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Background: Triple-negative breast cancer (TNBC) represents the most aggressive subtype of breast cancer and is frequently resistant to therapy, ultimately resulting in treatment failure. Clinical trials have demonstrated the potential of sensitizing radiation therapy (RT)-resistant TNBC through the combination of chemotherapy and RT. This study sought to explore the potential of CD151 as a therapy response marker in the co-treatment strategy involving ionizing radiation (IR) and the repurposed antiviral drug 2-Thio-6-azauridine (TAU) for sensitizing RT-resistant TNBC (TNBC/RR). Methods: The investigation encompassed a variety of assessments, including viability using MTT and LDH assays, cell proliferation through BrdU incorporation and clonogenic assays, cell cycle analysis via flow cytometry, cell migration using wound scratch and Boyden chamber invasion assays, DNA damage assessment through γH2AX analysis, apoptosis evaluation through acridine-orange and ethidium bromide double staining assays, as well as caspase 3 activity measurement using a colorimetric assay. CD151 expression was examined through ELISA, flow cytometry and RT-qPCR. Results: The results showed a significant reduction in TNBC/RR cell viability following co-treatment. Moreover, the co-treatment reduced cell migration, induced apoptosis, downregulated CD151 expression, and increased caspase 3 activity in TNBC/RR cells. Additionally, CD151 was predicted to serve as a therapy response marker for co-treatment with TAU and IR. Conclusion: These findings suggest the potential of combination treatment with IR and TAU as a promising strategy to overcome RT resistance in TNBC. Furthermore, CD151 emerges as a valuable therapy response marker for chemoradiotherapy. [ABSTRACT FROM AUTHOR]

Purpose: Uterine serous carcinoma (USC) is generally associated with poor prognosis due to a high recurrence rate and frequent treatment resistance; hence, there is a need for improved therapeutic strategies. Molecular analysis of USC identified several molecular markers, useful to improve current treatments or identify new druggable targets. PPP2R1A, encoding the Aα subunit of the tumor suppressive Ser/Thr phosphatase PP2A, is mutated in up to 40% of USCs. Here, we investigated the effect of the p.R183W PPP2R1A hotspot variant on treatment response to the nucleoside analogue clofarabine. Methods and results: USC cells stably expressing p.R183W Aα showed increased resistance to clofarabine treatment in vitro and, corroborated by decreased clofarabine-induced apoptosis, G1 phase arrest, DNA-damage (γH2AX) and activation of ATM and Chk1/2 kinases. Phenotypic rescue by pharmacologic PP2A inhibition or dicer-substrate siRNA (dsiRNA)-mediated B56δ subunit knockdown supported a gain-of-function mechanism of Aα p.R183W, promoting dephosphorylation and inactivation of deoxycytidine kinase (dCK), the cellular enzyme responsible for the conversion of clofarabine into its bioactive form. Therapeutic assessment of related nucleoside analogues (gemcitabine, cladribine) revealed similar effects, but in a cell line-dependent manner. Expression of two other PPP2R1A USC mutants (p.P179R or p.S256F) did not affect clofarabine response in our cell models, arguing for mutant-specific effects on treatment outcome as well. Conclusions: While our results call for PPP2R1A mutant and context-dependent effects upon clofarabine/nucleoside analogue monotherapy, combining clofarabine with a pharmacologic PP2A inhibitor proved synergistically in all tested conditions, highlighting a new generally applicable strategy to improve treatment outcome in USC. [ABSTRACT FROM AUTHOR]

Thymus is the important immune organ, responsible for T cell development and differentiation. The lower circulating T counts have been observed in patients who died from COVID-19 compared with survivors. Azvudine, also known as FNC, is a thymus-homing anti-SARS-CoV-2 drug in treating COVID-19 patients. In this study, single-cell transcriptome, proteomics, and parallel reaction monitoring (PRM) were applied to insight into the activation process of FNC in rat and SARS-CoV-2 rhesus monkey thymus. The results indicated that thymic immune cells possess a robust metabolic capacity for cytidine-analogue drugs such as FNC. Key enzymes involved in the FNC phosphorylation process, such as Dck, Cmpk1, and Nme2, were highly expressed in CD4+ T cells, CD8+ T cells, and DP (CD4+ CD8+) cells. Additionally, FNC could upregulate multiple phosphorylated kinases in various cell types while downregulating the phosphatases, phosphoribosyl transferases, and deaminases, respectively. The robust phosphorylation capacity of the thymus for cytidine analogue drug FNC, and the activation effect of FNC on the NAs metabolism system potentially contribute to its enrichment in the thymus and immune protection effect. This suggests that it is crucial to consider the expression level of phosphorylation kinases when evaluating NA drug properties, as an important factor during antiviral drug design.

Thymus is the important immune organ, responsible for T cell development and differentiation. The lower circulating T counts have been observed in patients who died from COVID-19 compared with survivors. Azvudine, also known as FNC, is a thymus-homing anti-SARS-CoV-2 drug in treating COVID-19 patients. In this study, single-cell transcriptome, proteomics, and parallel reaction monitoring (PRM) were applied to insight into the activation process of FNC in rat and SARS-CoV-2 rhesus monkey thymus. The results indicated that thymic immune cells possess a robust metabolic capacity for cytidine-analogue drugs such as FNC. Key enzymes involved in the FNC phosphorylation process, such as Dck, Cmpk1, and Nme2, were highly expressed in CD4+ T cells, CD8+ T cells, and DP (CD4+ CD8+) cells. Additionally, FNC could upregulate multiple phosphorylated kinases in various cell types while downregulating the phosphatases, phosphoribosyl transferases, and deaminases, respectively. The robust phosphorylation capacity of the thymus for cytidine analogue drug FNC, and the activation effect of FNC on the NAs metabolism system potentially contribute to its enrichment in the thymus and immune protection effect. This suggests that it is crucial to consider the expression level of phosphorylation kinases when evaluating NA drug properties, as an important factor during antiviral drug design. The activation effect of FNC on the nucleoside metabolism system potentially contribute to its enrichment in the thymus and immune protection effect. [Display omitted] [ABSTRACT FROM AUTHOR]

Introduction and Objectives: Treatment of chronic hepatitis B (CHB) with nucelos(t)ide analogues (NA) can improve outcomes, but NA treatment is expensive for insurance plans. Materials and Methods: The Centers for Medicare & Medicaid Services database was assessed from 2012 to 2021 to assess the use of NA for CHB in patients on Medicaid. Data extracted included the number of claims, units, and costs of each agent stratified by originator and generic. Results: Over the study period, 1.9 billion USD was spent on NA, with spending peaking in 2016 at $289 million US, which has subsequently decreased. Lower expenditures since 2016 have been associated with increased use of generics. The use of generic tenofovir or entecavir led to savings of $669 million US over the study period. Conclusions: Increased generic use has significantly reduced expenditures for NA drugs; policy shifts towards generic drug use may help with sustainability. [ABSTRACT FROM AUTHOR]

