Intermediate Half-life Research Articles

The roles of 3′-exoribonucleases and the exosome in trypanosome mRNA degradation

The degradation of eukaryotic mRNAs can be initiated by deadenylation, decapping, or endonuclease cleavage. This is followed by 5'-3' degradation by homologs of Xrn1, and/or 3'-5' degradation by the exosome. We previously reported that, in African trypanosome Trypanosoma brucei, most mRNAs are deadenylated prior to degradation, and that depletion of the major 5'-3' exoribonuclease XRNA preferentially stabilizes unstable mRNAs. We now show that depletion of either CAF1 or CNOT10, two components of the principal deadenylation complex, strongly inhibits degradation of most mRNAs. RNAi targeting another deadenylase, PAN2, or RRP45, a core component of the exosome, preferentially stabilized mRNAs with intermediate half-lives. RRP45 depletion resulted in a 5' bias of mRNA sequences, suggesting action by a distributive 3'-5' exoribonuclease. Results suggested that the exosome is involved in the processing of trypanosome snoRNAs. There was no correlation between effects on half-lives and on mRNA abundance.

Cyclotron production of 44Sc for clinical application

Abstract 44Sc is a promising β +-emitter for molecular imaging with intermediate half-life of 4 h. Due to the chemical similarity of Sc3+ to the Lu3+ and Y3+ cations, 44Sc-DOTA bioconjugates are expected to demonstrate similar properties in vivo as the 177Lu- and 90Y-bioconjugates, what is important in planning the radionuclide therapy. 44Sc can be obtained from the 44 Ti/44Sc generator. An alternative method for 44Sc production can be the irradiation of 44Ca target at small cyclotrons. The aim of our work was to optimize the parameters of 44CaCO3 irradiation and to develop a simple procedure for 44Sc separation from the calcium target. For optimization study, 44CaCO3 targets were irradiated by protons in the energy range of 5.6–17.5 MeV with 9 MeV being found to be the best energy for 44Ca irradiations. A simple and fast separation procedure of 44Sc from calcium target was developed using chelating resin Chelex 100. DOTATATE conjugate was successfully radiolabelled with high yield at elevated temperature using the produced 44Sc. While 44CaCO3 is relatively expensive, the cost of 44Sc-DOTATATE production can be reduced by target recovery. Due to low proton energy required to produce GBq activity level of 44Sc, the availability of 44Sc radioisotope could be enhanced to open new opportunities for applications in medical imaging.

Clinical PET of Neuroendocrine Tumors Using64Cu-DOTATATE: First-in-Humans Study

The use of positron emitter-labeled compounds for somatostatin receptor imaging (SRI) has become attractive because of the prospect of improved spatial resolution, accelerated imaging procedures, and the ability to quantify tissue radioactivity concentrations. This paper provides results from first-in-humans use of (64)Cu-DOTATATE, an avidly binding somatostatin receptor ligand linked to a radioisotope with intermediate half-life and favorable positron energy (half-life, 12.7 h; maximum positron energy, 0.653 MeV). In a prospective setup, 14 patients with a history of neuroendocrine tumors underwent both PET/CT with (64)Cu-DOTATATE and SPECT/CT with our current routine imaging agent (111)In-diethylenetriaminepentaacetic acid-octreotide. After intravenous injection of 193-232 MBq of (64)Cu-DOTATATE, whole-body PET scans were acquired at 1 h (n = 14), 3 h (n = 12), and 24 h (n = 5) after administration. Tissue radioactivity concentrations for normal organs and lesions were quantified, and standardized uptake values were calculated for the early (1 h) and delayed (3 h) scans. Using the data for 5 patients, we assessed the radiation dose with OLINDA/EXM software. Furthermore, the clinical performance of (64)Cu-DOTATATE with respect to lesion detection was compared with conventional SRI. SRI with (64)Cu-DOTATATE produced images of excellent quality and high spatial resolution. Images were characterized by high and stable tumor-to-background ratios over an imaging time window of at least 3 h. Compared with conventional scintigraphy, (64)Cu-DOTATATE PET identified additional lesions in 6 of 14 patients (43%). In 5 patients, lesions were localized in organs and organ systems not previously known as metastatic sites, including the early-stage detection of a secondary neuroendocrine tumor in a patient with a known mutation in the multiple endocrine neoplasia type I gene. All major additional findings seen only on PET could be confirmed on the basis of a clinical follow-up interval of 18 mo. Calculated radiation dose estimates yielded an effective dose of 6.3 mSv for an injected activity of 200 MBq of (64)Cu-DOTATATE, with the liver being the organ with the highest absorbed radiation dose (0.16 mGy/MBq). This first-in-humans study supports the clinical use of (64)Cu-DOTATATE for SRI with excellent imaging quality, reduced radiation burden, and increased lesion detection rate when compared with (111)In-diethylenetriaminepentaacetic acid-octreotide.

