title: Targeting Bcl-2 family proteins modulates the sensitivity of B-cell lymphoma to rituximab-induced apoptosis.
abstract: The chimeric monoclonal antibody rituximab is the standard of care for patients with B-cell non-Hodgkin lymphoma (B-NHL). Rituximab mediates complement-dependent cytotoxicity and antibody-dependent cellular cytotoxicity of CD20-positive human B cells. In addition, rituximab sensitizes B-NHL cells to cytotoxic chemotherapy and has direct apoptotic and antiproliferative effects. Whereas expression of the CD20 antigen is a natural prerequisite for rituximab sensitivity, cell-autonomous factors determining the response of B-NHL to rituximab are less defined. To this end, we have studied rituximab-induced apoptosis in human B-NHL models. We find that rituximab directly triggers apoptosis via the mitochondrial pathway of caspase activation. Expression of antiapoptotic Bcl-xL confers resistance against rituximab-induced apoptosis in vitro and rituximab treatment of xenografted B-NHL in vivo. B-NHL cells insensitive to rituximab-induced apoptosis exhibit increased endogenous expression of multiple antiapoptotic Bcl-2 family proteins, or activation of phosphatidylinositol-3-kinase signaling resulting in up-regulation of Mcl-1. The former resistance pattern is overcome by treatment with the BH3-mimetic ABT-737, the latter by combining rituximab with pharmacologic phosphatidylinositol-3-kinase inhibitors. In conclusion, sensitivity of B-NHL cells to rituximab-induced apoptosis is determined at the level of mitochondria. Pharmacologic modulation of Bcl-2 family proteins or their upstream regulators is a promising strategy to overcome rituximab resistance.
authors.affiliation: Department of Medicine (Cancer Research), West German Cancer Center, University Hospital Essen, Essen, USA.
authors.forename: Claudia
authors.initials: C
authors.lastname: Stolz
authors.forename: Georg
authors.initials: G
authors.lastname: Hess
authors.forename: Patricia S
authors.initials: PS
authors.lastname: Hähnel
authors.forename: Florian
authors.initials: F
authors.lastname: Grabellus
authors.forename: Sandra
authors.initials: S
authors.lastname: Hoffarth
authors.forename: Kurt W
authors.initials: KW
authors.lastname: Schmid
authors.forename: Martin
authors.initials: M
authors.lastname: Schuler
mesh_terms: D000818:Animals; D000911:Antibodies, Monoclonal / Q000494:pharmacology*; D058846:Antibodies, Monoclonal, Murine-Derived; D018951:Antigens, CD20 / Q000096:biosynthesis*; D000970:Antineoplastic Agents / Q000494:pharmacology; D017209:Apoptosis; D001713:Biphenyl Compounds / Q000494:pharmacology; D045744:Cell Line, Tumor; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D016393:Lymphoma, B-Cell / Q000188:drug therapy* / Q000378:metabolism*; D051379:Mice; D016513:Mice, SCID; D064549:Myeloid Cell Leukemia Sequence 1 Protein; D009368:Neoplasm Transplantation; D009596:Nitrophenols / Q000494:pharmacology; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D010879:Piperazines / Q000494:pharmacology; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000378:metabolism*; D000069283:Rituximab; D015398:Signal Transduction; D013449:Sulfonamides / Q000494:pharmacology
chemical_list: C501332:ABT-737; D000911:Antibodies, Monoclonal; D058846:Antibodies, Monoclonal, Murine-Derived; D018951:Antigens, CD20; D000970:Antineoplastic Agents; D001713:Biphenyl Compounds; C579094:Mcl1 protein, mouse; D064549:Myeloid Cell Leukemia Sequence 1 Protein; D009596:Nitrophenols; D010879:Piperazines; D019253:Proto-Oncogene Proteins c-bcl-2; D013449:Sulfonamides; D000069283:Rituximab; D019869:Phosphatidylinositol 3-Kinases