Monday Parallel Session 18, October 30, 2006
HCV: Pre-Clinical and Early Development
E. W. Godofsky; J. S. Shan.
Background:
Bavituximab is a novel monoclonal antibody that
specifically targets phosphatidylserine (PS) on the
outer surface of the plasma membrane of virally infected cells and enveloped
viruses. Once bound, it is believed to direct the host’s immune system to clear
virally infected cells and viruses. Its antiviral activity has been previously
demonstrated in animal models of murine
cytomegalovirus and pichinde virus.
Aim:
To determine the safety, tolerability and pharmacokinetics of
a single intravenous (IV) infusion of bavituximab in
a phase I, open-label, dose-escalation study in subjects with chronic HCV
infection who failed to respond to or relapsed after pegylated interferon plus
ribavirin combination therapy.
Methods:
Sequential cohorts of 6 subjects were given a single 90 min
IV infusion of bavituximab at 0.1, 0.3, 1, 3 or 6
mg/kg and were followed for 12 weeks. Vital signs, physical exams, safety
laboratory parameters, serum bavituximab levels were
monitored and serum HCV RNA levels were measured by NGI SuperQuant.
Results:
The infusion was safe and well tolerated by all subjects. All
adverse events were mild or moderate in severity, except for 1 report of severe
headache at 1 mg/kg and 1 of severe vertigo at 3mg/kg, both unrelated to study
drug. The majority of AEs were considered not related
to study drug, with the most common being injection site bruises, nausea,
rhinitis, and headache. There were no laboratory AEs
except for expected subclinical transient
prolongation of aPTT for the 3 and 6 mg/kg dose
groups on day 1 postdose. After IV infusion, bavituximab reaches Cmax at 1h postdose with a mean elimination half-life of ~31h. There
was a trend towards a bimodal decrease in mean serum HCV RNA levels. The first
decrease was seen within 24 hours postdose and the
second began around day 4 and appeared sustained up to several weeks in some
subjects. Serum cytokine analyses are ongoing.
Conclusions:
Single IV doses of bavituximab up
to 6 mg/kg were safe and well tolerated. It has a predictable pharmacokinetic
profile. The transient reductions in serum viral load were consistent with the
proposed mechanism of immune stimulation. Unlike conventional therapy, bavituximab is a unique therapeutic that targets viruses
and virally infected cells by channeling host’s defense against them. Since it does not target viral
proteins, bavituximab is unlikely to elicit
traditional viral resistance.
R.
Wagner; D. Larson; T. Bosse; W. Kati; H. Mo; G. Koev; S. Masse; W. Jiang; Y. Liu; D. Montgomery; T.
Middleton; V. S. Stoll; K. D. Stewart; D. Beno; R. Lanford; W. Kohlbrenner; D.
Kempf; A. Molla.
Background:
The identification of small-molecule drugs to treat HCV
infection is an area of intense research. Combinations of such agents have the
potential to avoid resistance emergence and yield higher SVR with fewer side
effects. We report the discovery of a new potent HCV polymerase inhibitor,
A-837093, with excellent pharmacokinetics (PK), that shows “viral clearance” in
the replicon assay in combination with another small molecule inhibitor and has
demonstrated efficacy in the chimpanzee.
Methods:
In vitro activity was measured in subgenomic
HCV genotype 1a and 1b replicons. Resistant replicon
colonies were selected by treating replicon cells with A-837093 at a
concentration 10x above its EC50. Rats, monkeys and dogs were dosed orally at 5
mpk and plasma levels of A-837093 were determined by
HPLCMS. HCV drug-naive genotype 1a- and 1b-infected chimpanzees were dosed
orally with a suspension of A-837093 for 14 days at 30 mpk
BID. Blood samples were periodically withdrawn to determine viral load, viral
sequence, plasma trough drug levels and clinical chemistry parameters.
Results:
A-837093, a subnanomolar enzyme
inhibitor, inhibits HCV genotype 1 with EC50s of 3-11 nM.
In the presence of 40% human serum, EC50s are attenuated up to 17-fold.
