HIV Life Cycle - In Search of Drug Targets. Jump to first page

Transcription

1

2 HIV Life Cycle - In Search of Drug Targets

3 A Closer Look at Reverse Transcription Viral RNA C-G-C-A-A-U-A-A-A-G-C-U-U-G-C-C-U-U-G-A-G... Template G-A-A-C-U-C Reverse Transcriptase dntp s dgtp, dctp datp, dttp Transfer RNA Primer RNA-Directed Polymerase Activity Viral RNA C-G-C-A-A-U-A-A-A-G-C U-U-G C-C-U-U-G-A-G... Template T-C-G-A-A-C-G-G-A-A-C-U-C Viral DNA Transfer RNA Primer

4 A Closer Look at Reverse Transcription Viral RNA C-G-C-A-A-U-A-A-A-G-C-U-U-G-C-C-U-U-G-A-G... Template T-C-G-A-A-C-G-G-A-A-C-U-C Reverse Transcriptase Viral DNA Transfer RNA Primer RNase H Activity C Viral RNA C- G-C-A-A-U-A-A-A-G-C U U G U-U-G-A- G... Template T-C-G-A-A-C-G-G-A-A-C-U-C Viral DNA C Transfer RNA Primer

5 A Closer Look at Reverse Transcription RNA-directed DNA polymerase/rnase H RNA-directed DNA polymerase/rnase H DNA-directed DNA polymerase DNA-directed DNA polymerase Full-length, double-stranded pro-viral DNA

6 Nucleotide Analogs Anatomy of a dntp Triphosphate O Sugar HO O O O O H Base HO O

7 Nucleotide Analogs Triphosphate O O X MODIFIED Sugar O O X Base

8

9 Nucleotide Analogs Triphosphate Can not get into cells Nucleoside Analog (no Phosphate) X MODIFIED Sugar O HO Base X Transport/Diffusion into Cells Cellular Enzymes

10 NRTIs = Nucleoside reverse transcriptase inhibitors NtRTIs = Nucleotide reverse transcriptase inhibitors

11 HIV-Infected Cell Selectivity? NRTI or NtRTI Uninfected Host Cell DNA Synthesis (Reverse Transcriptase) Active Triphosphate Form DNA Synthesis (Pol-gamma - mitochondria) Viral Replication Cell Growth and Metabolism

12 Examples of Clinically Useful Anti-HIV NRTIs and NtRTIs - ZDV Zidovudine (1987) - ddi Didanosine (1991) - ddc Zalcitabine (1992) - d4t Stavudine (1994) - 3TC Lamivudine (1995) -Abacavir (Ziagen) - (1998) -Tenofovir disoproxil (Viread) (2001)

13

14 HIV Infection Critical Insights from HIV RNA Quantification Studies CD4+ Cells (cells per mm 3 ) Virions / Day ~180 generations/yr Latent Period 10 7 HIV RNA (copies per ml plasma) weeks years

15 RESISTANCE replications/day x 10-5 mutations per nucleotide per replication x 10 4 nucleotides/genome = 10 9 mutants a day! RESISTANCE is due to Mutation Mutations (Resistance) can Happen BEFORE Drug Therapy - Drugs Select for Mutant Virus Mutations (Resistance) can Happen DURING Drug Therapy - If replication is not inhibited completely

16 Resistance AZT Correlation with Stage, CD4, duration e.g. After 1 year monotherapy in AIDS -> 90% resistance vs 30% in asymptomatic Specific mutations in Reverse Transcriptase not only in dntp binding site, but also in primer-template binding site New infections with resistant strains on the rise 1/3 high-level resistance

17 Resistance Develops quickly with monotherapy Cross resistance: ddi resistant strains - cross resistant to ddc, D4T, 3TC D4T resistant strains - cross resistant to ddi, ddc, 3TC etc. Abacavir resistant strains resistant to ddi, ddc but increased sensitivity to AZT Similarly, 3TC can cause AZT-resistant strains to become more sensitive.

18 Reverse Transcriptase Resistance to NRTIs NTRI-TP Mutant RT Mutant RT Mutant RT Decreased Binding Primer Unblocking Mutant RT Chain-Terminated (Dead-end) Product

19

20

21 Combinations of Nucleoside Analogs ddi + AZT - More effective than AZT alone in delaying progression and death in initial to late stage HIV disease. Other combinations: AZT + 3TC d4t + 3TC d4t + ddi Slower onset of resistance Cumulative, not synergistic, toxicities

22 Nucleoside Analogs - In Development D-D4FC (Reverset) - ddc analog with increased potency against AZT-resistant virus - once a day dosing. In Phase III clinical trials. Elvucitabine - novel nucleoside analog with unique resistance profile. Failed Phase I/II clinical trials due to bone marrow toxicity.

23 Non-Nucleoside Reverse Transcriptase Inhibitors (NNRTI s) Results of Random Screening Efforts Many different compounds found (over 30 separate classes) Specific for HIV-1 Unique Mechanism

24 Non-Nucleoside Reverse Transcriptase Inhibitors (NNRTI s) Nevirapine (Viramune) Delaviridine (Rescriptor) Efavirenz (Sustiva) Common problems: Resistance! Side Effects (Fever/rash) Drug Drug Interactions (Induce metabolism of protease inhibitors) Twice/Three-times a day dosing (except Sustiva)

25 NNRTIs In Development Capravirine - Very promising activity, higher than any approved NNRTI, slower development of resistance Phase II TMC125 - Active against virus resistant to other NNRTIs Phase II

26 HIV Protease Inhibitors HIV Protease: An Autocatalytic Enzyme gag-pol polyprotein (contains the protease) protease Other HIV proteins (RT, IN, gp120, p24, etc) protease

27

28

29

30

31 Immature HIV virions budding from infected T-cell

32 Protease Inhibitors - Lead Compounds Hypertensive Cascade: Angiotensinogen Renin Similar to HIV Protease Angiotensin I Angiotensin-Converting Enzyme (ACE) Angiotensin II (Increases Blood Pressure)

33 Protease Inhibitors

34 Protease Inhibitors

35 Protease Inhibitors

36 Protease Inhibitors Indinavir (Crixivan) (1996) Saquinavir (Fortovase) ( ) Ritonavir (Norvir) ( ) Nelfinavir (Viracept) (1997) Amprenavir (Agenerase) (1999) Kaletra (ritonavir + lopinavir) (2000)

37 HIV Protease Inhibitors Major problems with existing drugs: Resistance Pharmacokinetics - drugs are eliminated quickly, primarily via metabolism. Requires multiple or restrictive dosing. Inhibition or extensive metabolism by cytochrome enzymes Hyperlipidemia - Current drugs can exacerbate HIV-related elevation in lipid levels in certain patients

38 Protease Inhibitors - Resistance

39 HIV Protease Inhibitors in Development Tipranivir - Phase 3. Active against HIV strains resistant to other protease inhibitors. - requires ritonavir boosting for pharmacokinetics.

40 Triple-Drug Cocktails AZT + 3TC + (indinavir or ritonavir) AZT + ddc + saquinavir Sustiva + AZT + 3TC (Current standard) * Time-to-Treatment-Failure FDA standard Lower viral load (RNA copies / ml plasma) to undetectable levels (From 200,000-1,000,000 copies / ml to less than 50) For up to 1 year in 90% of patients Lower rate of progression to AIDS

41

42 Triple-Drug Cocktails Resistance (increased viral load) does eventually develop in some patients However, cessation of therapy causes rapid onset of symptoms Even in face of increased viral load, continued therapy helps

43

44

45