Abstract #3632: In vitro and in vivo studies of novel recombinant immunotoxins targeting the Her-2/NEU oncogene: Impact of design on biological effects

Abstract

The Her2/neu oncogene represents an attractive target for antibody-mediated immunotherapy in a variety of tumor types. The goal of this study was to demonstrate the construction and characterization of a series of immunotoxins containing humanized scFv C6.5 or murine E23 scFv genetically fused to a highly toxic recombinant gelonin (rGel) molecule. C6.5/rGel was compared with E23/rGel to evaluate the specific cytotoxic effects against 6 HER2-positive and 2 HER2-negative tumor lines. We additionally introduced a number of modified furin linkers for improved intracellular release of the toxin to determine the impact of these design changes on selectivity and specificity. Comparing C6.5/rGel and E23/rGel, we found that both constructs retained the specificity of the original antibody, as well as the biological activity of rGel toxin (Rabbit Reticulocyte Lysate Assay (RRLA) IC₅₀ of 15.4 pM and 15.5 pM respectively, vs 10.6 pM for rGel). The two constructs also displayed similar cytotoxicity against different carcinoma cell lines (e.g. IC₅₀ of 9.1nM and 6.0nM for the fusion constructs vs 1671 nM for rGel on SKBR3 cells). Introduction of cleavable furin linkers into the molecules showed dissimilar stability and rGel intracellular release, but very similar kinetics of cytotoxicity in in vitro studies. Animal model efficacy studies against SKOV3 ovarian cancer tumors (subcutaneous) of the various constructs are ongoing and will be reported. Based on our in vitro results, these studies suggest that humanized C6.5-rGel could be an effective novel clinical agent warranted in patients with Her2/neu-expressing malignancies. Research conducted, in part, by the Clayton Foundation for Research.

Citation Information: In: Proc Am Assoc Cancer Res; 2009 Apr 18-22; Denver, CO. Philadelphia (PA): AACR; 2009. Abstract nr 3632.