The current study describes the impact of particle size and/or molecular targeting (epidermal growth factor, EGF) on the in vivo transport of block copolymer micelles (BCMs) in athymic mice bearing human breast cancer xenografts that express differential levels of EGF receptors (EGFR). BCMs with diameters of 25 nm (BCM-25) and 60 nm (BCM-60) were labeled with indium-111 ((111)In) or a fluorescent probe to provide a quantitative and qualitative means of evaluating their whole body, intratumoral, and subcellular distributions. BCM-25 was found to clear rapidly from the plasma compared to BCM-60, leading to an almost 2-fold decrease in their total tumor accumulation. However, the tumoral clearance of BCM-25 was delayed through EGF functionalization, enabling the targeted BCM-25 (T-BCM-25) to achieve a comparable level of total tumor deposition as the nontargeted BCM-60 (NT-BCM-60). Confocal fluorescence microscopy combined with MATLAB analyses revealed that NT-BCM-25 diffuses further away from the blood vessels (D(mean) = 42 +/- 9 microm) following extravasation, compared to NT-BCM-60 which mainly remains in the perivascular regions (D(mean) = 23 +/- 4 microm). The introduction of molecular targeting imposes the "binding site barrier" effect, which retards the tumor penetration of T-BCM-25 (D(mean) = 29 +/- 7 microm, p < 0.05). The intrinsic nuclear translocation property of EGF/EGFR leads to a significant increase in the nuclear uptake of T-BCM-25 in vitro and in vivo via active transport. Overall, these results highlight the need to consider multiple design parameters in the development of nanosystems for delivery of anticancer agents.

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.

In this study, we have looked at enhancing tumor uptake and intracellular delivery of gold nanoparticles (AuNPs) while reducing the systemic exposure by systematic evaluation of the impact of targeting and route of administration on organ distribution. High-resolution microSPECT/CT imaging was used to track the in vivo fate of (111)In-labeled nontargeted and human epidermal growth factor receptor-2 (HER-2) targeted AuNPs following intravenous (i.v.) or intratumoral (i.t.) injection. For i.v. injection, the effects of GdCl3 (for deactivation of macrophages) and nonspecific (anti-CD20) antibody rituximab (for blocking of Fc mediated liver and spleen uptake) were studied. It was found that HER-2 targeting via attachment of trastuzumab paradoxically decreased tumor uptake as a result of faster elimination of the targeted AuNPs from the blood while improving internalization in HER-2-positive tumor cells as compared to nontargeted AuNPs. I.T. injections with HER-2 targeted AuNPs resulted in high tumor retention with low systemic exposure and represents an attractive delivery strategy. Our results provide a strategy for optimizing tumor delivery and quantifying organ distribution of this widely studied class of nanomaterial.