CROI 2017 Abstract e-Book

Abstract eBook

Poster and Themed Discussion Abstracts

Results: Results: GS-PI1 is a potent inhibitor of HIV replication in MT4 cells with an EC 50

of 4.9 nM (ATV and DRV EC 50

values are 10.7 and 7.5 nM, respectively), a Hill-slope of 5.0,

and a protein-adjusted EC 95 of 310 nM. Similar antiretroviral potency was observed in PBMCs. GS-PI1 potency was reduced <2-fold against major PI RAMs, whereas ATV and DRV potency shifts are as high as 56 and 35-fold, respectively. GS-PI1 retains a high barrier to resistance emergence in vitro , as evidenced by the lack of viral breakthrough in HIV- infected MT2 cells at a fixed drug concentration equal to 2x its EC 50 . GS-PI1 has oral bioavailabilities of 37% and 18%, and half-lives of 13 and 14 hours in rat and dog respectively. The in vivo half-lives of GS-PI1 are 10 to 40-fold longer than those of ATV (0.37 h rat, 1.3 h dog) or DRV (0.32 h rat, 0.34 h dog). The human predicted clearance (CL) for GS-PI1 is 0.05 L/h/kg (4% hepatic extraction) compared to predicted CLs of 1.20 and 1.07 L/h/kg for DRV and ATV (92% and 83% hepatic extraction), respectively. Conclusion: Conclusion: GS-PI1 represents a new class of HIV protease inhibitor possessing favorable potency, resistance barrier, and in vivo half-lives relative to marketed HIV PIs and has been designed to achieve metabolic stability without pharmacokinetic boosting. GS-PI1 has the potential for once-daily oral dosing without boosting in the treatment of HIV infection. 434 NOVEL NON-CATALYTIC SITE INTEGRASE INHIBITOR WITH IMPROVED RESISTANCE PROFILE Michael L. Mitchell , Mini Balakrishnan, Gediminas Brizgys, Ruby Cai, Eric Lansdon, Andrew Mulato, Mark Osier, Jianhong Wang, Helen Yu, Roman Sakowicz Gilead Scis, Inc, Foster City, CA, USA Background: Non-catalytic site integrase inhibitors (NCINIs) are a promising class of novel antiretrovirals (ARV). Here we describe the search for an NCINI with the potential for low-dose, unboosted once-daily oral dosing, potency against NCINI binding-pocket variants, a high barrier to resistance, and a favorable safety profile. Methods: Novel NCINIs were evaluated against wild-type (WT) and integrase (IN) polymorphic variants of HIV-1, and DMPK properties. Resistance associated mutations were identified through dose-escalation resistance selection. Barrier to resistance was evaluated in a viral breakthrough assay at fixed drug concentrations. Interactions of NCINIs with WT and mutant catalytic core domains of IN were elucidated by X-ray crystallography. Pre-clinical toxicology was assessed in rats and cynomolgus monkeys. Results: GS-9695 was identified as an initial lead with excellent potency against WT HIV-1 (EC50: 1.2 ± 0.2 nM) and majority of IN polymorphic variants (fold shift: 0.2 to 4.7). However, GS-9695 resistance associated with the IN T174I mutation emerged rapidly in vitro. Subsequent NCINI compound optimization screened against the T174I mutant and lead to the identification of GS-9822 with similar antiviral potency (EC50: 3.0 ± 0.9 nM) and superior profile against IN polymorphic variants (fold shift: 0.4 to 1.3). Potent antiviral activity was observed against HIV-1 clinical isolates (mean EC50: 0.7 nM, range: 0.13 to 3.1 nM). GS-9822 had improved potency against the T174I mutant compared to GS-9695 (EC50: 143 vs 917 nM, respectively). Viral breakthrough assays also demonstrated a superior resistance profile for GS-9822 relative to GS-9695. GS-9822 but not GS-9695 maintained interactions with W131 in both wild-type and T174I mutant IN. GS-9822 had high in vitro metabolic stability and favorable oral pharmacokinetic profiles with low systemic clearance in rat, dog and monkeys. However, a key unexpected finding in cynomolgus monkey toxicology studies was a dose-dependent vacuolation of the urothelium of kidney, bladder and ureter. Conclusion: GS-9822 is a novel, potent NCINI with a higher barrier to resistance relative to early prototype NCINIs, and a resistance profile orthogonal to existing antiretroviral agents. GS-9822 exhibited potential for once-daily oral dosing, making it suitable for combination with other ARVs. However, a unique and difficult-to-monitor urothelial toxicity observed in cynomolgus monkeys poses a formidable challenge for further development of GS-9822. 