A DXd/TLR7-Agonist Dual-Conjugate Anti-HER2 ADC Exerts Robust Antitumor Activity Through Tumor Cell Killing and Immune Activation

Abstract The emergence of trastuzumab deruxtecan (T-DXd), a new-generation antibody–drug conjugate (ADC), has profoundly altered the therapeutic paradigm for HER2-positive solid tumors, demonstrating remarkable clinical benefits. However, the combined outcomes of T-DXd with immunotherapy agents remain ambiguous. In this study, we introduce Tras-DXd-MTL1, an innovative HER2 targeting ADC that integrates the topoisomerase inhibitor DXd and a toll like receptor 7 (TLR7) agonist MTT5, linked to trastuzumab via a GGFG tetrapeptide linker. Mechanistically, Tras-DXd-MTL1 retains the DNA-damaging and cell-killing properties of topoisomerase inhibitors while simultaneously enhancing the immune response within the tumor microenvironment. This is achieved by promoting immune cell infiltration and activating dendritic cells and CD8+T cells via MTT5. In vivo evaluation of Tras-DXd-MTL1’s antitumor potency revealed a notably superior performance compared with the T-DXd (Tras-DXd) or Tras-MTL1 in immunocompetent mice with trastuzumab-resistant EMT6-HER2 tumor and immunodeficient mice with JIMT-1 tumor. This improved efficacy is primarily attributed to its dual functions of immune stimulation and cytotoxicity. Our findings highlight the potential of incorporating immunostimulatory agents into ADC design to potentiate antitumor effects and establish durable immune memory, thereby reducing tumor recurrence risks. Therefore, our study offers a novel strategy for the design of immune-activating ADCs and provides a potential approach for targeting solid tumors with different levels of HER2 expression.