We report a pair of fluorinated, redox-active copper complexes for potential use as (19)F MRI contrast agents for detecting cellular hypoxia. Trifluorinated Cu(II) ATSM-F3 displays the appropriate redox potential for selective accumulation in hypoxic cells and a completely quenched (19)F NMR signal that is "turned on" following reduction to Cu(I). Incubation of cancer cells with CuATSM-F3 resulted in a selective detection of (19)F signal in cells grown under hypoxic conditions.

Elevated levels of reactive oxygen species and peroxidase expression are often associated with inflammation and inflammatory diseases. We developed two novel Co(II) complexes that can be used to detect oxidative activity associated with inflammation using F magnetic resonance imaging (MRI). These agents display a large change inF chemical shift upon oxidation from Co(II) to Co(III), facilitating selective visualization of both species using chemical shift selective pulse sequences. This large chemical shift change is attributed to a large magnetic anisotropy in the high spin Co(II) complexes. Importantly, the differing reactivity of the two agents allows for detection of either HO production and/or the activity of peroxidase enzymes, providing two useful platforms for F MR hot spot imaging of oxidative events associated with biological inflammation.

F magnetic resonance imaging (MRI), an emerging modality in biomedical imaging, has shown promise for in vitro and in vivo preclinical studies. Here we present a series of fluorinated Cu(II)ATSM derivatives for potential use as F magnetic resonance agents for sensing cellular hypoxia. The synthesized complexes feature a hypoxia-targeting Cu coordination core, nine equivalent fluorine atoms connected via a variable-length poly(ethylene glycol) linker. Introduction of the fluorine moiety maintains the planar coordination geometry of the Cu center, while the linker length modulates the Cu reduction potential, F NMR relaxation properties, and lipophilicity. In particular, theF NMR relaxation properties were quantitatively evaluated by the Solomon-Bloembergen model, revealing a regular pattern of relaxation enhancement tuned by the distance between Cu and F atoms. Finally, the potential utility of these complexes for sensing reductive environments was demonstrated using both F MR phantom imaging andF NMR, including experiments in intact live cells.

CONSPECTUS: Fluorine magnetic resonance imaging ( 19 F MRI) is a promising bioimaging technique due to the favorable magnetic resonance properties of the 19 F nucleus and the lack of detectable biological background signal. A range of imaging agents have been developed for this imaging modality including small molecule perfluorocarbons, fluorinerich macromolecules and nanoparticles, and paramagnetic metal-containing agents. Incorporation of paramagnetic metals into fluorinated agents provides a unique opportunity to manipulate relaxation and chemical shift properties of 19 F nuclei. Paramagnetic centers will enhance relaxation rates of nearby 19 F nuclei through paramagnetic relaxation enhancement (PRE). Further, metals with anisotropic unpaired electrons can induce changes in 19 F chemical shift through pseudocontact shift (PCS) effects. PRE and PCS are dependent on the nature of the metal center itself, the molecular scaffold surrounding it, and the position of the 19 F nucleus relative to the metal center. One intriguing prospect in 19 F magnetic resonance molecular imaging is to design responsive agents that can serve to provide a read out biological activity, including the activity of enzymes, redox activity, the activity of ions, etc. Paramagnetic agents are well suited for this activity-based sensing as metal complexes can be designed to respond to specific biological activities and give a corresponding 19 F response that results from changes in the metal complex structure and subsequently PRE/PCS. Broadly speaking, when designing paramagnetic 19 F MR biosensors, one can envision that in response to changes in analyte activity, the number of unpaired electrons of the metal changes or the ligand conformation/chemical composition changes. This Account highlights activity-based probes from the Que lab that harness paramagnetic metals to modulate 19 F signal. We discuss probes that use conversion from Cu 2+ to Cu + in response to reducing environments to dequench the 19 F MR signal. Probes in which oxidants convert Co 2+ to Co 3+ , resulting in chemical shift responses, are also described. Finally, we explore our foray into using Ni 2+ coordination switching to furnish probes with different 19 F signals when they are converted between 4-coordinate square planar and higher coordination numbers. A major barrier for 19 F MR molecular imaging is in vivo application, as signal sensitivity is relatively low, requiring long imaging times to detect imaging agents. Nanoparticle and macromolecular agents show promise due to their higher fluorine density and longer circulation times; however, their analyte scope is limited to analytes that induce cleavage events. A grand challenge for researchers in this area is adapting lessons learned from small molecule paramagnetic probes with promising in vitro activities for the development of probes with enhanced in vivo utility for basic biological and clinical applications.

Radiation-induced bystander effect (RIBE) describes a set of biological effects in non-targeted cells that receive bystander signals from the irradiated cells. RIBE brings potential hazards to adjacent normal tissues in radiotherapy, and imparts a higher risk than previously thought. Excessive release of some substances from irradiated cells into extracellular microenvironment has a deleterious effect. For example, cytokines and reactive oxygen species have been confirmed to be involved in RIBE process via extracellular medium or gap junctions. However, RIBE-mediating signals and intercellular communication pathways are incompletely characterized. Here, we first identified a set of differentially expressed miRNAs in the exosomes collected from 2 Gy irradiated human bronchial epithelial BEP2D cells, from which miR-7-5p was found to induce autophagy in recipient cells. This exosome-mediated autophagy was significantly attenuated by miR-7-5p inhibitor. Moreover, our data demonstrated that autophagy induced by exosomal miR-7-5p was associated with EGFR/Akt/mTOR signaling pathway. Together, our results support the involvement of secretive exosomes in propagation of RIBE signals to bystander cells. The exosomes-containing miR-7-5p is a crucial mediator of bystander autophagy.