A Novel Self‐Regulated, Non‐Directional Magnetic Thermos‐Brachytherapy ¹²⁵ I Seed Enhances Anticancer Efficacy by Rescuing Immune Escape

Abstract Integrating mild hyperthermia (MH) with ¹²⁵ I brachytherapy holds potential for overcoming treatment resistance and improving anticancer efficacy. Here, magnetic nanoparticles (MNPs) with a suitable Curie temperature are constructed and incorporated with silver rods coated with ¹²⁵ I to form composite seeds. In vitro simulations and in vivo validations demonstrated their effective performance in radiation dose and temperature control. Compared with traditional thermoseeds and previously reported MNPs, this composite seed exhibits direction‐independent and self‐regulated heating efficiency. Additionally, the titanium shell prevented MNPs leakage and enabled its repeated hyperthermia treatment capacity. Subsequently, the enhanced pancancer anticancer efficacy of the composite seed‐relied ¹²⁵ I@MH therapy is confirmed through cellular and animal experiments involving liver cancer and prostate cancer. Further tumor microenvironment investigations based on a subcutaneous liver cancer mouse model identified that ¹²⁵ I therapy recruited Cd274/Pd‐l1 ⁺ neutrophils and induced T‐cell exhaustion, leading to immune evasion and brachytherapy resistance. The addition of MH significantly reversed this effect, restoring the function of effector T cells (IFN‐γ ⁺ T cells) and activating T‐cell immunity. In conclusion, this study developed a novel composite seed with superior anticancer efficacy, which holds promising therapeutic potential for the treatment of malignancies, particularly solid tumors, in future clinical practice.