Center for Biologics Evaluation and Research

About: Center for Biologics Evaluation and Research is a facility organization based out in Silver Spring, Maryland, United States. It is known for research contribution in the topics: Virus & Vaccination. The organization has 3024 authors who have published 4648 publications receiving 228078 citations. The organization is also known as: CBER.

Glucuronidation of 3'-azido-3'-deoxythymidine (zidovudine) by human liver microsomes : relevance to clinical pharmacokinetic interactions with atovaquone, fluconazole, methadone, and valproic acid

Abstract: Zidovudine (3′-azido-3′-deoxythymidine [AZT]), an antiviral nucleoside analog effective in the treatment of human immunodeficiency virus infection, is primarily metabolized to an inactive glucuronide form, GAZT, via uridine-5′-diphospho-glucuronosyltransferase (UGT) enzymes. UGT enzymes exist as different isoforms, each exhibiting substrate specificity. Published clinical studies have shown that atovaquone, fluconazole, methadone, and valproic acid decreased GAZT formation, presumably due to UGT inhibition. The effect of these drugs on AZT glucuronidation was assessed in vitro by using human hepatic microsomes to begin understanding in vitro-in vivo correlations for UGT metabolism. The concentrations of each drug studied were equal to those reported with the usual clinical doses and at concentrations at least 10 times higher than would be expected with these doses. High-performance liquid chromatography was used to assess the respective metabolism and formation of AZT and GAZT. All four drugs exhibited concentration-dependent inhibition of AZT glucuronidation. The respective concentrations of atovaquone and methadone which caused 50% inhibition of GAZT were >100 and 8 μg/ml, well above their usual clinical concentrations. Fluconazole and valproic acid exhibited 50% inhibition of GAZT at 50 and 100 μg/ml, which are within the clinical ranges of 10 to 100 and 50 to 100 μg/ml, respectively. These data suggest that inhibition of AZT glucuronidation may be more clinically significant with concomitant fluconazole and valproic acid. Factors such as inter- and intraindividual pharmacokinetic variability and changes in AZT intracellular concentrations should be considered as other mechanisms responsible for changes in AZT pharmacokinetics with concomitant therapies.

Fas Ligand Induction in Human NK Cells Is Regulated by Redox Through a Calcineurin-Nuclear Factors of Activated T Cell-Dependent Pathway

Abstract: Fas ligand (FasL) on cytotoxic lymphocytes is important for mediating apoptosis of activated lymphocytes and other target cells. We have reported that NK cell functions, such as proliferation, cell death, and killing activity, are subject to regulation by cellular redox status. Here, we report that expression of FasL protein and mRNA in activated NK cells is also regulated by redox. Ligation of CD16 on IL-2-preactivated NK cells resulted in reduction of intracellular peroxide level as well as induction of FasL expression. This CD16-induced FasL expression was suppressed by oxidative stress, including thiol deprivation or treatment with hydrogen peroxide (H 2 O 2 ). Addition of thiol-reducing compounds, such as l-cystine, 2-ME, or N -acetyl cysteine, restored FasL expression. These data suggest that CD16 stimulation requires cellular reducing status for FasL induction in NK cells. Because FasL gene activation following CD16 cross-linking is regulated by the NF of activated T cells (NFAT), we examined the effect of oxidative stresses on NFAT activation. Electrophoretic mobility shift assays revealed that both thiol insufficiency and H 2 O 2 treatment suppressed DNA-binding activity of NFAT and that addition of thiol-reducing compounds reversed or even enhanced it. Furthermore, these oxidative stresses inhibited activity of calcineurin, a serine/threonine phosphatase that regulates NFAT activation. These results suggest that suppression of calcineurin and NFAT activation is a mechanism by which oxidative stress inhibits FasL induction in activated NK cells and further support the hypothesis that thiol-reducing compounds might be required for maintenance of optimal NK functions under physiologic oxidative conditions.

Suppressive Oligodeoxynucleotides Inhibit Th1 Differentiation by Blocking IFN-γ- and IL-12-Mediated Signaling

Abstract: Repetitive TTAGGG motifs present at high frequency in mammalian telomeres can suppress Th1-mediated immune responses. Synthetic oligonucleotides (ODN) containing TTAGGG motifs mimic this activity and have proven effective in the prevention/treatment of certain Th1-dependent autoimmune diseases. This work explores the mechanism by which suppressive ODN block the induction of Th1 immunity. Findings indicate that these ODN inhibit IFN-gamma-induced STAT1 phosphorylation and IL-12-induced STAT3 and STAT4 phosphorylation. As a result, T-bet expression is reduced as is the maturation of naive CD4+ cells into Th1 effectors. These changes indirectly support the generation of Th2-dominated immune responses. Suppressive ODN may thus represent a novel approach to influence the Th1:Th2 balance in vivo.

