Effects of Extracellular Surface Interactions on Mass Transport across Epithelial Cells.

Abstract

Transport of molecules across cells is an important determinant of the absorption, distribution, and elimination properties of therapeutic agents in the body. While the ability to predict and control those properties of therapeutic agents has been a long-standing goal in pharmaceutical sciences, cells are structurally and functionally complex, and in many cases transport phenomena have proved difficult to accurately predict, purely based on the internal organization of the cell. To address why this may be the case, this thesis combined imaging, mass transport measurements, and computational modeling, to investigate two complex cellular transport phenomena: i) uptake and permeation of magnetic nanoparticles across canine kidney epithelial cells in the presence of a magnetic field; and, ii) uptake and permeation of small molecules across airway epithelial cells of different origins. For experiments, four different transport probes were used: 1) superparamagnetic iron oxide nanoparticles that exhibited variations in transport under a pulsed vs. constant magnetic field; 2) two fluorescent probes (MitoTracker Red or Hoechst 33342) that exhibited differences in distribution in the airway and alveoli; 3) a passively diffusing small molecule (propranolol) that exhibited differences in transport behavior across different airway epithelial cells; and, 4) a highly insoluble compound (curcumin) that exhibited differences in transport across airway epithelial cells in the presence of a complexing agent. Effects of spatiotemporal variations in a magnetic field on the extent of particle aggregation on the extracellular cell surface should be considered to optimize particle formulations and magnetic field applications for magnetically-guided targeting. For local lung delivery, absorption and distribution of inhaled formulations should be screened in the biorelevant cell model, by considering effects of local extracellular interactions. Altogether, the results of experiments and analyses show innovative approaches to interpret cell-based transport data in a more accurate manner by analyzing local molecular interactions and diffusion phenomena occurring at the extracellular surface of cells for a variety of transported materials ranging from small molecules to nanoparticles. Based on cell-based transport studies, quantitative microscopic imaging and in situ cellular pharmacokinetic modeling can potentially predict transport phenomena of drug-like molecules in vivo by dissecting variables resulting from extracellular surface properties.