4th Annual Clinical Care Options for Hepatitis Symposium: HCV Highlights

1
4th Annual Clinical Care Options for Hepatitis
Symposium HCV Highlights
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Interferon and RibavirinMechanisms of Action,
Resistance, and Why It Matters
Raymond T. Chung, MDDirector of
HepatologyMassachusetts General
HospitalAssociate Professor of MedicineHarvard
Medical School Boston, Massachusetts
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Innate Immunity An IFN Amplification Loop
Hepatitis Virus
IFN-?
IFN-?
IFN-?/?
IFN-?
IFN-?
IFN signaling Jak-STAT
IFN-?
IFN-?
IRF-3 activation
IFN-?
TLR3
IFNAR-1
IFNAR-2
Viral PAMP dsRNA
Tyk2
Jak1
IRF-9
STAT 2
IRF-3
RIG-I
STAT 1
IRF-7
IKK-?
JAK-STAT pathway
TBK1
P
P
P
P
IRF-7
IRF-3
STAT 2
STAT 1
ISGF3
P
P
P
IRF-7
IRF-7
IRF-3
P
P
P
IRF-9
IRF-3
IRF-3
IRF-7
Cytoplasm
ISRE
PRD
IFN-stimulated genes OAS, IRF-7, PKR, ISG56 etc
VRE
IFN-?
IFN-?
Nucleus
ISG expression IFN amplification loop
IRF-7
IFN-? production
Adapted from Gale M Jr, et al. Nature.
2005436939-945.
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The Adaptive (Cellular) Immune Response Finishes
the Job
Activation,
Clonal expansion
differentiation
B cell
Neutralizing
HCV antibodies
Th2 cytokines
HCV
(IL-4, IL-5, IL-6,
Viral entry
Lysis
IL-9, IL-10, IL-13)
MHC II
CD4
MHC I
TCR
Th
cell
Hepatocyte
TCR
CD8
CTL
CD4
Th1 cytokines
Clonal
expansion
cell
Th
(IFN-?TNF-a)
(Th1 or Th2)
IFN-a
Adapted from Liang TJ, et al. Ann Intern Med.
2000132296-305.
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Viral Kinetics After IFN Therapy
Viral kinetics
IFN (efficacy e)
0
1st phase antiviral efficacy (r) (innate)
-1
2nd phase clearance ofinfected hepatocytes (d)
(adaptive)
HCV RNA (log IU mL-1)
-2
Two phases ofviral decline
-3
-4
-7
0
7
14
21
28
Days After Start of Therapy
Adapted from Feld JJ, et al. Nature.
2005436967-972.
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Ribavirin

• Initially developed as an antiviralguanosine
  analogue
• No antiviral activity but improved ALT when given
  as monotherapy
• Combination with IFN improved ETR but greatly
  enhanced SVR rates by decreasing relapse
• Does not alter 1st phase kinetics appreciably
• Modest ? of PEG-IFN antiviral effect (0.5-1.0
  log)
• Mechanistic models must explain clinical
  observations

