Predictive value of local control by 4'-[methyl-11C]-thiotymidine PET volume parameters in p16-negative oropharyngeal, hypopharyngeal, and supraglottic squamous cell carcinoma

PURPOSE

We investigated the potential of baseline 4'-[methyl- 11 C]-thiothymidine ([ 11 C]4DST) PET for predicting loco-regional control of head and neck squamous cell carcinoma (HNSCC).

METHODS

A retrospective analysis was performed using volumetric parameters, such as SUVmax, proliferative tumor volume (PTV), and total lesion proliferation (TLP), of pretreatment [ 11 C]4DST PET for 91 patients with HNSCC with primary lesions in the oral cavity, hypopharynx, supraglottis, and oropharynx, which included p16-negative patients. PTV and TLP were calculated for primary lesions and metastatic lymph nodes combined. We examined the association among the parameters and relapse-free survival and whether case selection focused on biological characteristics improved the accuracy of prognosis prediction.

RESULTS

The area under the curves (AUCs) using PTV and TLP were high for the oropharyngeal/hypopharyngeal/supraglottis groups (0.91 and 0.87, respectively), whereas that of SUVmax was 0.66 ( P  < 0.01). On the other hand, the oral group had lower AUCs for PTV and TLP (0.72 and 0.77, respectively). When all cases were examined, the AUCs using PTV and TLP were 0.84 and 0.83, respectively.

CONCLUSION

Baseline [ 11 C]4DST PET/CT volume-based parameters can provide important prognostic information with p16-negative oropharyngeal, hypopharyngeal, and supraglottic cancer patients.

Tritiated thymidine induces developmental delay, oxidative stress and gene overexpression in developing zebrafish (Danio rerio)

Tritium is a betta emitter radionuclide. Being an isotope of hydrogen, it is easily transferred to different environmental compartments, and to human and non-human biota. Considering that tritium levels are expected to rise in the upcoming decades with the development of nuclear facilities producing tritium using fission processes, investigating the potential toxicity of tritium to human and non-human biota is necessary. Tritiated thymidine, an organic form of tritium, has been used in this study to assess its toxicity on fish embryo development. Zebrafish embryos (3.5 hpf; hours post fertilization) have been exposed to tritiated thymidine at three different activity concentrations (7.5; 40; 110 kBq/mL) for four days. These experiments highlighted that zebrafish development was affected by the exposure to organic tritium, with smaller larvae at 3 dpf after exposure to the two lowest dose rates (22 and 170 µGy/h), a delayed hatching after exposure to the two highest dose rates (170 and 470 µGy/h), an increase in the spontaneous tail movement (1 dpf) and a decrease in the heartbeat (3 dpf) after exposure to the highest dose rate. The results also highlighted an increase in ROS production in larvae exposed to the intermediate dose rate. A dysregulation of many genes, involved in apoptosis, DNA repair or oxidative stress, was also found after 1 day of exposure to the lowest tritium dose rate. Our results thus suggest that exposure to tritiated thymidine from a dose rate as low as 22 µGy/h can lead to sublethal effects, with an effect on the development, dysregulation of many genes and increase of the ROS production. This paper provides valuable information on toxic effects arising from the exposure of fish to an organic form of tritium, which was the main objective of this study.

Hybrids of 1,4-Naphthoquinone with Thymidine Derivatives: Synthesis, Anticancer Activity, and Molecular Docking Study

One of the most essential health problems is cancer, the first or second cause of death worldwide. Head and neck cancers are hard to detect due to non-specific symptoms. The treatment often relies on a combination of radio and chemotherapy. For this reason, the research of new anticancer compounds is fundamental. The natural and synthetic compounds with 1,4-naphthoquinone scaffold is characterized by high anticancer activity. The study aimed to evaluate the synthesis and anticancer activity of hybrids 1,4-naphthoquinone with thymidine derivatives. The series of compounds allows us to check the influence of the substituent in the C3' position of the thymidine moiety on the cytotoxicity against squamous cancer cell lines (SCC-9 and SCC-25) and submandibular gland cancer (A-253). An annexin V/propidium iodide (PI) co-staining assay shows that derivatives cause the apoptotic in SCC-25 and A-253 cell lines. The molecular docking study examined the interaction between the active site of the BCL-2 protein and the hybrids.

Evaluation of deoxythymidine-based cationic amphiphiles as antimicrobial, antibiofilm, and anti-inflammatory agents

OBJECTIVES

We recently designed a series of cationic deoxythymidine-based amphiphiles that mimic the cationic amphipathic structure of antimicrobial peptides (AMPs). Among these amphiphiles, ADG-2e and ADL-3e displayed the highest selectivity against bacterial cells. In this study, ADG-2e and ADL-3e were evaluated for their potential as novel classes of antimicrobial, antibiofilm, and anti-inflammatory agents.

METHODS

Minimum inhibitory concentrations of ADG-2e and ADL-3e against bacteria were determined using the broth microdilution method. Proteolytic resistance against pepsin, trypsin, α-chymotrypsin, and proteinase K was determined by radial diffusion and HPLC analysis. Biofilm activity was investigated using the broth microdilution and confocal microscopy. The antimicrobial mechanism was investigated by membrane depolarization, cell membrane integrity analysis, scanning electron microscopy (SEM), genomic DNA influence and genomic DNA binding assay. Synergistic activity was evaluated using checkerboard method. Anti-inflammatory activity was investigated using ELISA and RT-PCR.

RESULTS

ADG-2e and ADL-3e showed good resistance to physiological salts and human serum, and a low incidence of drug resistance. Moreover, they exhibit proteolytic resistance against pepsin, trypsin, α-chymotrypsin, and proteinase K. ADG-2e and ADL-3e were found to kill bacteria by an intracellular target mechanism and bacterial cell membrane-disrupting mechanism, respectively. Furthermore, ADG-2e and ADL-3e showed effective synergistic effects when combined with several conventional antibiotics against methicillin-resistant Staphylococcus aureus (MRSA) and multidrug-resistant Pseudomonas aeruginosa (MDRPA). Importantly, ADG-2e and ADL-3e not only suppressed MDRPA biofilm formation but also effectively eradicated mature MDRPA biofilms. Furthermore, ADG-2e and ADL-3e drastically decreased tumor necrosis factor-α (TNF-α) and interleukin-6 (IL-6) gene expression and protein secretion in lipopolysaccharide (LPS)-stimulated macrophages, implying potent anti-inflammatory activity in LPS-induced inflammation.

CONCLUSION

Our findings suggest that ADG-2e and ADL-3e could be further developed as novel antimicrobial, antibiofilm, and anti-inflammatory agents to combat bacterial infections.

In silico and POM analysis for potential antimicrobial agents of thymidine analogs by using molecular docking, molecular dynamics and ADMET profiling

Nucleoside analogs are an important, well-established class of clinically useful medicinal agents that exhibit potent antimicrobial activity. Thus, we designed to explore the synthesis and spectral characterization of 5'-O-(myristoyl)thymidine esters (2-6) for in vitro antimicrobial, molecular docking, molecular dynamics, SAR, and POM analyses. An unimolar myristoylation of thymidine under controlled conditions furnished the 5'-O-(myristoyl)thymidine and it was further converted into four 3'-O-(acyl)-5'-O-(myristoyl)thymidine analogs. The chemical structures of the synthesized analogs were ascertained by analyzing their physicochemical, elemental, and spectroscopic data. In vitro antimicrobial tests along with PASS, prediction indicated expectant antibacterial functionality of these thymidine esters compared to the antifungal activities. In support of this observation, their molecular docking studies have been performed against lanosterol 14α-demethylase (CYP51A1) and Aspergillus flavus (1R51) and significant binding affinities and non-bonding interactions were observed. The stability of the protein-ligand complexes was monitored by a 100 ns MD simulation and found the stable conformation and binding mode in a stimulating environment of thymidine esters. Pharmacokinetic predictions were studied to assess their ADMET properties and showed promising results in silico. SAR investigation indicated that acyl chains, lauroyl (C-12) and myristoyl (C-14), combined with deoxyribose, were most effective against the tested bacterial and fungal pathogens. The POM analyses provide the structural features responsible for their combined antibacterial/antifungal activity and provide guidelines for further modifications, with the aim of improving each activity and selectivity of designed drugs targeting potentially drug-resistant microorganisms. It also opens avenues for the development of newer antimicrobial agents targeting bacterial and fungal pathogens.

Thymidine rescues ATR kinase inhibitor-induced deoxyuridine contamination in genomic DNA, cell death, and interferon-α/β expression

ATR kinase is a central regulator of the DNA damage response (DDR) and cell cycle checkpoints. ATR kinase inhibitors (ATRi's) combine with radiation to generate CD8+ T cell-dependent responses in mouse models of cancer. We show that ATRi's induce cyclin-dependent kinase 1 (CDK1)-dependent origin firing across active replicons in CD8+ T cells activated ex vivo while simultaneously decreasing the activity of rate-limiting enzymes for nucleotide biosynthesis. These pleiotropic effects of ATRi induce deoxyuridine (dU) contamination in genomic DNA, R loops, RNA-DNA polymerase collisions, and interferon-α/β (IFN-α/β). Remarkably, thymidine rescues ATRi-induced dU contamination and partially rescues death and IFN-α/β expression in proliferating CD8+ T cells. Thymidine also partially rescues ATRi-induced cancer cell death. We propose that ATRi-induced dU contamination contributes to dose-limiting leukocytopenia and inflammation in the clinic and CD8+ T cell-dependent anti-tumor responses in mouse models. We conclude that ATR is essential to limit dU contamination in genomic DNA and IFN-α/β expression.