Background: The use of antiviral agents, specifically tenofovir disoproxil fumarate (TDF), in pregnant women to prevent mother‐to‐child HBV transmission is a key step towards hepatitis elimination. However, data on using tenofovir alafenamide (TAF) is insufficient. The frequent occurrence of postpartum ALT flares may impact the clinical implementation. Methods: The maternal and infant outcomes were compared in multi‐centre trials of high viral load HBsAg/HBeAg+ pregnant women receiving TAF or TDF from the third trimester until 2 weeks postpartum with intensive follow‐ups. To explore the dynamic pre‐ and postpartum changes in ALT levels, we used a group‐based trajectory model for analysing data of 332 women from three prospective studies. Results: After treatment, the maternal HBV DNA levels significantly decreased from baseline to delivery: 7.87 ± 0.59 to 3.99 ± 1.07 Log10 IU/mL TAF (n = 78) and 8.30 ± 0.36 to 4.47 ± 0.86 Log10 IU/mL (TDF, n = 53), with viral load reductions of 3.87 versus 3.83 Log10 IU/mL. The HBsAg‐positive rates among 12‐month‐old infants were 1.28% (1/78) versus 1.82% (1/55) respectively (p = 1.00). Of the TAF or TDF‐treated mothers, 25.64% versus 16.98% experienced ALT > 2X ULN, and 11.54% versus 1.89% received extended antiviral treatment. Our model revealed four distinct ALT patterns: stable ALT (87.2%), moderate (8.0%) or marked (2.4%) postpartum flares, or prepartum elevations (2.4%). Conclusions: TAF effectively reduces mother‐to‐child HBV transmission, but prophylaxis failure still occurred in few cases. Postpartum ALT flares are common in women receiving TAF or TDF during pregnancy. Approximately 12.8% of mothers may require extended postpartum antiviral treatment. Clinical trial number: NCT03695029 (ClinicalTrials.gov). [ABSTRACT FROM AUTHOR]

Zika virus (ZIKV) causes microcephaly and congenital eye disease. The cellular and molecular basis of congenital ZIKV infection are not well understood. Here, we utilized a biologically relevant cell-based system of human fetal retinal pigment epithelial cells (FRPEs), hiPSC-derived retinal stem cells (iRSCs), and retinal organoids to investigate ZIKV-mediated ocular cell injury processes. Our data show that FRPEs were highly susceptible to ZIKV infection exhibiting increased apoptosis, whereas iRSCs showed reduced susceptibility. Detailed transcriptomics and proteomics analyses of infected FRPEs were performed. Nucleoside analogue drug treatment inhibited ZIKV replication. Retinal organoids were susceptible to ZIKV infection. The Asian genotype ZIKV exhibited higher infectivity, induced profound inflammatory response, and dysregulated transcription factors involved in retinal organoid differentiation. Collectively, our study shows that ZIKV affects ocular cells at different developmental stages resulting in cellular injury and death, further providing molecular insight into the pathogenesis of congenital eye disease.

Introduction and Objectives: Treatment of chronic hepatitis B (CHB) with nucelos(t)ide analogues (NA) can improve outcomes, but NA treatment is expensive for insurance plans. Materials and Methods: The Centers for Medicare & Medicaid Services database was assessed from 2012 to 2021 to assess the use of NA for CHB in patients on Medicaid. Data extracted included the number of claims, units, and costs of each agent stratified by originator and generic. Results: Over the study period, 1.9 billion USD was spent on NA, with spending peaking in 2016 at $289 million US, which has subsequently decreased. Lower expenditures since 2016 have been associated with increased use of generics. The use of generic tenofovir or entecavir led to savings of $669 million US over the study period. Conclusions: Increased generic use has significantly reduced expenditures for NA drugs; policy shifts towards generic drug use may help with sustainability.

Background. Acute hepatitis B infection is associated with severe liver disease and chronic sequelae in some cases. The purpose of this review was to determine the efficacy of nucleoside analogues (NA) (lamivudine versus entecavir) compared to placebo or no intervention for treating acute primary HBV infection. Methods. A meta-analysis for drug intervention was performed, following a fixed-effect model. Randomized controlled trials (RCTs) and quasi-randomized studies that evaluated the outcomes of NA in acute hepatitis B infection were included. The following outcomes were considered: virological cure (PCR negative), elimination of acute infection (seroconversion of HBsAg), mortality, and serious adverse events. Results. Five trials with 627 adult participants with severe acute hepatitis B defined by biochemical and serologic parameters were included. Virological cure did not favor any intervention: OR 0.96, 95% CI 0.54 to 1.7 (p = 0.90), I2 = 58%. Seroconversion of HBsAg to negative favored placebo/standard-of-care compared to lamivudine: OR 0.54, 95% CI 0.33 to 0.9 (p = 0.02), I2 = 31%. The only trial that compared entecavir and lamivudine favored entecavir over lamivudine (OR: 3.64, 95% CI 1.31–10.13; 90 participants). Adverse events were mild. Conclusion. There is insufficient evidence that NA obtain superior efficacy compared with placebo/standard-of-care in patients with acute viral hepatitis, based on low quality evidence. [ABSTRACT FROM AUTHOR]

Objectives: Feline infectious peritonitis (FIP) is a serious disease that arises due to feline coronavirus infection. The nucleoside analogues remdesivir and GS-441524 can be effective in its treatment, but most studies have used unregulated products of unknown composition. The aim of the present study was to describe the treatment of FIP using legally sourced veterinary-prescribed regulated veterinary compounded products containing known amounts of remdesivir (injectable) or GS-441524 (oral tablets). Methods: Cats were recruited via email advice services, product sales contacts and study publicity. Cats were excluded if they were deemed unlikely to have FIP, were not treated exclusively with the veterinary compounded products, or if there was a lack of cat and/or treatment (including response) data. Extensive cat and treatment data were collected. Results: Among the 307 cats recruited, the predominant type of FIP was most commonly abdominal effusive (49.5%) and then neurological (14.3%). Three treatment protocols were used; remdesivir alone (33.9%), remdesivir followed by GS-441524 (55.7%) and GS-441524 alone (10.4%). The median (range) initial treatment period duration and longest follow-up time point after starting treatment were 84 (1–330) days and 248 (1–814) days, respectively. The most common side effect was injection pain (in 47.8% of those given subcutaneous remdesivir). Of the 307 cats, 33 (10.8%) relapsed, 15 (45.5%) during and 18 (54.5%) after the initial treatment period. At the longest follow-up time point after completion of the initial treatment period, 84.4% of cats were alive. The cats achieving a complete response within 30 days of starting treatment were significantly more likely to be alive at the end of the initial treatment period than those cats that did not. Conclusions and relevance: Legally sourced remdesivir and GS-441524 products, either alone or used sequentially, were very effective in the treatment of FIP in this group of cats. Variable protocols precluded statistical comparison of treatment regimens. [ABSTRACT FROM AUTHOR]

Cytosolic 5'-nucleotidase Ⅱ(cN-Ⅱ), the protein encoded by NT5C2, can catalyze the dephosphory-lation of nucleoside monophosphate and is mainly involved in the regulation of purine nucleotide pool in cells. High expression of cN-Ⅱ mRNA is associated with poor prognosis of patients with acute leukemia (AL). Acquired NT5C2 mutation will hinder the formation of DNA and thioguanine nucleotide (TGN) conjugate, resulting in 6-mercaptpurine(6-MP) resistance. In addition, NT5C2 is a risk factor associated with type Ⅱ diabetes, schizophrenia and other diseases.

