Pharmaceutical Approaches to Antiviral Drug Discovery

1. Pharmaceutical Approaches to Antiviral Drug Discovery Peter S. Dragovich Pfizer Global Research and Development La Jolla Laboratories

2. Today's Focus Drug Discovery/Development Pipeline • Multifaceted, complicated, lengthy process Pre-clinical Pharmacology Clinical Pharmacology & Safety Pre-clinical Safety Products Exploratory Development Full Development Discovery Phase I Phase II Phase III 0 15 5 10 Drug Idea 12 -15 Years

3. Product Profiles Target Identification Lead generation Lead optimization Clinical Commercial TA Lead. Virology Cell Biol. Mol. Biol. Biochem. HT Screening HT Chem. Comp. Chem. Crystallog. Med. Chem. Res. Pharm. PDM Safety Process Chem. Drug Discovery Pipeline • Multifaceted, complicated, lengthy process • Up to 5 years to complete development transition Start 3-5 years Dev.

4. Identify differentiation basis for new therapy • potency/efficacy • dose size/frequency 0.01 0.1 1.0 10.0 Concentration (g/ml) Lab objectives which address desired profiles Patient/Product Profiles • Identify areas of high unmet medical need • Sub-optimal or no existing therapies • resistance profile • safety/tolerability

5. Target Identification • Biological entity associated with disease of interest (host or virus origin) • Appropriate modulation of target anticipated to impact disease in manner consistent with product profile Drug Discovery Pipeline Start 0.5-1 year Product Profiles Lead generation Lead optimization Dev.

6. 2. Replication 1. Entry 4. Release 3. Assembly Target Identification • Analyze virus life cycle • Identify critical points for intervention (host or virus origin) Host Cell Nucleus

7. Well defined active (binding) site Difficult to incorporate all criteria in single target Target Identification Criteria • Activity/function essential for viral replication • Proven or inferred through biological experimentation • Drugable target (subjective!) • Known small molecule inhibitors • Historical success against related targets • Conservation across virus variants (where applicable) • Selectivity vs human proteins

8. 1 2 3 4 Pr55 gag p24 p1 p9 p6 p17 8 6 7 5 p24 p1 TF PR RT RN IN Pr5160 gag-pol p17 • Aspartyl protease • Potent renin inhibitor examples • Large, lipophilic molecules Ki <1 nM (human renin) Target Identification • Example: HIV Protease • Importance inferred from biology; proven through experimentation1,2 1. Kohl, N. E.; et al. Proc. Natl. Acad. Sci. USA1988, 85, 4686. 2. Kramer, R. A.; et al. Science1986, 231, 1580.

9. Identify molecule(s) which interact with chosen target • Biological properties attractive/promising but not ideal • Amenable to analog production Drug Discovery Pipeline Start 0.5-1 year Product Profiles Target Identification Lead generation Lead optimization Dev.

10. Need reliable and accurate biological assays • Routine production of target protein • Primary biochemical assay • Primary antiviral assay Lead Generation • Secondary assays (counterscreens)

11. DNA/RNA template Synthesized DNA • Incorporated into viral DNA by RT enzyme • Terminates synthesis (lacks 3'-hydroxyl) AZT AZT Lead Generation • Substrate/Ligand analogs • Biology or target mechanism must be known • Example: HIV RT nucleoside inhibitors Deoxythymine substrate

12. Lead Generation • High-throughput screening • Large chemical archives (500K to 2MM compounds) • Miniaturization = improved cost-effectiveness

13. Efavirenz Lead Generation • High-throughput screening • Allows for chance discovery of novel inhibitors • Example: HIV RT non-nucleoside inhibitors • Bind to allosteric site on enzyme surface • Disrupt enzyme structure/function

14. Prepare/synthesize analogs of leads • Improve biological properties • Optimized compound(s) suitable for clinical development Drug Discovery Pipeline Start 2-3 years Product Profiles Target Identification Lead generation Lead optimization Dev.

15. Structure-based design Combinatorial Chemistry Computational evaluation Biochemical assays Antiviral assays Met./abs./sol. assays Pharmacokinetics in vitro / in vivo Safety assessments Typical project progression Development Candidate Lead Optimization • Iterative process impacted by technology Idea Generation Chemical Synthesis Data Analysis Biological Evaluation

16. Future AV Discovery Needs • Continued understanding of patient and physician needs Product Profiles Target Identification Lead generation Lead optimization Start Dev

17. Target Identification Future AV Discovery Needs • Good understanding of patient and physician needs • Better understanding of virus biology • New target opportunities • Rapid identification of new viral diseases (SARS) • Improved association of viral infection with existing diseases Product Profiles Lead generation Lead optimization Start Dev

18. Future AV Discovery Needs • Improvements in drug discovery/development processes • Shorten timelines • Reduce attrition Lead optimization cycle times Safety predictions Clinical development times Products Exploratory Development Full Development Discovery Phase I Phase II Phase III 0 15 5 10 Drug Idea 12 -15 Years

19. Product Profiles Target Identification Lead generation Lead optimization Summary • Antiviral drug discovery • Multifaceted, complicated, lengthy process • Application will lead to future antiviral therapies which address areas of high unmet medical need Start 3-5 years Dev.

20. Acknowledgements Marc Deller Jay Davies Amy Patick Rich Michitsch Larry Truesdale