Voluntary exploratory data submissions to the US FDA and the EMA: experience and impact

Abstract: Heterogeneity in the underlying mechanisms of disease processes and inter-patient variability in drug responses are major challenges in drug development. To address these challenges, biomarker strategies based on a range of platforms, such as microarray gene-expression technologies, are increasingly being applied to elucidate these sources of variability and thereby potentially increase drug development success rates. With the aim of enhancing understanding of the regulatory significance of such biomarker data by regulators and sponsors, the US Food and Drug Administration initiated a programme in 2004 to allow sponsors to submit exploratory genomic data voluntarily, without immediate regulatory impact. In this article, a selection of case studies from the first 5 years of this programme - which is now known as the voluntary exploratory data submission programme, and also involves collaboration with the European Medicines Agency - are discussed, and general lessons are highlighted.

A Live Attenuated Influenza A(H5N1) Vaccine Induces Long-Term Immunity in the Absence of a Primary Antibody Response

Abstract: (See the editorial commentary by Falsey on pages 1857–9.) Since the first reported human infections by avian influenza A(H5N1) in Hong Kong in 1997 [1], >600 cases of influenza A(H5N1) infection with >380 deaths have been reported to the World Health Organization from 15 countries [2]. Vaccines are the most effective option for the control and prevention of influenza virus infection. Since 2005, there has been a global effort to develop and evaluate vaccines against influenza A(H5N1) and other influenza viruses of pandemic potential [3], using traditional and novel strategies, with the goal of rapid vaccine development and deployment in the event of a pandemic. Live attenuated influenza vaccines (LAIVs) bearing the 6 internal protein genes of the A/AA/6/60 cold-adapted (AA ca) donor virus and the hemagglutinin (HA) and neuraminidase (NA) genes from seasonal human influenza viruses are licensed in the United States for healthy individuals 2–49 years of age. LAIVs may have great potential for use during influenza pandemics by virtue of their high yield in eggs, ability to rapidly induce immunity, and ability to provide protection against antigenically drifted viruses [4, 5]. As part of our efforts to prepare vaccines for influenza viruses with pandemic potential, we generated candidate pandemic LAIVs (pLAIVs) against 2 influenza A(H5N1) strains that caused human infections, A/Hong Kong/213/2003 (HK 2003) and A/VietNam/1203/2004 (VN 2004), by plasmid-based reverse genetics on the AA ca backbone. On the basis of promising preclinical data in mice and ferrets [6], phase 1 clinical trials of the safety and immunogenicity of the vaccines for healthy adults were undertaken in 2007 [7]. In these trials, 2 doses of 107.5 50% tissue culture infectious dose were administered 4–8 weeks apart. The vaccines were generally well tolerated. Vaccine virus was detected by culture or real-time reverse-transcription polymerase chain reaction in few subjects. Serum antibody responses were not detected by the hemagglutination inhibition (HAI) assay or microneutralization (MN) assay in any subject after either dose of the HK 2003 vaccine and were only detected in 1 subject each following the first and second dose of the VN 2004 vaccine [7]. These data suggested that the influenza A(H5N1) HK 2003 and VN 2004 pLAIVs were poorly infectious and poorly immunogenic in humans. Unadjuvanted inactivated influenza A(H5N1) subvirion vaccines (ISIVs) are also poorly immunogenic in humans, requiring up to 2 doses of 90 μg each to achieve an HAI titer of 1:40 in >50% of subjects [8]. However, studies of other influenza A(H5N1) vaccines led us to hypothesize that subclinical priming may have been achieved in the influenza A(H5N1) pLAIV studies and that these responses were undetectable by the traditional methods used to measure them. VN 2004 pLAIV primed for a robust antibody response to inactivated influenza A(H5N1) vaccine in ferrets [9], and clinical studies demonstrated that robust serum antibody responses were observed following booster vaccinations with influenza A(H5N1) ISIVs even in individuals who had no detectable antibody response to the initial vaccine [10–16]. On the basis of these reports, we hypothesized that previous receipt of an influenza A(H5N1) pLAIV would immunologically prime subjects for a robust response that could subsequently be unmasked by administration of a dose of influenza A(H5N1) ISIV [8].