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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]

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.

Simple Summary: Feline infectious peritonitis is a fatal disease classified into the effusive form, the non-effusive form, or their mixture showing clinical signs of both forms. To determine whether the therapeutic effect of Mutian on the non-effusive and the mixed forms of feline infectious peritonitis can be predicted using clinical indicators before starting treatment, we entered 161 cats with the mixed form and 163 cats with the non-effusive form into this study. Physical assessment, detection of viral genes, and several clinical laboratory tests were performed before Mutian was administered. These indicators were compared between the disease groups that survived after receiving Mutian for 84 days and those that died before the completion of treatment. Significant differences in body temperature, appetite scores, and activity scores were confirmed between the surviving and non-surviving groups. The therapeutic effect was insufficient when total bilirubin levels increased in cats with the mixed form. In both forms of feline infectious peritonitis, therapeutic effects were difficult to obtain when neurological clinical signs had been observed. The therapeutic effects of Mutian on the cats with these forms of feline infectious peritonitis can be predicted based on pre-treatment body temperature, appetite scores, and activity scores, as well as the presence of neurological signs. Feline infectious peritonitis (FIP) is a fatal disease classified as either effusive, non-effusive ('dry'), or a mixture ('mixed') of the forms of FIP, with mixed showing signs of both effusive and dry. To determine whether the therapeutic effect of Mutian on dry and mixed FIP can be predicted using clinical indicators before starting treatment, we entered 161 cats with mixed FIP and 163 cats with dry FIP into this study. Physical assessments, the reverse transcriptase-PCR detection of viral genes, and clinical laboratory tests (hematocrit, albumin/globulin ratio, serum amyloid A, α1-acid glycoprotein, and total bilirubin) were performed before Mutian was administered. These indicators were compared between the FIP groups that survived after receiving Mutian for 84 days and those that died before the completion of treatment. Significant differences in body temperature, appetite, and activity scores were confirmed between the surviving and non-surviving groups. The therapeutic effect was insufficient when total bilirubin levels increased in cats with the mixed form. In both of the FIP types, therapeutic effects were difficult to obtain when neurological clinical signs were observed. The therapeutic effects of Mutian on the cats with dry and mixed FIP can be predicted based on pre-treatment body temperature, appetite scores, and activity scores, as well as the presence of neurological signs. [ABSTRACT FROM AUTHOR]

Remdesivir (RDV, Veklury®) is the first FDA-approved antiviral treatment for COVID-19. It is a nucleotide analogue (NA) carrying a 1′-cyano (1′-CN) group on the ribose and a pseudo-adenine nucleobase whose contributions to the mode of action (MoA) are not clear. Here, we dissect these independent contributions by employing RDV-TP analogues. We show that while the 1′-CN group is directly responsible for transient stalling of the SARS-CoV-2 replication/transcription complex (RTC), the nucleobase plays a role in the strength of this stalling. Conversely, RNA extension assays show that the 1′-CN group plays a role in fidelity and that RDV-TP can be incorporated as a GTP analogue, albeit with lower efficiency. However, a mutagenic effect by the viral polymerase is not ascertained by deep sequencing of viral RNA from cells treated with RDV. We observe that once added to the 3′ end of RNA, RDV-MP is sensitive to excision and its 1′-CN group does not impact its nsp14-mediated removal. A >14-fold RDV-resistant SARS-CoV-2 isolate can be selected carrying two mutations in the nsp12 sequence, S759A and A777S. They confer both RDV-TP discrimination over ATP by nsp12 and stalling during RNA synthesis, leaving more time for excision-repair and potentially dampening RDV efficiency. We conclude that RDV presents a multi-faced MoA. It slows down or stalls overall RNA synthesis but is efficiently repaired from the primer strand, whereas once in the template, read-through inhibition adds to this effect. Its efficient incorporation may corrupt proviral RNA, likely disturbing downstream functions in the virus life cycle. • Several simultaneous MoAs have been attributed to the 1′-CN group and pseudo-base modifications of RDV. • The 1′-CN group promotes transient stalling after RDV-TP incorporation, which is easily overcome at high NTP concentrations. • RDV-MP can be excised from the extending RNA, and its pseudo-base contributes to this excision sensitivity. • A >14-fold RDV-resistant SARS-CoV-2 isolate selected containing S759A and A777S substitution mutations in nsp12 sequence. • RDV-resistant mutant RdRp prefers native ATP over RDV-TP and causes increased stalling that likely favors excision repair. [ABSTRACT FROM AUTHOR]

Remdesivir is a broad-spectrum antiviral drug which has been approved to treat COVID-19. Remdesivir is in fact a prodrug, which is metabolized in vivo into the active form remdesivir triphosphate (RTP), an analogue of adenosine triphosphate (ATP) with a cyano group substitution in the carbon 1' of the ribose (1'-CN). RTP is a substrate for RNA synthesis and can be easily incorporated by viral RNA-dependent RNA polymerases (RdRp). Importantly, once remdesivir is incorporated (now monophosphate), it will act as a delayed chain terminator, thus blocking viral RNA synthesis. It has been reported that mitochondrial Polγ is also blocked in vitro by RTP , but the low impact in vivo on mitochondrial DNA replication stalling is likely due to repriming by the human DNA-directed DNA Primase/Polymerase (Hs PrimPol), which also operates in mitochondria. In this work, we have tested if RTP is a valid substrate for both DNA primase and DNA polymerase activities of Hs PrimPol, and its impact in the production of mature DNA primers. RTP resulted to be an invalid substrate for elongation, but it can be used to initiate primers at the 5´site, competing with ATP. Nevertheless, RTP -initiated primers are abortive, ocassionally reaching a maximal length of 4–5 nucleotides, and do not support elongation mediated by primer/template distortions. However, considering that the concentration of ATP , the natural substrate, is much higher than the intracellular concentration of RTP , it is unlikely that Hs PrimPol would use RTP for primer synthesis during a remdesivir treatment in real patients. • RTP is a valid substrate for Hs PrimPol as the first nucleotide of a primer. • RTP competes with ATP , being 5-fold less efficient to form dimers. • RTP -initiated dimers cannot be elongated to a mature primer. • RTP competes with dNTPs at the Hs PrimPol elongation site but it is not incorporated. • RTP treatment would not affect Hs PrimPol protective role against Polγ toxicity. [ABSTRACT FROM AUTHOR]

