The conjugate Rituximab/saporin-S6 completely inhibits clonogenic growth of CD20-expressing cells and produces a synergistic toxic effect with Fludarabine.
Immunotoxins are chimeric proteins consisting of a toxin coupled to an antibody. To date, several clinical trials have been conducted, and some are still ongoing, to evaluate their anti-tumor efficacy. In this view, we chemically constructed an anti-CD20 immunotoxin with the mAb Rituximab and the type 1 ribosome-inactivating protein (RIP) saporin-S6, designed for B cells non-Hodgkin's lymphoma (NHL) therapy. This immunotoxin showed a specific cytotoxicity for the CD20+ cell lines Raji and D430B, evidenced by inhibition of protein synthesis, evaluation of apoptosis and clonogenic assay. Upon conjugation, saporin-S6 increased its toxicity on target cells by at least 2 logs, with IC(50) values of 0.1-0.3 nM. The percentage of AnnexinV+ cells was over 95% in both cell lines treated with 10 nM immunotoxin. A complete elimination of Raji clones was reached with the 10 nM immunotoxin, whereas a mixture of free RIP and mAb gave about 90% of clonogenic growth. Rituximab/saporin-S6, at 10 nM concentration, also induced apoptosis in 80% of lymphoma cells from NHL patients. Moreover, sensitivity of Raji to Rituximab/saporin-S6 was augmented when cells were coincubated with Fludarabine. The synergistic toxic effect of the two drugs led to a total elimination of the neoplastic population.
Polito
L
L
Dipartimento di Patologia Sperimentale, Università di Bologna, Bologna, Italy.
Bolognesi
A
A
Tazzari
P L
PL
Farini
V
V
Lubelli
C
C
Zinzani
P L
PL
Ricci
F
F
Stirpe
F
F
D000911:Antibodies, Monoclonal / Q000494:pharmacology*; D058846:Antibodies, Monoclonal, Murine-Derived; D018951:Antigens, CD20; D000971:Antineoplastic Combined Chemotherapy Protocols / Q000494:pharmacology; D001402:B-Lymphocytes / Q000187:drug effects* / Q000276:immunology / Q000473:pathology; D002455:Cell Division / Q000187:drug effects; D002461:Cell Line, Transformed; D002999:Clone Cells / Q000187:drug effects / Q000473:pathology; D004357:Drug Synergism; D006801:Humans; D000922:Immunotoxins / Q000494:pharmacology*; D009699:N-Glycosyl Hydrolases / Q000494:pharmacology*; D010940:Plant Proteins / Q000494:pharmacology*; D054789:Ribosome Inactivating Proteins, Type 1; D000069283:Rituximab; D000076985:Saporins; D014407:Tumor Cells, Cultured; D014740:Vidarabine / Q000031:analogs & derivatives* / Q000494:pharmacology*
D000911:Antibodies, Monoclonal; D058846:Antibodies, Monoclonal, Murine-Derived; D018951:Antigens, CD20; D000922:Immunotoxins; D010940:Plant Proteins; D054789:Ribosome Inactivating Proteins, Type 1; D000069283:Rituximab; D009699:N-Glycosyl Hydrolases; D000076985:Saporins; D014740:Vidarabine; C024352:fludarabine