Background:  The lack of biomarkers predictive of efficacy and safety is a major gap in topical pre-exposure prophylaxis (PrEP) development. High costs and limited access to animals are significant limitations with non-human primate (NHP) SHIV models. In addition, poor reproducibility of ex vivo HIV or SHIV challenge of human or NHP cervical and vaginal biopsies highlights the need for new models.

Methods:  We used a dual-chamber model with polarized epithelial cells to evaluate the bio-permeability and pharmacokinetics/pharmacodynamics (PK/PD) of an intravaginal ring (IVR) formulation of IQP-0528, a pyrimidinedione with potent reverse transcriptase inhibitory activity against HIV-1/2. Cells were apically exposed to mini-IVR and basolateral supernatants were collected and analyzed for drug level and ability to inhibit HIV-1_BaL infection of TZM-baseline cells. IVR loaded with 10 wt% IQP-0528 (n = 6), or placebo (n = 2), were inserted into pigtailed macaques. Vaginal biopsies were collected prior to and 7 and 14 days post-IVR insertion. IQP-0528 tissue levels were determined by LC-MS/MS. The ability of the biopsied tissue to function as a drug reservoir and block infection of PBMC was evaluated by co-culturing minced biopsies with activated human PBMC prior to challenge with 10³ TCID₅₀ HIV-1_BaL.

Results:  IQP-0528 released from IVR crossed the epithelial barrier at a rate comparable to that observed in the absence of epithelial cells and sufficient drug was present within 24 hours in basolateral compartments to abrogate HIV infection. Co-cultures of biopsies collected from 6 of 6 animals exposed to IQP-0528 IVR were protected from HIV or RT-Env-SHIV challenge compared to baseline, whereas no protection was observed in 2 of 2 animals exposed to placebo IVR. The concentration of drug in proximal and distal biopsies 14 days post application was 20.2±14.9 and 10.4±11.8 ng/mg tissue, respectively (NS, p = 0.24). There was a significant PK /PD correlation (r² = 0.77).

Conclusions:  The dual-chamber model suggests that IQP-0528 rapidly crosses epithelial barriers to reach submucosal immune cells and NHP studies indicate that sufficient drug is released into the tissue, to protect PBMC that exist in or might be recruited into the genital tract. These data support further development of an IQP-0528 IVR. Moreover, the models provide important insights into drug permeability, PK and PD. Biopsies from planned human safety trials of pyrimidinediones should be evaluated in the co-culture model.