Dose-ranging pharmacokinetics, safety, and efficacy of a 90-day intravaginal ring delivering islatravir in pigtail macaques

Intravaginal rings (IVRs) are attractive user-controlled delivery systems that can achieve sustained release of compounds for several weeks. We modeled in macaques a three-dimensional (3D)–printed IVR delivering the investigational nucleoside reverse transcriptase translocator inhibitor islatravir (ISL). Three IVRs with 15, 30, or 60 milligrams of ISL were used in 30-day pharmacokinetic and safety studies followed by 90-day studies to identify a dose that maintains the concentration of the active intracellular metabolite islatravir triphosphate (ISL-TP) above protective benchmarks. IVRs were safe and delivered ISL in a dose-dependent manner. In a challenge study involving 12 weekly low-dose vaginal exposures to SHIV162p3, six macaques treated with 60-milligram ISL IVRs for 90 days remained seronegative and SHIV RNA negative, while two untreated controls were infected. These data provide initial preclinical evidence that a 90-day extended-release ISL IVR is safe and offers complete protection in a stringent challenge model, warranting further clinical investigation.