Radiation-responsive Salmonella mediate therapeutics precise delivery for synergistic tumor radio-immunotherapy.

Direct cytosolic delivery of proteins represents a transformative approach for developing next-generation therapeutic proteins targeting intracellular pathways. Leveraging the unique tumor-targeting capabilities of attenuated Salmonella Typhimurium, including its propensity for tumor-localized colonization and cellular internalization, we have developed a genetically engineered strain regulated by an ionizing radiation-responsive promoter element (rRPE) for precise tumor-specific protein delivery. This innovative rRPE system operates through a radiation-induced molecular cascade: ionizing radiation triggers DNA damage, activating RecA, which subsequently promotes LexA self-hydrolysis, thereby relieving radiation-associated operator gene (rAO) inhibition and enabling PpagC-mediated expression of downstream genes. This radiation-responsive regulatory mechanism allows Salmonella to maintain controlled expression of therapeutic proteins while minimizing premature leakage, with protein production specifically triggered by therapeutic radiation doses. The system demonstrates remarkable therapeutic efficacy through the controlled intracellular release of Shiga toxin's active moiety, STx1A, within bacteria-colonized tumor cells. The intracellularly delivered STx1A effectively disrupts DNA damage repair mechanisms. The synergistic combination of an engineered bacterial system with radiotherapy not only achieves direct tumor growth inhibition but also elicits robust anti-tumor immune responses. Therefore, our investigation establishes a novel paradigm for enhancing radiotherapy efficacy and provides a versatile platform for radio-genetically controlled therapy, potentially revolutionizing the field of bacteria-mediated precision medicine.