In Vivo Distribution of Polymeric Nanoparticles at the Whole-Body, Tumor, and Cellular Levels

Block copolymer micelles (BCMs) were functionalized with indium-111 and/or epidermal growth factor (EGF), which enabled investigation of the in vivo transport of passively and actively targeted BCMs. The integration of conventional and image-based techniques afforded novel quantitative means to achieve an in-depth insight into the fate of polymeric nanoparticles in vivo. Pharmacokinetics and biodistribution studies were performed in athymic mice bearing human breast xenografts to evaluate the whole-body transport of NT-BCMs (non-targeted, EGF-) and T-BCMs (targeted, EGF+). The intratumoral distribution of BCMs was investigated using MicroSPECT/CT and autoradiographic imaging, complemented with quantitative MATLABA (R) analyses. Tumors were fractionated for quantifying intracellular uptake of BCMs via gamma-counting. The intratumoral distribution of NT-BCMs and T-BCMs were found to be heterogeneous, and positively correlated with tumor vascularization (r > 0.68 +/- 0.04). The enhanced in vivo cell uptake and cell membrane binding of T-BCMs were found to delay their clearance from tumors overexpressing EGFR, and therefore resulted in enhanced tumor accumulation for the T-BCMs in comparison to the NT-BCMs. Adequate passive targeting is required in order to achieve effective active targeting. Tumor physiology has a significant impact on the transvascular and intratumoral transport of passively and actively targeted BCMs.