A caged luciferin analogue generating near-infrared bioluminescence for activity-sensing of labile iron

Iron plays a vital role in physiological processes due to its high oxygen affinity and efficient redox capability. However, perturbations in iron homeostasis, particularly in its labile forms that drive oxidative stress, have been implicated in a spectrum of pathologies, including infectious diseases, malignancies, and neurodegenerative disorders. Despite the critical importance of detecting labile Fe²⁺, conventional fluorescent and bioluminescent probes are constrained by inherent limitations, such as suboptimal sensitivity, elevated background noise, and inadequate tissue penetration depth. To overcome these challenges, we report the development of a novel caged luciferin analogue, O-Akalumine (O-Aka), designed with an Fe²⁺-specific switchable N-oxide bond to enable turn-on near-infrared (NIR) bioluminescence imaging of labile Fe²⁺. The bioluminescence emitted by O-Aka in the presence of native firefly luciferase is centered in the NIR spectrum (λ_max = 677 nm), substantially improving signal penetration through biological tissues. Exhibiting low intrinsic background noise, high sensitivity, and deep tissue imaging capability, O-Aka effectively visualized exogenous Fe²⁺ in cellular models and a murine breast cancer model, as well as endogenous Fe²⁺ in an acute cardiac injury model. These results underscore the utility of O-Aka as a robust bioluminescent probe for elucidating the physiological and pathological roles of Fe²⁺ and exploring its potential anticancer mechanisms.