Bacterial backpacks for targeted delivery of piezoelectric nanoparticles to enhance sonodynamic immunotherapy

Abstract Living bacterial therapy offers strong tumor‐targeting and deep penetration into hypoxic regions, but its therapeutic potential is hindered by biosafety risks from bacterial proliferation after treatment. Herein, we designed a trigger‐destructive bacterial system that combines precise tumor targeting with controllable bacterial elimination to ensure safety. Specially, sonosensitizer barium titanate nanoparticles (BTO NPs) grafted by amino silane coupling agent (γ‐aminopropyltriethoxysilane, KH550) were electrostatically anchored onto Salmonella VNP20009 to construct a nano‐biohybrid delivery system (KBTO‐VNP). Upon systemic administration, the inherent hypoxia‐targeting capability of the bacteria enabled efficient accumulation and deep penetration of the sonosensitizer into tumor tissues. In vitro studies demonstrated that, the nano‐biohybrid exhibited markedly enhanced penetration in 3D tumor spheroid models, achieving over a 100 μm increase in penetration depth compared to free nanoparticles. In vivo experiments revealed that bacterial surface modification improved the tumor‐targeting efficiency of KBTO NPs by 7‐fold. Importantly, no bacteria were recovered from normal organs after US irradiation, confirming the controllable proliferation and efficient clearance of bacteria from off‐target tissues. Therapeutic evaluations on the B16F10 subcutaneous tumor model further confirmed that KBTO‐VNP achieved remarkable tumor suppression, with an inhibition rate exceeding 96%. Moreover, immunological mechanism analysis revealed that the ultrasound‐triggered cell apoptosis released abundant tumor‐associated and bacterial antigens, which subsequently promoted robust immune cell infiltration, leading to approximately a 3‐fold increase in the intratumoral infiltration of dendritic cells and T cells. This nano‐biohybrid system offers valuable theoretical support for the advancement of sonodynamic therapy and holds great potential for future cancer treatments.