Hayley J Paholak

University of Michigan, Ann Arbor, MI, United States

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Publications (9)40.03 Total impact

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    ABSTRACT: Nanoparticles designed for biomedical applications are often coated with polymers containing reactive functional groups, such as -COOH and -NH2, to conjugate targeting ligands or drugs. However, introducing highly charged surfaces promotes binding of the nanoparticles to biomolecules in biological systems through ionic interactions, causing the nanoparticles to aggregate in biological environments and consequently undergo strong non-specific binding to off-target cells and tissues. Developing a unique polymer with neutral surfaces that can be further functionalized directly would be critical to develop suitable nanomaterials for nanomedicine. Here, we report a thiol-reactive amphiphilic block copolymer poly(ethylene oxide)-block-poly(pyridyldisulfide ethylmeth acrylate) (PEO-b-PPDSM) for coating gold nanoparticles (AuNPs). The resultant polymer-coated AuNPs have almost neutral surfaces with slightly negative zeta potentials from -10 to 0 mV over a wide pH range from 2 to 12. Although the zeta potential is close to zero we show that the PEO-b-PPDSM copolymer-coated AuNPs have both good stability in various physiological conditions and reduced non-specific adsorption of proteins/biomolecules. Because of the multiple pyridyldisulfide groups on the PPDSM block, these individually dispersed nanocomplexes with an overall hydrodynamic size around 43.8 nm can be directly functionalized via disulfide-thiol exchange chemistry.
    Polymer Chemistry 04/2014; 5(8):2768-2773. · 5.23 Impact Factor
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  • Peng Zou, Hongwei Chen, Hayley J Paholak, Duxin Sun
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    ABSTRACT: Understanding in vivo drug release kinetics is critical for the development of nanoparticle-based delivery systems. In this study, we developed a fluorescence resonance energy transfer (FRET) imaging approach to noninvasively monitor in vitro and in vivo cargo release from polymeric nanoparticles. The FRET donor dye (DiO or DiD) and acceptor dye (DiI or DiR) were individually encapsulated into poly(ethylene oxide)-b-polystyrene (PEO-PS) nanoparticles. When DiO (donor) nanoparticles and DiI (acceptor) nanoparticles were co-incubated with cancer cells for 2 h, increased FRET signals were observed from cell membranes, suggesting rapid release of DiO and DiI to cell membranes. Similarly, increased FRET ratios were detected in nude mice after intravenous co-administration of DiD (donor) nanoparticles and DiR (acceptor) nanoparticles. In contrast, another group of nude mice i.v. administrated with DiD/DiR co-loaded nanoparticles showed decreased FRET ratios. Based on the difference in FRET ratios between the two groups, in vivo DiD/DiR release half-life from PEO-PS nanoparticles was determined to be 9.2 min. In addition, it was observed that the presence of cell membranes facilitated burst release of lipophilic cargos while incorporation of oleic acid-coated iron oxide into PEO-PS nanoparticles slowed the release of DiD/DiR to cell membranes. The developed in vitro and in vivo FRET imaging techniques can be used to screening stable nano-formulations for lipophilic drug delivery.
    Molecular Pharmaceutics 09/2013; · 4.57 Impact Factor
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    ABSTRACT: We report and demonstrate biomedical applications of a new technique-'living' PEGylation-that allows control of the density and composition of heterobifunctional PEG (HS-PEG-R; thiol-terminated poly(ethylene glycol)) on gold nanoparticles (AuNPs). We first establish 'living' PEGylation by incubating HS-PEG5000-COOH with AuNPs (∼20 nm) at increasing molar ratios from zero to 2000. This causes the hydrodynamic layer thickness to differentially increase up to 26 nm. The controlled, gradual increase in PEG-COOH density is revealed after centrifugation, based on the ability to re-suspend the pellet and increase the AuNP absorption. Using a fluorescamine-based assay we quantify differential HS-PEG5000-NH2 binding to AuNPs, revealing that it is highly efficient until AuNP saturation is reached. Furthermore, the zeta potential incrementally changes from -44.9 to +52.2 mV and becomes constant upon saturation. Using 'living' PEGylation we prepare AuNPs with different ratios of HS-PEG-RGD (RGD: Arg-Gly-Asp) and incubate them with U-87 MG (malignant glioblastoma) and non-target cells, demonstrating that targeting ligand density is critical to maximizing the efficiency of targeting of AuNPs to cancer cells. We also sequentially control the HS-PEG-R density to develop multifunctional nanoparticles, conjugating positively charged HS-PEG-NH2 at increasing ratios to AuNPs containing negatively charged HS-PEG-COOH to reduce uptake by macrophage cells. This ability to minimize non-specific binding/uptake by healthy cells could further improve targeted nanoparticle efficacy.
