Rituximab modifies the cisplatin-mitochondrial signaling pathway, resulting in apoptosis in cisplatin-resistant non-Hodgkin's lymphoma.
OBJECTIVE
Rituximab (chimeric anti-CD20) can reverse the cisplatin-resistant phenotype of AIDS-related non-Hodgkin's lymphoma cell lines and results in cisplatin-mediated apoptosis. The mechanism by which apoptosis is achieved by the combination treatment was examined.


METHODS
The AIDS-related lymphoma (ARL) cell line 2F7 was treated with rituximab, cisplatin, and a combination of the two and analyzed by Western blot analyses for signaling proteins involved in the death receptor-mediated and mitochondrial pathways.


RESULTS
Rituximab selectively inhibited the expression of Bcl-2 in the ARL cells. However, other proteins analyzed [namely, Apaf-1, Bax, Bid, caspase-3, caspase-8, caspase-9, X-linked inhibitor of apoptosis protein (XIAP), cellular inhibitor of apoptosis protein (cIAP)-1, cIAP-2, cytochrome c, Fas, Fas ligand, FLIP, p53, and poly(ADP-ribose) polymerase] were not affected by either rituximab or cisplatin. Treatment with cisplatin induced the generation of mitochondrial reactive oxygen species, specifically intracellular peroxides. Furthermore, cisplatin alone was unable to induce the mitochondrial apoptotic events; however, the rituximab-cisplatin combination was able to synergistically induce significant apoptosis and mitochondria-mediated apoptotic events [mitochondrial membrane depolarization (DeltaPsi(m)), cytochrome c release from mitochondria, and caspase-3 and -9 activation]. The combination treatment facilitated the down-regulation of Bcl-2 by rituximab at an early time point. Decreased expression of additional proteins (Apaf-1, cIAP-1, cIAP-2, and XIAP) paralleled apoptosis detected at 24 h.


CONCLUSIONS
These findings show that the selective down-regulation of Bcl-2 by rituximab leading to apoptosis in ARL cells by cisplatin is through the mitochondria-dependent caspase pathway.
Alas
Steve
S
Department of Microbiology, Immunology, and Molecular Genetics, University of California Los Angeles School of Medicine and Jonsson Comprehensive Cancer Center, University of California, Los Angeles, California 90095, USA.
Ng
Chuen-Pei
CP
Bonavida
Benjamin
B
D000911:Antibodies, Monoclonal / Q000494:pharmacology*; D058846:Antibodies, Monoclonal, Murine-Derived; D000971:Antineoplastic Combined Chemotherapy Protocols; D017209:Apoptosis / Q000187:drug effects*; D053477:Apoptotic Protease-Activating Factor 1; D015153:Blotting, Western; D053446:CASP8 and FADD-Like Apoptosis Regulating Protein; D002352:Carrier Proteins; D061945:Caspase Inhibitors; D020169:Caspases / Q000378:metabolism; D002945:Cisplatin / Q000494:pharmacology*; D003131:Combined Modality Therapy; D003574:Cytochrome c Group / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D019008:Drug Resistance, Neoplasm; D004789:Enzyme Activation / Q000187:drug effects; D004791:Enzyme Inhibitors / Q000494:pharmacology; D053222:Fas Ligand Protein; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins; D016483:Lymphoma, AIDS-Related / Q000378:metabolism* / Q000473:pathology / Q000628:therapy; D008562:Membrane Glycoproteins / Q000378:metabolism; D008928:Mitochondria / Q000187:drug effects* / Q000378:metabolism; D011506:Proteins / Q000378:metabolism; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000378:metabolism; D017382:Reactive Oxygen Species / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D000069283:Rituximab; D015398:Signal Transduction / Q000187:drug effects*; D014407:Tumor Cells, Cultured / Q000187:drug effects; D019014:fas Receptor / Q000378:metabolism
C506592:APAF1 protein, human; D000911:Antibodies, Monoclonal; D058846:Antibodies, Monoclonal, Murine-Derived; D053477:Apoptotic Protease-Activating Factor 1; D053446:CASP8 and FADD-Like Apoptosis Regulating Protein; C506386:CFLAR protein, human; D002352:Carrier Proteins; D061945:Caspase Inhibitors; D003574:Cytochrome c Group; D004791:Enzyme Inhibitors; C505661:FASLG protein, human; D053222:Fas Ligand Protein; D047908:Intracellular Signaling Peptides and Proteins; D008562:Membrane Glycoproteins; D011506:Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; D017382:Reactive Oxygen Species; D019014:fas Receptor; D000069283:Rituximab; D020169:Caspases; D002945:Cisplatin