Toxicology evaluation of radiotracer doses of 3'-deoxy-3'-[18F]fluorothymidine (18F-FLT) for human PET imaging: Laboratory analysis of serial blood samples and comparison to previously investigated therapeutic FLT doses

Background: 18F-FLT is a novel PET radiotracer which has demonstrated a strong potential utility for imaging cellular proliferation in human tumors in vivo. To facilitate future regulatory approval of 18F-FLT for clinical use, we wished to demonstrate the safety of radiotracer doses of 18F-FLT administered to human subjects, by: 1) performing an evaluation of the toxicity of 18F-FLT administered in radiotracer amounts for PET imaging, 2) comparing a radiotracer dose of FLT to clinical trial doses of FLT. Methods: Twenty patients gave consent to a 18F-FLT injection, subsequent PET imaging, and blood draws. For each patient, blood samples were collected at multiple times before and after 18F-FLT PET. These samples were assayed for a comprehensive metabolic panel, total bilirubin, complete blood and platelet counts. 18F-FLT doses of 2.59 MBq/Kg with a maximal dose of 185 MBq (5 mCi) were used. Blood time-activity curves were generated for each patient from dynamic PET data, providing a measure of the area under the FLT concentration curve for 12 hours (AUC12). Results: No side effects were reported. Only albumin, red blood cell count, hematocrit and hemoglobin showed a statistically significant decrease over time. These changes are attributed to IV hydration during PET imaging and to subsequent blood loss at surgery. The AUC12 values estimated from imaging data are not significantly different from those found from serial measures of FLT blood concentrations (p = 0.66). The blood samples-derived AUC12 values range from 0.232 ng*h/mL to 1.339 ng*h/mL with a mean of 0.802 � 0.303 ng*h/mL. This corresponds to 0.46% to 2.68% of the lowest and least toxic clinical trial AUC12 of 50 ng*h/mL reported by Flexner et al (1994). This single injection also corresponds to a nearly 3,000-fold lower cumulative dose than in Flexner's twice daily trial. Conclusion: This study shows no evidence of toxicity or complications attributable to 18F-FLT injected intravenously.This study was supported by NIH grant R01 CA115559, 1R01 CA107264, and 1R01 CA80907

Total Synthesis of Paracaseolide A

The total synthesis of paracaseolide A, a valuable cell-cycle progression inhibitor, was accomplished in 8 steps from known compounds, with 6.6% overall yield. The synthetic strategy creates strong potential for diversification

Use of molecular modelling to probe the mechanism of the nucleoside transporter NupG.

Nucleosides play key roles in biology as precursors for salvage pathways of nucleotide synthesis. Prokaryotes import nucleosides across the cytoplasmic membrane by proton- or sodium-driven transporters belonging to the Concentrative Nucleoside Transporter (CNT) family or the Nucleoside:H(+) Symporter (NHS) family of the Major Facilitator Superfamily. The high resolution structure of a CNT from Vibrio cholerae has recently been determined, but no similar structural information is available for the NHS family. To gain a better understanding of the molecular mechanism of nucleoside transport, in the present study the structures of two conformations of the archetypical NHS transporter NupG from Escherichia coli were modelled on the inward- and outward-facing conformations of the lactose transporter LacY from E. coli, a member of the Oligosaccharide:H(+) Symporter (OHS) family. Sequence alignment of these distantly related proteins (∼ 10% sequence identity), was facilitated by comparison of the patterns of residue conservation within the NHS and OHS families. Despite the low sequence similarity, the accessibilities of endogenous and introduced cysteine residues to thiol reagents were found to be consistent with the predictions of the models, supporting their validity. For example C358, located within the predicted nucleoside binding site, was shown to be responsible for the sensitivity of NupG to inhibition by p-chloromercuribenzene sulphonate. Functional analysis of mutants in residues predicted by the models to be involved in the translocation mechanism, including Q261, E264 and N228, supported the hypothesis that they play important roles, and suggested that the transport mechanisms of NupG and LacY, while different, share common features

Triad pattern algorithm for predicting strong promoter candidates in bacterial genomes

Abstract Background Bacterial promoters, which increase the efficiency of gene expression, differ from other promoters by several characteristics. This difference, not yet widely exploited in bioinformatics, looks promising for the development of relevant computational tools to search for strong promoters in bacterial genomes. Results We describe a new triad pattern algorithm that predicts strong promoter candidates in annotated bacterial genomes by matching specific patterns for the group I σ70 factors of Escherichia coli RNA polymerase. It detects promoter-specific motifs by consecutively matching three patterns, consisting of an UP-element, required for interaction with the α subunit, and then optimally-separated patterns of -35 and -10 boxes, required for interaction with the σ70 subunit of RNA polymerase. Analysis of 43 bacterial genomes revealed that the frequency of candidate sequences depends on the A+T content of the DNA under examination. The accuracy of in silico prediction was experimentally validated for the genome of a hyperthermophilic bacterium, Thermotoga maritima, by applying a cell-free expression assay using the predicted strong promoters. In this organism, the strong promoters govern genes for translation, energy metabolism, transport, cell movement, and other as-yet unidentified functions. Conclusion The triad pattern algorithm developed for predicting strong bacterial promoters is well suited for analyzing bacterial genomes with an A+T content of less than 62%. This computational tool opens new prospects for investigating global gene expression, and individual strong promoters in bacteria of medical and/or economic significance.</p