Intracellular delivery mechanism and brain delivery kinetics of biodegradable cationic bovine serum albumin-conjugated polymersomes

Background: A novel brain drug delivery system using cationic bovine serum albumin (CBSA)-conjugated biodegradable polymersomes (CBSA-PO) was prepared, and its intracellular delivery mechanism and brain delivery kinetics were evaluated. Methods and results: Biodegradable poly(ethylene glycol)-poly(epsilon-caprolactone) (PEG-PCL) was used to prepare the polymersomes, and thiolated CBSA was conjugated with the surface of the polymersome. Transmission electron microscopy and dynamic light scattering showed that the CBSA-PO had a round and vesicle-like shape, with a mean diameter of around 100 nm. Coupling of CBSA with polymersomes was confirmed by X-ray photoelectron spectroscopy. Uptake of CBSA-PO by bEnd.3 cells was significantly higher than that of unconjugated polymersomes, but was inhibited by low temperature, free CBSA, and poly-L-lysine, indicating that endocytosis was energy-driven and absorptive-mediated. Cell viability assays confirmed the good safety profile of biodegradable CBSA-PO. Pharmacokinetic results demonstrated that the polymersomes had long circulation times, and CBSA conjugation on the polymersomes significantly increased the blood-brain barrier permeability surface area product by 3.6-fold and the percentage of injected dose per gram brain (% ID/g brain) by 2.1-fold. Capillary depletion experiments showed that CBSA-PO was distributed into the brain parenchyma in a time-dependent manner, with few polymersomes detected, indicating that conjugation of polymersomes with CBSA significantly improved their transcytosis across the brain-blood barrier. Conclusion: These results suggest that CBSA-PO is a promising drug brain delivery carrier with low toxicity.