Will There Be a Cure for Ebola?

Despite the unprecedented Ebola virus outbreak response in West Africa, no Ebola medical countermeasures have been approved by the US Food and Drug Administration. However, multiple valuable lessons have been learned about the conduct of clinical research in a resource-poor, high risk-pathogen setting. Numerous therapeutics were explored or developed during the outbreak, including repurposed drugs, nucleoside and nucleotide analogues (BCX4430, brincidofovir, favipiravir, and GS-5734), nucleic acid-based drugs (TKM-Ebola and AVI-7537), and immunotherapeutics (convalescent plasma and ZMapp). We review Ebola therapeutics progress in the aftermath of the West Africa Ebola virus outbreak and attempt to offer a glimpse of a path forward.

An E460D Substitution in the NS5 Protein of Tick-Borne Encephalitis Virus Confers Resistance to the Inhibitor Galidesivir (BCX4430) and Also Attenuates the Virus for Mice.

The adenosine analogue galidesivir (BCX4430), a broad-spectrum RNA virus inhibitor, has entered a phase 1 clinical safety and pharmacokinetics study in healthy subjects and is under clinical development for treatment of Ebola and yellow fever virus infections. Moreover, galidesivir also inhibits the reproduction of tick-borne encephalitis virus (TBEV) and numerous other medically important flaviviruses. Until now, studies of this antiviral agent have not yielded resistant viruses. Here, we demonstrate that an E460D substitution in the active site of TBEV RNA-dependent RNA polymerase (RdRp) confers resistance to galidesivir in cell culture. Galidesivir-resistant TBEV exhibited no cross-resistance to structurally different antiviral nucleoside analogues, such as 7-deaza-2'-C-methyladenosine, 2'-C-methyladenosine, and 4'-azido-aracytidine. Although the E460D substitution led to only a subtle decrease in viral fitness in cell culture, galidesivir-resistant TBEV was highly attenuated in vivo, with a 100% survival rate and no clinical signs observed in infected mice. Furthermore, no virus was detected in the sera, spleen, or brain of mice inoculated with the galidesivir-resistant TBEV. Our results contribute to understanding the molecular basis of galidesivir antiviral activity, flavivirus resistance to nucleoside inhibitors, and the potential contribution of viral RdRp to flavivirus neurovirulence.IMPORTANCE Tick-borne encephalitis virus (TBEV) is a pathogen that causes severe human neuroinfections in Europe and Asia and for which there is currently no specific therapy. We have previously found that galidesivir (BCX4430), a broad-spectrum RNA virus inhibitor, which is under clinical development for treatment of Ebola and yellow fever virus infections, has a strong antiviral effect against TBEV. For any antiviral drug, it is important to generate drug-resistant mutants to understand how the drug works. Here, we produced TBEV mutants resistant to galidesivir and found that the resistance is caused by a single amino acid substitution in an active site of the viral RNA-dependent RNA polymerase, an enzyme which is crucial for replication of the viral RNA genome. Although this substitution led only to a subtle decrease in viral fitness in cell culture, galidesivir-resistant TBEV was highly attenuated in a mouse model. Our results contribute to understanding the molecular basis of galidesivir antiviral activity.

Pharmacokinetics and Safety of the Nucleoside Analog Antiviral Drug Galidesivir Administered to Healthy Adult Subjects.

Galidesivir (BCX4430) is an adenosine nucleoside analog broadly active in cell culture against multiple RNA virus families, and active in animal models of viral diseases associated with Ebola, Marburg, yellow fever, Zika, and Rift Valley fever. Current studies demonstrated the pharmacokinetics and safety of the first-in-human evaluations of galidesivir as intramuscular (IM) and intravenous (IV) formulations. Two double-blind, placebo-controlled, dose-ranging studies were conducted enrolling 126 healthy subjects. Study 1 evaluated the safety and tolerability of IM galidesivir over single day dosing, single day dosing ± lidocaine, and 7-day dosing with lidocaine. Study 2 evaluated the safety and tolerability of single ascending doses of IV galidesivir. Safety and tolerability were evaluated via clinical and laboratory monitoring. The plasma concentration-time profile of galidesivir at doses 0.3 to 10 mg/kg IM was characterized by rapid absorption, an initial rapid distribution and clearance phase, and an extended terminal elimination phase. The initial rapid distribution and extended terminal elimination were mimicked in the profile of galidesivir at doses 5 to 20 mg/kg IV. No fatal events or related serious adverse events were reported. No clinically significant dose-related trends in laboratory values, vital signs, electrocardiograms, or echocardiograms were noted. Galidesivir was safe and generally well tolerated.

