34 research outputs found
Rational Design, Synthesis, and Biological Evaluation of Progesterone-Modified MRI Contrast Agents
SummaryA series of contrast agents for magnetic resonance imaging (MRI) aimed at noninvasively determining the hormone receptor status of cancer in vitro was developed. These MRI contrast agents were prepared by conjugating progesterone to clinically used Gd(III) chelates. These agents exhibited higher progesterone receptor binding affinities in the nanomolar range and intracellular accumulation. High logP values of the modified compounds suggested that the lipophilicity of the steroid conjugates may have contributed to membrane permeability. Synchrotron radiation X-ray fluorescence microscopy and magnetic resonance images revealed that the synthesized conjugates showed the greatest cellular accumulation and significant increase in relaxivity in vitro compared to the previously developed steroid-modified agent. Transcriptional assays using the progesterone response element linked to luciferase indicated that the contrast agents entered the cell, interacted with the biological target, and drove specific progesterone-mediated transcription
Quantitative Imaging of Cell-Permeable Magnetic Resonance Contrast Agents Using X-Ray Fluorescence
The inability to transduce cellular membranes is a limitation of current magnetic resonance imaging probes used in biologic and clinical settings. This constraint confines contrast agents to extracellular and vascular regions of the body, drastically reducing their viability for investigating processes and cycles in developmental biology. Conversely, a contrast agent with the ability to permeate cell membranes could be used in visualizing cell patterning, cell fate mapping, gene therapy, and, eventually, noninvasive cancer diagnosis. Therefore, we describe the synthesis and quantitative imaging of four contrast agents with the capability to cross cell membranes in sufficient quantity for detection. Each agent is based on the conjugation of a Gd(III) chelator with a cellular transduction moiety. Specifically, we coupled Gd(III)–diethylenetriaminepentaacetic acid DTPA and Gd(III)–1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid with an 8–amino acid polyarginine oligomer and an amphipathic stilbene molecule, 4-amino-4'-( N,N -dimethylamino)stilbene. The imaging modality that provided the best sensitivity and spatial resolution for direct detection of the contrast agents is synchrotron radiation x-ray fluorescence (SR-XRF). Unlike optical microscopy, SR-XRF provides two-dimensional images with resolution 10 3 better than 153 Gd gamma counting, without altering the agent by organic fluorophore conjugation. The transduction efficiency of the intracellular agents was evaluated by T 1 analysis and inductively coupled plasma mass spectrometry to determine the efficacy of each chelate-transporter combination
Gd(III)-Dithiolane Gold Nanoparticles for T1Weighted Magnetic Resonance Imaging of the Pancreas
Gd(III)-Dithiolane Gold Nanoparticles for <i>T</i><sub>1</sub>‑Weighted Magnetic Resonance Imaging of the Pancreas
Pancreatic
adenocarcinoma has a 5 year survival of approximately 3% and median
survival of 6 months and is among the most dismal of prognoses in
all of medicine. This poor prognosis is largely due to delayed diagnosis
where patients remain asymptomatic until advanced disease is present.
Therefore, techniques to allow early detection of pancreatic adenocarcinoma
are desperately needed. Imaging of pancreatic tissue is notoriously
difficult, and the development of new imaging techniques would impact
our understanding of organ physiology and pathology with applications
in disease diagnosis, staging, and longitudinal response to therapy
in vivo. Magnetic resonance imaging (MRI) provides numerous advantages
for these types of investigations; however, it is unable to delineate
the pancreas due to low inherent contrast within this tissue type.
To overcome this limitation, we have prepared a new GdÂ(III) contrast
agent that accumulates in the pancreas and provides significant contrast
enhancement by MR imaging. We describe the synthesis and characterization
of a new dithiolane-GdÂ(III) complex and a straightforward and scalable
approach for conjugation to a gold nanoparticle. We present data that
show the nanoconjugates exhibit very high per particle values of <i>r</i><sub>1</sub> relaxivity at both low and high magnetic field
strengths due to the high GdÂ(III) payload. We provide evidence of
pancreatic tissue labeling that includes MR images, post-mortem biodistribution
analysis, and pancreatic tissue evaluation of particle localization.
