents; Apoptosis; Cell Cycle Checkpoints; Cell Line, Tumor; Cell Proliferation; Cyclin-Dependent Kinase Inhibitor p21; Cysteine Proteinase Inhibitors; Disease Models, Animal; DNA Damage; Interferon-gamma; Interleukin-6; Leupeptins; Lymphoma, B-Cell; Male; Mice; Mice, Inbred C57BL; Mice, Knockout; Mutation; Protein Binding; Protein Isoforms; Proto-Oncogene Proteins c-mdm2; Tumor Suppressor Protein p53

Chromosomal translocations and somatic mutations occurring in the 5' noncoding region of the BCL6 gene, encoding a transcriptional repressor, are most frequent genetic abnormalities associated with non-Hodgkin B-cell lymphoma and result in deregulated expression of BCL6. However, the significance of deregulated expression of BCL6 in lymphomagenesis and its effect on clinical outcomes of lymphoma patients have remained elusive. In the present study, we established Daudi and Raji B-cell lymphoma cell lines that overexpress BCL6 or its mutant, BCL6-Ala333/343, in which serine residues required for degradation through the proteasome pathway in B-cell receptor-stimulated cells are mutated. BCL6 overexpression did not have any significant effect on cell proliferation, but significantly inhibited apoptosis caused by etoposide, which induced a proteasome-dependent degradation of BCL6. BCL6-Ala333/343 was not degraded after etoposide treatment and strongly inhibited apoptosis. In these lymphoma cell lines, etoposide increased the generation of reactive oxygen species (ROS) and reduced mitochondria membrane potential, both of which were inhibited by the antioxidant N-acetyl-L-cysteine (NAC). NAC also inhibited apoptosis. Furthermore, BCL6 overexpression was found to inhibit the increase in ROS levels and apoptosis in response to etoposide and other chemotherapeutic reagents. These results raise the possibility that deregulated expression of BCL6 may endow lymphoma cells with resistance to chemotherapeutic reagents, most likely by enhancing the antioxidant defense systems.

Topics: Acetylcysteine; Antineoplastic Agents; Antioxidants; Apoptosis; Cysteine Endopeptidases; Cysteine Proteinase Inhibitors; DNA-Binding Proteins; Doxycycline; Etoposide; Free Radical Scavengers; Gene Expression Regulation, Neoplastic; Humans; Leupeptins; Lymphoma, B-Cell; Membrane Potentials; Mitochondria; Multienzyme Complexes; Mutation; Proteasome Endopeptidase Complex; Proto-Oncogene Proteins; Proto-Oncogene Proteins c-bcl-6; Reactive Oxygen Species; Transcription Factors; Tumor Cells, Cultured

Type II collagen (CII) is an arthritogenic self antigen in DBA/1 (H-2q) mice. To analyze the intracellular processing of this fibrillar protein in the context of I-Aq molecules, we have generated hybrid antigen-presenting cells (APC) by fusion of B lymphoma (A20 and M12) cells with CII-primed spleen cells from DBA/1 mice. Efficient presentation of CII by these APC to specific T cell hybridomas required prior cleavage of the antigen and intracellular handling of the peptides. Inhibition of protein transport by brefeldin A prevented the presentation of CII peptides to T cell hybridomas, indicating that the intracellular presentation of CII was dependent on neo-synthesis of I-Aq molecules. In contrast, exposure of hybrid B lymphomas to leupeptin, a protease inhibitor, induced a dose-dependent increase of CII-specific T cell response, while abrogating the I-Aq-restricted presentation of ovalbumin. The enhancing effect of leupeptin was also observed when immune B cells were used as APC. In contrast, leupeptin inhibited the presentation of CII peptides by macrophages or total spleen cells. Pulse-chase analysis of metabolically labeled hybrid APC and immunoprecipitation with antibodies specific for class II molecules or invariant (li) chain revealed that leupeptin did not affect the li chain processing or the formation of stable class II dimers. The stimulatory effect of leupeptin observed on CII presentation suggests that leupeptin protects CII epitopes by interfering with proteases involved in the intracellular degradation of CII.