Nucleotide analogues are the divergent scaffolds that are reliable potential therapeutic drugs to treat the wide range of diseases including viral infections. For instance, Remdesivir is a biologically important nucleotide analogue prodrug that can act as a key drug target for the diseases Ebola and COVID-19. Remdesivir is a structurally chiral aryloxy-phosphoramidate prodrug as it is metabolized into nucleoside triphosphate (active drug form) inside the cell through sequential reactions by ester mediated-hydrolysis. Thus, the current minireview focuses on the earlier reported synthetic approaches of key fragments of remdesivir and their developments to attain the scale-up yields of the drug for clinical/commercial applies. Further, this review serves as a template for the design and development of other complex organic molecules. [ABSTRACT FROM AUTHOR]

Abstract Background Serum hepatitis B core-related antigen (HBcrAg) is a potential surrogate marker for intra-hepatic covalently-closed circular DNA in chronic hepatitis B (CHB). We aimed to study the profiles of serum HBcrAg in CHB patients treated with first-line nucleos(t)ide analogues (NA): entecavir (ETV), tenofovir disoproxil fumarate (TDF) or tenofovir alafenamide (TAF). Method Serum HBcrAg was measured in 120 treatment-naïve CHB patients receiving one of the 3 NAs (ETV: TDF: TAF = 60: 26: 34) using the Lumipulse G HBcrAg assay in a Lumipulse G1200 analyzer (Fujirebio Inc, Toyko, Japan). Serum HBcrAg levels were measured at week 0, week 48 and week 96 of NA therapy. Results Among the 120 patients, 67 (55.8%) were hepatitis B e antigen (HBeAg) positive. Both tenofovir and ETV led to significantly lower serum HBcrAg at week 48 and week 96 compared to week 0. There were no significant differences for the magnitude of median HBcrAg decline at week 96 between tenofovir and ETV in HBeAg-positive (2.28 vs. 1.65 log U/mL, p > 0.05) and HBeAg-negative (0.83 vs. 0.54 log U/mL, p > 0.05) patients. TDF and TAF produced no significant differences in the magnitude of median HBcrAg decline at week 96 (HBeAg-positive: 2.63 vs. 1.83, respectively; HBeAg-negative: 1.04 vs. 0.40, respectively; both p > 0.05). Conclusion Magnitude of reduction of HBcrAg levels after 2-year first-line treatment did not differ statistically among the current first-line NAs, although HBcrAg reduction was numerically greater in tenofovir-treated group. More long-term studies are essential to determine whether tenofovir exerts a more pronounced effect on HBcrAg.

Feline infectious peritonitis (FIP) is a fatal disease classified as either effusive, non-effusive (‘dry’), or a mixture (‘mixed’) of the forms of FIP, with mixed showing signs of both effusive and dry. To determine whether the therapeutic effect of Mutian on dry and mixed FIP can be predicted using clinical indicators before starting treatment, we entered 161 cats with mixed FIP and 163 cats with dry FIP into this study. Physical assessments, the reverse transcriptase-PCR detection of viral genes, and clinical laboratory tests (hematocrit, albumin/globulin ratio, serum amyloid A, α1-acid glycoprotein, and total bilirubin) were performed before Mutian was administered. These indicators were compared between the FIP groups that survived after receiving Mutian for 84 days and those that died before the completion of treatment. Significant differences in body temperature, appetite, and activity scores were confirmed between the surviving and non-surviving groups. The therapeutic effect was insufficient when total bilirubin levels increased in cats with the mixed form. In both of the FIP types, therapeutic effects were difficult to obtain when neurological clinical signs were observed. The therapeutic effects of Mutian on the cats with dry and mixed FIP can be predicted based on pre-treatment body temperature, appetite scores, and activity scores, as well as the presence of neurological signs.

Background and Aims: Whether tenofovir or entecavir has different effects on the prevention of hepatitis B virus (HBV)-related hepatocellular carcinoma (HCC) in secondary and tertiary preventive settings is still a matter of debate. This study aimed to compare the long-term prognosis of HCC between tenofovir and entecavir in patients with chronic hepatitis B., Methods: Chronic hepatitis B patients diagnosed with HCC between November 2008 and December 2018 and treated with either entecavir or tenofovir at a tertiary center in Korea were included. The effect of tenofovir compared with entecavir on the prognosis of HBV-related HCC was assessed using multivariable-adjusted Cox and propensity score (PS)-matched analyses. Various predefined subgroup analyses were conducted., Results: During a median follow-up period of 3.0 years, the mortality rate for entecavir-treated patients (n = 3469) was 41.2%, while tenofovir-treated patients (n = 3056) had a mortality rate of 34.6%. Overall survival (OS) was better in the tenofovir group (adjusted hazard ratio [aHR], 0.79; P < .001), which were consistently observed in the PS-matched analysis. The magnitude of the risk difference in OS was more prominent 2 years after the diagnosis of HCC (aHR, 0.50; P < .001) than 2 years before (aHR, 0.88; P = .005), and it was more pronounced in patients with earlier HCC stages. In all subgroups, except for those with shorter life expectancy, such as those with compromised liver function, tenofovir was associated with better OS compared with entecavir., Conclusions: Among patients with HBV-related HCC, those treated with tenofovir had a better prognosis than those treated with entecavir, particularly among those with prolonged survival., (Copyright © 2024 AGA Institute. Published by Elsevier Inc. All rights reserved.)

