(M1330-05-29) Self-Nanoemulsifying Systems Containing Ionic Liquids of Rilpivirine for Improved Oral Bioavailability and Penetration in the HIV Sanctuary Sites

Purpose: Despite the availability of potent anti-retroviral (ARV) compounds, human immunodeficiency virus (HIV) has continued to pose a global problem, with nearly 40 million patients worldwide as of 2022 [1]. One of the factors contributing to this is that HIV replicates in immune privileged sanctuary sites within the body, such as the lymphatic system, central nervous system, and reproductive tract [2]. The existing ARV drugs have suboptimal penetration into the HIV reservoir sites. Rilpivirine (RPV) is a potent non-nucleoside reverse transcriptase inhibitor available as a combination pill for maintenance therapy [3,4]. However, RPV is a highly crystalline drug with low aqueous and lipid solubility, low and variable oral bioavailability, and limited penetration in the HIV sanctuary sites [5,6]. We hypothesize that the transformation of ionizable drugs such as RPV into amphiphilic drug-based ionic liquids and their subsequent incorporation into oral lipid-based formulations such as self-nanoemulsifying systems (SNES) would result in improved oral bioavailability and penetration into HIV sanctuary sites.

Methods: To develop ionic liquids (ILs) capable of improving the oral bioavailability of RPV, we evaluated a variety of anionic permeation enhancers for their ability to electrostatically interact with RPV to yield RPV-ILs. RPV-ILs developed by the salt metathesis reaction were characterized using Fourier-Transform Infrared (FT-IR) spectroscopy and nuclear magnetic resonance (NMR) spectroscopy, differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and powder x-ray diffraction (PXRD). The partition coefficient of resultant RPV-ILs or lipophilic complexes was evaluated. The RPV ILs were assessed for solubility in lipid vehicles used for the preparation of SNES. The shortlisted RPV-IL, RPV docusate (RPV-Doc) was transformed into SNES using our previously described method. The optimized SNES formulation containing RPV-Doc was evaluated for the droplet size and homogeneity after dilution with buffers representing gastrointestinal pH values. Finally, oral bioavailability and HIV sanctuary site penetration of optimized RPV-Doc-SNES and RPV suspension (RPV dose: 10 mg/kg) were evaluated in mice. The RPV levels in the plasma, mesenteric lymph nodes, brain, and testes were evaluated via LC-MS/MS.

Results: RPV successfully interacted with all anionic permeation enhancers shown in Figure 1 as evidenced by the displacement in both the characteristic ¹H NMR proton signals and FTIR spectra of RPV and counterions. The DSC and PXRD data showed that RPV docusate (RPV-Doc) and RPV lauryl sulfate (RPV-LS) were ionic liquids whereas other RPV-anionic permeation enhancer systems were deemed as lipophilic salts. RPV-Doc showed the highest solubility in various lipid vehicles used for the development of SNES compared to other RPV-ILs/lipophilic salts and RPV (Figure 2). The transformation of RPV to RPV-Doc resulted in ~ 200-fold improvement in the lipid solubility indicating the feasibility of developing SNES. Our screening studies identified Capryol 90, Capmul MCM, and Kolliphor ELP for the development of SNES containing RPV-Doc. The optimized RPV-Doc-SNES composition yielded nanoemulsion ≤ 100 nm when diluted with various buffers (Figure 2) Orally administered RPV-Doc-SNES showed ~6-fold improvement in oral bioavailability and remarkably higher RPV levels (~ 6-fold) in the HIV sanctuary sites such as the brain, mesenteric lymph nodes, and testes compared to RPV suspension.

Conclusion: Highly crystalline ionizable drugs with poor pharmaceutical processability, oral bioavailability, and tissue penetration such as RPV can be transformed into amphiphilic ILs with high lipid solubility to enable the development of oral lipid-based formulations such as SNES which will eventually result in enhanced oral bioavailability and tissue penetration. The improved oral bioavailability and penetration into HIV sanctuary sites of ARV drugs using our innovative strategy will result in effective drug utilization and better management of lifelong HIV infection.

References: 1) UNIAIDS/WHO estimates, 2023.
2) Chun, T.-W., et al., Early establishment of a pool of latently infected, resting CD4+ T cells during primary HIV-1 infection. Proceedings of the National Academy of Sciences, 1998. 95(15): p. 8869-8873
3) Casado, J.L. and S. Bañón, Recent advances in rilpivirine: new data and promising treatment option. AIDS Rev, 2014. 16(3): p. 172-81.
4) Imaz, A. and D. Podzamczer, The role of rilpivirine in clinical practice: strengths and weaknesses of the new nonnucleoside reverse transcriptase inhibitor for HIV therapy. AIDS Rev, 2012. 14(4): p. 268-78.
5) Usach, I., V. Melis, and J.E. Peris, Non-nucleoside reverse transcriptase inhibitors: a review on pharmacokinetics, pharmacodynamics, safety and tolerability. J Int AIDS Soc, 2013. 16(1): p. 1-14.
6) Hodge, D., et al., Pharmacokinetics and Drug-Drug Interactions of Long-Acting Intramuscular Cabotegravir and Rilpivirine. Clin Pharmacokinet, 2021. 60(7): p. 835-853.


Fig 1. Structure of rilpivirine and the counterions screened for the development of rilpivirine ionic liquids (ILs).


Fig 2. A) Kinetic solubility of RPV and RPV ILs/salts in lipid vehicles (n=3). B) Schematic for the preparation of self-nanoemulsifying system containing RPV-Doc subsequently leading to nanoemulsion upon dilution. C) Globule size of RPV-Doc containing self-nanoemulsifying systems (SNES) diluted with buffers representing gastrointestinal pH conditions (n=3)


Fig 3. Oral administration of RPV-Doc SNES showed significantly higher oral bioavailability (A) and penetration into HIV sanctuary sites (B-E) compared to RPV suspension (RPV dose: 10 mg/kg; n ≥ 5/group for bioavailability studies and n=3/tissue/group for tissue penetration studies. * P ≤ 0.05, ** P ≤ 0.01, *** P ≤ 0.001.