1. Pharmacology of antiretrovirals and chemoprophylaxis Stephen Kerr, PhD HIV-NAT, Thai Red Cross AIDS Research Centre Kirby Institute, UNSW

2. Introduction Urgent need for Primary HIV Prevention strategies –34 million people living with HIV in 2011 –2.5 million new HIV infections (UNAIDS 2012 Global Report) –High risk groups: young women, sero-discordant couples, MSM, IDU Evidence for ART as a tool in HIV prevention –Prevention of mother to child transmission –HPTN 052 - Reduced infectiousness of persons on ART –Prophylaxis after high risk exposure (PEP) –Continuous/intermittent use for persons with ongoing exposure – pre-exposure prophaylaxis (PrEP)

3. What are the desirable characteristics for PrEP? Safe –Low toxicity potential Effective –Should have significant efficacy in ‘real life’ situations Pharmacokinetic properties –Rapidly target the appropriate sites of infection, in the correct concentrations, and for the right amount of time Cost-effective –Must be affordable in ‘at risk’ populations Acceptable –Topical agents must be acceptable when used in conjunction with sex; oral agents should have low pill burden Good resistance profiles –Use for prevention should not limit therapeutic options for people who become infected

4. Balance of vulnerabilities between virus and host Infection established Small founder populations of immune cells in female genital tract, colo- rectum, male foreskin & urethra Local expansion Early signal amplification Influx of CD4+ cells Seeding to distal sites Systemic dissemination Establishment of lymphatic tissue reservoir High levels of viral replication Depletion of gut CD4+ cells Virus vulnerability Hours Window of opportunity for PrEP DaysWeeks Adapted from Garcia-Lerma, JG et al, Trends Pharm Sci, 2010; 31(2):74

5. Viral life cycle Shattock R J, and Rosenberg Z Cold Spring Harb Perspect Med 2012;2:a007385

6. Pharmacokinetic-pharmacodynamic relationships Dose administered Concentration at site of action Drug effects (therapeutic/adverse) Pharmacokinetics (PK) - Absorption - Distribution - Metabolism - Elimination Pharmacodynamics (PD) - How do in vivo drug concentrations relate to protective/toxic effects - Limited understanding for PrEP Inter-patient variability

7. Physical characteristics affect distribution Class/DrugPlasma protein binding PI95 – 99% NRTI7 – 49% Maraviroc85% Raltegravir83% Only free drug can freely diffuse across membranes: Other physical characteristics important (eg ionization state at physiological pH) Different relationships exist for systemic/genital/rectal compartments

8. Pharmacology of TFV and FTC TDF versus TVF TVF & FTC require intracellular phosphorylation NTRI-phosphates are ionized and persist in the cellular site of action after the drug is cleared from plasma 150

9. Drug distribution into compartments Modified from Nichol, MR. & Kashuba, ADM. Clin Pharm Ther. 2010; 88(5)598 Oral TDF±FTC Genital/rectal secretions Topical TVF Blood PlasmaGenital/rectal tissue Mononuclear cells TotalFUB TotalFUB TVF-DP FTC-TP TVF FTC Compartmental drug concentration vs time - Sufficient concentrations/time periods 1.Tissue compartments: multiple sub-compartments – homogeneous drug? 2.Only specific tissue sub-compartments are susceptible to HIV 3.Some susceptible target cells circulate in and out of compartments

10. Viral distribution and elimination after intercourse Advanced imaging techniques, with cell free and cell associated HIV radiolabelled surrogates and simulated intercourse Females (Louissant, NA. et al JID 2012; 205:725) : –Retention in the vaginal lumen, concentrated in peri-cervical area –1/3 of administered dose retained at 4 hours Males (Louissant, NA. et al JAIDS 2012; 59:10) : –Retention in the lumen, distribution to the rectosigmoid colon –Detectable at low levels at 24 hours ART compartmental concentrations need to be maintained at sufficient levels for 24 hours after viral exposure Modified from Nichol, MR. & Kashuba, ADM. Clin Pharm Ther. 2010; 88(5)598

11. Conc vs time in plasma & female genital tract after oral TDF & FTC Drummond, JB et al. AIDS. 2007; 21(14)1899

12. C 24hrs of TDF/FTC after a single oral Truvada dose C 24hrs (ng/mL, ng/g or fmol/g) Patterson, KB et al. Sci Trans Med. 2011; 3(112)112re4 100X10X

13. TVF concentrations – different administration routes MTN-001: crossover study of oral TDF:1% vaginal gel TFV C plasma 60x higher after oral vs vaginal administration TFV-DP C vaginal tissue 130x higher with vaginal vs oral administration TFV C rectal fluid 5x higher with vaginal vs oral administration Hendrix et al. (2013) PLoS ONE 8(1): e55013

14. Human clinical studies reported Stopped early for futility Percent effectiveness - ITT 44% 39% 62-75% 49% Lower or undetectable drug concentrations in subjects who seroconverted versus those who did not

15. PrEP Studies with positive results N= 4747 M, F N= 4747 M, F N= 1219 M, F N= 1219 M, F N= 2499 MSM, TG N= 2499 MSM, TG 82% TDF detected 80% TDF detected 51% TDF detected N= 2413 IDU, M,F N= 2413 IDU, M,F 66% TDF detected Effectiveness Slide adapted from Kiat Ruxrungtham

16. The STRAND Study Open label, randomized, crossover study of TDF. 12 men and 12 women, HIV-negative Each subject received 2, 4 or 7 TDF per week, for 6 weeks Doses were directly observed M-F, and confirmed by text messaging or telephone on weekends TDF-DP was measured in PBMC at the end of each 6 week dosing period A pre-specified analysis was conducted with subjects from iPrEx

17. Estimated HIV incidence in iPrEx Anderson, PL et al. Science Translational Medicine (2012) 4(151):151ra125 16 fmol/10 6 PBMC reduced HIV incidence by 90%

18. Infection rates in CAPRISA 004, by TDF concentrations in CVF Abdool Karim, SS et al. The Lancet (2011) 378:279

19. Studies with negative results? Discordant results may relate to: –Incidence of HIV in the population –Trial design/dosing regimen –Adherence to the study medications –Sexual behaviours FEM-PrEP –Less than 30% of subjects who acquired HIV had TFV concentrations in plasma ≥ 10ng/mL (discordant pill count data) VOICE –<30% had detectable TDF in plasma, and adherence was worse amongst younger, unmarried women most at risk for HIV (based on pill and un-used applicator counts, adherence was ~90%)

20. Improving our understanding of PK/PD relationships Non-human primates and humanized mice models –Histologic/biologic similarities & differences to humans –Optimization and standardization of sampling & processing –Standaridzation of dosing and virus challenge Ex vivo studies – suggest dose response relationships, but further development needed Dose fractionation studies to establish concentration- time relationships: C max, AUC, MIC and time > MIC Assays need to discriminate between free and protein-bound concentrations in sub-compartments Aromano, J et al. AIDS Research Human Retroviruses (2013) doi: 10.1089/aid.2013/0122

21. Summary Drug concentrations for protection relate to route of viral exposure (vaginal, penile, rectal) Drug concentrations at active sites differ by drug and administration route Consistent PrEP use is associated with a protective effect in individuals with ongoing/repeated exposure to HIV Limited data is available from human clinical studies and greater understanding of PK-PD relationships in animal and ex vivo models is needed to inform evidence based practice