Cell-assembled nanoclusters of MSC-targeting Gd-DOTA-peptide as a T2 contrast agent for MRI cell tracking

Naphthalene-facilitated self-assembly of a Gd-chelate as a novel T2 MRI contrast agent for visualization of stem cell transplants

Naphthalene is coupled with DOTA via a peptide sequence to yield an amphipathic MRI probe Nap-CFGKTG-DOTA-Gd (Nap-Gd) that can self-assemble into nanofibers. Incubation of NSCs, hMSCs and L929 cells in the presence of Nap-Gd in the μM level can introduce a significant amount of Nap-Gd into the cells as nanoclusters or nanofibers. The resultant intracellular Gd content is 10-60 times that achieved by incubation with Dotarem at the same concentration. The labelled cells exhibit a significant hyperintensive effect under T1-weighted MRI and a significant hypointensive effect under T2-weighted MRI. The hypointensive effect is more persistent than the hyperintensive effect, which allows in vivo tracking of labelled hMSCs for over 12 days under T2-weighted MRI. A comprehensive interpretation of the MRI signal intensity and the associated relaxation times reveals the structure-function relationship between the binding status of Nap-Gd in cells (structure) and the magnetic relaxation processes (function) toward a full understanding of the observed hyperintensive and hypointensive effects.

IQF characterization of a cathepsin B-responsive nanoprobe for report of differentiation of HL60 cells into macrophages

Tracking of in vivo fates of exogenous cell transplants in terms of viability, migration, directional differentiation and function delivery by a suitable method of medical imaging is of great significance in the development and application of various cell therapies. In this contribution directional differentiation of HL60 cells into macrophages and granulocytes, and a difference in the associated expression level of cathepsin B (Cat B) among the parent and daughter cells is used as a model to guide and evaluate the development of a Cat B-responsive Abz-FRFK-Dnp@PLGA nanoprobe for an optical report of the differentiation process. A well-documented internally quenched fluorescence (IQF) pair coupled with a peptide substrate FRFK of Cat B was synthesized and imbedded in PLGA to form the nanoprobe. The nanoprobe is resistant to leakage when dispersed in water for 10 days. Degradation of the nanoprobe is dominated by Cat B. HL60 cells were then labelled with the Abz-FRFK-Dnp@PLGA nanoprobe to track the differentiation process. Differentiation of labelled HL60 cells into macrophages exhibited a significantly higher fluorescence relative to the granulocytes or the labelled parent cells. The fluorescence difference allows the differentiation process to be followed. The established characterization and assessment procedure is to be used for the development and evaluation of nanoprobes for other imaging modalities.

A Cat B-responsive Abz-FRFK-Dnp@PLGA nanoprobe for an optical report of the differentiation of HL60 cells into macrophages.

Evaluation of methotrexate-conjugated gadolinium(III) for cancer diagnosis and treatment

Background

Gliomas are one of the most common types of primary brain tumors. It is usually evaluated by gadolinium(III)-based contrast agents by magnetic resonance imaging (MRI) in the clinic. Methotrexate (MTX), as a type of folate analog that inhibits the enzyme dihydrofolate reductase, is widely used as a chemotherapeutic agent to treat gliomas in the experiment.

Purpose

In this study, a novel theranostic agent MTX-DOTA-Gd (MTX-Gd) was synthesized, which integrates magnetic resonance imaging (MRI) with anticancer treatment.

Methods

MTX-Gd was synthesized by connecting MTX and Gd through 1,4,7,10-tetraazacy-clododecane-1,4,7,10-tetraacetic acid (DOTA). The characterization of MTX-Gd was detected by ultraviolet (UV) and infrared spectroscopy (IR). To confirm the antitumor effect of MTX-Gd, the cytotoxicity of MTX-Gd was examined by the MTT assay. The contrast enhancement of the MTX-Gd was measured through MRI in vitro. Then, nude mice bearing C6 tumor xenografts were used to study in vivo imaging capabilities.

Results

The ultraviolet-visible-near infrared radiation (UV-NIR) absorption curve indicated that MTX-Gd had a broad absorption in the region of 500-700 nm. The formation of MTX-Gd was confirmed from the characteristic bands of MTX-DOTA-Gd in the 1413 cm⁻¹ (C-N), 1577 cm⁻¹ (−NH₂), and 3429 cm⁻¹ (N-H), in the fourier-transform infrared (FTIR) spectra. MTX-Gd showed little difference in the cell viability compared with MTX, except for the highest concentration (270 μM). In vitro, the imaging of MTX-Gd was significantly brighter than Gd-DOTA at the same concentration, and the brightness and signal intensity of MRI were increased followed by the increased concentration of MTX-Gd. And it also showed that MTX was not visualized on MRI. The other images revealed that the concentration of 4 mM MTX-Gd had the same imaging effect with the concentration of 10 mM Gd-DOTA. Then, MTX-Gd was injected in nude mice bearing C6 tumor xenografts through the tail vein. Significant contrast enhancement was observed at the tumor site from 0.5 h to 3 h. The signal of tumor area was strongest at 3 h due to accumulation by size effect of macromolecules.

Conclusion

A novel stable and unique theranostic agent (MTX-Gd) was successfully synthe-sized, and it has good stability, strong anticancer ability and excellent magnetic capacity. The methotrexate component of MTX-Gd, as a chemotherapeutic agent, played an important role in targeted therapies of cancer. The DOTA-Gd component of MTX-Gd performed as the MRI contrast agent. The superior MRI imaging performance and synergetic chemical antineoplastic ability of MTX-Gd was revealed, and it has great potential in the diagnosis and treatment of glioma and potentially other cancers, with prospects of clinical application in the near future.