A transesterification reaction is implicated in the covalent binding of benzo[b]acronycine anticancer agents with DNA and glutathion

The benzo[b]acronycine derivative S23906-1 has been recently identified as a promising antitumor agent, showing remarkable in vivo activities against a panel of solid tumors. The anticancer activity is attributed to the capacity of the drug to alkylate DNA, selectively at the exocyclic 2-amino group of guanine residues. Hydrolysis of the C-1 and C-2 acetate groups of S23906-1 provides the diol compound S28907-1 which is inactive whereas the intermediate C-2 monoacetate derivative S28687-1 is both highly reactive toward DNA and cytotoxic. The reactivity of this later compound S28687-1 toward two bionucleophiles, DNA and the tripeptide glutathion, has been investigated by mass spectrometry to identify the nature of the (type II) covalent adducts characterized by the loss of the acetate group at position 2. On the basis of NMR and molecular modeling analyses, the reaction mechanism is explained by a transesterification process where the acetate leaving group is transferred from position C-2 to C-1. Altogether, the study validates the reaction scheme of benzo[b]acronycine derivative with its target.     

Comparison of bulk enucleation methods for porcine oocytes

Cloning of mammalian oocytes requires that the recipient oocyte is enucleated to remove all genetic material associated with the chromosomes. The procedure currently used in most species requires careful micromanipulation of oocytes treated with cytochalasin B to prevent structural damage. Although functional, this procedure requires time and limits the number of oocytes available for cloning, and our ability to understand the mechanisms of nuclear reprogramming. Therefore, this study aimed at evaluating different procedures to enucleate large pools of oocytes in a time-efficient manner. Two different approaches were tested. The first approach involved centrifugation of zona-free oocytes through a percoll gradient to separate the portion containing the chromatin from the cytoplasmic portion. The second used etoposide to prevent chromatin segregation at first metaphase and resulting in the expulsion of all chromosomes in the polar body. Using the chemical approach an average enucleation rate of 39.4 +/- 7.5% was obtained, while the centrifugation approach resulted in an average enucleation rate of 66.9 +/- 6. In terms of time efficiency, the control manipulation method takes 0.11 min and the centrifugation took an average of 0.52 min per oocyte. The MPF activity at the end of procedure was estimated through the measurement of H1 activity and as expected, the etoposide-cycloheximide treated oocytes had lower H1 activity which was restored by further incubation in the maturation medium for 5 hr while the centrifugation gave a nonsignificant intermediary result. In conclusion, the results presented suggest that both the chemical and the mechanical methods are usable alternatives to micromanipulation of oocytes to generate a large number of chromosome free cytoplasm for biochemical analysis. Mol. Reprod. Dev. 67: 70-76, 2004.     

On-resin assembly of a linkerless lanthanide(III)-based luminescence label and its application to the total synthesis of site-specifically labeled mechanosensitive channels

A synthesis strategy for the on-resin assembly of luminescent lanthanide chelates from commercially available compounds was developed. Advantages of the approach include the absence of spacers between the metal ion and the attachment site, and the compatibility with typical chemical protein synthesis protection schemes. Methoxycoumarin-labeled lysine and tris(tert-butyl)-DOTA were consecutively coupled with high efficiency to a free amino group in otherwise fully protected peptide segments using standard peptide synthesis methods. Addition of stoichiometric amounts of Tb(3+) to the modified, cleaved, and purified peptides yielded the desired lanthanide chelate. Incorporation of this label into a chemically synthesized, full-length mechanosensitive channel of large conductance (MscL) of E. coli and subsequent reconstitution into vesicles resulted in a functional mechanosensitive channel of comparable conductance to the wild-type channel. However, this channel required increased suction to gate. Excitation of the antenna molecule methoxycoumarin at 336 nm resulted in an emission spectrum typical for Tb(3+) and a luminescence lifetime of 0.67 ms. The location of the probe close to the backbone of this protein may provide precise information about conformational changes during channel opening from LRET studies.     

18F]Galacto-RGD: synthesis, radiolabeling, metabolic stability, and radiation dose estimates

It has been demonstrated in various murine tumor models that radiolabeled RGD-peptides can be used for noninvasive determination of alphavbeta3 integrin expression. Introduction of sugar moieties improved the pharmacokinetic properties of these peptides and led to tracer with good tumor-to-background ratios. Here we describe the synthesis, radiolabeling, and the metabolic stability of a glycosylated RGD-peptide ([18F]Galacto-RGD) and give first radiation dose estimates for this tracer. The peptide was assembled on a solid support using Fmoc-protocols and cyclized under high dilution conditions. It was conjugated with a sugar amino acid, which can be synthesized via a four-step synthesis starting from pentaacetyl-protected galactose. For radiolabeling of the glycopeptide, 4-nitrophenyl-2-[18F]fluoropropionate was used. This prosthetic group allowed synthesis of [18F]Galacto-RGD with a maximum decay-corrected radiochemical yield of up to 85% and radiochemical purity >98%. The overall radiochemical yield was 29 +/- 5% with a total reaction time including final HPLC preparation of 200 +/- 18 min. The metabolic stability of [18F]Galacto-RGD was determined in mouse blood and liver, kidney, and tumor homogenates 2 h after tracer injection. The average fraction of intact tracer in these organs was approximately 87%, 76%, 69%, and 87%, respectively, indicating high in vivo stability of the radiolabeled glycopeptide. The expected radiation dose to humans after injection of [18F]Galacto-RGD has been estimated on the basis of dynamic PET studies with New Zealand white rabbits. According to the residence times in these animals the effective dose was calculated using the MIRDOSE 3.0 program as 2.2 x 10(-2) mGy/MBq. In conclusion, [18F]Galacto-RGD can be synthesized in high radiochemical yields and radiochemical purity. Despite the time-consuming synthesis of the prosthetic group 185 MBq of [18F]Galacto-RGD, a sufficient dose for patient studies, can be produced starting with approximately 2.2 GBq of [18F]flouride. Moreover, the fast excretion, the suitable metabolic stability and the low estimated radiation dose allow to evaluate this tracer in human studies.     

