Abstract 3617: Trastuzumab-conjugated gold nanoparticles as novel HER2-targeted therapeutics against trastuzumab-resistant gastric cancer

While trastuzumab (Tmab), a monoclonal antibody that targets the human epidermal growth factor receptor 2 (HER2), has greatly contributed to improve survival outcomes in metastatic gastric cancer, an issue of concern is that no current HER2-targeted therapeutic agent is effective against Tmab-resistant gastric cancer. Nanotechnology, which has progressed rapidly in recent years, greatly contributes to progress in medical fields including cancer therapy, and especially, gold nanoparticles (AuNPs) are attention-grabbing nanomaterials that are promising drug carriers with unique properties of high in vivo stability and a large surface area available for attachment of materials such as antibodies. Methods: We created HER2-targeted AuNPs by conjugating Tmab onto their surface (T-AuNPs) and examined their therapeutic efficacy and cytotoxic mechanisms using HER2-postive Tmab-resistant (MKN7) or Tmab-sensitive (NCI-N87) gastric cancer cell lines in vitro and in vivo. We also examined T-AuNPs on HER2-negative MKN74 gastric cancer cells with adenoviral vector-mediated overexpression of the HER2 extracellular domain (HER2-ECD). Results: The size of T-AuNPs was 85.39 ± 0.68 nm and the surface was negatively charged with 39.43 ± 0.85 mV. In in vitro assays, T-AuNPs showed 6-fold higher cytotoxic activity than Tmab against NCI-N87 cells. Then, T-AuNPs showed significantly stronger cytotoxic effects than controls against both MKN7 and NCI-N87 cells although Tmab had no effect on MKN7 cells. Autophagy was proven to play an important role in T-AuNPs cytotoxic mechanisms. This autophagy was considered to be induced by HER2-dependent internalization of T-AuNPs, some of which were interestingly located in the cytoplasm independent of lysosomal encapsulation. Although T-AuNPs were not cytotoxic towards MKN74 cells, they became cytotoxic following HER2-ECD overexpression. Finally, Intratumoral injection of T-AuNPs showed potent antitumor effects, which were mediated by autophagy, against NCI-N87 and MKN7 subcutaneous tumors in vivo mouse models. Conclusion: HER2-targeted AuNPs with conjugated Tmab can be a promising strategy for the development of novel therapeutic agents to overcome Tmab resistance in gastric cancer. Citation Format: Kento Kumon, Tetsushi Kubota, Shinji Kuroda, Nobuhiko Kanaya, Yoshihiko Kakiuchi, Tomoko Tsumura, Satoru Kikuchi, Shunsuke Kagawa, Hiroshi Tazawa, Toshiyoshi Fujiwara. Trastuzumab-conjugated gold nanoparticles as novel HER2-targeted therapeutics a