Use of the “Ru‐ ¹ O ₂ ‐Hydrazide” System Catalyzed by Metallic Ruthenium Complexes to Decipher the Interaction Between Microbes and Host Cancer Cells

ABSTRACT The dynamic interplay between bacteria and host cancer cells plays a critical role in tumor microenvironment modulation, bacterial pathogenesis, and potential oncotherapy applications. However, traditional methods often fail to capture transient or spatially restricted molecular interactions at the bacteria‐cancer cell interface. Proximity labeling has emerged as a promising technology for capturing the interaction between bacteria and host‐cancer cell. Photocatalytic proximity labeling is more efficient, faster, and higher in resolution than enzyme‐catalyzed proximity labeling. Here, we employ photoactivatable proximity labeling technology—the “Ru‐ ¹ O ₂ ‐hydrazide” system to rapidly capture the interaction between bacteria and host cancer cells. This system is using the singlet oxygen ( ¹ O ₂ ) mechanism with biotin hydrazide by anchoring the photosensitizer Ru(bpy) ₃ ²⁺ on the bacteria surface to efficiently and discriminatively capture the bacteria‐host cancer cell interactions (BHIs). Furthermore, we established a quantitative strategy based on the “Ru‐ ¹ O ₂ ‐hydrazide” system to characterize bacteria‐host cell interaction strength. This strategy allows for systematic evaluation of drug effects on BHIs, offering novel insight into pharmaceutical modulation of bacteria‐host cancer cell crosstalk.