A novel form of T cell antagonism by trapping of immunological synapse (106.49)

Abstract T cell activation results from productive T cell receptor (TCR) engagement by a cognate peptide-MHC (pMHC) complex on the antigen presenting cell (APC) surface, a process leading to the polarization of the T cell secretory machinery towards the interface of APC. We have previously shown that the half-life of the TCR/pMHC interaction and the density of pMHC on the APC are two parameters determining T cell activation. Here, by using APLs conferring different half-lives to the TCR/pMHC interaction we have tested how this parameter can control T cell polarization. We observed that only TCR/pMHC interactions with intermediate half-lives can promote the assembly of synapses that lead to T cell activation. Strikingly, intermediate half-life interactions can be competed out by short half-life interactions, which can efficiently promote T cell polarization and antagonize T cell activation that was induced by activating intermediate half-life interactions. However, short TCR/pMHC interactions fail at promoting phosphorylation of signaling molecules at the T cell-APC contact interface, which are needed for T cell activation. Our data suggest that while intermediate half-life pMHC ligands promote assembly of activating synapses, this process can be inhibited by short half-life antagonistic pMHC ligands, which promote the assembly of non activating synapses.

An Open-Label Phase I Pharmacokinetic Study of [14c] Bendamustine in Patients with Relapsed or Refractory Malignancy

