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

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.