Engineering Cell Permeable Constrained Peptides for Precise Targeted Alpha Radionuclide Therapy of Osteosarcoma

Osteosarcoma is an aggressive malignancy that often resists conventional therapies. Targeted α‑radiopharmaceutical therapy (TAT) provides a promising solution, offering potent localized cytotoxicity, reduced recurrence, and minimal acquired resistance. Mouse Double Minute 2 (MDM2), often amplification in osteosarcoma, serving as an ideal TAT target. Here, we present a TAT strategy that leverages the cell nucleus-enrichment capability of a 225Ac-labeled, MDM2-targeting stapled peptide for effective treatment of osteosarcoma. Rapid PET/CT-based screening enables precise identification of an optimized MDM2-targeting stapled peptide ligand (tumor uptake: 8.26 %ID/g; nucleus uptake fraction: 18.9 %). A single micro-dose (17 KBq) markedly suppressed osteosarcoma growth with satisfactory safety, resulting in growth arrest in over 50% of tumors without signs of recurrence. Mechanistically, the 225Ac-labeled stapled peptide rapidly triggers cellular stress programs in osteosarcoma and progressively induces the formation of the senescence-associated secretory phenotype (SASP). Our findings suggest that TAT represents an effective therapeutic strategy for osteosarcoma, with MDM2-targeting stapled peptide serving as an ideal ligand for this approach.