Yihui Deng

Esterase-catalyzed dePEGylation of pH-sensitive vesicles modified with cleavable PEG-lipid derivatives

To make vesicles for the better controlled content release, we modified cholesteryl hemisuccinate (CHEMS)-derived vesicles with PEG-lipid derivatives. Two cholesterol analogs, cholesteryl hemisuccinate (CHEMS) and cholesteryl chloroformate (CHM), have been conjugated to the polyethylene glycol (PEG) via their ester bonds for the vesicle modifications, so the PEGs can be cleaved by esterases. The effects of PEG-lipid proportions, serum concentrations and the lipid types on the esterase-catalyzed cleavage of PEG polymer off the vesicles surface were determined. We observed that PEG cleavages decreased as the molar ratios of the PEG-lipids in vesicles increased; on the other hand, PEG cleavages gradually increased with the increased serum concentrations. In contrast to conventional long circulation materials mPEG-DSPE and mPEG-CHOL, the two new conjugates enabled higher degrees of PEG cleavages from modified vesicles. After incubation in the serum at acidic conditions, esterase-catalyzed dePEGylation destabilized these vesicles, increasing the mean particle sizes and promoting content releases. These results suggested that ester linkages between the PEG and lipid anchors allow faster content releases in the suitable conditions. Together, the two esterase cleavable PEG-lipid conjugations may be applied not only to stabilize vesicles and prolong their circulation time, but also to provide more efficient content releases by the esterase controlled dePEGylation.

Development of novel self-assembled DS-PLGA hybrid nanoparticles for improving oral bioavailability of vincristine sulfate by P-gp inhibition

To improve the encapsulation efficiency and oral bioavailability of vincristine sulfate (VCR), novel self-assembled dextran sulphate-PLGA hybrid nanoparticles (DPNs) were successfully developed using self-assembly and nanoprecipitation method. By introducing the negative polymer of dextran sulphate sodium (DS), VCR was highly encapsulated (encapsulation efficiency up to 93.6%) into DPNs by forming electrostatic complex. In vitro release of VCR solution (VCR-Sol) and VCR-loaded DPNs (VCR-DPNs) in pH 7.4 PBS showed that about 80.4% of VCR released from VCR-DPNs after 96h and burst release was effectively reduced, indicating pronounced sustained-release characteristics. In vivo pharmacokinetics in rats after oral administration of VCR-Sol and VCR-DPNs indicated that the apparent bioavailability of VCR-DPNs was increased to approximate 3.3-fold compared to that of VCR-Sol. The cellular uptake experiments were conducted by quantitative assay of VCR cellular accumulation and fluorescence microscopy imaging of fluorescent labeled DPNs in two human breast cancer cells including MCF-7 and P-glycoprotein over-expressing MCF-7/Adr cells. The relative cellular uptake of VCR-DPNs was 12.4-fold higher than that of VCR-Sol in MCF-7/Adr cells implying that P-glycoprotein-mediated drug efflux was diminished by the introduction of DPNs. The new DPNs might provide an effective strategy for oral delivery of VCR with improved encapsulation efficiency and oral bioavailability.

Characterization and Body Distribution of β-Elemene Solid Lipid Nanoparticles (SLN)

ABSTRACT Solid lipid nanoparticles (SLN) containing β-elemene, a volatile oil used for the treatment of cancer, were prepared by the method combining probe sonication and membrane extrusion. Effects of the formulations and procedures on the characteristics of SLN were investigated. Body distribution of β-elemene SLN in rats after intravenous administration was compared with that of the commercial emulsion. The results showed that dispersing the surfactant in the melted lipid matrix could obtain smaller particles than that dispersing in the water phase. Increasing the ratio of monostearin in the lipid matrix or the concentration of surfactant reduced the mean volume size of the SLN. Optimized formulation was composed of monostearin and precirol ATO 5 at a mass ratio of 3:7, which was quite stable for 8 months at room temperature. In vitro release of β-elemene from the SLN was slow and stable without obvious burst release and was found to follow the Higuich equation. After intravenous administration, the β-elemene levels after 5 min injection of SLN formulation were 1.5, 2.9, and 1.4 times higher than those of β-elemene emulsion in liver, spleen, and kidney, respectively, while the concentrations of β-elemene were decreased 30% in heart and lung. Therefore, the SLN containing β-elemene might be an attractive candidate for the treatment of liver cancer.

Galactosylated solid lipid nanoparticles with cucurbitacin B improves the liver targetability.

