The Impact of PEGylation on Cellular Uptake and In Vivo Biodistribution of Gold Nanoparticle MRI Contrast Agents

Gold nanoparticles (GNPs) have immense potential in biomedicine, but understanding their interactions with serum proteins is crucial as it could change their biological profile due to the formation of a protein corona, which could then affect their ultimate biodistribution in the body. Grafting GNPs with polyethylene glycol (PEG) is a widely used practice in research in order to decrease opsonization of the particles by serum proteins and to decrease particle uptake by the mononuclear phagocyte system. We investigated the impact of PEGylation on the formation of protein coronae and the subsequent uptake by macrophages and MDA-MB-231 cancer cells. Furthermore, we investigated the in vivo biodistribution in xenograft tumor-bearing mice using a library of 4 and 10 nm GNPs conjugated with a gadolinium chelate as MRI contrast agent, cancer-targeting aptamer AS1411 (or CRO control oligonucleotide), and with or without PEG molecules of different molecular weight (Mw: 1, 2, and 5 kDa). In vitro results showed that PEG failed to decrease the adsorption of proteins; moreover, the cellular uptake by macrophage cells was contingent on the different configurations of the aptamers and the length of the PEG chain. In vivo biodistribution studies showed that PEG increased the uptake by tumor cells for some GNPs, albeit it did not decrease the uptake of GNPs by macrophage-rich organs.

Simple Host-Guest Assembly for High-Resolution Magnetic Resonance Imaging of Microvasculature

Magnetic resonance angiography (MRA) is an important imaging technique that can be used to identify and characterize various types of vascular diseases. However, currently used molecular contrast agents are unsuitable for MRA due to the short intravascular retention time, the whole-body distribution, and the relatively low contrast effect. In this study, we developed a vascular analysis contrast agent (i.e., VasCA) for MRA, which is a simple and biocompatible 1:1 host-guest assembly of PEGylated β-cyclodextrin and gadolinium chelate with renal clearable size and high relaxivity (r1 = 9.27 mM-1 s-1). Its biocompatibility was confirmed by in vivo animal studies as well as in vitro 3D cell culture. In a tumor-bearing rat model, VasCA circulated in the blood vessels much longer (4.3-fold increase) than gadoterate meglumine (Dotarem) and was mainly excreted by the renal system after intravenous injection. This feature of VasCA allows characterization of tumor microvasculature (e.g., feeding and draining vessels) as well as visualization of small vessels in the brain and body organs. Furthermore, after treatment with an angiogenesis inhibitor (i.e., sorafenib), VasCA revealed the vessel normalization process and allowed the assessment of viable and necrotic tumor regions. Our study provides a useful tool for diverse MRA applications, including tumor characterization, early-stage evaluation of drug efficacy, and treatment planning, as well as diagnosis of cardiovascular diseases.

Improving Longitudinal Transversal Relaxation Of Gadolinium Chelate Using Silica Coating Magnetite Nanoparticles

Introduction and objective

Precisely and sensitively diagnosing diseases especially early and accurate tumor diagnosis in clinical magnetic resonance (MR) scanner is a highly demanding but challenging task. Gadolinium (Gd) chelate is the most common T ₁ magnetic resonance imaging (MRI) contrast agent at present. However, traditional Gd-chelates are suffering from low relaxivity, which hampers its application in clinical diagnosis. Currently, the development of nano-sized Gd based T ₁ contrast agent, such as incorporating gadolinium chelate into nanocarriers, is an attractive and feasible strategy to enhance the T ₁ contrast capacity of Gd chelate. The objective of this study is to improve the T ₁ contrast ability of Gd-chelate by synthesizing nanoparticles (NPs) for accurate and early diagnosis in clinical diseases.

Methods

Reverse microemulsion method was used to coat iron oxide (IO) with tunable silica shell and form cores of NPs IO@SiO₂ at step one, then Gd-chelate was loaded on the surface of silica-coated iron oxide NPs. Finally, Gd-based silica coating magnetite NPs IO@SiO₂-DTPA-Gd was developed and tested the ability to detect tumor cells on the cellular and in vivo level.

