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 one of the most difficult malignancies to treat owing to high relapse, enrichment of cancer stem cells (CSCs), and constitutive activation of pro-survival signaling such as NF-κB. We conceived a new therapeutic concept—A Priori Activation of Apoptosis Pathways (AAAPT)—designed to pre-empt and circumvent tumor tactics that desensitize cells to diverse interventions by restoring apoptotic checkpoints while suppressing dysregulated survival pathways (e.g., NF-κB) that are upregulated in resistant clones. CSCs and therapy-refractory TNBC subpopulations overexpress Cathepsin B and exhibit organelle fragility in lysosomes and mitochondria. To target these liabilities, we designed Cathepsin B–cleavable vitamin E analogs (AAAPT leading drugs: AMP-001/002/003) that selectively release active agents inside tumor and CSC populations.In vitro, AMP-001/002/003 showed selective cytotoxicity toward Cathepsin B–positive TNBC cells, inhibited mammosphere formation (a functional surrogate for CSC self-renewal), and spared non-malignant epithelial cells and human iPSC-derived cardiomyocytes. Combination studies revealed strong synergy with doxorubicin, lowering its effective IC50. In vivo, AMP-001 significantly reduced TNBC xenograft burden without overt systemic or cardiac toxicity, consistent with the in-vitro safety profile.These findings support Cathepsin B–activated vitamin E analogs as tumor-selective chemosensitizers that address key TNBC liabilities—CSCs, NF-κB–mediated resistance, and organelle-level stress responses—while mitigating doxorubicin-associated cardiotoxicity.