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.

The validation of high sensitivity and high resolution microSPECT/CT imaging for tracking the in vivo pathway and fate of an 111Indium-labeled (111In) amphiphilic diblock copolymer micelle formulation is presented. Heterobifunctional poly(ethylene glycol) was used to initiate cationic ring opening polymerization of epsilon-caprolactone, which was then conjugated to 2-(4-isothiocyanatobenzyl)-diethylenetriaminepentaacetic acid (p-SCN-Bn-DTPA) for chelation with 111In. The micelles were characterized in terms of their physicochemical properties including size, size distribution, zeta-potential, and radiochemical purity. Elimination kinetics and tissue deposition were evaluated in healthy mice following administration of 111In-micelles, 111In-DTPA-b-PCL unimers (i.e., administered under the critical micelle concentration) or 111In-Bn-DTPA. Healthy and MDA-MB-231 tumor-bearing mice were imaged using microSPECT/CT following iv administration of 111In-micelles or 111In-Bn-DTPA. Overall, incorporation of 111In onto the surface of thermodynamically stable micelles results in long plasma residence times for the radionuclide and preferential localization within the spleen (22 +/- 5% i.d/g), liver (13 +/- 3% i.d./g), and tumor (9 +/- 2% i.d./g). MicroSPECT/CT imaging provided noninvasive longitudinal visualization of circulation dynamics and tissue deposition. A strong correlation between image-based region of interest (ROI) analysis and biodistribution data was found, implying that nuclear imaging can be used as a noninvasive tool to accurately quantify tissue distribution. As well, the image-based assessment provided unique insight into the intratumoral distribution of the micelles in vivo.