Biocompatible Nanocomplexes for Molecular Targeted MRI Contrast Agent

Accurate diagnosis in early stage is vital for the treatment of Hepatocellular carcinoma. The aim of this study was to investigate the potential of poly lactic acid–polyethylene glycol/gadolinium–diethylenetriamine-pentaacetic acid (PLA–PEG/Gd–DTPA) nanocomplexes using as biocompatible molecular magnetic resonance imaging (MRI) contrast agent. The PLA–PEG/Gd–DTPA nanocomplexes were obtained using self-assembly nanotechnology by incubation of PLA–PEG nanoparticles and the commercial contrast agent, Gd–DTPA. The physicochemical properties of nanocomplexes were measured by atomic force microscopy and photon correlation spectroscopy. The T1-weighted MR images of the nanocomplexes were obtained in a 3.0 T clinical MR imager. The stability study was carried out in human plasma and the distribution in vivo was investigated in rats. The mean size of the PLA–PEG/Gd–DTPA nanocomplexes was 187.9 ± 2.30 nm, and the polydispersity index was 0.108, and the zeta potential was −12.36 ± 3.58 mV. The results of MRI test confirmed that the PLA–PEG/Gd–DTPA nanocomplexes possessed the ability of MRI, and the direct correlation between the MRI imaging intensities and the nano-complex concentrations was observed (r = 0.987). The signal intensity was still stable within 2 h after incubation of the nanocomplexes in human plasma. The nanocomplexes gave much better image contrast effects and longer stagnation time than that of commercial contrast agent in rat liver. A dose of 0.04 mmol of gadolinium per kilogram of body weight was sufficient to increase the MRI imaging intensities in rat livers by five-fold compared with the commercial Gd–DTPA. PLA–PEG/Gd–DTPA nanocomplexes could be prepared easily with small particle sizes. The nanocomplexes had high plasma stability, better image contrast effect, and liver targeting property. These results indicated that the PLA–PEG/Gd–DTPA nanocomplexes might be potential as molecular targeted imaging contrast agent

Inhaled Oxygen as a Quantitative Intravascular MRI Contrast Agent

Increasing the fraction of inspired oxygen (FiO2) generates MR contrast by two distinct mechanisms: increased T2 from deoxyhemoglobin dilution in venous compartments (blood oxygenation level-dependent effect or BOLD) and reduced T­1 from paramagnetic molecular oxygen dissolved in blood plasma and tissues. Many research and clinical applications using hyperoxic contrast have recently emerged, including delineating ischemic stroke penumbra, oxygen delivery to tumors, and functional MRI data calibration. However, quantitative measurements using this contrast agent depend on the precise knowledge of its effects on the MR signal – of which there remain many crucial missing pieces. This thesis aims to obtain a more quantitative understanding of intravascular hyperoxic contrast in vivo, with the hope of increasing its precision and utility. Specifically, our work focuses on the following areas: (1) paramagnetic effects of molecular oxygen BOLD and arterial spin labeling (ASL) data, (2) degree and temporal characteristics of hyperoxia-induced reductions in cerebral blood flow (CBF), (3) use of oxygen in quantitative measurements of metabolism, and (4) biophysical mechanisms of hyperoxic T1 contrast. In Chapter 2, the artifactual influence of paramagnetic molecular oxygen on BOLD-modulated hyperoxic gas studies is characterized as a function of static field strength, and we show that optimum reduction in FiO2 mitigates this effect while maintaining BOLD contrast. Since ASL measurements are highly sensitive to arterial blood T­1 (T1a), the value of T1a in vivo is determined as a function of arterial oxygen partial pressure in Chapter 3. The effect of both the degree and duration of hyperoxic exposure on absolute CBF are quantified using simultaneous ASL and in vivo T1a measurements, as described in Chapter 4. In Chapter 5, hyperoxic gas calibration of BOLD/ASL data is used to measure cerebral oxygen metabolism in a hypermetabolic swine model, with our results comparing favorably to 17O2 measurements of absolute metabolism. In Chapter 6, a model to describe the relationship between CBF, oxygen consumption, and hyperoxic T1 reduction is developed, which allows for a more rigorous physiological interpretation of these data. Taken together, this work represents several important steps towards making hyperoxia a more quantitative MRI contrast agent for research and clinical applications

A cancer-targeted gold nanoparticle-based MRI contrast agent.

