Increased HDL cholesterol and apoA-I in humans and mice treated with a novel SR-BI inhibitor

Genetic and pharmacological perturbation of hepatitis-C virus entry

Hepatitis-C virus (HCV) chronically infects 58 million individuals worldwide with variable disease outcome. While a subfraction of individuals exposed to the virus clear the infection, the majority develop chronic infection if untreated. Another subfraction of chronically ill proceeds to severe liver disease. The underlying causes of this interindividual variability include genetic polymorphisms in interferon genes. Here, we review available data on the influence of genetic or pharmacological perturbation of HCV host dependency factors on the clinically observed interindividual differences in disease outcome. We focus on host factors mediating virus entry into human liver cells. We assess available data on genetic variants of the major entry factors scavenger receptor class-B type I, CD81, claudin-1, and occludin as well as pharmacological perturbation of these entry factors. We review cell culture experimental and clinical cohort study data and conclude that entry factor perturbation may contribute to disease outcome of hepatitis C.

Discovery of a fused bicyclic derivative of 4-hydroxypyrrolidine and imidazolidinone as a new anti-HCV agent

Hepatitis C virus (HCV) infection causes severe liver diseases and remains a major global public health concern. Current direct-acting antiviral (DAA)-based therapies that target viral proteins involving HCV genome replication are effective, however a minority of patients still fail to cure HCV, rendering a window to develop additional antivirals particularly targeting host functions involving in HCV infection. Here, we utilized the HCV infection cell culture system (HCVcc) to screen in-house compounds bearing host-interacting preferred scaffold for the antiviral activity. Compound HXL-10, a novel fused bicyclic derivative of pyrrolidine and imidazolidinone, was identified as a potent anti-HCV agent with a low cytotoxicity and high specificity. Mechanistic studies showed that HXL-10 neither displayed a virucidal effect nor inhibited HCV genomic RNA replication. Instead, HXL-10 might inhibit HCV assembly by targeting host functions. In summary, we developed a novel anti-HCV agent that may potentially offer additive benefits to the current anti-HCV DDA.

Alterations of HDL's to piHDL's Proteome in Patients with Chronic Inflammatory Diseases, and HDL-Targeted Therapies

Chronic inflammatory diseases, such as rheumatoid arthritis, steatohepatitis, periodontitis, chronic kidney disease, and others are associated with an increased risk of atherosclerotic cardiovascular disease, which persists even after accounting for traditional cardiac risk factors. The common factor linking these diseases to accelerated atherosclerosis is chronic systemic low-grade inflammation triggering changes in lipoprotein structure and metabolism. HDL, an independent marker of cardiovascular risk, is a lipoprotein particle with numerous important anti-atherogenic properties. Besides the essential role in reverse cholesterol transport, HDL possesses antioxidative, anti-inflammatory, antiapoptotic, and antithrombotic properties. Inflammation and inflammation-associated pathologies can cause modifications in HDL's proteome and lipidome, transforming HDL from atheroprotective into a pro-atherosclerotic lipoprotein. Therefore, a simple increase in HDL concentration in patients with inflammatory diseases has not led to the desired anti-atherogenic outcome. In this review, the functions of individual protein components of HDL, rendering them either anti-inflammatory or pro-inflammatory are described in detail. Alterations of HDL proteome (such as replacing atheroprotective proteins by pro-inflammatory proteins, or posttranslational modifications) in patients with chronic inflammatory diseases and their impact on cardiovascular health are discussed. Finally, molecular, and clinical aspects of HDL-targeted therapies, including those used in therapeutical practice, drugs in clinical trials, and experimental drugs are comprehensively summarised.

Scavenger Receptors in the Pathogenesis of Viral Infections

Scavenger receptors (SR) are not only pattern recognition receptors involved in the immune response against pathogens but are also important receptors exploited by different virus to enter host cells, and thus represent targets for antiviral therapy. The high mutation rates of viruses, as well as their small genomes are partly responsible for the high rates of virus resistance and effective treatments remain a challenge. Most currently approved formulations target viral-encoded factors. Nevertheless, host proteins may function as additional targets. Thus, there is a need to explore and develop new strategies aiming at cellular factors involved in virus replication and host cell entry. SR-virus interactions have implications in the pathogenesis of several viral diseases and in adenovirus-based vaccination and gene transfer technologies, and may function as markers of severe progression. Inhibition of SR could reduce adenoviral uptake and improve gene therapy and vaccination, as well as reduce pathogenesis. In this review, we will examine the crucial role of SR play in cell entry of different types of human virus, which will allow us to further understand their role in protection and pathogenesis and its potential as antiviral molecules. The recent discovery of SR-B1 as co-factor of SARS-Cov-2 (severe acute respiratory syndrome coronavirus 2) entry is also discussed. Further fundamental research is essential to understand molecular interactions in the dynamic virus-host cell interplay through SR for rational design of therapeutic strategies.

Cholesterol Auxotrophy as a Targetable Vulnerability in Clear Cell Renal Cell Carcinoma

Clear cell renal cell carcinoma (ccRCC) is characterized by large intracellular lipid droplets containing free and esterified cholesterol; however, the functional significance of cholesterol accumulation in ccRCC cells is unknown. We demonstrate that, surprisingly, genes encoding cholesterol biosynthetic enzymes are repressed in ccRCC, suggesting a dependency on exogenous cholesterol. Mendelian randomization analyses based on 31,000 individuals indicate a causal link between elevated circulating high-density lipoprotein (HDL) cholesterol and ccRCC risk. Depriving ccRCC cells of either cholesterol or HDL compromises proliferation and survival in vitro and tumor growth in vivo; in contrast, elevated dietary cholesterol promotes tumor growth. Scavenger Receptor B1 (SCARB1) is uniquely required for cholesterol import, and inhibiting SCARB1 is sufficient to cause ccRCC cell-cycle arrest, apoptosis, elevated intracellular reactive oxygen species levels, and decreased PI3K/AKT signaling. Collectively, we reveal a cholesterol dependency in ccRCC and implicate SCARB1 as a novel therapeutic target for treating kidney cancer.

SIGNIFICANCE

We demonstrate that ccRCC cells are auxotrophic for exogenous cholesterol to maintain PI3K/AKT signaling pathway and ROS homeostasis. Blocking cholesterol import through the HDL transporter SCARB1 compromises ccRCC cell survival and tumor growth, suggesting a novel pharmacologic target for this disease. This article is highlighted in the In This Issue feature, p. 2945.

Inhibition of Scavenger Receptor Class B Type 1 (SR-B1) Expression and Activity as a Potential Novel Target to Disrupt Cholesterol Availability in Castration-Resistant Prostate Cancer

There have been several studies that have linked elevated scavenger receptor class b type 1 (SR-B1) expression and activity to the development and progression of castration-resistant prostate cancer (CRPC). SR-B1 facilitates the influx of cholesterol to the cell from lipoproteins in systemic circulation. This influx of cholesterol may be important for many cellular functions, including the synthesis of androgens. Castration-resistant prostate cancer tumors can synthesize androgens de novo to supplement the loss of exogenous sources often induced by androgen deprivation therapy. Silencing of SR-B1 may impact the ability of prostate cancer cells, particularly those of the castration-resistant state, to maintain the intracellular supply of androgens by removing a supply of cholesterol. SR-B1 expression is elevated in CRPC models and has been linked to poor survival of patients. The overarching belief has been that cholesterol modulation, through either synthesis or uptake inhibition, will impact essential signaling processes, impeding the proliferation of prostate cancer. The reduction in cellular cholesterol availability can impede prostate cancer proliferation through both decreased steroid synthesis and steroid-independent mechanisms, providing a potential therapeutic target for the treatment of prostate cancer. In this article, we discuss and highlight the work on SR-B1 as a potential novel drug target for CRPC management.

HDL-scavenger receptor B type 1 facilitates SARS-CoV-2 entry

Responsible for the ongoing coronavirus disease 19 (COVID-19) pandemic, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infects host cells through binding of the viral spike protein (SARS-2-S) to the cell-surface receptor angiotensin-converting enzyme 2 (ACE2). Here we show that the high-density lipoprotein (HDL) scavenger receptor B type 1 (SR-B1) facilitates ACE2-dependent entry of SARS-CoV-2. We find that the S1 subunit of SARS-2-S binds to cholesterol and possibly to HDL components to enhance viral uptake in vitro. SR-B1 expression facilitates SARS-CoV-2 entry into ACE2-expressing cells by augmenting virus attachment. Blockade of the cholesterol-binding site on SARS-2-S1 with a monoclonal antibody, or treatment of cultured cells with pharmacological SR-B1 antagonists, inhibits HDL-enhanced SARS-CoV-2 infection. We further show that SR-B1 is coexpressed with ACE2 in human pulmonary tissue and in several extrapulmonary tissues. Our findings reveal that SR-B1 acts as a host factor that promotes SARS-CoV-2 entry and may help explain viral tropism, identify a possible molecular connection between COVID-19 and lipoprotein metabolism, and highlight SR-B1 as a potential therapeutic target to interfere with SARS-CoV-2 infection.

β-glucans and cholesterol (Review)

Hypercholesterolemia is one of primary risk factors of cardiovascular disease, together with metabolic syndrome, hypertension and diabetes. Although progress has been made, the search for novel methods of preventing and treating dyslipidemia is ongoing and current therapies for cardiovascular disease induce various side effects. β-glucans are linear unbranched polysaccharides found in various natural sources, such as mushrooms. Due to their structure they are able to interact with innate immunity receptors, however they also act as dietary fibers in the digestive tract. As there are two forms of β-glucans, insoluble and soluble forms, they are able to interact with lipids and biliary salts in the bowel and consequently reduce cholesterol levels. Therefore, they may be developed as a suitable therapeutic option to treat patients with dyslipidemia, as they are natural molecules that do not induce any significant side effects. The current review discusses the evidence supporting the effects of β-glucans on cholesterol levels.

High-density Lipoprotein and Low-density Lipoprotein Therapeutic Approaches in Acute Coronary Syndromes

BACKGROUND

Low-density lipoprotein cholesterol (LDL), and especially its oxidized form, renders the atherosclerotic plaque vulnerable to rupture in acute coronary syndromes (ACS). On the other hand, high-density lipoprotein (HDL) is considered an anti-atherogenic molecule. The more recent HDL-targeted drugs may prove to be superior to those used before. Indeed, delipidated HDL and HDL mimetics are efficient in increasing HDL levels, while the apoA-I upregulation with RVX-208 appears to offer a clinical benefit which is beyond the HDL related effects. HDL treatment however has not shown a significant improvement in the outcomes of patients with ACS so far, studies have therefore focused again on LDL. In addition to statins and ezetimibe, novel drugs such as PSCK9 inhibitors and apolipoprotein B inhibitors appear to be both effective and safe for patients with hyperlipidemia.

CONCLUSION

Data suggest these could potentially improve the cardiovascular outcomes of patient with ACS. Yet, there is still research to be done, in order to confirm whether ACS patients would benefit from LDL- or HDL-targeted therapies or a combination of both.

SR-B1: A Unique Multifunctional Receptor for Cholesterol Influx and Efflux

The scavenger receptor, class B type 1 (SR-B1), is a multiligand membrane receptor protein that functions as a physiologically relevant high-density lipoprotein (HDL) receptor whose primary role is to mediate selective uptake or influx of HDL-derived cholesteryl esters into cells and tissues. SR-B1 also facilitates the efflux of cholesterol from peripheral tissues, including macrophages, back to liver. As a regulator of plasma membrane cholesterol content, SR-B1 promotes the uptake of lipid soluble vitamins as well as viral entry into host cells. These collective functions of SR-B1 ultimately affect programmed cell death, female fertility, platelet function, vasculature inflammation, and diet-induced atherosclerosis and myocardial infarction. SR-B1 has also been identified as a potential marker for cancer diagnosis and prognosis. Finally, the SR-B1-linked selective HDL-cholesteryl ester uptake pathway is now being evaluated as a gateway for the delivery of therapeutic and diagnostic agents. In this review, we focus on the regulation and functional significance of SR-B1 in mediating cholesterol movement into and out of cells.

Hepatitis C Virus-Genotype 3: Update on Current and Emergent Therapeutic Interventions

PURPOSE OF REVIEW

Direct-acting antiviral agents (DAAs) have markedly improved the prognosis of hepatitis C virus (HCV)-genotype 3 (GT3), a highly prevalent infection worldwide. However, in patients with hepatic fibrosis, cirrhosis, or hepatocellular carcinoma (HCC), GT3 infection presents a treatment challenge compared with other genotypes. The dependence of the HCV life cycle on host lipid metabolism suggests the possible utility of targeting host cellular factors for combination anti-HCV therapy. We discuss current and emergent DAA regimens for HCV-GT3 treatment. We then summarize recent research findings on the reliance of HCV entry, replication, and virion assembly on host lipid metabolism.

RECENT FINDINGS

Current HCV treatment guidelines recommend the use of daclatasvir plus sofosbuvir (DCV/SOF) or sofosbuvir plus velpatasvir (SOF/VEL) for the management of GT3 based upon clinical efficacy [≥88% overall sustained virological response (SVR)] and tolerability. Potential future DAA options, such as SOF/VEL co-formulated with GS-9857, also look promising in treating cirrhotic GT3 patients. However, HCV resistance to DAAs will likely continue to impact the therapeutic efficacy of interferon-free treatment regimens. Disruption of HCV entry by targeting required host cellular receptors shows potential in minimizing HCV resistance and broadening therapeutic options for certain subpopulations of GT3 patients. The use of cholesterol biosynthesis and transport inhibitors may also improve health outcomes for GT3 patients when used synergistically with DAAs. Due to the morbidity and mortality associated with HCV-GT3 infection compared to other genotypes, efforts should be made to address current limitations in the therapeutic prevention and management of HCV-GT3 infection.

Anti-hepatitis C virus strategy targeting host entry factor claudin-1

Chronic hepatitis C virus (HCV) infection is a major threat to global public health, because it is significantly correlated with the development of severe liver diseases including cirrhosis and hepatocellular carcinomas. Host molecules as well as viral factors are promising targets for anti-HCV preventive and therapeutic strategies. Multiple host factors such as CD81, SRBI, claudin-1, and occludin are involved in HCV entry into hepatocytes. In this paper, I first introduce our anti-HCV strategy targeting for host tight junction protein claudin-1. And this review also summarizes developments of other entry inhibitors to prevent initiation of HCV infection and spread. Entry inhibitors might be useful in blocking primary infections, such those as after liver transplantation, and in combination therapies with other anti-HCV agents such as direct-acting antivirals.

Targeting a host-cell entry factor barricades antiviral-resistant HCV variants from on-therapy breakthrough in human-liver mice

OBJECTIVE

Direct-acting antivirals (DAAs) inhibit hepatitis C virus (HCV) infection by targeting viral proteins that play essential roles in the replication process. However, selection of resistance-associated variants (RAVs) during DAA therapy has been a cause of therapeutic failure. In this study, we wished to address whether such RAVs could be controlled by the co-administration of host-targeting entry inhibitors that prevent intrahepatic viral spread.

DESIGN

We investigated the effect of adding an entry inhibitor (the anti-scavenger receptor class B type I mAb1671) to a DAA monotherapy (the protease inhibitor ciluprevir) in human-liver mice chronically infected with HCV of genotype 1b. Clinically relevant non-laboratory strains were used to achieve viraemia consisting of a cloud of related viral variants (quasispecies) and the emergence of RAVs was monitored at high resolution using next-generation sequencing.

RESULTS

HCV-infected human-liver mice receiving DAA monotherapy rapidly experienced on-therapy viral breakthrough. Deep sequencing of the HCV protease domain confirmed the manifestation of drug-resistant mutants upon viral rebound. In contrast, none of the mice treated with a combination of the DAA and the entry inhibitor experienced on-therapy viral breakthrough, despite detection of RAV emergence in some animals.

CONCLUSIONS

This study provides preclinical in vivo evidence that addition of an entry inhibitor to an anti-HCV DAA regimen restricts the breakthrough of DAA-resistant viruses. Our approach is an excellent strategy to prevent therapeutic failure caused by on-therapy rebound of DAA-RAVs. Inclusion of an entry inhibitor to the newest DAA combination therapies may further increase response rates, especially in difficult-to-treat patient populations.

SR-BI: Linking Cholesterol and Lipoprotein Metabolism with Breast and Prostate Cancer

Studies have demonstrated the significant role of cholesterol and lipoprotein metabolism in the progression of cancer. The SCARB1 gene encodes the scavenger receptor class B type I (SR-BI), which is an 82-kDa glycoprotein with two transmembrane domains separated by a large extracellular loop. SR-BI plays an important role in the regulation of cholesterol exchange between cells and high-density lipoproteins. Accordingly, hepatic SR-BI has been shown to play an essential role in the regulation of the reverse cholesterol transport pathway, which promotes the removal and excretion of excess body cholesterol. In the context of atherosclerosis, SR-BI has been implicated in the regulation of intracellular signaling, lipid accumulation, foam cell formation, and cellular apoptosis. Furthermore, since lipid metabolism is a relevant target for cancer treatment, recent studies have focused on examining the role of SR-BI in this pathology. While signaling pathways have initially been explored in non-tumoral cells, studies with cancer cells have now demonstrated SR-BI's function in tumor progression. In this review, we will discuss the role of SR-BI during tumor development and malignant progression. In addition, we will provide insights into the transcriptional and post-transcriptional regulation of the SCARB1 gene. Overall, studying the role of SR-BI in tumor development and progression should allow us to gain useful information for the development of new therapeutic strategies.

Interferon alpha bioactivity critically depends on Scavenger receptor class B type I function

Scavenger receptor class B type I (SR-B1) binds pathogen-associated molecular patterns participating in the regulation of the inflammatory reaction but there is no information regarding potential interactions between SR-B1 and the interferon system. Herein, we report that SR-B1 ligands strongly regulate the transcriptional response to interferon α (IFNα) and enhance its antiviral and antitumor activity. This effect was mediated by the activation of TLR2 and TLR4 as it was annulled by the addition of anti-TLR2 or anti-TLR4 blocking antibodies. In vivo, we maximized the antitumor activity of IFNα co-expressing in the liver a SR-B1 ligand and IFNα by adeno-associated viruses. This gene therapy strategy eradicated liver metastases from colon cancer with reduced toxicity. On the other hand, genetic and pharmacological inhibition of SR-B1 blocks the clathrin-dependent interferon receptor recycling pathway with a concomitant reduction in IFNα signaling and bioactivity. This effect can be applied to enhance cancer immunotherapy with oncolytic viruses. Indeed, SR-B1 antagonists facilitate replication of oncolytic viruses amplifying their tumoricidal potential. In conclusion, SR-B1 agonists behave as IFNα enhancers while SR-B1 inhibitors dampen IFNα activity. These results demonstrate that SR-B1 is a suitable pharmacology target to enhance cancer immunotherapy based on IFNα and oncolytic viruses.

Restoring Mitochondrial Function: A Small Molecule-mediated Approach to Enhance Glucose Stimulated Insulin Secretion in Cholesterol Accumulated Pancreatic beta cells

Dyslipidemia, particularly the elevated serum cholesterol levels, aggravate the pathophysiology of type 2 diabetes. In the present study we explored the relationship between fasting blood sugar and serum lipid parameters in human volunteers which revealed a significant linear effect of serum cholesterol on fasting blood glucose. Short term feeding of cholesterol enriched diet to rodent model resulted in elevated serum cholesterol levels, cholesterol accumulation in pancreatic islets and hyperinsulinemia with modest increase in plasma glucose level. To explore the mechanism, we treated cultured BRIN-BD11 pancreatic beta cells with soluble cholesterol. Our data shows that cholesterol treatment of cultured pancreatic beta cells enhances total cellular cholesterol. While one hour cholesterol exposure enhances insulin exocytosis, overnight cholesterol accumulation in cultured pancreatic beta cells affects cellular respiration, and inhibits Glucose stimulated insulin secretion. We further report that (E)-4-Chloro-2-(1-(2-(2,4,6-trichlorophenyl) hydrazono) ethyl) phenol (small molecule M1) prevents the cholesterol mediated blunting of cellular respiration and potentiates Glucose stimulated insulin secretion which was abolished in pancreatic beta cells on cholesterol accumulation.

Identification of nonabsorbable inhibitors of the scavenger receptor-BI (SR-BI) for tissue-specific administration

The identification of a low-permeability scavenger receptor BI (SR-BI) inhibitor starting from the ITX-5061 template is described. Structure-activity and structure-permeability relationships were assessed for analogs leading to the identification of compound 8 as a potent and nonabsorbable SR-BI inhibitor.

DJ. Effect of scavenger receptor class B type I antagonist ITX5061 in patients with hepatitis C virus infection undergoing liver transplantation

Hepatitis C virus (HCV) entry inhibitors have been hypothesized to prevent infection of the liver after transplantation. ITX5061 is a scavenger receptor class B type I antagonist that blocks HCV entry and infection in vitro. We assessed the safety and efficacy of ITX5061 to limit HCV infection of the graft. The study included 23 HCV-infected patients undergoing liver transplantation. The first 13 "control" patients did not receive drug. The subsequent 10 patients received 150 mg of ITX5061 immediately before and after transplant and daily for 1 week thereafter. ITX5061 pharmacokinetics and plasma HCV RNA were quantified. Viral genetic diversity was measured by ultradeep pyrosequencing (UDPS). ITX5061 was well tolerated with measurable plasma concentrations during therapy. Although the median HCV RNA reduction was greater in ITX-treated patients at all time points in the first week after transplantation, there was no difference in the overall change in the area over the HCV RNA curve in the 7-day treatment period. However, in genotype (GT) 1-infected patients, treatment was associated with a sustained reduction in HCV RNA levels compared to the control group (area over the HCV RNA curve analysis, P = 0.004). UDPS revealed a complex and evolving pattern of HCV variants infecting the graft during the first week. ITX5061 significantly limited viral evolution where the median divergence between day 0 and day 7 was 3.5% in the control group compared to 0.1% in the treated group. In conclusion, ITX5061 reduces plasma HCV RNA after transplant notably in GT 1-infected patients and slows viral evolution. Following liver transplantation, the likely contribution of extrahepatic reservoirs of HCV necessitates combining entry inhibitors such as ITX5061 with inhibitors of replication in future studies.

Entry inhibitors: New advances in HCV treatment

Hepatitis C virus (HCV) infection affects approximately 3% of the world's population and causes chronic liver diseases, including liver fibrosis, cirrhosis, and hepatocellular carcinoma. Although current antiviral therapy comprising direct-acting antivirals (DAAs) can achieve a quite satisfying sustained virological response (SVR) rate, it is still limited by viral resistance, long treatment duration, combined adverse reactions, and high costs. Moreover, the currently marketed antivirals fail to prevent graft reinfections in HCV patients who receive liver transplantations, probably due to the cell-to-cell transmission of the virus, which is also one of the main reasons behind treatment failure. HCV entry is a highly orchestrated process involving initial attachment and binding, post-binding interactions with host cell factors, internalization, and fusion between the virion and the host cell membrane. Together, these processes provide multiple novel and promising targets for antiviral therapy. Most entry inhibitors target host cell components with high genetic barriers and eliminate viral infection from the very beginning of the viral life cycle. In future, the addition of entry inhibitors to a combination of treatment regimens might optimize and widen the prevention and treatment of HCV infection. This review summarizes the molecular mechanisms and prospects of the current preclinical and clinical development of antiviral agents targeting HCV entry.

Lipoprotein profiles in human heterozygote carriers of a functional mutation P297S in scavenger receptor class B1

The scavenger receptor class B type 1 (SR-B1) is an important HDL receptor involved in cholesterol uptake and efflux, but its physiological role in human lipoprotein metabolism is not fully understood. Heterozygous carriers of the SR-B1(P297S) mutation are characterized by increased HDL cholesterol levels, impaired cholesterol efflux from macrophages and attenuated adrenal function. Here, the composition and function of lipoproteins were studied in SR-B1(P297S) heterozygotes.Lipoproteins from six SR-B1(P297S) carriers and six family controls were investigated. HDL and LDL/VLDL were isolated by ultracentrifugation and proteins were separated by two-dimensional gel electrophoresis and identified by mass spectrometry. HDL antioxidant properties, paraoxonase 1 activities, apoA-I methionine oxidations and HDL cholesterol efflux capacity were assessed.Multivariate modeling separated carriers from controls based on lipoprotein composition. Protein analyses showed a significant enrichment of apoE in LDL/VLDL and of apoL-1 in HDL from heterozygotes compared to controls. The relative distribution of plasma apoE was increased in LDL and in lipid-free form. There were no significant differences in paraoxonase 1 activities, HDL antioxidant properties or HDL cholesterol efflux capacity but heterozygotes showed a significant increase of oxidized methionines in apoA-I.The SR-B1(P297S) mutation affects both HDL and LDL/VLDL protein compositions. The increase of apoE in carriers suggests a compensatory mechanism for attenuated SR-B1 mediated cholesterol uptake by HDL. Increased methionine oxidation may affect HDL function by reducing apoA-I binding to its targets. The results illustrate the complexity of lipoprotein metabolism that has to be taken into account in future therapeutic strategies aiming at targeting SR-B1.

Host-Targeting Agents to Prevent and Cure Hepatitis C Virus Infection

Chronic hepatitis C virus (HCV) infection is a major cause of liver cirrhosis and hepatocellular carcinoma (HCC) which are leading indications of liver transplantation (LT). To date, there is no vaccine to prevent HCV infection and LT is invariably followed by infection of the liver graft. Within the past years, direct-acting antivirals (DAAs) have had a major impact on the management of chronic hepatitis C, which has become a curable disease in the majority of DAA-treated patients. In contrast to DAAs that target viral proteins, host-targeting agents (HTAs) interfere with cellular factors involved in the viral life cycle. By acting through a complementary mechanism of action and by exhibiting a generally higher barrier to resistance, HTAs offer a prospective option to prevent and treat viral resistance. Indeed, given their complementary mechanism of action, HTAs and DAAs can act in a synergistic manner to reduce viral loads. This review summarizes the different classes of HTAs against HCV infection that are in preclinical or clinical development and highlights their potential to prevent HCV infection, e.g., following LT, and to tailor combination treatments to cure chronic HCV infection.

Targeting Viral Entry for Treatment of Hepatitis B and C Virus Infections

Hepatitis B virus (HBV) and hepatitis C virus (HCV) infections remain major health problems worldwide, with 400-500 million chronically infected people worldwide. Chronic infection results in liver cirrhosis and hepatocellular carcinoma, the second leading cause of cancer death. Current treatments for HBV limit viral replication without efficiently curing infection. HCV treatment has markedly progressed with the licensing of direct-acting antivirals (DAAs) for HCV cure, yet limited access for the majority of patients is a major challenge. Preventative and curative treatment strategies, aimed at novel targets, are needed for both viruses. Viral entry represents one such target, although detailed knowledge of the entry mechanisms is a prerequisite. For HBV, the recent discovery of the NTCP cell entry factor enabled the establishment of an HBV cell culture model and showed that cyclosporin A and Myrcludex B are NTCP-targeting entry inhibitors. Advances in the understanding of HCV entry revealed it to be a complex process involving many factors, offering several antiviral targets. These include viral envelope proteins E1 and E2, virion-associated lipoprotein ApoE, and cellular factors CD81, SRBI, EGFR, claudin-1, occludin, and the cholesterol transporter NPC1L1. Small molecules targeting SR-BI, EGFR, and NPC1L1 have entered clinical trials, whereas other viral- and host-targeted small molecules, peptides, and antibodies show promise in preclinical models. This review summarizes the current understanding of HBV and HCV entry and describes novel antiviral targets and compounds in different stages of clinical development. Overall, proof-of-concept studies indicate that entry inhibitors are a promising class of antivirals to prevent and treat HBV and HCV infections.

High-density lipoprotein-based drug discovery for treatment of atherosclerosis

INTRODUCTION

Although there has been great progress achieved by the use of intensive statin therapy, the burden of atherosclerotic cardiovascular disease (CVD) remains high. This has initiated the search for novel high-density lipoprotein (HDL)-based therapeutics. Recent years have witnessed a shift from traditional raising HDL-C levels to enhancing HDL functionality, in which the process of reverse cholesterol transport (RCT) has acquired much attention.

AREAS COVERED

In this review, the authors describe the key factors involved in RCT process for potential drug targets to reduce the CVD risk. Furthermore, the review provides a summary of the effective screening methods that have been developed to target RCT and their applications. This review also introduces some new strategies currently being clinically developed, which have the potential to improve HDL function in the RCT process.

EXPERT OPINION

It is rational that the functionality of HDL is more important than the plasma HDL-C level in the evaluation of pharmacological treatment in atherosclerosis. HDL-based strategies designed to promote macrophage RCT are a major area of current drug discovery and development for atherosclerotic diseases. A better understanding of the functionality of HDL and its relationship with atherosclerosis will expand our knowledge of the role of HDL in lipid metabolism, holding promise for a future successful HDL-based therapy.

Innovative pharmaceutical interventions in cardiovascular disease: Focusing on the contribution of non-HDL-C/LDL-C-lowering versus HDL-C-raising: A systematic review and meta-analysis of relevant preclinical studies and clinical trials

Non-HDL-cholesterol is well recognised as a primary causal risk factor in cardiovascular disease. However, despite consistent epidemiological evidence for an inverse association between HDL-C and coronary heart disease, clinical trials aimed at raising HDL-C (AIM-HIGH, HPS2-THRIVE, dal-OUTCOMES) failed to meet their primary goals. This systematic review and meta-analysis investigated the effects of established and novel treatment strategies, specifically targeting HDL, on inhibition of atherosclerosis in cholesteryl ester transfer protein-expressing animals, and the prevention of clinical events in randomised controlled trials. Linear regression analyses using data from preclinical studies revealed associations for TC and non-HDL-C and lesion area (R(2)=0.258, P=0.045; R(2)=0.760, P<0.001), but not for HDL-C (R(2)=0.030, P=0.556). In clinical trials, non-fatal myocardial infarction risk was significantly less in the treatment group with pooled odd ratios of 0.87 [0.81; 0.94] for all trials and 0.85 [0.78; 0.93] after excluding some trials due to off-target adverse events, whereas all-cause mortality was not affected (OR 1.05 [0.99-1.10]). Meta-regression analyses revealed a trend towards an association between between-group differences in absolute change from baseline in LDL-C and non-fatal myocardial infarction (P=0.066), whereas no correlation was found for HDL-C (P=0.955). We conclude that the protective role of lowering LDL-C and non-HDL-C is well-established. The contribution of raising HDL-C on inhibition of atherosclerosis and the prevention of cardiovascular disease remains undefined and may be dependent on the mode of action of HDL-C-modification. Nonetheless, treatment strategies aimed at improving HDL function and raising apolipoprotein A-I may be worth exploring.

Discovery of bisamide-heterocycles as inhibitors of scavenger receptor BI (SR-BI)-mediated lipid uptake

A new series of potent inhibitors of cellular lipid uptake from HDL particles mediated by scavenger receptor, class B, type I (SR-BI) was identified. The series was identified via a high-throughput screen of the National Institutes of Health Molecular Libraries Small Molecule Repository (NIH MLSMR) that measured the transfer of the fluorescent lipid DiI from HDL particles to CHO cells overexpressing SR-BI. The series is characterized by a linear peptidomimetic scaffold with two adjacent amide groups, as well as an aryl-substituted heterocycle. Analogs of the initial hit were rapidly prepared via Ugi 4-component reaction, and select enantiopure compounds were prepared via a stepwise sequence. Structure-activity relationship (SAR) studies suggest an oxygenated arene is preferred at the western end of the molecule, as well as highly lipophilic substituents on the central and eastern nitrogens. Compound 5e, with (R)-stereochemistry at the central carbon, was designated as probe ML279. Mechanistic studies indicate that ML279 stabilizes the interaction of HDL particles with SR-BI, and its effect is reversible. It shows good potency (IC50=17 nM), is non-toxic, plasma stable, and has improved solubility over our alternative probe ML278.

Benzo-fused lactams from a diversity-oriented synthesis (DOS) library as inhibitors of scavenger receptor BI (SR-BI)-mediated lipid uptake

We report a new series of 8-membered benzo-fused lactams that inhibit cellular lipid uptake from HDL particles mediated by Scavenger Receptor, Class B, Type I (SR-BI). The series was identified via a high-throughput screen of the National Institutes of Health Molecular Libraries Small Molecule Repository (NIH MLSMR), measuring the transfer of the fluorescent lipid DiI from HDL particles to CHO cells overexpressing SR-BI. The series is part of a previously reported diversity-oriented synthesis (DOS) library prepared via a build-couple-pair approach. Detailed structure-activity relationship (SAR) studies were performed with a selection of the original library, as well as additional analogs prepared via solution phase synthesis. These studies demonstrate that the orientation of the substituents on the aliphatic ring have a critical effect on activity. Additionally, a lipophilic group is required at the western end of the molecule, and a northern hydroxyl group and a southern sulfonamide substituent also proved to be optimal. Compound 2p was found to possess a superior combination of potency (av IC50=0.10μM) and solubility (79μM in PBS), and it was designated as probe ML312.

Successful anti-scavenger receptor class B type I (SR-BI) monoclonal antibody therapy in humanized mice after challenge with HCV variants with in vitro resistance to SR-BI-targeting agents

Hepatitis C virus (HCV)-induced endstage liver disease is currently a major indication for liver transplantation. After transplantation the donor liver inevitably becomes infected with the circulating virus. Monoclonal antibodies (mAbs) against the HCV coreceptor scavenger receptor class B type I (SR-BI) inhibit HCV infection of different genotypes, both in cell culture and in humanized mice. Anti-SR-BI mAb therapy is successful even when initiated several days after HCV exposure, supporting its potential applicability to prevent HCV reinfection of liver allografts. However, HCV variants with reduced SR-BI dependency have been described in the literature, which could potentially limit the use of SR-BI targeting therapy. In this study we show, both in a preventative and postexposure setting, that humanized mice infected with HCV variants exhibiting increased in vitro resistance to SR-BI-targeting molecules remain responsive to anti-SR-BI mAb therapy in vivo. A 2-week antibody therapy readily cleared HCV RNA from the circulation of infected humanized mice. We found no evidence supporting increased SR-BI-receptor dependency of viral particles isolated from humanized mice compared to cell culture-produced virus. However, we observed that, unlike wild-type virus, the in vitro infectivity of the resistant variants was inhibited by both human high density lipoprotein (HDL) and very low density lipoprotein (VLDL). The combination of mAb1671 with these lipoproteins further increased the antiviral effect.

CONCLUSION

HCV variants that are less dependent on SR-BI in vitro can still be efficiently blocked by an anti-SR-BI mAb in humanized mice. Since these variants are also more susceptible to neutralization by anti-HCV envelope antibodies, their chance of emerging during anti-SR-BI therapy is severely reduced. Our data indicate that anti-SR-BI receptor therapy could be an effective way to prevent HCV infection in a liver transplant setting.

Role of hypervariable region 1 for the interplay of hepatitis C virus with entry factors and lipoproteins

Hepatitis C virus (HCV) particles associate with lipoproteins and infect cells by using at least four cell entry factors. These factors include scavenger receptor class B type I (SR-BI), CD81, claudin 1 (CLDN1), and occludin (OCLN). Little is known about specific functions of individual host factors during HCV cell entry and viral domains that mediate interactions with these factors. Hypervariable region 1 (HVR1) within viral envelope protein 2 (E2) is involved in the usage of SR-BI and conceals the viral CD81 binding site. Moreover, deletion of this domain alters the density of virions. We compared lipoprotein interaction, surface attachment, receptor usage, and cell entry between wild-type HCV and a viral mutant lacking this domain. Deletion of HVR1 did not affect CD81, CLDN1, and OCLN usage. However, unlike wild-type HCV, HVR1-deleted viruses were not neutralized by antibodies and small molecules targeting SR-BI. Nevertheless, modulation of SR-BI cell surface expression altered the infection efficiencies of both viruses to similar levels. Analysis of affinity-purified virions revealed comparable levels of apolipoprotein E (ApoE) incorporation into viruses with or without HVR1. However, ApoE incorporated into these viruses was differentially recognized by ApoE-specific antibodies. Thus, SR-BI has at least two functions during cell entry. One of them can be neutralized by SR-BI-targeting molecules, and it is critical only for wild-type HCV. The other one is important for both viruses but apparently is not inactivated by the SR-BI binding antibodies and small molecules evaluated here. In addition, HVR1 modulates the conformation and/or epitope exposure of virus particle-associated ApoE.

IMPORTANCE

HCV cell entry is SR-BI dependent irrespective of the presence or absence of HVR1. Moreover, this domain modulates the properties of ApoE on the surface of virus particles. These findings have implications for the development of SR-BI-targeting antivirals. Furthermore, these findings highlight separable functions of SR-BI during HCV cell entry and reveal a novel role of HVR1 for the properties of virus-associated lipoproteins.

Novel concepts in HDL pharmacology

High-density lipoproteins (HDL) are a target for drug development because of their proposed anti-atherogenic properties. In this review, we will briefly discuss the currently established drugs for increasing HDL-C, namely niacin and fibrates, and some of their limitations. Next, we will focus on novel alternative therapies that are currently being developed for raising HDL-C, such as CETP inhibitors. Finally, we will conclude with a review of novel drugs that are being developed for modulating the function of HDL based on HDL mimetics. Gaps in our knowledge and the challenges that will have to be overcome for these new HDL based therapies will also be discussed.

Hepatitis C virus cell-cell transmission and resistance to direct-acting antiviral agents

Hepatitis C virus (HCV) is transmitted between hepatocytes via classical cell entry but also uses direct cell-cell transfer to infect neighboring hepatocytes. Viral cell-cell transmission has been shown to play an important role in viral persistence allowing evasion from neutralizing antibodies. In contrast, the role of HCV cell-cell transmission for antiviral resistance is unknown. Aiming to address this question we investigated the phenotype of HCV strains exhibiting resistance to direct-acting antivirals (DAAs) in state-of-the-art model systems for cell-cell transmission and spread. Using HCV genotype 2 as a model virus, we show that cell-cell transmission is the main route of viral spread of DAA-resistant HCV. Cell-cell transmission of DAA-resistant viruses results in viral persistence and thus hampers viral eradication. We also show that blocking cell-cell transmission using host-targeting entry inhibitors (HTEIs) was highly effective in inhibiting viral dissemination of resistant genotype 2 viruses. Combining HTEIs with DAAs prevented antiviral resistance and led to rapid elimination of the virus in cell culture model. In conclusion, our work provides evidence that cell-cell transmission plays an important role in dissemination and maintenance of resistant variants in cell culture models. Blocking virus cell-cell transmission prevents emergence of drug resistance in persistent viral infection including resistance to HCV DAAs.

In spite of the rapid development of antiviral agents, antiviral resistance remains a challenge for the treatment of viral infections including hepatitis B and C virus (HBV, HCV), human immunodeficiency virus (HIV) and influenza. Virus spreads from infected cells to surrounding uninfected host cells to develop infection through cell-free and cell-cell transmission routes. Understanding the spread of resistant virus is important for the development of novel antiviral strategies to prevent and treat antiviral resistance. Here, we characterize the spread of resistant viruses and its impact for emergence and prevention of resistance using HCV as a model system. Our results show that cell-cell transmission is the main transmission route for antiviral resistant HCV strains and is crucial for the maintenance of infection. Monoclonal antibodies or small molecules targeting HCV entry factors are effective in inhibiting the spread of resistant HCV in cell culture models and thus should be evaluated clinically for prevention and treatment of HCV resistance. Combination of inhibitors targeting viral entry and clinically used direct-acting antivirals (DAAs) prevents antiviral resistance and leads to viral eradication in cell culture models. Collectively, the investigation provides a new strategy for prevention of viral resistance to antiviral agents.

Recent advances in HCV entry

ABSTRACT: 

The elucidation of the mechanisms by which HCV infects hepatocytes and replicates has been paramount for identifying therapeutic targets and developing the highly efficacious antiviral drugs from which we benefit today. The earliest stage of HCV infection is viral entry, a process in which a complex interplay is thought to occur between host molecules (including glycosaminoglycans, low-density lipoprotein receptor, CD81, SR-B1, CLDN1, OCLN, EGF receptor, ephrin type A receptor 2 and transferrin receptor 1) and envelope viral glycoproteins E1 and E2. The wealth of experimental data produced in the field of HCV entry is summarized in a proposed mechanism, updated to include the most recently published data on the topic. Compounds with putative entry-blocking and/or entry-inhibiting activity in vitro and in vivo are also briefly reviewed.

Pharmacological interventions in human HDL metabolism

PURPOSE OF REVIEW

This review focuses on the recent developments in the field of drugs that affect HDL metabolism. Additionally, some general (retrospective) thoughts on fighting cardiovascular disease through modulating circulating lipids are discussed.

RECENT FINDINGS

Recently, the large 'Atherothrombosis Intervention in Metabolic Syndrome with Low HDL/High Triglycerides: Impact on Global Health Outcomes', 'Treatment of HDL to Reduce the Incidence of Vascular Events' and dal-OUTCOMES studies have challenged the idea that raising HDL cholesterol (HDL-c) decreases cardiovascular disease risk. Concerning the failure of these trials, it may, however, be noted that patients with close to normal HDL-c levels were included. It is shown that anacetrapib and evacetrapib massively increase HDL-c, and both compounds are currently tested in phase-III clinical trials. More specific and stronger activators of liver X receptor and peroxisome proliferator-activated receptor (PPAR) are being developed and tested in a preclinical setting. RVX-208 treatment failed to decrease atheroma volume in coronary artery disease patients. Lecithin:cholesterol acyltransferase replacement therapy showed positive results in a patient with lecithin:cholesterol acyltransferase deficiency.

SUMMARY

Inhibition of cholesteryl ester transfer protein, antagomirs against microRNA-33, ApoA-I mimetics and PPARα or PPARα/δ agonists hold on the basis of the current data most promise. However, it will in our opinion be the key that patients with low HDL-c and increased triglyceride should be treated and not those at generally increased risk only. In the poststatin era, personalized medicine, which is inevitably on the horizon, is likely to be helpful for patients who do not reach the goals for LDL cholesterol and HDL-c according to the guidelines. Furthermore, functions of HDL will hopefully be identified as future pharmacological targets.

Opportunities and Risks of Host-targeting Antiviral Strategies for Hepatitis C

Hepatitis C virus (HCV) infects more than 2 % of the world population with highest prevalence in parts of Africa and Asia. Past standard of care using interferon α and ribavirin had adverse effects and showed modest efficacy for some HCV genotypes spurring the development of direct acting antivirals (DAAs). Such DAAs target viral proteins and are thus better tolerated but they suffer from emergence of vial resistance. Furthermore, DAAs are often HCV genotype specific. Novel drug candidates targeting host factors required for HCV propagation, so called host-targeting antivirals (HTAs), promise to overcome both caveats. The genetic barrier to resistance is usually considered to be high for HTAs and all HCV genotypes presumably use the same host factors. Recent data, however, challenge these assumptions, at least for some HTAs. Here, we highlight the most important host-targeting strategies against hepatitis C and critically discuss their opportunities and risks.

Host-targeting agents in the treatment of hepatitis C: a beginning and an end?

The development of two distinct classes of hepatitis C antiviral agents, direct-acting antivirals (DAAs) and host-targeting antivirals (HTAs), have distinctly impacted the hepatitis C virus (HCV) field by generating higher sustained virological response (SVR) rates within infected patients, via reductions in both adverse side effects and duration of treatment when compared to the old standard of care. Today DAAs are actively incorporated into the standard of care and continue to receive the most advanced clinical trial analysis. With a multitude of innovative and potent second-generation DAA compounds currently being tested in clinical trials, it is clear that the future of DAAs looks very bright. In comparison to the other class of compounds, HTAs have been slightly less impactful, despite the fact that primary treatment regimens for HCV began with the use of an HTA - interferon alpha (IFNα). The compound was advantageous in that it provided a broad-reaching antiviral response; however deleterious side effects and viral/patient resistance has since made the compound outdated. HTA research has since moved onward to target a number of cellular host factors that are required for HCV viral entry and replication such as scavenger receptor-BI (SR-BI), 3-hydroxy-3-methyl-glutaryl-CoA reductase (HMGCoA reductase), cyclophilin A (CypA), fatty acid synthase (FASN) and miRNA-122. The rationale behind pursuing these HTAs is based upon the extremely low mutational rate that occurs within eukaryotic cells, thereby creating a high genetic barrier to drug resistance for anti-HCV compounds, as well as pan-genotypic coverage to all HCV genotypes and serotypes. As the end appears near for HCV, it becomes important to ask if the development of novel HTAs should also be analyzed in combination with other DAAs, in order to address potential hard-to-treat HCV patient populations. Since the treatment regimens for HCV began with the use of a global HTA, could one end the field as well?

Safety and antiviral activity of the HCV entry inhibitor ITX5061 in treatment-naive HCV-infected adults: a randomized, double-blind, phase 1b study

BACKGROUND

Hepatitis C virus (HCV) entry involves scavenger receptor B1 (SRB1). In vitro, SRB1 inhibition by ITX5061 impedes HCV replication.

METHODS

Multicenter study to assess safety/activity of ITX5061 in previously untreated, noncirrhotic, HCV genotype 1 infected adults. Design included sequential cohorts of 10 subjects with ITX5061 (n = 8) or placebo (n = 2) to escalate duration (3 to 14 to 28 days) or deescalate dose (150 to 75 to 25 mg) based on predefined criteria for safety and activity (≥ 4 of 8 subjects with HCV RNA decline ≥ 1 log10 IU/mL).

RESULTS

Thirty subjects enrolled in 3 cohorts: ITX5061 150 mg/day by mouth for 3 (A150), 14 (B150), and 28 (C150) days. Six subjects had grade ≥ 3 adverse events (one in placebo); none were treatment related. One of the 7 C150 subjects (14.3%, 95% confidence interval [CI], .7%-55.4%) had ≥ 1 log10 IU/mL decline in HCV RNA (1.49 log10 IU/mL), whereas none of the 6 placebo, 8 A150 or 8 B150 subjects showed such decline.

CONCLUSIONS

Oral ITX5061 150 mg/day for up to 28 days was safe and well tolerated. In the 28-day cohort, 1 of 7 subjects showed antiviral activity; however, predefined criteria for antiviral activity were not met at the doses and durations studied.

Update on the Development of Anti-Viral Agents Against Hepatitis C

Hepatitis C virus (HCV) infects nearly 170 million people worldwide and causes chronic hepatitis, cirrhosis, and hepatocellular carcinoma. The search for a drug regimen that maximizes efficacy and minimizes side effects is quickly evolving. This review will discuss a wide range of drug targets currently in all phases of development for the treatment of HCV. Direct data from agents in phase III/IV clinical trials will be presented, along with reported side-effect profiles. The mechanism of action of all treatments and resistance issues are highlighted. Special attention is given to available trial data supporting interferon-free treatment regimens. HCV has become an increasingly important public health concern, and it is important for physicians to stay up to date on the rapidly growing novel therapeutic options.

Serum IF1 concentration is independently associated to HDL levels and to coronary heart disease: the GENES study

HDL is strongly inversely related to cardiovascular risk. Hepatic HDL uptake is controlled by ecto-F1-ATPase activity, and potentially inhibited by mitochondrial inhibitor factor 1 (IF1). We recently found that IF1 is present in serum and correlates with HDL-cholesterol (HDL-C). Here, we have evaluated the relationship between circulating IF1 and plasma lipoproteins, and we determined whether IF1 concentration is associated with the risk of coronary heart disease (CHD). Serum IF1 was measured in 648 coronary patients ages 45-74 and in 669 matched male controls, in the context of a cross-sectional study on CHD. Cardiovascular risk factors were documented for each participant, including life-style habits and biological and clinical markers. In controls, multivariate analysis demonstrated that IF1 was independently positively associated with HDL-C and apoA-I (r = 0.27 and 0.28, respectively, P < 0.001) and negatively with triglycerides (r = -0.23, P < 0.001). Mean IF1 concentration was lower in CHD patients than in controls (0.43 mg/l and 0.53 mg/l, respectively, P < 0.001). In multivariate analyses, following adjustments on cardiovascular risk factors or markers, IF1 was negatively related to CHD (P < 0.001). This relationship was maintained after adjustment for HDL-C or apoA-I. This study identifies IF1 as a new determinant of HDL-C that is inversely associated with CHD.

A coding variant in SR-BI (I179N) significantly increases atherosclerosis in mice

Human coding variants in scavenger receptor class B member 1 (SR-BI; gene name SCARB1) have recently been identified as being associated with plasma levels of HDL cholesterol. However, a link between coding variants and atherosclerosis has not yet been established. In this study we set out to examine the impact of a SR-BI coding variant in vivo. A mouse model with a coding variant in SR-BI (I179N), identified through a mutagenesis screen, was crossed with Ldlr (-/-) mice, and these mice were maintained on a Western-type diet to promote atherosclerosis. Mice showed 56 and 125 % increased atherosclerosis in female and male Ldlr (-/-) Scarb1 (I179N) mice, respectively, when compared to gender-matched Ldlr (-/-) control mice. As expected, HDL cholesteryl ester uptake was impaired in Ldlr (-/-) Scarb1 (I179N) mice compared to Ldlr (-/-) control mice, with a net effect of increased small and very small LDL cholesterol in Ldlr (-/-) Scarb1 (I179N) mice being the most probable cause of the observed increased atherosclerosis. Our data show that non-null coding variants in SR-BI can have a large significant impact on atherosclerosis, even if plasma lipid levels are not dramatically affected, and that human mutations in other candidate lipid genes could significantly impact atherosclerosis.

HDL, Atherosclerosis, and Emerging Therapies

This review aims to provide an overview on the properties of high-density lipoproteins (HDLs) and their cardioprotective effects. Emergent HDL therapies will be presented in the context of the current understanding of HDL function, metabolism, and protective antiatherosclerotic properties. The epidemiological association between levels of HDL-C or its major apolipoprotein (apoA-I) is strong, graded, and coherent across populations. HDL particles mediate cellular cholesterol efflux, have antioxidant properties, and modulate vascular inflammation and vasomotor function and thrombosis. A link of causality has been cast into doubt with Mendelian randomization data suggesting that genes causing HDL-C deficiency are not associated with increased cardiovascular risk, nor are genes associated with increased HDL-C, with a protective effect. Despite encouraging data from small studies, drugs that increase HDL-C levels have not shown an effect on major cardiovascular end-points in large-scale clinical trials. It is likely that the cholesterol mass within HDL particles is a poor biomarker of therapeutic efficacy. In the present review, we will focus on novel therapeutic avenues and potential biomarkers of HDL function. A better understanding of HDL antiatherogenic functions including reverse cholesterol transport, vascular protective and antioxidation effects will allow novel insight on novel, emergent therapies for cardiovascular prevention.