Abstract 2476 Background:Bendamustine is a unique alkylating agent which combines a nitrogen mustard moiety of mechlorethamine with a benzimidazole. This study was conducted to characterize the distribution, metabolism, and elimination of [14C] bendamustine and its metabolites (M3, M4, and dihydroxy bendamustine [HP2]) and to assess the roles of renal and hepatic pathways in the drug's metabolism and excretion. A secondary objective was to further characterize the safety profile of single-agent bendamustine. Methods:This open-label, phase I study enrolled 6 patients, age ≥18 years, with confirmed relapsed or refractory malignancy. The study was divided into 2 assessment periods: period A, during which the mass balance and pharmacokinetics of [14C] bendamustine were investigated, and period B, an extended-use period of up to 6 cycles with non-labeled bendamustine, during which safety continued to be assessed. Patients received intravenous (IV) bendamustine (120 mg/m2), containing 80–95 μCi of [14C] bendamustine, on day 1 of cycle 1 and non-labeled IV bendamustine (120 mg/m2) on day 2 of cycle 1 (period A). Pharmacokinetic parameters of bendamustine and metabolites M3, M4, and HP2 were calculated through plasma and urine concentrations, which were determined through 24 hours following administration of bendamustine on day 1. Total radioactivity (TRA) levels were measured in plasma, urine, and feces collected prior to drug administration and at time points through 168 hours after patients received [14C] bendamustine. Collection of excreta could continue (after the 7-day period) on an outpatient basis: if radiolabeled bendamustine ≥1% of dose was measurable in the 144- to 168-hour urine or feces collection, collection continued until the recovery in each 24-hour urine or feces collection was <1% of dose. Results:Six patients (3 males; 3 females) with a median age of 66 (48–75) years were enrolled and completed the pharmacokinetic portion of the study. For bendamustine, the decline from peak plasma concentration was characterized by an initial rapid distribution phase, followed by a somewhat slower intermediate phase. The pharmacologically relevant half-life (t½) was approximately 40 minutes. The plasma concentrations of M3, M4, and HP2 were very low relative to the bendamustine concentrations.Of the TRA dose administered, approximately half of the dose was recovered in the urine and approximately a quarter of the dose was recovered in the feces. Less than 5% of TRA dose was recovered in the urine as unchanged bendamustine. Mean recovery of TRA in excreta was approximately 76% of the radiochemical dose. Total recovery was incomplete due to continued slow excretion of TRA at the end of the collection period. The sustained levels of radioactivity in the plasma as compared with plasma concentrations of bendamustine suggest that, despite the rapid clearance of bendamustine, 1 or more longer-lived [14C] bendamustine-derived materials remain in the plasma. These longer-lived materials likely include by-products of alkylation. As previously noted, bendamustine volume of distribution was small (Vss∼20 L). The steady-state volume of distribution for TRA was ∼50 L. These results confirm previous data and provide evidence that neither bendamustine nor TRA are extensively distributed into the tissues. All 6 patients withdrew prior to completion of period B due to disease progression (n = 4), an adverse event (n = 1), or refusal to continue treatment (n=1). Bendamustine was well tolerated when administered at a dosage of 120 mg/m2 for 2 to 3 cycles. The most frequent treatment-related adverse events were fatigue (50%) and vomiting (50%). A grade 3/4 absolute lymphocyte count decrease occurred in all patients at some point during the study. There were no other grade 3/4 hematologic adverse events. Conclusions:Bendamustine was extensively metabolized via multiple metabolic pathways, with subsequent excretion in both urine and feces. Bendamustine accumulation is not anticipated in cancer patients with renal or hepatic impairment due to the dose administration schedule and short intermediate half-life. Adverse events and hematologic changes were consistent with the known safety profile of bendamustine.This research was sponsored by and conducted by Cephalon, Inc., Frazer, PA. Disclosures:Darwish:Cephalon, Inc.: Employment. D'Andrea:Cephalon, Inc.: Employment. Bond:Cephalon, Inc.: Employment. Hellriegel:Cephalon, Inc.: Employment.

Road traffic accidents and psychotropic medication use in the Netherlands: a case–control study

To examine the association between the use of commonly prescribed psychotropic medications and road traffic accident risk. A record-linkage database was used to perform a case-control study in The Netherlands. The data came from three sources: pharmacy prescription data, police traffic accident data and driving licence data. Cases were defined as drivers, who had a traffic accident that required medical assistance between 2000 and 2007. Controls were defined as adults, who had a driving licence and had no traffic accident during the study period. Four controls were matched for each case. The following psychotropic medicine groups were examined: antipsychotics, anxiolytics, hypnotics and sedatives, and antidepressants stratified in the two groups, SSRIs and other antidepressants. Various variables, such as age, gender, medicine half-life and alcohol use, were considered for the analysis. Three thousand nine hundred and sixty-three cases and 18,828 controls were included in the case-control analysis. A significant association was found between traffic accident risk and exposure to anxiolytics (OR = 1.54, 95% CI 1.11, 2.15), and SSRIs (OR = 2.03, 95% CI 1.31, 3.14). A statistically significant increased risk was also seen in chronic anxiolytic users, females and young users (18 to 29 years old), chronic SSRI users, females and middle-aged users (30 to 59 years old), and intermediate half-life hypnotic users. The results of this study support previous findings and confirm that psychoactive medications can constitute a problem in traffic safety. Both health care providers and patients should be properly informed of the potential risks associated with the use of these medicines.

