Improved automated synthesis of [18F]fluoroethylcholine as a radiotracer for cancer imaging

[(18)F]Fluoroethylcholine has been recently introduced as a promising (18)F-labelled analogue of [(11)C]choline which had been previously described as a tracer for metabolic cancer imaging with positron emission tomography (PET). Due to the practical advantages of using the longer-lived radioisotope (18)F (t(1/2)=110 min), offering the opportunity of a more widespread clinical application, we established a reliable, fully automated synthesis for its production using a modified, commercially available module. [(18)F]Fluoroethylcholine was prepared from N,N-dimethylaminoethanol by iodide catalyzed alkylation with 1-[(18)F]fluoro-2-tosylethane as alkylating agent, resulting in a total radiochemical yield of 30+/-6% after a synthesis time of 50 min. The specific activity of [(18)F]fluoroethylcholine was >55 GBq/micromol and the radiochemical purity 95-99%.     

Genbank accession #: AJ131961

Plant Molecular Biology -     

Exploiting the mosaic structure of trans-acyltransferase polyketide synthases for natural product discovery and pathway dissection

Modular polyketide synthases (PKSs) are giant bacterial enzymes that synthesize many polyketides of therapeutic value. In contrast to PKSs that provide acyltransferase (AT) activities in cis, trans-AT PKSs lack integrated AT domains and exhibit unusual enzymatic features with poorly understood functions in polyketide assembly. This has retarded insight into the assembly of products such as mupirocin, leinamycin and bryostatin 1. We show that trans-AT PKSs evolved in a fundamentally different fashion from cis-AT systems, through horizontal recruitment and assembly of substrate-specific ketosynthase (KS) domains. The insights obtained from analysis of these KS mosaics will facilitate both the discovery of novel polyketides by genome mining, as we demonstrate for the thailandamides of Burkholderia thailandensis, and the extraction of chemical information from short trans-AT PCR products, as we show using metagenomic DNA of marine sponges. Our data also suggest new strategies for dissecting polyketide biosynthetic pathways and engineering polyketide assembly.     

A new approach to the synthesis of a protected 2-aminopurine derivative and its incorporation into oligodeoxynucleotides containing the Eco RI and Bam HI recognition sites.

A protected 2-aminopurine nucleoside suitable for incorporation into oligodeoxynucleotides using phosphite triester chemical synthesis procedures has been prepared via oxidation of a purine hydrazino derivative with silver (I) oxide. Five oligodeoxynucleotides containing Eco RI and Bam HI recognition sites have been prepared such that, in the double stranded form, the 2-aminopurine base has either a complementary thymine or cytosine nucleobase. The helix character and thermodynamic parameters for helix formation have been examined.     

The Experimental Design as Practical Approach to Develop and Optimize a Formulation of Peptide-Loaded Liposomes

To investigate the encapsulation of Print 3G, a peptidic agent that could reduce the angiogenic development of breast tumors, pegylated liposomes used as intravenous vectors were studied and characterized. Recently, the path of liposomes has been explored with success to improve the pharmacological properties of peptidic drugs and to stabilize them. In this study, loaded unilamellar vesicles composed of SPC:CHOL:mPEG2000-DSPE (47:47:6) were prepared by the hydration of lipid film technique. An HPLC method was developed and validated for the determination of Print 3G to calculate its encapsulation efficiency. Observed Print 3G adsorption on different materials employed during liposome preparation (such as glass beads, tubing, and connections for extrusion) led to the modification of the manufacturing method. The freeze-thawing technique was used to enhance the amount of Print 3G encapsulated into blank liposomes prepared using the hydration of lipid film procedure. Many factors may influence peptide entrapment, namely the number of freeze-thawing cycles, the lipid concentration, the peptide concentration, and the mixing time. Consequently, a design of experiments was performed to obtain the best encapsulation efficiency while minimizing the number of experiments. The lipid concentration and the number of freeze-thawing cycles were identified as the positive factors influencing the encapsulation. As a result of the optimization, an optimum was found and encapsulation efficiencies were improved from around 30% to 63%. Liposome integrity was evaluated by photon correlation spectroscopy and freeze-fracture electron microscopy to ensure that the selected formulation possesses the required properties to be a potential candidate for further in vitro and in vivo experiments.     

Comparative genomics of chondrichthyan Hoxa clusters

Background  

The chondrichthyan or cartilaginous fish (chimeras, sharks, skates and rays) occupy an important phylogenetic position as the sister group to all other jawed vertebrates and as an early lineage to diverge from the vertebrate lineage following two whole genome duplication events in vertebrate evolution. There have been few comparative genomic analyses incorporating data from chondrichthyan fish and none comparing genomic information from within the group. We have sequenced the complete Hoxa cluster of the Little Skate (Leucoraja erinacea) and compared to the published Hoxa cluster of the Horn Shark (Heterodontus francisci) and to available data from the Elephant Shark (Callorhinchus milii) genome project.     

Gene conversion and natural selection in the evolution of X-linked color vision genes in higher primates

During higher primate evolution, gene conversion seems to have occurred often between the red and green photo-pigment genes, which are tandemly linked on the X chromosome. To understand this phenomenon better, intron 4 sequences of the red and green pigment genes of a male human (an Asian Indian), a male chimpanzee, and a male baboon were amplified by PCR and sequenced. The data show that the intron 4 sequences between the two genes have been strongly or completely homogenized in the three species studied. Apparently recent gene conversion events have occurred in introns 4 of the red and green pigment genes in humans and chimpanzees. Two or more conversion events may have occurred at different times in introns 4 of the two pigment genes in baboons. The divergence between the two genes is significantly lower in intron 4 than in exons 4 and 5 in each species, contrary to the usual situation that introns evolve faster than exons. It is most likely that strong natural selection for maintaining the distinct functions of exons 4 and 5 of the red and green pigment genes has acted against sequence homogenization of these exons.