PEGylated Cationic Serum Albumin for Boosting Retroviral Gene Transfer

Retroviral vectors are common tools for introducing genes into the genome of a cell. However, low transduction rates are a major limitation in retroviral gene transfer, especially in clinical applications. We generated cationic human serum albumin (cHSA) protected by a shell of poly(ethylene glycol) (PEG); this significantly enhanced retroviral gene transduction with potentially attractive pharmacokinetics and low immunogenicity. By screening a panel of chemically optimized HSA compounds, we identified a very potent enhancer that boosted the transduction rates of viral vectors. Confocal microscopy revealed a drastically increased number of viral particles attached to the surfaces of target cells. In accordance with the positive net charge of cationic and PEGylated HSA, this suggests a mechanism of action in which the repulsion of the negatively charged cellular and viral vector membranes is neutralized, thereby promoting attachment and ultimately transduction. Importantly, the transduction-enhancing PEGylated HSA derivative evaded recognition by HSA-specific antibodies and macrophage activation. Our findings hold great promise for facilitating improved retroviral gene transfer.

A core-shell albumin copolymer nanotransporter for high capacity loading and two-step release of doxorubicin with enhanced anti-leukemia activity

The native transportation protein serum albumin represents an attractive nano-sized transporter for drug delivery applications due to its beneficial safety profile. Existing albumin-based drug delivery systems are often limited by their low drug loading capacity as well as noticeable drug leakage into the blood circulation. Therefore, a unique albumin-derived core-shell doxorubicin (DOX) delivery system based on the protein denaturing-backfolding strategy was developed. 28 DOX molecules were covalently conjugated to the albumin polypeptide backbone via an acid sensitive hydrazone linker. Polycationic and pegylated human serum albumin formed two non-toxic and enzymatically degradable protection shells around the encapsulated DOX molecules. This core-shell delivery system possesses notable advantages, including a high drug loading capacity critical for low administration doses, a two-step drug release mechanism based on pH and the presence of proteases, an attractive biocompatibility and narrow size distribution inherited from the albumin backbone, as well as fast cellular uptake and masking of epitopes due to a high degree of pegylation. The IC50 of these nanoscopic onion-type micelles was found in the low nanomolar range for Hela cells as well as leukemia cell lines. In vivo data indicate its attractive potential as anti-leukemia treatment suggesting its promising profile as nanomedicine drug delivery system.

A quantum dot photoswitch for DNA detection, gene transfection, and live-cell imaging

Quantum dots (QDs) coated with an albumin-derived copolymer shell exhibit significant photoresponsiveness to DNA loading and have great potential for investigating gene delivery processes. The QDs reported herein are positively charged, have attractive optical properties, and are noncytotoxic and notably stable in live cells. Their complex formation with plasmid DNA leads to proportionally decreased photoluminescence and efficient gene transfection is observed. Therefore, they are suitable for live-cell bioimaging and mechanistic studies of nonviral gene delivery. Fluorescence correlation spectroscopy is applied for the first time to investigate individual QDs diffusing in large endosomes inside living cells, and serves as a valuable tool to study the physical properties of QDs inside live cells. The data obtained in this study strongly support the notable stability of these QDs, even in cell endosomes.

PEGylation of bovine serum albumin using click chemistry for the application as drug carriers

Monomethyl poly(ethylene glycol) (mPEG)-modified bovine serum albumin (BSA) conjugates (BSA-mPEG) were obtained by the mild Cu(I)-mediated cycloaddition reaction of azided BSA (BSA-N(3) ) and alkyne-terminated mPEG. The structure and characteristics of BSA-mPEG conjugates were thoroughly investigated. There were about two PEG chains conjugated onto each BSA molecule as determined by matrix-assisted laser desorption/ionization time of flight (MALDI-TOF) analysis. The intrinsic nonspecific binding ability of BSA was used for adsorption and sustained release of both rifampicn and 5-fluorouracil (5-FU). The helical structures of BSA were preserved to a large extent after modification and drug adsorption on BSA was confirmed via circular dichroism spectroscopy. Drugs adsorbed onto the conjugated formulation to a lesser extent than on BSA due to mPEG modification. The in vitro release of both rifampicin and 5-FU, however, indicated that BSA-mPEG can function as a drug carrier. Overall, the click reaction provided a convenient tool for the pegylation of BSA. The biological activity of the BSA-mPEG conjugates, including the drug transportation capacity and biocompatibility, were largely retained.

Nano-sized albumin-copolymer micelles for efficient doxorubicin delivery

We present the discovery of a nano-sized protein-derived micellar drug delivery system based on the polycationic albumin precursor protein cBSA-147. The anticancer drug doxorubicin (DOX) was efficiently encapsulated into nanosized micelles based on hydrophobic interactions with the polypeptide scaffold. These micelles revealed attractive stabilities in various physiological buffers and a wide pH range as well as very efficient uptake into A549 cells after 1 h incubation time only. In vitro cytotoxicity was five-times increased compared to free DOX also indicating efficient intracellular drug release. In addition, multiple functional groups are available for further chemical modifications. Based on the hydrophobic loading mechanism, various classical anti-cancer drugs, in principle, could be delivered even synergistically in a single micelle. Considering these aspects, this denatured albumin-based drug delivery system represents a highly attractive platform for nanomedicine approaches towards cancer therapy.

Cationized albumin-biocoatings for the immobilization of lipid vesicles

Tethered lipid membranes or immobilized lipid vesicles are frequently used as biomimetic systems. In this article, the authors presented a suitable method for efficient immobilization of lipid vesicles onto a broad range of surfaces, enabling analysis by quantitative methods even under rigid, mechanical conditions-bare surfaces such as hydrophilic glass surfaces as well as hydrophobic polymer slides or metal surfaces such as gold. The immobilization of vesicles was based on the electrostatic interaction of zwitterionic or negatively charged lipid vesicles with two types of cationic chemically modified bovine serum albumin (cBSA) blood plasma proteins (cBSA-113 and cBSA-147). Quantitative analysis of protein adsorption was performed as the cBSA coatings were characterized by atomic force microscopy, surface zeta potential measurement, fluorescence microscopy, and surface plasmon spectroscopy, revealing a maximal surface coverage 270-280 ng/cm(2) for 0.02 mg/ml cBSA on gold. Small unilamellar vesicles as well as giant unilamellar vesicles (GUVs) were readily immobilized (∼15 min) on cBSA coated surfaces. GUVs with 5-10 mol% negatively charged 1,2,-dipalmitoyl-sn-glycero-3-phosphoglycerol remained stable in liquid for at least 5 weeks.