Xiaoyuan Chen

Bio: Xiaoyuan Chen is an academic researcher from National University of Singapore. The author has contributed to research in topics: Physics & Photothermal therapy. The author has an hindex of 149, co-authored 994 publications receiving 89870 citations. Previous affiliations of Xiaoyuan Chen include Brown University & University of Southern California.

Microsurgery guided by sequential preoperative lymphography using 68 Ga-NEB PET and MRI in patients with lower-limb lymphedema.

Abstract: The popularity of contemporary microsurgical techniques in treatment of lower-limb lymphedema calls for better visualization of the lymphatic system, both preoperatively and intra-operatively. The aim of this prospective study was to investigate the feasibility of a novel combination of 68Ga-NEB positron emission tomography (PET) with magnetic resonance lymphography (MRL) in evaluating lymphedema and guiding surgical intervention. A total of 11 patients (F 9, M 2, age range 29–69 y) with lower-limb lymphedema classified into stage I to III were recruited. PET acquisition was performed at 30, 60 and 90 min after subcutaneous injection of the albumin-binding radiotracer 68Ga-NEB into the bilateral first web spaces of the feet. All the patients were also subjected to 99mTc-sulfur colloid (SC) lymphoscintigraphy for comparison. Gd-DTPA-enhanced magnetic resonance imaging (MRI) was performed using sequences specialized for lymphatic vessel scans. All the patients underwent surgical interventions within a week. The surgical approach includes the use of a linear marker for edema localization and indocyanine green (ICG) lymphography with a near-infrared surgical navigation system intra-operatively. Lymph transport in lymphatic channels was clearly observed by visualization of 68Ga-NEB activity in the lymphatic vessels and within lymph nodes for all 11 patients as well as the visualization of the edema section plane with dermal backflow (DB), abnormally increased and disconnected uptake along the lymphatic channels. Preoperative 68Ga-NEB PET combined with MRL provides advantageous three-dimensional images, higher temporal resolution, significantly shorter time lapse before image acquisition after tracer injection and more accurate pathological lymphatic vessel distribution than 99mTc-SC lymphoscintigraphy combined with MRI. This study documented an effective imaging pattern to combine 68Ga-NEB PET and MRL in patients with lower-limb lymphedema. This strategy demonstrated significant advantage over 99mTc-SC lymphoscintigraphy/MRL in the evaluation of lymphedema severity, staging and pathological location of lymph vessels to make an individualized treatment plan. Dual 68Ga-NEB PET/MRL is thus recommended before the operation for staging and therapy planning.

New Methods for Labeling RGD Peptides with Bromine-76

Abstract: Direct bromination of the tyrosine residues of peptides and antibodies with bromine-76, to create probes for PET imaging, has been reported. For peptides that do not contain tyrosine residues, however, a prosthetic group is required to achieve labeling via conjugation to other functional groups such as terminal α-amines or lysine e-amines. The goal of this study was to develop new strategies for labeling small peptides with Br-76 using either a direct labeling method or a prosthetic group, depending on the available functional group on the peptides. A new labeling agent, N-succinimidyl-3-[ 76 Br]bromo-2,6-dimethoxybenzoate ([ 76 Br]SBDMB) was prepared for cyclic RGD peptide labeling. N-succinimidyl-2, 6-dimethoxybenzoate was also used to pre-attach a 2, 6-dimethoxybenzoyl (DMB) moiety to the peptide, which could then be labeled with Br-76. A competitive cell binding assay was performed to determine the binding affinity of the brominated peptides. PET imaging of U87MG human glioblastoma xenografted mice was performed using [ 76 Br]-BrE[c(RGDyK)]2 and [ 76 Br]-BrDMB-E[c (RGDyK)]2. An ex vivo biodistribution assay was performed to confirm PET quantification. The mechanisms of bromination reaction between DMB-c(RGDyK) and the brominating agent CH3COOBr were investigated with the SCRF-B3LYP/6-31G* method with the Gaussian 09 program package. The yield for direct labeling of c(RGDyK) and E[c(RGDyK)]2 using chloramine-T and peracetic acid at ambient temperature was greater than 50%. The yield for [ 76 Br]SBDMB was over 60% using peracetic acid. The conjugation yields for labeling c(RGDfK) and c(RGDyK) were over 70% using the prosthetic group at room temperature. Labeling yield for pre-conjugated peptides was over 60%. SDMB conjugation and bromination did not affect the binding affinity of the peptides with integrin receptors. Both [ 76 Br]Br-E[c(RGDyK)]2 and [ 76 Br]BrDMB-E[c(RGDyK)]2 showed high tumor uptake in U87MG tumor bearing mice. The specificity of the imaging tracers was confirmed by decreased tumor uptake after co-administration of unlabeled dimeric RGD peptides. The energy barrier of the transition state of bromination for the dimethoxybenzoyl group was about 9 kcal/mol lower than that for the tyrosine residue. In conclusion, the newly developed N-succinimidyl-2, 6-dimethoxybenzoate molecule can be used either for one step labeling through pre-conjugation or as the precursor for a Br-76 labeled prosthetic group for indirect labeling. Radiobromination on a dimethoxybenzoyl group has selectivity over radiobromination on tyrosine. The energy barrier difference of the transition states of bromination between the dimethoxybenzoyl group and the tyrosine residue may account for the reaction selectivity when both groups are present in the same molecule. Ivyspring