A Novel Labeling Approach Identifies Three Stability Levels of Acetylcholine Receptors in the Mouse Neuromuscular Junction In Vivo

BackgroundThe turnover of acetylcholine receptors at the neuromuscular junction is regulated in an activity-dependent manner. Upon denervation and under various other pathological conditions, receptor half-life is decreased.Methodology/Principal FindingsWe demonstrate a novel approach to follow the kinetics of acetylcholine receptor lifetimes upon pulse labeling of mouse muscles with 125I-α-bungarotoxin in vivo. In contrast to previous assays where residual activity was measured ex vivo, in our setup the same animals are used throughout the whole measurement period, thereby permitting a dramatic reduction of animal numbers at increased data quality. We identified three stability levels of acetylcholine receptors depending on the presence or absence of innervation: one pool of receptors with a long half-life of ∼13 days, a second with an intermediate half-life of ∼8 days, and a third with a short half-life of ∼1 day. Data were highly reproducible from animal to animal and followed simple exponential terms. The principal outcomes of these measurements were reproduced by an optical pulse-labeling assay introduced recently.Conclusions/SignificanceA novel assay to determine kinetics of acetylcholine receptor turnover with small animal numbers is presented. Our data show that nerve activity acts on muscle acetylcholine receptor stability by at least two different means, one shifting receptor lifetime from short to intermediate and another, which further increases receptor stability to a long lifetime. We hypothesize on possible molecular mechanisms.

Determination of chemical weathering rates from U series nuclides in soils and weathering profiles: Principles, applications and limitations

The development of U-series nuclides for investigating weathering processes has been significantly stimulated by the analytical improvement made over the last decades in measuring the 238 U series with intermediate half-lives (i.e., 234 U– 230 Th– 226 Ra). It is proposed in this paper to present principles and methods that are now being developed to determine weathering rates from the study of U-series nuclides in soils and weathering profiles. Mathematical approaches, developed to calculate such rates, are based on some implicit assumptions that are also presented and must be kept in mind if one wants to correctly interpret the obtained ages.

Plasmodium vivax recurrence following falciparum and mixed species malaria: risk factors and effect of antimalarial kinetics.

Plasmodium vivax malaria commonly follows treatment of falciparum malaria in regions of co-endemicity. This is an important cause of preventable morbidity. We examined the factors contributing to the risk of recurrence of P. vivax infection after treatment of acute falciparum malaria in a series of clinical trials conducted on the Thai-Myanmar border from 1991 through 2005. Overall, 10,549 patients (4960 children aged <15 years and 5589 adults) were treated for falciparum malaria; of these patients, 9385 (89.0%) had Plasmodium falciparum monoinfection and 1164 (11.0%) had mixed P. falciparum/P. vivax infections according to microscopic examinations performed at screening. The cumulative proportion of patients with P. falciparum infection recurrence by day 63 was 21.5% (95% confidence interval [CI], 20.3%-22.8%), and the cumulative proportion with P. vivax infection recurrence was 31.5% (95% CI, 30.1%-33.0%). Significant risk factors for P. vivax infection recurrence were mixed infection at enrollment, male sex, younger age, lower hematocrit, higher asexual P. falciparum parasite density (P < .001 for all factors), and P. falciparum gametocytemia at enrollment (P = .001). By day 63, the cumulative risk of vivax malaria after P. falciparum monoinfection was 51.1% (95% CI, 46.1%-56.2%) after treatment with rapidly eliminated drugs (t(1/2) <1 day), 35.3% (95% CI, 31.8%-39.0%) after treatment with intermediate half-life drugs (t(1/2) 1-7 days), and 19.6% (95% CI, 18.1%-21.3%) after treatment with slowly eliminated drugs (t(1/2) > 7 days) (P < .001, by test for trend). Artemisinin-based combinations containing mefloquine or piperaquine, compared with the artemether-lumefantrine and artesunate-atovaquone-proguanil combinations, were associated with a 3.6-fold to 4.2-fold lower adjusted hazard ratio for P. vivax infection recurrence within 63 days after pure or mixed P. falciparum infections (P < .001, for comparisons with artesunate-mefloquine). On the Thai-Myanmar border, P. vivax is the most common cause of parasitological failure after treatment for falciparum malaria. Slowly eliminated antimalarials reduce the risk of early P. vivax infection recurrence.

