# Biparatopic HER2-targeted nanobody binder synergizes with trastuzumab in resistant tumor cells

## TL;DR

A new nanobody-based drug shows better results than existing treatments in HER2-positive cancer cells, especially those resistant to trastuzumab.

## Contribution

A novel biparatopic nanobody binder was developed that synergizes with trastuzumab in resistant tumor cells.

## Key findings

- AH induced greater HER2 receptor saturation, internalization, and degradation than trastuzumab and pertuzumab combined.
- AH showed superior antitumor efficacy with trastuzumab in resistant cancer cells compared to trastuzumab plus pertuzumab.
- Structural modeling suggests a trans-binding mode enabling multivalent HER2 clustering.

## Abstract

Human epidermal growth factor receptor 2 (HER2) is a key oncogenic driver in diverse solid tumors. Although HER2-targeted therapies such as trastuzumab and pertuzumab confer substantial clinical benefits, therapeutic resistance remains a major challenge, necessitating the development of next-generation agents. Here, we engineered a biparatopic nanobody-based binder, A9F5-H2F5-Fc (AH), designed to target ECD I and ECD II of HER2. In HER2-expressing tumor cells, AH induced greater receptor saturation, internalization, and degradation than the combination of trastuzumab and pertuzumab. Notably, in trastuzumab-resistant cancer cells, AH exhibited superior synergistic antitumor efficacy in combination with trastuzumab, outperforming trastuzumab plus pertuzumab. Structural modeling predicted a trans-binding mode that enables multivalent HER2 clustering, indicative of a distinct mechanism of action. These findings highlight AH as a rationally designed biparatopic binder with potential to overcome trastuzumab resistance and underscore the potential of nanobody-based biparatopic strategies to enhance antitumor efficacy in HER2-positive cancers.