Predicting drug-induced side effects in the cardiovascular system is very important because it can lead to the discontinuation of new drugs/candidates or the withdrawal of marketed drugs. Although chronic assessment of cardiac contractility is an important issue in safety pharmacology, an in vitro evaluation system has not been fully developed. We previously developed an imaging-based contractility assay system to detect acute cardiotoxicity using human iPS cell-derived cardiomyocytes (hiPSC-CMs). To extend the system to chronic toxicity assessment, we examined the effects of the antihepatitis C virus (HCV) drug candidate BMS-986094, a guanosine nucleotide analogue, which was withdrawn from phase 2 clinical trials because of unexpected contractility toxicities. Additionally, we examined sofosbuvir, another nucleotide analogue inhibitor of HCV that has been approved as an anti-HCV drug. Motion imaging analysis revealed the difference in cardiotoxicity between the cardiotoxic BMS-986094 and the less toxic sofosbuvir in hiPSC-CMs, with a minimum of 4 days of treatment. In addition, we found that BMS-986094-induced contractility impairment was mediated by a decrease in calcium transient. These data suggest that chronic treatment improves the predictive power for the cardiotoxicity of anti-HCV drugs. Thus, hiPSC-CMs can be a useful tool to assess drug-induced chronic cardiotoxicity in non-clinical settings. [ABSTRACT FROM AUTHOR]

Background: Serum hepatitis B core-related antigen (HBcrAg) is a potential surrogate marker for intra-hepatic covalently-closed circular DNA in chronic hepatitis B (CHB). We aimed to study the profiles of serum HBcrAg in CHB patients treated with first-line nucleos(t)ide analogues (NA): entecavir (ETV), tenofovir disoproxil fumarate (TDF) or tenofovir alafenamide (TAF).Method: Serum HBcrAg was measured in 120 treatment-naïve CHB patients receiving one of the 3 NAs (ETV: TDF: TAF = 60: 26: 34) using the Lumipulse G HBcrAg assay in a Lumipulse G1200 analyzer (Fujirebio Inc, Toyko, Japan). Serum HBcrAg levels were measured at week 0, week 48 and week 96 of NA therapy.Results: Among the 120 patients, 67 (55.8%) were hepatitis B e antigen (HBeAg) positive. Both tenofovir and ETV led to significantly lower serum HBcrAg at week 48 and week 96 compared to week 0. There were no significant differences for the magnitude of median HBcrAg decline at week 96 between tenofovir and ETV in HBeAg-positive (2.28 vs. 1.65 log U/mL, p > 0.05) and HBeAg-negative (0.83 vs. 0.54 log U/mL, p > 0.05) patients. TDF and TAF produced no significant differences in the magnitude of median HBcrAg decline at week 96 (HBeAg-positive: 2.63 vs. 1.83, respectively; HBeAg-negative: 1.04 vs. 0.40, respectively; both p > 0.05).Conclusion: Magnitude of reduction of HBcrAg levels after 2-year first-line treatment did not differ statistically among the current first-line NAs, although HBcrAg reduction was numerically greater in tenofovir-treated group. More long-term studies are essential to determine whether tenofovir exerts a more pronounced effect on HBcrAg. [ABSTRACT FROM AUTHOR]

Abstract SARS‐CoV‐2, a member of the coronavirus family, has caused a global public health emergency. Based on our analysis of hepatitis C virus and coronavirus replication, and the molecular structures and activities of viral inhibitors, we previously reasoned that the FDA‐approved hepatitis C drug EPCLUSA (Sofosbuvir/Velpatasvir) should inhibit coronaviruses, including SARS‐CoV‐2. Here, using model polymerase extension experiments, we demonstrate that the active triphosphate form of Sofosbuvir is incorporated by low‐fidelity polymerases and SARS‐CoV RNA‐dependent RNA polymerase (RdRp), and blocks further incorporation by these polymerases; the active triphosphate form of Sofosbuvir is not incorporated by a host‐like high‐fidelity DNA polymerase. Using the same molecular insight, we selected 3’‐fluoro‐3’‐deoxythymidine triphosphate and 3’‐azido‐3’‐deoxythymidine triphosphate, which are the active forms of two other anti‐viral agents, Alovudine and AZT (an FDA‐approved HIV/AIDS drug) for evaluation as inhibitors of SARS‐CoV RdRp. We demonstrate the ability of two of these HIV reverse transcriptase inhibitors to be incorporated by SARS‐CoV RdRp where they also terminate further polymerase extension. Given the 98% amino acid similarity of the SARS‐CoV and SARS‐CoV‐2 RdRps, we expect these nucleotide analogues would also inhibit the SARS‐CoV‐2 polymerase. These results offer guidance to further modify these nucleotide analogues to generate more potent broad‐spectrum anti‐coronavirus agents.

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 genetic code is considered to use five nucleic bases (adenine, guanine, cytosine, thymine and uracil), which form two pairs for encoding information in DNA and two pairs for encoding information in RNA. Nevertheless, in recent years several artificial base pairs have been developed in attempts to expand the genetic code. Employment of these additional base pairs increases the information capacity and variety of DNA sequences, and provides a platform for the site-specific, enzymatic incorporation of extra functional components into DNA and RNA. As a result, of the development of such expanded systems, many artificial base pairs have been synthesized and tested under various conditions. Following many stages of enhancement, unnatural base pairs have been modified to eliminate their weak points, qualifying them for specific research needs. Moreover, the first attempts to create a semi-synthetic organism containing DNA with unnatural base pairs seem to have been successful. This further extends the possible applications of these kinds of pairs. Herein, we describe the most significant qualities of unnatural base pairs and their actual applications. [ABSTRACT FROM AUTHOR]

We report on the ability of the reverse transcriptases (RTs) from avian myeloblastosis virus (AMV), Moloney murine leukemia virus (M‐MLV), and human immunodeficiency virus 1 (HIV‐1) to generate labeled DNA using the fluorescent tricyclic cytidine analogues d(tC)TP and d(DEAtC)TP as substrates. Michaelis‐Menten kinetics for the insertion of these analogues show Vmax/KM from 0.09–5 times that of natural dCTP across from G, depending on the polymerase and whether the template is RNA or DNA. The analogues are prone to misinsertion across from adenosine with both RNA and DNA templates. Elongation after analogue insertion is efficient with RNA templates, but the analogues cause stalling after insertion with DNA templates. A model reverse transcription assay using HIV‐1‐RT, including RNA‐dependent DNA synthesis, degradation of the RNA template by the RT's RNase H activity, and synthesis of a second DNA strand to form fluorescently labeled dsDNA, shows that d(tC)TP and d(DEAtC)TP are compatible with a complete reverse transcription cycle in vitro. [ABSTRACT FROM AUTHOR]