The diversity of protein turnover and abundance under nitrogen-limited steady-state conditions in Saccharomyces cerevisiae

To establish more advanced models of molecular dynamics within cells, protein characteristics such as turnover rate and absolute instead of relative abundance have to be analyzed. We applied a proteomics strategy to analyze protein degradation and abundance in Saccharomyces cerevisiae. We used steady-state chemostat cultures to ascertain well-defined growth conditions and nitrogen limited media, which allowed us to rapidly switch from (14)N to (15)N-isotope containing media and to monitor the decay of the (14)N mono-isotope signals in time. We acquired both protein abundance information and degradation rates of 641 proteins. Half-lives of individual proteins were very diverse under nitrogen-limited steady-state conditions, ranging from less than 30 min to over 20 h. Proteins that act as single physical complexes do not always show alike half-lives. For example the chaperonin-containing TCP-1 complex showed similar intermediate half-lives ranging from 7 to 20 h. In contrast, the ribosome exhibited a wide diversity of half-lives ranging from 2.5 to over 20 h, although their cellular abundances were rather similar. The stabilities of proteins involved in the central sugar metabolism were found to be intermediary, except for the glycolytic enzymes Hxk1p and Fba1p and the TCA-cycle proteins Lsc2p and Kgd1p, which showed half-lives of over 20 h. These data stress the need for inclusion of quantitative data of protein turn-over rates in yeast systems biology.

T-cell antagonism by short half-life pMHC ligands can be mediated by an efficient trapping of T-cell polarization toward the APC.

T-cell activation results from productive T-cell receptor (TCR) engagement by a cognate peptide-MHC (pMHC) complex on the antigen presenting cell (APC) surface, a process leading to the polarization of the T-cell secretory machinery toward the APC interface. We have previously shown that the half-life of the TCR/pMHC interaction and the density of pMHC on the APC are two parameters determining T-cell activation. However, whether the half-life of the TCR/pMHC interaction can modulate the efficiency of T-cell secretory machinery polarization toward an APC still remains unclear. Here, by using altered peptide ligands conferring different half-lives to the TCR/pMHC interaction, we have tested how this parameter can control T-cell polarization. We observed that only TCR/pMHC interactions with intermediate half-lives can promote the assembly of synapses that lead to T-cell activation. Strikingly, intermediate half-life interactions can be competed out by short half-life interactions, which can efficiently promote T-cell polarization and antagonize T-cell activation that was induced by activating intermediate half-life interactions. However, short TCR/pMHC interactions fail at promoting phosphorylation of signaling molecules at the T-cell-APC contact interface, which are needed for T-cell activation. Our data suggest that although intermediate half-life pMHC ligands promote assembly of activating synapses, this process can be inhibited by short half-life antagonistic pMHC ligands, which promote the assembly of non activating synapses.

Rapid Sequence Intubation: A Review of Recent Evidences

Rapid sequence intubation is an essential bullet in the maintenance of patency of the airway during intubation in emergency. It is a valid method in all those situations where you can not determine whether the patient is fasting or not. But RSI is not applicable in all critically ill patients. The presence of severe acidosis, depletion of intravascular volume, heart failure and severe pulmonary disease may complicate the pre-induction period as the induction, leading to the onset of vasodilatation and hypotension. Another complication is represented by Hypoxemia during the manoeuvre. The algorithm of RSI consists in six steps: pre-oxygenation, premedication, myo-relaxation and induction, intubation, primary and secondary confirmation, post-intubation patient management. Propofol has replaced Thiopental as the most common intravenous ipnotic. In hypotensive patients Ketamine represents a viable alternative. Succinylcholine is the most common neuromuscular relaxant used in the RSI. The not depolarizing NMBAs are an alternative to Succinylcholine. Among these, the most important is the Rocuronium. This drug is characterized by a fairly rapid onset (1-2 min) and an intermediate half-life (45-70 min). The onset depends on the dosage used. The problem that limits the use of Rocuronium is the fact that its duration of action is much longer than that of Succinylcholine, especially when used at higher doses. This problem can be solved through the use of Sugammadex. As a muscle relaxant chelating Sugammadex antagonizes the effects induced by Rocuronium on muscle tissue and quickly resolve the blockade.

