1. HIV-1 Resistance - Implications For Clinicians Joseph J. Eron Jr., MD Professor of Medicine University of North Carolina

2. Disclosures

3. Types of Resistance Tests Genotype and Phenotype

4. Types of Resistance Tests Genotype –HIV gene sequencing of the patient’s virus to detect mutations known to confer drug resistance Phenotype –Measures ability of a recombinant virus derived from the patient sample to grow in different concentrations of antiretroviral drugs Hirsch et al. Clin Infect Dis. 2003;37:113-28.

5. Interpretation of Genotypic Assays Is an indirect measure of resistance –Requires knowledge of which mutation are associated with a change in susceptibility Expert advice –May not be available –Experts’ views may be inconsistent Rules-based algorithms –Provided by most labs, third-party sites –Need regular updating Virtual Phenotype (VircoType) –Phenotypic information using genotype –Database of matched genotypes and phenotypes

6. Question: What is the significance of the RT mutation K103N? Confers resistance to 3TC/FTC Confers resistance to tenofovir Confers resistance to efavirenz All of the above None of the above

7. Provider Knowledge of Specific Resistance Mutations Mutations % Providers Recognizing Specific Mutations Salama et al. Clin Infect Dis. 2003;36:101-4. N = 100

8. Phenotypic Susceptibility Relationship Between Drug Concentration and Viral Inhibition Inhibition of Virus Replication (%) 50 0 100 Fold resistance Wild-type IC 50 Resistant IC 50 Wild-type Resistant Drug Concentration

9. Interpretation of Phenotypic Assays Results reported as IC50 or fold-change (FC) compared with IC50 of wild-type virus Individual results provided for each drug Thresholds to define reduced susceptibility –Biologic cutoff: based on biologic variations in treatment- naïve patients (usually 2 SD > median) –Clinical cutoff: As good as clinical data used to estimate cut points Resistance is a continuum – precise breakpoints unlikely Two relevant breaks? –Decreased response and –Minimal response

10. Question: Resistance testing should be obtained in which treatment naïve patients? Only in HIV infected patients with acute infection Individuals thought to have been infected within the last 2 years All treatment naïve patients

11. Transmitted ARV Resistance Clinically Important in the Developed World Surveillance Essential in the Developing World

12. How Common is Drug Resistance at Diagnosis? US Variant, Atypical and Resistant HIV Surveillance System (VARHS) –Estimate prevalence of transmitted resistant mutations –Determine distribution of HIV subtypes March 2003 to October 2006; 11 states, 409 sites, n=3130 10% 5% AnyNRTINNRTIPI MDR M41L 45.1% of NRTI K103N 70.1% of NNRTI L90M 40.0% of PI 95% Subtype B Wheeler et al. 14 th CROI, 2007. Abs 648 6.9% 3.6% 2.4% 1.9%

13. FTC-301A: Impact of Baseline Resistance on Treatment Outcome Borroto-Esoda et al. AIDS Res Hum Retroviruses 2007;23:988-95. Mutation type: Naïve pts, baseline VL > 5000 copies/mL FTC + ddI + EFV (n=270) d4T + ddI + EFV (n=276) Incidence (%) of Virologic Failure

14. How Important Are Minority Variants?

15. Standard Genotype 181C 103N 190A 108I

16. Antiretroviral Response Following sdNVP Lockman et al. NEJM 2007;356:135-47. Cumulative Rate of Failure (%) Women Starting ART <6 Months Post Partum Months Since the Start of ART Women Starting ART ≥6 Months Post Partum 60 50 40 30 20 10 0 Placebo Single dose of NVP Placebo Single dose of NVP 061218243036 Months Since the Start of ART 60 50 40 30 20 10 0 061218243036

17. Resistance and Virologic Failure Multiple Causes of Virologic Failure Replication in the Presence of Antiretrovirals Results in Resistance

18. Resistant virus Social/personal issues Regimen issues Toxicities Poor potency Wrong dose Host genetics Poor absorption Rapid clearance Poor activation Drug interactions Insufficient drug level Viral replication in the presence of drug Resistant virus Poor adherence Treatment-Experienced Patients: ARV Treatment Failure ART resistance testing. National resource center. Available at: http://www.aidsetc.org/aidsetc?page=et-01-00. Accessed November 29, 2006. Pre-existing resistance

