Engineered bacteria as ultrasound-responsive carbon monoxide vehicles for Cancer gas therapy and synergistic immunotherapy

Biomineralization of bacterial as a ultrasound (US)-triggered CO generator. • Engineered bacteria can decompose through acid-response in tumor microenvironment. • Self-supplying H 2 O 2 , amelioration of hypoxia, Ca 2+ -induced mitochondria damage. • US-triggered CO release for apoptosis in tumor cells. • Activating anti-tumor immune responses for significant inhibition of tumor growth. Carbon monoxide (CO) gas therapy is emerging as a highly promising strategy in cancer treatment. However, the tumor-targeted delivery and on-demand release of CO remain formidable challenges, and monotherapeutic efficacy is inherently limited. To address these issues, we report a self-guided “CO-releasing bomb” constructed by armoring Escherichia coli ( E. coli ) with 3-hydroxyflavone-D-alanine (HF-D-Ala) and calcium peroxide (CaO 2 ) nanoparticles (EHC). Upon reaching the acidic, hypoxic tumor microenvironment (TME), CaO 2 instantly generates Ca 2+ and H 2 O 2 ; the bacterium then self-catalyzes H 2 O 2 to produce a local O 2 burst. Subsequent ultrasound irradiation triggers HF-D-Ala to liberate a high concentration of CO owing to the O 2 -rich environment, selectively damaging tumor-cell mitochondria and inducing apoptotic death. Moreover, the O 2 generation alleviates tumor hypoxia and reverses the immunosuppressive TME. Concurrently, E. coli antigens promote dendritic cell maturation and enhance T-lymphocyte recruitment and infiltration. In vivo studies demonstrate that the EHC under US irradiation significantly suppresses tumor growth and potently activates antitumor immunity. These findings provide compelling evidence to support the potential application of combined CO gas therapy and immunotherapy for in vivo tumor treatment. Download: Download high-res image (58KB) Download: Download full-size image