Calibration of nitric oxide flux generation from diazeniumdiolate [rad]NO donors

The 1-(secondary amino) diazen-1-ium-1,2-diolates (NONOates) are the most commonly utilized nitric oxide ( NO, nitrogen monoxide) donor because of the ability of different NONOates to spontaneously break down liberating NO at different rates, which can be utilized to control NO fluxes. However, the parameters that determine these fluxes of NO generation, half-lives and stoichiometry of NO per donor, can vary significantly with specific experimental conditions in addition to the donor chosen. Here we report straightforward methods that can be used to determine these parameters. For donors of intermediate half-life (10–80 min) a real-time oxymyoglobin (oxyMb) assay can be analyzed to simultaneously determine both the half-life and the total amount of NO liberated, from which the NO flux can be obtained for any given donor concentration. The half-lives obtained by oxyMb assay are very similar to those obtained by following NONOate decomposition kinetics spectrophotometrically, and a survey of several NONOates from different commercial sources show consistent results. These data provide validation for the methodologies employed. In addition, procedures are described for calibration of donors with shorter (<10 min) and longer (>80 min) half-lives. These procedures can be used to reproducibly and routinely calibrate NO fluxes for a variety of donors under any specific condition.

High efficiency production and purification of 86Y based on electrochemical separation

As an intermediate half-life positron emitter 86Y is an attractive radioisotope for positron emission tomography (PET) studies, particularly for patient specific dosimetry planning of 90Y-based radiotherapy procedures. It can be conveniently produced by a small-sized cyclotron via the 86Sr(p, n) 86Y nuclear reaction. The optimization of the electrochemical separation of 86Y from the target material and its purification was done by modeling the whole production cycle using 90Y. The radionuclide was isolated using four electrodes in two electrolytic steps. In the first step two Pt plate anodes and a Pt Winkler cathode were used and the electro-deposition yield was determined in constant current mode of operation. In addition, the influence of pH on the efficiency of this first step was investigated. The second electrolysis, with Winkler electrode as anode and a Pt wire as cathode, was also performed in constant current mode of operation. The kinetics of recovery of the deposited activity on the Pt wire was investigated in acidic solutions. The optimized electrochemical method was then applied for 86Y separation and purification. This modified procedure was proved to be faster and simpler than the previously proposed electrochemical techniques and is more convenient for automation of the routine production of 86Y.

The Impact of Benzodiazepines on Safe Driving

Objective. Benzodiazepines are prescribed to relieve anxiety and aid sleep. Studies demonstrate that benzodiazepines increase odds of crash involvement, but little evidence exists regarding their impact on crash responsibility. We examined the impact of benzodiazepines on crash responsibility by drug half-life and driver age, using a case-control design with drivers aged 20 and over involved in fatal crashes in the United States from 1993–2006. Methods. Drivers (all with BAC = 0) were classified as having no benzodiazepines detected versus short, intermediate, or long half-life benzodiazepines. Cases were drivers with at least one potentially unsafe driving action (UDA) in relation to the crash (e.g., speeding), a proxy measure for crash responsibility; controls had no UDAs recorded. Odds ratios (ORs) of any UDA by benzodiazepines half-life exposure were calculated, with adjustment for age, sex, other medication usage, and prior driving record. Results. Compared with drivers not using benzodiazepines, drivers taking intermediate or long half-life benzodiazepines demonstrated increased odds of an UDA from ages 25 (intermediate OR: 1.59; 95% CI = 1.08, 2.33; long OR: 1.68; 95% CI = 1.34, 2.12) to 55 (intermediate OR: 1.50; 95% CI = 1.09, 2.06; long OR: 1.33; 95% CI = 1.12, 1.57). Drivers taking short half-life benzodiazepines did not demonstrate increased odds compared to drivers not using benzodiazepines. Conclusions. Given the potential impact of benzodiazepines on driver safety, further experimental research is needed to better understand the effect of benzodiazepines on crash responsibility.

