Pretargeted Multimodal Tumor Imaging by Enzymatic Self-Immobilization Labeling and Bioorthogonal Reaction

Covalent modification of cell membranes has shown promise for tumor imaging and therapy. However, existing membrane labeling techniques face challenges such as slow kinetics and poor selectivity for cancer cells, leading to off-target effects and suboptimal in vivo efficacy. Here, we present an enzyme-triggered self-immobilization labeling strategy, termed E-SIM, which enables rapid and selective labeling of tumor cell membranes with bioorthogonal trans-cycloctene (TCO) handles in vivo. E-SIM utilizes P-TCO, an alkaline phosphatase (ALP) responsive quinone methide (QM) precursor with a TCO group, facilitating the rapid conjugation of high-density TCO handles onto tumor cell membranes via proximity labeling. These TCO groups then react efficiently with tetrazine (Tz)-bearing reporters via a fast bioorthogonal reaction, resulting in significant enrichment of reporters of various sizes and imaging modalities on tumor cell membranes. We demonstrate the efficacy of E-SIM labeling and bioorthogonal reaction for pretargeted multimodality imaging of tumors in vivo. Notably, we achieve selective and efficient installation of Tz-modified Renilla luciferase on tumor cells in vivo, thereby offering highly sensitive bioluminescence signals for detecting and guiding the surgical removal of small human HepG2 liver tumor peritoneal metastases. E-SIM represents a robust tool for precise tumor cell labeling in complex in vivo environments, feasible for pretargeted enrichment of various reporters in tumors for multimodal imaging applications.