4′-Ethynyl-2-fluoro-2′-deoxyadenosine (EFdA) and 4′-ethynyl-2′-deoxyadenosine (EdA) are nucleoside analogues which inhibit human immunodeficiency virus type 1 (HIV-1) reverse transcriptase. EdAP, a cyclosaligenyl (cycloSal) phosphate derivative of EdA, inhibits the replication of the influenza A virus. The common structural feature of these compounds is the ethynyl group at the 4′-position. In this study, these nucleoside analogues were prepared by a common synthetic strategy starting from the known 1,2-di-O-acetyl-D-ribofuranose. Biological evaluation of EdAP revealed that this compound reduced hepatitis B virus (HBV) replication dose-dependently without cytotoxicity against host cells tested in this study. Synthesis of nucleotide analogues, EFdA, EdA and EdAP, and the effect of EdAP on hepatitis B virus replication. [ABSTRACT FROM AUTHOR]

Introduction: Chronic hepatitis C virus (HCV) persists as a public health concern worldwide. Consequently, optimizing HCV therapy remains an important objective. While current therapies are generally highly effective, advanced antiviral agents are needed to maximize cure rates with potentially shorter treatment durations in a broader patient population, particularly those patients with advanced diseases who remain difficult to treat., Areas Covered: This review summarizes the in vitro anti-HCV activity, preclinical pharmacological properties of bemnifosbuvir (BEM, AT-527), a novel prodrug that is metabolically converted to AT-9010, the active guanosine triphosphate analogue that potently and selectively inhibits several viral RNA polymerases, including the HCV NS5B polymerase. Results from clinical proof-of-concept and phase 2 combination studies are also discussed., Expert Opinion: BEM exhibits potent pan-genotype activity against HCV, and has favorable safety, and drug interaction profiles. BEM is approximately 10-fold more potent than sofosbuvir against HCV genotypes (GT) tested in vitro. When combined with a potent NS5A inhibitor, BEM is expected to be a promising once-daily oral antiviral for chronic HCV infection of all genotypes and fibrosis stages with potentially short treatment durations.

• Among oral antivirals for HBV infection, only tenofovir has revealed no genotypically resistant HBV. • However, there are patients with incomplete viral response during tenofovir-containing treatment. • We consistently identified 7 common mutations including rtS106C (C), rtH126Y (Y), rtD134E (E), and rtL269I (I). • The mutations C, Y, and E were novel mutations associated with drug resistance. • The quadruple CYEI mutation increases the amount of tenofovir required to inhibit HBV by 15.3-fold in IC 50 and 26.3-fold in IC 90. • All tenofovir-resistant mutants with/without entecavir resistance were susceptible to a novel capsid assembly modulator. Tenofovir disoproxil fumarate (TDF) is one the most potent nucleot(s)ide analogues for treating chronic hepatitis B virus (HBV) infection. Phenotypic resistance caused by genotypic resistance to TDF has not been reported. This study aimed to characterize HBV mutations that confer tenofovir resistance. Two patients with viral breakthrough during treatment with TDF-containing regimens were prospectively enrolled. The gene encoding HBV reverse transcriptase was sequenced. Eleven HBV clones harboring a series of mutations in the reverse transcriptase gene were constructed by site-directed mutagenesis. Drug susceptibility of each clone was determined by Southern blot analysis and real-time PCR. The relative frequency of mutants was evaluated by ultra-deep sequencing and clonal analysis. Five mutations (rtS106C [C], rtH126Y [Y], rtD134E [E], rtM204I/V, and rtL269I [I]) were commonly found in viral isolates from 2 patients. The novel mutations C, Y, and E were associated with drug resistance. In assays for drug susceptibility, the IC 50 value for wild-type HBV was 3.8 ± 0.6 µM, whereas the IC 50 values for CYE and CYEI mutants were 14.1 ± 1.8 and 58.1 ± 0.9 µM, respectively. The IC 90 value for wild-type HBV was 30 ± 0.5 µM, whereas the IC 90 values for CYE and CYEI mutants were 185 ± 0.5 and 790 ± 0.2 µM, respectively. Both tenofovir-resistant mutants and wild-type HBV had similar susceptibility to the capsid assembly modulator NVR 3–778 (IC 50 <0.4 µM vs. IC 50 = 0.4 µM, respectively). Our study reveals that the quadruple (CYEI) mutation increases the amount of tenofovir required to inhibit HBV by 15.3-fold in IC 50 and 26.3-fold in IC 90. These results demonstrate that tenofovir-resistant HBV mutants can emerge, although the genetic barrier is high. Tenofovir is the most potent nucleotide analogue for the treatment of chronic hepatitis B virus infection and there has been no hepatitis B virus mutation that confers >10-fold resistance to tenofovir up to 8 years. Herein, we identified, for the first time, a quadruple mutation that conferred 15.3-fold (IC 50) and 26.3-fold (IC 90) resistance to tenofovir in 2 patients who experienced viral breakthrough during tenofovir treatment. [ABSTRACT FROM AUTHOR]

Summary: Nucleos(t)ide analogues (NA) are effective in suppressing hepatitis B virus (HBV) replication, but most patients require long‐term treatment. This study aimed to investigate switching to peginterferon as a strategy to stop NA. Hepatitis B e antigen (HBeAg)‐positive chronic hepatitis B patients who developed HBeAg seroconversion during NA treatment were studied. All patients received open‐label peginterferon alfa‐2a 180 μg/wk for 48 weeks, and NA was stopped at week 4 of peginterferon treatment. The primary endpoint was sustained response, which was defined as negative HBeAg, positive anti‐HBe and HBV DNA <2000 IU/mL at week 72. Other secondary endpoints including HBsAg loss at week 72 were also studied. Forty‐one patients treated with entecavir for 56 ± 23 months were recruited. Sustained response was achieved in 30 patients (73%, 95% confidence interval 58%‐84%). At week 72, 31 (76%) patients had HBeAg seroconversion, 56 (23%) patients had undetectable HBV DNA, 31 (76%) patients had normal ALT, and 6 patients (15%) had HBsAg loss. Baseline HBsAg level was the best predictor for both sustained response and HBsAg loss; the best HBsAg cut‐off for sustained response was <1500 IU/mL and that for HBsAg loss was <500 IU/mL by receiver operating characteristic curve analysis. Twenty‐two of 25 (88%) patients with baseline HBsAg <1500 IU/mL had sustained response. Five of 10 (50%) patients with baseline HBsAg <500 IU/mL developed HBsAg loss. Switching to peginterferon can be considered as a treatment option in NA‐treated patients with HBeAg seroconversion, particularly among those with lower HBsAg levels. [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.