Objectives: Feline infectious peritonitis (FIP), a common disease in cats caused by feline coronavirus (FCoV), is usually fatal once clinical signs appear. Successful treatment of FIP with oral GS-441524 for 84 days was demonstrated recently by this research group. The aim of this study was to evaluate the long-term outcome in these cats. Methods: A total of 18 successfully treated cats were followed for up to 1 year after treatment initiation (9 months after completion of the antiviral treatment). Follow-up examinations were performed at 12-week intervals, including physical examination, haematology, serum biochemistry, abdominal and thoracic ultrasound, FCoV ribonucleic acid (RNA) loads in blood and faeces by reverse transciptase-quantitative PCR and anti-FCoV antibody titres by indirect immunofluorescence assay. Results: Follow-up data were available from 18 cats in week 24, from 15 cats in week 36 and from 14 cats in week 48 (after the start of treatment), respectively. Laboratory parameters remained stable after the end of the treatment, with undetectable blood viral loads (in all but one cat on one occasion). Recurrence of faecal FCoV shedding was detected in five cats. In four cats, an intermediate short-term rise in anti-FCoV antibody titres was detected. In total, 12 cats showed abdominal lymphadenomegaly during the follow-up period; four of them continuously during the treatment and follow-up period. Two cats developed mild neurological signs, compatible with feline hyperaesthesia syndrome, in weeks 36 and 48, respectively; however, FCoV RNA remained undetectable in blood and faeces, and no increase in anti-FCoV antibody titres was observed in these two cats, and the signs resolved. Conclusions and relevance: Treatment with GS-441524 proved to be effective against FIP in both the short term as well as the long term, with no confirmed relapse during the 1-year follow-up period. Whether delayed neurological signs could be a long-term adverse effect of the treatment or associated with a 'long FIP syndrome' needs to be further evaluated. [ABSTRACT FROM AUTHOR]

Abacavir Sulfate is a nucleoside analog and reverse transcriptase inhibitor which is used in combination with Lamivudine and Zidovudine for the treatment of HIV and AIDS. Abacavir has higher toxicity levels and is least stable in heat. The specified temperature for the drug was proposed to be not more than 25°C. The present study focuses on the stability-related problem of the ABC. The new synthetic moiety will help to stabilize the drug, it can be used as a pro-drug formulation and can take the present scenario of the market which supplies any anti-retroviral drug. The aim of the current study is to synthesize a novel drug using Schiff base synthesis and perform its structural elucidation by different modes of Instrumental Analysis and perform in silico studies. From the above study, we can conclude that the novel moiety is safe to use as a drug and could be explored furthermore for its use. [ABSTRACT FROM AUTHOR]

Cytosolic 5’-nucleotidase Ⅱ (cN-Ⅱ), the protein encoded by NT5C2, can catalyze the dephosphory-lation of nucleoside monophosphate and is mainly involved in the regulation of purine nucleotide pool in cells. High expression of cN-Ⅱ mRNA is associated with poor prognosis of patients with acute leukemia (AL). Acquired NT5C2 mutation will hinder the formation of DNA and thioguanine nucleotide (TGN) conjugate, resulting in 6-mercaptpurine (6-MP) resistance. In addition, NT5C2 is a risk factor associated with type Ⅱ diabetes, schizophrenia and other diseases. [ABSTRACT FROM AUTHOR]

Gastrointestinal malignancies are common digestive system tumor worldwide. Nucleoside analogues have been widely used as anticancer drugs for the treatment of a variety of conditions, including gastrointestinal malignancies. However, low permeability, enzymatic deamination, inefficiently phosphorylation, the emergence of chemoresistance and some other issues have limited its efficacy. The prodrug strategies have been widely applied in drug design to improve pharmacokinetic properties and address safety and drug-resistance issues. This review will provide an overview of the recent developments of prodrug strategies in nucleoside analogues for the treatment of gastrointestinal malignancies.

The first concise and efficient synthesis of some fluorine‐containing morpholino nucleosides has been developed. One synthetic strategy was based on the oxidative ring cleavage of the vicinal diol unit of uridine, cytidine adenosine and guanosine derivatives, followed by cyclisation of the dialdehyde intermediates by double reductive amination with fluorinated primary amines to obtain various N‐fluoroalkylated morpholinos. Another approach involved cyclisation of the diformyl intermediates with ammonia source, followed by dithiocarbamate formation and desulfurization‐fluorination with diethylaminosulfur trifluoride yielding the corresponding morpholine‐based nucleoside analogues with a N‐CF3 element in their structure. [ABSTRACT FROM AUTHOR]

ATI‐2173 is an active site polymerase inhibitor nucleotide in development as part of a potentially curative regimen for chronic hepatitis B virus (HBV) infection. This study evaluated the safety, tolerability, pharmacokinetics (PK) and antiviral activity of ATI‐2173. This was a phase 1b, randomized, double‐blind, placebo‐controlled trial in treatment‐naive adults with chronic HBV infection conducted in the Republic of Moldova and Ukraine (ClinicalTrials.gov: NCT04248426). Patients positive for hepatitis B surface antigen were randomized 6:2 to receive once‐daily oral doses of ATI‐2173 10, 25, or 50 mg (n = 6 per dose) or placebo (n = 7) for 28 days, with off‐treatment monitoring for 24 weeks. Endpoints included PK parameters of ATI‐2173 and its metabolite clevudine, maximum reduction from baseline in HBV DNA, and safety and tolerability. Treatment‐emergent adverse events occurred in eight patients (47%) receiving ATI‐2173 and five (71%) receiving placebo; headache was the most common (n = 4). ATI‐2173 PK was generally dose proportional. Systemic clevudine exposure with ATI‐2173 dosing was substantially reduced compared with historical values observed with clevudine administration. On Day 28, mean changes from baseline in HBV DNA were −2.72 to −2.78 log10 IU/ml with ATI‐2173 and +0.17 log10 IU/ml with placebo. Off‐treatment sustained viral suppression and decreases in covalently closed circular DNA biomarkers were observed in most patients; one maintained undetectable HBV DNA at 24 weeks off treatment. In this 28‐day monotherapy study, ATI‐2173 demonstrated safety and antiviral activity, with sustained off‐treatment effects and substantially reduced systemic clevudine exposure. These results support evaluation of ATI‐2173 with tenofovir disoproxil fumarate in phase 2 studies. [ABSTRACT FROM AUTHOR]

[Display omitted] • Gram-negative bacterial infections pose a major threat to global public health. • Permeability of antibiotics in Gram-negative bacteria is poorly understood. • A novel library design strategy has been developed to probe permeability. • A uniform reagent set is used to decouple substituent and scaffold effects. • Library screening will now enable development of predictive models for permeability. Gram-negative bacteria pose a major challenge in antibiotic drug discovery because their cell envelope presents a permeability barrier that affords high intrinsic resistance to small-molecule drugs. The identification of correlations between chemical structure and Gram-negative permeability would thus enable development of predictive tools to facilitate antibiotic discovery. Toward this end, have advanced a library design paradigm in which various chemical scaffolds are functionalized at different regioisomeric positions using a uniform reagent set. This design enables decoupling of scaffold, regiochemistry, and substituent effects upon Gram-negative permeability of these molecules. Building upon our recent synthesis of a library of C2-substituted sulfamidoadenosines, we have now developed an efficient synthetic route to an analogous library of regioisomeric C8-substituted congeners. The C8 library samples a region of antibiotic-relevant chemical space that is similar to that addressed by the C2 library, but distinct from that sampled by a library of analogously substituted oxazolidinones. Selected molecules were tested for accumulation in Escherichia coli in a pilot analysis, setting the stage for full comparative evaluation of these libraries in the future. [ABSTRACT FROM AUTHOR]