In oncology, imaging plays a major role in terms of early detection and treatment of most types of cancer. Magnetic resonance imaging (MRI) is mostly used for cancer diagnosis due to its excellent contrast resolution. However, MRI for cancer diagnosis is somewhat limited by its sensitivity. In this thesis, we assessed the ability of theranostic platform consisting of gold nanoparticles functionalized with a cancer targeting aptamer; AS1411 and gadolinium chelate (Dotarem thiol derivative; Gd (III)-DO3A) as a MRI contrast agent to target malignant tumors by enhancing the MRI contrast of the detected tumor. The proposed technology is a novel injectable contrast agent for detection and monitoring of malignancies by MRI. The gold nanoparticle core (GNPs) enhances the pharmacokinetic properties of the proposed contrast agent, increases its potency, and provides a good way to co-localize the aptamer with the contrast agent. AS1411 is anti-nucleolin aptamer that binds to nucleolin protein, which is highly expressed in cancer cells, leading to selective accumulation in cancers cells. The ability of the proposed contrast agent to target cancer cells and enhance MRI contrast was assessed using MDA-MB-231 triple negative breast cells and MCF-10 human mammary epithelial cells. Moreover we assessed the biodistribution and toxicity of the proposed contrast agent in vivo. The results presented in this thesis demonstrate the superiority of the proposed contrast agent with respect to the current commercial contrast agents (e.g., MultiHance)

Synthesis and Relaxivity of a Target-Specific MRI Contrast Agent

Magnetic resonance imaging (MRI) is a medically important test that provides a painless, noninvasive way to visualize images of the body by using a strong magnetic field. The machine quickly changes the direction of the magnetic field in certain increments and measures the time it takes for protons to change their direction, lining up with the magnetic field again. The time taken for the protons to realign is called the overall relaxivity rate (R1). Abnormalities, especially tumors, are expressed in MRI images because their relaxivity rates are quite different from the relaxivity rates of normal tissues. To help enhance MRI images, several contrast agents have been developed in the past that can be injected into the patient\u27s bloodstream. The contrast agents studied and synthesized in this research contain a metal called gadolinium. Contrast agents containing gadolinium can be excreted in the urine by glomerular filtration, which is a key characteristic of most contrast agents in general. In the last few decades, the use of contrast agents has drastically increased due to their enhancement and increased specificity. The most common contrast agents currently used include Magnevist, ProHance, and Omniscan. For the contrast agent to be useful and effective, it must have several key characteristics. First, it must have an adequate amount of tissue specificity. When injected into the patient, it should go to one area of the body in a higher concentration than anywhere else. The agent must also stay there long enough to allow for image enhancement. Second, the contrast agent must have a long shelf life. If the material isn\u27t stable, not only is it unsafe to use, it won\u27t be available for long-term use. A contrast agent should have a shelf life of years, not months or days. Third, as mentioned before, the body must be able to completely remove the contrast agent from the targeted area or organ. While most contrast agents are excreted in the urine, it must also have low toxicity as to prevent harming the patient. Lastly, to minimize dosage, the contrast agent must be able to alter the image intensity at a low concentration. This helps keep the dosage at a minimum while still producing enhance images (Contrast Media 454). In this research several different synthesis reactions were completed and tested for accuracy, using NMR and thin-layer chromatography (TLC). The results ensured that the desired product was produced before proceeding with the next reaction. This thesis describes the synthesis, purification, characterization, and testing of a novel contrast agent, comparing it to current contrast agents being used today. The final product was tested using T1 relaxation rates to compare the newly developed agent, which was synthesized using a piperazine-methoxyphenyl group, to those contrast agents in use today