    Nanotechnology 08/2013; 24(35):355101. · 3.84 Impact Factor
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    ABSTRACT: Although inactivation of the PTEN gene has been implicated in the development of resistance to the HER2 targeting antibody trastuzumab, the mechanisms mediating this resistance remain elusive. We generated trastuzumab resistant cells by knocking down PTEN expression in HER2 overexpressing breast cancer cell lines and demonstrate that development of trastuzumab resistance in these cells is mediated by activation of an IL6 inflammatory feedback loop leading to expansion of the cancer stem cell (CSC) population. Long term trastuzumab treatment generates highly enriched CSCs which display an EMT phenotype secreting over 100-fold more IL6 than parental cells. An IL6 receptor antibody interrupted this inflammatory feedback loop reducing the cancer stem cell population resulting in decreased tumor growth and metastasis in mouse xenographs. These studies demonstrate that trastuzumab resistance may be mediated by an IL6 inflammatory loop and suggest that blocking this loop may provide alternative strategy to overcome trastuzumab resistance.
    Molecular cell 07/2012; 47(4):570-84. · 14.61 Impact Factor
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    ABSTRACT: Quantitative estimations of first-in-human (FIH) doses are critical for phase I clinical trials in drug development. Human pharmacokinetic (PK) prediction methods have been developed to project the human clearance (CL) and bioavailability with reasonable accuracy, which facilitates estimation of a safe yet efficacious FIH dose. However, the FIH dose estimation is still very challenging and complex. The aim of this article is to review the common approaches for FIH dose estimation with an emphasis on PK-guided estimation. We discuss 5 methods for FIH dose estimation, 17 approaches for the prediction of human CL, 6 methods for the prediction of bioavailability, and 3 tools for the prediction of PK profiles. This review may serve as a practical protocol for PK- or pharmacokinetic/pharmacodynamic-guided estimation of the FIH dose.
    The AAPS Journal 03/2012; 14(2):262-81. · 4.39 Impact Factor
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    ABSTRACT: Polymer-coated nanoparticles are widely used for drug delivery in cancer therapy. However, it is not clear whether the polymer coating is disrupted in the lipid bilayer or intracellular space. Our current work suggests that the polymer coating of inorganic nanoparticles is disrupted after internalization by cancer cells. Single dispersed red quantum dots (QDs) labeled with 5-carboxyfluorescein (5-FAM) (green) (diameter = 28 nm) were incubated with cancer cells (PC-3) and imaged via fluorescence microscopy. Initially the 5-FAM-labeled polymer coating was attached to the QD and its green fluorescence was quenched when the nanoparticles were internalized after 4 h incubation, but the 5-FAM-labeled polymer became separated from the QD once inside the lysosomes of cells and its fluorescence becomes visible after 8 h. The fluorescence ratio (5-FAM/QDs) was increased 29-fold after 8 h incubation compared to 2 h. The fluorescence quenching effect of PEG-5-FAM after conjugation in solution (quenched by 44%) was compared to free poly(ethylene glycol)-5-FAM (PEG-5-FAM) mixing with QDs, which only exhibited slight (6.9%) quenching of 5-FAM. In addition, the intracellular dissociation of polymer coating from QD loaded micelles (diameter = 300 nm) was also observed. Furthermore, amphiphilic polymer labeled with the hydrophobic dye 6-((4,4-difluoro-1,3-dimethyl-5-(4-methoxyphenyl)-4-bora-3a,4a-diaza-s-indacene-2-propionyl)amino)hexanoic acid (BODIPY® TMR) (red) was applied to encapsulate hydrophobic iron oxide nanoparticles (IONPs). The BODIPY dye was quenched by both the encapsulated IONPs and the hydrophobic region inside the micelles, while an 8-fold fluorescence enhancement was observed after polymeric micelle dissociation. Our in vitro results also reveal the polymeric dissociation after internalization by cancer cells as the dye signal becomes detectable after 24 h incubation. These results suggest that the polymer coating is stable in the lipid bilayer and becomes dissociated from nanoparticles in the lysosome of cancer cells. These data will provide guidance for intracellular drug delivery using polymer coated nanoparticles. Graphical abstract
    Nano Research 5(11). · 7.39 Impact Factor

Publication Stats

36 Citations
40.03 Total Impact Points


  • 2012–2013
    • University of Michigan
      • Department of Pharmaceutical Sciences
      Ann Arbor, MI, United States
    • Concordia University–Ann Arbor
      Ann Arbor, Michigan, United States