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Generation of Rituximab Polymer May Cause Hyper-Cross-linking–Induced Apoptosis in Non-Hodgkin's Lymphomas

Authors' Affiliation: Department of Pathology, Keck School of Medicine, University of Southern California, Los Angeles, California

Requests for reprints: Alan L. Epstein, Department of Pathology, Keck School of Medicine, University of Southern California, 2011 Zonal Avenue, HMR 205, Los Angeles, CA 90033. Phone: 323-442-1172; Fax: 323-442-3049; E-mail: aepstein{at}usc.edu.

Purpose: Although Rituximab has produced significant tumor regressions in lymphoma patients, only 50% respond. Clinically, it has been shown that the major mechanism of action of Rituximab is antibody-dependent cytotoxicity requiring presentation by Fc-bearing cells. To improve the clinical efficacy of Rituximab for the treatment of CD20⁺ lymphomas, we now describe a new formulation of Rituximab, which, on direct binding to target, can induce apoptosis.

Methods: In this report, enhanced apoptosis was observed by treating CD20⁺ lymphoma cells with a new polymer formulation of Rituximab. The polymer was produced by formation of a peptide bond using the sugar moiety of dextran (MW 6,000) to generate a clinically relevant reagent for use in vivo.

Results: Comparison of Rituximab with a previously described dimer and the newly generated polymer shows that the polymer induced apoptosis more effectively in CD20⁺ cells as shown by the terminal deoxyribonucleotidyl transferase–mediated dUTP nick end labeling assay (Rituximab, 3%; dimer, 3%; polymer, 58%). Consistent with these results, the polymer produced marked regression in CD20⁺ lymphoma xenografts, whereas the dimer and monomer reagents showed little effect. In addition, we were able to show that the level of apoptosis induced in human lymphoma cell lines was in accordance with the extent of both surface CD20 clustering and caspase-3 activation.

Conclusions: These data suggest that hyper-cross-linking–induced apoptosis can be simulated by the use of a dextran polymer of Rituximab, which, when used in vivo, can directly kill CD20⁺ lymphoma cells and improve the clinical efficacy of this important therapeutic for human B-cell lymphomas.

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