Cathepsin B-activated vitamin E prodrugs target cancer stem cells and enhance chemotherapy response in triple-negative breast cancer with minimal cardiotoxicity.

Triple-negative breast cancer (TNBC) remains difficult to treat because of therapeutic resistance, cancer stem cell (CSC) enrichment, and constitutive NF-κB activation. We developed a new therapeutic strategy, A Priori Activation of Apoptosis Pathways (AAAPT), to restore apoptotic competence before chemotherapy by suppressing survival signaling and reactivating programmed cell death. Since TNBC and CSC-enriched populations overexpress Cathepsin B and exhibit lysosomal and mitochondrial vulnerabilities, we designed Cathepsin B-cleavable vitamin E analogues (AMP-001/002/003) that selectively release the active pharmacophore within tumor cells. AMP-001/002/003 demonstrated selective cytotoxicity toward Cathepsin B-positive TNBC cells, inhibited mammosphere formation, and spared normal epithelial cells and human iPSC-derived cardiomyocytes. AMP-001 synergized strongly with doxorubicin, markedly reducing its effective IC₅。 while restoring chemosensitivity. In TNBC xenograft models, AMP-001 significantly reduced tumor burden without overt systemic or cardiac toxicity. Collectively, these findings establish AAAPT as a tumor-selective chemosensitization platform that targets CSCs, reverses NF-κB-mediated resistance, exploits lysosomal-mitochondrial vulnerabilities, and expands the therapeutic index of doxorubicin by maintaining antitumor efficacy while reducing cardiotoxicity.