A tandem activity-based sensing and labeling strategy reveals antioxidant response element regulation of labile iron pools
Abstract
Iron is an essential element for life owing to its ability to participate in a diverse array of oxidation–reduction reactions. However, misregulation of iron-dependent redox cycling can also produce oxidative stress, contributing to cell growth, proliferation, and death pathways underlying aging, cancer, neurodegeneration, and metabolic diseases. Fluorescent probes that selectively monitor loosely bound Fe(II) ions, termed the labile iron pool, are potentially powerful tools for studies of this metal nutrient; however, the dynamic spatiotemporal nature and potent fluorescence quenching capacity of these bioavailable metal stores pose challenges for their detection. Here, we report a tandem activity-based sensing and labeling strategy that enables imaging of labile iron pools in live cells through enhancement in cellular retention. Iron green-1 fluoromethyl (IG1-FM) reacts selectively with Fe(II) using an endoperoxide trigger to release a quinone methide dye for subsequent attachment to proximal biological nucleophiles, providing a permanent fluorescent stain at sites of elevated labile iron. IG1-FM imaging reveals that degradation of the major iron storage protein ferritin through ferritinophagy expands the labile iron pool, while activation of nuclear factor-erythroid 2-related factor 2 (NRF2) antioxidant response elements (AREs) depletes it. We further show that lung cancer cells with heightened NRF2 activation, and thus lower basal labile iron, have reduced viability when treated with an iron chelator. By connecting labile iron pools and NRF2-ARE activity to a druggable metal-dependent vulnerability in cancer, this work provides a starting point for broader investigations into the roles of transition metal and antioxidant signaling pathways in health and disease.
Significance:
Iron sustains fundamental chemical processes across all kingdoms of life. However, the fluorescence quenching properties and dynamic nature of this metal nutrient make it challenging to study in complex biological systems. We present a tandem activity-based sensing/labeling strategy to enable iron detection with a turn-on fluorescence response and enhanced cellular retention through iron-dependent release of a dye that covalently traps at sites of high iron. This platform reveals complementary expansion or depletion of labile iron pools driven by degradation of ferritin or activation of the nuclear factor-erythroid 2-related factor 2 (NRF2) antioxidant response element, respectively. We further found that cancer cells with heightened NRF2 activation, and thus lower labile iron, are susceptible to iron chelation, establishing a potential druggable metal-dependent vulnerability in cancer.
Supplementary Information can be accessed here.
Ke Cheng
Postdoctoral Researcher
My research interests lie at the surface of chemistry and biology, where I am deeply passionate about applying innovative chemistry to advance fields such as chemoproteomics, drug discovery, nanomedicine, and theranostics. My aim is to provide robust methodologies for mapping biological interactomes, accelerating drug development, and expanding therapeutic opportunities.