19. Management of Virologic Failure in Treatment Experienced Patients Definition: detectable plasma HIV RNA on therapy ‘Is it time to switch therapy?’ –Obtain resistance testing –Assess clinical situation Adherence Previous treatment history – ARV tolerability and toxicity Balance clinical urgency with availability of active agents including new drugs and expanded access New agents – especially those in a new class are likely to have the most activity

20. New Agents in Existing Classes (PI and NNRTI) Resistance Patterns Are More Complex Darunavir 10 codons; 11 substitutions Tipranavir 16 codons; 21 substitutions Etravirine 8 codons; 13 substitutions

21. New Agents in Existing Classes Mutations to older agents are likely to be present –Majority variants –Minority variants Some degree of cross resistance can be anticipated –Cross resistance increases with the number and type of mutations The activity of a new agent from a new class is likely to be more predictable even with state of the art resistance testing

22. New Agents in New Classes CCR5 Inhibitors Integrase Inhibitor

23. CCR5 Inhibitors HIV-1 entry into CD4 cells is dependent on a second receptor: CCR5 (R5 viruses) or CXCR4 (X4 viruses) Early in HIV disease course most individuals have only R5 virus detectable In more advanced disease and highly treatment experienced patients dual tropic virus or mixtures of R5 and X4 viruses are more common CCR5 Inhibitors bind to CCR5 blocking entry –Activity only in patients with R5 virus –Maraviroc and vicriviroc

24. Association Between Emergence of SI Virus and CD4+ Cell Count CD4+ cell count decline accelerates following detection of SI in patients in whom NSI-only virus was previously detected Will emergence of X4 variants on R5 inhibitor therapy lead to CD4 cell decline? -36 Mean (SE) CD4+ Cell Count (cells/mm 3 ) Koot et al. Ann Intern Med. 1993;118:681-688. NSI NSI → SI 800 600 400 200 -12-240122436 Time (Months) 0 -48 SI

25. Prevalence of Coreceptor Tropism 1. Demarest et al. ICAAC 2004. Abstract H-1136. 2. Brumme et al. J Infect Dis. 2005;192:466-474. 3. Moyle et al. J Infect Dis. 2005;191:866-872. 4. Melby et al. J Infect Dis. 2006;194:238-246. 5. Wilkin et al. Clin Infect Dis. 2007;44:591-595. 6. Nelson et al. CROI 2007. Abstract 104aLB. 7. Lalezari et al. CROI 2007. Abstract 104bLB. Study AuthorsPopulation Sample (n)R5 OnlyDual/MixedX4 Only Demarest et al [1] Naive32588%12%0% HOMER [2] Naive97982%18%0.1% Moyle et al [3] Naive40281%19%NA Demarest et al [1] Experienced11767%28%5.0% Moyle et al [3] Experienced12578%22%NA Melby et al [4] Experienced72450%48%2.0% Wilkin et al [5] Experienced39149%47%4.0% Nelson, Lalezari et al [6,7] Experienced107656%44%

26. HIV-1 Resistance to CCR5 Antagonists Two mechanisms –Selection for (emergence of) viral variants that use CXCR4 (dual tropic viruses or mixed populations) Occurs about 2/3 of the time As yet NOT associated with rapid fall in CD4 cell count –Alterations (mutations) in HIV gp 120 No Change in viral tropism Allows virus to use CCR5 with inhibitor bound Plateau in antiviral effect as opposed to change in IC50 –The drug is unable to fully inhibit virus regardless of concentrations achieved

27. Integrase Inhibitors Integrase mechanism has 3 steps –Association with dsHIV DNA – pre-integration complex –3’ processing by integrase enzyme –Strand transfer of HIV DNA into host chromosome Potent inhibitors of stand transfer now in development –Raltegravir – Phase III studies recently presented –Elvitegravir – Phase II studies

28. Integrase Inhibitor Resistance Primary mutations surround the catalytic site Raltegravir –Resistance emerged in 3/4 patients with virologic failure who had genotype results –Two major pathways with apparent primary mutations but one or more additional mutations Likely compensatory for fitness –Cross resistance between integrase inhibitors currently in development appears likely

29. Question: In those patients who have experienced virologic failure on multiple regimens including NNRTI, NRTI and PI, which agent is most likely to be fully active? Darunavir Etravirine Tipranavir Integrase Inhibitors CCR5 inhibitors 4 and 5