Is there any need for new, long-acting nucleos(t)ide analogues for the treatment of hepatitis B infection?

Abstract

See Article, pages 1075–1086 See Article, pages 1075–1086 In worldwide clinical settings, several nucleos(t)ide analogues (NAs), including tenofovir disoproxil fumarate (TDF), entecavir (ETV), and tenofovir alafenamide fumarate (TAF) are used to treat patients chronically infected with HBV.[1]EASL 2017 Clinical Practice Guidelines on the management of hepatitis B virus infection.J Hepatol. 2017; 67: 370-398Abstract Full Text Full Text PDF PubMed Scopus (2252) Google Scholar,[2]Fanning G.C. Zoulim F. Hou J. Bertoletti A. Therapeutic strategies for hepatitis B virus infection: towards a cure.Nat Rev Drug Discov. 2019; 18: 827-844Crossref PubMed Scopus (147) Google Scholar NAs are easily administrated orally and have favorable pharmacologic profiles.[3]Chaudhuri S. Symons J.A. Deval J. Innovation and trends in the development and approval of antiviral medicines: 1987-2017 and beyond.Antivir Res. 2018; 155: 76-88Crossref PubMed Scopus (79) Google Scholar Their use is generally preferred to that of the immune stimulator pegylated-interferon (Peg-IFN)-alpha, which induces more adverse effects (AEs) and less virological suppression (i.e. HBV DNA decline in serum), although it is associated with a higher rate of HBsAg loss.[1]EASL 2017 Clinical Practice Guidelines on the management of hepatitis B virus infection.J Hepatol. 2017; 67: 370-398Abstract Full Text Full Text PDF PubMed Scopus (2252) Google Scholar,[2]Fanning G.C. Zoulim F. Hou J. Bertoletti A. Therapeutic strategies for hepatitis B virus infection: towards a cure.Nat Rev Drug Discov. 2019; 18: 827-844Crossref PubMed Scopus (147) Google Scholar,[4]Yeo Y.H. Ho H.J. Yang H.I. Tseng T.C. Hosaka T. Trinh H.N. et al.Factors associated with rates of HBsAg seroclearance in adults with chronic HBV infection: a systematic review and meta-analysis.Gastroenterology. 2019; 156 (635-646.e639)Abstract Full Text Full Text PDF PubMed Scopus (72) Google Scholar Treatment indications for these NAs have been clearly defined by international societies, including EASL.[1]EASL 2017 Clinical Practice Guidelines on the management of hepatitis B virus infection.J Hepatol. 2017; 67: 370-398Abstract Full Text Full Text PDF PubMed Scopus (2252) Google Scholar Their efficacy to suppress/reduce HBV viremia and overall safety have been properly assessed in randomized controlled phase III clinical trials (i.e. registration trials) and in long-term real-world studies.[1]EASL 2017 Clinical Practice Guidelines on the management of hepatitis B virus infection.J Hepatol. 2017; 67: 370-398Abstract Full Text Full Text PDF PubMed Scopus (2252) Google Scholar,[2]Fanning G.C. Zoulim F. Hou J. Bertoletti A. Therapeutic strategies for hepatitis B virus infection: towards a cure.Nat Rev Drug Discov. 2019; 18: 827-844Crossref PubMed Scopus (147) Google Scholar,[4]Yeo Y.H. Ho H.J. Yang H.I. Tseng T.C. Hosaka T. Trinh H.N. et al.Factors associated with rates of HBsAg seroclearance in adults with chronic HBV infection: a systematic review and meta-analysis.Gastroenterology. 2019; 156 (635-646.e639)Abstract Full Text Full Text PDF PubMed Scopus (72) Google Scholar When “no virologic resistance” occurs, long-term treatments with 1 of the 3 most used NAs (TDF, ETV, TAF) are associated with a prolonged virologic responses (i.e. viremia below detection levels by qPCR) in most patients (>95%), normalized alanine aminotransferase levels, regression of fibrosis, and altogether with the prevention of disease progression, including hepatocellular carcinoma development (See Fig. 1).[1]EASL 2017 Clinical Practice Guidelines on the management of hepatitis B virus infection.J Hepatol. 2017; 67: 370-398Abstract Full Text Full Text PDF PubMed Scopus (2252) Google Scholar Yet, currently, NAs are to be taken daily and long-term, as treatment cessation is quasi-universally associated with virological rebound,[2]Fanning G.C. Zoulim F. Hou J. Bertoletti A. Therapeutic strategies for hepatitis B virus infection: towards a cure.Nat Rev Drug Discov. 