The cyclophilin inhibitor CRV431 inhibits liver HBV DNA and HBsAg in transgenic mice

Cyclophilin A: promising target in cancer therapy

Cyclophilin A (CypA), a member of the immunophilin family, stands out as the most prevalent among the cyclophilins found in humans. Beyond serving as the intracellular receptor for the immunosuppressive drug cyclosporine A (CsA), CypA exerts critical functions within the cell via its peptidyl-prolyl cis-trans isomerase (PPIase) activity, which is crucial for processes, such as protein folding, trafficking, assembly, modulation of immune responses, and cell signaling. Increasing evidence indicates that CypA is up-regulated in a variety of human cancers and it may be a novel potential therapeutic target for cancer treatment. Therefore, gaining a thorough understanding of CypA's contribution to cancer could yield fresh perspectives and inform the development of innovative therapeutic approaches. This review delves into the multifaceted roles of CypA in cancer biology and explores the therapeutic potential of targeting CypA.

Exploration of the Role of Cyclophilins in Established Hepatitis B and C Infections

Cyclophilin (Cyp) inhibitors are of clinical interest in respect to their antiviral activities in the context of many viral infections including chronic hepatitis B and C. Cyps are a group of enzymes with peptidyl-prolyl isomerase activity (PPIase), known to be required for replication of diverse viruses including hepatitis B and C viruses (HBV and HCV). Amongst the Cyp family, the molecular mechanisms underlying the antiviral effects of CypA have been investigated in detail, but potential roles of other Cyps are less well studied in the context of viral hepatitis. Furthermore, most studies investigating the role of Cyps in viral hepatitis did not investigate the potential therapeutic effects of their inhibition in already-established infections but have rather been performed in the context of neo-infections. Here, we investigated the effects of genetically silencing Cyps on persistent HCV and HBV infections. We confirm antiviral effects of CypA and CypD knock down and demonstrate novel roles for CypG and CypH in HCV replication. We show, furthermore, that CypA silencing has a modest but reproducible impact on persistent HBV infections in cultured human hepatocytes.

Cyclophilin inhibition as a strategy for the treatment of human disease

Cyclophilins (Cyps), characterized as peptidyl-prolyl cis-trans isomerases (PPIases), are highly conserved and ubiquitous, playing a crucial role in protein folding and cellular signaling. This review summarizes the biochemical pathways mediated by Cyps, including their involvement in pathological states such as viral replication, inflammation, and cancer progression, to underscore the therapeutic potential of Cyp inhibition. The exploration of Cyp inhibitors (CypI) in this review, particularly non-immunosuppressive cyclosporine A (CsA) derivatives, highlights their significance as therapeutic agents. The structural and functional nuances of CsA derivatives are examined, including their efficacy, mechanism of action, and the balance between therapeutic benefits and off-target effects. The landscape of CypI is evaluated to emphasize the clinical need for targeted approaches to exploit the complex biology of Cyps and to propose future directions for research that may enhance the utility of non-immunosuppressive CsA derivatives in treating diseases where Cyps play a key pathological role.

Cyclophilin D knockout significantly prevents HCC development in a streptozotocin-induced mouse model of diabetes-linked NASH

A family of Peptidyl-prolyl isomerases (PPIases), called Cyclophilins, localize to numerous intracellular and extracellular locations where they contribute to a variety of essential functions. We previously reported that non-immunosuppressive pan-cyclophilin inhibitor drugs like reconfilstat (CRV431) or NV556 decreased multiple aspects of non-alcoholic fatty liver disease (NAFLD) in mice under two different non-alcoholic steatohepatitis (NASH) mouse models. Both CRV431 and NV556 inhibit several cyclophilin isoforms, among which cyclophilin D (CypD) has not been previously investigated in this context. It is unknown whether it is necessary to simultaneously inhibit multiple cyclophilin family members to achieve therapeutic benefits or if loss-of-function of one is sufficient. Furthermore, narrowing down the isoform most responsible for a particular aspect of NAFLD/NASH, such as hepatocellular carcinoma (HCC), would allow for more precise future therapies. Features of human diabetes-linked NAFLD/NASH can be reliably replicated in mice by administering a single high dose of streptozotocin to disrupt pancreatic beta cells, in conjunction with a high sugar, high fat, high cholesterol western diet over the course of 30 weeks. Here we show that while both wild-type (WT) and Ppif-/- CypD KO mice develop multipe severe NASH disease features under this model, the formation of HCC nodules was significantly blunted only in the CypD KO mice. Furthermore, of differentially expressed transcripts in a qPCR panel of select HCC-related genes, nearly all were downregulated in the CypD KO background. Cyclophilin inhibition is a promising and novel avenue of treatment for diet-induced NAFLD/NASH. This study highlights the impact of CypD loss-of-function on the development of HCC, one of the most severe disease outcomes.

