Rituximab-mediated cell signaling and chemo/immuno-sensitization of drug-resistant B-NHL is independent of its Fc functions.
OBJECTIVE
Rituximab [chimeric anti-CD20 monoclonal antibody], alone or combined with chemotherapy, is used in the treatment of non-Hodgkin's lymphoma (NHL). Rituximab binds to CD20 and inhibits intracellular survival/growth pathways leading to chemo/immunosensitization of tumor cells in vitro. The contribution of rituximab Fc-FcR interaction in signaling is not known. This study examined the role of Fc-FcR interactions in rituximab-induced signaling using rituximab (Fab')(2) fragments as well as rituximab devoid of the CH2 Fc-binding domain (CH2(-)).


METHODS
Rituximab (CH2(-)) and rituximab (Fab')(2) were tested for their activity on B-NHL cell lines. Cell signaling and sensitization to chemotherapy and immunotherapy were examined. The in vitro studies were validated in mice bearing tumor xenografts.


RESULTS
Although the modified antibodies were defective in antibody-dependent cellular cytotoxicity and complement-dependent cytotoxicity functions, they retained all other biological activities such as inhibition of cell proliferation, induction of cell aggregation, and apoptosis induction. In addition, similar to rituximab, the modified antibodies inhibited the activity of cell survival/growth pathways and their associated transcription factors (e.g., NF-kappaB, YY1, SP-1), and signal transducers and activators of transcription 3 (STAT-3), and downregulated the expression of antiapoptotic gene products, such as Bcl-2/Bcl(xl), which regulate drug resistance. The modified antibodies, similar to rituximab, sensitized resistant B-NHL cells to both CDDP and Fas ligand-induced apoptosis. Furthermore, treatment of nude mice bearing Raji tumor cell xenografts with the combination of rituximab (Fab')(2) or rituximab and CDDP resulted in similar and significant inhibition of tumor growth.


CONCLUSIONS
These findings reveal that rituximab-mediated inhibition of intracellular signaling pathways and leading to chemo/immuno-sensitization of resistant B-NHL is Fc independent.
Department of Microbiology, Immunology, and Molecular Genetics, Jonsson Comprehensive Cancer, David Geffen School of Medicine, University of California, Los Angeles, California 90095-1747, USA.
Mario I
MI
Vega
Sara
S
Huerta-Yepez
Melisa
M
Martinez-Paniagua
Bernardo
B
Martinez-Miguel
Rogelio
R
Hernandez-Pando
Cesar R
CR
González-Bonilla
Paul
P
Chinn
Nabil
N
Hanna
Kandasamy
K
Hariharan
Ali R
AR
Jazirehi
Benjamin
B
Bonavida
D000818:Animals; D000911:Antibodies, Monoclonal / Q000627:therapeutic use*; D058846:Antibodies, Monoclonal, Murine-Derived; D017209:Apoptosis; D045744:Cell Line, Tumor; D002470:Cell Survival; D019008:Drug Resistance, Neoplasm; D007140:Immunoglobulin Fab Fragments / Q000627:therapeutic use*; D007141:Immunoglobulin Fc Fragments / Q000502:physiology*; D007167:Immunotherapy; D016393:Lymphoma, B-Cell / Q000188:drug therapy* / Q000276:immunology* / Q000378:metabolism; D051379:Mice; D008819:Mice, Nude; D000069283:Rituximab; D015398:Signal Transduction; D023041:Xenograft Model Antitumor Assays
D000911:Antibodies, Monoclonal; D058846:Antibodies, Monoclonal, Murine-Derived; D007140:Immunoglobulin Fab Fragments; D007141:Immunoglobulin Fc Fragments; D000069283:Rituximab