Targeted doxorubicin nanotherapy strongly suppressing growth of multidrug resistant tumor in mice Dai Hai Nguyen a , Jung Seok Lee b , Jin Woo Bae a , Jong Hoon Choi a , Yunki Lee a , Joo Young Son a , Ki Dong Park a, * a Department of Molecular Science and Technology, Ajou University, 5 Woncheon, Yeoungtong, Suwon 443-749, Republic of Korea b Biomedical Engineering, Yale University, CT 06511, USA A R T I C L E I N F O Article history: Received 20 July 2015 Accepted 26 August 2015 Available online 14 September 2015 Keywords: Pluronic micelles Doxorubicin Multidrug-resistant tumor Redox-sensitive pH-sensitive targeted chemotherapy A B S T R A C T The rational design of nanomedicine to treat multidrug resistant (MDR) tumors in vivo is described in the study. We prepared multifunctionalized Pluronic micelles that are already well-established to be responsive to low pH and redox in order to systemically deliver doxorubicin (DOX) to MDR tumors. Folic acids (FAs) were introduced on the micelle surface as tumor-targeting molecules. In vitro, the DOX- loaded micelles exerted high cytotoxicity in the DOX-resistant cells by bypassing MDR efflux. Cellular uptake studies clearly demonstrated that FA-conjugated DOX micelles (FA/DOX micelles) were efficiently internalized and accumulated in the MDR cells. In vivo studies indicated significant efficacy of FA/DOX micelles for MDR tumors in mice, and that the volume of tumors was 3 times smaller in this group than that of tumors in the free DOX group, and 8 times smaller than the tumors in the saline group. To the best of our knowledge, this methodology has been recognized to have significantly high efficacy, compared to previously reported DOX nanoparticle formulations. This superior anti-tumor efficacy of FA/DOX micelles in MDR tumor-bearing mice can be attributed to FA-targeted and -mediated endocytosis, inhibition of MDR effect, and subsequent DOX release triggered by dual stimuli (low pH and redox) inside the tumor. Given the promise of the multifunctional micelle mediated delivery on inhibition of MDR tumor growth, FA/DOX micelle platform is a much sought after goal for cancer chemotherapy, especially for cancers resistant to anticancer drugs. ã 2015 Elsevier B.V. All rights reserved. 1. Introduction Multidrug resistance has been considered as an insuperable obstacle to the desired cancer chemotherapy (Szakacs et al., 2006; Kim et al., 2008). Cancer cells can exhibit multidrug resistance through many mechanisms, including excessive expression of metabolic enzymes (e.g., cytochrome P450 and glutathione/ glutathione S-transferase), changes in proteins within tumor cells (topoisomerase or b-tubulin), and overexpression of multidrug efflux transporters such as P-glycoprotein (P-gp), which is the best known key factor contributing to multidrug-resistant (MDR) tumor. P-gp is overexpressed in the plasma membrane of MDR tumor cells and effuses anticancer drugs from the cells, thus lowering intracellular drug concentrations (Szakacs et al., 2006; Ogawara et al., 2009). Recently, several generations of P-gp inhibitors were developed and evaluated in clinical trials to overcome multidrug resistance in cancer (Szakacs et al., 2006; Kitazaki et al., 2005). This approach is, however, often associated with non-specific toxicity of the inhibitors, for instance, dysfunc- tion of P-gp in healthy tissues (Szakacs et al., 2006; Lee et al., 2005). As one of the alternative approaches, nanoparticles provide an attractive way to circumvent drug resistance without exerting high toxicity on healthy tissues by encapsulating or conjugating drugs to nanocarriers such as liposomes (Kundu et al., 2012), polymeric micelles (Wei et al., 2012), nanospheres (Laurand et al., 2004), and solid-core nanoparticles (Li et al., 2012). Among those nano- particles, micelles are of interest and have gained particular attention in the pharmaceutical fields for their advantages, including low cytotoxicity, high loading of lipophilic drugs, sustained drug release, prolonged blood circulation time, and protection of host substances from metabolism (Hamidi et al., 2012). In addition, the size range of micelles deems them appropriate for enhanced permeability and retention (EPR)- mediated cancer therapy (Lee et al., 2010). One of the most commonly used polymers for micelle preparation is triblock copolymers of poly(ethylene oxide) (PEO) and poly(propylene * Corresponding author. Fax: +82 1 219 1592. E-mail address: kdp@ajou.ac.kr (K.D. Park). http://dx.doi.org/10.1016/j.ijpharm.2015.08.083 0378-5173/ ã 2015 Elsevier B.V. All rights reserved. International Journal of Pharmaceutics 495 (2015) 329–335 Contents lists available at ScienceDirect International Journal of Pharmaceutics journal homepage: www.elsev ier.com/locate /ijpharm