Mice lacking cyclophilin B, but not cyclophilin A, are protected from the development of NASH in a diet and chemical-induced model

Cyclophilins are a diverse family of peptidyl-prolyl isomerases (PPIases) of importance in a variety of essential cellular functions. We previously reported that the pan-cyclophilin inhibitor drug reconfilstat (CRV431) decreased disease in mice under the western-diet and carbon tetrachloride (CCl4) non-alcoholic steatohepatitis (NASH) model. CRV431 inhibits several cyclophilin isoforms, among which cyclophilin A (CypA) and B (CypB) are the most abundant. It is not known whether simultaneous inhibition of multiple cyclophilin family members is necessary for the observed therapeutic effects or if loss-of-function of one is sufficient. Identifying the responsible isoform(s) would enable future fine-tuning of drug treatments. Features of human liver fibrosis and complete NASH can be reliably replicated in mice by administration of intraperitoneal CCl4 alone or CCl4 in conjunction with high sugar, high cholesterol western diet, respectively. Here we show that while wild-type (WT) and Ppia-/- CypA KO mice develop severe NASH disease features under these models, Ppib-/- CypB KO mice do not, as measured by analysis of picrosirius red and hematoxylin & eosin-stained liver sections and TNFα immuno-stained liver sections. Cyclophilin inhibition is a promising and novel avenue of treatment for diet-induced NASH. In this study, mice without CypB, but not mice without CypA, were significantly protected from the development of the characteristic features of NASH. These data suggest that CypB is necessary for NASH disease progression. Further investigation is necessary to determine whether the specific role of CypB in the endoplasmic reticulum secretory pathway is of significance to its effect on NASH development.

Role of hepatitis B virus non-structural protein HBx on HBV replication, interferon signaling, and hepatocarcinogenesis

Hepatitis B, a global health concern caused by the hepatitis B virus (HBV), infects nearly 2 billion individuals worldwide, as reported by the World Health Organization (WHO). HBV, a hepatotropic DNA virus, predominantly targets and replicates within hepatocytes. Those carrying the virus are at increased risk of liver cirrhosis and hepatocellular carcinoma, resulting in nearly 900,000 fatalities annually. The HBV X protein (HBx), encoded by the virus's open reading frame x, plays a key role in its virulence. This protein is integral to viral replication, immune modulation, and liver cancer progression. Despite its significance, the precise molecular mechanisms underlying HBx remain elusive. This review investigates the HBx protein's roles in HBV replication, interferon signaling regulation, and hepatocellular carcinoma progression. By understanding the complex interactions between the virus and its host mediated by HBx, we aim to establish a solid foundation for future research and the development of HBx-targeted therapeutics.

Assessment of hepatitis B virus infection and interhost cellular responses using intrahepatic cholangiocyte organoids

The intrahepatic cholangiocyte organoids (ICOs) model was evaluated for host differences in hepatitis B virus (HBV) infection, cellular responses, antiviral and immunomodulator responses. Twelve ICOs generated from liver resections and biopsies were assessed for metabolic markers and functional HBV entry receptor expression throughout differentiation. Structural changes relevant to HBV infection were characterized using histology, confocal, and electron microscopy examinations. Optimal ICO culture conditions for HBV infection using HepAD38 (genotype D) and plasma-derived HBV (genotype B and C) were described. HBV infection was confirmed using HBcAg immunostaining, qRT-PCR (RNA, covalently closed circular DNA [cccDNA], extracellular DNA) and ELISA (HBsAg and HBeAg). Drug response to antiviral and immunosuppressive agent, and cellular responses (interferon-stimulated genes [ISG]) to interferon-α and viral mimic (PolyI:C) were assessed. ICOs underwent metabolic and structural remodeling following differentiation. Optimal HBV infection was achieved in well-differentiated ICOs using spinoculation, with time and donor-dependent increase in HBV RNA, cccDNA, extracellular DNA, HBeAg and HBsAg. Donor-dependent drug responsiveness to entry inhibitor and JAK inhibitor was observed. Despite having a robust ISG response to interferon-α and PolyI:C, HBV infection in ICOs did not upregulate ISGs. Human ICOs support HBV infection and replication with donor-dependent variation in viral dynamics and cellular responses. These features can be utilized for the development of personalized drug testing platform for antivirals.

