Developing a Fundamental Understanding of Nano-Bio Interactions
In order to develop effective delivery systems, it is essential to develop a more fundamental understanding of nanomaterial-cell interactions. We have found that positively-charged polyamidoamine (PAMAM) dendrimers and other polycationic polymers induce the formation of transient pores in cellular membranes. This phenomenon plays a key role in cellular uptake of these materials, competing with endocytic mechanisms of uptake.
Related Publications: Bioconjugate Chem., 2004, 15(4), 774-82; Bioconjugate Chem., 2006, 17(3), 728-34; J. Chem. Health Safety, 2006, 13(3), 16-20; Acc. Chem. Res., 2007, 40(5), 335-42.
Efficient target tissue permeation is crucial for achieving desired drug responses. Dense biological tissues and their complex localized matrices present significant barriers towards efficient nanoparticle delivery. Using dendrimers, we have studied the effect of nanoparticle size and surface charge on transport into multicellular tumor spheroids. By precisely tuning the size and charge of dendrimers, we are able to control their penetration and accumulation within the spheroids, with smaller generation dendrimers penetrating to the spheroid core, and larger dendrimers accumulating on the periphery of the spheroids. Moreover, simple surface charge modifications dictate the accumulation of dendrimers within the spheroids. We have also found that dendrimer penetration through skin layers is similarly dependent on both the dendrimer size and surface charge. Our findings illuminate how nanoparticle size, surface charge, and functionalization can be tuned for highly controlled biodistributions.
Related Publications: Biomacromolecules, 2012, 13(7), 2154-2162; Polymer Chem., 2013, 4(9), 2651-2657; Adv. Funct. Mater., 2014, 24(17), 2442-2449; Mol. Pharm., 2016, 13(7), 2155-2163.
Novel Nanocarrier Platforms Using Multivalent Targeting and Multiscaled Hybrid Designs
Linear-Dendron Block Copolymer Micelles
Using our basic understanding of nano-bio interactions we have prepared engineered polymeric nanoparticles combining advantageous properties of multiple systems. Micelles self-assembled from linear and dendritic amiphilic copolymers represent a promising class of nanocarriers. We have developed dendron-based micelles consisting of a hydrophobic, biodegradable poly(ε-caprolactone) core, a hyperbranched generation 3 polyester dendrimer, and a poly(ethylene glycol) outer layer. Owing to the hyperbranched dendron structure, our micelles demonstrated enhanced thermodynamic stability, a high degree of surface PEG coverage, and are able to maintain ligand-mediated cell targeting in the presence of serum proteins. The dendron micelles further allow for control over the surface distribution of targeting ligands.
Related Publications: Chem. Comm., 2011, 47(37), 10302-10304; ACS Macro. Lett., 2013, 2, 77-81; Adv. Func. Mater., 2014, 24(17), 2441-2449; Macromolecules, 2014, 47, 6911-6918; ACS Nano, 2016, 10(7), 6905-6914.
Multiscale Hybrid Nanoparticles
We have developed a multiscale, hybrid nanoparticle delivery system consisting of smaller PAMAM dendrimers (<10 nm) encapsulated within a larger poly(lactide)-b-poly(ethylene glycol) shell (150 nm). Whereas the larger outer PEG coating allows for increased circulation time and tumor accumulation due to the enhanced permeability and retention effect, the encapsulated smaller dendrimers exhibit improved tumor penetration capabilities. Folate-targeted dendrimers encapsulated within hybrid NPs displayed significantly enhanced tumor accumulation compared to their free counterparts. These findings demonstrate the potential for using hybrid approaches to take advantage of multiple drug delivery systems.
Related Publications: Biomacromolecules, 2012, 13(4), 1223-1230; Mol. Pharm., 2013, 10(6), 2157-2166; J. Control. Release, 2014, 191, 115-122.
Highly Efficient Capture of Circulating Tumor Cells
Metastatic cancer colonies are initiated with an adhesion mechanism hijacked from the inflammation response. The first step in this process involves transient, reversible, adhesive interactions between selectin molecules expressed on the endothelial venules and glycoprotein receptors on the leukocyte/invasive cancer cell, resulting in cell rolling. By exploiting this natural process, circulating tumor cells (CTCs) may be selectively captured on devices containing selectins and other cancer cell specific ligands. To translate this technique to realistic devices, capturing surfaces need to be non-fouling, stable, and controllable with minimum batch-by-batch variations, which are major drawbacks of current immobilization methods of the ligands, i.e. physisorption. Covalent immobilization of cell-specific ligands using non-toxic chemical reactions can enhance these properties as compared to physisorbed surfaces both in model and in vitro studies. The results suggest that cancer cell specific capturing devices based on cell rolling can be achieved if the ligands are covalently immobilized in a controlled way and present high specificity against their targets. An optimized, polymer-based nanovector is employed for this application in order to enhance the specific capturing capacity of the devices via multivalent effects.
Related Publications: Langmuir, 2010, 26(11), 8589-8596; Angew. Chem. Int. Ed., 2011, 50(49), 11769-11772; Anal. Chem., 2011, 83(3), 1078-1083; Anal. Chem., 2014, 86(12), 6088-6094; Anal. Chem., 2015, 87(19), 10096-100102.