DOI: 10.1002/adfm.200500611 Multifunctional Core/Shell Nanoparticles Self-Assembled from pH-Induced Thermosensitive Polymers for Targeted Intracellular Anticancer Drug Delivery** By Kumaresh S. Soppimath, Li-Hong Liu, Wei Yang Seow , Shao-Qiong Liu, Ross Powell, Peggy Chan, and Yi Yan Yang* 1. Introduction Numerous new chemotherapeutic compounds have been de- veloped for combating cancer. However, medical advance- ments have been limited because of the serious side effects caused by many of these compounds. Most anticancer drugs are taken up nonspecifically, by all types of cells. Therefore, an ideal delivery carrier for an anticancer drug should be able to transport the drug specifically to the cancer cells and release the drug molecules inside the cells, at the site where their phar- macological activity is desired. Polymeric core/shell nanoparti- cles have emerged recently as promising colloidal carriers for targeting poorly water-soluble and amphiphilic drugs as well as genes to tumor tissues. [1–3] Using these nanoparticles, drug tar- geting to solid cancers can be achieved passively by an en- hanced permeability and retention effect, because of the hyper- permeable angiogenic vasculature of solid cancers. [4] Drug targeting can also be achieved by using a polymer sensitive to the surrounding temperature or pH. [5–8] Moreover, active drug targeting can be realized by attaching biological signals to the surface of nanoparticles, including antibodies, hormones, pep- tides, and small compounds such as folic acid that can recog- nize cancer cells. [9,10] Compared to antibodies, hormones, and peptides, folic acid is less expensive, more easily conjugated to the nanoparticles, and more stable during transportation, stor- age, and use. Unlike the other ligands listed, folate is nonim- munogenic because it is naturally found in the body. [11] More importantly, the folate receptor is frequently expressed on the surface of many human cancer cell types, and cell uptake of folate–drug conjugates or folate-conjugated nanocarriers is based on folate-receptor-mediated endocytosis. In a recent pa- per, we reported pH-triggered, thermally responsive core/shell nanoparticles self-assembled from the amphiphilic tercopoly- mer poly(N-isopropylacrylamide-co-N,N-dimethylacrylamide- co-10-undecenoic acid) (P(NIPAAm-co-DMAAm-co-UA)). [12] These nanoparticles exhibited a pH-dependent lower critical solution temperature (LCST). In a normal physiological envi- ronment (pH 7.4), the LCST of the nanoparticles was well Adv. Funct. Mater. 2007, 17, 355–362 © 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim 355 – [*] Dr. Y. Y. Yang,Dr. K. S. Soppimath, L.-H. Liu, S.-Q. Liu, R. Powell, Dr. P. Chan Institute of Bioengineering and Nanotechnology 31 Biopolis Way, The Nanos, 04-01, 138669 (Singapore) E-mail: yyyang@ibn.a-star.edu.sg W. Y. Seow Department of Materials Science and Engineering National University of Singapore Blk EA, 07-40, 9 Engineering Drive 1, 117576 (Singapore) [**] This work was funded by the Institute of Bioengineering and Nano- technology, Agency for Science, Technology and Research, Singapore. We thank Prof. P. S. Low (Purdue University, USA) for valuable dis- cussions on cancer cells that over express folate receptors. We also acknowledge the technical assistance and contribution of Cherng- wen Tan (Institute of Bioengineering and Nanotechnology). Support- ing Information is available online from Wiley InterScience or from the author. Core/shell nanoparticles that display a pH-sensitive thermal response, self-assembled from the amphiphilic tercopolymer, poly(N-isopropylacrylamide-co-N,N-dimethylacrylamide-co-10-undecenoic acid) (P(NIPAAm-co-DMAAm-co-UA)), have re- cently been reported. In this study, folic acid is conjugated to the hydrophilic segment of the polymer through the free amine group (for targeting cancer cells that overexpress folate receptors) and cholesterol is grafted to the hydrophobic segment of the polymer. This polymer also self-assembles into core/shell nanoparticles that exhibit pH-induced temperature sensitivity, but they possess a more stable hydrophobic core than the original polymer P(NIPAAm-co-DMAAm-co-UA) and a shell containing folate molecules. An anticancer drug, doxorubicin (DOX), is encapsulated into the nanoparticles. DOX release is also pH- dependent. DOX molecules delivered by P(NIPAAm-co-DMAAm-co-UA) and folate-conjugated P(NIPAAm-co-DMAAm- co-UA)-g-cholesterol nanoparticles enter the nucleus more rapidly than those transported by P(NIPAAm-co-DMAAm)-b- poly(lactide-co-glycolide) nanoparticles, which are not pH sensitive. More importantly, these nanoparticles can recognize folate-receptor-expressing cancer cells. Compared to the nanoparticles without folate, the DOX-loaded nanoparticles with folate yield a greater cellular uptake because of the folate-receptor-mediated endocytosis process, and, thus, higher cytotoxicity results. These multifunctional polymer core/shell nanoparticles may make a promising carrier to target drugs to cancer cells and release the drug molecules to the cytoplasm inside the cells. FULL PAPER