Glioma-targeting micelles for optical/magnetic resonance dual-mode imaging

Abstract

Surgical resection is the primary mode for glioma treatment, while gross total resection is difficult to achieve, due to the invasiveness of the gliomas. Meanwhile, the tumor-resection region is closely related to survival rate and life quality. Therefore, we developed optical/magnetic resonance imaging (MRI) bifunctional targeted micelles for glioma so as to delineate the glioma location before and during operation. The micelles were constructed through encapsulation of hydrophobic superparamagnetic iron oxide nanoparticles (SPIONs) with polyethylene glycol-block-polycaprolactone (PEG-b-PCL) by using a solvent-evaporation method, and modified with a near-infrared fluorescent probe, Cy5.5, in addition to the glioma-targeting ligand lactoferrin (Lf). Being encapsulated by PEG-b-PCL, the hydrophobic SPIONs dispersed well in phosphate-buffered saline over 4 weeks, and the relaxivity (r₂) of micelles was 215.4 mM⁻¹·s⁻¹, with sustained satisfactory fluorescent imaging ability, which might have been due to the interval formed by PEG-b-PCL for avoiding the fluorescence quenching caused by SPIONs. The in vivo results indicated that the nanoparticles with Lf accumulated efficiently in glioma cells and prolonged the duration of hypointensity at the tumor site over 48 hours in the MR image compared to the nontarget group. Corresponding with the MRI results, the margin of the glioma was clearly demarcated in the fluorescence image, wherein the average fluorescence intensity of the tumor was about fourfold higher than that of normal brain tissue. Furthermore, 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2-H-tetrazolium bromide assay results showed that the micelles were biocompatible at Fe concentrations of 0–100 μg/mL. In general, these optical/MRI bifunctional micelles can specifically target the glioma and provide guidance for surgical resection of the glioma before and during operation.

Keywords:

• MRI
• fluorescence image
• micelles
• lactoferrin
• glioma

Supplementary materials

FTIR spectrum

The Fourier-transform infrared (FTIR) spectrum was used to achieve qualitative analysis of the lactoferrin (Lf) conjugation. As shown in the FTIR spectra (Figure S1), in the pure Lf group and Cy5.5-Lf-superparamagnetic iron oxide (SPIO) micelle group, the bands around 3,400 cm⁻¹ were for the acylamino-stretching vibration, which indicated that the Lf existed. In the Cy5.5-Lf-SPIO micelle group, the bands around 700 cm⁻¹ appeared due to S–C bond formation, which indicated that Lf successfully conjugated to micelles.

Biodistribution of the nanoparticles

The animals treated with Cy5.5-Lf-SPIO micelles were killed at 48 hours postinjection. The IVIS Lumina XR system was used to collect optical images of the rats’ organs. As shown in Figure S2, the fluorescence signals were mainly distributed in the brain-tumor site. There were also some weaker signals in the liver and kidney, which are usually known as the organs related to the metabolism of nanoparticle.

Figure S1 Fourier-transform infrared spectra of SPIO micelles, lactoferrin, and Cy5.5-Lf-SPIO micelle.

Abbreviation: SPIO, superparamagnetic iron oxide.

Figure S2 Optical images of rat organs.

Notes: (A) Lung; (B) liver; (C) spleen; (D) heart; (E) brain; (F) kidney.

Acknowledgments

This work was financially supported by a grant from National Basic Research Program of China (program 973, 2012CB932500), the National Science Foundation of China (NSFC, 31170960/C1007), and the National Program of Ministry of Science and Technology of China under the 12th Five-Year Plan (2011BAI08B10). We give thanks to the Analysis and Test Center of Huazhong University of Science and Technology. We also give special thanks to Professor Yuzeng Zhang (MOE Key Lab of Environment and Health, School of Public Health, Tongji Medical College, Huazhong University of Science and Technology) for help in the AAS analysis.

Disclosure

The authors report no conflicts of interest in this work.