Trastuzumab treatment is associated with ferroptosis-related alterations in HER2-positive breast cancer organoids.

Trastuzumab is widely used for HER2-positive breast cancer, but its relationship with ferroptosis remains unclear. In this study, patient-derived breast cancer organoids were used to examine trastuzumab-associated ferroptosis-related changes and the possible involvement of p53 signaling. Three independent HER2-positive breast cancer organoid lines were used for the main functional experiments, and three HER2-low organoid lines were included as control models. The IC50-based working concentration of trastuzumab was 66.31 µg/mL. Transcriptome analysis revealed enrichment of ferroptosis- and p53-related pathways after trastuzumab treatment. In HER2-positive organoids, trastuzumab reduced organoid viability and altered organoid morphology, accompanied by increased MDA, Fe²⁺, and ROS levels and decreased GSH/GSSG, SLC7A11, and GPX4 expression. The same treatment did not produce comparable changes in HER2-low organoids. Fer-1 partially attenuated the changes in organoid viability and ferroptosis-related indicators. PFT-α showed a similar partial rescue effect. In addition, p53 knockdown weakened several trastuzumab-associated changes, including alterations in viability, oxidative stress-related markers, and SLC7A11/GPX4 expression. These findings suggest that trastuzumab treatment is associated with ferroptosis-related biochemical and molecular alterations in HER2-positive breast cancer organoids, and that p53-related signaling may participate in this process.