Targets for Anti-viral therapy

2. 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)

3. Acyclovir • FDA approved in 1982 • structural analog of deoxyguanosine • mechanism 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 CSF • effective in treating • primary Herpes infections (genital, encephalitis, neonatal) • chronic Herpes (does not cure but can reduce recurrence)

4. Acyclovir mechanism of action

5. Acyclovir is activated and concentrates in HSV infected cells

6. Treatment of HSV Recurrent infections • chronic therapy with acyclovir, valacyclovir, famciclovir • therapeutic vaccines: using HSV-2 surface protein gD2 -has shown 30% reduced recurrence • immune response modifiers: imiquimod/resiquimod -act by inducing cytokines (interferon alpha, interleukins) that stimulate macrophage and antigen presenting cells • -clinical trials were initially promising but have now been halted due to lack of sufficient therapeutic effect

7. Resistance to acyclovir • mutations 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

8. Virus prevents glycolipid antigen presentation to natural killer T cells by down regulating CD1d expression antigenic glycolipids endogenous phospholipids LTP=lipid transfer protein

9. Ganciclovir • for CMV, varicella zoster (chicken pox/shingles) • similar to acyclovir • 6-9% oral bioavailability • penetrates CSF • more active than acyclovir against CMV • toxicity: bone marrow suppression, CNS (headaches, convulsion, psychosis) • some toxic effects seen in about 40% of pts

10. Foscarnet • binds to pyrophosphate site of viral polymerase (also RTase) • 100 fold greater selective inhibitor or viral versus human polymerase • poor oral bioavailability • nephrotoxicity is high (~50%) but reversible • hypocalcemia and CNS toxicity is also significant (25% pts) • useful in acyclovir/ganciclovir resistant HSV or CMV

11. Interferons Interferons are glycoproteins that come in 3 varieties: a (made in leukocytes) b (made in fibroblasts) g (made in T cells) activated T cells produce g interferon to modulate the immune response induced by viral infection, IL1, IL2, TNF

12. Cytokine signaling pathway

13. Multiple Pathways of Interferon Action

14. Clinical use of Interferon • alpha 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

15. 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

16. Recent report (Oct. 2003) of a novel protease inhibitor that blocks protease required for Hepatitis C Virus function

17. Telaprevir (VX-950) with peg-IFN looks promising in clinical trials

18. Anti-influenza virus drugs • Amantadine, Rimantadine • 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

19. Targets for treatment of HIV (anti-retroviral drugs

20. Zidovudine (AZT)RTase inhibitor • from bench to bedside in about 1 yr. • Oct 85--in vitro activity • Feb 86--clinical trial halted • <1% death rate on AZT 12% death rate on placebo • Oct 86--available in Seattle • Jan 87--FDA approved • only drug specifically for HIV until lamivudine developed in 1995

21. Zidovudine • mechanism • selective reverse transcriptase inhibitor

22. Zidovudine (AZT) (thymidine analog)

23. Mechanism of selective toxicity of AZT DNA synthesis AZT concentration (uM)

24. Zidovudine • mechanism • selective reverse transcriptase inhibitor • pharmacokinetics: • 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

25. Lamivudine (3TC) • similar to zidovudine • resistance develops quickly: selects for met184val mutation in RTase • lamivudine + zidovudine combination dramatically slows resistance development

26. NNRTIs (non-nucleoside reverse transcriptase inhibitors)

28. HIV-1 protease stereo-structure with Sequinavir

29. SAQUINAVIR INDINAVIR RITONAVIR NELFINAVIR AMPRENAVIR LOPINAVIR

31. Drug regimen does not attack non-replicating virus

32. CCR5 and CXCR4 antagonists • Vicriviroc (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

33. gp120 gp41 virus

34. Effects of Fuzeon (enfuvirtide, T-20) treatment on viral load (FDA approved in March, 2003)

35. Initial Treatment: Preferred Components *Avoid in pregnant women and women with significant pregnancy potential. **Emtricitabine can be used in place of lamivudine and vice versa. NNRTI Option NRTI Options • Tenofovir + emtricitabine** • Zidovudine + lamivudine** OR + PI Options

36. Initial Treatment: Alternative Components *Nevirapine should not be initiated in women with CD4 counts >250 cells/mm3 or men with CD4 counts >400 cells/mm3 **Atazanavir must be boosted with ritonavir if used in combination with tenofovir NNRTI Option NRTI Options • Abacavir + lamivudine • Didanosine + (emtricitabine or lamivudine) OR PI Options

37. How does HIV escape the host defense mechanisms? • APOBEC3G is a host cytosine deaminase that mutates the viral DNA and would destroy it • HIV expresses a protein, vif, that binds C3G and targets it to the proteasome for degradation

38. APOBEC3G is a cellular cytidine deaminase that inactivates HIV by causing strand breaks or hypermutation • Viral vif protein targets APOBEC3G for degradation by the proteasomal pathway

39. Therapeutic Implications? • drugs that could interfere with APOBEC3G/vif interaction would block production of infectious virus • gene therapy with vif resistant APOBEC3G? • patients with polymorphisms in APOBEC3G may be more or less resistant to HIV infection? • high mutation rate due to cytidine deaminase activity of APOBEC3G may increase rate of drug resistance development • probably explains why HIV is so species specific • vif may interact with the primate APOBEC3G selectively

40. Number of people living with HIV