2019; 18: 827-844Crossref PubMed Scopus (147) Google Scholar,[5]Lai C.L. Wong D.K. Wong G.T. Seto W.K. Fung J. Yuen M.F. Rebound of HBV DNA after cessation of nucleos/tide analogues in chronic hepatitis B patients with undetectable covalently closed.JHEP Rep: innovation Hepatol. 2020; 2 (100112)Google Scholar except in selected patients for whom “NA stopping rules” have been applied with some success (note that this latter point will not be discussed here; please refer to the following references for recent discussions on this topic[6]Lampertico P. Berg T. Less can be more: a finite treatment approach for HBeAg-negative chronic hepatitis B.Hepatology. 2018; 68: 397-400Crossref PubMed Scopus (22) Google Scholar). Moreover it is also well acknowledged that NAs generally have a limited impact on HBsAg levels[1]EASL 2017 Clinical Practice Guidelines on the management of hepatitis B virus infection.J Hepatol. 2017; 67: 370-398Abstract Full Text Full Text PDF PubMed Scopus (2252) Google Scholar,[2]Fanning G.C. Zoulim F. Hou J. Bertoletti A. Therapeutic strategies for hepatitis B virus infection: towards a cure.Nat Rev Drug Discov. 2019; 18: 827-844Crossref PubMed Scopus (147) Google Scholar,[4]Yeo Y.H. Ho H.J. Yang H.I. Tseng T.C. Hosaka T. Trinh H.N. et al.Factors associated with rates of HBsAg seroclearance in adults with chronic HBV infection: a systematic review and meta-analysis.Gastroenterology. 2019; 156 (635-646.e639)Abstract Full Text Full Text PDF PubMed Scopus (72) Google Scholar and that very long-term therapies are needed to reduce covalently closed circular DNA (cccDNA) levels.[7]Lai C.L. Wong D. Ip P. Kopaniszen M. Seto W.K. Fung J. et al.Reduction of covalently closed circular DNA with long-term nucleos(t)ide analogue treatment in chronic hepatitis B.J Hepatol. 2017; 66: 275-281Abstract Full Text Full Text PDF PubMed Scopus (88) Google Scholar,[8]Werle-Lapostolle B. Bowden S. Locarnini S. Wursthorn K. Petersen J. Lau G. et al.Persistence of cccDNA during the natural history of chronic hepatitis B and decline during adefovir dipivoxil therapy.Gastroenterology. 2004; 126: 1750-1758Abstract Full Text Full Text PDF PubMed Scopus (725) Google Scholar As these viral parameters are instrumental to a proper HBV cure (at minima functional, and at maxima sterilizing), there is some room for improvement. First, even if some of the NAs are very potent at inhibiting HBV polymerase (Pol) activity and neo-synthesis of encapsidated relaxed circular DNA (rcDNA, i.e. viral genome within nucleocapsid), which is then used to either produce secreted infectious viral particles (i.e. maintenance of viremia) or to maintain the level of cccDNA following recycling of rcDNA to the nucleus,[9]Seeger C. Zoulim F. Mason W.S. Hepadnaviruses.in: Field's Virology. 2. Lippincott Williams & Wilkins, Philadelphia2015: 2185Google Scholar careful/close monitoring of viremia using very potent qPCR technology has demonstrated partial virologic responses in long-term NA-treated patients, with viremia varying between “non detectable” and very low levels.[10]Mak L.Y. Cloherty G. Wong D.K. Gersch J. Seto W.K. Fung J. HBV RNA profiles in chronic hepatitis B patients under different disease phases and anti-viral therapy.2020Google Scholar This indicates that the blockade of HBV Pol activity is not 100%. This also has consequences for cccDNA levels, as residual HBV Pol activity might be sufficient to maintain the cccDNA pool. More potent NAs that further block cccDNA replenishment and accelerate decay would be required for HBV cure. Second, pure potency (EC50 value) is not everything. Indeed to be potent, a NA needs to be efficiently matured by host-cell enzymes to its triphosphorylated (TP) (or equivalent form)[11]Deville-Bonne D. El Amri C. Meyer P. Chen Y. Agrofoglio