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Blood, 15 December 2005, Vol. 106, No. 13, pp. 4308-4314.
Prepublished online as a Blood First Edition Paper on August 18, 2005; DOI 10.1182/blood-2005-03-1033.
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Submitted March 14, 2005
Accepted August 11, 2005
Effective therapy of human lymphoma xenografts with a novel recombinant ribonuclease/anti-CD74 humanized IgG4 antibody immunotoxin
Chien-Hsing Chang, Puja Sapra, Sailaja S Vanama, Hans J Hansen, Ivan D Horak, and David M Goldenberg*
Immunomedics, Inc., Morris Plains, NJ, USA
Garden State Cancer Center, Center for Molecular Medicine and Immunology, Belleville, NJ, USA
* Corresponding author; email: dmg.gscancer{at}att.net.
Ranpirnase (Rap) is a cytotoxic ribonuclease (RNase) isolated from frog oocytes. Here we describe high antitumor activity of a novel immunotoxin, 2L-Rap-hLL1- 4P, composed of two Rap molecules, each fused to the N-terminus of the light chain of hLL1, an internalizing anti-CD74 humanized antibody. To reduce unwanted side effects, the constant region of hLL1 was changed from 1 to - 4 and further to 4P by replacing serine228 to proline to prevent the formation of a half-IgG common for IgG4. In vitro, 2L-Rap-hLL1- 4P retained RNase activity, specific binding to CD74,- and was significantly more potent against CD74-positive cell lines (Daudi, Raji and MC/CAR) than naked hLL1. In vivo, the pharmacokinetic profile of 2L-Rap-hLL1- 4P was similar to that of naked hLL1. The maximum tolerated dose of 2L-Rap-hLL1- 4P in SCID or BALB/c mice was 50 µg/mouse. In Raji and Daudi Burkitt's lymphoma xenograft models, treatment with a single 5- to 50-µg dose of 2L-Rap-hLL1- 4P, given as early or delayed treatment, resulted in cures of most animals. Treatment with 2L-Rap-hLL1- 4P was significantly better than all controls, including saline, naked hLL1 and non-specific immunotoxin. In conclusion, 2L-Rap-hLL1- 4P demonstrated excellent in vitro and in vivo efficacy, and thus merits further consideration as a therapeutic for CD74-positive tumors.

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