Background. Acute hepatitis B infection is associated with severe liver disease and chronic sequelae in some cases. The purpose of this review was to determine the efficacy of nucleoside analogues (NA) (lamivudine versus entecavir) compared to placebo or no intervention for treating acute primary HBV infection. Methods. A meta-analysis for drug intervention was performed, following a fixed-effect model. Randomized controlled trials (RCTs) and quasi-randomized studies that evaluated the outcomes of NA in acute hepatitis B infection were included. The following outcomes were considered: virological cure (PCR negative), elimination of acute infection (seroconversion of HBsAg), mortality, and serious adverse events. Results. Five trials with 627 adult participants with severe acute hepatitis B defined by biochemical and serologic parameters were included. Virological cure did not favor any intervention: OR 0.96, 95% CI 0.54 to 1.7 (p = 0.90), I2 = 58%. Seroconversion of HBsAg to negative favored placebo/standard-of-care compared to lamivudine: OR 0.54, 95% CI 0.33 to 0.9 (p = 0.02), I2 = 31%. The only trial that compared entecavir and lamivudine favored entecavir over lamivudine (OR: 3.64, 95% CI 1.31–10.13; 90 participants). Adverse events were mild. Conclusion. There is insufficient evidence that NA obtain superior efficacy compared with placebo/standard-of-care in patients with acute viral hepatitis, based on low quality evidence.

d-Arabinofuranosyl-pyrimidine and -purine nucleoside analogues containing alkylthio-, acetylthio- or 1-thiosugar substituents at the C2' position were prepared from the corresponding 3',5'-O-silylene acetal-protected nucleoside 2'-exomethylenes by photoinitiated, radical-mediated hydrothiolation reactions. Although the stereochemical outcome of the hydrothiolation depended on the structure of both the thiol and the furanoside aglycone, in general, high d-arabino selectivity was obtained. The cytotoxic effect of the arabinonucleosides was studied on tumorous SCC (mouse squamous cell) and immortalized control HaCaT (human keratinocyte) cell lines by MTT assay. Three pyrimidine nucleosides containing C2'-butylsulfanylmethyl or -acetylthiomethyl groups showed promising cytotoxicity at low micromolar concentrations with good selectivity towards tumor cells. SAR analysis using a methyl β-d-arabinofuranoside reference compound showed that the silyl-protecting group, the nucleobase and the corresponding C2' substituent are crucial for the cell growth inhibitory activity. The effects of the three most active nucleoside analogues on parameters indicative of cytotoxicity, such as cell size, division time and cell generation time, were investigated by near-infrared live cell imaging, which showed that the 2'-acetylthiomethyluridine derivative induced the most significant functional and morphological changes. Some nucleoside analogues also exerted anti-SARS-CoV-2 and/or anti-HCoV-229E activity with low micromolar EC50 values; however, the antiviral activity was always accompanied by significant cytotoxicity. [ABSTRACT FROM AUTHOR]

The on-going global pandemic of COVID-19 is caused by SARS-CoV-2, which features a proofreading mechanism to facilitate the replication of its large RNA genome. The 3′-to-5′ exoribonuclease (ExoN) activity of SARS-CoV-2 non-structural protein 14 (nsp14) removes nucleotides misincorporated during RNA synthesis by the low-fidelity viral RNA-dependent RNA polymerase (RdRp) and thereby compromises the efficacy of antiviral nucleoside/nucleotide analogues. Here we show biochemically that SARS-CoV-2 nsp14 can excise the natural antiviral chain-terminating nucleotide, 3′-deoxy-3′,4′-didehydro-cytidine 5′-monophosphate (ddhCMP), incorporated by RdRp at the 3′ end of an RNA strand. Nsp14 ExoN processes an RNA strand terminated with ddhCMP more efficiently than that with a non-physiological chain terminator 3′-deoxy-cytidine monophosphate (3′-dCMP), whereas RdRp is more susceptible to chain termination by 3′-dCTP than ddhCTP. These results suggest that nsp14 ExoN could play a role in protecting SARS-CoV-2 from ddhCTP, which is produced as part of the innate immune response against viral infections, and that the SARS-CoV-2 enzymes may have adapted to minimize the antiviral effect of ddhCTP. [ABSTRACT FROM AUTHOR]

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Nucleoside analogues are the mainstay of treatment for patients with chronic HBV infection but have no direct effect on covalently closed circular DNA. Long-term HBV viral suppression is now routine, but the desirable endpoint of functional cure is rarely achieved. Newer therapies, targeting other aspects of the replicative life cycle of HBV, present opportunities to deliver finite therapy and HBV 'cure'. This is an area of keen focus for the HBV community. We describe a severe case of hepatitis B reactivation, occurring shortly after the withdrawal of a nucleoside analogue within the protocol of a clinical trial (REEF-2). Despite best supportive care and prompt re-introduction of tenofovir, the patient developed subacute liver failure, requiring emergency orthotopic liver transplantation. As we strive to achieve HBV cure, this case highlights the potential risks of finite therapy and highlights the need for improved biomarker-driven strategies and re-evaluation of study protocols. [ABSTRACT FROM AUTHOR]

Short interfering RNA (siRNA)-triggered gene knockdown through the RNA interference (RNAi) pathway is widely used to study gene function, and siRNA-based therapeutics are in development. However, as the guide strand of an siRNA can function like a natural microRNA (miRNA), siRNAs often repress hundreds of off-target transcripts with complementarity only to the seed region (nucleotides 2-8) of the guide strand. Here, we describe novel guide strand 3'-end modifications derived from 1-ethynylribose (1-ER) and copper-catalyzed azide-alkyne cycloaddition reactions and evaluate their impact on target versus miRNA-like off-target knockdown. Surprisingly, when positioned at the guide strand 3'-end, the parent 1-ER modification substantially reduced off-target knockdown while having no measurable effect on on-target knockdown potency. In addition, these modifications were shown to modulate siRNA affinity for the hAgo2 PAZ domain. However, the change in PAZ domain binding affinity was not sufficient to predict the modification's effect on miRNA-like off targeting.

Background and Aims: Scarce data exist on the effect of nucleos(t)ide analogue (NA) discontinuation on hepatocellular carcinoma (HCC) risk in HBeAg‐negative chronic hepatitis B (CHBe−). Therefore, we assessed whether HCC risk is increased in non‐cirrhotic CHBe− patients who discontinue compared to those remaining on NAs. Methods: This cohort study included 650 consecutive non‐cirrhotic Caucasian or Asian patients with CHBe− without a history of HCC who discontinued NAs after a median of 5 or 3 years (cases, n = 325; Caucasians: 143, Asians: 182) or remained on NA therapy beyond 5 or 3 years respectively (controls, n = 325; Caucasians: 223, Asians: 102). Propensity score (PS) 1:1 matching was applied to adjust for patients' origin, age and sex. Results: During a median follow‐up of 44 months, HCC developed in 7/325 cases and 9/325 controls or 7/245 PS‐matched cases and 7/245 PS‐matched controls with 5‐year cumulative HCC incidence of 5.1% and 4.9% respectively (log‐rank, P =.836). No difference in 5‐year HCC risk was observed between cases and controls of Caucasian (3.0% vs 4.8%; log‐rank, P =.510) or Asian origin (1.3% vs 2.2%; log‐rank, P =.873). In both cases and controls, HCC incidence was independently associated with age and PAGE‐B score. In cases alone, HCC development after NA discontinuation was associated only with pretreatment platelet counts and PAGE‐B score, but not with any type of relapse or HBsAg loss. Conclusions: Our findings suggest that discontinuation of effective long‐term NA therapy in non‐cirrhotic CHBe− patients are not associated with increased HCC risk, which is not affected by post‐NA relapses and/or HBsAg loss. [ABSTRACT FROM AUTHOR]

