Are animal models a good surrogate of efficacy? / Division of HIV/AIDS Prevention Are animal models a good surrogate of efficacy? J. Gerardo Garcia-Lerma, Ph.D. Laboratory Branch, Division of HIV/AIDS Prevention, Centers for Disease Control and Prevention, Atlanta, GA, USA

Conflict of Interest Named in patents on “Inhibition of HIV Infection Through Chemoprophylaxis”

Importance of animal models for HIV prevention research Possibility to model PrEP under highly controlled conditions (dose of drug and timing of dosing, size of virus inoculum, route of virus exposure) Assess relationship between efficacy and pharmacologic parameters (PK-PD relationship) Help product prioritization and advancement of most promising products into human clinical trials

Key considerations for assessing PrEP strategies in animal models Pharmacological aspects Transmission component Model clinically-relevant drug doses Adjust doses based on differences in size/metabolism with humans (allometric scaling) Incorporate drug measurements at the mucosal sites of infection Use physiologic virus doses that better mimic HIV infectious doses in humans Select appropriate animal species (humanized mice, rhesus/pigtail macaques) and transmission model (single vs. repeated virus exposures) Combine relevant drug pharmacology and physiologic HIV transmission

Key features of the repeat low dose macaque model Exposures to low and more physiologic virus doses Virus exposures repeated to mimic high-risk human exposures to HIV Better simulate HIV exposures in humans than do previous models with single high-dose virus challenge Stronger statistics but small animal numbers Rectal and vaginal models in rhesus and pigtail macaques Pigtails are preferred species to evaluate efficacy against vaginal infection

Pre-clinical testing in the repeat low dose macaque model Dose selection Protective efficacy (rectal/vaginal) Drug correlate of protection Oral FTC/TDF Injectable cabotegravir long-acting Oral tenofovir alafenamide Oral maraviroc

Clinically-relevant doses of FTC and TDF in macaques

Efficacy of oral FTC/TDF combination in the repeat low-dose macaque model Garcia-Lerma et al., PLoS Med 2008 Radzio et al., PLoS One 2012

High efficacy of oral FTC/TDF in the presence of potential modifiers Exposure to FTC and TFV-resistant viruses containing M184V or K65R (Cong et al., J Virol 2011; Cong et al., J Infect Dis 2013) Thinning of the vaginal epithelium associated with DMPA treatment (Radzio et al., AIDS 2014; Radzio et al., J AIDS 2014) Increased susceptibility to infection due to co-infection with Chlamydia trachomatis and Trichomonas vaginalis (Radzio et al., J Infect Dis 2016)

Biological efficacy of FTC and TDF in macaques and correlation with humans

iPrEX: 16 fmols/106 cells (95% CI; 3-28) TFV-DP EC90 for protective efficacy 23 fmols/106 cells (95% CI; 14-61) (5 fmols/106 cells ~ 40% reduction in risk of SHIV acquisition) Anderson et al., J Antimicrob Chemother 2014 Anderson et al., Sci Trans Med 2012

Injectable cabotegravir long-acting

Cabotegravir long-acting: dose selection studies HUMANS MACAQUES Half-life; 20-50 days Half-life; ~11 days I am going to now move on into 2 next-generation PrEP agents that are now in clinical testing. The first is cabotegravir, an HIV integrase inhibitor analog of dolutegravir that has been formulated as a long-acting nanosuspension. As you know, one of the most attractive characteristic of this formulation is the long plasma half-life life that makes it suitable for administration every 2 months. Indeed, pre-clinical evaluation of CAB LA in macaque first required dose-selection studies to identify clinically-relevant doses. This is the work that was done at the ADARC where they identified a 50 mg/kg dose as sufficient to maintain drug concentrations above the target 4x PA-IC90. Now, because of the shorter half-life of CAB in macaques and humans, this dose needs to be administered every month and not every 2-3 months as in humans. Andrews et al., Science 2014 Spreen et al., J AIDS 2014

The same research group designed a series of very elegant studies where they investigated both the protective efficacy of CAB LA and the concentrations of plasma CAB that are associated with protection. In these studies the macaques received a dose of CAB and were exposed weekly to SHIV as the concentrations of drug declined over the weeks. This panel shows how virus breakthroughs started to come up as the concentrations of CAB fell below the significant delayed infection. Andrews et al., Science 2014

CAB LA protects macaques against high and low dose intravaginal SHIV challenges High dose SHIV transmission model Low dose SHIV transmission model Andrews et al., Sci Trans Med 2015 Radzio et al., Sci Trans Med 2015

Oral tenofovir alafenamide

Tenofovir alafenamide: dose selection Massud et al., J Infect Dis 2016 Cottrell et al., J Antimicrob Chemother 2017

Efficacy of oral FTC/TAF and TAF against rectal SHIV infection FTC/TAF combination TAF alone (1 weekly dose) Massud et al., J Infect Dis 2016 Garcia-Lerma et al., J Virol 2011

Oral maraviroc

Lack of prophylactic efficacy of oral maraviroc despite high drug concentrations in rectal tissues High and durable MVC concentrations in rectal tissues not sufficient to prevent infection in macaques [MVC] below the threshold required to block a dense population of CCR5+ cells in the rectal mucosa Biochemical differences between human and macaque CCR5 Other mechanisms associated with MVC treatment including potential modulation of immune responses and susceptibility to infection Massud et al., J Virol 2013

Summary Macaque modeling that incorporates clinically-relevant drug doses predicted efficacy of PrEP with FTC/TDF Identified similar TFV-DP protective levels than in humans Reassuring data with FTC/TDF reinforces the need to build on this modeling approach Proof of concept studies with CAB LA and TAF; defined CAB protective levels in macaques Data on efficacy in humans (Discover, HPTN 083/084) will further inform on predictive value of the model Approach may help prioritization and advancement of promising products; large product pipeline (implants, inserts, others) and increased cost of phase 3 trials

Acknowledgements Division of HIV/AIDS Prevention, CDC Jessica Radzio Ivana Massud Mian-er Cong Wutyi Aung James Mitchell Shanon Ellis Frank Deyounks Kristen Kelley Leecresia Jenkins David Garber Debra Hanson Chou-Pong Pau Amy Martin Angela Holder Susan Kuklenyik (NCEH) John Barr (NCEH) Ron Otten Tom Folks Walid Heneine UCSF David Glidden University of Colorado Peter Anderson Lane Bushman Gilead Sciences Darius Babusis Adrian Ray Michael Miller James Rooney ViiV Healthcare Yun Lan Yueh William Spreen