Galidesivir limits Rift Valley fever virus infection and disease in Syrian golden hamsters.

Rift Valley fever virus (RVFV) is a mosquito-borne pathogen endemic to sub-Saharan Africa and the Arabian Peninsula. There are no approved antiviral therapies or vaccines available to treat or prevent severe disease associated with RVFV infection in humans. The adenosine analog, galidesivir (BCX4430), is a broad-spectrum antiviral drug candidate with in vitro antiviral potency (EC50 of less than 50 µM) in more than 20 different viruses across eight different virus families. Here we report on the activity of galidesivir in the hamster model of peracute RVFV infection. Intramuscular and intraperitoneal treatments effectively limited systemic RVFV (strain ZH501) infection as demonstrated by significantly improved survival outcomes and the absence of infectious virus in the spleen and the majority of the serum, brain, and liver samples collected from infected animals. Our findings support the further development of galidesivir as an antiviral therapy for use in treating severe RVFV infection, and possibly other related phleboviral diseases.

Inhibitory effects of Galidesivir(BCX4430)on rabies virus in vitro / 中国人兽共患病学报

This study analyzed the inhibitory effects of BCX4430 on rabies virus with different virulence(CVS-11 and SC16)in vitro.Direct immunofluorescence(DFA),quantitative real-time PCR and half tissue culture infective dose(TCID50)assays were used.BCX4430(250 pmol/L),compared with T-705,significantly decreased the viral titer and the relative expres-sion level of viral mRNA,similarly to the inhibitory effects of ribavirin.Thus,our study demonstrated that BCX4430 signifi-cantly inhibits the replication of rabies virus in vitro.

Efficacy of the broad-spectrum antiviral compound BCX4430 against Zika virus in cell culture and in a mouse model.

Zika virus (ZIKV) is currently undergoing pandemic emergence. While disease is typically subclinical, severe neurologic manifestations in fetuses and newborns after congenital infection underscore an urgent need for antiviral interventions. The adenosine analog BCX4430 has broad-spectrum activity against a wide range of RNA viruses, including potent in vivo activity against yellow fever, Marburg and Ebola viruses. We tested this compound against African and Asian lineage ZIKV in cytopathic effect inhibition and virus yield reduction assays in various cell lines. To further evaluate the efficacy in a relevant animal model, we developed a mouse model of severe ZIKV infection, which recapitulates various human disease manifestations including peripheral virus replication, conjunctivitis, encephalitis and myelitis. Time-course quantification of viral RNA accumulation demonstrated robust viral replication in several relevant tissues, including high and persistent viral loads observed in the brain and testis. The presence of viral RNA in various tissues was confirmed by an infectious culture assay as well as immunohistochemical staining of tissue sections. Treatment of ZIKV-infected mice with BCX4430 significantly improved outcome even when treatment was initiated during the peak of viremia. The demonstration of potent activity of BCX4430 against ZIKV in a lethal mouse model warrant its continued clinical development.

Antiviral activity of the adenosine analogue BCX4430 against West Nile virus and tick-borne flaviviruses.

There are currently no approved antiviral therapies against medically important human flaviviruses. The imino-C-nucleoside BCX4430 shows broad-spectrum antiviral activity against a wide range of RNA viruses. Here, we demonstrate that BCX4430 inhibits tick-borne species of the genus Flavivirus; however, the antiviral effect varies against individual species. Micro-molar BCX4430 levels inhibited tick-borne encephalitis virus (TBEV); while, approximately 3-8-fold higher concentrations were needed to inhibit louping ill virus and Kyasanur Forest disease virus. Moreover, the compound strongly inhibited in vitro replication of West Nile virus, a typical mosquito-transmitted flavivirus. Two chemical forms of the compound, i.e. BCX4430 and BCX4430 hydrochloride, were compared and both exerted similar inhibitory profiles in our in vitro antiviral assay systems and no or negligible cytotoxicity in porcine kidney stable and Vero cells. The obtained data indicate that, in addition to mosquito-borne flaviviruses, the compound has strong antiviral activity against members of the TBEV serocomplex.

