Antiretroviral Penetration and Drug Transporter Concentrations in the Spleens of Three Preclinical Animal Models and Humans

Abstract

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.

Quantitative Imaging Analysis of the Spatial Relationship between Antiretrovirals, Reverse Transcriptase Simian-Human Immunodeficiency Virus RNA, and Fibrosis in the Spleens of Nonhuman Primates

“…LC-MS/MS methods for spleen tissue homogenate samples have been detailed previously. (13) The workflow for IR-MALDESI MSI analyses has been described in greater detail by our group, (16) but is also placed within the Supplemental Material, page 3. Using MATLAB, per-volumetric pixel (voxel) drug response was quantified based on calibration on matched blank spleen tissue.…”

Pharmacology of HIV Cure: Site of Action

“…The median TPRs across species were high for maraviroc (3.3) and emtricitabine (3.0), modest for atazanavir (1.7), tenofovir (1.7), and efavirenz (1.5), and low for raltegravir (0.3). Importantly, all of these TPRs exceeded 1 (meaning tissue exposure is high relative to blood exposure), with the exception of raltegravir 49 . Interestingly, despite a TPR of > 1, emtricitabine and tenofovir exhibited IQ values that were < 1, which would suggest subtherapeutic exposure in both the spleen and blood 49 .…”

“…Importantly, all of these TPRs exceeded 1 (meaning tissue exposure is high relative to blood exposure), with the exception of raltegravir. 49 Interestingly, despite a TPR of > 1, emtricitabine and tenofovir exhibited IQ values that were < 1, which would suggest subtherapeutic exposure in both the spleen and blood. 49 One important limitation of the human samples included in this study is that ART doses were not witnessed.…”

“…49 Interestingly, despite a TPR of > 1, emtricitabine and tenofovir exhibited IQ values that were < 1, which would suggest subtherapeutic exposure in both the spleen and blood. 49 One important limitation of the human samples included in this study is that ART doses were not witnessed. Thus, these low spleen and plasma concentrations may be attributable to poor adherence, which highlights the importance of considering tissue distribution in the context of plasma exposure rather than absolute concentration alone.…”

“…Data regarding ART penetration into the spleen is also extremely limited, but splenic ART pharmacology has been evaluated in preclinical models (humanized mice and NHPs) as well as 13 humans post mortem 49 . The median TPRs across species were high for maraviroc (3.3) and emtricitabine (3.0), modest for atazanavir (1.7), tenofovir (1.7), and efavirenz (1.5), and low for raltegravir (0.3).…”