Xiaoyue Chen

Reducing the object orientation dependence of susceptibility effects in gradient echo MRI through quantitative susceptibility mapping.

This study demonstrates the dependence of non‐local susceptibility effects on object orientation in gradient echo MRI and the reduction of non‐local effects by deconvolution using quantitative susceptibility mapping. Imaging experiments were performed on a 3T MRI system using a spoiled 3D multi‐echo GRE sequence on phantoms of known susceptibilities, and on human brains of healthy subjects and patients with intracerebral hemorrhages. Magnetic field measurements were determined from multiple echo phase data. To determine the quantitative susceptibility mapping, these field measurements were deconvolved through a dipole inversion kernel under a constraint of consistency with the magnitude images. Phantom and human data demonstrated that the hypointense region in GRE magnitude image corresponding to a susceptibility source increased in volume with TE and varied with the source orientation. The induced magnetic field extended beyond the susceptibility source and varied with its orientation. In quantitative susceptibility mapping, these blooming artifacts, including their dependence on object orientation, were reduced, and the material susceptibilities were quantified. Magn Reson Med, 2012.

Tumor suppression via paclitaxel-loaded drug carriers that target inflammation marker upregulated in tumor vasculature and macrophages

Clinically approved chemotherapeutic nanoparticles may provide advantages over free drugs by achieving slower clearance and preferential accumulation in tumors. However, the lack of leaky vasculatures can create barriers to the permeation of ~100 nm-sized nanoparticles in solid tumors. We hypothesized that nanoparticles designed to target both tumor and tumor stroma would penetrate deeper into the tumors. To construct such comprehensive drug carriers, we utilized cross-linked amphiphilic polymer nanoparticles and functionalized them to target ICAM-1, a biomarker prevalent in various tumors and inflamed tumor stroma. The targeting moiety was derived from the modular domain present in α(L) integrin, which was engineered for high affinity and cross-reactivity with human and murine ICAM-1. ICAM-1-selective delivery of paclitaxel produced potent tumor suppression of not only ICAM-1-positive cervical cancer cells but also ICAM-1-negative tumors, presumably by causing cytotoxicity in tumor-associated endothelium (CD31(+)) and macrophages (CD68(+)) over-expressing ICAM-1. Contrary to the strategies of targeting only the tumor or specific tumor stromal constituents, we present a strategy in delivering therapeutics to the major cellular components of solid tumors. Drug carriers against inflammation-biomarkers may be effective against many different types of tumors, while being less susceptible to the highly mutable nature of tumor markers.

Tunable physiologic interactions of adhesion molecules for inflamed cell-selective drug delivery

Dysregulated inflammation contributes to the pathogenesis of various diseases. Therapeutic efficacy of anti-inflammatory agents, however, falls short against resilient inflammatory responses, whereas long-term and high-dose systemic administration can cause adverse side effects. Site-directed drug delivery systems would thus render more effective and safer treatments by increasing local dosage and minimizing toxicity. Nonetheless, achieving clinically effective targeted delivery to inflammatory sites has been difficult due to diverse cellular players involved in immunity and endogenous targets being expressed at basal levels. Here we exploit a physiological molecular interaction between intercellular adhesion molecule (ICAM)-1 and lymphocyte function associated antigen (LFA)-1 to deliver a potent anti-inflammatory drug, celastrol, specifically and comprehensively to inflamed cells. We found that affinity and avidity adjusted inserted (I) domain, the major binding site of LFA-1, on liposome surface enhanced the specificity toward lipopolysaccharides (LPS)-treated or inflamed endothelial cells (HMEC-1) and monocytes (THP-1) via ICAM-1 overexpression, reflecting inherent affinity and avidity modulation of these molecules in physiology. Targeted delivery of celastrol protected cells from recurring LPS challenges, suppressing pro-inflammatory responses and inflammation-induced cell proliferation. Targeted delivery also blocked THP-1 adhesion to inflamed HMEC-1, forming barriers to immune cell accumulation and to aggravating inflammatory signals. Our results demonstrate affinity and avidity of targeting moieties on nanoparticles as important design parameters to ensure specificity and avoid toxicities. We anticipate that such tunable physiologic interactions could be used for designing effective drug carriers for in vivo applications and contribute to treating a range of immune and inflammatory diseases.