Assessment of HBV infection and inter-host cellular responses using intrahepatic cholangiocyte organoids

Intrahepatic cholangiocyte organoids (ICOs) model was evaluated for host differences in hepatitis B virus (HBV) infection, cellular responses, antiviral, and immunomodulator responses. Twelve ICOs generated from liver resections and biopsies were assessed for metabolic markers and functional HBV entry receptor expression throughout differentiation. Structural changes relevant to HBV infection were characterized using histology, confocal, and electron microscopy examinations. Optimal ICO culture conditions for HBV infection using HepAD38 (genotype D) and plasma derived HBV (genotype B & C) were described. HBV infection was confirmed using HBcAg immunostaining, qRT-PCR (RNA, cccDNA, extracellular DNA), and ELISA (HBsAg and HBeAg). Drug response to antiviral and immunosuppressive agent, and cellular responses (interferon-stimulated genes [ISG]) to interferon-α and viral mimic (PolyI:C) were assessed. ICOs underwent metabolic and structural remodeling following differentiation. Optimal HBV infection was achieved in well-differentiated ICOs using spinoculation, with time and donor dependent increase in HBV RNA, cccDNA, extracellular DNA, HBeAg, and HBsAg. Donor dependent drug-responsiveness to entry inhibitor and JAK inhibitor was observed. Despite having a robust ISG response to interferon-α and PolyI:C, HBV infection in ICOs did not upregulate ISGs. Human ICOs support HBV infection and replication with donor dependent variation in viral dynamics and cellular responses. These features can be utilized for development of personalized drug testing platform for antivirals.

Proline Isomerization: From the Chemistry and Biology to Therapeutic Opportunities

Proline isomerization, the process of interconversion between the cis- and trans-forms of proline, is an important and unique post-translational modification that can affect protein folding and conformations, and ultimately regulate protein functions and biological pathways. Although impactful, the importance and prevalence of proline isomerization as a regulation mechanism in biological systems have not been fully understood or recognized. Aiming to fill gaps and bring new awareness, we attempt to provide a wholistic review on proline isomerization that firstly covers what proline isomerization is and the basic chemistry behind it. In this section, we vividly show that the cause of the unique ability of proline to adopt both cis- and trans-conformations in significant abundance is rooted from the steric hindrance of these two forms being similar, which is different from that in linear residues. We then discuss how proline isomerization was discovered historically followed by an introduction to all three types of proline isomerases and how proline isomerization plays a role in various cellular responses, such as cell cycle regulation, DNA damage repair, T-cell activation, and ion channel gating. We then explore various human diseases that have been linked to the dysregulation of proline isomerization. Finally, we wrap up with the current stage of various inhibitors developed to target proline isomerases as a strategy for therapeutic development.

Emerging Therapies for Chronic Hepatitis B and the Potential for a Functional Cure

Worldwide, an estimated 296 million people are living with chronic hepatitis B virus (HBV) infection, with a significant risk of morbidity and mortality. Current therapy with pegylated interferon (Peg-IFN) and indefinite or finite therapy with nucleoside/nucleotide analogues (Nucs) are effective in HBV suppression, hepatitis resolution, and prevention of disease progression. However, few achieve hepatitis B surface antigen (HBsAg) loss (functional cure), and relapse often occurs after the end of therapy (EOT) because these agents have no direct effect on durable template: covalently closed circular DNA (cccDNA) and integrated HBV DNA. Hepatitis B surface antigen loss rate increases slightly by adding or switching to Peg-IFN in Nuc-treated patients and this loss rate greatly increases up to 39% in 5 years with finite Nuc therapy with currently available Nuc(s). For this, great effort has been made to develop novel direct-acting antivirals (DAAs) and immunomodulators. Among the DAAs, entry inhibitors and capsid assembly modulators have little effect on reducing HBsAg levels; small interfering RNA, antisense oligonucleotides, and nucleic acid polymers in combination with Peg-IFN and Nuc may reduce HBsAg levels significantly, even a rate of HBsAg loss sustained for > 24 weeks after EOT up to 40%. Novel immunomodulators, including T-cell receptor agonists, check-point inhibitors, therapeutic vaccines, and monoclonal antibodies may restore HBV-specific T-cell response but not sustained HBsAg loss. The safety issues and the durability of HBsAg loss warrant further investigation. Combining agents of different classes has the potential to enhance HBsAg loss. Compounds directly targeting cccDNA would be more effective but are still in the early stage of development. More effort is required to achieve this goal.

Overview of the development of HBV small molecule inhibitors

Like tuberculosis and Acquired Immune Deficiency Syndrome (AIDS), hepatitis B is a globally recognized major public health threat. Although there are many small-molecule drugs for the treatment of hepatitis B, the approved drugs cannot eradicate the pathogenic culprit covalently closed circular DNA in patients, so the patients need long-term medication to control HBV amplification. Driven by a high unmet medical need, many pharmaceutical companies and research institutions have been engaged in the development of anti-HBV drugs to achieve a functional cure for chronic hepatitis B as soon as possible. This review summarizes the pathogenesis of hepatitis B virus and the research progress in the development of anti-HBV small molecule drugs, and introduces the cccDNA formation and transcription inhibitors and core inhibitors in detail, especially emphasizes the role of chinese herbal medicine in the treatment of chronic hepatitis B. Furthermore, this review proposes three potential strategies for cccDNA eradication in the future. We believe this review will provide meaningful guidance to achieve a functional cure for viral hepatitis B in the future.