Cladribine triphosphate is the active compound of the anti-cancer and multiple sclerosis drug Mavenclad (cladribine). Biosynthesis of such non-natural deoxyribonucleotides is challenging but important in order to study the pharmaceutical modes of action. In this study, we developed a novel one-pot enzyme cascade for the biosynthesis of cladribine triphosphate, starting with the nucleobase 2Cl-adenine and the generic co-substrate phosphoribosyl pyrophosphate. The cascade is comprised of the three enzymes, namely, adenine phosphoribosyltransferase (APT), polyphosphate kinase (PPK), and ribonucleotide reductase (RNR). APT catalyzes the binding of the nucleobase to the ribose moiety, followed by two consecutive phosphorylation reactions by PPK. The formed nucleoside triphosphate is reduced to the final product 2Cl-deoxyadenonsine triphosphate (cladribine triphosphate) by the RNR. The cascade is feasible, showing comparative product concentrations and yields to existing enzyme cascades for nucleotide biosynthesis. While this study is limited to the biosynthesis of cladribine triphosphate, the design of the cascade offers the potential to extend its application to other important deoxyribonucleotides.

Currently, 5-fluorouracil (5-FU)-based combination chemotherapy is the mainstay in the treatment of metastatic colorectal cancer (CRC), which benefits approximately 50% of the patients. However, these tumors inevitably acquire chemoresistance resulting in treatment failure. The molecular mechanisms driving acquired chemotherapeutic drug resistance in CRC is fundamental for the development of novel strategies for circumventing resistance. However, the specific phenomenon that drives the cancer cells to acquire resistance is poorly understood. Understanding the molecular mechanisms that regulate chemoresistance will uncover new avenues for the treatment of CRC. Among the various mechanisms of acquired chemoresistance, defects in the drug metabolism pathways could play a major role. In the case of 5-FU, it gets converted into various active metabolites, which, directly or indirectly, interferes with the replication and transcription of dividing cells causing DNA and RNA damage. In this project, we developed a high-resolution mass spectrometry-based method to effectively extract and quantify levels of the 5-FU metabolites in cell lysates and media of parental and 5-FU resistant LIM1215 CRC cells. The analysis highlighted that the levels of 5-FU metabolites are significantly reduced in 5-FU resistant cells. Specifically, the level of the nucleotide fluorodeoxyuridine monophosphate (FdUMP) is reduced with treatment of 5-FU clarifying the compromised 5-FU metabolism in resistant cells. Corroborating the metabolomic analysis, treatment of the resistant cells with FdUMP, an active metabolite of 5-FU, resulted in effective killing of the resistant cells. Overall, in this study, an effective protocol was developed for comparative quantitation of polar metabolites and nucleotide analogues from the adherent cells efficiently. Furthermore, the utility of FdUMP as an alternative for CRC therapy is highlighted.

Direct acting antivirals (DAAs) revolutionized the therapy of chronic hepatitis C infection. However, unexpected high recurrence rates of hepatocellular carcinoma (HCC) after DAA treatment became an issue in patients with advanced cirrhosis and fibrosis. In this study, we aimed to investigate an impact of DAA treatment on the molecular changes related to HCC development and progression in hepatoma cell lines and primary human hepatocytes. We found that treatment with sofosbuvir (SOF), a backbone of DAA therapy, caused an increase in EGFR expression and phosphorylation. As a result, enhanced translocation of EGFR into the nucleus and transactivation of factors associated with cell cycle progression, B-MYB and Cyclin D1, was detected. Serine/threonine kinase profiling identified additional pathways, especially the MAPK pathway, also activated during SOF treatment. Importantly, the blocking of EGFR kinase activity by erlotinib during SOF treatment prevented all downstream events. Altogether, our findings suggest that SOF may have an impact on pathological processes in the liver via the induction of EGFR signaling. Notably, zidovudine, another nucleoside analogue, exerted a similar cell phenotype, suggesting that the observed effects may be induced by additional members of this drug class.

Aim: Sustained suppression of hepatitis B surface antigen (HBsAg) production after interferon (IFN) treatment has not been reported for children with genotype C chronic hepatitis B virus (HBV) infection, which is prevalent in Asia. Among children with hepatitis B envelope antigen‐positive genotype C chronic HBV infection, we compared the efficacy of combination therapy with nucleotide analogues and IFN‐α in 11 children with 12 historical cases treated with IFN monotherapy. Methods: The combination of lamivudine and conventional IFN‐α was introduced for the first three patients; the other eight patients were treated with entecavir and pegylated IFN. Results: Demographic factors as well as baseline HBsAg titers and HBV‐DNA levels were similar between the two groups. In the combination therapy group, viral loads were suppressed in 9/11 to below 4.0 log copies/mL both at the end of the therapy (EOT) and at 6 months after EOT. In contrast, in the IFN monotherapy group, suppression of viral loads was observed in 2/12 and 3/12 at EOT and at 6 months after EOT, respectively. In the combination therapy group, HBsAg titers dropped from 4.03 at pretreatment to 2.91 log IU/mL at 6 months after EOT with 4/11 showing a drop to below 1000 IU/mL (one patient achieved HBsAg clearance). In contrast, the amount of HBsAg did not change during the corresponding periods in the IFN monotherapy group. Conclusions: Our preliminary results suggest that combination therapy might be effective in the suppression of HBsAg production as well as HBV‐DNA production for children with genotype C chronic HBV infection. [ABSTRACT FROM AUTHOR]

Exocyclic olefin variants of thymidylate (dTMP) recently have been proposed as reaction intermediates for the thymidyl biosynthesis enzymes found in many pathogenic organisms, yet synthetic reports on these materials are lacking. Here we report two strategies to prepare the exocyclic olefin isomer of dTMP, which is a putative reaction intermediate in pathogenic thymidylate biosynthesis and a novel nucleotide analog. Our most effective strategy involves preserving the existing glyosidic bond of thymidine and manipulating the base to generate the exocyclic methylene moiety. We also report a successful enzymatic deoxyribosylation of a non-aromatic nucleobase isomer of thymine, which provides an additional strategy to access nucleotide analogs with disrupted ring conjugation or with reduced heterocyclic bases. The strategies reported here are straightforward and extendable towards the synthesis of various pyrimidine nucleotide analogs, which could lead to compounds of value in studies of enzyme reaction mechanisms or serve as templates for rational drug design. [ABSTRACT FROM AUTHOR]