Mise à jour sur les considérations pharmacocinétiques, pharmacodynamiques et les interactions médicamenteuses dans le choix d’une benzodiazépine

Over the past 50 years, significant clinical information has been obtained on numerous aspects of benzodiazepines, notably on their pharmacokinetics and pharmacodynamic properties, drug interactions and therapeutic usage. The main objective of this review is to determine which of these aspects a clinician should consider when choosing a benzodiazepine. Benzodiazepines can be distinguished by their half-lives and those with an intermediate half-life (6–12 h) are indicated for punctual usage and for initial insomnia while those with a longer half-life (over 12 h) are indicated for clinical situations requiring sustained therapeutic treatment. Benzodiazepines with longer half-lives are more at risk of causing side effects due to accumulation of the drug. Most, but not all, benzodiazepines are metabolized by the liver and should be used carefully in patients known to have a hepatic disease, in geriatric patients or in patients taking other medication modifying hepatic metabolism. In these cases, lorazepam, oxazepam or temazepam should be chosen because they are less dependant on hepatic metabolism. Most but not all benzodiazepines are metabolized by the intestinal and hepatic cytochrome P-450 3A4 system. A number of medication namely ketoconazole, erythromycin, corticosteroids, fluoxetine, fluvoxamine, sertraline, calcium channel blockers and grapefruit juice may increase plasma concentrations of some benzodiazepines by inhibiting P-450 3A4 cytochrome activity. Cigarette smoking has been reported to significantly increase the clearance of alprazolam. The mechanism of action of benzodiazepines consists in increasing the inhibitory effect of gamma-aminobutyrique acid (GABA) in the central nervous system. GABA receptor contains five sub-units organised in the form of a rosette. The canal in the centre of the rosette permits the entrance of chloride ions and the opening of the channel is modulated by GABA through changing the configuration of the proteins constituting the rosette. Benzodiazepines alone have no inhibitory activity on neurones but will potentiate the effect of GABA by binding to the sub-units α, β and γ of the rosette. Binding to the sub-unit α 1 localised mainly in the brain stem will increase sedation while binding to the sub-unit α 2 in the limbic system will confer anxiolytic properties to benzodiazepines. No differences among benzodiazepines have been reported concerning their binding to different sub-units. However, clonazepam does appear to modify serotoninergic transmission and this pharmacodynamic characteristic may increase clonazepam inhibitory properties and also stabilise mood in patient with unipolar depression. Benzodiazepines prolonged usage will modify the DNA expression and decrease synthesis m-RNA coding for sub-units α 1, α 2, α 3 and possibly β. These modifications in the composition of GABA receptors are thought to be a mechanism of autoregulation of the receptor and could explain tolerance which is observed in prolonged usage of benzodiazepines. Overall, pharmacokinetics properties and drug interaction remain the most important characteristics when choosing a benzodiazepine while pharmacodynamic properties have little relevance because differences are not significant within this class of medication.

A Phase 1 Pharmacokinetic and Pharmacodynamic Study of the Histone Deacetylase Inhibitor Belinostat in Patients with Advanced Solid Tumors

To determine the safety, dose-limiting toxicity, maximum tolerated dose, and pharmacokinetic and pharmacodynamic profiles of the novel hydroxamate histone deacetylase inhibitor belinostat (previously named PXD101) in patients with advanced refractory solid tumors. Sequential dose-escalating cohorts of three to six patients received belinostat administered as a 30-min i.v. infusion on days 1 to 5 of a 21-day cycle. Pharmacokinetic variables were evaluated at all dose levels. Pharmacodynamic measurements included acetylation of histones extracted from peripheral blood mononuclear cells, caspase-dependent cleavage of cytokeratin-18, and interleukin-6 levels. Forty-six patients received belinostat at one of six dose levels (150-1,200 mg/m(2)/d). Dose-limiting toxicities were grade 3 fatigue (one patient at 600 mg/m(2); one patient at 1,200 mg/m(2)), grade 3 diarrhea combined with fatigue (one patient at 1,200 mg/m(2)), grade 3 atrial fibrillation (one patient at 1,200 mg/m(2); one patient at 1,000 mg/m(2)), and grade 2 nausea/vomiting leading to inability to complete a full 5-day cycle (two patients at 1,000 mg/m(2)). The maximum tolerated dose was 1,000 mg/m(2)/d. I.v. belinostat displayed linear pharmacokinetics with respect to C(max) and AUC. The intermediate elimination half-life was 0.3 to 1.3 h and was independent of dose. Histone H4 hyperacetylation was observed after each infusion and was sustained for 4 to 24 h in a dose-dependent manner. Increases in interleukin-6 levels were detected following belinostat treatment. Stable disease was observed in a total of 18 (39%) patients, including 15 treated for > or =4 cycles, and this was associated with caspase-dependent cleavage of cytokeratin-18. Of the 24 patients treated at the maximum tolerated dose (1,000 mg/m(2)/d), 50% achieved stable disease. I.v. belinostat is well tolerated, exhibits dose-dependent pharmacodynamic effects, and has promising antitumor activity.

