High throughput magnetic resonance imaging for evaluating targeted nanoparticle probes.

The ability to image specific molecular targets in vivo would have significant impact in allowing earlier disease detection and in tailoring molecular therapies. One of the rate-limiting steps in the development of novel compounds as reporter probes has been the lack of cell-based, biologically relevant, high throughput screening methods. Here we describe the development and validation of magnetic resonance imaging (MRI) as a technique to rapidly screen compounds that are potential MR reporter agents for their interaction with specific cellular targets. We show that MR imaging can (1) evaluate thousands of samples simultaneously and rapidly, (2) provide exceedingly accurate measurements, and (3) provide receptor binding/internalization data as validated by radioactive assays. The technique allows the screening of libraries of peptide-nanoparticle conjugates against target cells and the identification of conjugates that may be subsequently used as reporter agents in vivo. The technology should greatly accelerate the development of target-specific or cell-specific MR contrast agents.     

Low paramagnetic-ion content in cancer cells: its significance in cancer detection by magnetic resonance imaging

In previous publications, one of us demonstrated that variation in paramagnetic-ion contents is a major contributing factor to the different NMR relaxation times, T1 and T2, of water protons among normal mouse tissues; and between normal tissues and cancer cells. The nature of the paramagnetic ions involved was not determined. In the present communication, we report results of analysis of the contents of three biologically prominent paramagnetic ions (manganese, iron and copper) in 9 normal mouse tissues (brain, heart, small intestine, kidney, liver, lung, voluntary muscle, spleen and stomach); one strain of rat cancer cells (As-30, rat hepatoma); and 6 strains of mouse cancer cells (Ehrlich mammary adenocarcinoma, LSA lymphoma, Krebs carcinoma of the inguinal region; sarcoma 180; Klein TA3 mammary adenocarcinoma; P815 mast cell leukemia). Our data indicate that manganese and iron are by far the two most important paramagnetic ions contributing to the diversity of NMR relaxation times. The average manganese content of all the normal mouse tissues studied (29.6 +/- 4.99 mu mole/kg) is 24 times higher than the average manganese contents of all the cancer cells studied (1.22 +/- 0.27 mu moles/kg) and there is essentially no overlap between the two groups of data. The average iron content of the normal mouse tissues (281.6 +/- 51.2 mumoles/kg) is 4 times the average in cancer cells (66.7 +/- 7.74 mumoles/kg) but there is some overlap here. The observed differences in both the manganese and iron contents are statistically highly significant, with P's below 0.0001. The copper contents of the cancer cells is lower than the average of normal mouse tissues but only by some 20%. The difference is statistically insignificant at the 0.05 level but significant at the 0.2 level.     

Breast cancer detection using magnetic resonance imaging in breasts injected with liquid silicone

Two patients who had received silicone injections in their breasts several years ago presented with breast complaints. Excluding cancer in these patients was very difficult. Mammograms were very difficult to interpret, as were the physical findings. Carcinoma was successfully detected by magnetic resonance imaging. When women who underwent the injudicious injection of silicone reach the cancer-prone age, the examining physicians should have a greater awareness of the detection and management of carcinoma coexistent with silicone mastopathy. We think that MRI is potentially valuable in the evaluation of the breast lesions; it plays an important role in the detection of breast cancer in breasts augmented with liquid silicone.     

Cellular magnetic resonance imaging: potential for use in assessing aspects of cardiovascular disease

There is rapidly increasing interest in the use of magnetic resonance imaging (MRI) to track cell migration in vivo. Iron oxide MR contrast agents can be detected at micromolar concentrations of iron, and offer sufficient sensitivity for T2*-weighted imaging. Cellular MRI shows potential for assessing aspects of cardiovascular disease. Labeling in vivo and tracking macrophages using iron oxide nanoparticles has been a goal for cellular MRI because macrophages play a pivotal role in the pathophysiology of many human diseases, including atherosclerosis. Cellular MRI has also been using to track transplanted therapeutic cells in myocardial regeneration. This review looked at iron oxide nanoparticles, methods of cell labeling, image acquisition techniques and limitations encountered for visualization. Particular attention was paid to stem cells and macrophages for the cardiovascular system.     

Synthesis and biological evaluation of water-soluble progesterone-conjugated probes for magnetic resonance imaging of hormone related cancers

Progesterone receptor (PR) is strongly associated with disease prognosis and therapeutic efficacy in hormone-related diseases such as endometriosis and breast, ovarian, and uterine cancers. Receptor status is currently determined by immunohistochemistry assays. However, noninvasive PR imaging agents could improve disease detection and help elucidate pathological molecular pathways, leading to new therapies and animal disease models. A series of water-soluble PR-targeted magnetic resonance imaging (MRI) probes were synthesized using Cu(I)-catalyzed click chemistry and evaluated in vitro and in vivo. These agents demonstrated activation of PR in vitro and preferential accumulation in PR(+) compared to PR(-) human breast cancer cells with low toxicity. In xenograft tumor models, the agents demonstrated enhanced signal intensity in PR(+) tumors compared to PR(-) tumors. The results suggest that these agents may be promising MRI probes for PR(+) diseases.     