Hepatitis B virus (HBV) polymerase gene is targeted by nucleos(t)ide analogues (NUC), but it is unclear how HBV quasispecies of whole genome changes during early period of NUC treatment. To understand the unknown region of drug sensitivity and treatment resistance, HBV quasispecies of whole genome during early period of NUC treatment was examined using ultra‑deep sequencing. Eleven patients with chronic HBV infection who received NUC treatment were enrolled in the current study. Viral DNA was extracted from serum samples before and early period of NUC treatment. Polymerase chain reaction analysis was subsequently performed on the DNA products. The viral quasispecies of the entire genome was analyzed by ultra‑deep sequencing. The regions and positions corresponding to the changes in the quasispecies were investigated before and early period of NUC treatment. The secondary structure changes were predicted by mutations/substitutions detected using Lasergene Protean v14.1 software. The frequency of quasispecies variants increased significantly in the polymerase domain from before to early period of NUC treatment (3.08±1.28 vs. 3.51±1.47%, P<0.008), particularly the reverse transcription (RT) domain (3.76±1.25 vs. 4.52±1.37%, P<0.012). In addition, increased variation detected from HBsAg domain showed statistically significant during NUC treatment (6.81±3.26 vs. 7.81±3.26%, P<0.040). The amino acid (aa) mutations/substitutions were detected and compared from before to early period of treatment. Interestingly, most of them were located in the RT region (RT1 motif: aa21‑aa51) and small S region in the early duration of NUC treatment. Furthermore, several mutation patterns, such as cI97L and cP130T showed alterations in the secondary structure and predicted antigenicity of HBV protein. Although the HBV whole genome can be affected by NUC treatment, RT 1 motif region and small S region are more sensitive to the early period of NUC treatment. This study suggested the initial changes of HBV quasispecies might affect the long‑term drug sensitivity and resistance to NUC treatment. [ABSTRACT FROM AUTHOR]

Combining peginterferon-alfa-2a (peg IFN) with a nucleotide analogue can result in higher rates of HBsAg loss than either therapy given alone. Here, we investigated the durability of the response to combination therapy in chronic hepatitis B ( CHB) patients after 5 years of follow-up. In the initial study, 92 CHB patients (44 HBeAg-positive, 48 HBeAg-negative) with HBV DNA >100 000 c/ mL (~20 000 IU/ mL) and active hepatitis were treated for 48 weeks with peg IFN 180 μg/week and 10 mg adefovir dipivoxil daily. For the long-term follow-up (LTFU) study, patients were followed up for 5 years after the end of treatment. At year 5, 70 (32 HBeAg-positive, 38 HBeAg-negative) patients remained in the study. At year 5, 19% (6/32) of HBeAg-positive patients and 16% (6/38) of HBeAg-negative patients lost HBsAg, and no HBsAg seroreversion was observed. The 5-year cumulative Kaplan-Meier estimate for HBsAg loss was 17.2% for HBeAg-positive patients and 19.3% for HBeAg-negative patients. Fourteen of sixteen patients who lost HBsAg at any time point during follow-up developed anti- HBs antibodies (>10 IU/L). At year 5, in total 63% (20/32) of HBeAg-positive and 71% (27/38) of HBeAg-negative patients were retreated with nucleos(t)ide analogues during follow-up. The cumulative Kaplan-Meier estimate for retreatment was 60% of patients at year 5. At year 5 of follow-up, 18% of CHB patients treated with peg IFN/nucleotide analogue combination therapy had durable HBsAg loss and 88% of these had developed anti- HBs antibodies. [ABSTRACT FROM AUTHOR]

Nucleoside analogues and nucleotide analogues can not only achieve long-term viral suppression in the treatment of most CHB patients but also have a positive impact on other CHB therapeutic goals and an improved prognosis. A certain difference can be observed in the impact of nucleotide analogues such as TDF and TAF and nucleoside analogues such as ETV on the clinical outcomes of CHB. Studies on the mechanism of action indicate that apart from inhibiting the direct antiviral effects of HBV reverse transcriptase, these two categories of drugs exhibit distinct impacts on immune-related signaling pathways, gene expression, genome stability, and other non-antiviral mechanisms. This article reviews the evidence on the potential non-antiviral mechanism of action of nucleoside analogues and nucleotide analogues and proposes a preliminary explanation for the observation trend of nucleotide analogues having a comparative advantage in clinical outcomes in CHB patients based on the latest research advancement.

Although much advancement has been achieved in the treatment of chronic hepatitis B, antiviral resistance is still a challenging issue. Previous generation antiviral agents have already developed resistance in a number of patients, and it is still being used especially in resource limited countries. Once antiviral resistance occurs, it predisposes to subsequent resistance, resulting in multidrug resistance. Therefore, prevention of initial antiviral resistance is the most important strategy, and appropriate choice and modification of therapy would be the cornerstone in avoiding treatment failures. Until now, management of antiviral resistance has been evolving from sequential therapy to combination therapy. In the era of tenofovir, the paradigm shifts again, and we have to decide when to switch and when to combine on the basis of newly emerging clinical data. We expect future eradication of chronic hepatitis B virus infection by proper prevention and optimal management of antiviral resistance.