¿Se hace un buen uso de las benzodiazepinas en el anciano?

Benzodiazepines are substances susceptible of producing drug dependence in addition to tolerability to sedative effects and frequent interactions when associated with other drugs. Thus, use of long half life benzodiazepines and inadequate intermediate and short half life dosage is related with falls and fractures in elderly patients. A retrospective study was conducted on the official prescriptions made during 2000-2003 and the daily dose defined per thousand patients/day (DDD/I) was used as a measurement of drug consumption. Prescription of benzodiazepines that are eliminated by oxidative metabolism should be revaluated and modified by other of conjunctive metabolism when treating elderly patients to decrease adverse reactions such as excess sedation, risk of falls and associated fractures.

Radioiodinated versus Radiometal-Labeled Anti–Carcinoembryonic Antigen Single-Chain Fv-Fc Antibody Fragments: Optimal Pharmacokinetics for Therapy

Antibody fragments with optimized pharmacokinetic profiles hold potential for detection and therapy of tumor malignancies. We studied the behavior of three anti-carcinoembryonic antigen (CEA) single-chain Fv-Fc (scFv-Fc) variants (I253A, H310A, and H310A/H435Q; Kabat numbering system) that exhibited differential serum persistence. Biodistribution studies done on CEA-positive tumor xenografted mice revealed that the 111In-labeled I253A fragment with the slowest clearance kinetics (T1/2beta, 27.7 h) achieved the highest tumor uptake (44.6% ID/g at 24 h), whereas the radiometal-labeled H310A/H435Q fragment with the most rapid elimination (T1/2beta, 7.05 h) reached a maximum of 28.0% ID/g at 12 h postinjection. The H310A protein was characterized by both intermediate serum half-life and tumor uptake. The 111In-based biodistribution studies showed that all three fragments were eliminated primarily through the liver, and hepatic radiometal activity correlated with the rate of fragment clearance. The 111In-labeled H310A/H435Q protein exhibited the highest liver uptake (23.5% ID/g at 24 h). Metabolism of the 125I-labeled scFv-Fc proteins resulted in low normal organ activity. Finally, the 125I/111In biodistribution data allowed for dose estimations, which suggest the 131I-labeled scFv-Fc H310A/H435Q as a promising candidate for radioimmunotherapy.

Optimization of the production of [61Cu]Diacetyl-bis(N4-methylthiosemicarbazone) for PET studies

Copper-61 produced via the natZn(p,x)61Cu nuclear reaction was used for the preparation of [61Cu]diacetyl-bis(N4-methylthiosemicarbazone) ([61Cu]ATSM) (4) using a house-made ATSM ligand. After a proton irradiation of an electroplated zinc layer by 22 MeV protons at 180 mA for 3.2 hours, 61Cu was recovered by two-step chromatography using a cation and an anion exchange column. About 222 GBq (6.00 Ci) of 61Cu2+ was obtained with a radiochemical separation yield of more than 95% and a radionuclidic purity of better than 99%. Colorimetric methods showed that traces of chemical impurities in the product were below the accepted limits. The [61Cu]ATSM production was optimized for reaction conditions (buffer concentration and temperature) with a radiochemical yield of higher than 80%, radiochemical purity of better than 98% and a specific activity of about 246 Ci/mmol. The produced [61Cu]ATSM is a PET radiotracer for hypoxia imaging with an intermediate half life and a satisfactory quality, suitable for future PET studies.