Scientific Abstract

Background: SPIO contrast agents along with antibodies are used to improve MRI sensitivity for molecular imaging but they cannot cross an intact blood-brain-barrier (BBB), limiting their use for CNS receptor/transporter imaging. Our goal was to enable MR imaging of DAT in METH addiction using novel clathrin-nanoprobes carrying SPIO and anti-DAT-antibodies, which noninvasively pass a BBB.

Methods: Anti-DAT-antibody and SPIO were conjugated to clathrin using polyethylene glycol at 1:1:1 molar ratio. 24h before MRI, C57BL/6J mice were given intraperitoneal injections of saline or METH (30 mg/kg). 4h before MRI, mice were given saline or clathrin-nanoprobes intranasally (68pmol, 50µL). In-vivo or ex-vivo brain MRI was performed at 9.4T. Voxel-wise R₂* relaxation rates were obtained using a series of gradient-echo images, and estimated in the striatum (STR), substantia nigra (SN) and visual cortex (vCTX, a control region).

 Results: R₂* values were lower in STR (p=0.0077) and SN (p=0.0030) in METH vs. saline treated mice. R₂* values were higher in the STR (p=0.0010) and SN (p=0.0007) compared to  vCTX in animals that received clathrin-nanoprobes, but not in saline treated animals. Clathrin-nanoprobes significantly increased R₂* in the STR (p<0.0001) and SN (p=0.0002) compared to saline without significantly altering R₂* in vCTX.  Microscopy showed an accumulation of iron-stained CT-nanoprobes in brain regions rich in DAT. 

Conclusions: Clathrin-nanoprobes noninvasively delivered SPIO contrast agents along with anti-DAT-antibody to the mouse brain, enabling MRI detection of decreased DAT levels in METH toxicity. Clathrin may be used as a new neurotheranostic for noninvasive molecular brain imaging and targeted drug delivery.