L.A. Janin J. Human and viral nucleoside/nucleotide kinases involved in antiviral drug activation: structural and catalytic properties.Antivir Res. 2010; 86: 101-120Crossref PubMed Scopus (77) Google Scholar and to be delivered/distributed at the right place (i.e. hepatocytes, when HBV is concerned). In other words, this means that potency is also highly dependent on adequate subcellular bio-distribution and biologic activation of NAs only (or mainly) within hepatocytes. The latter also has implications for toxicity and safety. Third, a better toxicity profile is also important. The toxicity of NAs comes mainly from off-target activity (i.e. non-HBV Pol). Indeed, many NAs inhibit mitochondrial polymerases leading to side effects in the long term.12Nucleoside analogues.in: LiverTox: Clinical and Research Information on Drug-Induced Liver Injury. National Institute of Diabetes and Digestive and Kidney Diseases, Bethesda (MD)2012Google Scholar, 13Fung J. Seto W.-K. Lai C.-L. Yuen M.-F. Extrahepatic effects of nucleoside and nucleotide analogues in chronic hepatitis B treatment.J Gastroenterol Hepatol. 2014; 29: 428-434Crossref PubMed Scopus (70) Google Scholar, 14Wang J. Eriksson S. Phosphorylation of the anti-hepatitis B nucleoside analog 1-(2'-deoxy-2'-fluoro-1-beta-D-arabinofuranosyl)-5-iodouracil (FIAU) by human cytosolic and mitochondrial thymidine kinase and implications for cytotoxicity.Antimicrob Agents Chemother. 1996; 40: 1555-1557Crossref PubMed Google Scholar For instance, renal and bone toxicity was observed with long-term administration of TDF; this problem was, at least partially, addressed by the research and development of TAF.[15]Agarwal K. Brunetto M. Seto W.K. Lim Y.S. Fung S. Marcellin P. et al.96 weeks treatment of tenofovir alafenamide vs. tenofovir disoproxil fumarate for hepatitis B virus infection.J Hepatol. 2018; 68: 672-681Abstract Full Text Full Text PDF PubMed Scopus (136) Google Scholar Even though such toxicity was not evident with ETV, toxicity remains a general issue in the case of systemic activity of a given medication. A way to further reduce toxicity would therefore be to strictly deliver and/or activate the NA in the target cell type (hepatocytes in the case of HBV).[16]Pierra Rouviere C. Dousson C.B. Tavis J.E. HBV replication inhibitors.Antivir Res. 2020; 179: 104815Crossref PubMed Scopus (10) Google Scholar In the current issue of Journal of Hepatology, Higashi-Kuwata and colleagues[17]Higashi-Kuwata N. Hayashi S. Kumamoto H. Ogata-Aoki H. Das D. Venzon D. et al.Identification of a novel long-acting 4’-modified nucleoside reverse transcriptase inhibitor against HBV.J Hepatol. 2021; 74: 1075-1086Abstract Full Text Full Text PDF PubMed Scopus (2) Google Scholar describe a novel nucleoside analogue with very potent and long-lasting anti-HBV activity. This NA, called E-CFCP (chemical name: (1S,3S,5S,E)-3-(2-amino-6-oxo-1,6-dihydro-9H-purin-9-yl)-2-(fluoromethylene)-5-hydroxy-1-(hydro-xymethyl)cyclo-pentane-1-carbonitrile), is a guanosine analogue derived from 4’-cyano-methylene-carbocyclic-2’-deoxyguanosine (CMCdG) and has a structure similar to ETV. Two enantiomers (E-CFCP and Z-CFCP) were initially synthesized, but E was further developed because it was far more active. E-CFCP was shown to be more potent, with a lower EC50 in various cell culture models and virtually 100% inhibition at the highest dose tested, as well as less toxic than ETV and TAF in side-by-side in vitro comparisons. Moreover E-CFCP was still active against ETV- (L180M/S202G/M204V)[18]Yim H.J. Hussain M. Liu Y. Wong S.N. Fung S.K. Lok A.S. Evolution of multi-drug resistant hepatitis B virus during sequential therapy.Hepatology. 2006; 44: 703-712Crossref PubMed Scopus (217) Google Scholar and adefovir- (A181T/N236T)[19]Villet S. Pichoud C. Billioud G. Barraud L. Durantel S. Trépo C. et al.Impact of hepatitis B virus rtA181V/T mutants on hepatitis B treatment failure.J Hepatol. 