Elsevier

Biomaterials

Volume 27, Issue 10, April 2006, Pages 2285-2291
Biomaterials

In vitro and in vivo studies on vitamin E TPGS-emulsified poly(d,l-lactic-co-glycolic acid) nanoparticles for paclitaxel formulation

https://doi.org/10.1016/j.biomaterials.2005.11.008Get rights and content

Abstract

This work shows a full spectrum of research on Vitamin E TPGS-emulsified Poly(d,l-lactic-co-glycolic acid) (PLGA) nanoparticles (NPs) for paclitaxel formulation to improve its therapeutic index and to reduce the adverse effects of adjuvant Cremophor EL in its current clinical formulation of Taxol®. Paclitaxel-loaded PLGA NPs were prepared by a modified solvent extraction/evaporation technique with vitamin E TPGS as emulsifier. The formulated NPs were found in quite uniform size of ∼240 nm diameter. The in vitro drug release profile exhibited a biphasic pattern with an initial burst followed by a sustained release. In vitro HT-29 cell viability experiment demonstrated that the drug formulated in the NPs was 5.64, 5.36, 2.68, and 1.45 times more effective than that formulated in the Taxol® formulation after 24, 48, 72, 96 h treatment, respectively at 0.25 μg/mL drug concentration, which should be even better with the sustainable release feature of the NPs formulation considered. In vivo PK measurement confirmed the advantages of the NP formulation versus Taxol®. The area-under-the-curve (AUC) for 48 h for Vitamin E TPGS emulsified PLGA NP formulation of paclitaxel were found 3.0 times larger than that for the Taxol® formulation. The sustainable therapeutic time, at which the drug concentration drops below the minimum effective value, for the NP formulation could be 1.67 times longer than that for the Taxol® formulation.

Introduction

Paclitaxel, a naturally occurring diterpenoid originally extracted from the Pacific Yew tree in the early 1960s, has been considered by the National Cancer Institute (NCI) as the most significant advance in drug discovery for chemotherapy and has become commercially most successful antineoplastic agent. The drug has been known to exhibit a significant activity against a wide spectrum of cancers, including breast cancer, ovarian cancer, colon cancer, bladder cancer, lung cancer, head and neck carcinomas, and acute leukemia [1], [2], [3], [4]. The main limitation for its clinical application is its low solubility in water and most of the pharmaceutical solvents [5]. The dosage form in its clinical application is Taxol®, which is formulated in an adjuvant called Cremophor EL (CrEL) and dehydrated alcohol at a 50:50 (v/v) ratio, which is diluted 5–20 folds in normal saline or dextrose solution (5%). This adjuvant has been found associated with severe side effects including hypersensitivity reactions, nephrotoxicity, neurotoxicity and cardiotoxicity [6], [7], [8], [9]. Alternative paclitaxel formulation strategies have been suggested to eliminate the CrEL-based vehicle and to improve the therapeutic efficacy of the drug, which include parenteral emulsions [10], [11], liposomes [12], [13], micelles [14], nanoparticles (NPs) [15], [16], [17] and microspheres [18], [19]. Among them, NPs of biodegradable polymers could provide an ideal solution for the alternative formulation devoid of CrEL, which may also provide a sustained, controlled and targeted delivery of the drug and with further development, promote oral chemotherapy [20], [21].

There has been intensive investigation directed to oral delivery of paclitaxel, which is expected to provide a long-time exposure at an appropriate therapeutic level of drug and to greatly improve the quality of life of the patients. However, the obstacle to the successful formulation of oral dosage form is its low oral bioavailability (less than 1%) due to the elimination of a multi-drug efflux pump transporter P-glycoprotein (P-gp) [22] and the first pass of cytochrome P450 (CYP 3A) enzymes [23]. Medical solution to overcome this problem is to apply P450/P-gp inhibitors such as cyclosporin A [24], [25]. However, the inhibitors would also fail the immune system of the patients and thus lead to medical complications. Moreover, most of the P450/P-gp inhibitors have their own side effects and difficulties in formulation [26]. NPs of biodegradable polymers represent a solution from chemotherapeutic engineering (or cancer nanotechnology or pharmaceutical nanotechnology) [20], [21]. NPs of biodegradable polymers for drug formulation and for oral chemotherapy have shown advantages in improving the pharmacokinetics and tissue distribution and thus the therapeutic effects of the formulated drug [27], [28]. Moreover, preliminary results have demonstrated that NPs can escape from the vasculature through the leaky endothelial tissue that surrounds the tumor and thus accumulate in solid tumors [29], [30].