Visualizing and quantifying acute inflammation using ICAM-1 specific nanoparticles and MRI quantitative susceptibility mapping.

As intense and prolonged inflammation correlates with the progression of various inflammatory diseases, locating specific regions of the body with dysregulated levels of inflammation could provide crucial information for effective medical diagnosis and treatment. In this study, we demonstrate high resolution spatiotemporal imaging of inflammation in mice treated with systemic injection of lipopolysaccharides (LPS) to mimic systemic inflammatory response or sepsis. Diagnosis of organ-level inflammation was achieved by magnetic resonance imaging (MRI) of inflammation-sensitive superparamagnetic iron oxide (SPIO)-based nanomicelle termed leukocyte-mimetic nanoparticle (LMN), designed to preferentially localize to cells with inflammation-induced overexpression of intercellular adhesion molecule (ICAM)-1. Using a novel MRI quantitative susceptibility mapping (QSM) technique for non-invasive quantification of SPIO nanoparticles, we observed greater accumulation of LMN in the liver, specific to ICAM-1 induction due to LPS-induced inflammation. However, the accumulation of nanoparticles into the spleen appeared to be due to an ICAM-1 independent, phagocytic activity, resulting in higher levels of both LMN and control nanoparticles in the spleen of LPS-treated than untreated mice. Overall, the amounts of nanoparticles in liver and spleen estimated by QSM were in a good agreement with the values directly measured by radioactivity, presenting an idea that spatiotemporal mapping of LMN by MRI QSM may provide a reliable, rapid, non-invasive method for identifying organ-specific inflammation not offered by existing diagnostic techniques.

Yeast Surface Two-hybrid for Quantitative in Vivo Detection of Protein-Protein Interactions via the Secretory Pathway

A quantitative in vivo method for detecting protein-protein interactions will enhance our understanding of protein interaction networks and facilitate affinity maturation as well as designing new interaction pairs. We have developed a novel platform, dubbed “yeast surface two-hybrid (YS2H),” to enable a quantitative measurement of pairwise protein interactions via the secretory pathway by expressing one protein (bait) anchored to the cell wall and the other (prey) in soluble form. In YS2H, the prey is released either outside of the cells or remains on the cell surface by virtue of its binding to the bait. The strength of their interaction is measured by antibody binding to the epitope tag appended to the prey or direct readout of split green fluorescence protein (GFP) complementation. When two α-helices forming coiled coils were expressed as a pair of prey and bait, the amount of the prey in complex with the bait progressively decreased as the affinity changes from 100 pm to 10 μm. With GFP complementation assay, we were able to discriminate a 6-log difference in binding affinities in the range of 100 pm to 100 μm. The affinity estimated from the level of antibody binding to fusion tags was in good agreement with that measured in solution using a surface plasmon resonance technique. In contrast, the level of GFP complementation linearly increased with the on-rate of coiled coil interactions, likely because of the irreversible nature of GFP reconstitution. Furthermore, we demonstrate the use of YS2H in exploring the nature of antigen recognition by antibodies and activation allostery in integrins and in isolating heavy chain-only antibodies against botulinum neurotoxin.

Cell Surface Assembly of HIV gp41 Six-Helix Bundles for Facile, Quantitative Measurements of Hetero-oligomeric Interactions

Helix-helix interactions are fundamental to many biological signals and systems and are found in homo- or heteromultimerization of signaling molecules as well as in the process of virus entry into the host. In HIV, virus-host membrane fusion during infection is mediated by the formation of six-helix bundles (6HBs) from homotrimers of gp41, from which a number of synthetic peptides have been derived as antagonists of virus entry. Using a yeast surface two-hybrid (YS2H) system, a platform designed to detect protein-protein interactions occurring through a secretory pathway, we reconstituted 6HB complexes on the yeast surface, quantitatively measured the equilibrium and kinetic constants of soluble 6HB, and delineated the residues influencing homo-oligomeric and hetero-oligomeric coiled-coil interactions. Hence, we present YS2H as a platform for the facile characterization and design of antagonistic peptides for inhibition of HIV and many other enveloped viruses relying on membrane fusion for infection, as well as cellular signaling events triggered by hetero-oligomeric coiled coils.