2008; 48: 747-755Abstract Full Text Full Text PDF PubMed Scopus (166) Google Scholar resistant strains. Very interestingly, a longer antiviral activity off-treatment was found with E-CFCP compared to ETV and TAF, suggesting that less frequent administration could be possible. The overall higher potency and longer off-treatment efficacy of E-CFCP over ETV is likely due to both a better uptake by hepatic cells, leading to higher intracellular concentrations, and a stronger conversion into the active TP form, as well as a longer intracellular half-life. Altogether E-CFCP presented a very favourable pharmacologic profile (bioavailability at 70% in mice), with excellent resistance to extremely low pH, which allowed a per os preclinical evaluation in a liver-humanized mouse model. In this model, E-CFCP (at 0.02 mg/kg/day) was more efficient than ETV (at 0.02 mg/kg/day) at reducing HBV viremia, while rebound after treatment cessation was further delayed in the E-CFCP arm; this strong antiviral activity was obtained in the absence of any toxicity over a period of 14 days of dosing. E-CFCP (at 0.2 mg/kg/day) was also capable of potently inhibiting replication of an ETV-resistant strain, in sharp contrast to ETV itself (and TAF), thus confirming in vitro data on this improved activity against possible circulating mutant strains in patients with CHB. In silico analysis indicated that the addition of the E-positioned fluorine and 4’cyano moities could allow E-CFCP-TP to retain important binding interactions with the mutated catalytic pocket in HBV pol, unlike ETV. Therefore, E-CFCP seems to fulfil many of the aforementioned expectations for improved NAs. Yet caution must be exercised in the absence of data on efficacy and safety in patients with CHB. We must keep in mind that despite demonstrating higher potency and an improved pharmacologic profile in preclinical and early clinical studies, TAF failed to demonstrate superiority to TDF in phase III trials.[15]Agarwal K. Brunetto M. Seto W.K. Lim Y.S. Fung S. Marcellin P. et al.96 weeks treatment of tenofovir alafenamide vs. tenofovir disoproxil fumarate for hepatitis B virus infection.J Hepatol. 2018; 68: 672-681Abstract Full Text Full Text PDF PubMed Scopus (136) Google Scholar Pharmacologic data in humans needs to be obtained, as fast as possible, for E-CFCP to be genuinely compared to ETV, which is an excellent NA in this respect. The intrinsic toxicologic properties of ETV-related NAs are better than the tenofovir derivatives, particularly regarding mitochondrial toxicity,[12]Nucleoside analogues.in: LiverTox: Clinical and Research Information on Drug-Induced Liver Injury. National Institute of Diabetes and Digestive and Kidney Diseases, Bethesda (MD)2012Google Scholar but again the safety profile of E-CFCP is yet to be properly established in humans and compared to ETV.[20]Yan J.H. Bifano M. Olsen S. Smith R.A. Zhang D. Grasela D.M. et al.Entecavir pharmacokinetics, safety, and tolerability after multiple ascending doses in healthy subjects.J Clin Pharmacol. 2006; 46: 1250-1258Crossref PubMed Scopus (58) Google Scholar To minimize further toxicity, by preventing off-target activity on host polymerases in too many cell types, it would be nice to have NAs that are either only bio-distributed to hepatocytes (using a specific hepatocyte delivery strategy) or only activated (into TP form) within hepatocytes by using novel/original pro-drugging strategies. In the case of E-CFCP, we are told that it is a poor inhibitor of HIV polymerase, yet subcellular bio-distribution and activation patterns are not disclosed. In other words, one should aim at an optimal hepatic extraction ratio for a NA with anti-HBV activity, with virtually no effect on HIV because of a lack of bio-distribution/activation in cells replicating HIV. Even if the potency of E-CFCP is confirmed in patients with CHB, including those infected with ETV-resistant strains, which represent a real clinical burden, it is crucial to determine whether this potentially improved efficacy on viremia would translate into a faster decline of cccDNA. Because, after all, this is one of the most important features required to improve the current functional cure rate of NAs. So far, long-term data indicate that NAs induce a (very) slow cccDNA decline in patients with CHB.