In vitro evaluation of humanized/de-immunized anti-PSMA immunotoxins for the treatment of prostate cancer

Abstract

Background: We generated humanized/deimmunized immunotoxins targeting the prostate-specific membrane antigen (PSMA) and tested their cytotoxic activity against prostate cancer cells in vitro. Materials and Methods: The humanized/de-immunized version of our murine anti-PSMA single-chain antibody fragment (scFv) D7, termed hD7-1(VL-VH), was ligated to the 40-kDa toxin domain of Pseudomonas aeruginosa exotoxin A (PE40), and to the deimmunized 24-kDa toxin domains PE24 or PE24mut. The immunotoxins designated as hD7-1(VL-VH)-PE40, hD7-1(VL-VH)-PE24 and hD7-1(VL-VH)-PE24mut were bacterially expressed and purified by affinity chromatography. Binding and cytotoxicity were examined by flow cytometry and viability assay, respectively. Results: All immunotoxins revealed strong binding to prostate cancer cells expressing PSMA and specific cytotoxicity, with half-maximal inhibitory concentration values in the picomolar range. Conclusion: We successfully created powerful anti-PSMA immunotoxins with reduced immunogenicity for further clinical development and application against advanced prostate cancer.