The objective of this study was to show a full spectrum of work in developing a polymeric NP drug delivery system for an alternative formulation as well as for oral delivery of paclitaxel, which is used in our research as a prototype anticancer drug due to its excellent efficiency against a wide spectrum of cancers and its great commercial success as the best seller among antineoplastic agents. The key factors which determine the performance of the drug-loaded NPs include the particle size and surface coating [31]. Modification of NP surface could be an important strategy to improve the half life of the NPs in plasma and the cellular uptake of the NPs. We have successfully developed a NP technique to coat NPs of biodegradable polymers by phospholipids, cholesterol and vitamin E TPGS, which showed great advantages over the traditional coating techniques by polyvinyl alcohol (PVA) [16], [32], [33], [34].

Vitamin E succinated polyethylene glycol 1000 (Vitamin E TPGS or simply TPGS) is a water soluble derivative of vitamin E, which has been found to be an excellent emulsifier/solubilizer/absorption enhancer of high emulsification efficiency and cellular adhesion [32], [33], [34]. Co-administration of vitamin E TPGS has been found to increase the oral bioavailability of cyclosporine A in healthy dogs by non-compartmental pharmacokinetic analysis [35]. Dintaman and Silverman reported vitamin E TPGS inhibits P-gp mediated multidrug resistance [36]. Vitamin E TPGS can also enhance the absorption flux of amprenavir, a HIV protease inhibitor, by increasing its solubility and permeability [37]. In our NP technique, vitamin E TPGS is used as a necessary auxiliary in NP formulation as well as a “mask” for the NPs to cross the GI barrier for oral chemotherapy. Paclitaxel-loaded, TPGS-emulsified PLGA NPs were prepared by a modified solvent extraction/evaporation single emulsion technique. NP of various recipes were characterized by various state-of-the-art techniques such as laser light scattering for particle size and size distribution, scanning electron microscopy (SEM) for surface morphology, X-ray photoelectron spectroscopy (XPS) for surface chemistry, and high-performance liquid chromatography (HPLC) for in vitro drug release kinetics. Human colon adenocarcinoma cells (HT-29 cells) were used for evaluation of the in vitro cytotoxicity of paclitaxel formulated in the NPs and Sprague-Dawley rats were used for in vivo pharmacokinetics investigation, both being made in a close comparison with its current clinical dosage form Taxol®.

Section snippets

Materials

Paclitaxel of purity 99.8% was purchased from Dabur India Ltd. (India). Poly (d,l-lactic-co-glycolic acid) (PLGA) (L:G molar ratio: 50:50, MW: 40,000–75,000), PVA (MW: 30,000–70,000), and coumarin-6 were purchased from Sigma (St. Louis, MO, USA). Vitamin E TPGS (d-α-tocopheryl polyethylene glycol 1000 succinate) was obtained from Eastman (TN, USA). Dichloromethane (DCM, analytical grade) was from Merck (Germany). Acetonitrile (HPLC grade) was from Fisher Scientific (NJ, USA). Phosphate buffered

Size, surface morphology and zeta-potential

The physicochemical characteristics of the formulated NPs such as particle size and size distribution, zeta potential and drug encapsulation efficiency were summarized in Table 1. It can be seen that TPGS has great advantages over PVA in the emulsification process. The emulsification efficiency of TPGS is 66.7 times higher than that of PVA, which means that the amount of TPGS needed to formulate the dug-loaded NPs is only 1/66.7 of that of PVA to formulate the same amount of the NPs. TPGS

Conclusion

Vitamin E TPGS-emulsified PLGA nanoparticles (NPs) were proposed in this study for NP formulation of anticancer drugs. Paclitaxel is chosen as a prototype drug due to its high therapeutic effects against a wide spectrum of cancers and its great commercial success as the best seller. The NP formulation of paclitaxel has great advantages versus the Taxol® formulation. The side effects associated with Cremophor EL contained in the Taxol® formulation can be avoided. In vitro cell viability

Acknowledgments

The authors would like to thank Ms. Cui Weiyi, a SCS Research Engineer for her efforts in the animal work. This research is supported by SCS Grant U0028 (NUS R397-000-606-305, 2004 and R279-000-187-305, 2005), Singapore Cancer Syndicate, BMRC, A*STAR (PI: Feng SS). Khin Yin Win is grateful of the National University of Singapore (NUS) for the financial support for her PhD study.

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