Controllable stripping of radiolabeled group in vivo to optimize nuclear imaging via NO-responsive bioorthogonal cleavage reaction

A novel “turn-off” strategy for controllable radionuclide clearance is established. 1,4-dihydropyridine (DHP) is used as a conditional linker to connect a radioisotope labeled moiety and nano-agent. A highly specific, sensitive and effective C–C bond cleavage of DHP happens in vivo when treated with nitric oxide which is provided by glyceryl trinitrate (GTN). The radioactive cut-off part from the nanoparticle is observed to be cleared quickly by microSPECT-CT. 3–5 times decreases of radioactivity in the blood, kidneys, intestine, heart and lungs are observed after GTN treatment in a biodistribution assay. The radioactivity redistribution indicates that the radioactive leaving part is indeed cut off and the radionuclide metabolism accelerated. Organ level internal dose assessment reveals the GTN treated groups carry only ½ the radiation dose of the control group. Collectively, a feasible pathway for controllable radionuclide clearance is for the first time provided for high contrast and low radiation nuclear imaging.


Supporting Information for
Controllable stripping of radiolabeled group in vivo to optimize nuclear imaging via NO-responsive bioorthogonal cleavage reaction Li

Experiments and characterization
Scheme S1. Synthetic route of standard compounds.

Verification of cleavage in solution
In a centrifuge tube, [ 131 I]3 (100 mCi) was dissolved in ethanol (1 mL), NO saturated water solution (20 μL) was added. Vortex mixing was used. Radio-TLC was used to monitor the cleavage.

Modification of nanoplates
Nanoplates (1.0 mg) were precipitated with acetone and re-dispersed in HS-PEG-NHS aqueous solution (20 mg mL -1 , 1.0 mL). The mixture was kept in a refrigerator overnight. Ultrafiltration was used to remove free PEG.
The resulting nanoplates were re-dispersed in [ 131 I]3 aqueous solution (1.0 mL). The mixture was kept in a refrigerator overnight. Ultrafiltration was used to remove free

SPECT-CT imaging in mice
All animal protocols were approved by the Institute's Animal Care and Use Committee.
About 200 μCi radiolabelled nanoplates were injected to normal male BALB/c mice which were anesthetized with isoflurane.

Biodistribution in mice
Biodistribution was performed on Balb/c mice. [ 131 I]4 was administered into each mouse through tail vein injection. The mice were sacrificed at different time points.
Radioactivities of major organs was measured by gamma counter. The results were shown as a percentage of the injected dose per gram of tissue (%ID/g).

Time points of injection and sacrifice
0 h, [ 131 I]4 was injected into each mouse.
24 h, GTN was injected to mice in the experiment group; saline was injected to mice in the control group.
25 h, mice were sacrificed to get the data which were performed as 1 h post injection.
26 h, mice were sacrificed to get the data which were performed as 2 h post injection.

Biodistribution of cut-off part
Biodistribution was performed on Balb/c mice. Cut-off part was administered into each 6 mouse through tail vein injection. The mice were sacrificed at different time points.
Radioactivities of major organs was measured by gamma counter. The results were shown as a percentage of the injected dose per gram of tissue (%ID/g). Figure S2. Biodistribution result of cut-off part in mice.