An ultralong-acting tenofovir ProTide nanoformulation achieves monthslong HBV suppression

Treatment of chronic hepatitis B virus (HBV) requires lifelong daily therapy. However, suboptimal adherence to the existing daily therapy has led to the need for ultralong-acting antivirals. A lipophilic and hydrophobic ProTide was made by replacing the alanyl isopropyl ester present in tenofovir alafenamide (TAF) with a docosyl phenyl alanyl ester, now referred to as M1TFV. NM1TFV and nanoformulated TAF (NTAF) nanocrystals were formulated by high-pressure homogenization. A single intramuscular injection of NM1TFV, but not NTAF, delivered at a dose of TFV equivalents (168 milligrams per kilogram) demonstrated monthslong antiviral activities in both HBV-transgenic and human hepatocyte transplanted TK-NOG mice. The suppression of HBV DNA in blood was maintained for 3 months. Laboratory experiments on HBV-transfected HepG2.2.15 cells affirmed the animal results and the critical role of docosanol in the sustained NM1TFV antiviral responses. These results provide clear "proof of concept" toward an emerging therapeutic paradigm for the treatment and prevention of HBV infection.

Patent Highlights June–July 2022

A snapshot of noteworthy recent developments in the patent literature of relevance to pharmaceutical and medical research and development.

Advances in Immunotherapy for Hepatitis B

Hepatitis B virus (HBV) is a hepatotropic virus with the potential to cause chronic infection, and it is one of the common causes of liver disease worldwide. Chronic HBV infection leads to liver cirrhosis and, ultimately, hepatocellular carcinoma (HCC). The persistence of covalently closed circular DNA (cccDNA) and the impaired immune response in patients with chronic hepatitis B (CHB) has been studied over the past few decades. Despite advances in the etiology of HBV and the development of potent virus-suppressing regimens, a cure for HBV has not been found. Both the innate and adaptive branches of immunity contribute to viral eradication. However, immune exhaustion and evasion have been demonstrated during CHB infection, although our understanding of the mechanism is still evolving. Recently, the successful use of an antiviral drug for hepatitis C has greatly encouraged the search for a cure for hepatitis B, which likely requires an approach focused on improving the antiviral immune response. In this review, we discuss our current knowledge of the immunopathogenic mechanisms and immunobiology of HBV infection. In addition, we touch upon why the existing therapeutic approaches may not achieve the goal of a functional cure. We also propose how combinations of new drugs, and especially novel immunotherapies, contribute to HBV clearance.

Non-Immunosuppressive Cyclophilin Inhibitors

Cyclophilins, enzymes with peptidyl-prolyl cis/trans isomerase activity, are relevant to a large variety of biological processes. The most abundant member of this enzyme family, cyclophilin A, is the cellular receptor of the immunosuppressive drug cyclosporine A (CsA). As a consequence of the pathophysiological role of cyclophilins, particularly in viral infections, there is a broad interest in cyclophilin inhibition devoid of immunosuppressive activity. This Review first gives an introduction into the physiological and pathophysiological roles of cyclophilins. The presentation of non-immunosuppressive cyclophilin inhibitors will commence with drugs based on chemical modifications of CsA. The naturally occurring macrocyclic sanglifehrins have become other lead structures for cyclophilin-inhibiting drugs. Finally, de novo designed compounds, whose structures are not derived from or inspired by natural products, will be presented. Relevant synthetic concepts will be discussed, but the focus will also be on biochemical studies, structure-activity relationships, and clinical studies.

Entry inhibition of hepatitis B virus using cyclosporin O derivatives with peptoid side chain incorporation

Hepatitis B virus (HBV) infection is a serious worldwide health problem causing liver cirrhosis and hepatocellular carcinoma. The development of novel therapeutics targeting distinct steps of the HBV life cycle and combination therapy with approved drugs (i.e., nucleot(s)ides, interferon-α) are considered effective strategies for curing HBV. Among these strategies is the development of entry inhibitors that interfere with the host entry step of HBV to prevent viral infection and transmission. Herein, we generated a novel library of cyclosporin O (CsO) derivatives that incorporate peptoid side chains. Twenty-two CsO derivatives were evaluated for membrane permeability, cytotoxicity, and in vitro HBV entry inhibitory activity. The lead compound (i.e., compound 21) showed the greatest potency in the in vitro HBV entry inhibition assay (IC₅₀ = 0.36 ± 0.01 μM) with minimal cytotoxicity. Our peptide-peptoid hybrid CsO scaffold can readily expand chemical diversity and is applicable for screening various targets requiring macrocyclic chemical entities.

