Calcium phosphate-mineralized nanoplatform for enhanced ferroptosis and synergistic anti-PDL1 therapy in triple-negative breast cancer through multi-pathway targeting

Ferrotherapy has risen as a promising therapeutic approach for triple-negative breast cancer (TNBC); however, its potency is frequently compromised due to tumor cells' ability to evade ferroptosis via various resistance pathways and insufficient immunogenicity. To overcome these limitations, we have engineered a calcium phosphate-mineralized ferroptosis inducer nanoplatform, termed Lf-PEG-CaP@iFSP1-Brequinar-Erastin-Fe³⁺-TA (LP-CaP@iBEFT), designed to augment ferroptosis by simultaneously targeting three key pathways: glutathione peroxidase 4 (GPX4), ferroptosis suppressor protein 1 (FSP1), and dihydroorotate dehydrogenase (DHODH). Once internalized and reached the acidic tumor microenvironment (TME), the nanoplatform discharges its therapeutic payloads, comprising inhibitors of FSP1 (iFSP), brequinar, erastin, and iron ions. The first three components were tailored to inhibit key pathways to ferroptosis, while the released iron ions initiate ferroptosis by catalyzing the generation of reactive oxygen species (ROS) via Fenton reactions. The calcium phosphate-mineralized ferroptosis inducer nanoplatform promotes the maturation of DC cells, enhances the infiltration of T cells and releases immunity-related factors, thereby altering the immunosuppressive microenvironment. In conjunction with anti-PD-L1 therapy, LP-CaP@iBEFT boosts T lymphocyte-mediated immune infiltration, thereby amplifying the anti-tumor response and offering a therapeutic approach for TNBC. STATEMENT OF SIGNIFICANCE: We developed an acid-responsive nanoplatform that specifically targets tumor cells that overexpress lactoferrin receptors. This nanoplatform degrades within the acidic tumor environment to release the payload components iFSP1, brequinar, erastin, and Fe³⁺, which collectively inhibit three pathways of ferroptosis. This approach effectively dismantles the "triple defense" mechanism that tumor cells employ to resist ferroptosis. In addition, this nanoplatform synergizes with anti-PD-L1 immune checkpoint blockade, enhancing the T cell-mediated destruction of tumor cells.