An Environmentally Sensitive Epidermal Growth Factor Receptor Probe for Turn-On Tumor Imaging and TGF-β1-Mediated Cancer Immunotherapy via the Selective Depletion of TI-Tregs

Disruptions of epidermal growth factor receptor (EGFR) are implicated in various cancers, and EGFR-overexpressing tumors are co-infiltrated with immunosuppressive tumor-infiltrating regulatory T cells (TI-Tregs) that remain difficult to target. Here, we developed a novel class of environment-sensitive EGFR probes (ES-JFTNs) by conjugating phthalimide or benzoxadiazole fluorophores to an anilinoquinazoline scaffold. The lead probe ES3-JFTN exhibits selectivity as a turn-on fluorescent agent upon EGFR binding. ES3-JFTN inhibits EGFR phosphorylation and suppresses the TGF-β1 pathway, leading to FOXP3 downregulation via the EGFR/glycogen synthase kinase 3β (GSK3β) axis and selectively depleting TI-Tregs while stimulating CD8+ T cell activation. In tumor-bearing mice, it achieves a 77.69% tumor inhibition rate, significantly outperforming gefitinib (52.40%). These findings establish ES3-JFTN as a dual-functional theranostic agent that overcomes the immunosuppressive tumor microenvironment and guides the rational design of EGFR-targeted immunotherapies.