Mechanism-based pharmacokinetic (MBPK) models describe the complex plasma kinetics of three antiretrovirals delivered by a long-acting anti-HIV drug combination nanoparticle formulation

Abstract

Existing oral antiretroviral (ARV) agents have been shown in human studies to exhibit limited lymph node penetration and lymphatic drug insufficiency. As lymph nodes are a reservoir of HIV, it is critical to deliver and sustain effective levels of ARV combinations in these tissues. To overcome lymph node drug insufficiency of oral combination ARV therapy (cART), we developed and reported a long-acting and lymphocyte-targeting injectable that contains three ARVs-hydrophobic lopinavir (LPV) and ritonavir (RTV), and hydrophilic tenofovir (TFV)-stabilized by lipid excipients in a nanosuspension. A single subcutaneous (SC) injection of this first-generation formulation of drug combination nanoparticles (DcNPs), named TLC-ART101, provided persistent ARV levels in macaque lymph node mononuclear cells (LNMCs) for at least 1 week, and in peripheral blood mononuclear cells (PBMCs) and plasma for at least 2 weeks, demonstrating long-acting pharmacokinetics for all three drugs. In addition, the lymphocyte-targeting properties of this formulation were demonstrated by the consistently higher intracellular drug concentrations in LNMCs and PBMCs versus those in plasma. To provide insights into the complex mechanisms of absorption and disposition of TLC-ART101, we constructed novel mechanism-based pharmacokinetic (MBPK) models. Based upon plasma PK data obtained after single administration of TLC-ART101 (DcNPs) and a solution formulation of free triple-ARVs, the models feature uptake from the SC injection site that respectively routes free and nanoparticle-associated ARVs via the blood vasculature and lymphatics, and their eventual distribution into and clearance from the systemic circulation. The models provided simultaneous description of the complex long-acting plasma and lymphatic PK profiles for all three ARVs in TLC-ART101. The long-acting PK characteristics of the three drugs in TLC-ART101 were likely due to a combination of mechanisms including: (1) DcNPs undergoing preferential lymphatic uptake from the subcutaneous space, (2) retention in nodes during lymphatic first-pass, (3) subsequent slow release of ARVs into blood circulation, and (4) limited extravasation of DcNP-associated ARVs that resulted in longer persistence in the circulation.

Keywords: 1,2-distearoyl-sn-glycero-3-phosphocholine (DSPC) (PubChem CID: 94190); 1,2-distearoyl-sn-glycero-3-phosphoethanolamine-N-[methoxy(polyethylene glycol)-2000] (ammonium salt) (DSPE-mPEG(2000)) (PubChem CID: 406952); Antiretrovirals; HIV drug combination treatment; Long-acting; Lopinavir (PubChem CID: 92727); Lymphatic drug insufficiency; Lymphatic targeted drug delivery; Mechanism-based pharmacokinetic modeling; Ritonavir (PubChem CID: 392622); Tenofovir (PubChem CID: 464205).

Figure 1. Plasma concentration-time profiles of lopinavir (LPV; panel A), ritonavir (RTV; panel B), and tenofovir (TFV; panel C) in macaques following a single SC dose of the triple-drug combination in either the soluble (“free”; red open circles [O] and dotted line) or TLC-ART101 (blue closed circles [•] and solid line) formulation

The top graphs in panels A, B, and C are plasma concentration-time profiles of the first 24 hr after SC dosing, and the bottom graphs are the entire time course over 336 hr (2 weeks). Please note the differences in the y-axis scales for the top graphs over 24 hr to highlight relevant plasma concentrations for each ARV. Plasma limit of quantification (LOQ)/limit of detection (LOD) = lopinavir: 10/5, ritonavir: 50/25, tenofovir: 250/100 pg/mL. Ritonavir (intended as a PK booster for lopinavir) in plasma after TLC-ART101 dosing was

Figure 2. Schematic representation of the differential absorption and disposition pathways of ARVs associated to DcNPs in TLC-ART101, free, or in a stationary depot in the SC or IM space

In the SC space, ARV combinations (e.g., lopinavir [LPV], ritonavir [RTV], and tenofovir [TFV]) associated to drug combination nanoparticles (DcNPs) and referred to as “TLC-ART101,” are too large to enter blood capillaries, and thus preferentially enter lymph capillaries. While free ARVs in the SC space can enter lymph capillaries initially due to a strong concentration gradient driving drug out of the SC space, free ARVs are not able to be retained in the lymphatics and can easily diffuse back into the SC space as the diffusion gradient reverses direction over time. Overall, free ARVs preferentially enter the blood from the SC space, largely due to the 100-500-fold faster blood flow via capillaries than lymph flow. A stationary SC or intramuscular (IM) depot that provides a sustained release reservoir of free drug would follow the same principles for free drug and thus would also be predominantly absorbed directly into the blood. Once in lymphatic capillaries, TLC-ART101 particles would undergo first-pass distribution throughout the lymphatic system before entering the systemic blood circulation. In contrast, free drug that mostly enters the systemic circulation would undergo distribution, metabolism, and excretion mechanisms characteristic to the free drug molecule.

Figure 3. Structural models for free drug disposition in the systemic circulation (panels A, B) and TLC-ART101 disposition in the lymphatics and systemic circulation (panels C, D) after SC dosing

Figure 4. Observed (symbols) and fitted (curves) plasma concentration-time profiles of lopinavir (LPV, panel A), ritonavir (RTV, panel B), and tenofovir (TFV, panel C) in macaques after a single SC dose of the free and soluble triple-drug combination (N=3)

Symbols represent the geometric mean plasma concentration, and green curves represent the fits that resulted from population analysis.

Figure 5. Observed (symbols) and fitted (curves) plasma concentration-time profiles of lopinavir (LPV, panel A), ritonavir (RTV, panel B), and tenofovir (TFV, panel C) in macaques after a single SC dose of TLC-ART101 (N=8)

Symbols represent the geometric mean plasma concentration, and blue curves represent the fits that resulted from population analysis.

Figure 6. Time-course of the percentage of injected dose (%ID) of lopinavir (LPV, panel A), ritonavir (RTV, panel B), and tenofovir (TFV, panel C) in the lymphatics after a single SC dose of TLC-ART101