A near-infrared fluorogenic dimer enables background-free imaging of endogenous GPCRs in living mice

Abstract

<p>A near-infrared emitting fluorogenic dimer with environment-sensitive folding and exceptional brightness enables background-free and target-specific imaging of the naturally expressed oxytocin GPCR in living mice.</p>

Fluorogenic Squaraine Dendrimers for Background‐Free Imaging of Integrin Receptors in Cancer Cells

“…The obtained conjugate, SQPEG‐oct‐RGD , was applied for imaging α V β 3 integrin receptor, overexpressed on the surface of cancer (U‐87 MG) cells. We expected that the ligand‐receptor binding would decrease the local polarity of the dendrimer environment, in line with previous data on solvatochromic and fluorogenic dimer probes for oxytocin GPCR, [14a, 17, 19, 34a] and biotin receptor [18] . Fluorescence microscopy of U‐87 MG cells incubated for 1 h with SQPEG‐oct‐RGD probe revealed strong intracellular signal despite the use of very low probe concentrations (3 n m ).…”

“…We hypothesized that dendrimer fluorophores may exhibit different intramolecular dye–dye aggregation states as a function of solvent. In water, hydrophobic interactions within low polar SQ dyes should drive formation of non‐emissive aggregates (collapsed OFF state, Scheme 1 A), similar to that observed before for fluorogenic dimers [17–20] . Then in organic media or in the low polar environment of the target membrane receptor, the dendrimer would switch from the collapsed state to the expanded state, where dyes are well separated from each other leading to the highly emissive dendrimer (ON state, Scheme 1 A).…”

“…This probe enabled imaging G‐protein coupled receptor (oxytocin) with high signal‐to‐background ratio in wash‐free conditions [17] as well as to detection of biotin receptors in cancer cells [18] . The concept was extended to near‐infrared cyanine 5.5 dyes for in vivo imaging of natively expressed oxytocin receptors in live mice [19] and to rhodamine‐based dimers to light up RNA aptamers in live cells [20] . However, it remains unclear whether environment‐sensitive dyes operating by ACQ principle can be designed using dendrimer systems, [21] which can combine larger number of dyes.…”

Fluorescence Response and Self‐Assembly of a Tweezer‐Type Synthetic Receptor Triggered by Complexation with Heme and Its Catabolites

“…To test this idea, compound 8 containing two sulfo‐Cy5 moieties was prepared (Figure 8) and compared with 4 . Compound 8 (1.5 μ m ) has a weak absorption band around 646 nm in the UV/Vis spectrum and exhibits weak fluorescence in comparison with 4 (3.0 μ m ) under the same conditions probably due to intramolecular interactions between the two sulfo‐Cy5 moieties of 8 (Figure S23) [37b,c, 39] . These results suggest that the pH‐dependent change in the fluorescence spectra of 2 is due to the quenching arising from intermolecular interactions between the sulfo‐Cy5 moieties in the self‐assembled structures [39] .…”

Real-time imaging of cell-surface proteins with antibody-based fluorogenic probes

“…We envisioned that two uorophores situated on the H/L chains of the same "Y" tip are prone to form dye-dye interaction, and it is likely to be disrupted upon antigen binding. Herein we focus on dyes that undergo self-quenching in aqueous media through H-type dimerization via p-p stacking, 9,[18][19][20][21] while getting restored upon disaggregation. In addition, improved signal-tobackground contrast would be achieved if the dye is environment-sensitive, due to its proximity to the hydrophobic plasma membrane upon interacting with cell-surface targets.…”