Herbal Lead as Ideal Bioactive Compounds Against Probable Drug Targets of Ebola Virus in Comparison with Known Chemical Analogue: A Computational Drug Discovery Perspective.

Ebola is a deadly virus that has recently emerged as an enormous public health concern which causes dangerous illness with high fatality rates of 90 %. The virus is not receptive to known antivirals, and hence, there is a promising need to identify novel inhibitors to combat the disease. The present study deals with identification of potential herbal leads that probably subdue the activity of four major drug targets of Ebola virus such as VP24, VP30, VP35 and VP40 by computer-aided virtual screening. The selection of receptors was performed based on their functional roles in the disease. The drug likeliness and ADMET parameters of 150 herbal ligands were computationally predicted. Those molecules that qualified these parameters were preferred for docking studies with the protein targets. An existing chemical antiviral drug, BCX4430 was also docked and its theoretical binding energy was scrutinized. The docking studies suggested that herbal ligand Limonin demonstrated high binding properties with VP24 and VP35 (binding energy -9.7 kcal/mol). Similarly, curcumin exhibited good binding with VP30 (binding energy -9.6 kcal/mol). Further, Mahanine displayed superior interaction with VP40 (binding energy -7.7 kcal/mol). These herbal leads demonstrated better binding potential than the known chemical analogue in the computational studies. This study serves to bestow paramount information for further experimental studies concerning the utility of herbal ligands as probable lead molecules against Ebola viral targets.

BCX4430 - A broad-spectrum antiviral adenosine nucleoside analog under development for the treatment of Ebola virus disease.

The adenosine nucleoside analog BCX4430 is a direct-acting antiviral drug under investigation for the treatment of serious and life-threatening infections from highly pathogenic viruses, such as the Ebola virus. Cellular kinases phosphorylate BCX4430 to a triphosphate that mimics ATP; viral RNA polymerases incorporate the drug's monophosphate nucleotide into the growing RNA chain, causing premature chain termination. BCX4430 is active in vitro against many RNA viral pathogens, including the filoviruses and emerging infectious agents such as MERS-CoV and SARS-CoV. In vivo, BCX4430 is active after intramuscular, intraperitoneal, and oral administration in a variety of experimental infections. In nonclinical studies involving lethal infections with Ebola virus, Marburg virus, Rift Valley fever virus, and Yellow Fever virus, BCX4430 has demonstrated pronounced efficacy. In experiments conducted in several models, both a reduction in the viral load and an improvement in survival were found to be related to the dose of BCX4430. A Phase 1 clinical trial of intramuscular administration of BCX4430 in healthy subjects is currently ongoing.

Ebola virus (EBOV) infection: Therapeutic strategies.

Within less than a year after its epidemic started (in December 2013) in Guinea, Ebola virus (EBOV), a member of the filoviridae, has spread over a number of West-African countries (Guinea, Sierra Leone and Liberia) and gained allures that have been unprecedented except by human immunodeficiency virus (HIV). Although EBOV is highly contagious and transmitted by direct contact with body fluids, it could be counteracted by the adequate chemoprophylactic and -therapeutic interventions: vaccines, antibodies, siRNAs (small interfering RNAs), interferons and chemical substances, i.e. neplanocin A derivatives (i.e. 3-deazaneplanocin A), BCX4430, favipiravir (T-705), endoplasmic reticulum (ER) α-glucosidase inhibitors and a variety of compounds that have been found to inhibit EBOV infection blocking viral entry or by a mode of action that still has to be resolved. Much has to be learned from the mechanism of action of the compounds active against VSV (vesicular stomatitis virus), a virus belonging to the rhabdoviridae, that in its mode of replication could be exemplary for the replication of filoviridae.