Research paper Poly-L-asparagine nanocapsules as anticancer drug delivery vehicles G.R. Rivera-Rodríguez a,b,1 , M.J. Alonso a,b , D. Torres b,⇑ a Center for Research in Molecular Medicine and Chronic Diseases (CIMUS), Health Research Institute of Santiago de Compostela (IDIS), University of Santiago de Compostela, Santiago de Compostela, Spain b Department of Pharmacy and Pharmaceutical Technology, School of Pharmacy, University of Santiago de Compostela, Santiago de Compostela, Spain article info Article history: Received 14 January 2013 Accepted in revised form 5 August 2013 Available online 13 August 2013 Keywords: Polyasparagine Nanocapsules Nanocarriers Anticancer drug delivery Biopolymers Nanomedicine Targeted therapy Docetaxel abstract This work presents for the first time the development of novel poly-L-asparagine (PASN) nanocapsules and the in vitro evaluation of their potential as anticancer drug delivery systems. The design of PASN nanocapsules was inspired by the well-known avidity of cancer cells for the amino acid L-asparagine together with the expected ability of this hydrophilic polymer to escape to the mononuclear phagocytic system. Besides, these nanocapsules have an oily reservoir, which enables the efficient encapsulation of lipophilic drugs. PASN nanocapsules were obtained by an emulsification-polymer layer deposition pro- cess, which involves using a cationic surfactant as a bridge for the interaction of PASN with the lipid core. PASN nanocapsules showed sizes of around 170–200 nm and negative zeta potential values (around À20 mV to À40 mV). The model anticancer drug docetaxel was efficiently encapsulated (around 75%) and retained within the nanocapsule’s structure upon dilution in a simulated physiological medium. Moreover, these nanocapsules exhibited the ability to interact with the NCI-H460 human cancer cells and to enhance the cellular toxicity of the anticancer drug. All these features together with their adequate stability profile render these nanocapsules a new attractive platform for anticancer intracellular drug delivery. Ó 2013 Elsevier B.V. All rights reserved. 1. Introduction The development of targeted drug nanocarriers is a revolution- ary field of research, which is expected to lead to significant bene- fits in cancer theranostics [1]. The rational design of these nanocarriers relies on the particular characteristics of the targeted cells and also the tumor microenvironment. Targeting to cancer cells has mainly relied on the identification of over-expressed receptors and the design of the corresponding targeting ligands [2]. Irrespective of the targeting approach, a prerequisite for the targeted nanocarriers is their capacity to evade the mononuclear phagocyte system (MPS) and, thus, to exhibit long-circulating properties. Overall, most of the nanocarriers marketed until now display this capacity [3–5]; however, targeted nanocarriers still re- main in the clinical development phase [6]. The general strategy to avoid the rapid plasmatic elimination of nanosystems is the modification of their surface with hydrophilic polymers, such as poly (ethylene glycol) (PEG), poly (amino acids), and polysaccharides. The shield with these hydrophilic polymers enable nanostructures to circulate in the bloodstream for long peri- ods of time and, eventually, to extravasate into the tumor tissues [7]. Among these polymers, the poly (amino acid) poly-L-aspara- gine (PASN) has been shown to fulfill this objective, with the addi- tional advantage of being biodegraded by lysosomal proteases, thus allowing its complete elimination from the body [8,9]. Furthermore, PASN offers a potential significant advantage for targeting cancer cells. This is related to the fact that the amino acid L-asparagine is an extremely-required nutrient for progression of cancer cells [10,11]. Thus, we have speculated about the dual func- tion of PASN based nanocarriers: long circulation and targeting. Among the variety of biodegradable nanocarriers designed so far for the delivery of anticancer drugs [12–14], our group has particularly focused the attention on biopolymer nanocapsules [15–17]. These are versatile nanocarriers whose core may easily accommodate lipophilic drugs, as most anticancer drugs are, whereas their shell can be conveniently adapted in order to con- front specific biological environments and provide the nanocarrier with targeting properties [18]. Based on the above information, the main goal of the current work was to develop a new type of nanocapsules comprising an oily core surrounded by a PASN shell and to assess their potential for the intracellular delivery of anticancer drugs. For the evaluation of this potential, we chose the hydrophobic anticancer drug doce- taxel as a model compound. 0939-6411/$ - see front matter Ó 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.ejpb.2013.08.001 ⇑ Corresponding author. Department of Pharmacy and Pharmaceutical Technol- ogy, School of Pharmacy, University of Santiago de Compostela, Campus Vida, 15782 Santiago de Compostela, Spain. Tel.: +34 881 814 880; fax: +34 981 547 148. E-mail address: dolores.torres@usc.es (D. Torres). 1 Current address: Institute of Plant Biology and Biotechnology, University of Münster, Schlossplatz 8, 48143 Münster, Germany. European Journal of Pharmaceutics and Biopharmaceutics 85 (2013) 481–487 Contents lists available at ScienceDirect European Journal of Pharmaceutics and Biopharmaceutics journal homepage: www.elsevier.com/locate/ejpb