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Open AccessArticle

High in Vitro Anti-Tumor Efficacy of Dimeric Rituximab/Saporin-S6 Immunotoxin

Department of Experimental, Diagnostic and Specialty Medicine-DIMES, Alma Mater Studiorum, University of Bologna, Via San Giacomo 14, 40126 Bologna, Italy
Author to whom correspondence should be addressed.
Academic Editors: Tomas Girbes and David J. Fitzgerald
Toxins 2016, 8(6), 192;
Received: 22 April 2016 / Revised: 27 May 2016 / Accepted: 14 June 2016 / Published: 21 June 2016
(This article belongs to the Collection Immunotoxins 2016)
The anti-CD20 mAb Rituximab has revolutionized lymphoma therapy, in spite of a number of unresponsive or relapsing patients. Immunotoxins, consisting of toxins coupled to antibodies, are being investigated for their potential ability to augment Rituximab efficacy. Here, we compare the anti-tumor effect of high- and low-molecular-weight Rituximab/saporin-S6 immunotoxins, named HMW-IT and LMW-IT, respectively. Saporin-S6 is a potent and stable plant enzyme belonging to ribosome-inactivating proteins that causes protein synthesis arrest and consequent cell death. Saporin-S6 was conjugated to Rituximab through an artificial disulfide bond. The inhibitory activity of HMW-IT and LMW-IT was evaluated on cell-free protein synthesis and in two CD20+ lymphoma cell lines, Raji and D430B. Two different conjugates were separated on the basis of their molecular weight and further characterized. Both HMW-IT (dimeric) and LMW-IT (monomeric) maintained a high level of enzymatic activity in a cell-free system. HMW-IT, thanks to a higher toxin payload and more efficient antigen capping, showed stronger in vitro anti-tumor efficacy than LMW-IT against lymphoma cells. Dimeric HMW-IT can be used for lymphoma therapy at least for ex vivo treatments. The possibility of using HMW-IT augments the yield in immunotoxin preparation and allows the targeting of antigens with low internalization rates. View Full-Text
Keywords: B-cell lymphomas; immunotherapy; immunotoxin; ribosome-inactivating protein; Rituximab; Saporin-S6 B-cell lymphomas; immunotherapy; immunotoxin; ribosome-inactivating protein; Rituximab; Saporin-S6
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Bortolotti, M.; Bolognesi, A.; Battelli, M.G.; Polito, L. High in Vitro Anti-Tumor Efficacy of Dimeric Rituximab/Saporin-S6 Immunotoxin. Toxins 2016, 8, 192.

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