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Targets for Anti-viral therapy
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AntiviralsLect 7,8 Sadia Anjum
Targets for Anti-viral therapy
1. viral attachment to cell and fusion (fusion inhibitors)
2. protein translation in infected cells (interferon)
3. protein processing (specific protease inhibitors)
4. DNA synthetic enzymes (reverse transcriptase inhibitors, DNA polymerase inhibitors)
5. DNA integrase
6. Immune system (effective vaccines, restore immune surveillance)
Targets for Anti-viral therapy
Interferons
Interferons are glycoproteins that come in 3 varieties:
ά (made in leukocytes) β (made in fibroblasts)γ (made in T cells) activated T cells produce g interferon
to modulate the immune response
induced by viral infection, IL1, IL2, TNF
Cytokine signaling pathway
Multiple Pathways of Interferon Action
Clinical use of Interferonalpha interferon FDA approved:
◦ genital warts (papillomavirus) note: resiquimod has also been shown to be effective
◦ hepatitis B and C◦ Kaposi’s sarcoma (HSV VIII)
Toxicity◦ fever, fatigue, marrow suppression, depression,
acute influenza like symptoms◦ about 10-20% discontinue therapy due to
toxicity
Hepatitis C Chronic hepatitis C virus (HCV) infection affects 2.7 million
people in the United States.
Cirrhosis of the liver resulting from chronic HCV infection is the leading reason for liver transplantation in the U.S.
Drug treatments such as interferon and ribavirin are not very effective
HCV protease inhibitors are a promising new class of antivirals for this disease
BILN 2061 (Boehringer) looked good but appears to have cardiovascular toxicity and is on hold
VX-950 (Vertex Pharmaceuticals) is now in phase II trials and looks promising
RibavirinA guanosine analogphosphorylated intracellularly by host enzymes inhibits capping of viral messenger RNA inhibits the viral RNA-dependent RNA polymerase inhibits replication of DNA and RNA viruses
Ribavirin antiviral HCV/Dengue
Telaprevir (VX-950) with peg-IFN looks promising in clinical trials
Anti-influenza virus drugs Amantadine, Rimantadine
◦ cyclic amines◦ inhibit the uncoating of viral RNA therefore inhibiting replication◦ only active against influenza A
◦ blocks the influenza M2 ion channel on endosomes and prevents passage of H+ ions required for acidification and viral uncoating
◦ mild CNS effects
Zanamivir, Oseltamivir◦ active against both influenza A and B◦ inhibits influenza viral neuraminidase.◦ Neuraminidase must cleave terminal sialic acid residues on receptors recognized by viral
hemagglutinin. ◦ Without this cleavage, virus remains trapped on infected cells --no release of infectious particles◦ treats uncomplicated influenza infections◦ administered intranasally
Anti-influenza
Targets for treatment of HIV (anti-retroviral drugs
Antiretroviral Agents1) Nucleoside Reverse Transcriptase
Inhibitors (NRTIs)
2) Nonnucleoside Reverse Transcriptase Inhibitors (NNRTIs)
3)Protease inhibitors
Antivirals: Purine NucleosidesAgent Antiviral Activityguanines
acyclovir HSV 1 & 2, VZVganciclovir (DHPG) CMV retinitis and systemic
CMV infectionribavirin (RTCD) Influenza types A and B,
RSV, LV, HVadenosines
didanosine (ddl) HIVvidarabine (Ara-A) HSV, herpes zoster
Antivirals: Pyrimidine Nucleosides
Agent Antiviral Activitycytosines
lamivudine (3TC) HIVzalcitabine (ddC) HIV
thymineidoxuridine (IDU) HSVstavudine (d4T) HIVtrifluridine HSVzidovudine (AZT) HIV
Zidovudine (AZT) RTase inhibitor
A deoxythymidine analogenters the cell via passive diffusionmust be converted to the
triphosphate form by mammalian thymidine kinase
competitively inhibits deoxythymidine triphosphate for the reverse transcriptase enzyme
causes chain termination
mechanism◦selective reverse transcriptase inhibitor
Zidovudine (AZT) RTase inhibitor
Mechanism of selective toxicity of AZT
AZT concentration (uM)
DNAsynthesis
Zidovudinemechanism
◦ selective reverse transcriptase inhibitorpharmacokinetics:
◦ orally active, penetrates CSF toxicity:
◦ bone marrow depression (anemia, leukopenia)◦ headache, nausea, myopathy, anorexia, fatigue
therapeutic effects:◦ increase CD4+ T cells partially restoring immune system◦ reverses AIDS dementia
resistance: major problem◦ RTase mutations