Novel therapeutic strategies for Chronic Hepatitis B

The last few years have seen a resurgence of activity in the hepatitis B drug pipeline, with many compounds in various stages of development. This review aims to provide a comprehensive overview of the latest advances in therapeutics for chronic hepatitis B (CHB). We will discuss the broad spectrum of direct-acting antivirals in clinical development, including capsids inhibitors, siRNA, HBsAg and polymerase inhibitors. In addition, host-targeted therapies (HTT) will be extensively reviewed, focusing on the latest progress in immunotherapeutics such as toll-like receptors and RIG-1 agonists, therapeutic vaccines and immune checkpoints modulators. A growing number of HTT in pre-clinical development directly target the key to HBV persistence, namely the covalently closed circular DNA (cccDNA) and hold great promise for HBV cure. This exciting area of HBV research will be highlighted, and molecules such as cyclophilins inhibitors, APOBEC3 deaminases and epigenetic modifiers will be discussed.

Repurposing of cyclophilin A inhibitors as broad-spectrum antiviral agents

Cyclophilin A (CypA) is linked to diverse human diseases including viral infections. With the worldwide emergence of severe acute respiratory coronavirus 2 (SARS-CoV-2), drug repurposing has been highlighted as a strategy with the potential to speed up antiviral development. Because CypA acts as a proviral component in hepatitis C virus, coronavirus and HIV, its inhibitors have been suggested as potential treatments for these infections. Here, we review the structure of cyclosporin A and sanglifehrin A analogs as well as synthetic micromolecules inhibiting CypA; and we discuss their broad-spectrum antiviral efficacy in the context of the virus lifecycle.

Ergosterol peroxide inhibits HBV infection by inhibiting the binding of the pre-S1 domain of LHBsAg to NTCP

Hepatitis B virus (HBV) infection leads to severe liver diseases, including cirrhosis and hepatocellular carcinoma (HCC). More than 257 million individuals are chronically infected, particularly in the Western Pacific region and Africa. Although nucleotide and nucleoside analogues (NUCs) and interferons (IFNs) are the standard therapeutics for HBV infection, none eradicates HBV covalently closed circular DNA (cccDNA) from the infected hepatocytes. In addition, long-term treatment with NUCs increases the risk of developing drug resistance and IFNs may cause severe side effects in patients. Thus, a novel HBV therapy that can achieve a functional cure, or even complete elimination of the virus, is highly desirable. Regarding the HBV life cycle, agents targeting the entry step of HBV infection reduce the intrahepatic cccDNA pool preemptively. The initial entry step in HBV infection involves interaction between the pre-S1 domain of the large hepatitis B surface protein (LHBsAg) and the sodium taurocholate cotransporting polypeptide (NTCP), which is a receptor for HBV. In this study, ergosterol peroxide (EP) was identified as a new inhibitor of HBV entry. EP inhibits an early step of HBV entry into DMSO-differentiated immortalized primary human hepatocytes HuS-E/2 cells, which were overexpressed NTCP. Also, EP interfered directly with the NTCP-LHBsAg interaction by acting on the NTCP. In addition, EP had no effect on HBV genome replication, virion integrity or virion secretion. Finally, the activity of EP against infection with HBV genotypes A-D highlights the therapeutic potential of EP for fighting HBV infection.

Novel Therapies That May Cure Chronic Hepatitis B Virus

The hepatitis B virus (HBV) is a member of the Hepadnaviridae family, which includes small DNA enveloped viruses that infect primates, rodents, and birds and is the causative factor of chronic hepatitis B. A common feature of all these viruses is their great specificity by species and cell type, as well as a peculiar genomic and replication organization similar to that of retroviruses. The HBV virion consists of an external lipid envelope and an internal icosahedral protein capsid containing the viral genome and a DNA polymerase, which also functions as a reverse transcriptase.

HBV/HIV Coinfection: Impact on the Development and Clinical Treatment of Liver Diseases

Hepatitis B virus (HBV) infection is a common contributor to chronic hepatitis, liver cirrhosis, and hepatocellular carcinoma. Approximately 10% of people with human immunodeficiency virus (HIV) also have chronic HBV co-infection, owing to shared transmission routes. HIV/HBV coinfection accelerates the progression of chronic HBV to cirrhosis, end-stage liver disease, or hepatocellular carcinoma compared to chronic HBV mono-infection. HBV/HIV coinfection alters the natural history of hepatitis B and renders the antiviral treatment more complex. In this report, we conducted a critical review on the epidemiology, natural history, and pathogenesis of liver diseases related to HBV/HIV coinfection. We summarized the novel therapeutic options for these coinfected patients.