Feline infectious peritonitis (FIP) is a fatal disease caused by feline coronavirus or its variant, referred to as the FIP virus. Recently, favorable treatment outcomes of the anti-viral drug Mutian® Xraphconn (Mutian X) were noted in cats with FIP. Thus, the therapeutic efficacy of Mutian X in cats with FIP must be explored, although the predictors of therapeutic success remain unknown. In the present study, we administered Mutian X to 141 pet cats with effusive FIP following initial veterinarian examinations. Of these, 116 cats survived but the remaining 25 died during treatment. Pre-treatment signalment, viral gene expression, and representative laboratory parameters for routine FIP diagnosis (i.e., hematocrit, albumin-to-globulin ratio, total bilirubin, serum amyloid-A, and 1-acid glycoprotein) were statistically compared between the survivor and non-survivor groups. The majority of these parameters, including hematocrit, albumin-to-globulin ratio, serum amyloid-A, α1-acid glycoprotein, and viral gene expression, were comparable between the two groups. Interestingly, however, total bilirubin levels in the survivor group were significantly lower than those in the non-survivor group (p < 0.0001). Furthermore, in almost all surviving cats with effusive FIP (96.6%, 28/29), the pre-treatment total bilirubin levels were below 0.5 mg/dL; however, the survival rate decreased drastically (14.3%, 1/7) when the pre-treatment total bilirubin levels exceeded 4.0 mg/dL. Thus, circulating total bilirubin levels may act as a prognostic risk factor for severe FIP and may serve as the predictor of the therapeutic efficacy of Mutian X against this fatal disease. [ABSTRACT FROM AUTHOR]

A male hepatitis B virus (HBV) carrier in his 40s under hemodialysis treatment exhibited chronic hepatitis (alanine aminotransferase: 41 IU/L, HBV-DNA: >9.1 log copies/mL). Following discontinuation of the initial treatment with pegylated interferon-α-2a at 24 weeks due to adverse effects, the administration of tenofovirdisoproxil fumarate (TDF) (300 mg/week) led to a rapid improvement in hepatitis markers: HBV DNA became undetectable at month 34, and seroconversion of hepatitis B envelope antigen was confirmed at 45 months. No side effects were recorded during TDF treatment. TDF is a newly approved nucleoside analogue that may cause severe side effects via proximal tubular injury in patients with renal dysfunction. However, few reports have described its use in hemodialysis patients, whose anuric state may render them less susceptible to side effects including kidney injury. Hepatitis improved remarkably without any adverse drug reactions in the present case. TDF may therefore be considered for chronic hepatitis B patients receiving hemodialysis.

Background Hepatitis B surface antigen (HBsAg) seroclearance is considered a functional cure for patients with chronic hepatitis B, but is rarely achievable with oral nucleos(t)ide analogues alone. We conducted a randomized controlled proof-of-concept trial to evaluate the impact of adding pegylated interferon (peg-IFN) alfa-2a plus sequential or concomitant hepatitis B virus (HBV) vaccination. Methods A total of 111 patients who achieved serum HBV DNA <20 IU/mL and quantitative HBsAg <3000 IU/mL with entecavir were randomly assigned (1:1:1) to the E + sVIP group (entecavir + peg-IFN alfa-2a [180 µg every week over 48 weeks] plus sequential HBV vaccination [20 µg of HBsAg on weeks 52, 56, 60, and 76]), the E + cVIP group (entecavir + peg-IFN alfa-2a + concomitant HBV vaccination [weeks 4, 8, 12, and 28]), or the control group (entecavir only). The primary endpoint was HBsAg seroclearance at week 100, and secondary endpoints included safety. Results No differences in baseline quantitative HBsAg were observed among the groups. The E + sVIP group in the intention-to-treat analysis showed a significantly higher chance of HBsAg seroclearance during week 100 than the control group (16.2% vs 0%; P =.025), but the E + cVIP group (5.4%) failed to reach a significant difference (P =.54). Adverse events were significantly more frequent in the E + sVIP (81.1%) and E + cVIP group (70.3%) than the control group (2.7%) (both P <.0001). However, the frequency of serious adverse events did not differ significantly among the 3 groups (2.7%, 5.4%, and 2.7%, respectively; P = 1.00). Conclusions Entecavir plus an additional peg-IFN alfa-2a treatment followed by sequential HBV vaccination under an intensified schedule significantly increases the chance of HBsAg seroclearance compared to entecavir alone. Clinical Trials Registration NCT02097004. [ABSTRACT FROM AUTHOR]

The outbreaks of severe acute respiratory syndrome-coronavirus-2 (SARS-CoV-2) in 2019, have highlighted the concerns about the lack of potential vaccines or antivirals approved for inhibition of CoVs infection. SARS-CoV-2 RNA dependent RNA polymerase (RdRp) which is almost preserved across different viral species can be a potential target for development of antiviral drugs, including nucleoside analogues (NA). However, ExoN proofreading activity of CoVs leads to their protection from several NAs. Therefore, potential platforms based on the development of efficient NAs with broad-spectrum efficacy against human CoVs should be explored. This study was then aimed to present an overview on the development of NAs-based drug repurposing for targeting SARS-CoV-2 RdRp by computational analysis. Afterwards, the clinical development of some NAs including Favipiravir, Sofosbuvir, Ribavirin, Tenofovir, and Remdesivir as potential inhibitors of RdRp, were surveyed. Overall, exploring broad-spectrum NAs as promising inhibitors of RdRp may provide useful information about the identification of potential antiviral repurposed drugs against SARS-CoV-2. [ABSTRACT FROM AUTHOR]

Carcinogenesis risk scores for chronic hepatitis B have been proposed, but it remains unclear whether these scores during nucleoside/nucleotide analogue (NA) therapy are useful for risk assessment. In this study, we examined changes of these scores and the predictability during NA treatment. 432 patients with no history of hepatocellular carcinoma (HCC) treated with NA were enrolled. PAGE‐B, modified PAGE‐B (mPAGE‐B), and REACH‐B scores were calculated at NA administration, 1 and 2 years after administration. The median follow‐up duration was 5.1 years, during which 37 patients (8.6%) developed HCC. Cumulative incidence HCC development in patients with high risk of PAGE at NA administration, and 1 and 2 years after NA administration was significantly higher than those with intermediate and low‐risk groups (p <.05 for all time points), whereas HCC incidence in patients with high risk of mPAGE‐B and REACH‐B at 2 years after NA administration were equivalent to those with intermediate and low‐risk groups (p =.2 for mPAGE‐B, and p =.1 for REACH‐B). The area under the receiver operating characteristic (AUROC) for HCC development of PAGE‐B at NA administration, and 1 and 2 years after administration were 0.773, 0.803 and 0.737, respectively. The AUROCs of PAGE‐B at each point were continuously higher than those of REACH‐B (0.646, 0.725, and 0.653, respectively) and mPAGE‐B (0.754, 0.734, and 0.678, respectively).PAGE‐B score has a high diagnostic accuracy for HCC development at any time point during NA treatment, indicating its potential use as a real‐time monitor of HCC development. [ABSTRACT FROM AUTHOR]

Hepatitis B virus (HBV) reactivation (HBVr) represents a severe and potentially life-threatening condition, and preventive measures are available through blood test screening or prophylactic therapy administration. The assessment of HBVr traditionally considers factors such as HBV profile, including hepatitis B surface antigen (HBsAg) and antibody to hepatitis B core antigen, along with type of medication (chemotherapy; immunomodulants). Nevertheless, consideration of possible patient's underlying tumor and the specific malignancy type (solid or hematologic) plays a crucial role and needs to be assessed for decision-making process., Competing Interests: Conflict-of-interest statement: All the authors report no relevant conflicts of interest for this article., (©The Author(s) 2024. Published by Baishideng Publishing Group Inc. All rights reserved.)

