Hyaluronic acid-coated nanostructured lipid carriers for targeting paclitaxel to cancer

Abstract

The aim of our study was to develop hyaluronic acid-coated, paclitaxel-loaded, nanostructured lipid carriers (HA-NLCs) prepared via electrostatic attraction for delivering paclitaxel (PTX) to tumors overexpressing CD44. First, cationic PTX-NLC was prepared by melt emulsion technology. Then, PTX-NLC were coated with hyaluronic acid (HA). The in vitro release of PTX was evaluated by the dialysis method. This analysis showed that PTX was released more slowly from HA-NLC than from Taxol®. The in vitro cytotoxicity of HA-NLC was investigated using the MTT method in B16, CT26 and HCT116 cell lines. The results showed that the cytotoxicity of HA-NLC against these three cancer cell lines was superior to that of Taxol®. The in vivo antitumor effect, the pharmacokinetics and the tissue distribution of HA-NLC were all evaluated in B16-bearing Kunming mice. The results showed that HA-NLC was better tolerated and had increased antitumor activity in B16-bearing Kunming mice compared with Taxol®. Furthermore, HA-NLC could prolong the circulation time of PTX in blood and increase the accumulation of PTX in the tumor. Therefore, HA-NLC prepared via electrostatic attraction was an effective carrier for delivering PTX to tumors overexpressing CD44.

Introduction

Paclitaxel (PTX), an effective chemotherapeutic drug isolated from the bark of Taxus brevifolia, is a microtubule-stabilizing agent that can induce mitotic arrest and cell apoptosis [1], [2]. Currently, PTX is widely used for the treatment of cancer, including ovarian, breast and nonsmall-cell lung cancer [3]. However, PTX is a hydrophobic drug, which has limited its clinical application. To date, there are two formulations approved by the FDA, PTX-Cre (Taxol®) and albumin-bound PTX (nab^TM-PTX; Abraxane®). Taxol® requires dissolving PTX in polyoxyethylated castor oil (Cremophor® EL) and ethanol (CrEL), which usually leads to severe adverse side effects, including hypersensitivity, neurotoxicity and nephrotoxicity [4], [5]. Therefore, premedication with corticosteroids and antihistamines is required to reduce the risk of hypersensitivity reactions when patients are treated with Taxol®. Abraxane®, a CrEL-free formulation that was approved by the FDA in 2005, reduces the risk of hypersensitivity reactions and does not require premedication. However, Abraxane® is a non-targeted drug carrier and accumulates in tumors by the enhanced permeability and retention effect (EPR) in cancer tissues [6]. The absence of selective targeting to the tumor usually results in low antitumor activity and severe side effects. Therefore, an active tumor-targeting delivery system of chemotherapeutic drugs is urgently needed.

Various targeting molecules have been applied to target PTX to tumor tissues, such as folic acid, RGD, biotin and hyaluronic acid (HA) [7], [8], [9], [10], [11]. Among these, hyaluronic acid has been widely investigated due to its unique properties. HA is a negatively charged linear polysaccharide composed of repeating units of glucuronic acid (GlcUA) and N-acetyl-D-glucosamine (GlcNAc) linked by alternating β-1,4 and β-1,3 glycosidic bonds. HA, the main component of the extracellular matrix, binds specifically to CD44, an extracellular protein on cell membranes, and regulates diverse cellular responses. CD44 is a cell surface marker that is overexpressed in tumors and has low expression in normal tissues. The specific binding of HA to CD44 and the EPR effect of macromolecules in cancers provide new options for active tumor targeting. In addition, several formulations have been developed: hyaluronic acid-drug conjugates, hyaluronic acid nanogels and hyaluronic acid-decorated nanoparticles [12]. Hyaluronic acid-conjugated nanoparticles have been extensively studied because of the following advantages: (1) most NPs can be modified with HA; (2) HA is on the outer shell of particles, which can bind specifically to CD44; (3) HA can protect NPs and regulate the circulation time and biodistribution of NPs; and (4) multifunctional NPs can be obtained with further modifications of HA or NPs. Hyaluronic acid-conjugated nanoparticles can be obtained by covalent bond modification or electrostatic attraction. Covalent bond modification requires chemical reactions, which are complex processes that are poorly reproducible. However, the process of electrostatic attraction is simple and controllable without introducing chemical reagents. Therefore, electrostatic attraction may be an alternative to covalent bond modification.

Nanostructured lipid carriers (NLC), introduced in late 1990s, are extensively applied in chemotherapeutic drug delivery because of their unique properties and advantages. NLC, developed from solid lipid nanoparticles (SLNs), are composed of solid lipid matrices and spatially incompatible liquid lipids, which results in imperfections in the crystal structure and increases drug loading [13]. The advantages of NLC are the following: biocompatibility and biodegradability; controlled drug release; high drug loading; passive and active targeting; and the possibility of large-scale production [14]. Furthermore, NLC can prolong the circulation time of PTX and increase the accumulation of drug in tumors due to the EPR effects in tumors. Therefore, NLC may be the ideal lipid-based carrier for a PTX delivery system.

In this work, we developed a new, active, tumor target delivery system: hyaluronic acid-coated nanostructured lipid carriers (HA-NLC) obtained via electrostatic attraction for targeting PTX to tumors. The schematic representation of the structure of the HA-NLC is shown in Fig. 1. The advantages of the system include the following: (1) the materials composing the HA-NLC were biocompatible and biodegradable; (2) the drug loading was high; (3) HA-NLC was an active tumor target delivery system; and (4) the HA-NLC was prepared via electrostatic attraction, which was simple and controllable without complex chemical reactions. To our knowledge, this report is the first to prepare HA-NLC via electrostatic attraction for tumor targeting. First, the cationic PTX-NLC was prepared, and the characterization was studied. Then, HA with a molecular weight of 300 kDa was selected for the preparation of HA-NLC. We investigated the in vitro cytotoxicity of HA-NLC in three CD44-overexpressing cell lines. Finally, the antitumor efficacy and tissue distribution were evaluated in B16-bearing Kunming mice.