Acquired resistance to rituximab is associated with chemotherapy resistance resulting from decreased Bax and Bak expression.
OBJECTIVE
Targeting malignant B cells using rituximab (anti-CD20) has improved the efficacy of chemotherapy regimens used to treat patients with non-Hodgkin's lymphoma. Despite the promising clinical results obtained using rituximab, many patients relapse with therapy-resistant disease following rituximab-based treatments. We have created a cell line model of rituximab resistance using three B-cell non-Hodgkin's lymphoma-derived cell lines (Raji, RL, and SUDHL-4). In an attempt to define strategies to overcome rituximab resistance, we sought to determine the chemotherapy sensitivity of our rituximab-resistant cell lines (RRCL).


METHODS
Parental, rituximab-sensitive cell lines (RSCL) Raji, RL, and SUDHL-4, along with RRCLs derived from them, were exposed to several chemotherapeutic agents with different mechanisms of action and the ability of these agents to induce apoptotic cell death was measured. Expression of multidomain Bcl-2 family proteins was studied as potential mediators of chemotherapy/rituximab resistance.


RESULTS
We found that RRCLs are resistant to multiple chemotherapeutic agents and have significantly decreased expression of the Bcl-2 family proteins Bax, Bak, and Bcl-2. RRCLs do not undergo rituximab- or chemotherapy-induced apoptosis but die in a caspase-dependent manner when either wild-type Bax or Bak is exogenously expressed. Furthermore, forced expression of Bak sensitized RRCL to chemotherapy-induced apoptosis.


CONCLUSIONS
Whereas a single or limited exposure of lymphoma cells to rituximab may lead to a favorable ratio of proapoptotic to antiapoptotic Bcl-2 family proteins, repeated exposure to rituximab is associated with a therapy-resistant phenotype via modulation of Bax and Bak expression.
Olejniczak
Scott H
SH
Departments of Immunology and Medicine, Roswell Park Cancer Institute, Buffalo, New York 14263, USA.
Hernandez-Ilizaliturri
Francisco J
FJ
Clements
James L
JL
Czuczman
Myron S
MS
D000911:Antibodies, Monoclonal / Q000494:pharmacology*; D058846:Antibodies, Monoclonal, Murine-Derived; D000920:Antibody-Dependent Cell Cytotoxicity; D000970:Antineoplastic Agents / Q000494:pharmacology*; D017209:Apoptosis / Q000187:drug effects; D015153:Blotting, Western; D020169:Caspases / Q000378:metabolism; D019008:Drug Resistance, Neoplasm; D006801:Humans; D016393:Lymphoma, B-Cell / Q000188:drug therapy* / Q000276:immunology / Q000378:metabolism; D053078:Membrane Potential, Mitochondrial / Q000187:drug effects; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000378:metabolism; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D000069283:Rituximab; D014407:Tumor Cells, Cultured; D050998:bcl-2 Homologous Antagonist-Killer Protein / Q000235:genetics / Q000378:metabolism*; D051028:bcl-2-Associated X Protein / Q000235:genetics / Q000378:metabolism*
D000911:Antibodies, Monoclonal; D058846:Antibodies, Monoclonal, Murine-Derived; D000970:Antineoplastic Agents; C494772:BAK1 protein, human; C494826:BAX protein, human; D019253:Proto-Oncogene Proteins c-bcl-2; D012333:RNA, Messenger; D050998:bcl-2 Homologous Antagonist-Killer Protein; D051028:bcl-2-Associated X Protein; D000069283:Rituximab; D020169:Caspases