Solvent-free Nanoparticle Assembly Protocol (SNAP): one-pot formulation of drug loaded polyester nanoparticles and their vessel size-dependent perivascular transport

This work describes a new approach for rapid and reproducible formulation of drug loaded biodegradable nanoparticles based on polyester copolymers, including poly(lactic acid)-poly(ethylene glycol) (PLA-PEG) and poly(caprolactone)-poly(ethylene glycol) (PCL-PEG). The new approach, termed Solvent-free Nanoparticle Assembly Protocol (SNAP), carries several advantages over conventional polyester formulation strategies, including very rapid formulation (minutes) and the ability to use nanoparticles immediately without lengthy solvent evaporation or washing steps. Altering polyester molecular weight and concentration, alongside the introduction of specific functional groups yielded precise control of nanoparticle properties, including size, shape, surface charge, drug release and loading. We examined loading of multiple therapeutic compounds, including diclofenac, loperamide, bortezomib, CT179, panobinostat, docetaxel, methotrexate, and camptothecin. The SNAP protocol facilitated the rapid production of stable, drug-loaded nanoparticles with a narrow size distribution and generally good drug loading. Using Fluorescence Resonance Energy Transfer (FRET) and size exclusion chromatography (SEC) with a focus on the model agent Rhodamine B, we were able to carefully examine stability of the nanoparticle and assess the distribution of small molecules within the polymer as well as nanoparticle stability. In vivo evaluation of fluorescently labeled nanoparticles using real-time, intravital microscopy showed that, after direct administration to cerebrospinal fluid (CSF) via the intrathecal cisterna magna (IT-CM) route, the dynamic accumulation of nanoparticles within the perivascular space (PVS) depends on the size of the vessel that is imaged. Nanoparticles accumulated steadily within the PVS of large vessels, while accumulating more slowly and exhibiting clearance from medium-sized and smaller vessels over the course of several hours. In sum, these studies present a new platform for facile production of polyester nanoparticles, demonstrate their ability to encapsulate a variety of hydrophobic small molecules, and expand our knowledge on the development of nanocarriers for intrathecal administration. Taken together, these data open new opportunities for development safer and more effective nanoparticle-based therapies.