This study intended to prepare liver-targeting solid lipid nanoparticles (SLNs) with a hepatoprotective drug, cucurbitacin B (Cuc B), using a galactosylated lipid, N-hexadecyl lactobionamide (N-HLBA). The galactosyl-lipid N-HLBA was prepared via the lactone form intermediates of lactobionic acid and synthesized by anchoring galactose to hexadecylamine lipid. The Cuc B-loaded galactosylated and conventional SLNs were successfully prepared by a high-pressure homogenization method. The two SLNs showed similar physical and pharmaceutical properties, including: the particle size measured by laser diffraction was 135 nm for galactosylated SLN (GalSLN) and 123 nm for conventional SLNs (CSLN); zeta potentials were −31.6 mV (GalSLN) and −34.3 mV(CSLN); in vitro release behavior of the two SLNs was similar, and both showed the biphasic drug release pattern with burst release at the initial stage and prolonged release afterwards. In contrast, the two SLNs demonstrated a marked difference in in vitro cellular cytotoxicity and in vivo tissue distribution performances. The IC50 values of Cuc B in the two SLNs were by far lower than those of Cuc B solution and further Cuc B-GalSLN had about half the IC50 value of Cuc B-CSLN. These results indicated that the encapsulation of Cuc B in SLNs resulted in the enhancement of cytotoxic activity, and galactosyl ligand could further enhance the cellular accumulation and cytotoxicity of Cuc B. The weighted-average overall drug targeting efficiency (Te) was used to evaluate the liver targetability. Cuc B-GalSLN gave a relatively high (Te)liver value of 63.6%, ∼ 2.5-times greater than that of Cuc B-CSLN (25.3%) and Cuc B solution (23.8%). In summary, the incorporation of N-HLBA into SLNs significantly enhanced the liver targetability of Cuc B-loaded SLNs and GalSLN had a great potential as a drug delivery carrier for improved liver targetability.

Influence of phospholipid types and animal models on the accelerated blood clearance phenomenon of PEGylated liposomes upon repeated injection

Abstract When polyethylene glycol (PEG)ylated liposomes were repeatedly injected into the same animal, the second dose of liposomes would rapidly clear from the bloodstream and enhance accumulation in the liver and spleen, and this phenomenon is called “accelerated blood clearance (ABC)”. There are many factors known to influence ABC phenomenon, in this study, we mainly focused on the effects of different phospholipids (PL) types and animal models. The effects of PL types on ABC phenomenon were examined by repeating injection of PEGylated liposomes prepared by five different types of PL (hydrogenated soy phosphatidylcholine, egg sphingomyelin, soybean phosphatidycholin, 1,2-dipalmitoyl-sn-glycero-3-phosphocholine and egg phosphatidycholin) in rats. Dramatically, repeated injection of different types of PL could induce ABC phenomenon altogether. Both t1/2 and AUC of experimental group (EG) were lower significantly than those of control group (CG). Our results also showed that the liver accumulation of second dose increased significantly (p < 0.01) in all EG as compared that of CG. Interestingly, ABC phenomenon of liposomes prepared by unsaturated PL was more obvious than that of saturated PL. All the first dose could induce the antibody (anti-PEG IgM) level increasing significantly (p < 0.01). For different animal models, we found that after repeated injection of PEGylated liposomes, rats, mice, rabbits and guinea pigs could produce ABC phenomenon. Various PL types and animal models could all produce the ABC phenomenon. However, their extent of accelerated clearance differed. ABC phenomenon is possibly a ubiquitous immune phenomenon in life.

An LC-MS/MS method for simultaneous determination of vincristine and verapamil in rat plasma after oral administration of a dual agent formulation.

A rapid and sensitive method for simultaneous determination of vincristine and verapamil in rat plasma was first developed and validated, using high-performance liquid chromatography-tandem mass spectrometry (LC-MS/MS) in multiple reaction monitoring (MRM) mode via electrospray ionization (ESI). The method, which required a small sample volume (25 µL) of plasma, was linear in the concentration range of 0.5-500 ng/mL for vincristine and 0.1-100.0 ng/mL for verapamil. Finally, the method was successfully employed in a pharmacokinetic study of vincristine and verapamil in rats after an oral administration of a dual-agent formulation containing vincristine and verapamil.

Preparation and Characterization of pH-Sensitive Vesicles Made of Cholesteryl Hemisuccinate

pH-sensitive vesicles are designed to promote efficient release of entrapped agents in response to low pH. In this study, such vesicles were prepared from cholesteryl hemisuccinate (CHEMS) in Tris-HCl buffer. Vesicles prepared by this direct hydration method had a small particle size of 74.1 nm based on intensity of Gaussian and a size of 65.8 nm based on volume of Gaussian. The mean zeta potential was about –73mV, indicating that the vesicle system was stable. Entrapment efficiency for calcein by these vesicles was measured at 37 ± 2.36%, which is higher than that by phospholipid MLVs. These calcein loaded vesicles exhibited excellent stability at pH 7.4 and underwent rapid destabilization upon acidification as showed by calcein release. However these vesicles were unstable in Fetal Bovine Serum (FBS). Optimization of formulation might improve their stability in serum.