Paramagnetic pharmaceuticals for magnetic resonance imaging

Complexes of paramagnetic ions that are tissue-, organ- or tumor-specific will supplement routine magnetic resonance imaging, help assess organ perfusion, and in some cases assess specific organ function. Studies are described in animals and man and the results suggest that dilute iron solutions may be useful for contrast-enhancement of the gastrointestinal tract; that ferrioxamine B, a stable ferric iron complex, appears to permit identification of focal blood-brain-barrier defects and to assess renal excretory function; and that gadolinium-DTPA can produce contrast-enhancement of a variety of lesions. In addition, gadolinium-DTPA can detect a breakdown in the blood-brain-barrier and can delineate functioning myocardium in the setting of acute ischemia.     

Development of high-sensitivity near-infrared fluorescence imaging device for early cancer detection

We have developed a high-sensitivity near-infrared (NIR) optical imaging system for noninvasive cancer detection based on the molecular-labeled fluorescent contrast agents. Recent developments in molecular beacons offer a way to selectively tag various precancer and cancer signatures and provide high tumor-to-background contrast. Near-infrared imaging can deeply probe tissue up to a couple of centimeters; thus, it possesses the potential for noninvasive detection of breast or lymph node cancer. A phase cancellation (in- and antiphase) device is used to increase the sensitivity in detecting fluorescent photons and the accuracy of tumor localization. The optoelectronic system consists of the laser diode sources, fiber optics, interference filter (to select the fluorescent photons), and the high-sensitivity photon detector (photomultiplier tube). The source-detector pair scans the tissue surface in multiple directions, and the localization image can be obtained by angular back-projection reconstruction. Simulations and experimental data demonstrated the feasibility of detection and localization offluorescent object embedded inside the highly scattering media. Tumor-bearing mouse model with injection of fluorescent contrast agents is used to simulate the human breast tumor labeled with molecular beacons. The system can detect fluorescent contrast agents as small as one nanomole at the depth of three centimeters, with a three-millimeter localization error. This instrument has the potential for tumor diagnosis and imaging, and the accuracy of the localization suggests that this system could help guide the clinical fine-needle biopsy. Also, this portable device would be complementary to x-ray mammography and provide add-on information on early diagnosis and localization of breast tumor.     

Contrast agents for nuclear magnetic resonance imaging

Nuclear magnetic resonance imaging relies upon differences in relaxation times for much of its ability to resolve anatomical structures and to detect changes in tissue. The natural differences can be changed by the administration of paramagnetic substances, such as metal complexes and stable organic free radicals, and ferromagnetic materials, such as small particles of magnetite. Detailed studies of the chemistry and biophysics of such substances in the body are required if they are to become safe and effective contrast agents for use in medical NMR imaging.     

Principles of magnetic resonance imaging

This article aims to provide an educational document of magnetic resonance imaging principles for applied biomedical users of the technology. Basic principles are illustrated using simple experimental models on a preclinical imaging system.     

Protein scaffold-based molecular probes for cancer molecular imaging

Protein scaffold molecules are powerful reagents for targeting various cell signal receptors, enzymes, cytokines and other cancer-related molecules. They belong to the peptide and small protein platform with distinct properties. For the purpose of development of new generation molecular probes, various protein scaffold molecules have been labeled with imaging moieties and evaluated both in vitro and in vivo. Among the evaluated probes Affibody molecules and analogs, cystine knot peptides, and nanobodies have shown especially good characteristics as protein scaffold platforms for development of in vivo molecular probes. Quantitative data obtained from positron emission tomography, single photon emission computed tomography/CT, and optical imaging together with biodistribution studies have shown high tumor uptakes and high tumor-to-blood ratios for these probes. High tumor contrast imaging has been obtained within 1 h after injection. The success of those molecular probes demonstrates the adequacy of protein scaffold strategy as a general approach in molecular probe development.     

Modularly assembled magnetite nanoparticles enhance in vivo targeting for magnetic resonance cancer imaging

Modularly assembled targeting nanoparticles were synthesized through self-assembly of targeting moieties on surfaces of functional nanoparticles. Specific molecular recognition of nickel nitrilotriacetate on Fe3O4 nanoparticles with hexahistidine tag on RGD4C peptides results in precisely controlled orientation of the targeting peptides. Better selectivity of the self-assembled RGD4C-Fe3O4 nanoparticles targeting oral cancer cells than that achievable through a conventional chemical cross-link strategy was demonstrated by means of atomic absorption spectrometry (AAS). An oral cancer hamster model was applied to reveal specific in vivo targeting and MR molecular imaging contrast in cancer lesions expressing alphavbeta3 integrin. Both AAS and MRI revealed that the self-assembled nanoparticles improved the targeting efficiency and reduced the hepatic uptake as compared with the conventional chemical cross-link particles. We investigated the biosafety, biodistribution, and kinetics of the nanoparticles and found that the nanoparticles were significantly cleared from the liver and kidneys after one week. By recombining the desired targeting moiety and various functional nanoparticles through self-assembly, this new modularly designed platform has the capability of enhancing the efficiency of targeted diagnosis and therapies for a wide spectrum of biomedical applications.