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.
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.
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.
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.