Novel Antivirals in Clinical Development for Chronic Hepatitis B Infection

Globally, chronic hepatitis B (CHB) infection is one of the leading causes of liver failure, decompensated cirrhosis, and hepatocellular carcinoma. Existing antiviral therapy can suppress viral replication but not fully eradicate the virus nor the risk of liver-related complications. Novel treatments targeting alternative steps of the viral cycle or to intensify/restore the host's immunity are being developed. We discuss novel drugs that have already entered clinical phases of development. Agents that interfere with specific steps of HBV replication include RNA interference, core protein allosteric modulation, and inhibition of viral entry or viral protein excretion (NAPs and STOPS). Agents that target the host's immunity include toll-like receptor agonists, therapeutic vaccines, immune checkpoint modulators, soluble T-cell receptors, and monoclonal antibodies. Most have demonstrated favorable results in suppression of viral proteins and genomic materials (i.e., HBV DNA and/or pre-genomic RNA), and/or evidence on host-immunity restoration including cytokine responses and T-cell activation. Given the abundant clinical experience and real-world safety data with the currently existing therapy, any novel agent for CHB should be accompanied by convincing safety data. Combination therapy of nucleos(t)ide analogue, a novel virus-directing agent, and/or an immunomodulatory agent will be the likely approach to optimize the chance of a functional cure in CHB.

Toward a new era of hepatitis B virus therapeutics: The pursuit of a functional cure

Hepatitis B virus (HBV) infection, although preventable by vaccination, remains a global health problem and a major cause of chronic liver disease. Although current treatment strategies suppress viral replication very efficiently, the optimal endpoint of hepatitis B surface antigen (HBsAg) clearance is rarely achieved. Moreover, the thorny problems of persistent chromatin-like covalently closed circular DNA and the presence of integrated HBV DNA in the host genome are ignored. Therefore, the scientific community has focused on developing innovative therapeutic approaches to achieve a functional cure of HBV, defined as undetectable HBV DNA and HBsAg loss over a limited treatment period. A deeper understanding of the HBV life cycle has led to the introduction of novel direct-acting antivirals that exert their function through multiple mechanisms, including inhibition of viral entry, transcriptional silencing, epigenetic manipulation, interference with capsid assembly, and disruption of HBsAg release. In parallel, another category of new drugs aims to restore dysregulated immune function in chronic hepatitis B accompanied by lethargic cellular and humoral responses. Stimulation of innate immunity by pattern-recognition receptor agonists leads to upregulation of antiviral cytokine expression and appears to contribute to HBV containment. Immune checkpoint inhibitors and adoptive transfer of genetically engineered T cells are breakthrough technologies currently being explored that may elicit potent HBV-specific T-cell responses. In addition, several clinical trials are attempting to clarify the role of therapeutic vaccination in this setting. Ultimately, it is increasingly recognized that elimination of HBV requires a treatment regimen based on a combination of multiple drugs. This review describes the rationale for progressive therapeutic interventions and discusses the latest findings in the field of HBV therapeutics.

HBV 2021: New therapeutic strategies against an old foe

Hepatitis B virus (HBV) affects more than 250 million people worldwide, and is one of the major aetiologies for the development of cirrhosis and hepatocellular carcinoma (HCC). In spite of universal vaccination programs, HBV infection is still a public health problem, and the limited number of available therapeutic approaches complicates the clinical management of these patients. Thus, HBV infection remains an unmet medical need that requires a continuous effort to develop new individual molecules, treatment combinations and even completely novel therapeutic strategies to achieve the goal of HBV elimination. The following review provides an overview of the current situation in chronic HBV infection, with an analysis of the scientific rationale of certain clinical interventions and, more importantly, explores the most recent developments in the field of HBV drug discovery.

From hepatitis A to E: A critical review of viral hepatitis

Viral infections affecting the liver have had an important impact on humanity, as they have led to significant morbidity and mortality in patients with acute and chronic infections. Once an unknown etiology, the discovery of the viral agents triggered interest of the scientific community to establish the pathogenesis and diagnostic modalities to identify the affected population. With the rapid scientific and technological advances in the last centuries, controlling and even curing the infections became a possibility, with a large focus on preventive medicine through vaccination. Hence, a comprehensive understanding of hepatitis A, B, C, D and E is required by primary care physicians and gastroenterologists to provide care to these patients. The review article describes the epidemiology, pathogenesis, clinical presentation, diagnostic tools and current medication regimens, with a focus on upcoming treatment options and the role of liver transplantation.

Moving Fast Toward Hepatitis B Virus Elimination

Currently, there are two safe and effective therapeutic strategies for chronic hepatitis B treatment, namely, nucleoside analogs and interferon alpha (pegylated or non-pegylated). These treatments can control viral replication and improve survival; however, they do not eliminate the virus and therefore require long-term continued therapy. In addition, there are significant concerns about virus rebound on discontinuation of therapy and the development of fibrosis and hepatocellular carcinoma despite therapy. Therefore, the search for new, more effective, and safer antiviral agents that can cure hepatitis B virus (HBV) continues. Anti-HBV drug discovery and development is fundamentally impacted by our current understanding of HBV replication, disease physiopathology, and persistence of HBV covalently closed circular DNA (cccDNA). Several HBV replication targets are the basis for novel anti-HBV drug development strategies. Many of them are already in clinical trial phase 1 or 2, while others with promising results are still in preclinical stages. As research intensifies, potential HBV curative therapies and modalities in the pipeline are now on the horizon.