Purpose of Review: The goal of chronic hepatitis B (CHB) therapy is an improvement in clinical outcomes, but surrogate markers include viral suppression, hepatitis B e-antigen (HBeAg) seroconversion, and, more recently, hepatitis B surface antigen (HBsAg) clearance, labeled as 'functional cure.' The current therapy of CHB is based on two strategies: either a finite course of pegylated interferon (pegIFN) or an indefinite duration of oral nucleos(t)ide analogues (NAs). NAs with high antiviral potency and barrier to resistance have become the mainstay of therapy due to ease of use, tolerability, and cost. However, optimization of these two therapeutic modalities has not been fully explored to maximize outcomes, which include combination therapy. Recent Findings: Initial randomized control trials with approved NAs and pegIFN as de novo combinations did not appear to show benefit compared to pegIFN alone, but meta-analyses now show that there are significant improvements in undetectable HBV DNA, HBeAg loss and seroconversion, and HBsAg loss. However, many patients remain on long-term NA therapy, and a strategy to increase HBeAg seroconversion and preferably HBsAg clearance are needed. Such strategies include switch (sequential) or add-on pegIFN to patients already on NAs. An add-on pegIFN strategy in HBeAg-negative CHB (PEGAN study) has shown 8% HBsAg clearance after 48 weeks of therapy, and a switch strategy (OSST study) showed a similar result-8.5% HBsAg clearance. However, the ultimate goal of HBsAg seroclearance remains still <10% despite these strategies. Summary: It may be possible to improve these outcomes further by selecting patients with lower quantitative HBsAg (qHBsAg) levels and to predict outcomes based on on-treatment qHBsAg responses. [ABSTRACT FROM AUTHOR]

BMS-986094, the prodrug of a guanosine nucleotide analogue (2'-C-methylguanosine), was withdrawn from clinical trials due to serious safety issues. Nonclinical investigative studies were conducted as a follow up to evaluate the potential for BMS-986094-related mitochondrial-toxicity. In vitro, BMS-986094 was applied to human hepatoma cells (HepG2 and Huh-7) or cardiomyocytes (hiPSCM) up to 19 days to assess mitochondrial DNA content and specific gene expression. There were no mitochondrial DNA changes at concentrations ≥10μM. Transcriptional effects, such as reductions in Huh-7MT-ND1 and MT-ND5 mRNA content and hiPSCM MT-ND1, MT-COXII, and POLRMT protein expression levels, occurred only at cytotoxic concentrations (≤10μM) suggesting these transcriptional effects were a consequence of the observed toxicity. Additionally, BMS-986094 has a selective weak affinity for inhibition of RNA polymerases as opposed to DNA polymerases. In vivo, BMS-986094 was given orally to cynomolgus monkeys for 3 weeks or 1 month at doses of 15 or 30 mg/kg/day. Samples of heart and kidney were collected for assessment of mitochondrial respiration, mitochondrial DNA content, and levels of high energy substrates. Although pronounced cardiac and renal toxicities were observed in some monkeys at 30 mg/kg/day treated for 3-4 weeks, there were no changes in mitochondrial DNA content or ATP/GTP levels. Collectively, these data suggest that BMS-986094 is not a direct mitochondrial toxicant. [ABSTRACT FROM AUTHOR]

Nucleotide/nucleoside analogues (antiviral therapy) are used in the therapy of HBeAg positive and HBeAg negative chronic hepatitis B. We analyzed ten selected randomized controlled with 2557 patients to estimate the effect of antiviral drugs in chronic hepatitis B with compared to placebo. Virological response, biochemical response, histological response, seroconversion of HBeAg, and loss of HBeAg were estimated as primary efficacy measures. The included studies were subjected for heterogeneity and publication bias. The heterogeneity was assessed with χ2 and I statistics. Publication bias was assessed by funnel plot. Greater rates of improvement obtained in antiviral group for virological response [43.96 % vs. 3.15 %, RR = 0.57, 95 % CI = 0.54-0.61, p-value <0.00001], biochemical response [58.37 % vs. 21.87 %, RR = 0.52, 95 % CI = 0.48-0.56, p-value <0.00001], histological response [58.99 % vs. 27.13 %, RR = 0.56, 95 % CI = 0.50-0.63, p-value <0.0001], seroconversion of HBeAg [10.66 % vs. 5.56 %, RR = 0.94, 95 % CI = 0.91-0.97, p-value = 0.0005], and HBeAg loss [14.59 % vs. 9.64 %, RR = 0.92, 95 % CI = 0.88-0.96, p-value = 0.0002]. The safety analysis were carried out for adverse events such as headache [17.22 % vs. 17.34 %, OR = 1.09, 95 % CI = 0.81-1.46, p-value = 0.58], abdominal pain [16.46 % vs. 14.34 %, OR = 1.24, 95 % CI = 0.90-1.72, p-value = 0.19], and pharyngitis [22.22 % vs. 18.23 %, OR = 1.12, 95 % CI = 0.86-1.45, p-value = 0.40]. Excluding adverse events, all primary efficacy measures shown statistical significant result for chronic hepatitis treatment ( p-value <0.05). Antiviral therapy provided significant benefit for the treatment of chronic hepatitis B with no measurable adverse effects. [ABSTRACT FROM AUTHOR]

Overactivation of the Wnt signalling pathway underlies oncogenic transformation and proliferation in many cancers, including the triple-negative breast cancer (TNBC), the deadliest form of tumour in the breast, taking about a quarter of a million lives annually worldwide. No clinically approved targeted therapies attacking Wnt signalling currently exist. Repositioning of approved drugs is a promising approach in drug discovery. In the present study we show that a multi-purpose drug suramin inhibits Wnt signalling and proliferation of TNBC cells in vitro and in mouse models, inhibiting a component in the upper levels of the pathway. Through a set of investigations we identify heterotrimeric G proteins and regulation of Wnt endocytosis as the likely target of suramin in this pathway. G protein-dependent endocytosis of plasma membrane-located components of the Wnt pathway was previously shown to be important for amplification of the signal in this cascade. Our data identify endocytic regulation within Wnt signalling as a promising target for anti-Wnt and anti-cancer drug discovery. Suramin, as the first example of such drug or its analogues might pave the way for the appearance of first-inclass targeted therapies against TNBC and other Wnt-dependent cancers. [ABSTRACT FROM AUTHOR]

A novel fluorescent guanosine 5′-triphosphate (GTP) analogue, 2′(3′)- O -{6-( N -(7-nitrobenz-2-oxa-l,3-diazol-4-yl)amino) hexanoic}-GTP (NBD-GTP), was synthesized and utilized to monitor the effect of mutations in the functional region of mouse K-Ras. The effects of the G12S, A59T and G12S/A59T mutations on GTPase activity, nucleotide exchange rates were compared with normal Ras. Mutation at A59T resulted in reduction of the GTPase activity by 0.6-fold and enhancement of the nucleotide exchange rate by 2-fold compared with normal Ras. On the other hand, mutation at G12S only slightly affected the nucleotide exchange rate and did not affect the GTPase activity. We also used NBD-GTP to study the effect of these mutations on the interaction between Ras and SOS1, a guanine nucleotide exchange factor. The mutation at A59T abolished the interaction with SOS1. The results suggest that the fluorescent GTP analogue, NBD-GTP, is applicable to the kinetic studies for small G-proteins. [ABSTRACT FROM AUTHOR]