The purpose of this study was to compare the efficacy of nucleoside analogues (NAs) in the treatment of HBV-related liver failure. The data of patients with HBV-related liver failure treated with nucleoside analogues were used to conduct a network meta-analysis. A total of 1660 patients from 12 articles about the efficacy of lamivudine, entecavir, telbivudine and tenofovir for HBV-related liver failure treatment were recruited in the study. The highest two- and three-month survival rate was recorded for patients using tenofovir. The end-stage liver disease (MELD) score and mortality in patients undergoing tenofovir treatment were the lowest. Patients treated with telbivudine had the highest one-month survival rate. Patients receiving enticavir therapy showed the lowest HBV DNA level. Our results indicate that tenofovir may be the best therapy for the treatment of HBV-related liver failure compared to other nucleoside analogues (including lamivudine, entecavir and telbivudine) and non-NAs treatment.

A recent study in Asian patients with chronic hepatitis B (CHB) reported that the incidence of hepatocellular carcinoma (HCC) was lower in patients treated with tenofovir disoproxil fumarate (TDF) than entecavir (ETV), but this finding remains controversial. We aimed to identify any differences in HCC incidence, or other patient outcomes, between patients receiving TDF or ETV in the well monitored, multicenter European PAGE-B cohort. We included 1,935 Caucasians with CHB, with or without compensated cirrhosis, treated with ETV (n = 772) or TDF (n = 1,163) monotherapy. Mean follow-up was 7.1 ± 3.0 years from ETV/TDF onset. The 5-year cumulative HCC incidence was 5.4% in ETV- and 6.0% in TDF-treated patients (log-rank, p = 0.321), with no significant difference in any patient subgroup (with or without cirrhosis, naïve or experienced to oral antiviral(s) [total, with or without cirrhosis]). In multivariable Cox regression analyses, the hazard of HCC was similar between ETV- and TDF-treated patients after adjustment for several HCC risk factors. ETV- and TDF-treated patients had similar rates of on-therapy biochemical and virological remission, HBsAg loss, liver transplantation and/or death. Elastographic reversion of cirrhosis at year 5 (liver stiffness <12 kPa) was observed in 245/347 (70.6%) patients with pretreatment cirrhosis, being more frequent in TDF- than ETV- treated patients (73.8% vs. 61.5%, p = 0.038). In Caucasian patients with CHB, with or without cirrhosis, long-term ETV or TDF monotherapy is associated with similar HCC risk, rates of biochemical/virological remission, HBsAg loss and liver transplantation or death, but elastographic reversion of cirrhosis at year 5 was more frequent with TDF. In a large cohort of Caucasians with chronic hepatitis B treated with entecavir (ETV) or tenofovir disoproxil fumarate (TDF) monotherapy, cumulative rates of hepatocellular carcinoma did not differ (up to 12 years). Nor did rates of biochemical/virological remission, HBsAg loss and liver transplantation or death. However, elastographic reversion of cirrhosis at year 5 was more frequent in TDF- than ETV-treated patients with pretreatment cirrhosis. • Caucasians with chronic hepatitis B treated with entecavir vs. tenofovir had: • Similar rates of hepatocellular carcinoma up to 12 years • Similar rates of biochemical/virological response, HBsAg loss and mortality • Less frequent elastographic reversion of cirrhosis at year 5 [ABSTRACT FROM AUTHOR]

The development of drug resistance to chemotherapeutic agents has consistently presented a challenge in terms of the treatment of patients with triple-negative breast cancer (TNBC). In the present study, gemcitabine (dFdC)-resistant TNBC cells were established, and the effects of lentivirus-deoxyribonucleoside kinase (dNK) and a mutated form of dNK (lentivirus-dNKmut) on reversing the acquired drug resistance in dFdC-resistant TNBC cells were explored. Quantitative PCR and western blotting experiment results suggested that Drosophila melanogaster (Dm)-dNK was stably expressed in the lentivirus-infected MDA-MB-231 and MDA-MB-231R cells in the nucleus or cytosol, and autoradiography experiments revealed similar levels of enzymatic activity in the cells expressing dNK or dNKmut. In vitro cytotoxicity assay revealed that the IC50 values of dFdC were decreased 30~50-fold in the dFdC-resistant MDA-MB-231 cells following lentiviral transfection with dNK or dNKmut, and this effect was associated with a significantly increased rate of apoptosis compared with the cells transfected with the negative control lentivirus. In conclusion, Dm-dNK in the nucleus or cytosol may be a potential candidate for reversing acquired dFdC resistance in TNBC cells, which may form the basis of novel strategies for the treatment of patients with drug-resistant TNBC. [ABSTRACT FROM AUTHOR]

Combinatorial antitumor therapies using different combinations of drugs and genes are emerging as promising ways to overcome drug resistance, which is a major cause for the failure of cancer treatment. However, dramatic pharmacokinetic differences of drugs greatly impede their combined use in cancer therapy, raising the demand for drug delivery systems (DDSs) for tumor treatment. By employing fluorescent dithiomaleimide (DTM) as a linker, we conjugate two paclitaxel (PTX) molecules with a floxuridine (FdU)‐integrated antisense oligonucleotide (termed chemogene) to form a drug–chemogene conjugate. This PTX–chemogene conjugate can self‐assemble into a spherical nucleic acid (SNA)‐like micellular nanoparticle as a carrier‐free DDS, which knocks down the expression of P‐glycoprotein and subsequently releases FdU and PTX to exert a synergistic antitumor effect and greatly inhibit tumor growth. [ABSTRACT FROM AUTHOR]

A male hepatitis B virus (HBV) carrier in his 40s under hemodialysis treatment exhibited chronic hepatitis (alanine aminotransferase: 41 IU/L, HBV-DNA: >9.1 log copies/mL). Following discontinuation of the initial treatment with pegylated interferon-α-2a at 24 weeks due to adverse effects, the administration of tenofovirdisoproxil fumarate (TDF) (300 mg/week) led to a rapid improvement in hepatitis markers: HBV DNA became undetectable at month 34, and seroconversion of hepatitis B envelope antigen was confirmed at 45 months. No side effects were recorded during TDF treatment. TDF is a newly approved nucleoside analogue that may cause severe side effects via proximal tubular injury in patients with renal dysfunction. However, few reports have described its use in hemodialysis patients, whose anuric state may render them less susceptible to side effects including kidney injury. Hepatitis improved remarkably without any adverse drug reactions in the present case. TDF may therefore be considered for chronic hepatitis B patients receiving hemodialysis. [ABSTRACT FROM AUTHOR]

