Development and in-depth characterization of biodegradable polymeric nanoparticles as drug delivery systems

Drug delivery systems based on nanoparticles (NPs) are engineered technologies with great advantages of targeted delivery and controlled release of therapeutic agents, overcoming biological barriers and limitations of free therapeutics. Biodegradable poly (lactic acid) (PLA), poly (lactic-co-glycolic acid) (PLGA) (co)polymers with well-known biocompatible profile remain the most employed materials to prepare drug nanocarriers. However, some limitations remain affecting mainly their transition into clinics : i) insufficient drug loadings (DLs) lowering the therapeutic efficiency of the NPs ii) lack of methodologies to characterize individual NP for high quality control of the formulations ; iii) in depth studies of the nano-bio interactions and in particular of protein fate in contact with the NPs. Therefore, the aim of the current work was to prepare a series of PLA and PLGA NPs to achieve high DLs and to further characterize them deeply.
Vancomycin (VCM) is a last resort antibiotic used to treat serious bacterial infections that are resistant to other drugs. VCM loading into NPs is a good strategy to overcome its low bioavailability and to decrease the administered doses and associated side effects. NPs were prepared using a series of PLA and PLGA (co)polymers. Formulations were optimized to achieve drug loadings close to 25 wt% and pH-responsive release. Drug-polymer interactions were revealed by solid state NMR investigations. The drug located in inner compartments where it experienced strong electrostatic interactions with the (co)polymer end groups. Various electron microscopies were employed to unravel the NPs’ structures. Remarkably, the inner compartments were found in VCM-loaded NPs, and not in the unloaded ones. These studies pave the way to achieve stable NPs with low drug release at physiological conditions and triggered release at acidic pH, which sometimes is associated infected sites or intracellular compartments.
A systematic study was carried on individual NP characterization with the aim to localize the drug (chapter II). This challenging task was achieved through a range of techniques combining visualization of individual NPs (high resolution microscopy) with simultaneous chemical analysis of the NP (spectroscopic analysis). By using state-of-the-art techniques (SEM-EDX, STEM-EDX and AFM-IR), the NPs components were chemically identified, drug location and homogeneity of the DL into the NPs were successfully investigated.
To go a step further, we established a quantification method that enables to measure local DL on a single NP basis. To do so, a series of films and NPs were prepared from mixtures of PLA and a hydrophobic [Re] anticancer drug. These two materials possess intense IR fingerprints meeting the needs of the study at best. Chapter III presents a proof of concept of quantification achieved by AFM-IR that offers two acquisition modes : i) chemical mapping at selected IR absorptions and ii) recording a local IR spectrum with AFM resolution (10-15 nanometers). First, a calibration curve was obtained by IR-microspectroscopy which provided the accurate quantitative information to build the grounds of quantification by AFM-IR. A high discrepancy was obtained in terms of loadings of individual NPs highlighting the usefulness of our approach.
Finally, a comprehensive study was carried on to investigate nano-bio interactions. PLGA NPs were studied together with nanoMOFs, possessing different characteristics, and compared with their PEGylated counterparts as PEG has been shown to shield nano-bio interactions, thus increase NPs’ blood circulation time. The methodology proposed in chapter IV includes protein corona investigations. By combining quantitative and qualitative approaches it gives insights on NPs’ in vivo fate as well as the NP induced alterations on protein’s structure and stability that might affect its functionality.