SPECT/CT Imaging of Pluronic Nanocarriers with Varying Poly(ethylene oxide) Block Length and Aggregation State

Optimal biodistribution and prolonged
circulation of nanocarriers
improve diagnostic and therapeutic effects of enhanced permeability
and retention-based nanomedicines. Despite extensive use of Pluronics
in polymer-based pharmaceuticals, the influence of different poly­(ethylene
oxide) (PEO) block length and aggregation state on the biodistribution
of the carriers is rather unexplored. In this work, we studied these
effects by evaluating the biodistribution of Pluronic unimers and
cross-linked micelles with different PEO block size. In vivo biodistribution
of 111In-radiolabeled Pluronic nanocarriers was investigated
in healthy mice using single photon emission computed tomography.
All carriers show fast uptake in the organs from the reticuloendothelial
system followed by a steady elimination through the hepatobiliary
tract and renal filtration. The PEO block length affects the initial
renal clearance of the compounds and the overall liver uptake. The
aggregation state influences the long-term accumulation of the nanocarriers
in the liver. We showed that the circulation time and elimination
pathways can be tuned by varying the physicochemical properties of
Pluronic copolymers. Our results can be beneficial for the design
of future Pluronic-based nanomedicines.