Purpose: We postulate that the deoxyguanosine analogue CNDAG [9-(2-C-cyano-2-deoxy-1-β-D-arabino-pentofuranosyl)guanine] likely causes a single-strand break after incorporation into DNA, similar to the action of its cytosine congener CNDAC, and that subsequent DNA replication across the unrepaired nick would generate a double-strand break. This study aimed at identifying cellular responses and repair mechanisms for CNDAG prodrugs, 2-amino-9-(2-C-cyano-2-deoxy-1-β-D-arabino-pentofuranosyl)-6-methoxy purine (6-OMe) and 9-(2-C-cyano-2-deoxy-1-β-D-arabino-pentofuranosyl)-2,6-diaminopurine (6-NH2). Each compound is a substrate for adenosine deaminase, the action of which generates CNDAG.Methods: Growth inhibition assay, clonogenic survival assay, immunoblotting, and cytogenetic analyses (chromosomal aberrations and sister chromatid exchanges) were used to investigate the impact of CNDAG on cell lines.Results: The 6-NH2 derivative was selectively potent in T cell malignant cell lines. Both prodrugs caused increased phosphorylation of ATM and its downstream substrates Chk1, Chk2, SMC1, NBS1, and H2AX, indicating activation of ATM-dependent DNA damage response pathways. In contrast, there was no increase in phosphorylation of DNA-PKcs, which participates in repair of double-strand breaks by non-homologous end-joining. Deficiency in ATM, RAD51D, XRCC3, BRCA2, and XPF, but not DNA-PK or p53, conferred significant clonogenic sensitivity to CNDAG or the prodrugs. Moreover, hamster cells lacking XPF acquired remarkably more chromosomal aberrations after incubation for two cell cycle times with CNDAG 6-NH2, compared to the wild type. Furthermore, CNDAG 6-NH2 induced greater levels of sister chromatid exchanges in wild-type cells exposed for two cycles than those for one cycle, consistent with increased double-strand breaks after a second S phase.Conclusion: CNDAG-induced double-strand breaks are repaired mainly through homologous recombination. [ABSTRACT FROM AUTHOR]

Coronaviruses (CoVs) have emerged from animal reservoirs to cause severe and lethal disease in humans, but there are currently no FDA-approved antivirals to treat the infections. One class of antiviral compounds, nucleoside analogues, mimics naturally occurring nucleosides to inhibit viral replication. While these compounds have been successful therapeutics for several viral infections, mutagenic nucleoside analogues, such as ribavirin and 5-fluorouracil, have been ineffective at inhibiting CoVs. This has been attributed to the proofreading activity of the viral 3'-5' exoribonuclease (ExoN). β-d-N4-Hydroxycytidine (NHC) (EIDD-1931; Emory Institute for Drug Development) has recently been reported to inhibit multiple viruses. Here, we demonstrate that NHC inhibits both murine hepatitis virus (MHV) (50% effective concentration [EC50] = 0.17 μM) and Middle East respiratory syndrome CoV (MERS-CoV) (EC50 = 0.56 μM) with minimal cytotoxicity. NHC inhibited MHV lacking ExoN proofreading activity similarly to wild-type (WT) MHV, suggesting an ability to evade or overcome ExoN activity. NHC inhibited MHV only when added early during infection, decreased viral specific infectivity, and increased the number and proportion of G:A and C:U transition mutations present after a single infection. Low-level NHC resistance was difficult to achieve and was associated with multiple transition mutations across the genome in both MHV and MERS-CoV. These results point to a virus-mutagenic mechanism of NHC inhibition in CoVs and indicate a high genetic barrier to NHC resistance. Together, the data support further development of NHC for treatment of CoVs and suggest a novel mechanism of NHC interaction with the CoV replication complex that may shed light on critical aspects of replication. IMPORTANCE The emergence of coronaviruses (CoVs) into human populations from animal reservoirs has demonstrated their epidemic capability, pandemic potential, and ability to cause severe disease. However, no antivirals have been approved to treat these infections. Here, we demonstrate the potent antiviral activity of a broad-spectrum ribonucleoside analogue, β-d-N4-hydroxycytidine (NHC), against two divergent CoVs. Viral proofreading activity does not markedly impact sensitivity to NHC inhibition, suggesting a novel interaction between a nucleoside analogue inhibitor and the CoV replicase. Further, passage in the presence of NHC generates only low-level resistance, likely due to the accumulation of multiple potentially deleterious transition mutations. Together, these data support a mutagenic mechanism of inhibition by NHC and further support the development of NHC for treatment of CoV infections. [ABSTRACT FROM AUTHOR]

[Display omitted] Antibiotic resistance is a major threat to public health, and Gram-negative bacteria pose a particular challenge due to their combination of a low permeability cell envelope and efflux pumps. Our limited understanding of the chemical rules for overcoming these barriers represents a major obstacle in antibacterial drug discovery. Several recent efforts to address this problem have involved screening compound libraries for accumulation in bacteria in order to understand the structural properties required for Gram-negative permeability. Toward this end, we used cheminformatic analysis to design a library of sulfamidoadenosines (AMSN) having diverse substituents at the adenine C2 position. An efficient synthetic route was developed with installation of a uniform cross-coupling reagent set using Sonogashira and Suzuki reactions of a C2-iodide. The potential utility of these compounds was demonstrated by pilot analysis of selected analogues for accumulation in Escherichia coli. [ABSTRACT FROM AUTHOR]

Abstract Background Canine distemper (CD) is a widespread infectious disease that can severely impact a variety of species in the order Carnivora, as well as non-carnivore species such as non-human primates. Despite large-scale vaccination campaigns, several fatal outbreaks have been reported in wild and domestic carnivore populations. This, in association with expansion of the disease host range and the development of vaccine-escape strains, has contributed to an increased demand for therapeutic strategies synergizing with vaccine programs for effectively controlling canine distemper. 6-methylmercaptopurine riboside (6MMPr) is a modified thiopurine nucleoside with known antiviral properties against certain RNA viruses. Methods We tested the inhibitory effects of 6MMPr against a wild-type CDV strain infection in cell culture. We measured infectious particle production and viral RNA levels in treated and untreated CDV-infected cells. Ribavirin (RIB) was used as a positive control. Results Here, we report for the first time the antiviral effects of 6MMPr against canine distemper virus (CDV) in vitro. 6MMPr was able to reduce viral RNA levels and to inhibit the production of infectious CDV particles. The therapeutic selectivity of 6MMPr was approximately six times higher than that of ribavirin. Conclusion Our results indicate that 6MMPr has high anti-CDV potential and warrants further testing against other paramyxoviruses, as well as clinical testing of the compound against CDV.

Background: β-d-N4-Hydroxycytidine (NHC) is the active metabolite of molnupiravir, a broad-spectrum antiviral approved by the MHRA for COVID-19 treatment. NHC induces lethal mutagenesis of the SARS-CoV-2 virus, undergoing incorporation into the viral genome and arresting viral replication. It has previously been reported that several nucleoside analogues elicit off-target inhibition of mitochondrial DNA (mtDNA) or RNA replication. Although NHC does not exert these effects in HepG2 cells, HepaRG are proven to be advantageous over HepG2 for modelling nucleoside analogue-induced mitochondrial dysfunction. Therefore, the objective of this work was to assess the mitotoxic potential of NHC in HepaRG cells, a model more closely resembling physiological human liver., Methods: Differentiated HepaRG cells were exposed to 1-60 μM NHC for 3-14 days to investigate effects of sub-, supra-, and clinically-relevant exposures (in the UK, molnupiravir for COVID-19 is indicated for 5 days and reported Cmax is 16 μM). Following drug incubation, cell viability, mtDNA copy number, mitochondrial protein expression, and mitochondrial respiration were assessed., Results: NHC induced minor decreases in cell viability at clinically relevant exposures, but did not decrease mitochondrial protein expression. The effects on mtDNA were variable, but typically copy number was increased. At supra-clinical concentrations (60 μM), NHC reduced mitochondrial respiration, but did not appear to induce direct electron transport chain dysfunction., Conclusions: Overall, NHC does not cause direct mitochondrial toxicity in HepaRG cells at clinically relevant concentrations, but may induce minor cellular perturbations. As HepaRG cells have increased physiological relevance, these findings provide additional assurance of the mitochondrial safety profile of NHC., (© The Author(s) 2024. Published by Oxford University Press.)