Al[18F]NOTA-T140 Peptide for Noninvasive Visualization of CXCR4 Expression.

Abstract: Chemokine receptor CXCR4 plays an important role in tumor aggressiveness, invasiveness, and metastasis formation. Quantification of CXCR4 expression by tumors may have an impact on prediction and evaluation of tumor response to therapies. In this study, we developed a robust and straightforward F-18 labeling route of T140, a CXCR4 peptide-based antagonist. T140 derivative was conjugated to 1,4,7-triazacyclononane-triacetic acid (NOTA) and labeled with Al[18F]. Al[18F]NOTA-T140 was evaluated in vitro in cell-based assay and stability in mouse serum and in vivo using CXCR4 positive and negative tumor xenograft models. Labeling of Al[18F]NOTA-T140 was completed within 30 min with a radiochemical yield of 58 ± 5.3 % at the end of synthesis, based on fluoride-18 activity. Al[18F]NOTA-T140 accumulated in CHO-CXCR4 positive but not negative tumors. Al[18F]NOTA-T140 uptake in the tumors correlated with CXCR4 protein expression. Moreover, Al[18F]NOTA-T140 had high accumulation in CXCR4-positive metastatic tumors. The simplicity of Al[18F]NOTA-T140 labeling along with its properties to specifically image CXCR4 expression by tumors warrant further clinical application for the diagnosis of CXCR4 clinically.

I and i

Abstract: There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality. Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

疟原虫var基因转换速率变化导致抗原变异[英]／Paul H, Robert P, Christodoulou Z, et al//Proc Natl Acad Sci U S A

Abstract: 抗原变异可使得多种致病微生物易于逃避宿主免疫应答。表达在感染红细胞表面的恶性疟原虫红细胞表面蛋白1（PfPMP1）与感染红细胞、内皮细胞、树突状细胞以及胎盘的单个或多个受体作用，在黏附及免疫逃避中起关键的作用。每个单倍体基因组var基因家族编码约60种成员，通过启动转录不同的var基因变异体为抗原变异提供了分子基础。

Chemistry and properties of nanocrystals of different shapes.

Abstract: The interest in nanoscale materials stems from the fact that new properties are acquired at this length scale and, equally important, that these properties * To whom correspondence should be addressed. Phone, 404-8940292; fax, 404-894-0294; e-mail, mostafa.el-sayed@ chemistry.gatech.edu. † Case Western Reserve UniversitysMillis 2258. ‡ Phone, 216-368-5918; fax, 216-368-3006; e-mail, burda@case.edu. § Georgia Institute of Technology. 1025 Chem. Rev. 2005, 105, 1025−1102