Fynomer-antibody fusions targeting HER2 and CD3 for selective killing of HER2 overexpressing tumor cells.

3066 Background: A promising approach in the immunotherapy of cancer is to recruit T cells to attack tumor cells using bispecific therapeutics targeting a tumor-associated surface antigen and CD3 on T cells. Such therapeutics elicit T cell mediated lysis of tumor cells independent of T cell specificity. Fynomers are small 7 kDa globular proteins derived from the SH3 domain of the human Fyn kinase (Fyn SH3) that can be engineered to bind with antibody-like affinity and specificity to virtually any target of choice. Fynomers can be fused to N-terminal and/or C-terminal ends of antibodies to generate bispecific therapeutics (FynomAbs) with tailored architectures. Here, we describe the generation and characterization of anti-CD3/HER2 FynomAbs. Methods: Using phage display technology we have isolated Fynomers binding to HER2. After genetic fusion of these Fynomers to anti-CD3 antibodies the resulting bispecific fusion proteins were evaluated for their anti-tumoral activity. Results: We have generated novel bispecific FynomAbs which can simultaneously bind HER2 on tumor cells and CD3 on T cells. The bispecific HER2/CD3 targeting FynomAbs potently redirect T cells to HER2 expressing tumor cells showing picomolar tumor cell lysis activity on multiple cell lines. The activity was found to be highly specific, as no lysis of cells was observed in the absence of HER2 expression. In addition, the FynomAbs demonstrate an antibody-like pharmacokinetic profile in mice, which may translate into a convenient administration route without the need for continuous infusion. Conclusions: FynomAbs represent an attractive platform to generate bispecific molecules and can be produced using standard antibody technology (GMP production yield of 3.3 g/L at 1000 L scale achieved). We show here the successful generation of bispecific T cell recruiting FynomAbs with antibody-like biophysical and pharmacokinetic properties that allow the redirection of T cells specifically to tumor cells.