We report the synthesis of pyrene-conjugated azanucleoside-incorporated oligodeoxynucleotides (aza-ODNs). Combination of liquid-phase synthesis by alkyl-chain-soluble-support (ACSS) and electrochemical C–H activation realized efficient access to aza-ODNs without requiring an excess amount of reagent or solvent. The fluorescent properties of pyrene-conjugated aza-ODNs were also investigated. The resulting fluorescence spectrum indicated that the modification of the position of the nitrogen atom was suitable for the preparation of artificial functionalized oligonucleotides. A synthetic route to azaribose, as a precursor of aza-ODNs, was also reinvestigated to realize more efficient production. Electrochemical N-α-acetoxylation in 0.1 M lithium perchlorate/nitromethane/50 mM AcOH medium was found to be a suitable medium for this route. These results represent a new efficient synthetic route to aza-ODNs. [ABSTRACT FROM AUTHOR]

Purpose of Review: Chronic HBV (CHB) remains a global public health problem with over 257 million people chronically infected worldwide. Without appropriate management, 20% of individuals infected with CHB will die from complications of cirrhosis, liver failure, or hepatocellular carcinoma (HCC). Despite an effective vaccination to prevent infection, HBV has yet to be successfully eradicated globally. Current treatments can only control and suppress the virus but cannot cure. Updates in the management of chronic HBV will be reviewed, including latest treatments and treatment strategies as well as potential curative therapeutic agents in clinical trial. Recent Findings: A new nucleotide analogue drug, tenofovir alafenamide fumarate (TAF), has been added to the HBV therapeutic armamentarium. A more potent drug showing non-inferiority, TAF has shown to improve renal and bone laboratory safety parameters compared to TDF. In addition, new treatment recommendations have been made for both general and special populations including pregnancy and HBV reactivation. There is growing data supporting the importance of antiviral therapy in patients with advanced liver disease and liver decompensation which has resulted in improved outcomes. In addition, at least 30 potential therapeutics are in clinical trials in the pursuit of curative treatments for chronic HBV with the goal of "functional cure." Summary: CHB remains a global public health problem with complications including cirrhosis, liver failure, and HCC. Current antiviral therapy can cause reversal of liver disease, improve outcomes, and prevent complications such as reactivation but still requires long-term use. Curative treatments for HBV are greatly needed with promising curative drugs in early phase studies. [ABSTRACT FROM AUTHOR]

Abstract Nucleoside analogue reverse transcriptase (RT) inhibitors (NRTIs) are major antiviral agents against hepatitis B virus (HBV) and human immunodeficiency virus type-1 (HIV-1). However, the notorious insoluble property of HBV RT has prevented atomic-resolution structural studies and rational anti-HBV drug design. Here, we created HIV-1 RT mutants containing HBV-mimicking sextuple or septuple amino acid substitutions at the nucleoside-binding site (N-site) and verified that these mutants retained the RT activity. The most active RT mutant, HIV-1 RT7MC, carrying Q151M/G112S/D113A/Y115F/F116Y/F160L/I159L was successfully crystallized, and its three-dimensional structure was determined in complex with DNA:dGTP/entecavir-triphosphate (ETV-TP), a potent anti-HBV guanosine analogue RT inhibitor, at a resolution of 2.43 Å and 2.60 Å, respectively. The structures reveal significant positional rearrangements of the amino acid side-chains at the N-site, elucidating the mechanism underlying the differential susceptibility of HIV-1 and HBV against recently reported 4ʹ-modified NRTIs. Highlights • HIV-1 RTs with HBV-mimicking mutations at the nucleoside-binding site were created. • The HIV-1 RTs with HBV-mimicking sextuple/septuple mutations retain RT activity. • X-ray structures of the HIV-1 RT7MC:DNA:dGTP/ETV-TP ternary complex are reported. • The structures elucidate the differential drug susceptibility of HIV-1 and HBV. [ABSTRACT FROM AUTHOR]

Abstract Background Entecavir (ETV) is a nucleoside analogue (NA) that is effective for treatment of chronic hepatitis B (CHB) due to its low resistance rates and potent antiviral effects. We aimed to evaluate the clinical, biochemical and virological response to ETV in patients without a prior use of nucleos(t)ide (NA-naïve) vs. those who failed prior NA use (NA-experienced) in the treatment of CHB. Methods Patients treated between April 2012 and December 2017 were retrospectively studied. A comparison was made between patients treated with ETV in NA-naïve Vs. NA-experienced. Complete virological response (CVR) was defined as achieving undetectable HBV-DNA level, up to 15 IU/ml, partial virological response (PVR) as 15–200 IU/ml and >200 IU/ml for no virological response (NVR) after one year of therapy. Results Overall, 148 patients were included (69 NA-naïve and 79 NA-experienced). In NA-naïve group, 51%, 17% and 32% achieved CVR, PVR and NVR vs. 17%, 9% and 75% in NA-experienced group, respectively (p < 0.001). HBsAg seroconversion was achieved in 5.8% in NA-naïve group vs. 6.3% in NA-experienced group (p = 1.00). HBeAg seroconversion was 17% in NA-naïve group and 25% in NA-experienced group (p = 0.24). There was no significant difference in alanine transaminase normalization or in mortality rate between both groups; p = 0.87 and p = 1.00 respectively. Conclusion ETV therapy in CHB results in a better virological response in NA-naïve patients compared to NA-experienced. There were no differences between both groups in regards to the rate of HBsAg or HBeAg seroconversions, biochemical improvements or mortality. [ABSTRACT FROM AUTHOR]

Nucleoside and nucleotide analogues are essential antivirals in the treatment of infectious diseases such as human immunodeficiency virus (HIV), hepatitis B virus (HBV), hepatitis C virus (HCV), herpes simplex virus (HSV), varicella-zoster virus (VZV), and human cytomegalovirus (HCMV). To celebrate the 80th birthday of Prof. Dr. Erik De Clercq on 28 March 2021, this review provides an overview of his contributions to eight approved nucleos(t)ide drugs: (i) three adenosine nucleotide analogues, namely tenofovir disoproxil fumarate (Viread®) and tenofovir alafenamide (Vemlidy®) against HIV and HBV infections and adefovir dipivoxil (Hepsera®) against HBV infections; (ii) two thymidine nucleoside analogues, namely brivudine (Zostex®) against HSV-1 and VZV infections and stavudine (Zerit®) against HIV infections; (iii) two guanosine analogues, namely valacyclovir (Valtrex®, Zelitrex®) against HSV and VZV and rabacfosadine (Tanovea®-CA1) for the treatment of lymphoma in dogs; and (iv) one cytidine nucleotide analogue, namely cidofovir (Vistide®) for the treatment of HCMV retinitis in AIDS patients. Although adefovir dipivoxil, stavudine, and cidofovir are virtually discontinued for clinical use, tenofovir disoproxil fumarate and tenofovir alafenamide remain the most important antivirals against HIV and HBV infections worldwide. Overall, the broad-spectrum antiviral potential of nucleos(t)ide analogues supports their development to treat or prevent current and emerging infectious diseases worldwide.