Inhaled nebulized nitrite is a hypoxia-sensitive NO-dependent selective pulmonary vasodilator

The blood anion nitrite contributes to hypoxic vasodilation through a heme-based, nitric oxide (NO)-generating reaction with deoxyhemoglobin and potentially other heme proteins. We hypothesized that this biochemical reaction could be harnessed for the treatment of neonatal pulmonary hypertension, an NO-deficient state characterized by pulmonary vasoconstriction, right-to-left shunt pathophysiology and systemic hypoxemia. To test this, we delivered inhaled sodium nitrite by aerosol to newborn lambs with hypoxic and normoxic pulmonary hypertension. Inhaled nitrite elicited a rapid and sustained reduction ( approximately 65%) in hypoxia-induced pulmonary hypertension, with a magnitude approaching that of the effects of 20 p.p.m. NO gas inhalation. This reduction was associated with the immediate appearance of NO in expiratory gas. Pulmonary vasodilation elicited by aerosolized nitrite was deoxyhemoglobin- and pH-dependent and was associated with increased blood levels of iron-nitrosyl-hemoglobin. Notably, from a therapeutic standpoint, short-term delivery of nitrite dissolved in saline through nebulization produced selective, sustained pulmonary vasodilation with no clinically significant increase in blood methemoglobin levels. These data support the concept that nitrite is a vasodilator acting through conversion to NO, a process coupled to hemoglobin deoxygenation and protonation, and evince a new, simple and inexpensive potential therapy for neonatal pulmonary hypertension.     

PlasmoDB: the Plasmodium genome resource. A database integrating experimental and computational data

PlasmoDB (http://PlasmoDB.org) is the official database of the Plasmodium falciparum genome sequencing consortium. This resource incorporates the recently completed P. falciparum genome sequence and annotation, as well as draft sequence and annotation emerging from other Plasmodium sequencing projects. PlasmoDB currently houses information from five parasite species and provides tools for intra- and inter-species comparisons. Sequence information is integrated with other genomic-scale data emerging from the Plasmodium research community, including gene expression analysis from EST, SAGE and microarray projects and proteomics studies. The relational schema used to build PlasmoDB, GUS (Genomics Unified Schema) employs a highly structured format to accommodate the diverse data types generated by sequence and expression projects. A variety of tools allow researchers to formulate complex, biologically-based, queries of the database. A stand-alone version of the database is also available on CD-ROM (P. falciparum GenePlot), facilitating access to the data in situations where internet access is difficult (e.g. by malaria researchers working in the field). The goal of PlasmoDB is to facilitate utilization of the vast quantities of genomic-scale data produced by the global malaria research community. The software used to develop PlasmoDB has been used to create a second Apicomplexan parasite genome database, ToxoDB (http://ToxoDB.org).     

Utilization of acidic amino acids and their amides by pseudomonads: role of periplasmic glutaminase-asparaginase

The acidic amino acids (Asp, Glu) and their amides (Asn, Gln) support rapid growth of a variety of Pseudomonas strains when provided as the sole source of carbon and nitrogen. All key enzymes of glutamate metabolism were detected in P. fluorescence, with glutaminase and asparaginase showing the highest specific activities. A periplasmic glutaminase/asparaginase activity (PGA) was found in all pseudomonads examined, including a number of root-colonizing biocontrol strains. The enzyme was purified and shown to be identical with the ansB gene product described previously. In addition to PGA, P. fluorescens contains a cytoplasmic asparaginase with marked specificity for Asn. PGA is strongly and specifically induced by its substrates (Asn, Gln) but also by the reaction products (Asp, Glu). In addition, PGA is subject to efficient carbon catabolite repression by glucose and by citrate cycle metabolites. A mutant of P. putida KT2440 with a disrupted ansB gene was unable to utilize Gln, whereas growth of the mutant on other amino acids was normal.     

Repair of a minimal DNA double-strand break by NHEJ requires DNA-PKcs and is controlled by the ATM/ATR checkpoint

Mammalian cells primarily rejoin DNA double-strand breaks (DSBs) by the non-homologous end-joining (NHEJ) pathway. The joining of the broken DNA ends appears directly without template and accuracy is ensured by the NHEJ factors that are under ATM/ATR regulated checkpoint control. In the current study we report the engineering of a mono-specific DNA damaging agent. This was used to study the molecular requirements for the repair of the least complex DSB in vivo. Single-chain PvuII restriction enzymes fused to protein delivery sequences transduce cells efficiently and induce blunt end DSBs in vivo. We demonstrate that beside XRCC4/LigaseIV and KU, the DNA-PK catalytic subunit (DNA-PKcs) is also essential for the joining of this low complex DSB in vivo. The appearance of blunt end 3′-hydroxyl and 5′-phosphate DNA DSBs induces a significantly higher frequency of anaphase bridges in cells that do not contain functional DNA-PKcs, suggesting an absolute requirement for DNA-PKcs in the control of chromosomal stability during end joining. Moreover, these minimal blunt end DSBs are sufficient to induce a p53 and ATM/ATR checkpoint function.