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Ribavirin Proposed Mechanisms of Action
TH2
Defective HCV particles (decreased fitness)
Ribavirin
Immunomodulation (2nd phase)
TH1
CTL
IFN-?, TNF-?
Hepatocyte
RDP
RTP
RMP
Ribavirin
(-)
IMP
GMP
RdRp
HCV RNA
HCV RNA
IMPDH
RNA Mutagen
Replication
GTP
Inhibition of HCV RdRp (1st phase)
Inhibition of IMPDH (1st phase)
RNA mutagenesis (2nd phase)
Adapted from Feld JJ, et al. Nature.
2005436967-972.
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HCV NS3-4A Blocks IFN Induction at Multiple Levels
TLR3
TRIF
NS3/4A
RIP-1
IRF-3
IRF-3
RIG-I
MDA5
IKK-?
TBK1
IPS-1
RIP-1
P
FADD
IRF-3
l??
TRAF6
mitochondria
P
IKK
IRF-3
P
HCV NS3/4A
l??
CBP/p300
IRF-3/NF-?? Target genes (IFN-b)
P
IRF-3
P
CBP/p300
IRF-3
Adapted from Gale M Jr, et al. Nature.
2005436939-945.
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HCV Blocks IFN Signal Transduction
IFN-?
IFN-?
IFN-?/?
IFN-?
IFN-?
IFN-?
IFN-?
HCV proteins
Core
Core
IFNAR-1
IFNAR-2
Tyk2
Jak1
SOCS-1
SOCS Inhibition of Jak-STAT signaling
STAT 1
STAT 2
SOCS-3
Inhibit P-STAT1 Degrade STAT1
IRF-9
Cytoplasm
P
P
Block STAT function
STAT 1
STAT 2
PP2A PIAS
ISGF3
Nucleus
ISG expression attenuated
IRF-9
IL-8
NS5A
ISRE
Adapted from Gale M Jr, et al. Nature.
2005436939-945.
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IFN-Stimulated Genes as the Antiviral Workhorses
Antiviral Actions of Interferon
IFN
IFN
Oligoadenylate synthetase OAS
Protein kinase PKRInactive
Inactive
NS5A
dsRNA
ssRNA
E2
Oligoadenylate synthetase OASActive(multiple
forms nuclear and cytoplasmic)
Protein kinase PKRActive(Ribosome associated)
Phosphorylatedinitiation factorelF-2a P
InitiationfactorelF-2a
2, 5-oligoadenylic acid
ATPAMP
Pi
(2, 5 A)
Phosphodiesterase
Phosphatase(Soluble)
Paucity of recognition sites
RNase LActive
RNase LInactive
mRNA translationinhibition
HCV
RNA degradation
Microarray studies have identified gt 100
IFN-stimulated genes
Adapted from Samuel CE. Clin Microbiol Rev.
200114778-809.
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Treatment of Hepatitis C inBlacks SVR
PEG-IFN ?-2a 180 ?g/ wk RBV 1000-1200 mg/d x
48 wks 100 genotype 1
PEG-IFN ?-2b 1.5 ?g/ kg/wk x 48 weeks RBV 1000
800 mg/d 100 genotype 1
PEG-IFN ?-2a 180 ?g/wk RBV 1000-1200 mg/d x
48 wks 98 genotype 1
Virologic Response Rates ()
100
Black
80
White
P lt .001
P lt .001
60
52
52
39
40
28
26
19
20
n 196 n 205
n 100
n 100
n 78
n 28
0
Muir et al1
Jeffers et al2
Virahep-C3
1. Muir AJ, et al. N Engl J Med.
20043502265-227. 2. Jeffers LJ, et al.
Hepatology. 2004391702-1708. 3. Conjeevaram H,
et al. AASLD 2005. Abstract 199.
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Impaired Host Antiviral Responses as the Basis
for Inferior SVR Rates?

• Differences between A-A and C-A appear to reside
  primarily in 1st phase viral decay
• These findings suggest intrinsic defects in
  innate immunity (signal transduction or ISGs)
• Search for genetic polymorphisms in innate
  immunity underway (Virahep-C)

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Obesity and Impaired Antiviral Response Rates

• Obesity also associated with impaired antiviral
  response rates (likely related to steatosis)
• SOCS-3 as key mediator
• Upregulated in obesity
• Increased by HCV
• Promotes degradation of IRS1 and IRS2 ? insulin
  resistance

Kawaguchi T, et al. Am J Path. 20041651499-1508.
Walsh MJ, et al. Gut. 200655529-535.
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Higher-Dose IFN or Further Refinements in IFN PK

• Theory overcome intrinsic blocks to IFN action
  with higher doses of exogenous IFN
• High dose PEG-IFN RBV recent studies showing
  modest SVR rates in prior PEG-IFN/RBV
  nonresponders
• Albumin-IFN extend half-life of IFN to permit
  extended dosing interval
• Limitations tolerability, toxicities, downstream
  block

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Strategies to Improve or Replace RBV

