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A sensitive in vivo model for quantifying interstitial convective transport of injected macromolecules and nanoparticles

¹Institute of Bioengineering, École Polytechnique Fédérale de Lausanne, Lausanne, Switzerland; ²Department of Biomedical Engineering, Northwestern University, Evanston, Illinois; ³School of Pharmacy and Pharmaceutical Sciences, University of Manchester, Manchester, United Kingdom; and ⁴Department of Radiation Oncology, Massachusetts General Hospital and Harvard Medical School, Boston, Massachusetts

Submitted 2 April 2006 ; accepted in final form 30 May 2006

Effective interstitial transport of particles is necessary for injected drug/diagnostic agents to reach the intended target; however, quantitative methods to estimate such transport parameters are lacking. In this study, we develop an in vivo model for evaluating interstitial convection of injected macromolecules and nanoparticles. Fluorescently labeled macromolecules and particles are coinfused with a reference solute at constant infusion pressure intradermally into the mouse tail tip, and their relative convection coefficients are determined from spatial and temporal interstitial concentration profiles. Quantifying relative solute velocity with a coinfused reference solute eliminates the need to estimate interstitial fluid velocity profiles, greatly reducing experimental variability. To demonstrate sensitivity and usefulness of this model, we compare the effects of size (dextrans of 3, 40, 71, and 2,000 kDa and 40-nm diameter particles), shape (linear dextran 71 kDa vs. 69 kDa globular protein albumin), and charge (anionic vs. neutral dextran 3 kDa) on interstitial convection. We find significant differences in interstitial transport rates between each of these molecules and confirm expected transport phenomena, testifying to sensitivity of the model in comparing solutes of different size, shape, and charge. Our data show that size exclusion (within a specific size range) dominates molecular convection, while mechanical hindrance slows larger molecules and nanoparticles; proteins convect slower than linear molecules of equal molecular mass, and negative surface charges increase convection through matrix repulsion. Our in vivo model is presumably a sensitive and reliable tool for evaluating and optimizing potential drug/diagnostic vehicles that utilize interstitial and lymphatic delivery routes.

drug delivery; size exclusion; lymphatic uptake; extracellular matrix; subcutaneous

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