How Stealthy are PEG-PLA Nanoparticles? An NIR In Vivo Study Combined with Detailed Size Measurements

Detailed in vivo and ex vivo analysis of nanoparticle distribution, accumulation and elimination processes were combined with comprehensive particle size characterizations. The in vivo fate of near infrared (NIR) nanoparticles in nude mice was carried out using the Maestro (TM) in vivo fluorescence imaging system. Asymmetrical field flow field fractionation (AF4) coupled with multi-angle laser light scattering (MALLS), photon correlation spectroscopy (PCS) and transmission electron microscopy (TEM) were employed for detailed in vitro characterization. PEG-PLA block polymers were synthesized and used for the production of defined, stable, nontoxic nanoparticles. Nanoparticle analysis revealed narrow size distribution; AF4/MALLS permitted further accurate size evaluation. Multispectral fluorescence imaging made it possible to follow the in vivo fate non-invasively even in deep tissues over several days. Detailed fluorescence ex vivo imaging studies were performed and allowed to establish a calculation method to compare nanoparticle batches with varying fluorescence intensities. We combined narrow-size distributed nanoparticle batches with detailed in vitro characterization and the understanding of their in vivo fate using fluorescence imaging, confirming the wide possibilities of the non-invasive technique and presenting the basis to evaluate future size-dependent passive tumor accumulation studies.