[7]Lai C.L. Wong D. Ip P. Kopaniszen M. Seto W.K. Fung J. et al.Reduction of covalently closed circular DNA with long-term nucleos(t)ide analogue treatment in chronic hepatitis B.J Hepatol. 2017; 66: 275-281Abstract Full Text Full Text PDF PubMed Scopus (88) Google Scholar,[8]Werle-Lapostolle B. Bowden S. Locarnini S. Wursthorn K. Petersen J. Lau G. et al.Persistence of cccDNA during the natural history of chronic hepatitis B and decline during adefovir dipivoxil therapy.Gastroenterology. 2004; 126: 1750-1758Abstract Full Text Full Text PDF PubMed Scopus (725) Google Scholar Yet, a near 100% inhibition of encapsidated rcDNA production and the prevention of recycling to the nucleus to replenish the cccDNA pool should lead to a faster decline of cccDNA in infected cells, irrespective of immune action and/or cell division (e.g. micro-regeneration). Unfortunately, there is no preclinical model available to evaluate this before entering clinical trials, meaning that such data will not be available soon for E-CFCP. When it comes to the rate of HBsAg loss, which is the newly defined clinical endpoint,[21]Cornberg M. Lok A.S.-F. Terrault N.A. Zoulim F. Faculty E-AHTEC. guidance for design and endpoints of clinical trials in chronic hepatitis B - Report from the 2019 EASL-AASLD HBV Treatment Endpoints Conference(‡).J Hepatol. 2020; 72: 539-557Abstract Full Text Full Text PDF PubMed Scopus (66) Google Scholar the best documented approach is to combine NAs with Peg-IFN-alpha,22Janssen H.L. van Zonneveld M. Senturk H. Zeuzem S. Akarca U.S. Cakaloglu Y. et al.Pegylated interferon alfa-2b alone or in combination with lamivudine for HBeAg-positive chronic hepatitis B: a randomised trial.Lancet (London, England). 2005; 365: 123-129Abstract Full Text Full Text PDF PubMed Scopus (993) Google Scholar, 23Lau G.K. Piratvisuth T. Luo K.X. Marcellin P. Thongsawat S. Cooksley G. et al.Peginterferon Alfa-2a, lamivudine, and the combination for HBeAg-positive chronic hepatitis B.N Engl J Med. 2005; 352: 2682-2695Crossref PubMed Scopus (1323) Google Scholar, 24Marcellin P. Ahn S.H. Ma X. Caruntu F.A. Tak W.Y. Elkashab M. et al.Combination of tenofovir disoproxil fumarate and peginterferon α-2a increases loss of hepatitis B surface antigen in patients with chronic hepatitis B.Gastroenterology. 2016; 150 (134-144.e110)Abstract Full Text Full Text PDF PubMed Scopus (216) Google Scholar, 25Marcellin P. Lau G.K. Bonino F. Farci P. Hadziyannis S. Jin R. et al.Peginterferon alfa-2a alone, lamivudine alone, and the two in combination in patients with HBeAg-negative chronic hepatitis B.N Engl J Med. 2004; 351: 1206-1217Crossref PubMed Scopus (1033) Google Scholar as NAs alone have little effect on HBsAg decline[4]Yeo Y.H. Ho H.J. Yang H.I. Tseng T.C. Hosaka T. Trinh H.N. et al.Factors associated with rates of HBsAg seroclearance in adults with chronic HBV infection: a systematic review and meta-analysis.Gastroenterology. 2019; 156 (635-646.e639)Abstract Full Text Full Text PDF PubMed Scopus (72) Google Scholar; this would have to be considered for the potential clinical R&D of E-CFCP. Finally, there are still debates around the capacity of some NAs to be more active than others to prevent disease progression and hepatocellular carcinoma occurrence.26Hsu Y.-C. Nguyen M.H. Inhibitory effect of nucleos(t)ide analogs on telomerase activity and risk of hepatocellular carcinoma in patients with chronic hepatitis B.Off J Am Coll Gastroenterol ACG. 2020; 115: 302-303Crossref PubMed Scopus (2) Google Scholar, 27Hsu Y.C. Wong G.L. Chen C.H. Peng C.Y. Yeh M.L. Cheung K.S. et al.Tenofovir versus entecavir for hepatocellular carcinoma prevention in an international consortium of chronic hepatitis B.Am J Gastroenterol. 