Engineered hemolysin-secreting bacteria enable intracellular bisphosphonate self-assembly to enhance antitumor...

Intracellular self-assembly is emerging as a precision drug-delivery strategy, which effectively enhances drug accumulation within target cells and improves therapeutic efficacy. Zoledronic acid, due to its excellent Fe²⁺-chelating capability, serves as an ideal building block for constructing self-assembled systems. However, precisely inducing the self-assembly of zoledronic acid at tumor sites remains a critical challenge for achieving effective therapy. Here, a hemolysin-secreting Salmonella typhimurium strain is engineered to exploit its tumor colonization capacity to disrupt tumor vasculature and induce local hemorrhage. Infiltrated erythrocytes (RBCs) are phagocytosed by macrophages in the tumor. Heme oxygenase-1 (HMOX-1) then degrades heme and releases ferrous ions (Fe²⁺), which coordinate with zoledronic acid to form assemblies. The intracellularly formed Fe-zoledronic acid assemblies generate reactive oxygen species (ROS), reprogram macrophages into an antitumor phenotype, and enhance immune responses. This bacteria-mediated intracellular self-assembly strategy exploits endogenous metal ions to realize intracellular assembly, expanding the scope of self-assembly approaches and offering novel means for precise modulation of the tumor immune microenvironment by engineered bacteria.