A Tandem‐Locked Chemiluminescent Probe for Imaging of Macrophage Polarization

Tumor‐associated macrophages (TAMs) play a role in both pro‐and anti‐tumor functions; and detection of M1 TAMs is imperative to assess cancer immunotherapeutic efficacy. However, many optical probes suffer from shallow tissue penetration depth and poor specificity toward M1 TAMs. Herein, we report a tandem‐locked NIR chemiluminescent (CL) probe for imaging of M1 TAM during cancer immunotherapy. Through a combined molecular engineering approach via both atomic alternation and introduction of electron‐withdrawing groups, near‐infrared (NIR) chemiluminophores are screened out to possess record‐long emission (over 800 nm), record‐high CL quantum yield (2.7% einstein/mol), and prolonged half‐life (7.7 h). Based on an ideal chemiluminophore, the tandem‐locked probe (DPDGN) is developed to only activate CL signal in the presence of both tumour (γ‐glutamyl transpeptidase) and M1 macrophage biomarkers (nitric oxide). Such a tandem‐lock design ensures its high specificity towards M1 macrophages in the tumor microenvironment over those in normal tissues or peripheral blood. Thus, DPDGN permits noninvasive imaging and tracking of M1 TAM activation in the tumor of living mice during therapy, showing a good correlation with ex vivo methods. This study not only reports a new molecular approach towards highly efficient chemiluminophores but also reveals the first tandem‐locked CL probes for enhanced imaging specificity.