Myocardial matrix hydrogel acts as a reactive oxygen species scavenger and supports a proliferative microenvironment for cardiomyocytes

As the native regenerative potential of adult cardiac tissue is limited post-injury, stimulating endogenous repair mechanisms in the mammalian myocardium is a potential goal of regenerative medicine therapeutics. Injection of myocardial matrix hydrogels into the heart post-myocardial infarction (MI) has demonstrated increased cardiac muscle and promotion of pathways associated with cardiac development, suggesting potential promotion of cardiomyocyte turnover. In this study, the myocardial matrix hydrogel was shown to have native capability as an effective reactive oxygen species scavenger and protect against oxidative stress induced cell cycle inhibition in vitro. Encapsulation of cardiomyocytes demonstrated an enhanced turnover in in vitro studies, and in vivo assessments of myocardial matrix hydrogel treatment post-MI showed increased thymidine analog uptake in cardiomyocyte nuclei compared to saline controls. Overall, this study provides evidence that properties of the myocardial matrix material provide a microenvironment mitigating oxidative damage and supportive of cardiomyocytes undergoing DNA synthesis, toward possible DNA repair or cell cycle activation. STATEMENT OF SIGNIFICANCE: Loss of adult mammalian cardiomyocyte turnover is influenced by shifts in oxidative damage, which represents a potential mechanism for improving restoration of cardiac muscle after myocardial infarction (MI). Injection of a myocardial matrix hydrogel into the heart post-MI previously demonstrated increased cardiac muscle and promotion of pathways associated with cardiac development, suggesting potential in promoting proliferation of cardiomyocytes. In this study, the myocardial matrix hydrogel was shown to protect cells from oxidative stress and increase proliferation in vitro. In a rat MI model, greater presence of tissue free thiol content spared from oxidative damage, lesser mitochondrial superoxide content, and increased thymidine analog uptake in cardiomyocytes was found in matrix injected animals compared to saline controls. Overall, this study provides evidence that properties of the myocardial matrix material provide a microenvironment supportive of cardiomyocytes undergoing DNA synthesis, toward possible DNA repair or cell cycle activation.

Synthesis, antimicrobial, molecular docking and molecular dynamics studies of lauroyl thymidine analogs against SARS-CoV-2: POM study and identification of the pharmacophore sites

Nucleoside precursors and nucleoside analogs occupy an important place in the treatment of viral respiratory pathologies, especially during the current COVID-19 pandemic. From this perspective, the present study has been designed to explore and evaluate the synthesis and spectral characterisation of 5́-O-(lauroyl) thymidine analogs 2–6 with different aliphatic and aromatic groups through comprehensive in vitro antimicrobial screening, cytotoxicity assessment, physicochemical aspects, molecular docking and molecular dynamics analysis, along with pharmacokinetic prediction. A unimolar one-step lauroylation of thymidine under controlled conditions furnished the 5́-O-(lauroyl) thymidine and indicated the selectivity at C-5́ position and the development of thymidine based potential antimicrobial analogs, which were further converted into four newer 3́-O-(acyl)-5́-O-(lauroyl) thymidine analogs in reasonably good yields. The chemical structures of the newly synthesised analogs were ascertained by analysing their physicochemical, elemental, and spectroscopic data. In vitro antimicrobial tests against five bacteria and two fungi, along with the prediction of activity spectra for substances (PASS), indicated promising antibacterial functionality for these thymidine analogs compared to antifungal activity. In support of this observation, molecular docking experiments have been performed against the main protease of SARS-CoV-2, and significant binding affinities and non-bonding interactions were observed against the main protease (6LU7, 6Y84 and 7BQY), considering hydroxychloroquine (HCQ) as standard. Moreover, the 100 ns molecular dynamics simulation process was performed to monitor the behaviour of the complex structure formed by the main protease under in silico physiological conditions to examine its stability over time, and this revealed a stable conformation and binding pattern in a stimulating environment of thymidine analogs. Cytotoxicity determination confirmed that compounds were found less toxic. Pharmacokinetic predictions were investigated to evaluate their absorption, distribution, metabolism and toxic properties, and the combination of pharmacokinetic and drug-likeness predictions has shown promising results in silico. The POM analysis shows the presence of an antiviral (O1^δ-, O2^δ-) pharmacophore site. Overall, the current study should be of great help in the development of thymidine-based, novel, multiple drug-resistant antimicrobial and COVID-19 drugs.

Synthetic Thymidine Analog Labeling without Misconceptions

Tagging proliferating cells with thymidine analogs is an indispensable research tool; however, the issue of the potential in vivo cytotoxicity of these compounds remains unresolved. Here, we address these concerns by examining the effects of BrdU and EdU on adult hippocampal neurogenesis and EdU on the perinatal somatic development of mice. We show that, in a wide range of doses, EdU and BrdU label similar numbers of cells in the dentate gyrus shortly after administration. Furthermore, whereas the administration of EdU does not affect the division and survival of neural progenitor within 48 h after injection, it does affect cell survival, as evaluated 6 weeks later. We also show that a single injection of various doses of EdU on the first postnatal day does not lead to noticeable changes in a panel of morphometric criteria within the first week; however, higher doses of EdU adversely affect the subsequent somatic maturation and brain growth of the mouse pups. Our results indicate the potential caveats in labeling the replicating DNA using thymidine analogs and suggest guidelines for applying this approach.

Cell Cycle Synchronization of Primary and Cultured Articular Chondrocytes

Cell cycle synchronization allows cells in a culture, originally at different stages of the cell cycle, to be brought to the same phase. It is normally performed by applying cell cycle arresting chemical agents to cells cultured in monolayer. While effective, isolated chondrocytes tend to dedifferentiate when cultured in monolayer and typically require 3D culturing methods to ensure phenotypic stability. Here, we describe both the conventional cell cycle synchronization method for cells in monolayer culture and an adapted method of synchronizing primary chondrocytes directly during the cell isolation process to limit potential dedifferentiation. Different methods including serum-starvation and treatment with thymidine, nocodazole, aphidicolin, and RO-3306 can synchronize the chondrocytes at different discrete phases. A cell purity of more than 90% in the S phase can be achieved with simultaneous cell isolation and synchronization using double thymidine treatment, generating a population of synchronized chondrocytes that show increased matrix synthesis when subsequently cultured in 3D.

Acanthaster planci Inhibits PCSK9 and Lowers Cholesterol Levels in Rats

Atherosclerosis is the main cause of cardiovascular diseases which in turn, lead to the highest number of mortalities globally. This pathophysiological condition is developed due to a constant elevated level of plasma cholesterols. Statin is currently the widely used treatment in reducing the level of cholesterols, however, it may cause adverse side effects. Therefore, there is an urgent need to search for new alternative treatment. PCSK9 is an enzyme responsible in directing LDL-receptor (LDL-R)/LDL-cholesterols (LDL-C) complex to lysosomal degradation, preventing the receptor from recycling back to the surface of liver cells. Therefore, PCSK9 offers a potential target to search for small molecule inhibitors which inhibit the function of this enzyme. In this study, a marine invertebrate Acanthaster planci, was used to investigate its potential in inhibiting PCSK9 and lowering the levels of cholesterols. Cytotoxicity activity of A. planci on human liver HepG2 cells was carried out using the MTS assay. It was found that methanolic extract and fractions did not exhibit cytotoxicity effect on HepG2 cell line with IC50 values of more than 30 µg/mL. A compound deoxythymidine also did not exert any cytotoxicity activity with IC50 value of more than 4 µg/mL. Transient transfection and luciferase assay were conducted to determine the effects of A. planci on the transcriptional activity of PCSK9 promoter. Methanolic extract and Fraction 2 (EF2) produced the lowest reduction in PCSK9 promoter activity to 70 and 20% of control at 12.5 and 6.25 μg/mL, respectively. In addition, deoxythymidine also decreased PCSK9 promoter activity to the lowest level of 60% control at 3.13 μM. An in vivo study using Sprague Dawley rats demonstrated that 50 and 100 mg/kg of A. planci methanolic extract reduced the total cholesterols and LDL-C levels to almost similar levels of untreated controls. The level of serum glutamate oxalate transaminase (SGOT) and serum glutamate pyruvate transaminase (SGPT) showed that the administration of the extract did not produce any toxicity effect and cause any damage to rat liver. The results strongly indicate that A. planci produced a significant inhibitory activity on PCSK9 gene expression in HepG2 cells which may be responsible for inducing the uptake of cholesterols by liver, thus, reducing the circulating levels of total cholesterols and LDL-C. Interestingly, A. planci also did show any adverse hepato-cytotoxicity and toxic effects on liver. Thus, this study strongly suggests that A. planci has a vast potential to be further developed as a new class of therapeutic agent in lowering the blood cholesterols and reducing the progression of atherosclerosis.

