Abstract
The ability to monitor molecules volumetrically throughout the body could provide valuable biomarkers for studies of healthy function and disease, but noninvasive detection of molecular targets in living subjects often suffers from poor sensitivity or selectivity. Here we describe a family of potent imaging probes that can be activated by molecules of interest in deep tissue, providing a basis for mapping nanomolar-scale analytes without the radiation or heavy metal content associated with traditional molecular imaging agents. The probes are reversibly caged vasodilators that induce responses detectable by hemodynamic imaging; they are constructed by combining vasoactive peptides with synthetic chemical appendages and protein blocking domains. We use this architecture to create ultrasensitive biotin-responsive imaging agents, which we apply for wide-field mapping of targets in rat brains using functional magnetic resonance imaging. We also adapt the sensor design for detecting the neurotransmitter dopamine, illustrating versatility of this approach for addressing biologically important molecules.
Highlights
The ability to monitor molecules volumetrically throughout the body could provide valuable biomarkers for studies of healthy function and disease, but noninvasive detection of molecular targets in living subjects often suffers from poor sensitivity or selectivity
Magnetic resonance imaging (MRI) contrast agents are detectable in deep tissue, and can be sensitized to a variety of biologically relevant targets[8], but imaging agents for MRI are usually only detectable at micromolar concentrations, or at similar mass doses when nanoparticle contrast agents are used
We demonstrate the generality of our design by creating a second activatable vasoprobes for analyte targeting (AVATars) for detection of the neurotransmitter dopamine, indicating the potential of vasoprobe technology for addressing a wide variety of molecular phenomena in the brain and other organs
Summary
BT-AVATar is strongly activated by both biotinylated bovine serum albumin and HEK293 cells, exhibiting increases in PAC1 receptor activation by 675 ± 69% and 227 ± 30%, respectively, versus minimal responses to unbiotinylated controls (Fig. 3d) These results show that BT-AVATar maintains sensitivity and selectivity for biotin even in biological environments, suggesting the suitability of vasoprobe-based sensors for applications in vivo. Simple modeling of the DAAVATar mechanism indicates that its neurotransmitter sensitivity could be altered by changing the number of DA conjugation sites on PACAP, as well as the affinity of the IgG for both tethered and free DA (Supplementary Fig. 10) In keeping with these predictions, we found that a triply dopaminylated PACAP could be used to assemble a DA-AVATar with higher EC50 but enhanced dynamic range (Supplementary Fig. 11). These results demonstrate that the AVATar principle can be used to create tunable probes with high sensitivity for a variety of small molecules
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