Lipid raft-mediated and upregulated coordination pathways assist transport of glycocholic acid-modified nanoparticle in a human breast cancer cell line of SK-BR-3.

Bile acid transporter-targeting has been proven to be an effective strategy to improve drug delivery to hepatocytes and enterocytes. With increasing discoveries of bile acid transporter expression on tumor cells, bile acid-modified anticancer drugs are gradually attaining interests. In our previous study, we confirmed the efficacy of glycocholic acid-conjugated polystyrene nanoparticles (GCPN) on apical sodium bile acid transporter (ASBT)-expressed SK-BR-3 cells. However, the transport mechanisms remain unknown, due to the nanosized carriers are unlikely to be pumped through the narrow cavities of ASBT. To clarify their transport pathways, in this article, pharmacological inhibition and gene knocking-down studies were performed, which revealed that GCPN were primarily internalized via non-caveolar lipid raft-mediated endocytosis. Proteomics was analyzed to explore the in-depth mechanisms. In total 561 proteins were identified and statistical overrepresentation test was used to analyze the gene ontology (GO) upregulated pathways based on the highly expressed proteins. It was found that multiple pathways were upregulated and might coordinate to assist the location of the GCPN-ASBT complex and the recycling of ASBT. Among the highly expressed proteins, myelin and lymphocyte protein 2 (MAL2) was selected and confirmed to colocalize with GCPN, which further supported the lipid raft-mediated process. These findings will help set up a platform for designing the bile acid-modified nanomedicines and regulating their transport to improve their anticancer efficacy.

Stability of bovine serum albumin complexed with PEG-poly(L-histidine) diblock copolymer in PLGA microspheres.

The aim of this study was to examine the stability of bovine serum albumin (BSA) in poly(DL-lactic acid-co-glycolic acid) (PLGA) microspheres upon addition of a new excipient, poly(ethylene glycol)-poly(L-histidine) diblock copolymer (PEG-PH). Poly(L-histidine) component can form an ionic complex with BSA under acidic conditions within a narrow pH range. To optimize the ionic complexation conditions for BSA with PEG-PH, the resulting complex sizes were monitored using the Zetasizer. PLGA microspheres containing BSA as a model protein were prepared by w/o/w double emulsion method. BSA stability in aqueous solutions and after release from PLGA microspheres was determined using circular dichroism (CD) spectroscopy for secondary structure analyses and fluorescence measurements for tertiary structure analyses. The release profile of BSA from the microspheres was monitored using UV spectrophotometry. The rate of PLGA degradation was monitored by gel permeation chromatography. The pH profile within microspheres was further evaluated by confocal microscopy using a pH-sensitive dye. Approximately 19 PEG-PH molecules and one BSA molecule coalesced to form an ionic complex around a pH range of 5.0-6.0. Plain BSA/PLGA and BSA/PEG-PH/PLGA microspheres had a mean size of 27-35 microm. PLGA microspheres with a BSA loading efficiency >80% were prepared using the double emulsion method. PEG-PH significantly improved the stability of BSA both in aqueous solutions and in PLGA microspheres. The release profiles of BSA from different formulations of PLGA microspheres were significantly different. PEG-PH effectively buffered the local acidity inside the microspheres and improved BSA release kinetics by reducing initial burst release and extending continuous release over a period of time, when encapsulated as an ionic complex. PLGA degradation rate was found to be delayed by PEG-PH. There was clear evidence that PEG-PH played multiple roles when complexed with BSA and incorporated into PLGA microspheres. PEG-PH is an effective excipient for preserving the structural stability of BSA in aqueous solution and BSA/PLGA microspheres formulation.