Abstract P5-18-25: Bispecific Fynomer-antibody fusion proteins targeting two epitopes on HER2

Abstract

Abstract Background: Fynomers are small binding proteins (7 kDa) derived from the human SH3 domain of Fyn kinase. They can be engineered to yield specific and high-affinity binding domains to target proteins of interest. In the past, we have isolated Fynomers with excellent physico-chemical properties binding to 16 different antigens. One important application of the Fynomer technology represents the genetic fusion of a Fynomer to an antibody to provide bispecific fusion proteins with enhanced activity compared to the unmodified antibody. Method: Using phage display technology we have isolated Fynomers binding to an epitope on HER2 which is different from the epitopes recognized by trastuzumab and pertuzumab. After genetic fusion of the HER2 binding Fynomers to pertuzumab the resulting bispecific fusion proteins were evaluated in vitro and in vivo for their antitumoral activity. Results: The fusion of Fynomers to pertuzumab did not alter the favorable biophysical properties of pertuzumab: First, the Fynomer-antibody fusion proteins could be purified with the same high yields from the supernatant of transiently transfected CHO cells as the unmodified antibody pertuzumab (in the range of 100 mg/L). Second, the purified fusion proteins were monomeric and showed no signs of aggregation even after four months of storage at 4 °C or −20 °C in PBS as determined by size exclusion chromatography. Third, the fusion of Fynomers to antibodies did not alter their Fc-mediated effector functions. Antibody-dependent cellular cytotoxicity (ADCC) was maintained, and the affinity to the neonatal Fc-receptor (FcRn) was similar as observed for pertuzumab. In addition, the bispecific Fynomer-antibody fusion proteins demonstrated excellent growth inhibition of tumor cells in vitro compared to pertuzumab and trastuzumab. In particular, the most potent molecule COVA208 exhibited impressive efficacy in vivo in tumor xenograft mouse models. Conclusion: These encouraging preclinical results indicate that the bispecific Fynomer-antibody fusions have highly promising properties with a great potential for further preclinical and clinical development, both alone and in combination with trastuzumab. Citation Information: Cancer Res 2012;72(24 Suppl):Abstract nr P5-18-25.