PARP Activity Fine-tunes the DNA Replication Choreography of Chk1-depleted Cells

Checkpoint Kinase 1 (Chk1) prevents DNA damage by adjusting the replication choreography in the face of replication stress. Chk1 depletion provokes slow and asymmetrical fork movement, yet the signals governing such changes remain unclear. We sought to investigate whether poly(ADP-ribose) polymerases (PARPs), key players of the DNA damage response, intervene in the DNA replication of Chk1-depleted cells. We demonstrate that PARP inhibition selectively alleviates the reduced fork elongation rates, without relieving fork asymmetry in Chk1-depleted cells. While the contribution of PARPs to fork elongation is not unprecedented, we found that their role in Chk1-depleted cells extends beyond fork movement. PARP-dependent fork deceleration induced mild dormant origin firing upon Chk1 depletion, augmenting the global rates of DNA synthesis. Thus, we have identified PARPs as novel regulators of replication fork dynamics in Chk1-depleted cells.

α-Difluoromethylornithine-Induced Cytostasis is Reversed by Exogenous Polyamines, Not by Thymidine Supplementation

Polyamine spermidine is essential for the proliferation of eukaryotic cells. Administration of polyamine biosynthesis inhibitor α-difluoromethylornithine (DFMO) induces cytostasis that occurs in two phases; the early phase which can be reversed by spermidine, spermine, and some of their analogs, and the late phase which is characterized by practically complete depletion of cellular spermidine pool. The growth of cells at the late phase can be reversed by spermidine and by very few of its analogs, including (S)-1-methylspermidine. It was reported previously (Witherspoon et al. Cancer Discovery 3(9); 1072–81, 2013) that DFMO treatment leads to depletion of cellular thymidine pools, and that exogenous thymidine supplementation partially prevents DFMO-induced cytostasis without affecting intracellular polyamine pools in HT-29, SW480, and LoVo colorectal cancer cells. Here we show that thymidine did not prevent DFMO-induced cytostasis in DU145, LNCaP, MCF7, CaCo2, BT4C, SV40MES13, HepG2, HEK293, NIH3T3, ARPE19 or HT-29 cell lines, whereas administration of functionally active mimetic of spermidine, (S)-1-methylspermidine, did. Thus, the effect of thymidine seems to be specific only for certain cell lines. We conclude that decreased polyamine levels and possibly also distorted pools of folate-dependent metabolites mediate the anti-proliferative actions of DFMO. However, polyamines are necessary and sufficient to overcome DFMO-induced cytostasis, while thymidine is generally not.

Thymidine decreases the DNA damage and apoptosis caused by tumor-treating fields in cancer cell lines

BACKGROUND

Tumor-treating fields (TTFields) is an emerging non-invasive cancer-treatment modality using alternating electric fields with low intensities and an intermediate range of frequency. TTFields affects an extensive range of charged and polarizable cellular factors known to be involved in cell division. However, it causes side-effects, such as DNA damage and apoptosis, in healthy cells.

OBJECTIVE

To investigate whether thymidine can have an effect on the DNA damage and apoptosis, we arrested the cell cycle of human glioblastoma cells (U373) at G1/S phase by using thymidine and then exposed these cells to TTFields.

METHODS

Cancer cell lines and normal cell (HaCaT) were arrested by thymidine double block method. Cells were seeded into the gap of between the insulated wires. The exposed in alternative electric fields at 120 kHz, 1.2 V/cm. They were counted the cell numbers and analyzed for cancer malignant such as colony formation, Annexin V/PI staining, γH2AX and RT-PCR.

RESULTS

The colony-forming ability and DNA damage of the control cells without thymidine treatment were significantly decreased, and the expression levels of BRCA1, PCNA, CDC25C, and MAD2 were distinctly increased. Interestingly, however, cells treated with thymidine did not change the colony formation, apoptosis, DNA damage, or gene expression pattern.

CONCLUSIONS

These results demonstrated that thymidine can inhibit the TTFields-caused DNA damage and apoptosis, suggesting that combining TTFields and conventional treatments, such as chemotherapy, may enhance prognosis and decrease side effects compared with those of TTFields or conventional treatments alone.

Targeting the nucleotide salvage factor DNPH1 sensitizes BRCA-deficient cells to PARP inhibitors

Mutations in the BRCA1 or BRCA2 tumor suppressor genes predispose individuals to breast and ovarian cancer. In the clinic, these cancers are treated with inhibitors that target poly(ADP-ribose) polymerase (PARP). We show that inhibition of DNPH1, a protein that eliminates cytotoxic nucleotide 5-hydroxymethyl-deoxyuridine (hmdU) monophosphate, potentiates the sensitivity of BRCA-deficient cells to PARP inhibitors (PARPi). Synthetic lethality was mediated by the action of SMUG1 glycosylase on genomic hmdU, leading to PARP trapping, replication fork collapse, DNA break formation, and apoptosis. BRCA1-deficient cells that acquired resistance to PARPi were resensitized by treatment with hmdU and DNPH1 inhibition. Because genomic hmdU is a key determinant of PARPi sensitivity, targeting DNPH1 provides a promising strategy for the hypersensitization of BRCA-deficient cancers to PARPi therapy.

Dietary serine-microbiota interaction enhances chemotherapeutic toxicity without altering drug conversion

The gut microbiota metabolizes drugs and alters their efficacy and toxicity. Diet alters drugs, the metabolism of the microbiota, and the host. However, whether diet-triggered metabolic changes in the microbiota can alter drug responses in the host has been largely unexplored. Here we show that dietary thymidine and serine enhance 5-fluoro 2'deoxyuridine (FUdR) toxicity in C. elegans through different microbial mechanisms. Thymidine promotes microbial conversion of the prodrug FUdR into toxic 5-fluorouridine-5'-monophosphate (FUMP), leading to enhanced host death associated with mitochondrial RNA and DNA depletion, and lethal activation of autophagy. By contrast, serine does not alter FUdR metabolism. Instead, serine alters E. coli's 1C-metabolism, reduces the provision of nucleotides to the host, and exacerbates DNA toxicity and host death without mitochondrial RNA or DNA depletion; moreover, autophagy promotes survival in this condition. This work implies that diet-microbe interactions can alter the host response to drugs without altering the drug or the host.

PLK1 facilitates chromosome biorientation by suppressing centromere disintegration driven by BLM-mediated unwinding and spindle pulling

Centromeres provide a pivotal function for faithful chromosome segregation. They serve as a foundation for the assembly of the kinetochore complex and spindle connection, which is essential for chromosome biorientation. Cells lacking Polo-like kinase 1 (PLK1) activity suffer severe chromosome alignment defects, which is believed primarily due to unstable kinetochore-microtubule attachment. Here, we reveal a previously undescribed mechanism named 'centromere disintegration' that drives chromosome misalignment in PLK1-inactivated cells. We find that PLK1 inhibition does not necessarily compromise metaphase establishment, but instead its maintenance. We demonstrate that this is caused by unlawful unwinding of DNA by BLM helicase at a specific centromere domain underneath kinetochores. Under bipolar spindle pulling, the distorted centromeres are promptly decompacted into DNA threadlike molecules, leading to centromere rupture and whole-chromosome arm splitting. Consequently, chromosome alignment collapses. Our study unveils an unexpected role of PLK1 as a chromosome guardian to maintain centromere integrity for chromosome biorientation.

Lamin B receptor (LBR) is involved in the induction of cellular senescence in human cells

Cellular senescence is a phenomenon of irreversible growth arrest in mammalian somatic cells in culture. Various stresses induce cellular senescence and indeed, we have found that excess thymidine effectively induces cellular senescence in human cells. Further, many reports indicate the implication of chromatin proteins in cellular senescence. Here we analysed the role of lamin B receptor (LBR), a nuclear envelope protein that regulates heterochromatin organization, in cellular senescence induced by excess thymidine. We then found that the LBR protein was down-regulated and showed aberrant localization in cells upon induction of cellular senescence by excess thymidine. Additionally, we also found that knock-down of LBR facilitated the induction of cellular senescence by excess thymidine in cancerous HeLa cells, and importantly, it induced cellular senescence in normal human diploid fibroblast TIG-7 cells. These results suggested that decreased LBR function is involved in the induction of cellular senescence in human cells.