Efforts to develop synthetic methodologies allowing the preparation of α,α– difluorophosphonothioates, α,α–difluorophosphonodithioates, α,α–difluorophosphono- trithioates, and α,α–difluorophosphinates are reviewed in the light of applications in the field of modified oligonucleotides and cyclitol phosphates. Two successful approaches have been developed, based either on the addition of phosphorus-centered radicals onto gem–difluoroalkenes or on a process involving the addition of lithiodifluorophosphono- thioates 91 onto a ketone and the subsequent deoxygenation reaction of the adduct. The radical route successfully developed a practical route to α,α–difluoro–H–phosphinates which proved to be useful intermediates to a variety of phosphate isosters. The ionic route led to the first preparation of phosphonodifluoromethyl analogues of nucleoside– 3’–phosphates.

[Display omitted] • 8-Br-7-deaza-dA was synthesized and found to resemble the syn -preference of 8-oxo-dA. • Oligodeoxynucleotides incorporating dA, 8-oxo-dA, 7-deaza-dA, 8-Br-dA and 8-Br-7-deaza-dA were synthesized. • The base pairing preferences, mutagenic potentials and repair of 8-oxo-dA and its analogs in duplex DNAs were evaluated. • This study provides an insight into the structure-function relationship of 8-oxo-dA by 8-oxo-dA analogues. Oxidative lesions, such as 8-oxo-dG and 8-oxo-dA, are continuously generated from exposure to reactive oxygen species. While 8-oxo-dG has been extensively studied, 8-oxo-dA has not received as much attention until recently. Herein, we report the synthesis of duplex DNAs incorporating dA, 8-oxo-dA, 7-deaza-dA, 8-Br-dA, and 8-Br-7-deaza-dA, which have different substitutions at 7- and 8-position, for the investigation into the implications of N7-hydrogen and C8-keto on the base pairing preference, mutagenic potential and repair of 8-oxo-dA. Base pairing study suggested that the polar N7-hydrogen and C8-keto of 8-oxo-dA, rather than the syn -preference, might be essential for 8-oxo-dA to form a stable base pair with dG. Insertion and extension studies using KF-exo− and human DNA polymerase β indicated that the efficient dGTP insertion opposite 8-oxo-dA and extension past 8-oxo-dA:dG are contingent upon not only the stable base pair with dG, but also the flexibility of the active site in polymerase. The N7-hydrogen in 8-oxo-dA or C7-hydrogen in 7-deaza-dA and 8-Br-7-deaza-dA was suggested to be important for the recognition by hOGG1, although the excision efficiencies of 7-deaza-dA and 8-Br-7-deaza-dA were much lower than 8-oxo-dA. This study provides an insight into the structure-function relationship of 8-oxo-dA by nucleotide analogues. [ABSTRACT FROM AUTHOR]

Background: Tenofovir disoproxil fumarate (TDF) is a first-line nucleotide analog (NA) drug for hepatitis B therapy. Long-term NA therapy increases peripheral T cell levels to enhance antiviral response, while CTLA-4 inhibits the activation., Objective: This study analyzed the interaction between TDF and CTLA-4 through molecular docking., Methods: Target protein and ligand data mining were performed, and proteins were prepared by removing water molecules in the Discovery Studio 2019 software. The energy minimization was performed on ligands using Pyrx v.0.9.8 software. Protein-ligand docking was performed using Autodock Vina integrated with Pyrx v.09.8. Meanwhile, the docking of proteins was accomplished using the Haddock server. The BioVia Discovery Studio 2019 software visualized the interaction between the compound and the docked protein. Molecular dynamics simulations were carried out using the YASARA Dynamic program developed by Biosciences GmbH., Results: TDF ligand has good and stable inhibitory activity against the CTLA-4/B7-1 and CTLA4/B7-2 complexes. TDF docking has been shown to initiate conformational changes, indicating the ligand's inhibitory activity. The significant conformational changes based on superimposition results were shown by the CTLA-4/TDF/B7-2 and CTLA-4/B7-1/TDF complexes. TDF in all ligands undergoes bonding and displacement of binding sites., Conclusion: Treatment with TDF was predicted to have inhibitory activity against CTLA-4, especially in its complex form with B7-1 and B7-2., Competing Interests: None declared., (© 2023 Darmadi Darmadi, Dharma Lindarto, Jelita Siregar, Tri Widyawati, Muhammad Rusda, Mustafa Mahmud Amin, Fauzi Yusuf, Putri Chairani Eyanoer, Masrul Lubis, Imelda Rey.)

Since the licensing of lamivudine in 1999, the treatment of chronic hepatitis B has been revolutionized by the introduction of oral nucleoside and nucleotide analogues (NAs), which act as inhibitors of the HBV polymerase. The effectiveness of the first of these substances was limited by incomplete response and resistance development in many patients, but today, highly potent substances are available that make a reliable and durable suppression of HBV replication, a reduction of necroinflammatory activity in the liver, and even a reversion of liver fibrosis achievable for almost all patients. Beyond that, NA treatment can prevent the development of hepatocellular carcinoma in many patients. HBeAg seroconversion appears in approximately 50% of all HBeAg-positive patients during NA treatment. However, the ideal treatment endpoint, the serologic loss of HBsAg, remains a rare event almost exclusively achievable for HBeAg-positive patients. After cessation of the treatment, HBV replication tends to relapse in most patients, which is why the duration of NA treatment is indefinite. Future treatment strategies should aim at tailoring individual NA treatment regimens to increase HBs loss rates and optimize treatment duration. © 2014 S. Karger AG, Basel [ABSTRACT FROM AUTHOR]

Highlights: [•] Learning from HIV PEP, we attempted to analyze the efficiency of NAs in HBV PEP. [•] ETV alone or combined with vaccine were analyzed using the Chinese woodchuck model. [•] NA-based strategies prevented hepadnavirus viremia and induced protective immunity. [•] NA-based strategies may be an alternative for HBV PEP. [•] Further clinical trials are warrant for confirming NA-based HBV PEP strategies. [ABSTRACT FROM AUTHOR]