Significant contrast enhancement was observed allowing clear identification
of the pancreas with contrast-to-noise ratios exceeding 35:1
High Relaxivity Gd(III)–DNA Gold Nanostars: Investigation of Shape Effects on Proton Relaxation
Gadolinium(III) nanoconjugate contrast agents (CAs) have distinct advantages over their small-molecule counterparts in magnetic resonance imaging. In addition to increased Gd(III) payload, a significant improvement in proton relaxation efficiency, or relaxivity (<i>r</i><sub>1</sub>), is often observed. In this work, we describe the synthesis and characterization of a nanoconjugate CA created by covalent attachment of Gd(III) to thiolated DNA (Gd(III)–DNA), followed by surface conjugation onto gold nanostars (DNA–Gd@stars). These conjugates exhibit remarkable <i>r</i><sub>1</sub> with values up to 98 mM<sup>–1</sup> s<sup>–1</sup>. Additionally, DNA–Gd@stars show efficient Gd(III) delivery and biocompatibility <i>in vitro</i> and generate significant contrast enhancement when imaged at 7 T. Using nuclear magnetic relaxation dispersion analysis, we attribute the high performance of the DNA–Gd@stars to an increased contribution of second-sphere relaxivity compared to that of spherical CA equivalents (DNA–Gd@spheres). Importantly, the surface of the gold nanostar contains Gd(III)–DNA in regions of positive, negative, and neutral curvature. We hypothesize that the proton relaxation enhancement observed results from the presence of a unique hydrophilic environment produced by Gd(III)–DNA in these regions, which allows second-sphere water molecules to remain adjacent to Gd(III) ions for up to 10 times longer than diffusion. These results establish that particle shape and second-sphere relaxivity are important considerations in the design of Gd(III) nanoconjugate CAs
Multimeric Near IR–MR Contrast Agent for Multimodal <i>In Vivo</i> Imaging
Multiple
imaging modalities are often required for <i>in vivo</i> imaging applications that require both high probe sensitivity and
excellent spatial and temporal resolution. In particular, MR and optical
imaging are an attractive combination that can be used to determine
both molecular and anatomical information. Herein, we describe the
synthesis and <i>in vivo</i> testing of two multimeric NIR–MR
contrast agents that contain three GdÂ(III) chelates and an IR-783
dye moiety. One agent contains a PEG linker and the other a short
alkyl linker. These agents label cells with extraordinary efficacy
and can be detected <i>in vivo</i> using both imaging modalities.
Biodistribution of the PEGylated agent shows observable fluorescence
in xenograft MCF7 tumors and renal clearance by MR imaging
Cell Labeling via Membrane-Anchored Lipophilic MR Contrast Agents
Cell tracking <i>in vivo</i> with MR imaging requires
the development of contrast agents with increased sensitivity that
effectively label and are <i>retained</i> by cells. Most
clinically approved GdÂ(III)-based contrast agents require high incubation
concentrations and prolonged incubation times for cellular internalization.
Strategies to increase contrast agent permeability have included conjugating
GdÂ(III) complexes to cell penetrating peptides, nanoparticles, and
small molecules which have greatly improved cell labeling but have
not resulted in improved cellular retention. To overcome these challenges,
we have synthesized a series of lipophilic GdÂ(III)-based MR contrast
agents that label cell membranes <i>in vitro</i>. Two of
the agents were synthesized with a multiplexing strategy to contain
three GdÂ(III) chelates (<b>1</b> and <b>2</b>) while the
third contains a single GdÂ(III) chelate (<b>3</b>). These new
agents exhibit significantly enhanced labeling and retention in HeLa
and MDA-MB-231-mcherry cells compared to agents that are internalized
by cells (<b>4</b> and Prohance)
Progesterone-Targeted Magnetic Resonance Imaging Probes
Determination
of progesterone receptor (PR) status in hormone-dependent
diseases is essential in ascertaining disease prognosis and monitoring
treatment response. The development of a noninvasive means of monitoring
these processes would have significant impact on early detection,
cost, repeated measurements, and personalized treatment options. Magnetic
resonance imaging (MRI) is widely recognized as a technique that can
produce longitudinal studies, and PR-targeted MR probes may address
a clinical problem by providing contrast enhancement that reports
on PR status without biopsy. Commercially available MR contrast agents
are typically delivered via intravenous injection, whereas steroids
are administered subcutaneously. Whether the route of delivery is
important for tissue accumulation of steroid-modified MRI contrast
agents to PR-rich tissues is not known. To address this question,
modification of the chemistry linking progesterone with the gadolinium
chelate led to MR probes with increased water solubility and lower
cellular toxicity and enabled administration through the blood. This
attribute came at a cost through lower affinity for PR and decreased
ability to cross the cell membrane, and ultimately it did not improve
delivery of the PR-targeted MR probe to PR-rich tissues or tumors
in vivo. Overall, these studies are important, as they demonstrate
that targeted contrast agents require optimization of delivery and
receptor binding of the steroid and the gadolinium chelate for optimal
translation in vivo
Structural Optimization of Zn(II)-Activated Magnetic Resonance Imaging Probes
We report the structural optimization
and mechanistic investigation of a series of bioactivated magnetic
resonance imaging contrast agents that transform from low relaxivity
to high relaxivity in the presence of ZnÂ(II). The change in relaxivity
results from a structural transformation of the complex that alters
the coordination environment about the GdÂ(III) center. Here, we have
performed a series of systematic modifications to determine the structure
that provides the optimal change in relaxivity in response to the
presence of ZnÂ(II). Relaxivity measurements in the presence and absence
of ZnÂ(II) were used in conjunction with measurements regarding water
access (namely, number of water molecules bound) to the GdÂ(III) center
and temperature-dependent <sup>13</sup>C NMR spectroscopy to determine
how the coordination environment about the GdÂ(III) center is affected
by the distance between the ZnÂ(II)-binding domain and the GdÂ(III)
chelate, the number of functional groups on the ZnÂ(II)-binding domain,
and the presence of ZnÂ(II). The results of this study provide valuable
insight into the design principles for future bioactivated magnetic
resonance probes