Activation of the oncogenic transcription factor B-Myb via multisite phosphorylation and prolyl cis/trans isomerization

The oncogenic transcription factor B-Myb is an essential regulator of late cell cycle genes whose activation by phosphorylation is still poorly understood. We describe a stepwise phosphorylation mechanism of B-Myb, which involves sequential phosphorylations mediated by cyclin-dependent kinase (Cdk) and Polo-like kinase 1 (Plk1) and Pin1-facilitated peptidyl-prolyl cis/trans isomerization. Our data suggest a model in which initial Cdk-dependent phosphorylation of B-Myb enables subsequent Pin1 binding and Pin1-induced conformational changes of B-Myb. This, in turn, initiates further phosphorylation of Cdk-phosphosites, enabling Plk1 docking and subsequent Plk1-mediated phosphorylation of B-Myb to finally allow B-Myb to stimulate transcription of late cell cycle genes. Our observations reveal novel mechanistic hierarchies of B-Myb phosphorylation and activation and uncover regulatory principles that might also apply to other Myb family members. Strikingly, overexpression of B-Myb and of factors mediating its activation strongly correlates with adverse prognoses for tumor patients, emphasizing B-Myb's role in tumorigenesis.

Acto-myosin force organization modulates centriole separation and PLK4 recruitment to ensure centriole fidelity

The presence of aberrant number of centrioles is a recognized cause of aneuploidy and hallmark of cancer. Hence, centriole duplication needs to be tightly regulated. It has been proposed that centriole separation limits centrosome duplication. The mechanism driving centriole separation is poorly understood and little is known on how this is linked to centriole duplication. Here, we propose that actin-generated forces regulate centriole separation. By imposing geometric constraints via micropatterns, we were able to prove that precise acto-myosin force arrangements control direction, distance and time of centriole separation. Accordingly, inhibition of acto-myosin contractility impairs centriole separation. Alongside, we observed that organization of acto-myosin force modulates specifically the length of S-G2 phases of the cell cycle, PLK4 recruitment at the centrosome and centriole fidelity. These discoveries led us to suggest that acto-myosin forces might act in fundamental mechanisms of aneuploidy prevention.

Comparative Analysis of the Formation of γH2AX Foci in Human Mesenchymal Stem Cells Exposed to 3H-Thymidine, Tritium Oxide, and X-Rays Irradiation

We performed a comparative study of the formation of γН2АХ foci (a marker of DNA doublestrand breaks) in human bone marrow mesenchymal stem cells after 24-h incubation with ³Н-thimidin and tritium oxide with low specific activities (50-800 MBq/liter). The dependence of the number of γH2AX foci on specific activity of 3H-thymidine was described by a linear equation y=2.21+43.45x (R²=0.96), where y is the number of γH2AX foci per nucleus and x is specific activity in 1000 MBq/liter. For tritium oxide, the relationship was described by a linear equation y=2.52+6.70x (R²=0.97). Thus, the yield of DNA double-strand breaks after exposure to ³H-thymidine was 6.5-fold higher than after exposure to tritium oxide. Comparison of the effects of tritium oxide and X-ray radiation on the yield of DNA double-strand breaks showed that the relative biological efficiency of tritium oxide in a dose range of 3.78-60.26 mGy was 1.6-fold higher than that of X-ray radiation. Improvement of the methods of analysis of DNA double-strand breaks repair foci is highly promising in the context of creation of highly sensitive biodosimetry technologies for tritium compounds in humans.

Reversal of Methotrexate-Induced Folate Pool Depletion by Thymidine in a Human Leukemia Cell Line in Vitro

In an In vitro study using a human monocytic leukemia cell line, U-937, the effects of interferon-γ (IFN-γ) in combination with the antifolate methotrexate and the role of thymidine introduced as a biochemical modulator were investigated. Methotrexate alone or in combination with INF-γ was found to enhance the induction of morphologic and functional monocytic differentiation in the U-937 cell line. Various cellular effects with the addition of thymidine to the medium with methotrexate and IFN-γ were studied. Enhanced inhibition of cell growth and perturbation of the cell cycle were noted when methotrexate and IFN-γ were used in combination, but not when methotrexate was used alone. The reduction of cellular folate by methotrexate was also enhanced in combination with IFN-γ. Cell cycle delay, resulting in cell growth inhibition of folate depletion, caused the induction of differentiation in U-937 cells, which was found to be greater with methotrexate + IFN-γ than with methotrexate alone. Cellular differentiation, as assessed by nitroblue tetrazolium reduction assay, indirect immunofluorescence and morphology, showed better effects towards the differentiation of U-937 cells when the agents were used in combination. However, addition of thymidine to the medium was found to cancel all the aforementioned effects. The addition of thymidine to the medium also caused reversal of the inhibitory effect of methotrexate and IFN-γ on cell growth and repletion of the endogenous folate level. Repletion of the folate level by exogenous thymidine is a new possibility for the role of the thymidine in cellular growth.

Trends in hepatitis B virus resistance to nucleoside/nucleotide analogues in North China from 2009-2016: A retrospective study

Nucleos(t)ide analogues (NAs) are widely used in anti-hepatitis B virus (anti-HBV) therapy for effective inhibition of HBV replication. However, HBV resistance to NAs has emerged, resulting in virus reactivation and disease recurrence. Data on the current dynamics of HBV resistance are still rare in China. This study analysed 4491 plasma samples with HBV primary genotypic resistance mutations representative of the general HBV resistance situation in northern China from 2009-2016. We found that entecavir (ETV), representing 57.6% (12 713/22 060) of NA users in North China in 2016, has become the major NA for treating Chinese patients infected with HBV. Despite >50% of M204I/V±L180M among all HBV resistance cases annually and extensive exposure of patients to lamivudine (LAM), telbivudine (LdT) and adefovir dipivoxil (ADV), ETV resistance also showed a dramatically increased incidence, which rose to 17.1% in 2016. Moreover, A181T/V, ETV resistance mutations and multidrug resistance mutations were found more frequently in HBV genotype C compared with genotype B (21.2% vs. 8.5%, 12.4% vs. 7.9% and 5.9% vs. 3.0%, respectively), whereas M204I and N236T were more predominant in genotype B than genotype C (40.3% vs. 20.8% and 11.3% vs. 1.8%, respectively). In conclusion, we report the dynamic changes of HBV NA resistance mutation patterns and the current NA usage profile for anti-HBV treatment in North China over the past 8 years. These data provide valuable information on HBV NA resistance that is an important reference for clinicians to devise more effective treatment regimens for individual patients.

Comparison of the Efficacies and Safety of Combined Therapy between Telbivudine Plus Adefovir and Lamivudine Plus Adefovir in Patients with Hepatitis B Virus Infection in Real-World Practice

Background and Aim

Chronic hepatitis B infection remains a significant health issue worldwide. This study evaluated the efficacy and safety of combined therapy using lamivudine plus adefovir (LAM+ADV) versus telbivudine plus adefovir (LdT+ADV) and the corresponding renal function change and safety.

Methods

This study enrolled a total of 171 patients (110 patients received LAM+ADV and 60 patients received LdT+ADV). We analyzed the changes in renal function using the estimated glomerular filtration rate (eGFR). The DNA undetectable rate, hepatitis B e antigen (HBeAg) seroconversion rate, and alanine aminotransferase (ALT) normalization rate were analyzed. We checked the serum uric acid, phosphate and creatine kinase, and lactic acid levels to analyze safety. We observed these patients for 48 to 240 weeks and checked their serum profile every 6 months.

Results

There was no statistically significant difference between the two groups in anti-hepatitis B virus (HBV) efficacy in terms of DNA undetectable rate, ALT normalization rate, and HBeAg seroconversion rate. Both the LAM+ADV and LdT+ADV groups had stable or improved renal function. However, a higher eGFR was found in the LdT+ADV group with continuous serum fluctuation during 3 years of combined therapy as well as a higher serum creatine kinase level.

Conclusions

Long-term LdT+ADV combined therapy and LAM+ADV combined therapy were both associated with stable or improved renal function. The clinical efficacy was similar between the two groups, but the LdT group had a higher serum creatine kinase level. We need to monitor the data regularly in clinical practice.

The Effect of a Methyl or 2-fluoroethyl Substituent at the N-3 Position of Thymidine, 3′-fluoro-3′-deoxythymi-dine and 1-β-D-arabinosylthymine on Their Antiviral and Cytostatic Activity in Cell Culture

Thymidine (Thd), 1-β-D-arabinosylthymine (ara-T) and 3′-fluoro-3′-deoxythymidine (FLT) have been substituted at N-3 by a methyl or a 2-fluoroethyl group. FLT and ara-T are markedly inhibitory against human immunodeficiency virus type 1 (HIV-1) and HIV-2, and herpes simplex virus type 1 (HSV-1) and HSV-2, respectively. Modification at N-3 of these compounds markedly decreases both the antiviral and cytostatic activity of the parent compounds FLT and ara-T except for N-3-(methyl)-Thd that proved highly cytostatic for murine leukaemia L1210 cells. The decreased biological activity of the N-3-substituted pyrimidine nucleo-side analogues coincides with a significantly lower affinity of the modified Thd analogues for the cellular and viral (activating) nucleoside kinases.