Topics: Animals; Antigen Presentation; Antigen-Presenting Cells; Antigens, Differentiation, B-Lymphocyte; Brefeldin A; Collagen; Cyclopentanes; Dimerization; Epitopes; Histocompatibility Antigens Class II; Immunophenotyping; Leupeptins; Lymphoma, B-Cell; Mice; Mice, Inbred DBA; Protease Inhibitors; Protein Synthesis Inhibitors; Sodium Dodecyl Sulfate; Tumor Cells, Cultured

Anti-idiotype antibody therapy of B-cell lymphomas, despite numerous promising experimental and clinical studies, has so far met with limited success. Tailor-made monoclonal anti-idiotype antibodies have been injected into a large series of lymphoma patients, with a few impressive complete tumour remissions but a large majority of negative responses. The results presented here suggest that, by coupling to antilymphoma idiotype antibodies a few molecules of the tetanus toxin universal epitope peptide P2 (830-843), one could markedly increase the efficiency of this therapy. We show that after 2-hr incubation with conjugates consisting of the tetanus toxin peptide P2 coupled by an S-S bridge to monoclonal antibodies directed to the lambda light chain of human immunoglobulin, human B-lymphoma cells can be specifically lysed by a CD4 T-lymphocyte clone specific for the P2 peptide. Antibody without peptide did not induce B-cell killing by the CD4 T-lymphocyte clone. The free cysteine-peptide was also able to induce lysis of the B-lymphoma target by the T-lymphocyte clone, but at a molar concentration 500 to 1000 times higher than that of the coupled peptide. Proliferation assays confirmed that the antibody-peptide conjugate was antigenically active at a much lower concentration than the free peptide. They also showed that antibody-peptide conjugates required an intact processing function of the B cell for peptide presentation, which could be selectively inhibited by leupeptin and chloroquine.(ABSTRACT TRUNCATED AT 250 WORDS)

Topics: Amino Acid Sequence; Animals; Antibodies, Anti-Idiotypic; Antibodies, Monoclonal; CD4-Positive T-Lymphocytes; Chloroquine; Histocompatibility Antigens Class II; Humans; Immunoglobulin Light Chains; Immunotoxins; Leupeptins; Lymphoma, B-Cell; Mice; Mice, Inbred BALB C; Molecular Sequence Data; Peptides; Tetanus Toxin

The successful clinical experience with antibody LL2 (an IgG2a, anti-B-cell lymphoma antibody) in radioimmunodetection and radioimmunotherapy suggests that this antibody may have potential as a carrier of cytotoxic agents. The internalization, cellular trafficking, and catabolism of this antibody in target human Burkitt lymphoma cells (Raji) were investigated. Internalization of intact antibody as well as of the F(ab')2 and Fab' fragments was detected by an FITC-labeled anti-mouse second antibody probe, and evaluated by fluorescence microscopy. Internalization of intact IgG (or the fragments) was observed as early as 5 min after incubation at 37 degrees C. Initially, the internalized antibodies were present as micro-particles inside the cell membrane, and were translocated to the lysosomal compartment within 2 hr. The anatomic location of the internalized antibody, before translocation to the lysosomal compartment, was deduced by comparing the fluorescence images obtained with the antibody to those obtained with fluorescent probes with known cellular distribution in a co-internalization study. A Golgi-like compartment was found to be involved in the translocation of the antibody. Cellular catabolism of the bound antibody was studied by using 125I-labeled antibody on the target cells. At 21 h, 40% of the radioactivity was released into the supernatant as degraded fragments. The observation suggested that the antibody was degraded mainly in the lysosomes, since the degradation was significantly inhibited in the presence of lysosomal inhibitors such as ammonium chloride or leupeptin. Subcellular fractionation of Raji cells after the binding of 125I-labeled LL2 indicated that the antibody was translocated to lysosomes as evidenced by SDS-PAGE. The rate of internalization (Ke) of LL2, and the re-expression of the antigen were determined. The rapid internalization of LL2 and the re-expression of the antigen suggest that this antibody may have potential as a therapeutic immunoconjugate, since it could deliver a higher accumulation of cytotoxic agents into lymphoma cells.

Topics: 4-Chloro-7-nitrobenzofurazan; Ammonium Chloride; Antibodies, Monoclonal; Burkitt Lymphoma; Ceramides; Fluorescein-5-isothiocyanate; Fluorescent Dyes; Golgi Apparatus; Humans; Immunoglobulin Fab Fragments; Kinetics; Leupeptins; Lymphoma, B-Cell; Lysosomes; Microscopy, Fluorescence; Tumor Cells, Cultured