Imaging the delivery of drug-loaded, iron-stabilized micelles

Abstract

Nanoparticle drug carriers hold potential to improve current cancer therapy by delivering payload to the tumor environment and decreasing toxic side effects. Challenges in nanotechnology drug delivery include plasma instability, site-specific delivery, and relevant biomarkers. We have developed a triblock polymer comprising a hydroxamic acid functionalized center block that chelates iron to form a stabilized micelle that physically entraps chemotherapeutic drugs in the hydrophobic core. The iron-imparted stability significantly improves the integrity of the micelle and extends circulation pharmacokinetics in plasma over that of free drug. Furthermore, the paramagnetic properties of the iron-crosslinking exhibits contrast in the tumors for imaging by magnetic resonance. Three separate nanoparticle formulations demonstrate improved anti-tumor efficacy in xenograft models and decreased toxicity. We report a stabilized polymer micelle that improves the tolerability and efficacy of chemotherapeutic drugs, and holds potential for non-invasive MRI to image drug delivery and deposition in the tumor.

Keywords: Chemotherapeutics; Iron-stabilization; MRI agent; Polymer micelle; Targeted delivery.

Copyright © 2017 The Author(s). Published by Elsevier Inc. All rights reserved.

Figures

Figure 1

Drug-loaded, iron-stabilized micelles self-assemble during formulation to form nanoparticles composed of an amphiphilic poly(ethylene glycol) corona, hydroxamic acid stabilizing middle block, and hydrophobic core block for drug encapsulation. Hydrophobic amino acids sequester drugs in the core of the micelle without the need for covalent attachment which requires chemical or enzymatic cleavage for release. Iron chelates with the hydroxamic acid moieties forming dative bonds among polymer strands to stabilize the micelle for intravenous administration and subsequent dilution. The final drug product is a lyophilized powder for reconstitution in saline for administration.

Figure 2

Drug-loaded, iron stabilized micelles average 100 nm in diameter. (A) DLS Correlation Function Graph representing IT-141 micelle, and (B) histogram showing diameter range of IT-141 micelle. (C, D) Low and high-mag TEM image of IT-141 micelle stained with 1% osmium tetroxide. (E,F) Low and high-mag TEM image of IT-147 micelle stained with 1% uranyl acetate.

Figure 3

Daunorubicin-loaded, iron-stabilized micelle formulation (IT-143) demonstrates prolonged circulation compared to unstabilized micelle formulation and free drug in a cannulated rat model. Intravenous administration of IT-143 resulted in exposure to the plasma compartment (AUC0-48h) of 913.7 µg*h/mL compared to 1.5 and 0.96 µg*h/mL for unstabilized micelle formulation and daunorubicin free drug, respectively.

Figure 4

MR imaging of iron-stabilized micelles in mouse subcutaneous xenograft models. (A) Time-course T1-weighted MRI of HCT116 mouse xenograft following IV administration of SN-38-loaded, iron-stabilized micelle formulation (IT-141). Tumor is identified by red circle in both panel (A) and (B). Signal peaks around 24-48 hours and is mainly cleared by 168 hours (B). Time-course T1-weighted MRI compared to T2-weighted MRI in HCT116 xenograft model. Pre-dose and 48 hours MRI image of HCT116 (C) and NCI-H460 (D) mouse xenograft following IV administration of epothilone D-loaded, iron-stabilized micelle formulation (IT-147).

Figure 5

Drug-loaded, iron-stabilized micelles increase anti-tumor efficacy compared to free drug in subcutaneous xenograft models. Body weights do not change more than 20% from starting weight in efficacy studies. Relative tumor volume in HCT116 colorectal model treated with IT-141 compared to irinotecan (A), HT-29 colorectal adenocarcinoma model treated with IT-141 (B), and HCT116 colorectal model treated with IT-147 (C). Arrows indicate dosing days. (D, E, F) Percent body weight change during HCT116 efficacy study using IT-141 (D), HT-29 efficacy study using IT-141 (E), and HCT116 efficacy study using IT-147 (F).

Figure 6

Immunohistochemistry compares the pharmacodynamics effects of SN-38 in the tumor from irinotecan compared to delivery by IT-4 . (A) mmunohistochemical staining of γ-H2AX for the presence of DNA double stranded breaks at time points between 24-144 hours showing irinotecan treatment compared to IT-141 treatment in HT-29 colorectal tumor model. (B) Quantification of γ-H AX positive stained cells at same time points (n ≥ 2 tumors). Results represent means ± SEM. * P < 0.05, ** P < 0.01, *** P < 0.001. (C) Intravenous administration of IT-141 results in more than a 10-fold exposure of SN-38 over irinotecan to the tumor compartment. IT-141 had an SN-38 exposure of (AUC0-24hrs) 7.2 compared to 0.65 of SN-38 following irinotecan administration.