Renal Function in Nucleos(t)ide Analog-Treated Patients With Chronic Hepatitis B: A Systematic Literature Review and Network Meta-Analysis

INTRODUCTION

Renal safety is an important factor in selecting the most appropriate nucleos(t)ide analog (NA) treatment for patients with chronic hepatitis B (CHB). This systematic literature review and network meta-analysis aimed to assess renal function associated with telbivudine treatment compared to other NAs in patients with CHB.

METHODS

A systematic literature search via Medline, Medline In-Process, Embase, and the Cochrane library for publications of randomized controlled trials and observational studies was conducted. Network meta-analysis was performed to compare renal function with telbivudine treatment versus other NAs after 1 year of therapy.

RESULTS

Overall, 40 (six randomized controlled and 34 observational) studies were included for review. Telbivudine consistently showed an improvement in renal function as measured by an estimated glomerular filtration rate (eGFR) over various time points regardless of the method of measurement. Changes in eGFR (mL/min) from baseline and corresponding 95% credible intervals with various NAs were as follows: monotherapies (telbivudine: 7.78 [6.91, 8.65], entecavir: -1.07 [-4.80, 2.62], lamivudine: -6.08 [-13.35, 1.15], tenofovir: -9.53 [-14.31, -4.89]) and combination therapies (telbivudine + adefovir: 8.37 [-34.00, 50.34], telbivudine + tenofovir: 8.29 [-0.05, 16.64], entecavir + adefovir: 4.15 [-38.55, 46.37], telbivudine + lamivudine: 0.51 [-11.77, 12.96], and lamivudine + adefovir: -0.39 [-42.48, 41.21]). At 1 year, the change in eGFR from baseline was significantly higher with telbivudine compared to other NAs.

CONCLUSION

The systematic literature review and network meta-analysis provide evidence that telbivudine is associated with significant improvement in renal function in patients with CHB, either alone or in combination with other NAs.

FUNDING

Novartis Pharma AG.

Effect of Telbivudine Versus Other Nucleos(t)ide Analogs on HBeAg Seroconversion and Other Outcomes in Patients with Chronic Hepatitis B: A Network Meta-Analysis

INTRODUCTION

A comprehensive and up-to-date network meta-analysis (NMA) helps to determine the comparative efficacies of nucleos(t)ide analogs (NAs) in patients with chronic hepatitis B (CHB). The aim of this NMA was to assess the efficacy of telbivudine versus adefovir, entecavir, lamivudine, and tenofovir in nucleos(t)ide-naïve hepatitis B e antigen (HBeAg)-positive patients with CHB.

METHODS

A systematic review was conducted to search Medline, Medline-In Process, EMBASE, and the Cochrane Central Register of Controlled Trials databases for publications of randomized controlled trials (RCTs). NMA was performed to compare the efficacy outcomes of telbivudine versus other approved NAs at 1- and 2-year time points.

RESULTS

A total of 75 RCTs were included in the systematic review. At the 1-year time point, telbivudine was associated with significantly higher rates of: (1) HBeAg seroconversion than adefovir [odds ratio (OR) 1.99 (95% credible interval (CrI): 1.05, 3.45)], entecavir [OR 2.00 (95% CrI: 1.44, 2.82)] and lamivudine [OR 1.49 (95% CrI: 1.10, 2.03)]; (2) HBeAg loss than entecavir [OR 1.85 (95% CrI: 1.28, 2.76)] and lamivudine [OR 1.62 (95% CrI: 1.20, 2.24)]; (3) alanine aminotransferase (ALT) normalization than lamivudine [OR 1.50 (95% CrI: 1.05, 2.21)]; and (4) hepatitis B virus (HBV) DNA suppression than adefovir [OR 2.77 (95% CrI: 1.28, 5.45)] and lamivudine [OR 2.97 (95% CrI: 1.99, 4.53)]. At the 2-year time point, the relative efficacy outcomes were not statistically significant.

CONCLUSION

At 1 year, telbivudine was superior to adefovir, entecavir and lamivudine in HBeAg seroconversion, and to entecavir and lamivudine in HBeAg loss. Telbivudine was also superior to lamivudine in ALT normalization and to adefovir and lamivudine in suppressing HBV DNA levels.

FUNDING

Novartis Pharma AG.

Efficacy of N-methanocarbathymidine against genital herpes simplex virus type 2 shedding and infection in guinea pigs

BACKGROUND

Current approved nucleoside therapies for genital herpes simplex virus (HSV) infections are effective but improved therapies are needed for treatment of both acute and recurrent diseases.

METHODS

The effects of N-methanocarbathymidine were evaluated and compared to acyclovir using guinea pig models of acute and recurrent infection. For acute disease following intravaginal inoculation of 10(6 )pfu HSV-2 (MS strain), animals were treated intraperitoneally beginning 24 h post-infection, and the effects on disease severity, vaginal virus replication, subsequent recurrences, and latent virus loads were evaluated. For evaluation of recurrent infection, animals were treated for 21 days beginning 14 days after infection and disease recurrence and recurrent shedding were evaluated.

RESULTS

Treatment of the acute disease with N-methanocarbathymidine significantly reduced the severity of acute disease and decreased acute vaginal virus shedding more effectively than acyclovir. Significantly, none of the animals developed visible disease in the high-dose N-methanocarbathymidine group and this was the only group in which the number of days with recurrent virus shedding was reduced. Treatment of recurrent disease was equivalent to acyclovir when acyclovir was continuously supplied in the drinking water.

CONCLUSION

N-methanocarbathymidine was effective as therapy for acute and recurrent genital HSV-2 disease in the guinea pig models.

Increased virus budding from Friend erythroleukemic cells treated with dimethyl sulfoxide, dimethyl formamide, and/or bromodeoxyuridine in vitro

Chronically infected Friend leukemia cells (FLC), grown in the presence of dimethyl sulfoxide (DMSO) (2%, v/v), dimethyl formamide (DMF) (1% v/v), or bromodeoxyuridine (BrdU) (3 or 20 mug/ml) for 4 or 7 days, were examined under the electron microscope. It was found that at the 4th day all three compounds induced comparable increases in the number of budding viruses (3 to 5 times that of the control). At the 7th day, the number had remained relatively constant in the BrdU-treated cells in contrast to the cells of the DMSO- or DMF-treated cultures, which showed a further increase of budding viruses. The greatest increase was seen when BrdU was added in combination with either DMSO or DMF, and this was reflected in the apparent increase in the number of extracellular viruses seen in cell pellets. Scanning electron microscopy on whole FLC mounts provided a rapid means of counting budding viruses and a good correlation was obtained between these counts and those made on thin sections by transmission electron microscopy. Attempts to quantitate the number of released viruses in controls and treated cultures after 4 days of growth revealed a 5- to 10-fold increase per cell in the samples treated with a combination of BrdU and either DMSO or DMF. Thymidine failed to prevent the increase of budding viruses induced by BrdU treatment. The number of budding viruses found after treatment with 3 mug/ml BrdU in the presence of 12 mug/ml thymidine was at a level comparable to that found after the individual BrdU treatment Finally, although FLC always contained varying amounts of intracisternal particles, their number, as compared to the paired controls, always decreased after BrdU treatment.

Modulation versus rescue of antimetabolite toxicity by salvage metabolites administered by continuous infusion

A system has been developed for the long-term continuous intravenous infusion of chemotherapeutic agents into unrestrained mice which allows new approaches to the toxicological and chemotherapeutic evaluation of antimetabolites. In mice, the concurrent infusion of thymidine and a source of preformed purine reversed both the toxicity and antitumor activity of MTX comparable to what was previously observed in cell culture. The infusion of thymidine alone, however, also blocked the toxicity of MTX without interfering with antitumor activity. A comparison of leucovorin rescue versus the utilization of thymidine plus preformed purine indicated that these salvage metabolites were as effective as leucovorin in reducing the toxicity of high-dose MTX while retaining antitumor activity.

A fatal combination: a thymidylate synthase inhibitor with DNA damaging activity

2′-deoxy-5-ethynyluridine (EdU) has been previously shown to be a cell poison whose toxicity depends on the particular cell line. The reason is not known. Our data indicates that different efficiency of EdU incorporation plays an important role. The EdU-mediated toxicity was elevated by the inhibition of 2′-deoxythymidine 5′-monophosphate synthesis. EdU incorporation resulted in abnormalities of the cell cycle including the slowdown of the S phase and a decrease in DNA synthesis. The slowdown but not the cessation of the first cell division after EdU administration was observed in all of the tested cell lines. In HeLa cells, a 10 μM EdU concentration led to the cell death in the 100% of cells probably due to the activation of an intra S phase checkpoint in the subsequent S phase. Our data also indicates that this EdU concentration induces interstrand DNA crosslinks in HeLa cells. We suppose that these crosslinks are the primary DNA damage resulting in cell death. According to our results, the EdU-mediated toxicity is further increased by the inhibition of thymidylate synthase by EdU itself at its higher concentrations.

[Effect of human concentration nucleoside transporters 1 and multi-drug resistance protein 4 gene polymorphism on response of chronic hepatitis B to nucleoside analogues treatment]

OBJECTIVE

To investigate the effect of human concentration nucleoside transporters 1 (hCNT1/ SLC28A1) and multi-drug resistance protein 4 (MRP4/ABCC4) gene polymorphism on the response of chronic hepatitis B patients to nucleoside analogues treatment.

