Polyphosphoesters: New Biocompatible, Biodegradable Polymers for Biomedical Applications. Jeniree A. Flores. Advisor: Prof. Karen L.

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1 Polyphosphoesters: New Biocompatible, Biodegradable Polymers for Biomedical Applications Jeniree A. Flores Advisor: Prof. Karen L. Wooley November 12 th, 2012 Polyphosphoesters (PPEs) are phosphorous containing polymers with repeated phosphoester linkages in the backbone. These polymers are well known for their biodegradability, biocompatibility and easy side chain functionalization which makes them desirable for biomedical applications. 1 The history of PPEs can be traced back to the 1970s when Prof. Penczek and co-workers focused on the development of efficient methods of polymerization for these materials. Their efforts were driven by the remarkable structural similarities between PPEs and teichoic and nucleic acids. 2 The backbone of PPEs is composed of phosphorous, carbon and oxygen, and triphosphoesters units are repeated thorough out the polymer. However, unlike the natural polynucleotides which are only anionic due to the presence of diphosphoester moeities, PPEs could be functionalized into cationic, anionic, or charge neutral polymers. 4 The most popular polymerization mechanism used in the synthesis of PPEs is ringopening polymerization (ROP) which produces polymers with high molecular weight (Mw), low polydispersity indexes (PDIs) and well defined structures. Furthermore, another advantage of utilizing ROP for the synthesis of PPEs is the availability of cyclic monomers synthesized by the condensation reaction between 2-chloro-2-oxo-1,3,2-dioxaphospholane (COP) and an alcohol (figure 1). Several cyclic phospholane monomers have been reported, including isopropylfunctionalized 4, PEG-ylated 5,6 and alkyne-functionalized 7 monomers which impart

2 hydrophobicity, hydrophilicity and functionality to the resulting polymers respectively. These properties allow for the synthesis of amphiphilic block copolymers capable of forming complex self-assemblies which can be used as gene and drug delivery vehicles. Cationic polymers are commonly used in gene therapy due to the formation of electrostatic complexes with the gene. These polymers encapsulate the Figure 1: Functionalized monomers for the synthesis of side chain modified polymers genes and provide a protective barrier to prevent the genes from being degraded by enzymes. 8 Moreover, cell internalization is facilitated by the electrostatic interactions between anionic cell membranes and cationic polymer-gene complexes Wang et al. have synthesized an amphiphilic, cationic, triblock copolymer composed of monomethoxy poly(ethylene glycol) (mpeg), poly(εcaprolactone) (PCL) and cationic poly(2-aminoethyl ethylene phosphate) (PAEEP) which was used to prepare micelle nanoparticles (MNPs) for sirna delivery. 11 Flow cytometric analysis showed that 90% of the incubated cells were fluorescent due to the internalization of fluorescein- labeled sirna (figure 2). 11 More than 90% gene suppression was achieved by incubation of cells with these MNPs; these results show a significant improvement over the 60% gene knockdown observed after the incubation with Lipofectamine TM 2000, a commercially available transfection agent. Moreover,

The inherent properties of Figure 1: Effect of N/P ratios on MNPs to sirna on gene silencing efficiency. Dose of sirna for Lipofectamine TM 2000 and MNPs was 20 and 100 nm/l, respectively.

3 a high percentage of cell viability was observed even at high concentrations of sirna. The data showed that gene suppression could be enhanced without inducing cytotoxicity by utilizing these PPEbased MNPs as an efficient and safe sirna delivery vehicle. The inherent properties of Figure 1: Effect of N/P ratios on MNPs to sirna on gene silencing efficiency. Dose of sirna for Lipofectamine TM 2000 and MNPs was 20 and 100 nm/l, respectively. biodegradability and biocompatibility of PPEs are also of interest in the field of drug delivery systems. The ease of post-polymerization functionalizations of PPEs allows for the conjugation of drug molecules to create targeted delivery systems. In 2011, Wang and co-workers designed a doubly ph-sensitive system for the delivery of anticancer drugs to fight drug-resistant cancer stem cells (figure 3) 12. Cationic and anionic segments showed ph-responsiveness that could be triggered by the ph gradients observed in tumor sites. The external ph of cancerous cells exhibits a mildly acidic environment; here, the PPE drug delivery vehicle becomes cationic in order to enhance the cell internalization. The second ph responsive trigger of the micellar system occurs once inside the cell. Figure 3: Self-assembly of conjugates in water results in charged NPs that undergo charge inversion as a result of the ph gradient encounter in tumor cells, followed by DOX release via cleavage of a hydrazone bond. At this stage, the highly acidic, intracellular environment causes a cleavage between the

4 polymer-drug complexes and allows for drug release. This system is based on an amphiphilic block copolymer consisting of monomethoxy polyethylene glycol (mpeg) and poly(allyl ethylene phosphate) (PAEP), which was post modified via thiol-ene click chemistry to create three distinct segments in the PAEP block. Moreover, the functional segment allowed for the covalent conjugation of doxorubicin (a commonly used anticancer drug) through an acid-labile hydrazone bond, cleavable under endo/lysosomal ph (~5.5). The incubation of cancer stem cells with this polymer-drug complex showed promising results in in vitro applications. This seminar will focus on the synthesis of polyphosphoester-based block copolymers and the chemical modifications that allows for their application as gene carriers and drug delivery systems.

5 References: 1. Wang, Y.; Yuan, Y.; Du, J.; Yang, J.; Wang, J. Macromol. Biosci. 2009, 9, Yasuhiko, Iwasaki. Modern Synthesis and Thermoresponsivity of Polyphosphoesters, Biomedical Engineering - Frontiers and Challenges; Reza Fazel-Rezai (Ed.): InTech, (2011); p 1. Available online at: 3. S. Penczek.; T. Biela.; P. Klosinski.; G. Lapienis. Makromol. Chem. Macromol. Sym. 1986, 6, Iwasaki, Y.; Nakagawa, C.; Ohtomi, M.; Ishihara, K.; Akiyoshi, K. Biomacromolecules 2004, 5, Du, J.; Chen, D.; Wang, Y.; Xiao, C.; Lu, Y.; Wang, J.; Zhang, G. Biomacromolecules 2006, 7, Zhu, W.; Sun, S.; Xu, N.; Gou, P.; Shen, Z. J. Appl. Polym. Sci. 2012, 123, Zhang, S.; Li, A.; Zou, J.; Lin, L. Y.; Wooley, K. L. ACS Macro Lett. 2012, 1, M. Elsabahy, M. Zhang, S. Gan, K. C. Waldron, J. C. Leroux, Soft Matter 2008, 4, M. Harada-Shiba, K. Yamauchi, A. Harada, I. Takamisawa, K. Shimokado, K. Kataoka, Gene Ther. 2002, 9, M. H. Dufresne, M. Elsabahy, J. C. Leroux, Pharm. Res. 2008, 25, Sun. T.; Du. J.; Yan. J.; Mao. H.; Wang. J. Biomaterials 2008, 29, Du, J.; Du, X.; Mao, C.; Wang, J. J. Am. Chem. Soc. 2011, 133,

nanoprecipitation mpeg-pla 2 nd Emulsion mpeg-pla in DCM

nanoprecipitation mpeg-pla 2 nd Emulsion mpeg-pla in DCM THERAPEUTIC NANOTECHNOLOGY LAB MODULE Location: BioNano Lab, 3119 Micro and Nanotechnology Laboratory (MNTL) Instructor: Jianjun Cheng, Assistant Professor of Materials Science and Engineering Lab Assistants: