An in vivo duck hepatitis B virus model recapitulates key aspects of nucleic acid polymer treatment outcomes in chronic hepatitis B patients

Nucleic acid polymers (NAPs) are an attractive treatment modality for chronic hepatitis B (CHB), with REP2139 and REP2165 having shown efficacy in CHB patients. A subset of patients achieve functional cure, whereas the others exhibit a moderate response or are non-responders. NAP efficacy has been difficult to recapitulate in animal models, with the duck hepatitis B virus (DHBV) model showing some promise but remaining underexplored for NAP efficacy testing. Here we report on an optimized in vivo DHBV duck model and explore several characteristics of NAP treatment. REP2139 was efficacious in reducing DHBV DNA and DHBsAg levels in approximately half of the treated ducks, whether administered intraperitoneally or subcutaneously. Intrahepatic or serum NAP concentrations did not correlate with efficacy, nor did the appearance of anti-DHBsAg antibodies. Furthermore, NAP efficacy was only observed in experimentally infected ducks, not in endogenously infected ducks (vertical transmission). REP2139 add-on to entecavir treatment induced a deeper and more sustained virological response compared to entecavir monotherapy. Destabilized REP2165 showed a different activity profile with a more homogenous antiviral response followed by a faster rebound. In conclusion, subcutaneous administration of NAPs in the DHBV duck model provides a useful tool for in vivo evaluation of NAPs. It recapitulates many aspects of this class of compound's efficacy in CHB patients, most notably the clear division between responders and non-responders.

Tumor Regression upon Intratumoral and Subcutaneous Dosing of the STING Agonist ALG-031048 in Mouse Efficacy Models

Stimulator of interferon genes (STING) agonists have shown potent anti-tumor efficacy in various mouse tumor models and have the potential to overcome resistance to immune checkpoint inhibitors (ICI) by linking the innate and acquired immune systems. First-generation STING agonists are administered intratumorally; however, a systemic delivery route would greatly expand the clinical use of STING agonists. Biochemical and cell-based experiments, as well as syngeneic mouse efficacy models, were used to demonstrate the anti-tumoral activity of ALG-031048, a novel STING agonist. In vitro, ALG-031048 is highly stable in plasma and liver microsomes and is resistant to degradation via phosphodiesterases. The high stability in biological matrices translated to good cellular potency in a HEK 293 STING R232 reporter assay, efficient activation and maturation of primary human dendritic cells and monocytes, as well as long-lasting, antigen-specific anti-tumor activity in up to 90% of animals in the CT26 mouse colon carcinoma model. Significant reductions in tumor growth were observed in two syngeneic mouse tumor models following subcutaneous administration. Combinations of ALG-031048 and ICIs further enhanced the in vivo anti-tumor activity. This initial demonstration of anti-tumor activity after systemic administration of ALG-031048 warrants further investigation, while the combination of systemically administered ALG-031048 with ICIs offers an attractive approach to overcome key limitations of ICIs in the clinic.

Novel non-HAP class A HBV capsid assembly modulators have distinct in vitro and in vivo profiles

IMPORTANCE

Chronic hepatitis B is the most important cause of liver cancer worldwide and affects more than 290 million people. Current treatments are mostly suppressive and rarely lead to a cure. Therefore, there is a need for novel and curative drugs that target the host or the causative agent, hepatitis B virus itself. Capsid assembly modulators are an interesting class of antiviral molecules that may one day become part of curative treatment regimens for chronic hepatitis B. Here we explore the characteristics of a particularly interesting subclass of capsid assembly modulators. These so-called non-HAP CAM-As have intriguing properties in cell culture but also clear virus-infected cells from the mouse liver in a gradual and sustained way. We believe they represent a considerable improvement over previously reported molecules and may one day be part of curative treatment combinations for chronic hepatitis B.

Class A capsid assembly modulator RG7907 clears HBV-infected hepatocytes through core-dependent hepatocyte death and proliferation

BACKGROUND AND AIMS

Effective therapies leading to a functional cure for chronic hepatitis B are still lacking. Class A capsid assembly modulators (CAM-As) are an attractive modality to address this unmet medical need. CAM-As induce aggregation of the HBV core protein (HBc) and lead to sustained HBsAg reductions in a chronic hepatitis B mouse model. Here, we investigate the underlying mechanism of action for CAM-A compound RG7907.

APPROACH AND RESULTS

RG7907 induced extensive HBc aggregation in vitro , in hepatoma cells, and in primary hepatocytes. In the adeno-associated virus (AAV)-HBV mouse model, the RG7907 treatment led to a pronounced reduction in serum HBsAg and HBeAg, concomitant with clearance of HBsAg, HBc, and AAV-HBV episome from the liver. Transient increases in alanine transaminase, hepatocyte apoptosis, and proliferation markers were observed. These processes were confirmed by RNA sequencing, which also uncovered a role for interferon alpha and gamma signaling, including the interferon-stimulated gene 15 (ISG15) pathway. Finally, the in vitro observation of CAM-A-induced HBc-dependent cell death through apoptosis established the link of HBc aggregation to in vivo loss of infected hepatocytes.

CONCLUSIONS

Our study unravels a previously unknown mechanism of action for CAM-As such as RG7907 in which HBc aggregation induces cell death, resulting in hepatocyte proliferation and loss of covalently closed circular DNA or its equivalent, possibly assisted by an induced innate immune response. This represents a promising approach to attain a functional cure for chronic hepatitis B.

The Substitutions L50F, E166A, and L167F in SARS-CoV-2 3CLpro Are Selected by a Protease Inhibitor In Vitro and Confer Resistance To Nirmatrelvir

The SARS-CoV-2 main protease (3CLpro) has an indispensable role in the viral life cycle and is a therapeutic target for the treatment of COVID-19. The potential of 3CLpro-inhibitors to select for drug-resistant variants needs to be established. Therefore, SARS-CoV-2 was passaged in vitro in the presence of increasing concentrations of ALG-097161, a probe compound designed in the context of a 3CLpro drug discovery program. We identified a combination of amino acid substitutions in 3CLpro (L50F E166A L167F) that is associated with a >20× increase in 50% effective concentration (EC₅₀) values for ALG-097161, nirmatrelvir (PF-07321332), PF-00835231, and ensitrelvir. While two of the single substitutions (E166A and L167F) provide low-level resistance to the inhibitors in a biochemical assay, the triple mutant results in the highest levels of resistance (6× to 72×). All substitutions are associated with a significant loss of enzymatic 3CLpro activity, suggesting a reduction in viral fitness. Structural biology analysis indicates that the different substitutions reduce the number of inhibitor/enzyme interactions while the binding of the substrate is maintained. These observations will be important for the interpretation of resistance development to 3CLpro inhibitors in the clinical setting. IMPORTANCE Paxlovid is the first oral antiviral approved for treatment of SARS-CoV-2 infection. Antiviral treatments are often associated with the development of drug-resistant viruses. In order to guide the use of novel antivirals, it is essential to understand the risk of resistance development and to characterize the associated changes in the viral genes and proteins. In this work, we describe for the first time a pathway that allows SARS-CoV-2 to develop resistance against Paxlovid in vitro. The characteristics of in vitro antiviral resistance development may be predictive for the clinical situation. Therefore, our work will be important for the management of COVID-19 with Paxlovid and next-generation SARS-CoV-2 3CLpro inhibitors.

ALG-097111, a potent and selective SARS-CoV-2 3-chymotrypsin-like cysteine protease inhibitor exhibits in vivo efficacy in a Syrian Hamster model

There is an urgent need for antivirals targeting the SARS-CoV-2 virus to fight the current COVID-19 pandemic. The SARS-CoV-2 main protease (3CLpro) represents a promising target for antiviral therapy. The lack of selectivity for some of the reported 3CLpro inhibitors, specifically versus cathepsin L, raises potential safety and efficacy concerns. ALG-097111 potently inhibited SARS-CoV-2 3CLpro (IC₅₀ = 7 nM) without affecting the activity of human cathepsin L (IC₅₀ > 10 μM). When ALG-097111 was dosed in hamsters challenged with SARS-CoV-2, a robust and significant 3.5 log₁₀ (RNA copies/mg) reduction of the viral RNA copies and 3.7 log₁₀ (TCID₅₀/mg) reduction in the infectious virus titers in the lungs was observed. These results provide the first in vivo validation for the SARS-CoV-2 3CLpro as a promising therapeutic target for selective small molecule inhibitors.

Synthesis and Anti-HCV Activity of Sugar-Modified Guanosine Analogues: Discovery of as an HCV NS5B Polymerase Inhibitor for the Treatment of Chronic Hepatitis C

Chronic hepatitis C (CHC) is a major liver disease caused by the hepatitis C virus. The current standard of care for CHC can achieve cure rates above 95%; however, the drugs in current use are administered for a period of 8-16 weeks. A combination of safe and effective drugs with a shorter treatment period is highly desirable. We report synthesis and biological evaluation of a series of 2',3'- and 2',4'-substituted guanosine nucleotide analogues. Their triphosphates exhibited potent inhibition of the HCV NS5B polymerase with IC₅₀ as low as 0.13 μM. In the HCV replicon assay, the phosphoramidate prodrugs of these analogues demonstrated excellent activity with EC₅₀ values as low as 5 nM. A lead compound AL-611 showed high levels of the nucleoside 5'-triphosphate in vitro in primary human hepatocytes and in vivo in dog liver following oral administration.

Abstract 4520: Preclinical characterization of ALG-031048, a novel STING agonist with potent anti-tumor activity in mice

Introduction: The STING (STimulator of INterferon Genes) protein has been identified as an attractive target for cancer immunotherapy due to its central role in inducing T-cell mediated tumor control. Here we describe the preclinical characteristics of the novel STING agonist, ALG-031048, that demonstrates potent anti-tumoral activity in in vivo mouse models.

Methods: Binding to STING was determined using differential scanning fluorimetry (DSF). Cellular activation and cytokine release were assessed using HEK 293T reporter cell lines as well as THP-1 and Raw264.7 cells. In vitro stability was measured in the presence of snake venom phosphodiesterase (SVPD). In vivo anti-tumoral activity was tested in the syngeneic CT26 and B16F10 mouse model.

Results: ALG-031048 demonstrated potent binding to the STING R232 protein in the DSF assay with a mean Kd of 3.12 ± 0.12 μM and a thermal shift of 12.8 °C, similar to the natural ligand 2'3'cGAMP (Kd of 2.75 ± 0.78 μM, shift of 16.7°C) or the clinical stage STING agonist, ADU-S100 (Kd of 4.61 ± 0.42 μM, shift of 10.7°C). In the HEK 293T R232 reporter assay, ALG-031048 was more potent than ADU-S100 with a mean EC50 of 55.9 ± 24.1 and 30.3 ± 17.1 nM for the IFNβ and IRF reporter, respectively, compared to ADU-S100 with EC50 values of 233 ± 179 and 88.7 ± 35.6 nM. Cellular activation was confirmed in THP-1 and Raw264.7 cells where ALG-031048 induced the secretion of IFNβ and CXCL-10. ALG-031048 was highly stable and exhibited no degradation for up to 24 hours in the presence of SVPD while ADU-S100 and 2'3'cGAMP were quickly degraded with less than 10% remaining after 24 hours. In vivo, 3 intra-tumoral (IT) doses of 100 μg ALG-031048 q3d caused complete tumor regression in 90% of animals in the CT26 mouse colon carcinoma model, while treatment with 25 μg ALG-031048 IT 3xq3d resulted in survival of 60 % of animals. In contrast, only 10 and 44% of mice showed complete tumor regression when treated IT 3xq3d with 25 or 100 μg ADU-S100, respectively. To study whether induction of a protective immune response was associated with STING agonist treatment, surviving animals were re-challenged with a second inoculation of CT26 cells on the contra-lateral side. All naïve animals formed tumors within 23-30 days. In contrast, 5 out of 5 and 8 out of 9 mice pre-treated with 25 or 100 μg ALG-031048, respectively, did not exhibit any significant tumor growth over 40 days, while 3 out of 4 animals pretreated with 100 μg ADU-S100 showed complete tumor suppression. Initial results using the B16F10 mouse melanoma model confirmed the potent anti-tumoral activity of ALG-031048 observed in the CT26 model.

Summary: ALG-031048 is a novel STING agonist combining high stability and excellent in vitro potency. In preclinical models, ALG-031048 demonstrated potent and long-lasting tumor suppression. ALG-031048 is advancing in toxicology studies for further profiling as a clinical candidate.

Citation Format: Andreas Jekle, Santosh Thatikonda, Sarah Stevens, Caroline Williams, April Kinkade, Suping Ren, Ruchika Jaisinghani, Qingling Zhang, Dinah Misner, Antitsa Stoycheva, Jerome Deval, Sucheta Mukherjee, Francois Gonzalvez, Sushmita Chanda, David B. Smith, Julian A. Symons, Lawrence M. Blatt, Leonid Beigelman. Preclinical characterization of ALG-031048, a novel STING agonist with potent anti-tumor activity in mice [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 4520.

Synthesis and Anti-HCV Activities of 4'-Fluoro-2'-Substituted Uridine Triphosphates and Nucleotide Prodrugs: Discovery of 4'-Fluoro-2'- C-methyluridine 5'-Phosphoramidate Prodrug (AL-335) for the Treatment of Hepatitis C Infection

We report the synthesis and biological evaluation of a series of 4'-fluoro-2'- C-substituted uridines. Triphosphates of the uridine analogues exhibited a potent inhibition of hepatitis C virus (HCV) NS5B polymerase with IC₅₀ values as low as 27 nM. In an HCV subgenomic replicon assay, the phosphoramidate prodrugs of these uridine analogues demonstrated a very potent activity with EC₅₀ values as low as 20 nM. A lead compound AL-335 (53) demonstrated high levels of the nucleoside triphosphate in vitro in primary human hepatocytes and Huh-7 cells as well as in dog liver following a single oral dose. Compound 53 was selected for the clinical development where it showed promising results in phase 1 and 2 trials.

Broad-spectrum virucidal activity of (NVC-422) N,N-dichloro-2,2-dimethyltaurine against viral ocular pathogens in vitro

PURPOSE

Viral conjunctivitis is a highly contagious infection often causing major epidemics. A safe broad-spectrum antiviral agent is needed to treat this unmet medical need. The purpose of this study is to demonstrate that in vitro NVC-422 is a safe, broad-spectrum topical virucidal agent with activity against ophthalmic viral pathogens.

METHODS

The virucidal activity of NVC-422 against several serotypes of human adenovirus (HAdV), coxsackievirus A24, enterovirus 70, and herpes simplex-virus-1 (HSV-1) was tested in standard in vitro titer reduction assays with or without tears. An in vitro irritancy score for NVC-422 was determined using the MatTek EpiOcular tissue system.

RESULTS

NVC-422 reduced the viral titer of HAdV-5, HAdV-8, HAdV-19, HAdV-37, and HSV-1 by at least 4 logs after 1 hour incubation at 250 μM. Incubation of coxsackievirus A24 and enterovirus 70 with 2.5 mM NVC-422 for 1 hour reduced the viral titer by 4 logs and 4.5 logs, respectively. The virucidal activity of NVC-422 is maintained in the presence of 10% synthetic tears. In the EpiOcular corneal tissue model, NVC-422 was nonirritating at concentrations up to 41 mM.

CONCLUSIONS

NVC-422 has potent, rapid in vitro virucidal activity against major causes of conjunctivitis. Its broad-spectrum virucidal activity combined with favorable safety profile validates NVC-422 as a potential new therapeutic agent against viral conjunctivitis.

N-chlorotaurine and its analogues N,N-dichloro-2,2-dimethyltaurine and N-monochloro-2,2-dimethyltaurine are safe and effective bactericidal agents in ex vivo corneal infection models

PURPOSE

N-chlorotaurine (NCT) and its analogues N-monochloro-2,2-dimethyltaurine (NVC-612) and N-dichloro-2,2-dimethyltaurine (NVC-422) are new anti-infectives for topical treatment for conjunctivitis. The aim of this study was to show that these compounds are safe in an EpiOcular model and effective in corneas infected ex vivo.

METHODS

Corneal buttons were excised from porcine eyes. In 183 of the 229 corneas, erosion and artificial superficial stromal incision were induced. They were bathed in suspensions of Pseudomonas aeruginosa or Staphylococcus aureus for 24 hr at 37°C and incubated in solutions of the test substances at 37°C and pH 7.1. Subsequently, they were subjected to histology (n = 20) or homogenized followed by quantitative bacterial cultures (n = 209). Ocular irritation was tested using the EpiOcular™ tissue system (MatTek Corporation).

RESULTS

Bacterial accumulations were detected histologically both on the corneal surface and also in the anterior third of the stroma of incised corneal buttons. All three test compounds at a concentration of 55 mm (equals 1% NCT) reduced the bacterial counts of P. aeruginosa and S. aureus by approximately 5 log10 after 60- and 120-min incubation, respectively. Significant killing was observed as early as after 5-min incubation. Also intrastromal bacteria were inactivated. In the EpiOcular™ tissue model, NCT, NVC-422 and NVC-612 had no or very low potential to irritate corneal tissue.

CONCLUSION

N-chlorotaurine, NVC-422 and NVC-612 are non-irritating in cornea and kill P. aeruginosa and S. aureus, even following penetration into the deeper corneal stromal layers.

Efficacy of NVC-422 against Staphylococcus aureus biofilms in a sheep biofilm model of sinusitis

BACKGROUND

Bacterial biofilms are a major obstacle in management of recalcitrant chronic rhinosinusitis. NVC-422 is a potent, fast-acting, broad-spectrum, nonantibiotic, antimicrobial with a new mechanism of action effective against biofilm bacteria in in vitro conditions. The aim of this study was to investigate the safety and efficacy of NVC-422 as local antibiofilm treatment in a sheep model of rhinosinusitis.

METHODS

After accessing and occluding frontal sinus ostia in 24 merino sheep via staged endoscopic procedures, S. aureus clinical isolate was instilled in frontal sinuses. Following biofilm formation, ostial obstruction was removed and sinuses irrigated with 0.1% and 0.5% NVC-422 in 5 mM acetate isotonic saline at pH 4.0. Sheep were monitored for adverse effects and euthanized 24 hours after treatment. Frontal sinuses were assessed for infection and changes in mucosa after the treatment. S. aureus biofilms were identified with Baclight-confocal scanning microscopy protocol and the biofilm biomass assayed by applying the COMSTAT2 program to recorded image stacks.

RESULTS

After 2 irrigations with 0.1% NVC-422, S. aureus biofilm biomass was reduced when compared to control sinuses (p = 0.0001), though this effect was variable in samples. NVC-422 0.5% solution irrigations reduced biofilm even more significantly and consistently over all samples (p < 0.0001). NVC-422 0.5% was also more effective than 0.1% NVC-422, vehicle control, and normal saline sinus irrigations in reducing biofilm biomass (p < 0.05 for all subgroups). No adverse events were observed in sheep after sinus irrigations with 0.1% and 0.5% NVC-422 solutions.

CONCLUSION

NVC-422 is an effective topical agent against S. aureus biofilms, with dose-dependent efficacy in this animal model of biofilm-associated sinusitis.

Virucidal mechanism of action of NVC-422, a novel antimicrobial drug for the treatment of adenoviral conjunctivitis

Human adenoviral conjunctivitis is a highly contagious eye infection affecting millions of people world-wide. If untreated, it can further develop into keratitis, corneal ulceration, scarring and possible blindness. Despite the significant patient morbidity and socio-economic costs, it is an unmet medical need with no FDA approved treatment. Here, we demonstrate the virucidal activity of NVC-422 (N,N-dichloro-2,2-dimethyltaurine) against adenovirus type 5 (Ad5) and investigated its mechanism of action of Ad5 inactivation. NVC-422 inhibits Ad5-induced loss of cell viability in vitro with 50% inhibitory concentration (IC(50)) ranging from 9 to 23 μM. NVC-422 does not cause any cytotoxicity at concentrations as high as 250 μM. Invitro, NVC-422 inactivates Ad5 but does not interfere with viral replication, indicating that NVC-422 acts on the extracellular adenovirus as a virucidal agent. NVC-422 inactivates Ad5 by oxidative inactivation of key viral proteins such as fiber and hexon as evidenced by SDS-PAGE, Western blotting and reversed-phase HPLC. These data, combined with measurements of the kinetics of the NVC-422 reactivity with selected amino acids, indicate that the changes in the viral proteins are caused by the selective oxidation of sulfur-containing amino acids. The conformational changes of the viral proteins result in the destruction of the viral morphology as shown by transmission electron microscopy. In summary, NVC-422 exhibits virucidal activity against Ad5 by the oxidative inactivation of key viral proteins, leading to the loss of viral integrity and infectivity.

Evaluation of amide replacements in CCR5 antagonists as a means to increase intrinsic permeability. Part 2: SAR optimization and pharmacokinetic profile of a homologous azacyle series

Replacement of a secondary amide with a piperidine or azetidine moiety in a series of CCR5 antagonists led to the discovery of compounds with increased intrinsic permeability. This effort led to the identification of a potent CCR5 antagonist which exhibited an improved in vivo pharmacokinetic profile.

Exploration of a new series of CCR5 antagonists: multi-dimensional optimization of a sub-series containing N-substituted pyrazoles

The introduction of N-substituted pyrazoles in a new series of CCR5 antagonists was shown to substantially increase antiviral activity.

Biochemical characterization of the inhibition of the dengue virus RNA polymerase by beta-d-2'-ethynyl-7-deaza-adenosine triphosphate

Dengue virus (DENV), an emerging pathogen from the Flaviviridae family with neither vaccine nor antiviral treatment available, causes a serious worldwide public health threat. In theory, there are several ways by which small molecules could inhibit the replication cycle of DENV. Here, we show that the nucleoside analogue beta-d-2'-ethynyl-7-deaza-adenosine inhibits representative strains of all four serotypes of DENV with an EC(50) around or below 1microM. Using membrane-associated native replicase complex as well as recombinant RNA polymerase from each DENV serotype in enzymatic assays, we provide evidence that beta-d-2'-ethynyl-7-deaza-adenosine triphosphate (2'E-7D-ATP) targets viral replication at the polymerase active site by competing with the natural nucleotide substrate with an apparent K(i) of 0.060+/-0.016microM. In single-nucleotide incorporation experiments, the catalytic efficiency of 2'E-7D-ATP is 10-fold lower than for natural ATP, and the incorporated nucleotide analogue causes immediate chain termination. A combination of bioinformatics and site-directed mutagenesis demonstrates that 2'E-7D-ATP is equipotent across all serotypes because the nucleotide binding site residues are conserved in dengue virus. Overall, beta-d-2'-ethynyl-7-deaza-adenosine provides a promising scaffold for the development of inhibitors of dengue virus polymerase.

Synthesis, SAR and evaluation of [1,4']-bipiperidinyl-4-yl-imidazolidin-2-one derivatives as novel CCR5 antagonists

Elaboration of our previously disclosed spiropiperidine template led to the development of a series of novel CCR5 antagonists. Results of SAR exploration and preliminary lead characterization are described.

Evaluation of a 4-aminopiperidine replacement in several series of CCR5 antagonists

The bicyclic 5-amino-3-azabicyclo[3.3.0]octanes were shown to be effective replacements for the conformationally restricted 4-aminopiperidine ring found in several series of CCR5 antagonists.

Evaluation of a 3-amino-8-azabicyclo[3.2.1]octane replacement in the CCR5 antagonist maraviroc

The bicyclic 5-amino-3-azabicyclo[3.3.0]octanes were shown to be effective replacements for the 3-amino-8-azabicyclo[3.2.1]octane found in the CCR5 antagonist maraviroc.

Evaluation of secondary amide replacements in a series of CCR5 antagonists as a means to increase intrinsic membrane permeability. Part 1: Optimization of gem-disubstituted azacycles

Replacement of a secondary amide with an N-acyl or N-sulfonyl gem-disubstituted azacyle in a series of CCR5 antagonists led to the identification of compounds with excellent in vitro HIV antiviral activity and increased intrinsic membrane permeability.

CD4-BFFI: a novel, bifunctional HIV-1 entry inhibitor with high and broad antiviral potency

Resistance to antiretroviral drugs is a common problem in the treatment of HIV-1-infected patients. To overcome resistance, we generated a novel, bifunctional HIV-1 entry inhibitor by combining the anti-CD4 monoclonal antibody (mAb) 6314 with a fusion inhibitor similar to T-651 (anti-CD4 mAb based BiFunctional Fusion Inhibitor, CD4-BFFI). CD4-BFFI has potent antiviral activity against a multitude of HIV-1 isolates independent of their co-receptor usage and genetic background. It has higher antiviral potency compared to the fusion inhibitor T-651 or the anti-CD4 mAb 6314 used independently. More importantly, every HIV-1 strain tested was fully inhibited by CD4-BFFI while many strains were only partially inhibited by 6314. CD4-BFFI also retained antiviral potency against virus strains resistant to two fusion inhibitors, a CCR5 antagonist and an anti-CCR5 mAb. Pre-incubation of cells with a saturating concentration of anti-CD4 mAbs reduced the antiviral potency of CD4-BFFI, suggesting that binding of CD4-BFFI to the cell surface via its CD4 mAb portion is required for the antiviral potency of its fusion inhibitor moiety. Collectively, we present a novel HIV-1 inhibitor with a dual mode of action and excellent antiviral potency against wildtype and entry-inhibitor resistant virus strains suggesting that CD4-BFFI may have a high barrier to resistance.

Novel CCR5 monoclonal antibodies with potent and broad-spectrum anti-HIV activities

To identify monoclonal antibodies (mAbs) with high potency and novel recognition sites, more than 25,000 of mouse hybridomas were screened and 4 novel anti-human CCR5 mAbs ROAb12, ROAb13, ROAb14, and ROAb18 showing potent activity in cell-cell fusion (CCF) assay were identified. These mAbs demonstrated potent antiviral activities in both single-cycle HIV infection (IC(50) range: 0.16-4.3 microg/ml) and PBMC viral replication (IC(50) range: 0.02-0.04 microg/ml) assays. These potent antiviral effects were donor-independent. All 4 mAbs were also highly potent in the PhenoSense assay against 29 HIV isolates covering clade A through G. In all antiviral assays, these mAbs showed potency superior to the previously reported mAb 2D7 in side-by-side comparison studies. All 4 mAbs were also fully active against viruses resistant to HIV fusion inhibitor enfuvirtide and CCR5 antagonist maraviroc. Although ROAb12, ROAb14, and ROAb18 inhibited RANTES, MIP1alpha and MIP1beta binding and cell activation, the other novel mAb ROAb13 was inactive in inhibiting cell activation by these three ligands. Furthermore, highly synergistic antiviral effects were found between mAb ROAb13 and 2D7 or ROAb12. In addition, none of these mAbs showed agonist activity or caused internalization of the CCR5 receptor.

A novel potassium channel in lymphocyte mitochondria

The margatoxin-sensitive Kv1.3 is the major potassium channel in the plasma membrane of T lymphocytes. Electron microscopy, patch clamp, and immunological studies identified the potassium channel Kv1.3, thought to be localized exclusively in the cell membrane, in the inner mitochondrial membrane of T lymphocytes. Patch clamp of mitoplasts and mitochondrial membrane potential measurements disclose the functional expression of a mitochondrial margatoxin-sensitive potassium channel. To identify unambiguously the mitochondrial localization of Kv1.3, we employed a genetic model and stably transfected CTLL-2 cells, which are genetically deficient for this channel, with Kv1.3. Mitochondria isolated from Kv1.3-reconstituted CTLL-2 expressed the channel protein and displayed an activity, which was identical to that observed in Jurkat mitochondria, whereas mitochondria of mock-transfected cells lacked a channel with the characteristics of Kv1.3. Our data provide the first molecular identification of a mitochondrial potassium conductance.

In vivo evolution of human immunodeficiency virus type 1 toward increased pathogenicity through CXCR4-mediated killing of uninfected CD4 T cells

The destruction of the immune system by progressive loss of CD4 T cells is the hallmark of AIDS. CCR5-dependent (R5) human immunodeficiency virus type 1 (HIV-1) isolates predominate in the early, asymptomatic stages of HIV-1 infection, while CXCR4-dependent (X4) isolates typically emerge at later stages, frequently coinciding with a rapid decline in CD4 T cells. Lymphocyte killing in vivo primarily occurs through apoptosis, but the importance of apoptosis of HIV-1-infected cells relative to apoptosis of uninfected bystander cells is controversial. Here we show that in human lymphoid tissues ex vivo, apoptosis of uninfected bystander CD4 T cells is a major mechanism of lymphocyte depletion caused by X4 HIV-1 strains but is only a minor mechanism of depletion by R5 strains. Further, X4 HIV-1-induced bystander apoptosis requires the interaction of the viral envelope glycoprotein gp120 with the CXCR4 coreceptor on CD4 T cells. These results emphasize the contribution of bystander apoptosis to HIV-1 cytotoxicity and suggest that in association with a coreceptor switch in HIV disease, T-cell killing evolves from an infection-restricted stage to generalized toxicity that involves a high degree of bystander apoptosis.

Actinomycin D-induced apoptosis involves the potassium channel Kv1.3

Several cytostatic agents are known to induce apoptosis in T-leukemic cells. Although a variety of studies show the central role of apoptosis in cytostatic drug-induced cell death, many molecular details require definition. Here, we demonstrate that cells genetically deficient for the potassium channel Kv1.3 are resistant to apoptosis initiated by the cytostatic drug actinomycin D. Retransfection of Kv1.3 restores sensitivity of the cells to actinomycin D. Cells lacking Kv1.3 fail to respond to actinomycin D with DNA fragmentation, release of cytochrome c, and loss of mitochondrial membrane potential (Delta Psi(m)), while cells functionally expressing Kv1.3 rapidly undergo those changes indicative for apoptosis. The data indicate a central role of the ion channel Kv1.3 in actinomycin D-triggered apoptosis.

Coreceptor phenotype of natural human immunodeficiency virus with nef deleted evolves in vivo, leading to increased virulence

The Sydney Blood Bank Cohort is a group of patients with slowly progressive infection by a human immunodeficiency virus strain containing spontaneous deletions within the nef long terminal repeat region. In 1999, 18 years after the initial infection, one of the members (D36) developed AIDS. In this work, we used an ex vivo human lymphoid cell culture system to analyze two viral isolates obtained from this patient, one prior to the onset of AIDS in 1995 and one after disease progression in 1999. Both D36 isolates were less potent in depleting CD4(+) T cells than a reference dualtropic, nef-bearing viral isolate. However, the 1999 isolate was measurably more cytotoxic to CD4(+) T cells than the 1995 isolate. Interestingly, although both isolates were nearly equally potent in depleting CCR5(+) CD4(+) T cells, the cytotoxic effect of the 1999 isolate toward CCR5(-) CD4(+) T cells was significantly higher. Furthermore, GHOST cell infection assays and blocking experiments with the CXCR4 inhibitor AMD3100 showed that the later D36 1999 isolate could infect both CCR5(+) and CCR5(-) CXCR4(+) cells efficiently, while infection by the 1995 isolate was nearly completely restricted to CCR5(+) cells. Sequence analysis of the V1/V2 and V3 regions of the viral envelope protein gp120 revealed that the more efficient CXCR4 usage of the later isolate might be caused by an additional potential N-glycosylation site in the V1/V2 loop. In conclusion, these data show that an in vivo evolution of the tropism of this nef-deleted strain toward an X4 phenotype was associated with a higher cytopathic potential and progression to AIDS.

CD95 signaling via ceramide-rich membrane rafts

Clustering seems to be employed by many receptors for transmembrane signaling. Here, we show that acid sphingomyelinase (ASM)-released ceramide is essential for clustering of CD95. In vitro and in vivo, extracellularly orientated ceramide, released upon CD95-triggered translocation of ASM to the plasma membrane outer surface, enabled clustering of CD95 in sphingolipid-rich membrane rafts and apoptosis induction. Whereas ASM deficiency, destruction of rafts, or neutralization of surface ceramide prevented CD95 clustering and apoptosis, natural ceramide only rescued ASM-deficient cells. The data suggest CD95-mediated clustering by ceramide is prerequisite for signaling and death.

Physiology of apoptosis

Ion fluxes and volume changes of the whole cell as well as of organelles belong to the hallmarks of apoptosis; however, the molecular mechanism regulating these changes is only poorly characterized. Several ion channels in the plasma membrane, in particular the N-type K(+) channel, the chloride channel cystic fibrosis conductance regulator, and an outward rectifying chloride channel, as well as the mitochondrial permeability transition pore, have been implicated to be involved in signal transduction cascades regulating apoptosis. Furthermore, Bcl-2-like proteins have been suggested to function, at least in part, as ion channels, because they display some homology to bacterial pore-forming toxins. In contrast to the demonstration of the involvement of these different ion channels in apoptosis, the molecular consequences regulated by these ion channels, and finally triggering apoptosis, are almost completely unknown.

CD95/CD95 ligand-mediated counterattack does not block T cell cytotoxicity

Expression of CD95 ligand on parenchymal, epithelial, or tumor cells has been suggested to downregulate the immune response and to control lymphocyte activation. Suppression might be mediated by induction of apoptosis or by inhibition of Ca(2+) channels upon CD95 triggering. We, therefore, aimed to employ this model to modify the immune response to an antigen presented to cytotoxic T cells by antigen-presenting MC57 cells. This model would be very useful to specifically downregulate the immune response to autoantigens in autoimmune situations. However, cytotoxic T cell lines tested in the present study were resistant to CD95 ligand expression on antigen-presenting MC57 cells. In addition, coincubation of the lymphocytes with antigen presenting cells failed to block cytotoxicity mediated by the T lymphocytes. We, therefore, conclude that single expression of CD95 ligand on antigen-presenting cells is insufficient to specifically downregulate an immune response by CD8(+-)triggered immune response.

Stimulation of CD95 (Fas) blocks T lymphocyte calcium channels through sphingomyelinase and sphingolipids

Calcium influx through store-operated calcium release-activated calcium channels (CRAC) is required for T cell activation, cytokine synthesis, and proliferation. The CD95 (Apo-1/Fas) receptor plays a role in self-tolerance and tumor immune escape, and it mediates apoptosis in activated T cells. In this paper we show that CD95-stimulation blocks CRAC and Ca(2+) influx in lymphocytes through the activation of acidic sphingomyelinase (ASM) and ceramide release. The block of Ca(2+) entry is lacking in CD95-defective lpr lymphocytes as well as in ASM-defective cells and can be restored by retransfection of ASM. C2 ceramide, C6 ceramide, and sphingosine block CRAC reversibly, whereas the inactive dihydroceramide has no effect. CD95-stimulation or the addition of ceramide prevents store-operated Ca(2+) influx, activation of the transcriptional regulator NFAT, and IL-2 synthesis. The block of CRAC by sphingomyelinase metabolites adds a function to the repertoire of the CD95 receptor inhibiting T cell activation signals.

The tyrosine kinase lck is required for CD95-independent caspase-8 activation and apoptosis in response to ionizing radiation

Induction of apoptosis is a hallmark of cytostatic drug and radiation-induced cell death in human lymphocytes and lymphoma cells. However, the mechanisms leading to apoptosis are not well understood. We provide evidence that ionizing radiation induces a rapid activation of caspase-8 (FLICE) followed by apoptosis independently of CD95 ligand/receptor interaction. The radiation induced cleavage pattern of procaspase-8 into mature caspase-8 resembled that following CD95 crosslinking and resulted in cleavage of the proapoptotic substrate BID. Overexpression of dominant-negative caspase-8 interfered with radiation-induced apoptosis. Caspase-8 activation by ionizing radiation was not observed in cells genetically defective for the Src-like tyrosine kinase Lck. Cells lacking Lck also displayed a marked resistance towards apoptosis induction upon ionizing radiation. After retransfection of Lck, caspase-8 activation and the capability to undergo apoptosis in response to ionizing radiation was restored. We conclude that radiation activates caspase-8 via an Lck-controlled pathway independently of CD95 ligand expression. This is a novel signaling event required for radiation induced apoptosis in T lymphoma cells.