METHODS

There were 136 patients of chronic hepatitis B treated with entecavir (68) or telbivudine (68). The allele and gene frequency distributing of the four loci of hCNT1/SLC28A1 and MRP4/ABCC4 as well as the polymorphisms were detected in all patients by multiplex snapshot single base extension method. Based on the treatment response, the patients were divided into primary partial response (PPR) group and complete viral response (CVR) group, hCNTI/SLC28A1 and MRP4/ABCC4 gene polymorphism between these two groups were analyzed.

RESULTS

The rates of PPR and CVR were 56. 6%00 (77 136) and 43. 4% (59/136) respectively. There was no statistical difference in baseline HBV DNA value, hepatitis B virus genotype and HBeAg status between PPR and CVR groups (P=0.148, P= 0. 622,P=0. 071) . The distribution of allelotype rs2290272 C/T and rs11568658 G/G in PPR group were higher than those in CVR group (P=0.043. P=0.049). Haplotype of C/A/T/C and C/C/G/G in CVR group were higher than those in PPR group (P=0. 024,P=0. 005).

CONCLUSION

The single nucleotide polymorphisms (SNPs) of two candidate genes, including rs2290272 C/T of hCNT1/SLC28A1 and rs11568658 G/G of MRP4/ABCC4, may weak the response of chronic hepatitis B to nucleoside analogues treatment, as well as haplotype of C/A/T/C and C/C/G/G may enhance the response.

Cell-cycle analyses using thymidine analogues in fission yeast

Thymidine analogues are powerful tools when studying DNA synthesis including DNA replication, repair and recombination. However, these analogues have been reported to have severe effects on cell-cycle progression and growth, the very processes being investigated in most of these studies. Here, we have analyzed the effects of 5-ethynyl-2′-deoxyuridine (EdU) and 5-Chloro-2′-deoxyuridine (CldU) using fission yeast cells and optimized the labelling procedure. We find that both analogues affect the cell cycle, but that the effects can be mitigated by using the appropriate analogue, short pulses of labelling and low concentrations. In addition, we report sequential labelling of two consecutive S phases using EdU and 5-bromo-2′-deoxyuridine (BrdU). Furthermore, we show that detection of replicative DNA synthesis is much more sensitive than DNA-measurements by flow cytometry.

Mouse beta cell proliferation is inhibited by thymidine analogue labelling

AIMS/HYPOTHESIS

Long-term labelling of mice with halogenated thymidine analogues is an established method for quantifying the contribution of beta cell proliferation to in vivo beta cell mass expansion in (re)generation models. The method is believed to give accurate information on the accrued number of cycling beta cells over a period of time. Multiple thymidine analogue labelling is applied for evaluating the duration of postmitotic quiescence in beta cells. We hypothesise, however, that long-term labelling by thymidine analogues hampers beta cell proliferation.

METHODS

Thymidine analogues were administered for 7-14 days via the i.p. route to neonatal mice, or via drinking water to young mice with normal pancreases or adult mice with injured pancreases. The proliferation of insulin-positive cells was assessed by their expression of the proliferation markers Ki67 or phosphorylated histone H3 and by their incorporation of nucleotide analogues.

RESULTS

In the mouse models of beta cell proliferation investigated herein, long-term administration of thymidine analogues decreased the percentage of Ki67(+) and phosphorylated histone H3(+) beta cells as compared with administration of normal drinking water. Proliferation was restored by washout of the analogue. Labelling with one analogue decreased the subsequent incorporation of another analogue by beta cells.

CONCLUSIONS/INTERPRETATION

Long-term labelling with halogenated thymidine analogues is a biased method that underestimates the proliferation and re-division potential of mouse beta cells.

In vitro cross-resistance profile of nucleoside reverse transcriptase inhibitor (NRTI) BMS-986001 against known NRTI resistance mutations

BMS-986001 is a novel HIV nucleoside reverse transcriptase inhibitor (NRTI). To date, little is known about its resistance profile. In order to examine the cross-resistance profile of BMS-986001 to NRTI mutations, a replicating virus system was used to examine specific amino acid mutations known to confer resistance to various NRTIs. In addition, reverse transcriptases from 19 clinical isolates with various NRTI mutations were examined in the Monogram PhenoSense HIV assay. In the site-directed mutagenesis studies, a virus containing a K65R substitution exhibited a 0.4-fold change in 50% effective concentration (EC50) versus the wild type, while the majority of viruses with the Q151M constellation (without M184V) exhibited changes in EC50 versus wild type of 0.23- to 0.48-fold. Susceptibility to BMS-986001 was also maintained in an L74V-containing virus (0.7-fold change), while an M184V-only-containing virus induced a 2- to 3-fold decrease in susceptibility. Increasing numbers of thymidine analog mutation pattern 1 (TAM-1) pathway mutations correlated with decreases in susceptibility to BMS-986001, while viruses with TAM-2 pathway mutations exhibited a 5- to 8-fold decrease in susceptibility, regardless of the number of TAMs. A 22-fold decrease in susceptibility to BMS-986001 was observed in a site-directed mutant containing the T69 insertion complex. Common non-NRTI (NNRTI) mutations had little impact on susceptibility to BMS-986001. The results from the site-directed mutants correlated well with the more complicated genotypes found in NRTI-resistant clinical isolates. Data from clinical studies are needed to determine the clinically relevant resistance cutoff values for BMS-986001.

Treatment with telbivudine positively regulates antiviral immune profiles in Chinese patients with chronic hepatitis B

Chronic infection with hepatitis B virus (HBV) is associated with impairment of T and NK cell immunity. This study was aimed at investigating the impact of treatment with telbivudine (LDT) on T and NK cell immunity in patients with chronic hepatitis B (CHB). A total of 54 CHB patients and 30 healthy controls (HC) were recruited. Individual patients were treated orally with 600 mg LDT daily for 13 months. The serum HBV DNA loads, the levels of the HBV-related biomarkers alanine aminotransferase (ALT) and aspartate transaminase (AST), and the numbers of different subsets of peripheral T and NK cells in subjects were measured before and longitudinally after LDT treatment. Following treatment with LDT, the serum HBV DNA loads and the percentages of HBsAg- or HBeAg-seropositive cases were gradually reduced, accompanied by decreased levels of serum ALT and AST. In comparison with the HC, fewer CD3(-) CD56(+) and CD244(+) NK cells and CD3(+) CD8(+) T cells, lower frequencies of cytokine(+) CD4(+) T cells, and more CD3(+) CD4(+), CD4(+) CD25(+) Foxp3(+), CD4(+) CD25(+) CD127(low), and CD8(+) PD-1(+) T cells were detected in CHB patients. Treatment with LDT increased the numbers of NK and CD8(+) cells and the frequencies of cytokine(+) CD4(+) T cells but reduced the numbers of CD4(+) CD25(+) Foxp3(+), CD4(+) CD25(+) CD127(low), and CD8(+) PD-1(+) T cells in CHB patients. The frequencies of cytokine(+) CD4(+) T cells were negatively associated with the levels of serum HBV DNA, ALT, and AST. Thus, treatment with LDT inhibits HBV replication, modulates T and NK cell immunity, and improves liver function in Chinese patients with CHB.

52-week efficacy and safety of telbivudine with conditional tenofovir intensification at week 24 in HBeAg-positive chronic hepatitis B

BACKGROUND AND AIMS

The Roadmap concept is a therapeutic framework in chronic hepatitis B for the intensification of nucleoside analogue monotherapy based on early virologic response. The efficacy and safety of this approach applied to telbivudine treatment has not been investigated.

METHODS

A multinational, phase IV, single-arm open-label study (ClinicalTrials.gov ID NCT00651209) was undertaken in HBeAg-positive, nucleoside-naive adult patients with chronic hepatitis B. Patients received telbivudine (600 mg once-daily) for 24 weeks, after which those with undetectable serum HBV DNA (<300 copies/mL) continued to receive telbivudine alone while those with detectable DNA received telbivudine plus tenofovir (300 mg once-daily). Outcomes were assessed at Week 52.

RESULTS

105 patients commenced telbivudine monotherapy, of whom 100 were included in the efficacy analysis. Fifty-five (55%) had undetectable HBV DNA at Week 24 and continued telbivudine monotherapy; 45 (45%) received tenofovir intensification. At Week 52, the overall proportion of undetectable HBV DNA was 93% (93/100) by last-observation-carried-forward analysis (100% monotherapy group, 84% intensification group) and no virologic breakthroughs had occurred. ALT normalization occurred in 77% (87% monotherapy, 64% intensification), HBeAg clearance in 43% (65% monotherapy, 16% intensification), and HBeAg seroconversion in 39% (62% monotherapy, 11% intensification). Six patients had HBsAg clearance. Myalgia was more common in the monotherapy group (19% versus 7%). No decrease in the mean glomerular filtration rate occurred in either treatment group at Week 52.