2020; 115: 271-280Crossref PubMed Scopus (38) Google Scholar, 28Papatheodoridis G.V. Dalekos G.N. Idilman R. Sypsa V. Van Boemmel F. Buti M. et al.Similar risk of hepatocellular carcinoma during long-term entecavir or tenofovir therapy in Caucasian patients with chronic hepatitis B.J Hepatol. 2020; 73: 1037-1045Abstract Full Text Full Text PDF PubMed Scopus (31) Google Scholar It is too early to say whether E-CFCP will be more efficient at reducing these residual risks in patients with CHB on long-term treatment. The authors argue that this long-acting compound could be clinically useful to reduce the risk of resistance and to improve compliance to treatment. However, the 10-year risk of drug resistance in naïve patients treated with current NAs, such as ETV or TDF/TAF, is negligible and the efficacy of TDF or TAF, as rescue therapies for NA-resistant patients, is excellent.[1]EASL 2017 Clinical Practice Guidelines on the management of hepatitis B virus infection.J Hepatol. 2017; 67: 370-398Abstract Full Text Full Text PDF PubMed Scopus (2252) Google Scholar In general, compliance to long-term NA administration is already very good in most clinical centres and the management of NA therapy, e.g. visits and monitoring, is not very demanding with check-ups being performed every 6 months in most patients. Whether a long-acting anti-HBV drug would help the scale-up of anti-HBV treatment in “low to middle” income countries, remains an open issue, although one of the top priorities in these countries is the identification and diagnosis of these patients in order to start a cost-effective treatment. To conclude, one can envision the identification, R&D and clinical development of novel NAs to better fight HBV infection. Indeed, NAs are “good value” and usually the best backbone for combination treatment. In particular, a NA with an “ideal” toxicity profile (i.e. no side effect whatsoever in a dream scenario) and an improved impact on cccDNA decay could open the door to more universal treatment schedules with NAs, as many identified and diagnosed patients with CHB do not receive any treatment. DD was funded by annual endowment/core grants from INSERM (Institut National de la Santé et de la Rehcerche Médicale) and by ANRS (Agence Nationale de Recherche sur le Sida et les hépatites virale) grants (several from CSS12 and ANR 16-IFEC-0005-01). All authors contributed equally. DD has received research grants from: Janssen , Gilead Sciences , Roche , Sanofi ; CBD is an employee of Ai-biopharma, a SME with interest in HBV drug discovery; PL served as member of the Advisory Board or Speaker Bureau for: BMS, Roche, Gilead Sciences, GSK, Abbvie, MSD, Arrowhead, Alnylam, Janssen, Spring Bank, MYR Pharmaceuticals, Eiger. Please refer to the accompanying ICMJE disclosure forms for further details. DD is Director of Research at INSERM and is mainly supported in his activity by INSERM, ANRS, and other public funding bodies. PL is Professor of Gastroenterology at University of Milan and runs clinical investigations with both public and private support. The following is/are the supplementary data to this article: Download .pdf (.24 MB) Help with pdf files Multimedia component 1 Identification of a novel long-acting 4’-modified nucleoside reverse transcriptase inhibitor against HBVJournal of HepatologyVol. 74Issue 5PreviewWhile certain nucleos(t)ide reverse transcriptase inhibitors (NRTIs) are efficacious in treating HBV infection, their effects are yet to be optimized and the emergence of NRTI-resistant HBV variants is an issue because of the requirement for lifelong treatment. The development of agents that more profoundly suppress wild-type and drug-resistant HBVs, and that have a long-acting effect, are crucial to improve patient outcomes. Full-Text PDF Open Access