Antiretroviral penetration and drug transporter concentrations in the spleens of three preclinical animal models and humans.

Adequate antiretroviral (ARV) concentrations in lymphoid tissues are critical for optimal antiretroviral therapy. While the spleen contains 25% of the body's lymphocytes, there are minimal data on ARV penetration in this organ. This study quantified total and protein-unbound splenic ARV concentrations, and determine whether drug transporters, sex, or infection status were modifiers of these concentrations in animal models and humans. Two humanized mice models [hu-HSC-Rag (n=36; 18 HIV+ and 18 HIV-); bone marrow-liver-thymus (n=13; 7 HIV+ and 6 HIV-)] and one nonhuman primate model [NHP; rhesus macaque (n=18; 10 SHIV+ and 8 SHIV-) were dosed to steady-state with ARV combinations. HIV+ human spleens (N=14) from National NeuroAIDS Tissue Consortium were analyzed post-mortem (up to 24h post-dose). ARV concentrations were measured by LC-MS/MS, drug transporter concentrations were measured with LC-MS proteomics, and protein binding in NHP spleens was determined by rapid equilibrium dialysis. Mice generally had the lowest splenic concentrations of the three species. Protein binding in splenic tissue was 6-96%, compared to 76-99% in blood plasma. NHPs had quantifiable Mrp4, Bcrp, and Ent1 concentrations, and humans had quantifiable ENT1 concentrations. None significantly correlated with tissue ARV concentrations. There was also no observable influence of infection status or sex. With these dosing strategies, NHP splenic penetration most closely resembled humans. These data can inform tissue pharmacokinetic scaling to humans to target HIV reservoirs by identifying important species related differences.