Publication Date:
2004-11-16
Description:
Following [R] binding, CD20 antigen redistributes into lipid raft domains (LRD) and initiates signaling events leading to apoptosis in malignant B-cells. In addition, the clustering of CD20 receptors into LRD results in a relative increase in the antigen density within a given area of the cell membrane, thus facilitating [R]-mediated complement mediated cytotoxicity (CMC) and/or antibody dependent cellular cytotoxicity (ADCC). Combinations of monoclonal antibodies (mAbs) directed against unique tumor-associated targets can potentially alter the reorganization of LRD and modify their anti-tumor activity. Our main objective was to study the effects of [A] upon [R]-mediated anti-tumor effects. For ADCC/CMC studies, 51Cr-labeled NHL cells (Raji, DHL-4, DHL-10, Karpas422 or Ramos cells) were exposed to concurrent [A+R], sequential [R→A] or [A→R] prior to the addition of peripheral blood mononuclear cells (effector:target ratio of 40:1) or human serum, respectively. Trastuzumab [I] served as isotype control. Following a 6-hour period incubation, supernatant was harvested and % lysis calculated. In addition, LRD of 1x108 Raji cells exposed to similar mAb-combinations were extracted by sucrose gradient ultracentrifugation. Reorganization of CD20 into LRD was determined by Western blotting. For in vivo studies six to 8 week old SCID mice were inoculated by tail vein injection (iv) with 1x106 Raji cells (day 0). After tumor engraftment (Day +7), animals were divided in seven cohorts to receive 8 doses of vehicle control, [R], [A], [I], alternating doses of [R+A], or sequential dosing of [A→R] or [R→A]. MAb were administered IV at 5mg/kg/dose. The end point of the study was overall survival. Statistical analysis was performed with Kaplan-Meier survival curves and P values calculated by log rank test. In vitro exposure to [A] prior to [R] therapy resulted a 30 to 50% decrease in rituximab-mediated ADCC. In addition, exposure of Raji cells to [A] led to a decrease in the amount of CD20 reorganized into LRD following rituximab exposure. No decrease in [R]-mediated ADCC or reorganization of CD20 into LRD was observed when [A] was administered following [R] therapy. In vivo studies demonstrated a better anti-tumor activity in animals treated with alternating doses of [R + A], when compared to [R→A], [A→R], [R] or [A] therapy. The median survival for mice treated with combination mAb therapy [R+A] was 90 days, compared to 43 and 70 days for those treated with [R→A] and [A→R] respectively. Combination therapy with [R+A] resulted in a statistically significant longer survival when compared to [R], [A], or [I] (P
Print ISSN:
0006-4971
Electronic ISSN:
1528-0020
Topics:
Biology
,
Medicine
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