Synergistic interaction between an anti-p185(HER-2) pseudomonas exotoxin fusion protein [scFv(FRP5)-ETA] and ionizing radiation for inhibiting growthof ovarian cancer cells that overexpress HER-2

Objectives. The HER-2 proto-oncogene is overexpressed in 15-30% of ovarian cancers, providing a target for therapy in a fraction of patients. We previ ously described the ability of a recombinant single-chain anti-p185(HER-2)- Pseudomonas exotoxin A fusion protein, scFv(FRP5)-ETA, to inhibit growth of cancer cells in culture and tumor xenografts in vivo. We have also describ ed synergistic interaction between an anti-p185(HER-2)-ricin A chain immuno toxin and ionizing radiation for inhibiting growth of ovarian and breast ca ncer cells that overexpress HER-2, Our objective in this report was to eval uate the in vitro and in vivo effects of scFv(FRP5)-ETA against SKOv3 ovari an cancer cells that have been transfected to express >10(6) p185(HER-2) re ceptors per cell (clone-9002-18). Methods. Inhibition of clonogenic growth was measured in vitro by limiting dilution analysis. Inhibition of tumor growth was measured in vivo using he terografts established with the same ovarian cancer cell lines. Results. Clone-9002-18 cells were substantially more sensitive than parenta l SKOv3 cells to the cytotoxic effects of scFv(FRP5)-ETA. Exotoxin fusion p rotein induced apoptosis in clone-9002-18 cells, but did not affect parenta l SKOv3 cells. Treatment of clone-9002-18 cells with 200- to 2000-cGy exter nal beam irradiation in combination with scFv(FRP5)-ETA produced synergisti c elimination of clonogenic tumor cells in culture. In vivo, subcutaneous o r intraperitoneal growth of tumor xenografts in nu/nu mice was significantl y inhibited (P = 0.004) by treatment for 10 days with scFv(FRP5)-ETA or wit h I-131-labeled-520C9 anti-p185(HER-2) radionuclide conjugate, but additive effects were not observed with combined treatment. Conclusion. ScFv(FRP5)-ETA deserves further evaluation for intraperitoneal therapy of ovarian cancers that overexpress p185(HER-2). (C) 2001 Academic Press.