Toremifene exerts chemopreventive effects against breast cancer through MTHFD1L suppression and ROS-mediated...

Chemoprevention represents a critical strategy for high-risk breast cancer populations. This study investigated the efficacy and potential mechanisms of toremifene as a preventive agent against breast carcinogenesis.

Breast tumorigenesis was induced in female Sprague-Dawley rats with a single dose 7,12-dimethylbenz[a]anthracene (DMBA, 100 mg/kg), followed by daily toremifene administration at low (5 mg·kg-1·day-1) or high (40 mg·kg-1·day-1) doses for short (4-week) or long (about 28-week) duration. Sodium carboxymethyl cellulose (CMC-Na) served as the vehicle control, and tamoxifen (13.3 mg·kg-1·day-1) as the positive chemopreventive control. Mass spectrometry-based proteomics was employed to identify differentially expressed proteins (DEPs) in normal, atypical hyperplasia, and cancerous breast tissues. Mechanistic insights were derived through bioinformatics, network pharmacology, molecular docking, in vitro validation, and analysis of clinical human breast cancer specimens. Redox homeostasis and apoptosis were assessed by measuring the ratio of reduced/oxidized nicotinamide adenine dinucleotide phosphate (NADPH/NADP+), along with cytochrome c (Cyt-c) release, B-cell lymphoma-2 (BCL-2) expression, and intracellular reactive oxygen species (ROS) levels.

Toremifene showed no obvious hepatotoxicity post-DMBA and significantly reduced tumor incidence, volume, multiplicity, and malignancy progression. Proteomic analysis revealed 798 conserved DEPs during breast carcinogenesis. Pathway enrichment tied toremifene's effects to metabolic reprogramming, transcriptional and translational regulation, apoptosis, and other cancer-related pathways. Mechanistically, toremifene suppressed methylenetetrahydrofolate dehydrogenase (NADP+ Dependent) 1-like (MTHFD1L) expression, disrupting redox homeostasis, increasing ROS levels and triggering apoptosis.

Toremifene exhibits potent chemopreventive activity by targeting MTHFD1L-mediated metabolic dysregulation and ROS-driven apoptosis, offering a promising alternative to tamoxifen for breast cancer prevention.