The liposomes as a FDA approved
The liposomes, as a FDA-approved drug delivery carrier, have been widely utilized for drug delivery , , . Liposomes are defined as self-assembled vesicles, which are composed of one or multiple concentric lipid bilayers and enclose an aqueous core. The advantages of utilizing liposomes as drug carrier include improving solubility for the encapsulated drug, reducing the drug\'s side-effects and toxicity, protecting the drug against chemical and biological degradation during the drug delivery, and enhancing biocompatibility .
Carboxylesterase (CaE) mediates the hydrolysis of carboxylic Garcinol structure ester into alcohols and acids , , . This enzyme acts not only as a catalyst that has been widely used in organic synthesis or industrial production, but also as a key participant that works in drug metabolism and detoxification. CaE has been found in most of human tissues, especially in liver, kidney, heart, small intestine and blood. It has been reported that CaE is overexpressed in some types of cancer cells, and the CaE level is significantly different between these cancer cells and normal tissues , . CaE also has been employed as a biomarker; and to date, a number of CaE level assays have been employed for cancer diagnosis , , but there are still few reports on the exploitation of this enzyme as a trigger for prodrug.
Considering the physiological and pathological significance of CaE, herein we fabricated a novel prodrug for which the drug release is achieved via employing the overexpressed CaE in tumor cells as the trigger (activating means), as shown in Scheme 1. This prodrug system contains an acetyl unit as the responsive unit toward CaE and the coumarin unit as the scaffold for building the cleavable linker and the reporter fluorophore for monitoring the release of anticancer drug (chlorambucil). This CaE-activatable prodrug system has several striking features: (1) the coumarin scaffold not only acts as the reporting fluorophore for assessing CaE level but also as a cleavable architecture for releasing the drug; (2) the acetyl group serves as the enzyme-responsive unit and quencher for coumarin\'s fluorescence via intramolecular charge transfer (ICT) ; (3) to evaluate the prodrug\'s performance, the prodrug is encapsulated into liposomes, which can enhance aqueous solubility/dispersibility and in the meantime reduce the nonspecific side effects. As for the prodrug, upon activation by the enzyme CaE, the ICT effect is diminished by the cleavage of the bond between the fluorophore (coumarin) and the quencher (acetyl group); due to the cleavable reaction, the active drug and the fluorophore are released simultaneously; consequently, the coumarin\'s fluorescence is restored.
Results and discussion
Acknowledgments We gratefully acknowledge the financial support by the Science and Technology Planning Project of Guangzhou (No. 201607020015) and the Science and Technology Planning Project of Guangdong Province (No. 2014A010105009).
Introduction Enzyme immobilization is a critical step in the preparation of most enzyme biocatalysts, as it is necessary to facilitate enzyme recovery and reuse, in case these are sufficiently stable [, , , ]. As a consequence, the potential of enzyme immobilization has been explored in many studies aiming at improving other enzyme properties, among which enzyme stability is considered the most critical aspect. This can be achieved with different techniques, e.g. multipoint covalent attachment . However, immobilization has been found to improve many other enzyme properties, such as activity, selectivity and specificity, resistance to inhibitors and chemicals, and even purity [, , , , ]. In this regard, the development of new supports presenting novel and improved properties are certainly of high interest to the area . Chitin is the main component of the exoskeleton of crustaceous and other animals. Treated as a waste in many fishing-related industries [12,13], its partial or total deacetylation produces an interesting new polymer that presents primary amino groups, known as chitosan [14,15]. As a natural polysaccharide extracted from crustacean shells, it is an attractive biopolymer for employment in a plethora of applications due to its inherent properties of biodegradability, biocompatibility and non-toxicity [16,17].