Investigational drugs with dual activity against HBV and HIV (Review)

Chronic hepatitis B (CHB) and acquired immunodeficiency syndrome (AIDS) are global public health problems that pose a significant health burden. Human immunodeficiency virus (HIV) and hepatitis B virus (HBV) coinfection is common, as these viruses have similar transmission routes, such as blood transmission, sexual transmission and mother-to-child transmission. Coinfection frequently leads to accelerated disease progression. For individuals coinfected with HIV/HBV, combination antiretroviral therapy containing dual anti-HBV drugs is recommended. Certain studies have also indicated the benefits of antiretroviral drugs with anti-HBV activity in patients with coinfection. A total of four Food and Drug Administration-approved HIV drugs also have anti-HBV activity; namely, emtricitabine, lamivudine, tenofovir disoproxil fumarate and tenofovir alafenamide, which are all nucleoside reverse transcriptase inhibitors. However, various issues, including drug resistance and side effects, limit their application. Therefore, it is necessary to develop more drugs with dual activity against HBV and HIV. The present review outlines the mechanisms, safety and efficacy of certain drugs that have been investigated for this purpose.

Recent Advances in Understanding, Diagnosing, and Treating Hepatitis B Virus Infection

Chronic hepatitis B virus (HBV) infection affects 292 million people worldwide and is associated with a broad range of clinical manifestations including cirrhosis, liver failure, and hepatocellular carcinoma (HCC). Despite the availability of an effective vaccine HBV still causes nearly 900,000 deaths every year. Current treatment options keep HBV under control, but they do not offer a cure as they cannot completely clear HBV from infected hepatocytes. The recent development of reliable cell culture systems allowed for a better understanding of the host and viral mechanisms affecting HBV replication and persistence. Recent advances into the understanding of HBV biology, new potential diagnostic markers of hepatitis B infection, as well as novel antivirals targeting different steps in the HBV replication cycle are summarized in this review article.

Cyclophilin A and CD147: novel therapeutic targets for the treatment of COVID-19

The outbreak of pneumonia caused by a new coronavirus (SARS-CoV-2) occurred in December 2019, and spread rapidly throughout the world. There have been other severe coronavirus outbreaks worldwide, namely, severe acute respiratory syndrome (SARS-CoV) and Middle East respiratory syndrome (MERS-CoV). Because the genetic diversity of coronaviruses renders the design of vaccines complicated, broad spectrum-anti-coronavirus drugs have become a critical approach to control the coronavirus epidemic. Cyclophilin A is an important protein needed for coronavirus replication, and its inhibitor cyclosporine A has the ability to suppress coronavirus on a broad spectrum. CD147-S protein was found to be one route by which SARS-CoV-2 invades host cells, while CD147 was found to play a functional role in facilitating the infection of host cells by SARS-CoV. The CyPA/CD147 interaction may play a critical role in the ability of the SARS-CoV-2 virus to enter the host cells. However, cyclosporine A has immunosuppressive effects, so the conditions for its use as an antiviral drug are limited. As a result, cyclosporine A analogues without immunosuppressive side effects have attracted lots of interest. This review primarily discusses the drug development prospects of cyclophilin A as a therapeutic target for the treatment of coronavirus infection, especially coronavirus disease 2019 (COVID-19), and non-immunosuppressive cyclosporine analogues.

Structurally distinct cyclosporin and sanglifehrin analogs CRV431 and NV556 suppress established HCV infection in humanized-liver mice

We previously reported that the non-immunosuppressive cyclophilin inhibitors (CypIs)—cyclosporin A analog CRV431 and sanglifehrin analog NV556—efficiently inhibit HCV replication in vitro. In this study, we asked whether they can also reduce HCV replication in vivo. We found that a single oral administration of CRV431 and NV556 to HCV-infected humanized-liver mice drastically reduced HCV blood levels. The antiviral effect was observed when CRV431 or NV556 were each individually administered with HCV, 3, 6 weeks or even 3 months post-infection when viral replication is robust. These results were confirmed in chimeric mice implanted with human hepatocytes isolated from three distinct donors. Remarkably, no viral rebound was observed 5 months after a single dose administration of 50 mg/kg of CRV431 or NV556 four weeks post-HCV infection, indicating the possibility of suppression of an established viral infection. Since we recently demonstrated that both CRV431 and NV556 also inhibit the development of liver fibrosis and hepatocellular carcinoma in nonviral-induced non-alcoholic steatohepatitis mouse models, our present data suggest that the two entirely structurally different CypIs—CRV431 and NV556—derived from unrelated natural products, represent attractive partners to current direct-acting agent (DAA) regimens for the treatment of hepatitis C and liver diseases.

