Novel <sup>18</sup>F Labeling Strategy for Polyester-Based
NPs for in Vivo PET-CT Imaging
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Abstract
Drug-loaded
nanocarriers and nanoparticulate systems used for drug
release require a careful in vivo evaluation in terms of physicochemical
and pharmacokinetic properties. Nuclear imaging techniques such as
positron emission tomography (PET) are ideal and noninvasive tools
to investigate the biodistribution and biological fate of the nanostructures,
but the incorporation of a positron emitter is required. Here we describe
a novel approach for the <sup>18</sup>F-radiolabeling of polyester-based
nanoparticles. Our approach relies on the preparation of the radiolabeled
active agent 4-[<sup>18</sup>F]fluorobenzyl-2-bromoacetamide ([<sup>18</sup>F]FBBA), which is subsequently coupled to block copolymers
under mild conditions. The labeled block copolymers are ultimately
incorporated as constituent elements of the NPs by using a modified
nano coprecipitation method. This strategy has been applied in the
current work to the preparation of peptide-functionalized NPs with
potential applications in drug delivery. According to the measurements
of particle size and zeta potential, the radiolabeling process did
not result in a statistically significant alteration of the physicochemical
properties of the NPs. Moreover, radiochemical stability studies showed
no detachment of the radioactivity from NPs even at 12 h after preparation.
The radiolabeled NPs enabled the in vivo quantification of the biodistribution
data in rats using a combination of imaging techniques, namely, PET
and computerized tomography (CT). Low accumulation of the nanoparticles
in the liver and their elimination mainly via urine was found. The
different biodistribution pattern obtained for the “free”
radiolabeled polymer suggests chemical and radiochemical integrity
of the NPs under investigation. The strategy reported here may be
applied to any polymeric NPs containing polymers bearing a nucleophile,
and hence our novel strategy may find application for the in vivo
and noninvasive investigation of a wide range of NPs