De Novo Design of High-Affinity HER2-Targeting Protein Minibinders.

Human Epidermal Growth Factor Receptor 2 (HER2) is a key therapeutic target in breast cancer. However, the application of existing anti-HER2 antibody drugs is limited by such issues as large molecular weight and poor stability. In this study, a series of small protein minibinders targeting HER2 domain IV were de novo designed using the RFdiffusion method. Candidate molecules were selected through a combination of ProteinMPNN and AlphaFold2 screening, and their binding capabilities were further evaluated using Escherichia coli surface display coupled with flow cytometry analysis. By integrating molecular dynamics simulations, confocal fluorescence imaging, and isothermal titration calorimetry (ITC) experiments, a highly efficient minibinder (0_703_6) with nanomolar affinity and a smaller molecular size was finally identified. Compared with the existing drug molecules, the identified minibinder exhibited approximately threefold higher affinity and a threefold reduction in molecular size. This study provides strong support for the development of novel, stable, and easily expressible HER2-targeted therapeutic molecules and also offers new insights into the rapid development of robust breast cancer drugs that may serve as ideal alternatives to monoclonal antibodies.