CONCLUSIONS

Telbivudine therapy with tenofovir intensification at Week 24, where indicated by the Roadmap strategy, appears effective and well tolerated for the treatment of chronic hepatitis B.

Synthesis of N3-substituted carboranyl thymidine bioconjugates and their evaluation as substrates of recombinant human thymidine kinase 1

Four different libraries of overall twenty three N3-substituted thymidine (dThd) analogues, including eleven 3-carboranyl thymidine analogues (3CTAs), were synthesized. The latter are potential agents for Boron Neutron Capture Therapy (BNCT) of cancer. Linker between the dThd scaffold and the m-carborane cluster at the N3-position of the 3CTAs contained amidinyl-(3e and 3f), guanidyl-(7e-7g), tetrazolylmethyl-(9b1/2-9d1/2), or tetrazolyl groups (11b1/2-11d1/2) to improve human thymidine kinase 1 (hTK1) substrate characteristics and water solubilities compared with 1st generation 3CTAs, such as N5 and N5-2OH. The amidinyl- and guanidyl-type N3-substitued dThd analogues (3a-3f and 7a-7g) had hTK1 phosphorylation rates of <30% relative to that of dThd, the endogenous hTK1 substrate, whereas the tetrazolyl-type N3-substitued dThd analogues (9a, 9b1/2-9d1/2 and 11a, 11b1/2-11d1/2) had relative phosphorylation rates (rPRs) of >40%. Compounds 9a, 9b1/2-9d1/2 and 11a, 11b1/2-11d1/2 were subjected to in-depth enzyme kinetics studies and the obtained rk(cat)/K(m) (k(cat)/K(m) relative to that of dThd) ranged from 2.5 to 26%. The tetrazolyl-type N3-substitued dThd analogues 9b1/2 and 11d1/2 were the best substrates of hTK1 with rPRs of 52.4% and 42.5% and rk(cat)/K(m) values of 14.9% and 19.7% respectively. In comparison, the rPR and rk(cat)/K(m) values of N5-2OH in this specific study were 41.5% and 10.8%, respectively. Compounds 3e and 3f were >1900 and >1500 times, respectively, better soluble in PBS (pH 7.4) than N5-2OH whereas solubilities for 9b1/2-9d1/2 and 11b1/2-11d1/2 were only 1.3-13 times better.

Growth characteristics of Juxta-alveolar smooth muscle cells derived from high-altitude-hypoxia sheeplung parenchyma

AIMS AND OBJECTIVES

Pathologic effects of environmental factors on smooth muscle cells (SMCs) near the air/blood interface have been difficult to study because it is impossible to dissect blood vessels and bronchi down to their alveolar terminals. SMCs derived from explants of lung terminal parenchyma were examined in order to detect any effect of chronic hypoxia on their growth profiles.

SUBJECTS AND METHODS

Lungs were obtained from sheep kept at 12, 470 ft altitude, PaO2 ~60 Torr for ~4 months and from age matched control sheep kept at sea level. SMC were allowed to migrate from terminal lung parenchyma. Monolayer growth profiles were studied by using tritiated thymidine incorporation as indicator of DNA synthesis.

RESULTS

The normal growth pattern, typified by intrapulmonary 7th generation vein SMCs, showed a peak at 72h and mean peak tritiated thymidine incorporation (counts per minute, cpm) of 2829.46±294.24. Fifteen SMC lines were obtained from hypoxic sheep lungs compared to control sheep which generated three lines. According to peaks and mean incorporated cpm, hypoxic cells showed five distinct growth profiles: normal, subprolific, prolific, retarded, and senescent. Mean peak cpm incorporated by subprolific and prolific cells were: 4480.80±240.22 and 7775.42±475.77 cpm. The normal cells incorporated 507.04, 1386.33, 936.08, and -944.29 cpm in the 1st, 2nd, 3rd and 4th 24h-periods respectively while the retarded cells incorporated 403.70, 491.7, 53.08, and -124.08 cpm, and the senescent cells incorporated 26.71, 7.04, 7.83, and -0.42 cpm respectively. Apoptotic cells were also derived from hypoxic tissues.

CONCLUSION

This report indicates an origin of pulmonary pathology, the SMC's near the air/blood interface.

In-vitro replication studies on O(2)-methylthymidine and O(4)-methylthymidine

O(2)- and O(4)-methylthymidine (O(2)-MdT and O(4)-MdT) can be induced in tissues of laboratory animals exposed with N-methyl-N-nitrosourea, a known carcinogen. These two O-methylated DNA adducts have been shown to be poorly repaired and may contribute to the mutations arising from exposure to DNA methylating agents. Here, in vitro replication studies with duplex DNA substrates containing site-specifically incorporated O(2)-MdT and O(4)-MdT showed that both lesions blocked DNA synthesis mediated by three different DNA polymerases, including the exonuclease-free Klenow fragment of Escherichia coli DNA polymerase I (Kf(-)), human DNA polymerase κ (pol κ), and Saccharomyces cerevisiae DNA polymerase η (pol η). Results from steady-state kinetic measurements and LC-MS/MS analysis of primer extension products revealed that Kf(-) and pol η preferentially incorporated the correct nucleotide (dAMP) opposite O(2)-MdT, while O(4)-MdT primarily directed dGMP misincorporation. While steady-state kinetic experiments showed that pol κ-mediated nucleotide insertion opposite O(2)-MdT and O(4)-MdT is highly promiscuous, LC-MS/MS analysis of primer extension products demonstrated that pol κ favorably incorporated the incorrect dGMP opposite both lesions. Our results underscored the limitation of the steady-state kinetic assay in determining how DNA lesions compromise DNA replication in vitro. In addition, the results from our study revealed that, if left unrepaired, O-methylated thymidine lesions may constitute important sources of nucleobase substitutions emanating from exposure to alkylating agents.

Biphasic addition strategy of hypoxanthine and thymidine for improving monoclonal antibody production

In our previous study, we demonstrated that combinatorial addition of hypoxanthine (10 mg/L) and thymidine (2 mg/L) was able to stimulate initial cell growth and elevate volumetric concentration of antibody by 22% (Chen et al., Appl. Microbiol. Biotechnol., 93, 169-178, 2012). In this study, a systematic study was carried out to investigate the effects of hypoxanthine and thymidine (H&T) on cell growth and antibody production in a much wider range of concentration. In addition, we pursued to establish a highly productive fed-batch culture via rationally designing H&T addition regime. It was found that both cell growth and antibody production in batch cultures were H&T concentration-dependent. Specifically, a low concentration stimulated cell growth while exerting no influence on specific productivity (q(mAb)), and a high concentration inhibited cell growth, however, significantly enhancing q(mAb). Subsequent experiments with fed-batch shaking flasks demonstrated the feasibility of improving antibody production using a biphasic addition strategy for H&T: supplementing a low concentration of H&T during initial cell growth phase and a high concentration of H&T at the production phase. By applying the optimized feeding regime, a maximum viable cell density (VCD) of 6.45 × 10(6)cells/mL and volumetric antibody production of 632 mg/L were achieved in a 2 L-B.Braun bioreactor. Taken together, in this study, a biphasic H&T addition strategy for cell culture was developed, which hold great promise to improve antibody production.

Replication stress induces micronuclei comprising of aggregated DNA double-strand breaks

Background

Micronuclei (MN) in mammalian cells serve as a reliable biomarker of genomic instability and genotoxic exposure. Elevation of MN is commonly observed in cells bearing intrinsic genomic instability and in normal cells exposed to genotoxic agents. DNA double-strand breaks are marked by phosphorylation of H2AX at serine 139 (γ-H2AX). One subclass of MN contains massive and uniform γ-H2AX signals. This study tested whether this subclass of MN can be induced by replication stress.

Principal Findings

We observed that a large proportion of MN, from 20% to nearly 50%, showed uniform staining by antibodies against γ-H2AX, a marker of DNA double-strand breaks (DSBs). Such micronuclei were designated as MN-γ–H2AX (+). We showed that such MN can be induced by chemicals that are known to cause DNA replication stress and S phase arrest. Hydroxyurea, aphidicolin and thymidine could all significantly induce MN-γ–H2AX (+), which were formed during S phase and appeared to be derived from aggregation of DSBs. MN-γ–H2AX (−), MN that were devoid of uniform γ-H2AX signals, were induced to a lesser extent in terms of fold change. Paclitaxel, which inhibits the disassembly of microtubules, only induced MN-γ–H2AX (−). The frequency of MN-γ–H2AX (+), but not that of MN-γ–H2AX (−), was also significantly increased in cells that experience S phase prolongation due to depletion of cell cycle regulator CUL4B. Depletion of replication protein A1 (RPA1) by RNA interference resulted in an elevation of both MN-γ–H2AX (+) and MN-γ–H2AX (−).

Conclusions/Significance

A subclass of MN, MN-γ–H2AX (+), can be preferentially induced by replication stress. Classification of MN according to their γ-H2AX status may provide a more refined evaluation of intrinsic genomic instabilities and the various environmental genotoxicants.

