PEG-like nanoprobes: multimodal, pharmacokinetically and optically tunable nanomaterials

Phosphorescent Ir(III) complexes conjugated with oligoarginine peptides serve as optical probes for in vivo microvascular imaging

Imaging the vascular structures of organ and tumor tissues is extremely important for assessing various pathological conditions. Herein we present the new vascular imaging probe BTQ-R_n (n = 8, 12, 16), a phosphorescent Ir(III) complex containing an oligoarginine peptide as a ligand. This microvasculature staining probe can be chemically synthesized, unlike the commonly used tomato lectins labeled with a fluorophore such as fluorescein isothiocyanate (FITC). Intravenous administration of BTQ-R₁₂ to mice and subsequent confocal luminescence microscope measurements enabled in vivo vascular imaging of tumors and various organs, including kidney, liver and pancreas. Dual color imaging of hepatic tissues of living mice fed a high-fat diet using BTQ-R₁₂ and the lipid droplet-specific probe PC6S revealed small and large lipid droplets in the hepatocytes, causing distortion of the sinusoidal structure. BTQ-R₁₂ selectively stains vascular endothelium and thus allows longer-term vascular network imaging compared to fluorescent dextran with a molecular weight of 70 kDa that circulate in the bloodstream. Furthermore, time-gated measurements using this phosphorescent vascular probe enabled imaging of blood vessel structures without interference from autofluorescence.

Radioactive Nanomaterials for Multimodality Imaging

Nuclear imaging techniques, including primarily positron emission tomography (PET) and single-photon emission computed tomography (SPECT), can provide quantitative information for a biological event in vivo with ultra-high sensitivity, however, the comparatively low spatial resolution is their major limitation in clinical application. By convergence of nuclear imaging with other imaging modalities like computed tomography (CT), magnetic resonance imaging (MRI) and optical imaging, the hybrid imaging platforms can overcome the limitations from each individual imaging technique. Possessing versatile chemical linking ability and good cargo-loading capacity, radioactive nanomaterials can serve as ideal imaging contrast agents. In this review, we provide a brief overview about current state-of-the-art applications of radioactive nanomaterials in the circumstances of multimodality imaging. We present strategies for incorporation of radioisotope(s) into nanomaterials along with applications of radioactive nanomaterials in multimodal imaging. Advantages and limitations of radioactive nanomaterials for multimodal imaging applications are discussed. Finally, a future perspective of possible radioactive nanomaterial utilization is presented for improving diagnosis and patient management in a variety of diseases.

Imaging PEG-like nanoprobes in tumor, transient ischemia, and inflammatory disease models

The iron chelator deferoxamine (DFO), approved for the treatment of iron overload, has been examined as a therapeutic in a variety of conditions which iron may exacerbate. To evaluate the potential of DFO-bearing PEG-like nanoprobes (DFO-PNs) as therapeutics, we determined their pharmacokinetics (PK) in normal mice, and imaged their accumulation in a tumor model and in models of transient brain ischemia and inflammation. DFO-PNs consist of a DFO, a Cy5.5, and PEG (5 kDa or 30 kDa) attached to Lys-Cys scaffold. Tumor uptake of a [(89)Zr]:DFO-PN(10) (30 kDa PEG, diameter 10 nm) was imaged by PET, surface fluorescence, and fluorescence microscopy. DFO-PN(10) was internalized by tumor cells (fluorescence microscopy) and by cultured cells (by FACS). [(89)Zr]:DFO-PN(4.3) (5 kDa PEG, diameter 4.3 nm) concentrated at incision generated inflammations but not at sites of transient brain ischemia. DFO-PNs are fluorescent, PK tunable forms of DFO that might be investigated as antitumor or anti-inflammatory agents.