Novel Strategy for Selection of Monoclonal Antibodies Against Highly Conserved Antigens: Phage Library Panning Against Ephrin-B2 Displayed on Yeast

Ephrin-B2 is predominately expressed in endothelium of arterial origin, involved in developmental angiogenesis and neovasculature formation through its interaction with EphB4. Despite its importance in physiology and pathological conditions, it has been challenging to produce monoclonal antibodies against ephrin-B2 due to its high conservation in sequence throughout human and rodents. Using a novel approach for antibody selection by panning a phage library of human antibody against antigens displayed in yeast, we have isolated high affinity antibodies against ephrin-B2. The function of one high affinity binder (named as ‘EC8’) was manifested in its ability to inhibit ephrin-B2 interaction with EphB4, to cross-react with murine ephrin-B2, and to induce internalization into ephrin-B2 expressing cells. EC8 was also compatible with immunoprecipitation and detection of ephrin-B2 expression in the tissue after standard chemical fixation procedure. Consistent with previous reports on ephrin-B2 induction in some epithelial tumors and tumor-associated vasculatures, EC8 specifically detected ephrin-B2 in tumors as well as the vasculature within and outside of the tumors. We envision that monoclonal antibody developed in this study may be used as a reagent to probe ephrin-B2 distribution in normal as well as in pathological conditions and to antagonize ephrin-B2 interaction with EphB4 for basic science and therapeutic applications.

Effect of aldosterone antagonists on obstructive sleep apnea in patients with resistant hypertension: a systematic review and meta-analysis

We read an article written by Wolley et al.1 with interest. We found that treatment of primary aldosteronism by adrenalectomy or aldosterone antagonists was associated with a reduction in the severity of obstructive sleep apnoea (OSA). Although resistant hypertension (RH) is highly prevalent in patients with OSA and hyperaldosteronism, the authors did not recruit participants with RH. We completed a meta-analysis to assess the effect of aldosterone antagonists on OSA in patients with RH.

In vivo ICAM-1 directed molecular imaging of tumor, inflamed milieu, and acute inflammation

We hypothesized that nanoparticles designed to mimic the molecular interactions occurring between inflamed leukocytes and endothelium may possess specificity toward diverse host inflammatory responses. Here, superparamagnetic iron oxide (SPIO) nanoparticles were conjugated with integrin lymphocyte function-associated antigen (LFA)-1 Inserted (I) domain, engineered to mimic activated LFA-1 in leukocytes. By whole body optical imaging and MRI, we found I domain-coated nanoparticles were localized specifically to the tumors with high ICAM-1 expression as well as to the vasculature with ICAM-1 induction within and in the invasive front of the tumor. Furthermore, with a newly developed MRI technique, we achieved quantitative mapping of nanoparticle distribution in vivo in a mouse model of acute inflammation. This study presents the first demonstration of in vivo detection of tumor-associated vasculature by targeting inflammation with systemically injected nanoparticles, offering a possibility of tumor detection not by tumor surface antigens but by an inflamed milieu present in the tumor microenvironment.

Probing sepsis and acute inflammation using ICAM-1 specific mSPIO nanoparticles

Sepsis is the leading cause of death in critically ill patients in the United States. Current diagnosis of sepsis relies heavily on the patients manifestation of septic symptoms, which occur at life-threatening late stage of sepsis. Because the underlying biological changes of sepsis occur hours to days before the clinical presentation of symptoms, early detection of the biological changes will provide crucial opportunities for early diagnosis and effective treatment of sepsis. As sepsis is resultant of acute inflammation, we propose using magnetic resonance imaging (MRI) to quantitatively observe a patients degree of inflammation as an indicator of sepsis progression. By quantitatively tracking the biodistribution of nanomicelle encapsulating superparamagnetic iron oxide (mSPIO) nanoparticles specific to intercellular adhesion molecule 1 (ICAM-1), an adhesion molecule which displays distinct spatiotemporal response to inflammation, we have found that septic in vivo mouse subjects showed greater mSPIO accumulation in the liver than that of non-septic and non-ICAM-1 specific controls, demonstrating the utility of MRI-based detection as a diagnosis method for sepsis.