Hepatitis C virus, cholesterol and lipoproteins--impact for the viral life cycle and pathogenesis of liver disease

Hepatitis C virus (HCV) is a leading cause of chronic liver disease, including chronic hepatitis, fibrosis, cirrhosis, and hepatocellular carcinoma. Hepatitis C infection associates with lipid and lipoprotein metabolism disorders such as hepatic steatosis, hypobetalipoproteinemia, and hypocholesterolemia. Furthermore, virus production is dependent on hepatic very-low-density lipoprotein (VLDL) assembly, and circulating virions are physically associated with lipoproteins in complexes termed lipoviral particles. Evidence has indicated several functional roles for the formation of these complexes, including co-opting of lipoprotein receptors for attachment and entry, concealing epitopes to facilitate immune escape, and hijacking host factors for HCV maturation and secretion. Here, we review the evidence surrounding pathogenesis of the hepatitis C infection regarding lipoprotein engagement, cholesterol and triglyceride regulation, and the molecular mechanisms underlying these effects.

New targets for treatment against HCV infection

Owing to the tremendous effort from both academia and industry, drug development for hepatitis C virus (HCV) infection has been flourishing, with a range of pipeline compounds at various stages of development. Although combination of the recently launched serine protease inhibitors will further improve the response rate of current interferon-based therapy, some intrinsic limitations of these compounds and the tendency of resistance development by the virus, urge the development of alternative or additional therapeutic strategies. In this article we provide an overview of different host and viral factors which have emerged as new potential targets for therapeutic intervention using state-of-the-art technologies.

Evaluation of ITX 5061, a scavenger receptor B1 antagonist: resistance selection and activity in combination with other hepatitis C virus antivirals

ITX 5061 is a scavenger receptor B1 antagonist that has entered phase 1 clinical trials in hepatitis C virus (HCV)-infected humans. We evaluated ITX 5061 in combination with interferon-α, ribavirin, and HCV protease and polymerase inhibitors in a genotype 2a infectious virus system. ITX 5061 is a potent inhibitor of HCV replication and is additive to synergistic with interferon-α, ribavirin, BILN2061, VX950, VX1, and 2'-C-methyladenosine. Resistance selection experiments were performed using a Jc1-FEO virus co-culture system and intermittent ITX 5061 exposure under neomycin selection. We identified a mutant virus with a substitution of aspartic acid for asparagine at the highly conserved position 415 in E2 (N415D). Introduction of this mutation into wild-type virus conferred high-level resistance to ITX 5061. There was no cross-resistance between ITX 5061 and HCV protease inhibitors or interferon-α. These results suggest that ITX 5061 is a promising compound for study in combination with other HCV inhibitors.

Emerging therapeutic strategies to enhance HDL function

Epidemiologic studies indicate a strong inverse correlation between plasma levels of high-density lipoproteins (HDL) and cardiovascular disease (CVD). The most relevant cardioprotective mechanism mediated by HDL is thought to be reverse cholesterol transport (RCT). New insights in HDL biology and RCT have allowed the development of promising agents aimed to increase HDL function and promote atherosclerosis regression. In this regard, apo-AI analogs and CETP inhibitors dalcetrapib and anacetrapib have aroused a great interest and opened new expectations in the treatment of CVD.

Exoplasmic cysteine Cys384 of the HDL receptor SR-BI is critical for its sensitivity to a small-molecule inhibitor and normal lipid transport activity

The HDL receptor, scavenger receptor, class B, type I (SR-BI), is a homooligomeric cell surface glycoprotein that controls HDL structure and metabolism by mediating the cellular selective uptake of lipids, mainly cholesteryl esters, from HDL. The mechanism underlying SR-BI-mediated lipid transfer, which differs from classic receptor-mediated endocytosis, involves a two-step process (binding followed by lipid transport) that is poorly understood. Our previous structure/activity analysis of the small-molecule inhibitor blocker of lipid transport 1 (BLT-1), which potently (IC(50) ∼ 50 nM) blocks SR-BI-mediated lipid transport, established that the sulfur in BLT-1's thiosemicarbazone moiety was essential for activity. Here we show that BLT-1 is an irreversible inhibitor of SR-BI, raising the possibility that cysteine(s) in SR-BI interact with BLT-1. Mass spectrometric analysis of purified SR-BI showed two of its six exoplasmic cysteines have free thiol groups (Cys251 and Cys384). Converting Cys384 (but not Cys251) to serine resulted in complete BLT-1 insensitivity, establishing that the unique molecular target of BLT-1 inhibition of cellular SR-BI dependent lipid transport is SR-BI itself. The C384S substitution reduced the receptor's intrinsic lipid uptake activity by approximately 60% without dramatically altering its surface expression, homooligomerization, or HDL binding. Thus, a small-molecule screening approach identified a key residue in SR-BI involved in lipid transport, providing a powerful springboard into the analyses of the structure and mechanism of SR-BI, and highlighting the power of this approach for such analyses.

Scavenger receptor class B type I and the hypervariable region-1 of hepatitis C virus in cell entry and neutralisation

Hepatitis C virus (HCV) infection is a leading cause of chronic liver disease worldwide and represents a major public health problem. Viral attachment and entry - the first encounter of the virus with the host cell - are major targets of neutralising immune responses. Thus, a detailed understanding of the HCV entry process offers interesting opportunities for the development of novel therapeutic strategies. Different cellular or soluble host factors mediate HCV entry, and considerable progress has been made in recent years to decipher how they induce HCV attachment, internalisation and membrane fusion. Among these factors, the scavenger receptor class B type I (SR-BI/SCARB1) is essential for HCV replication in vitro, through its interaction with the HCV E1E2 surface glycoproteins and, more particularly, the HVR1 segment located in the E2 protein. SR-BI is an interesting receptor because HCV, whose replication cycle intersects with lipoprotein metabolism, seems to exploit some aspects of its physiological functions, such as cholesterol transfer from high-density lipoprotein (HDL), during cell entry. SR-BI is also involved in neutralisation attenuation and therefore could be an important target for therapeutic intervention. Recent results suggest that it should be possible to identify inhibitors of the interaction of HCV with SR-BI that do not impair its important physiological properties, as discussed in this review.

Scavenger receptor class B, type I: a promising immunotherapy target

Scavenger receptor class B, type I (SR-BI) is a crucial molecule in lipid metabolism, since the interaction of high-density lipoproteins (HDLs) with SR-BI is involved in reverse cholesterol transport and cholesterol efflux. Recent findings also underscore a critical role of SR-BI in antimicrobial and immune responses. SR-BI is not only highly expressed in liver and steroidogenic glands, but also in endothelial cells, macrophages and dendritic cells. SR-BI mainly mediates anti-inflammatory responses, which may be altered by dysfunctional HDLs produced in several diseases. Moreover, SR-BI has been involved in the capture and cross-presentation of antigens from viruses, bacteria and parasites. It thus works as a pattern-recognition receptor that interacts with both damage-associated molecular patterns and pathogen-associated molecular patterns. These new findings in the microbiology and immunology fields present SR-BI as an unexplored therapeutic target that warrants further basic and applied research.