Preclinical animal acute toxicity studies of new developed MRI contrast agent based on gadolinium

Acute toxicity test of new developed MRI contrast agent based on disodium salt of gadopentetic acid complex were carried out on Mus musculus and Sprague Dawley rats according to guidelines of preclinical studies [1]. Groups of six animals each were selected for experiment. Death and clinical symptoms of animals were recorded during 14 days. As a result the maximum tolerated dose (MTD) for female mice is 2.8 mМ/kg of body weight, male mice - 1.4 mМ/kg, female rats - 2.8 mМ/kg, male rats - 5.6 mМ/kg of body weight. No Observed Adverse Effect Dose (NOAEL) for female mice is 1.4 mМ/kg, male mice - 0.7 mМ/kg, male and female rats - 0.7 mМ/kg. According to experimental data new developed MRI contrast agent based on Gd-DTPA complex is low-toxic

Preclinical animal acute toxicity studies of new developed MRI contrast agent based on gadolinium

Acute toxicity test of new developed MRI contrast agent based on disodium salt of gadopentetic acid complex were carried out on Mus musculus and Sprague Dawley rats according to guidelines of preclinical studies [1]. Groups of six animals each were selected for experiment. Death and clinical symptoms of animals were recorded during 14 days. As a result the maximum tolerated dose (MTD) for female mice is 2.8 mМ/kg of body weight, male mice - 1.4 mМ/kg, female rats - 2.8 mМ/kg, male rats - 5.6 mМ/kg of body weight. No Observed Adverse Effect Dose (NOAEL) for female mice is 1.4 mМ/kg, male mice - 0.7 mМ/kg, male and female rats - 0.7 mМ/kg. According to experimental data new developed MRI contrast agent based on Gd-DTPA complex is low-toxic

Synthesis of a Zn(II)-Responsive ParaCEST MRI Agent for Improved Diagnosis of Prostate Cancer

In the United States, prostate cancer is the leading type of cancer diagnosed in men. Prostate cancer is currently diagnosed with the Prostate-Specific Antigen (PSA) test; however, it leads to many false positives and therefore unneeded biopsies. Previous studies have shown that cancerous prostates have a much lower concentration of zinc than healthy prostates. The goal of this project is to create an MRI contrast agent capable of non-invasively quantifying zinc in the human prostate. Five out of the eight synthetic steps have been successfully completed so far, and the identities of these intermediate products have been verified by 1H-NMR and 13C-NMR Spectroscopy. Future work will include completion of the synthesis of the MRI contrast agent and investigation of its properties in the presence of different concentrations of zinc

In vivo imaging with a cell-permeable porphyrin-based MRI contrast agent

Magnetic resonance imaging (MRI) with molecular probes offers the potential to monitor physiological parameters with comparatively high spatial and temporal resolution in living subjects. For detection of intracellular analytes, construction of cell-permeable imaging agents remains a challenge. Here we show that a porphyrin-based MRI molecular imaging agent, Mn-(DPA-C[subscript 2])[subscript 2]-TPPS[subscript 3], effectively penetrates cells and persistently stains living brain tissue in intracranially injected rats. Chromogenicity of the probe permitted direct visualization of its distribution by histology, in addition to MRI. Distribution was concentrated in cell bodies after hippocampal infusion. Mn-(DPA-C2)2-TPPS3 was designed to sense zinc ions, and contrast enhancement was more pronounced in the hippocampus, a zinc-rich brain region, than in the caudate nucleus, which contains relatively little labile Zn[superscript 2+]. Membrane permeability, optical activity, and high relaxivity of porphyrin-based contrast agents offer exceptional functionality for in vivo imaging.National Institutes of Health (U.S.) (grant DP2-OD2441)United States. Dept. of Defense (grant DAMD17-03-1-0413)National Institutes of Health (U.S.) (grant R01-GM065519