Lamivudine (3TC)similar to zidovudineresistance develops quickly: selects
for met184val mutation in RTaselamivudine + zidovudine combination
dramatically slows resistance development
NNRTIs(non-nucleosidereverse transcriptaseinhibitors)
NevirapineDelavirdineEfavirenz
NNRTIs
Bind to site on viral reverse transcriptase, different from NRTIs
results in blockade of RNA and DNA dependent DNA polymerase activity
do not compete with nucleoside triphosphatesdo not require phosphorylation these drugs can not be given aloneNevirapine- prevents transmission of HIV from
mother to newborn when given at onset of labor and to the neonate at delivery
Protease InhibitorsThe protease enzyme cleaves
precursor molecules to produce mature, infectious virions
these agents inhibit protease and prevent the spread of infection
These agents cause a syndrome of altered body fat distribution, insulin resistance, and hyperlipidemia
Indinavir and Ritonavir Specific inhibitors of the HIV-1 protease enzyme mediated by expression of multiple and variable protease amino
acid substitutions Side Effects:hyperbilirubinemia Contraindications:inhibitor/substrate for CPY3A4, do not give
with antifungal azoles
Saquinavir A synthetic peptide-like substrate analog inhibits HIV-1 protease prevents cleavage of viral polyproteins
CCR5 and CXCR4 antagonistsVicriviroc (Schering):
Oct, 2005 discontinued Phase II trial due to therapeutic failure in some pts
Aplaviroc (GlaxoSmithKline): Oct, 2005 Phase III trials halted due to hepatotoxicity
Pfizer still has a compound in trials
Anti-viral drugs
Anti-herpes virus agents• Acyclovir / Valacyclovir• Famciclovir / Penciclovir • Ganciclovir / Cidofovir • Foscarnet • Trifluridine / Idoxuridine / Vidarabine
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Anti-viral drugsMechanism of action of Acyclovir and
congeners : All drugs are phosphorylated by a viral
thymidine-kinase, then metabolized by host cell kinases to nucleotide analogs.
The analog inhibits viral DNA-polymerase Only actively replicating viruses are inhibited Acyclovir is thus selectively activated in
cells infected with herpes virus. Uninfected cells do not phosphorylate acyclovir.
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Acyclovir FDA approved in 1982structural analog of deoxyguanosinemechanism of selective toxicity
phosphorylated by viral thymidine kinase (TK) preferential incorporation by viral DNA polymerase causes chain termination
~20% oral bioavailability (valacyclovir is 3-5X better)
penetrates CSFeffective in treating
◦ primary Herpes infections (genital, encephalitis, neonatal)
◦ chronic Herpes (does not cure but can reduce recurrence)
Acyclovirmechanism of action
Resistance to acyclovirchronic therapy with acyclovir, valacyclovir,
famciclovirmutations in viral TK gene
◦alter affinity for drug or just completely inactivate the gene
viral DNA polymerase mutations◦reduce recognition of phosphorylated
drug as substrate for DNA synthesis
Ganciclovirfor CMV, varicella zoster (chicken
pox/shingles)similar to acyclovir6-9% oral bioavailabilitypenetrates CSFmore active than acyclovir against CMVtoxicity: bone marrow suppression, CNS
(headaches, convulsion, psychosis)◦some toxic effects seen in about 40% of pts
Foscarnetbinds to pyrophosphate site of viral
polymerase (also RTase)100 fold greater selective inhibitor or viral
versus human polymerasepoor oral bioavailabilitynephrotoxicity is high (~50%) but reversiblehypocalcemia and CNS toxicity is also
significant (25% pts)useful in acyclovir/ganciclovir resistant HSV
or CMV
Virus
Diseases Drug(s) of choice
Alternative drugs
FLU A
Influenza
Amantadine Rimantadine
RSV Pneumonia,bronchiolitis
Ribavirin(aerosol)
HSV
Genital herpes
Acyclovir
Foscarnet
Keratitis
Conjunctivitis
Trifluridine IdoxuridineVidarabine
Encephalitis
Acyclovir
Neonatal HSV
infection
Acyclovir
Vidarabine Herpes infections in
immuno- compromised host
Acyclovir
Foscarnet37
VZV
In normal host
No therapy
In immunocompro-mised host, or during pregnancy
Acyclovir
Foscarnet
CMV
Retinitis
Ganciclovir
Foscarnet
HIV
AIDSHIV antibody positive with CD4 count < 500/mm3
Zidovudine ± protease inhibitors
Didanosine,Stavudine
HBVHCV
Hepatitis B, C
Interferons
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