Elsevier

Biomaterials

Volume 32, Issue 8, March 2011, Pages 2213-2221
Biomaterials

Multifunctional hollow nanoparticles based on graft-diblock copolymers for doxorubicin delivery

https://doi.org/10.1016/j.biomaterials.2010.11.051Get rights and content

Abstract

This article reports a flexible hollow nanoparticles, self-assembling from poly(N-vinylimidazole-co-N-vinylpyrrolidone)-g-poly(d,l-lactide) graft copolymers and methoxyl/functionalized-PEG-PLA diblock copolymers, as an anticancer drug doxorubicin (Dox) carrier for cancer targeting, imaging, and cancer therapy. This multifunctional hollow nanoparticle exhibited a specific on-off switch drug release behavior, owning to the pH-sensitive structure of imidazole, to release Dox in acidic surroundings (intracellular endosomes) and to capsulate Dox in neutral surroundings (blood circulation or extracellular matrix). Imaging by SPECT/CT shows that nanoparticle conjugated with folic acids ensures a high intratumoral accumulation due to the folate-binding protein (FBP)-binding effect. In vivo tumor growth inhibition shows that nanoparticles exhibited excellent antitumor activity and a high rate of apoptosis in cancer cells. After 80-day treatment course of nanoparticles, it did not appreciably cause heart, liver and kidney damage by inactive Dox or polymeric materials. The results indicate that the flexible carriers with an on-off switched drug release may be allowed to accurately deliver to targeted tumors for cancer therapy.

Introduction

For anticancer drug delivery systems, many systems have been discussed and exemplified regarding as traditional systems such as liposomes, polymer-based therapeutics, and inorganic particles. Polymer therapeutic is considered to be a potential candidate displaying well bioavailability and high molecular manipulation for use in cancer treatment. The term polymer therapeutics describes several distinct classes of agent, including polymer-drug conjugates [1], [2], micelles [3], [4], and mixed micelles [5], [6] that have now entered clinical development because of their intrinsic physical properties and their abilities to target specific locations. Much research has recently been focused on the study of mixed micelles as drug carriers in the hunt for improved cancer therapy. The potential advantages of mixed micelles as potential drug carriers include 1) the fact that they can be degraded into nontoxic substances that may be readily excreted by the body; 2) the possibility of modulating the micellar structure to improve intracellular drug delivery; and 3) the possibility of modifying the polymers for in vivo cancer targeting and imaging. Despite such potential advantages, in vivo studies on mixed micelles as potential anticancer drug delivery systems remain scanty. The major problem that limits the wider application of mixed micelles as a drug carrier is the uncertainty about the structure of micelles during micellization in individual and mixed micellar systems.

We have recently shown that mixed micelles with a solid core and a flexible shell prepared by mixing a graft copolymer with one or more diblock copolymers have an individual micellar structure [7], [8], [9]. We were able to control the core-shell structure and the particle size by varying the graft copolymer/diblock copolymer ratio. The core-shell structure and the micellar size are the two key parameters that need to be optimized for drug delivery applications in oncology. These factors govern the biodistribution and the intracellular uptake of drug carriers; of note, these parameters are highly dependent on the physical properties of the particles [10], [11]. To further investigate the usefulness of mixed micelles for drug delivery applications in the field of oncology, we have developed a mixed micellar system involving multifunctional micelles (115 nm in size) containing doxorubicin (Dox) for cancer therapy, cy5.5 dye for in vivo imaging, and folic acid for targeting cancer cells [6]. According to preliminary results, the targeting ligand, folic acid, allowed the accumulation of the cytotoxic agent into tumor cells.

In the present study, we describe the preparation of hollow multifunctional three-compartment nanoparticles that contain 1) Dox as an anticancer drug; 2) a radiotracer, and 3) a targeting molecule (Fig. 1). This multifunctional nanoparticle system containing both a hollow core and a flexible shell may be considered as a platform for treating, imaging, and targeting tumors in vivo. Firstly, we have investigated the nanoparticle structure and drug release behavior of multifunctional hollow nanoparticles to clarify whether they would release the loaded drug in the intracellular acidic regions such as endosomes and lysosomes. Secondly, we conducted biodistribution studies of multifunctional hollow nanoparticles in mice and assessed the therapeutic effects of micelles on experimental tumors and the induction of apoptosis in cancer cells. We subsequently investigated the nanoparticle stability in the liver and experimental tumors. To evaluate the potential long-term cytotoxic effects, we finally examined the effects of nanoparticles on hepatic and renal function at 80 days postinjection.

Section snippets

Synthesis of P(NVI-co-NVP)9600-g-PLA4900

First, PLA with an end-cap of methacrylated group (PLA-EMA, Mn 1630) was synthesized by ring-opening polymerization [7]. The graft copolymer, poly(NVI-co-NVP)-g-PLA was then synthesized by traditional free radical copolymerization. Briefly, PLA-EMA, NVI, NVP, and initiator AIBN were dissolved in acetone in a two-necked round-bottle flask with magnetic stirrer under nitrogen. The reaction was conducted at 70 °C for 24 h under nitrogen. After polymerization, the product was purified by

Polymers

In this study, multifunctional hollow nanoparticles consisted of the anticancer drug Dox, a graft copolymer, and three diblock copolymers. Each component performed a specific function in the final micelle, with the ultimate goal of improving tumor-selective delivery of cancer therapeutics. The graft copolymer poly(N-vinylimidazole-co-N-vinylpyrrolidone)-g-poly(d,l-lactide) (P(NVI-co-NVP)9600-g-PLA4900, [NVI]:[NVP]:[PLA] = 28:69:3) served for encapsulation and storage of the anticancer drug, as

Conclusions

We have described the preparation of hollow multifunctional hollow nanoparticles that may be obtained through the simple mix of four functional copolymers. All materials used in this study were relatively safe and highly sensitive to intracellular pH changes. The shape and size of micelles were suitable for successful drug delivery under physiological conditions. In vivo experiments clearly showed that animals treated with multifunctional hollow nanoparticles exhibited a significantly higher

Acknowledgment

The authors would like to thank the National Science Council of the Republic of China, Taiwan, for financial support (NSC 98-2320-B-010-032-MY2 and NSC 99-2120-M-033-001). TTY biopharm Co. Ltd. (Taiwan) is appreciated for kindly providing the doxorubicin hydrochloride.

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