435 MK-8591 CONCENTRATIONS AT SITES OF HIV TRANSMISSION AND REPLICATION Jay Grobler , Carolyn McHale, Carol Freddo, Dan Dreyer, Li Sun, Marissa Vavrek, Sheila Breidinger, Kerry Fillgrove, Daria Hazuda, Ming-Tain Lai Merck & Co, Inc, West Point, PA, USA Background: MK-8591 is a long acting nucleoside reverse transcriptase translocation inhibitor (NRTTI) that has demonstrated potent antiviral activity in HIV-1 infected subjects administered a once-weekly (QW) 10 mg dose as monotherapy in a clinical trial and in SIV-infected rhesus macaque models. MK-8591 extended duration dosing potential was suggested by the long-intracellular half-life of MK-8591-triphosphate (MK-8591-TP) in peripheral blood mononuclear cells (PBMCs) in vitro and in preclinical models. Here we describe the tissue distribution of MK-8591 and its anabolites in rats by quantitative whole body autoradiography and in rhesus vaginal and rectal mucosa by biopsy. Methods: Wistar Hannover rats dosed orally at 50 mpk (mg/kg) of [14C]-MK-8591 were sacrificed at 0.5 hr and 24 hr, cryo-sectioned (40 μm thick sagittal), and phosphor imaged for 4 days. Radioactivity in tissues was quantified using the blood standards along with Raytest AIDA image analysis software. For rectal and vaginal tissue distribution studies, monkeys were dosed 3.9 mpk orally on days 1 and 8. PBMCs were isolated from blood collected at day 1, 7, 14, and 21. Colorectal and vaginal biopsies were collected on days 7 (pre- dose) and 14, pooled separately, and snap-frozen with liquid nitrogen. PBMC and biopsy samples were analyzed by LC-MS/MS. Results: In rats, MK-8591 distributed widely within 30 min of dosing and was notably enriched in lymphoid tissue (75.9 nmol-eq/g) compared to blood (lymph node:blood ratio = 2.7). MK-8591 remained enriched in lymphoid tissue at 24 hr (11.1 nmol-eq/g; lymph node:blood ratio = 7.1). In rhesus macaques, on days 7 and 14, levels of MK-8591-TP in rectal tissues (36 pmol/g and 31 pmol/g) were similar to those measured in vaginal tissue (49 pmol/g and 78 pmol/g). Conclusion: The levels of MK-8591-TP achieved in both rectal and vaginal tissue are comparable to the levels of tenofovir diphosphate observed in rectal tissue from human subjects treated with tenofovir disoproxil fumarate. Given the significantly greater potency of MK-8591 (IC50=0.2 nM) compared to TDF (IC50=73 nM), these data suggest utility of MK-8591 for prophylaxis in both men and women. In addition, as lymphoid tissues are sites of active HIV replication and persistence, the observation that MK-8591 is enriched in lymphoid tissues in rats suggests the potential to address the ongoing replication of HIV in lymph nodes. 436 GS-9131 IS A NOVEL NRTI WITH ACTIVITY AGAINST NRTI-RESISTANT HIV-1 Kirsten L. White , Nicolas Margot, Kirsten Stray, Helen Yu, George Stepan, Constantine Boojamra, Richard Mackman, Adrian Ray, Michael D. Miller, Tomas Cihlar Gilead Scis, Inc, Foster City, CA, USA Background: There remains a need for an NRTI with potent activity against HIV-1 virus with NRTI resistance. GS-9131 is a monoamidate prodrug of the nucleotide analog GS-9148 (phosphonomethoxy-2’-fluoro-2’,3’-dideoxydidehydroadenosine). GS-9131 undergoes conversion in lymphocytes to GS-9148 diphosphate, a potent inhibitor of HIV-1 RT. GS-9148 has a low potential for mitochondrial toxicity and renal accumulation. Here we report on the antiviral activity and resistance profile of GS-9131. Methods: GS-9131 was subjected to extensive in vitro evaluation of antiviral activity and resistance profile. The PhenoSense HIV assay was used to compare the activity of GS-9131 and the NRTIs (ZDV, ddI, d4T, FTC, ABC, and TFV) against HIV-1 variants with all major types of NRTI resistance mutations. GS-9131 activity was also determined against 14 HIV-1 clinical isolates and 1 HIV-2 isolate in peripheral blood mononuclear cells. Results: GS-9131 had potent activity against laboratory strains of HIV-1 both in primary cells and T-cell lines (EC50 = 25-200 nM) and exhibited potent antiretroviral activity against HIV-1 isolates of subtypes A, B, C, D, E, F, group O and N (EC50 0.29-113 nM). GS-9131 also had potent activity against HIV-2 (EC50 = 21 nM) and showed low cytotoxicity in multiple cell types including renal cells (CC50 > 100 µM). The activity of GS-9131 was not affected by the presence of RT mutations K65R, L74V, M184V or their combinations (EC50 fold change < 1). Viruses with 4 or more thymidine analog mutations (TAMs), including one with the T69-insertion, showed minimal changes (0.68 to 1.5-fold) in susceptibility to GS-9131, a change smaller than any other tested NRTI. Passaging of HIV-1 in the presence of the parent drug GS-9148 selected for a primary K70E mutation in combination with D123N and T165I, or the poorly fit Q151L mutation in combination with K70E, L74I, and L187F/M in RT; these variants conferred <3-fold and 50-fold reduced susceptibility to GS-9131, respectively. GS-9131 (GS-9148) was synergistic in combination studies with AZT, FTC, ABC, efavirenz, the integrase inhibitors bictegravir and dolutegravir, and the PI lopinavir, and additive with TFV and TAF. Conclusion: GS-9131 exhibits potent in vitro antiretroviral activity and a favorable resistance profile including lower levels of resistance than approved NRTIs. GS-9131 is an attractive candidate for further clinical development with a potential for once daily dosing and efficacy in patients with NRTI resistance.

Poster and Themed Discussion Abstracts

CROI 2017 181