Orchestration of Intracellular Circuits by G Protein-Coupled Receptor 39 for Hepatitis B Virus Proliferation

Hepatitis B virus (HBV), a highly persistent pathogen causing hepatocellular carcinoma (HCC), takes full advantage of host machinery, presenting therapeutic targets. Here we aimed to identify novel druggable host cellular factors using the reporter HBV we have recently generated. In an RNAi screen of G protein-coupled receptors (GPCRs), GPCR39 (GPR39) appeared as the top hit to facilitate HBV proliferation. Lentiviral overexpression of active GPR39 proteins and an agonist enhanced HBV replication and transcriptional activities of viral promoters, inducing the expression of CCAAT/enhancer binding protein (CEBP)-β (CEBPB). Meanwhile, GPR39 was uncovered to activate the heat shock response, upregulating the expression of proviral heat shock proteins (HSPs). In addition, glioma-associated oncogene homologue signaling, a recently reported target of GPR39, was suggested to inhibit HBV replication and eventually suppress expression of CEBPB and HSPs. Thus, GPR39 provirally governed intracellular circuits simultaneously affecting the carcinopathogenetic gene functions. GPR39 and the regulated signaling networks would serve as antiviral targets, and strategies with selective inhibitors of GPR39 functions can develop host-targeted antiviral therapies preventing HCC.

A Pan-Cyclophilin Inhibitor, CRV431, Decreases Fibrosis and Tumor Development in Chronic Liver Disease Models

Previous studies show that cyclophilins contribute to many pathologic processes, and cyclophilin inhibitors demonstrate therapeutic activities in many experimental models. However, no drug with cyclophilin inhibition as the primary mode of action has advanced completely through clinical development to market. In this study, we present findings on the cyclophilin inhibitor, CRV431, that highlight its potential as a drug candidate for chronic liver diseases. CRV431 was found to potently inhibit all cyclophilin isoforms tested-A, B, D, and G. Inhibitory constant or IC50 values ranged from 1 to 7 nM, which was up to 13 times more potent than the parent compound, cyclosporine A (CsA), from which CRV431 was derived. Other CRV431 advantages over CsA as a nontransplant drug candidate were significantly diminished immunosuppressive activity, less drug transporter inhibition, and reduced cytotoxicity potential. Oral dosing to mice and rats led to good blood exposures and a 5- to 15-fold accumulation of CRV431 in liver compared with blood concentrations across a wide range of CRV431 dosing levels. Most importantly, CRV431 decreased liver fibrosis in a 6-week carbon tetrachloride model and in a mouse model of nonalcoholic steatohepatitis (NASH). Additionally, CRV431 administration during a late, oncogenic stage of the NASH disease model resulted in a 50% reduction in the number and size of liver tumors. These findings are consistent with CRV431 targeting fibrosis and cancer through multiple, cyclophilin-mediated mechanisms and support the development of CRV431 as a safe and effective drug candidate for liver diseases. SIGNIFICANCE STATEMENT: Cyclophilin inhibitors have demonstrated therapeutic activities in many disease models, but no drug candidates have yet advanced completely through development to market. In this study, CRV431 is shown to potently inhibit multiple cyclophilin isoforms, possess several optimized pharmacological properties, and decrease liver fibrosis and tumors in mouse models of chronic liver disease, which highlights its potential to be the first approved drug primarily targeting cyclophilin isomerases.

Cyclophilin Inhibitor NV556 Reduces Fibrosis and Hepatocellular Carcinoma Development in Mice With Non-Alcoholic Steatohepatitis

Hepatocellular carcinoma (HCC), the third major cause of cancer mortality, can result from non-alcoholic steatohepatitis (NASH). Due to limited efficacy of drugs approved for HCC and no drug available yet for NASH, identification of new effective treatments is crucial. Here, we investigated whether NV556, a cyclophilin inhibitor derived from sanglifehrins, would decrease the development of NASH and HCC in a preclinical mouse model. For our experiment, male mice were administered streptozotocin to disrupt pancreatic cells and nourished with high-fat diet since 3 weeks of age. Afterward, NV556 or vehicle was orally administered daily for 6 weeks before the 14-week-old time point for the development of NASH, or 10 weeks before the 30-week-old time point for the establishment of HCC. Body weight, blood glucose level, and liver weight were recorded. Moreover, for NASH, livers were histologically examined for inflammation and steatosis. Collagen was measured by Sirius Red staining of hepatic tissues. Systemic cytokine levels in serum were detected by multiplex assays. For HCC, nodules of livers were measured and scored according to a developed system with number and size of nodules as criteria. NV556 significantly decreased collagen deposition (p = 0.0281), but did not alter inflammation, steatosis, body and liver weight, and systemic cytokine production compared to control mice with NASH symptoms. For HCC, NV556 statistically reduced the number (p = 0.0091) and diameter of tumorous nodules (p = 0.0264), along with liver weight (p = 0.0026) of mice.Our study suggests NV556 as a promising candidate for treatment of NASH-derived fibrosis and HCC.