Stimuli-Responsive Hybrid Nanoparticles for Controlled Chemical Delivery

1. INTRODUCTION SYNTHESIS OF STIMULI-SENSITIVE POLYMERS BIOLOGICAL EVALUATION OF NANOPARTICLE CONJUGATES BIOCOMPATIBILITY • Recombinant polymer synthesis • Linear stimuli sensitive elastin like polymers (ELPs)3 • [(GVGVP)m–(GXGVP)n]Z X = His • Factors which influence pH / temperature-sensitive phase transition of ELPs: • - Length of elastin units (m) • - Polymer molecular weight (z) • - Presence of ionizable groups (n) • Histidine (pKa 6.0) is introduced into the polymer sequence to lower the pKa of the ELPs and shift their phase transition to lower pH values. The overall objective of this interdisciplinary research is to construct hybrid stimuli-responsive nanoparticles for controlled delivery of bioactive agents. The focus is on the fabrication of hybrid inorganic porous nanoparticles with “on-off” pore caps on their surface made of thermal and pH - responsive recombinant polymers1. These hybrid nanostructures provide the benefit of robust inorganic cores (gold, silica or iron-oxide) on one hand where their size and porosity do not change in biological environments, and the flexible surface grafted polymers on the other allowing controlled release of bioactive agents (Fig 1). The educational component of this project will facilitate training of new generations of students and scientists able to work at the interface of mechanical engineering, chemistry, material science and pharmaceutics designing novel nanoconstructs for use in biomedical applications. (A) (B) (C) Fig 6. Growth inhibition assay of gold nanoparticle-RGD peptide on model endothelial cells demonstrating biocompatibility of nanoparticle conjugates. Time (s) IN VITRO BIOMOLECULE RELEASE • Chemical polymer synthesis • Elastin-based side-chain polymers (EBPs) Fig 7. Doxorubicin release from porous model alumina particles (pore diameter ~11 nm and particle diameter < 20 m) at 37 °C (red) and 20 °C (black). A significant increase in both the rate and amount of release is observed at 37 °C. These results show that biomolecule release is a thermally activated process with a significant entropic component. • Synthetic polymers with pendant VPGVG peptide sequences are readily accessible ELP analogues4. • Stimuli sensitivity of EBP polymers is affected by the same parameters as linear ELPs. • EBPs are more responsive to pH changes than ELPs due the large number of pendant carboxylic acid groups of the terminal glycines. CELLULAR TARGETING Fig 1. Typical rationale of active nanoparticles for controlled chemical delivery EXPERIMENTS & RESULTS CORE NANOPARTICLE SYNTHESIS AND CHARACTERIZATION Fig 8. Binding of lactose functionalized gold nanoparticles to cell surface lactose receptors of Neisseria gonorrhoeae, a biological pathogen, leads to dramatically enhanced luminescence5. Fluorescence images under broadband UV irradiation with red and green filters. Lane 1: autofluorescence of cells with no additives. Lane 2: cells containing citrate coated 3 nm gold nanoparticles. Lane 3: cells containing glucose coated gold nanoparticles. Lane 4: cells containing lactose coated gold nanoparticles. Fig 4. Synthesis of comonomers and polymerization of stimuli sensitive elastin based polymers. REFERENCES Boc-VPG-COOH + HCl*H2NXGOEt + DIPEA, BOP / EtOAc Boc-VPGXG-COOH  H2NVPGXGCOOH X = Val, His SURFACE MODIFICATION OF NANOPARTICLES • Dandu,R, & Ghandehari,H, Progress in Polymer Science 32, 1008 (2007) • Kim,SH, Liu,BYH, & Zachariah,MR, Chem Mater 14, 2899 (2002) • Urry,DW et al., in Controlled drug delivery: challenges and strategies. ed. Park,K. 405-437, American Chemical Society, Washington, D.C. (1997) • Ferna´ndez-Trillo,F et al., Macromolecules, 40, 6094 (2007) • DeShong,P et al., U.S.Patent LS-2004-052 (2004) H2NVPGXGCOOH + 2-isocyanatoethyl methacrylate  methacrylate-functionalized VPGXG [ MA-VPGXG] X = Val, His mMAVPGVG + nMAVPGHG + EBIB, CuCl, bipy / DMSO –atom transfer radical polymerization Poly[(MA-VPGVG)m(MA-VPGHG)n] Fig 2. Fabrication of porous nanoparticles by controlled chemical evaporation2. The evaporation process results in increased concentration of reactants. Precipitation is basically a collision (coagulation process) which varies as the viscosity of the solvent increases due to solute precipitation. ACKNOWLEDGEMENTS National Science Foundation Grant 0608906 Active Nanostructures and Nanosystems Nanoscience Interdisciplinary Research Team Fig 5. Strategy for derivatization of nanoparticle surfaces using glucose as a model. This strategy will be similarly adapted to attach the stimuli sensitive polymers via the terminal lysine group to form a peptide (CONH) linkage. The other end of the chelator will permit modification of silica surfaces via the siloxane group (2) or gold surfaces via disulfide group (3). (inset) Example of a gold nanoparticle conjugated to a model peptide arginine-glycine-aspartic acid (RGD). Fig 3. Transmission electron microscopy images of (A) Porous and (B) Hollow silica nanoparticles. (C) Confocal microscopy image of hollow silica nanoparticles filled with a model compound Doxorubicin Stimuli-Responsive Hybrid Nanoparticles for Controlled Chemical Delivery Co-Investigators: Hamid Ghandehari1,2*, Philip DeShong1,3, Douglas English1,3, Michael R. Zachariah1,3,4 1Center for Nanomedicine & Cellular Delivery, 2Dept of Pharmaceutical Sciences,University of Maryland Baltimore; 3Dept of Chemistry & Biochemistry, 4Dept of Mechanical Engineering, University of Maryland College Park *Present Address: Departments of Pharmaceutics & Pharmaceutical Chemistry and Bioengineering, University of Utah