Metal- and Redox-Dependent Oxytocin Species Differentially Regulate Invasion and Migration in Triple-Negative Breast Cancer.

Oxytocin is a nine-amino-acid peptide hormone renowned for its roles in reproduction and childbirth. Beyond these classical functions, it has attracted increasing research interest for its broader biological activities. Additionally, clinical studies have proposed oxytocin as a potential therapeutic agent for breast cancer, particularly triple-negative breast cancer, due to its ability to modulate cell proliferation and migration. Despite its wide recognition across various biological systems, the full scope of oxytocin's activity remains incompletely understood. Early studies have shown that metal ions can affect oxytocin's function. Building on this, our group previously demonstrated that oxytocin's redox state, regulated by its two cysteine residues, also modulates oxytocin-dependent signaling through Cu(II) and Zn(II) binding in HEK293T cells expressing the oxytocin receptor. In this study, we investigated the effects of metal-oxytocin preparations on triple-negative breast cancer cells (MDA-MB-231), focusing on cell migration and invasion. Our findings show that samples containing both oxytocin and copper (CuOT) differentially influence cellular behavior in a manner that depends on the redox state of oxytocin. Preparations combining Cu(II) with oxidized oxytocin (CuoxOT) promote cell invasion, while preparations combining Cu(II) with reduced oxytocin (CurOT) enhance migration. LC-MS analysis revealed that the cellular environment promotes partial reduction of oxOT and distinct structural rearrangements among CuOT species, suggesting dynamic redox modulation of OT in a tumor microenvironment. To assess the signaling mechanisms underlying these effects, we found that CuoxOT significantly downregulated PI3K and β-arrestin 2 expressions. These changes may support the distinct cellular responses observed with CuoxOT, particularly in relation to migration and invasion. This study highlights the potential of redox- and metal state-dependent oxytocin species as modulators of distinct signaling pathways in triple-negative breast cancer, offering new perspectives for targeted therapeutic strategies.