Glycyrrhetinic acid-modified PEG-PCL copolymeric micelles for the delivery of curcumin
Introduction
Liver cancer, especially hepatocellular carcinoma, is a serious danger to human health and living. The liver surgery or transplantation is limited due to cancer multifocality, vascular invasion or shortage of donor. Chemotherapy is an effective treatment for several cancers because there are many choices including the use of drugs with different action mechanism and combination effects of drugs. Curcumin (CUR), a bioactive component originated from the root of rhizoma curcumae longae, shows activity against hepatocellular carcinoma in preclinical experiments via activating reactive oxygen species/TLR-4/caspase signaling pathway [1], inhibiting fatty acid synthase [2], inhibiting hypoxia inducible factor-1α-induced epithelial-mesenchymal transition [3], and other mechanisms [4]. It shows no toxicity to normal tissues and organs [5] with low activity against hepatocellular carcinoma [6]. In addition, its low water-solubility, non-target, easy metabolism, poor bioavailability and pharmacokinetic character also make its application as a drug limited [7].
Polymeric micelles have been widely and deeply studied as drug delivery vehicle because of their capability of enhancing hydrophobic drug water-solubility, passive or active cancer target, stabilizing drug, controlling the drugs release and improving its bioavailability or activity [8]. Poly (ethylene glycol)-b-poly (ε-caprolactone) (PEG-PCL) is a well-known copolymer [9], which can form nanoparticles [10], [11], [12], micelles [13], [14], hydrogels [15] and other aggregates [16] to realize the controlled release of CUR, improve its pharmacokinetic property, enhance its solubility in aqueous medium and its stability. They also show better [13], [17] activity than free drug, or comparable [11] one to it, which is relate to its passive target transportation and the release rate without targeting delivery.
Glycyrrhetinic acid (GA) shows different pharmacological activity including antiallergy [18], antioxidation [19], liver protection [20], [21], anti-inflammatory [22], [23], anticancer [24], [25], anti-Addison's disease [26]. It is noted that the structure of GA has been modified for developing less toxic chemosensitizing compounds [27], [28], [29]. It is recently reported that GA can selectively bond to corresponding receptors of animal [30] or human [31] liver with high affinity. The chitosan [32], [33], [34], [35], [36], [37] and PEG [38], [39] copolymers with GA decoration obviously increase selective accumulation of drug molecules in liver cells, especially liver cancers. At the same time, they also achieve drug's controlled release and promote its activity against cancer.
In this research, we bounded GA to one side of PEG chain, then PCL to another side of the chain to afford GA-PEG-PCL copolymer. In order to enhance CUR's water-solubility and study the effect of GA on the CUR release behavior from CUR-loaded GA-PEG-PCL (GA-CUR) micelles and selective transportation of drug-loaded micelles to HepG2 cells, we synthesized the copolymer and characterized drug-loaded micelles obtained from thin-film hydration procedure. The in vitro cytotoxicity in various cell lines was then researched.
Section snippets
Materials
CUR was sponsored by Henan Guangye Natural Pigment Co. Ltd. (Xingyang, China). H2N-PEG2400-PCL was synthesized with monoallyloxy PEG (Mn = 2400) as raw material according to a process reported formerly [14]. Succinic anhydride, N-(3-dimethylaminopropyl)-N′’-ethyl carbodiimide hydrochloride (EDC) and N-hydroxysuccimide (NHS) were bought from Sinopharm Chemical Reagent Co. Ltd. (Shanghai, China). GA was bought from Sigma-Aldrich Co. LLC (St. Louis, MO, USA). Methylene dichloride was dried with 4 Å
Synthesis of GA-PEG-PCL
GA-PEG-PCL copolymer was prepared by way of synthetic routine shown in Fig. 1. GA was firstly transformed into 4-carboxybutyloxy GA through O-acylation of GA with succinic anhydride. Then selective N-acylation of H2N-PEG-PCL with NHS and EDC as reaction catalyst and reagent afforded GA-PEG-PCL.
Its structure was verified by analysis of 1H NMR listed in Fig. 2. In the terms of 3-carboxybutyloxy GA, new peaks at 2.66 and 2.74 were the methylene group's characteristic signals of 3-carboxybutyloxy
Conclusion
With the aim of achieving hepatoma cell targeted delivery, GA was conjugated with monoamino poly (ethylene glycol)-b-poly (ε-caprolactone) through selective N-acylation of amino group to afford glycyrrhetinic acid-modified poly (ethylene glycol)-b-poly (ε-caprolactone) copolymer. The copolymer was biocompatible and encapsulated CUR with high EE. The drug-loaded glycyrrhetinic acid-modified poly (ethylene glycol)-b-poly (ε-caprolactone) micelles could increase curcumin's water solubility to 1.87
Disclosures
The authors report no conflicts of interest in this work.
Acknowledgments
This work is supported by a Project of Shandong Province Higher Educational Science and Technology Program (J14LM01) and International Cooperation Training Program of Shandong Province Higher School Outstanding Young and Middle-aged Backbone Teacher (2013).
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