A-837093-treated replicon cells produced resistant colonies that contained 1-3
mutations within the NS5B gene, resulting in potency losses >800- fold
relative to the wild-type (WT) replicon. However, the combination of A-837093
and the HCV protease inhibitor BILN-2061 produced a synergistic antiviral
effect and prevented development of resistance, “curing” the replicon cells.
Replication efficiency of mutant replicons was
impaired compared with the WT replicon. Oral bioavailability of A-837093 was
62% in rat, 100% in dog and 19% in monkey, partitioning into liver tissue (20:1
rat, 200:1 monkey) relative to plasma. Dosing in 1a- and 1b-infected
chimpanzees after 2 days at 30 mpk, resulted in a 1.4
log10 and 2.5 log10 drop in HCV RNA, respectively. By day 5, plasma HCV RNA in
the 1b-infected animal rebounded to within 0.6 log10 copies/mL of baseline,
while the 1a-infected chimpanzee experienced a sustained viral load reduction
throughout the treatment period.
Conclusion:
We have demonstrated that A-837093 is an efficacious
inhibitor of HCV infection in the chimpanzee model. While successful therapy
with any single agent is unlikely, in vitro combination studies suggest that
A-837093 may be useful in combination with other small-molecule HCV inhibitors
to effectively treat HCV infection.
G.
Kalkeri; B. Rao; D.
Brennan; A. Kwong.
Introduction/Purpose:
More than 80% of Hepatitis C virus (HCV) infections result
chronic hepatitis C. However, the factors responsible for viral
persistence/immune evasion are not clearly understood. HCV NS3/4A protease is
implicated in viral evasion of TLR3 or Rig- I mediated innate immunity by
cleaving the TRIF and IFN-b promoter stimulator 1 (IPS-1) protein adaptors
respectively. Cleavage of IPS-1 is observed in HCV infections both in vitro and
in vivo1. Telaprevir (TVR, VX-950) is a highly
selective inhibitor of the HCV NS3/4A protease that has demonstrated strong
antiviral activity in patients with genotype 1 HCV when dosed alone, or with
peginterferon (PEG-IFN) but has demonstrated the existence of NS3 variants with
reduced sensitivity to telaprevir. The purpose of
this study was to compare the cleavage of viral (5A/B) and innate immunity
(TRIF and IPS-1) substrates by HCV proteases from different genotypes (1b, 2a
& 3a), to demonstrate the inhibition of this cleavage by telaprevir, and to test the ability of telaprevir
resistance mutants to cleave these substrates.
Methods:
In vitro cleavage reactions of 35S-labeled HCV (5A/B) and
TRIF & IPS-1 substrates were performed and quantified. Computational
modeling analysis was performed using Quanta Molecular Mechanics program.
Results: NS3/4A protease from HCV genotypes 1, 2 and 3 were
able to cleave TRIF and IPS-1. Telaprevir, which
inhibits cleavage of the natural HCV substrate (5A/B), was also able to inhibit
the genotype 1 HCV protease-mediated cleavage of TRIF in a similar manner. This
supports a hypothesis wherein telaprevir might play a
dual role in the treatment of HCV infections by acting as a direct antiviral
agent as well as restoring innate immunity.
A156V/T variants with reduced sensitivity to telaprevir and impaired viral fitness compared to wild type
virus have been reported in vitro2 and in vivo3. These in vitro telaprevir-resistant mutants were found to have
significantly reduced ability to cleave HCV 5A/B consistent with their poor replicative fitness. Cleavage of TRIF & IPS-1
substrates by these mutants was also impaired. Computational modeling suggests
that steric hindrance might decrease binding of TRIF
to the A156T/V mutant protease, resulting in inefficient cleavage.
Conclusion:
The A156V/T variants exhibit impaired cleavage of TRIF and
IPS-1, suggesting that the emergence of these telaprevir
resistance mutants may not compromise the potential restoration of innate
immunity by telaprevir.
1) Loo et al (2006)
PNAS, 103:6001-6006
2) Lin et al (2005)
JBC 280:36784-36791
3) Sarrazin, et al (2005) AASLD, Abst LB06.