title: The anti-CD20 antibody rituximab augments the immunospecific therapeutic effectiveness of an anti-CD19 immunotoxin directed against human B-cell lymphoma.
abstract: The chimaeric anti-CD20 antibody rituximab (Rituxan) sensitises lymphoma cells to small molecule cytotoxic drugs and to protein toxins. We have explored the augmentive effect of rituximab on the anti-CD19 immunotoxin BU12-SAPORIN in a model of human lymphoma. Intact rituximab and its F(ab)2 derivative both augmented the immunospecific protein synthesis inhibitory effects of BU12-SAPORIN in a complement-independent manner. A combination of rituximab + BU12-SAPORIN completely abolished the proliferation of Ramos cells in vitro and also induced a significantly greater degree of apoptosis in these cells. Treatment with rituximab, BU12-SAPORIN or a combination of both induced poly(ADPribose) polymerase and caspase 3 cleavage, although this was always consistently greater in combination-treated cells. zVAD almost completely inhibited apoptosis in rituximab- or BU12-SAPORIN-treated cells but only partially in combination-treated cells. In severe combined immunodeficient (SCID)-Ramos mice the combination of rituximab + BU12-SAPORIN was significantly better therapeutically than either single agent. The immunological fidelity of the therapeutic effect because of combination treatment was demonstrated through the failure of rituximab to augment an irrelevant anti-CD7 immunotoxin. The therapeutic efficacy of rituximab and combination treatment was reduced in SCID-Ramos mice depleted of serum complement while natural killer cell depletion failed to show any convincing role for antibody-dependent cellular cytotoxicity. This study shows a clear therapeutic advantage from using rituximab to immunospecifically augment immunotoxin cytotoxicity warranting further investigation.
authors.affiliation: The Simon Flavell Leukaemia Research Unit and Cancer Research UK, Division of Cancer Sciences, Department of Medical Oncology, University of Southampton Medical School, Southampton General Hospital, Southampton, Hampshire, UK. d.j.flavell@soton.ac.uk
authors.forename: David J
authors.initials: DJ
authors.lastname: Flavell
authors.forename: Sarah L
authors.initials: SL
authors.lastname: Warnes
authors.forename: Christine J
authors.initials: CJ
authors.lastname: Bryson
authors.forename: Sarah A
authors.initials: SA
authors.lastname: Field
authors.forename: Armorel L
authors.initials: AL
authors.lastname: Noss
authors.forename: Graham
authors.initials: G
authors.lastname: Packham
authors.forename: Sopsamorn U
authors.initials: SU
authors.lastname: Flavell
mesh_terms: D000818:Animals; D000911:Antibodies, Monoclonal / Q000008:administration & dosage* / Q000276:immunology; D058846:Antibodies, Monoclonal, Murine-Derived; D000920:Antibody-Dependent Cell Cytotoxicity; D018941:Antigens, CD19 / Q000276:immunology* / Q000378:metabolism; D018951:Antigens, CD20 / Q000276:immunology / Q000378:metabolism; D000951:Antigens, Neoplasm / Q000378:metabolism; D000972:Antineoplastic Agents, Phytogenic / Q000008:administration & dosage; D000971:Antineoplastic Combined Chemotherapy Protocols / Q000627:therapeutic use*; D017209:Apoptosis / Q000187:drug effects; D018958:CD55 Antigens / Q000378:metabolism; D018957:CD59 Antigens / Q000378:metabolism; D003165:Complement System Proteins / Q000276:immunology; D003602:Cytotoxicity, Immunologic; D005260:Female; D006801:Humans; D000922:Immunotoxins / Q000008:administration & dosage* / Q000276:immunology; D007694:Killer Cells, Natural / Q000276:immunology; D016393:Lymphoma, B-Cell / Q000188:drug therapy* / Q000276:immunology / Q000473:pathology; D008297:Male; D051379:Mice; D016513:Mice, SCID; D009699:N-Glycosyl Hydrolases / Q000008:administration & dosage; D009363:Neoplasm Proteins / Q000096:biosynthesis; D010940:Plant Proteins / Q000008:administration & dosage; D054789:Ribosome Inactivating Proteins, Type 1; D000069283:Rituximab; D000076985:Saporins; D014407:Tumor Cells, Cultured
chemical_list: D000911:Antibodies, Monoclonal; D058846:Antibodies, Monoclonal, Murine-Derived; D018941:Antigens, CD19; D018951:Antigens, CD20; D000951:Antigens, Neoplasm; D000972:Antineoplastic Agents, Phytogenic; D018958:CD55 Antigens; D018957:CD59 Antigens; D000922:Immunotoxins; D009363:Neoplasm Proteins; D010940:Plant Proteins; D054789:Ribosome Inactivating Proteins, Type 1; D000069283:Rituximab; D003165:Complement System Proteins; D009699:N-Glycosyl Hydrolases; D000076985:Saporins