Otvodnikova, D. E.; Kirill, C. V.; Gornostaeva, S.; Meshechko, M.; Kuchur, O. A.; Vladimir, S. V.; Tsymbal, S. A.

In this work we present antibody-metal conjugate as a new subclass of antibody-drug conjugates (ADC) for the chemodynamic therapy of cancer based on the rapid generation of reactive oxygen species (ROS) upon copper reduction. We used conventional therapeutic antibody trastuzumab and DOTA-NHS ester for the design and initial proof-of-concept. Thus, trastuzumab-DOTA-copper conjugate (TDCC) was synthesized. We demonstrate that TDCC retains specific binding to HER2-positive cancer cells with approximately native immunoreactivity and achieves stable copper incorporation with an average drug-to-antibody ratio of up to ~8. In the presence of physiological reducing agents such as N-acetylcysteine or cysteine, TDCC generates substantial reactive oxygen species (ROS), leading to pronounced cytotoxicity and long-term suppression of clonogenic survival in HER2-positive SK-BR-3 and BT-474 cells. Notably, HER2-negative MDA-MB-231 cells and non-malignant HS5 fibroblasts remain largely unaffected, confirming target-dependent activity. The conjugate remains stable under storage conditions for up to 30 days, and the DOTA linker itself does not interfere with copper-mediated redox chemistry. Our findings identify TDCC as a novel class of targeted oxidative stress inducers that exploit the vulnerability of HER2-positive tumors to copper-mediated cytotoxicity. This strategy not only preserves the specificity of antibody-based delivery but also introduces a distinct mechanism of action capable of bypassing conventional resistance pathways, warranting further preclinical development.