• IMPDH inhibitors
• Likely not major mechanism of RBV against HCV
• Antiviral effect may be offset by
  immunosuppressive effects
• Higher RBV doses
• Further decreases in relapse among genotype 1
  patients?
• Prodrugs
• Permit targeted dosing of RBV (viramidine)

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New Therapies for Chronic Hepatitis C Rational
Drug Design
Gary Davis, MDDirector, Division of
HepatologyBaylor University Medical
CenterMedical Director, Liver TransplantationBay
lor Regional Transplant InstituteDallas, Texas
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Role of New Agents in Treating HCV

• Primary aim should remain eradication
• Chronic suppression may be achievable
• Interferon likely to remain foundation of therapy
• Combination therapy will be key
• Other agents may allow lower doses or shorter
  duration of poorly tolerated drugs
• New agents will be able to target different
  processes of the HCV replication cycle

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Target Infection of the Hepatocyte
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Therapeutics Infection of the Hepatocyte

• Polyclonal preparations1
• Neutralize infectious inoculae ex vivo
• Inhibit or prevent infection in chimps
• Studies in man disappointing to date
• Monoclonal antibodies2
• Anti-E2 human monoclonal XTL
• Mild HCV RNA suppression with daily dosing

• Vaccine-derived anti-E1E23
• Neutralizing antibody
• In vitro inhibition of CD81 and VSV pseudovirions

1. Davis, et al. Liver Transpl 2005. Willems, et
al. J Hepatol. 2002. 2. Schiano, et al. Hepatol.
2005. 3. DiBisceglie, et al. Hepatol. 2005.
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Therapeutics Infection of the Hepatocyte (contd)

• N-glycans in envelope glycoprotein (E1E2) are
  essential for protein folding, secretion/assembly,
  antigenicity, receptor binding, and cell entry
• Mutations in E2 eliminate infectivity1
• E2N2, E2N4 by blocking cell entry
• MX-3256 (celgosivir, Migenix)2
• In vitro synergy with interferon-ribavirin
• No reduction in HCV RNA

1. Goffard, et al. J Virol. 2005. 2. Yoshida, et
al. Gastroenterology. 2006.
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Target RNA Transport to the ER
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Therapeutics RNA Transport to the ER

• Oligonucleotides
• Ribozymes
• Antisense oligos
• siRNA

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Therapeutics RNA Transport to the ER (contd)
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Therapeutics siRNA

• Ancient host process of gene silencing, probably
  evolved for antiviral defense/genome protection
• siRNA
• Exogenous short synthetic ds nucleic acid
  molecules
• Highly modified to increase stability (nuclease
  resistance), prolong half-life, and reduce
  nonspecific (off-target) effects
• Incorporated into RNA-induced splicing complex
  (RISC) which pairs it with target mRNA
• Destruction of mRNA by RNase

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Target Translation and Protein Processing
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Therapeutics Translation and Protein Processing
Serine protease (trans)
HCV polyprotein
NS2
NS3
NS4A
NS4B
NS5A
NS5B
E1
E2
p7
C
Serine protease (cis)
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Therapeutics Translation and Protein Processing
(contd)

• Conclusions
• Potent antivirals
• Orally bioavailable
• Well tolerated
• Synergy with IFN increased IFN sensitivity
• Require maintenance of trough concentration
• May be able to shorten course of therapy
• Other PI in development ITMN B (InterMune)

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Target Viral RNA Transcription
-RNA
5
3
Subcellular Membrane
-RNA
5
3
Subcellular Membrane
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Therapeutics Viral RNA Transcription

• HCV polymerase inhibitors in development
• NM-283 (valopicitabine, Idenix)
• R1626 (Roche)
• HCV-796 (Viropharma)

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Target Virus Assembly
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Therapeutics Virus Assembly

• N-glycans in envelope glycoprotein (E1E2) are
  essential for protein folding, secretion/assembly,
  antigenicity, receptor binding, and cell entry
• Imino sugars inhibit a-glucosidases and prevent
  proper glycosylation of viral envelope proteins
  may inhibit secretion and infectivity of viruses
• Zitzmann, et al. PNAS 1999 Mehta, et al. FEBS
  Ltr 1998