Facile synthesis of rapamycin-loaded PEG-b-PLA nanoparticles and their application in immunotherapy

Poly(ethylene glycol)-block-poly(lactide) (PEG-b-PLA) micro- and nanoparticles (NPs) have been intensively investigated for applications in biomedicine, due to their inherent biocompatibility and biodegradability, which allows them to be used as sustained release systems. Current methods for preparing PEG-b-PLA NPs typically require two different steps that include polymer synthesis and NP assembly, with the necessary intermediate polymer purification and the use of a variety of organic solvents in the process. In order to facilitate the biomedical application of PEG-b-PLA NPs, it is of great interest to develop a strategy to formulate the NPs in a simplified manner. Here, we report a straightforward method to construct PEG-b-PLA NPs through a sequential two-step process without intermediate work-up, which involves synthesizing the polymer in a water-miscible organic solvent that is, N,N-dimethylformamide (DMF), followed by addition of water to the polymer solution. In this way, large NPs (similar to 600 nm) were prepared. We comprehensively characterized the NPs using turbidity studies, dynamic light scattering (DLS), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) techniques. We further demonstrated the ability of the NPs to encapsulate drugs, exemplified in the immunotherapeutic agent rapamycin, with relatively high encapsulation efficiency. In vitro drug release tests showed that rapamycin-encapsulating NPs had comparable sustained-release profiles at different pH conditions, highlighting the broad application window of our NP platform. Moreover, in vitro T cell suppression assays revealed that rapamycin-loaded NPs exhibited similar inhibitory performance to free rapamycin on CD8(+) cells at all rapamycin concentrations and on CD4(+) cells at high and intermediate rapamycin concentrations, while the performance of the NPs was superior on CD4(+) at low rapamycin concentration. Overall, this work provides a route for the scalable synthesis of biocompatible PEG-b-PLA NPs, which can be extended to other polymeric NPs, with potential in biomedical applications such as immunotherapy.