The effect of thymidine on the antibacterial and antiviral activity of zidovudine

The effect of thymidine and deoxyadenosine on the antiviral and antibacterial effect of zidovudine was studied in human immunodeficiency virus type 1 (HIV-1) Escherichia coli and Salmonella typhimurium. In quantitative assays, 10 μg mL−1 thymidine was shown to increase the 50% inhibitory concentration (IC50) of zidovudine for HIV-1 by approximately 100-fold and to reduce zidovudine (1 μm)-induced protection of C8166 cells from 204 to 0·18 log syncytial-forming units. Thymidine also antagonized the antibacterial effect of zidovudine for two E. coli and three S. typhimurium species in a dose-dependent manner; 10 μg mL of thymidine increased the minimum inhibitory concentration of zidovudine for E. coli strains by 10–40-fold and for S. typhimurium strains by three-fold. Deoxyadenosine reduced the minimum inhibitory concentration of zidovudine against all five bacterial strains but had no effect on the IC50 of zidovudine for HIV-1, nor did it significantly reverse the antagonism of the antibacterial and antiviral activity of thymidine. The induction of the SOS response in E. coli was reversed in a dose-dependent manner by thymidine while the presence of deoxyadenosine increased induction of the SOS response by zidovudine at suboptimal concentrations.

Phenotypic characterization of drug resistance-associated mutations in HIV-1 RT connection and RNase H domains and their correlation with thymidine analogue mutations

OBJECTIVES

HIV-1 reverse transcriptase (RT) mutations associated with antiviral drug resistance have been extensively characterized in the enzyme polymerase domain. Recent studies, however, have verified the involvement of the RT C-terminal domains (connection and RNase H) in drug resistance to RT inhibitors. In this work, we have characterized the correlation of recently described C-terminal domain mutations with thymidine analogue mutations (TAMs), as well as their phenotypic impact on susceptibility to zidovudine and nevirapine.

METHODS

HIV-1 RT sequences from Brazilian patients and from public sequence databases for which the C-terminal RT domains and treatment status were also available were retrieved and analysed for the association of C-terminal mutations and the presence of TAMs and treatment status. Several C-terminal RT mutations previously characterized were introduced by site-directed mutagenesis into an HIV-1 subtype B molecular clone in a wild-type, TAM-1 or TAM-2 pathway context. Mutants were tested for drug susceptibility to the prototypic drugs zidovudine and nevirapine.

RESULTS

Subtype B-infected patient database analysis showed that mutations N348I, A360V/T, T377M and D488E were found to be selected independently of TAMs, whereas mutations R358K, G359S, A371V, A400T, K451R and K512R increased in frequency with the number of TAMs in a dose-dependent fashion. Phenotypic analysis of C-terminal mutations showed that N348I, T369V and A371V conferred reduced susceptibility to zidovudine in the context of the TAM-1 and/or TAM-2 pathway, and also conferred dual resistance to nevirapine. Other mutations, such as D488E and Q547K, showed TAM-specific enhancement of resistance to zidovudine. Finally, mutation G359S displayed a zidovudine hypersusceptibility phenotype, both per se and when combined with A371V.

CONCLUSIONS

This study demonstrates that distinct RT C-terminal mutations can act as primary or secondary drug resistance mutations, and are associated in a complex array of phenotypes with RT polymerase domain mutations.

Supplementation of serum free media with HT is not sufficient to restore growth properties of DHFR-/- cells in fed-batch processes - Implications for designing novel CHO-based expression platforms

DHFR-deficient CHO cells are the most commonly used host cells in the biopharmaceutical industry and over the years, individual substrains have evolved, some have been engineered with improved properties and platform technologies have been designed around them. Unexpectedly, we have observed that different DHFR-deficient CHO cells show only poor growth in fed-batch cultures even in HT supplemented medium, whereas antibody producer cells derived from these hosts achieved least 2-3 fold higher peak cell densities. Using a set of different expression vectors, we were able to show that this impaired growth performance was not due to the selection procedure possibly favouring fast growing clones, but a direct consequence of DHFR deficiency. Re-introduction of the DHFR gene reproducibly restored the growth phenotype to the level of wild-type CHO cells or even beyond which seemed to be dose-dependent. The requirement for a functional DHFR gene to achieve optimal growth under production conditions has direct implications for cell line generation since it suggests that changing to a selection system other than DHFR would require another CHO host which - especially for transgenic CHO strains and tailor-suited process platforms - this could mean significant investments and potential changes in product quality. In these cases, DHFR engineering of the current CHO-DG44 or DuxB11-based host could be an attractive alternative.

Synchronization of HeLa cells

HeLa is one of the oldest and most commonly used cell lines in biomedical research. Owing to the ease of which they can be effectively synchronized by various methods, HeLa cells have been used extensively for studies of the cell cycle. Here we describe several protocols for synchronization of HeLa cells from different phases of the cell cycle. Synchronization in G(1) phase can be achieved with the HMG-CoA reductase inhibitor lovastatin, S phase with a double thymidine block procedure, and G(2) phase with the CDK inhibitor RO3306. Cells can also be enriched in mitosis by treating with nocodazole and mechanical shake-off. Release of the cells from these blocks enables researchers to follow gene expression and other events through the cell cycle. We also describe several protocols, including flow cytometry, BrdU labeling, immunoblotting, and time-lapse microscopy, for validating the synchrony of the cells and monitoring the progression of the cell cycle after release.

3'-(1,2,3-Triazol-1-yl)-3'-deoxythymidine analogs as substrates for human and Ureaplasma parvum thymidine kinase for structure-activity investigations

The pathogenic mycoplasma Ureaplasma parvum (Up) causes opportunistic infections and relies on salvage of nucleosides for DNA synthesis and Up thymidine kinase (UpTK) provides the necessary thymidine nucleotides. The anti-HIV compound 3 -azido-3'-deoxythymidine (AZT) is a good substrate for TK. Methods for a rapid and efficient synthesis of new 3'-alpha-[1,2,3]triazol-3'-deoxythymidine analogs from AZT under Huisgen conditions are described. Thirteen 3'-analogues were tested with human cytosolic thymidine kinase (hTK1) and UpTK. The new analogs showed higher efficiencies (K(m)/V(max) values) in all cases with UpTK than with hTK1. Still, hTK1 was preferentially inhibited by 9 out of 10 tested analogs. Structural models of UpTK and hTK1 were constructed and used to explain the kinetic results. Two different binding modes of the nucleosides within the active sites of both enzymes were suggested with one predominating in the bacterial enzyme and the other in hTK1. These results will aid future development of anti-mycoplasma nucleosides.

Development and characterization of HAT-sensitive Ewing tumour cells for immunotherapy

BACKGROUND

Despite improvements in the treatment of patients with Ewing family tumours (EFT) during the past decades, the prognosis for patients with advanced disease is still unsatisfying. New treatment strategies have to be developed.

MATERIALS AND METHODS

A hypoxanthine/aminopterin/thymidine (HAT)-sensitive EFT cell line was developed by repetitive treatment of the EFT cell line SK-N-MC with 8'-azaguanine (8AG). By using DNA microarrays, the gene expression profile of this cell line was characterized. Immunostimulatory activity was assessed by mixed lymphocyte/tumour cell culture (MLTC). Artificial fusion of tumour cells and dendritic cells was visualized by flow cytometry.

RESULTS

After selection of 8AG-resistant cells, a cell line with high sensitivity for treatment with HAT was obtained. Expression of the X chromosome inactivation specific transcript XIST was higher in HAT-sensitive cells. Nevertheless, HAT-sensitive cells retained the EFT-associated gene expression profile. Moreover, in the presence of HAT, it was possible to use these cells without irradiation as stimulatory cells in MLTC or as fusion partner for dendritic cells.

CONCLUSION

HAT-sensitive EFT cells might be an interesting tool for the development of new immunotherapeutic approaches for the treatment of EFT.

The nucleoside analogue D-carba T blocks HIV-1 reverse transcription

A major pathway for HIV-1 resistance to nucleoside reverse transcriptase inhibitors (NRTIs) involves reverse transcriptase (RT) mutations that enhance ATP-dependent pyrophosphorolysis, which excises NRTIs from the end of viral DNA. We analyzed novel NRTIs for their ability to inhibit DNA synthesis of excision-proficient HIV-1 RT mutants. D-carba T is a carbocyclic nucleoside that has a 3' hydroxyl on the pseudosugar. The 3' hydroxyl group allows RT to incorporate additional dNTPs, which should protect D-carba TMP from excision. D-carba T can be converted to the triphosphate form by host cell kinases with moderate efficiency. D-carba T-TP is efficiently incorporated by HIV-1 RT; however, the next dNTP is added slowly to a D-carba TMP at the primer terminus. D-carba T effectively inhibits viral vectors that replicate using NRTI-resistant HIV-1 RTs, and there is no obvious toxicity in cultured cells. NRTIs based on the carbocyclic pseudosugar may offer an effective approach for the treatment of HIV-1 infections.