Results

The r ₁ value of IO@SiO₂-DTPA-Gd NPs with the silica shell thickness of 12 nm was about 33.6 mM^-1s^-1, which was approximately 6 times higher than Gd-DTPA, and based on its high T ₁ contrast ability, IO@SiO₂-DTPA-Gd NPs could effectively detect tumor cells on the cellular and in vivo level.

Conclusion

Our findings revealed the improvement of T ₁ relaxation was not only because of the increase of molecular tumbling time caused by the IO@SiO₂ nanocarrier but also the generated magnetic field caused by the IO core. This nanostructure with high T ₁ contrast ability may open a new approach to construct high-performance T ₁ contrast agent.

Synthesis and in vivo magnetic resonance imaging evaluation of biocompatible branched copolymer nanocontrast agents

Branched copolymer nanoparticles (D_h =20–35 nm) possessing 1,4,7, 10-tetraazacyclododecane-N,N′,N″,N‴-tetraacetic acid macrocycles within their cores have been synthesized and applied as magnetic resonance imaging (MRI) nanosized contrast agents in vivo. These nanoparticles have been generated from novel functional monomers via reversible addition–fragmentation chain transfer polymerization. The process is very robust and synthetically straightforward. Chelation with gadolinium and preliminary in vivo experiments have demonstrated promising characteristics as MRI contrast agents with prolonged blood retention time, good biocompatibility, and an intravascular distribution. The ability of these nanoparticles to perfuse and passively target tumor cells through the enhanced permeability and retention effect is also demonstrated. These novel highly functional nanoparticle platforms have succinimidyl ester-activated benzoate functionalities within their corona, which make them suitable for future peptide conjugation and subsequent active cell-targeted MRI or the conjugation of fluorophores for bimodal imaging. We have also demonstrated that these branched copolymer nanoparticles are able to noncovalently encapsulate hydrophobic guest molecules, which could allow simultaneous bioimaging and drug delivery.

Manganese-enhanced MRI of minimally gadolinium-enhancing breast tumors

PURPOSE

To investigate the potential of manganese (Mn)-enhanced MRI for sensitive detection and delineation of tumors that demonstrate little enhancement on Gd-DTPA.

MATERIALS AND METHODS

Eighteen nude rats bearing 1 to 2 cm in diameter orthotopic breast tumors (ZR75 and LM2) were imaged on a 3 Tesla (T) clinical scanner. Gd-DTPA was administered intravenously and MnCl2 subcutaneously, both at 0.05 mmol/kg. T1 -weighted imaging and T1 measurements were performed precontrast, 10 min post-Gd-DTPA, and 24 h post-MnCl2 . Tumors were excised and histologically assessed using H&E (composition and necrosis) and CD34 (vascularity).

RESULTS

Most tumors (78%) demonstrated little enhancement (< 20% change in R1 ) on Gd-DTPA. MnCl2 administration achieved greater and more uniform enhancement throughout the tumor mass (i.e., not restricted to the tumor periphery), with R1 changing over 20% in 72% of tumors. MnCl2 -induced R1 changes compared with Gd-induced changes were significantly greater in both ZR75 (P < 0.01) and LM2 tumors (P < 0.05). Histology confirmed very low vascularity in both tumor models, and necrotic areas were well delineated only on Mn-enhanced MRI.

CONCLUSION

Mn-enhanced MRI is a promising approach for detection of low-Gd-enhancing tumors.

Sol and gel states in peptide hydrogels visualized by Gd(III)-enhanced magnetic resonance imaging

The hydrogels assembled from a pair of self-repulsive but mutually attractive decapeptides are visualized by magnetic resonance imaging (MRI). It is found that in the absence of Gd(III)-chelate, gelation has little effect on MRI signal intensity. In the presence of Gd(III)-chelate, gelation leads to significant changes in water relaxation and MR signal intensity. The sol to gel transition is best visualized by T2-weighted imaging using large echo time with the sol producing a bright spot and the gel producing a dark spot. MRI studies point to high local Gd(III)-chelate concentration. Small-angle X-ray scattering study indicates that this local enrichment of Gd(III)-chelate has two contributing processes: first, the aggregation of peptides into fibers; second, within peptide fibers, Gd(III)-chelate further aggregate into clusters. This work demonstrates that the status of peptide-based hydrogels can be visualized by MRI with the aid of covalently linked Gd(III)-chelates. This result has implications for monitoring peptide scaffolds in vivo.