Meng Gu 1, Tingjie Guo 1, Coen van Hasselt 1
1 Division of Systems Pharmacology and Pharmacy, Leiden Academic Centre for Drug Research, Leiden University (Leiden, Netherlands)
Background and Objectives:
Bacteriophages (phages) are viruses that selectively infect bacteria and are under renewed investigation as therapeutic agents against resistant infections. After systemic administration, their large size promotes rapid sequestration in reticuloendothelial organs with restricted extravasation, resulting in a pronounced and rapid clearance from plasma and heterogeneous tissue exposure, illustrating the complexity of phage biodistribution.
This study aimed to (1) develop a whole-body physiologically based pharmacokinetic (PBPK) model for vascular-interstitial distribution of phages in mice; (2) evaluate whether organ-specific, capacity-limited mononuclear phagocyte system (MPS) uptake explains observed biphasic plasma kinetics and tissue accumulation; and (3) assess whether a unified PBPK structure can be applied across multiple phages with minimal phage-specific parameter changes, while interpreting inter-phage differences in the context of reported particle size and morphology.
Methods:
A whole-body PBPK model was implemented in R to describe intravenous phage disposition in mice. Organs were represented by vascular, interstitial, cellular, and MPS-reservoir compartments. Tissue volumes and blood flows were fixed to literature mouse values [1]. Portal venous drainage to the liver and serial lung circulation were preserved.
Vascular-interstitial exchange was described by transcytosis and lymphatic convection, parameterized as first-order exchange processes. Transcytosis included uptake clearances from vascular/interstitial spaces into cells (CLup) and efflux clearances from cells back to vascular/interstitial spaces (CLex). Organ MPS uptake was modelled as saturable, capacity-limited: Uptake=kup∗Asourse∗(1−Ares/Amax), where kup is the maximal uptake rate, Asourse is the amount in the uptake source compartment (vascular or interstitial), Ares is the amount in the MPS reservoir, and Amax is the organ-specific phagocytic capacity derived from phagocyte density, organ volume, and a per-cell capacity (10^3.85 PFU per 10^5 cells). Intracellular and MPS degradation were modelled as first-order processes. A linear plasma clearance term represented systemic loss/inactivation not captured by organ uptake.
Parameters subject to calibration included plasma clearance, transcytosis exchange clearances, and MPS uptake and degradation rate constants, while physiological parameters were fixed to literature values. The model was calibrated to a published mouse dataset comprising plasma and tissue concentration-time profiles for three structurally distinct phages with different particle sizes and morphologies: (1) AB_SZ6 (Podoviridae; 54.2 nm), (2) PA_LZ7 (Myoviridae; 73.6 nm capsid × 138.6 nm tail), and (3) SE_SZW1 (Siphoviridae; 70.2 nm capsid × 158.6 nm tail) [2]. Parameter adjustments were performed within physiologically plausible ranges to achieve consistency with the data. Calibration was performed sequentially, with plasma plasma clearance, transcytosis exchange clearances, and MPS uptake and degradation rate constants first, followed by tissue refinement. SE_SZW1 data were used to build a base model. For AB_SZ6 and PA_LZ7, only these parameters were modified. Differences in phage-specific parameters were qualitatively examined in relation to reported particle dimensions. Predictive performance was summarized using geometric mean fold error (GMFE).
Results:
The model reproduced biphasic plasma decline following intravenous dosing, with an early rapid phase consistent with dominant hepatic and splenic sequestration, followed by a slower phase governed by capacity limitation in MPS reservoirs and first-order degradation. Liver and spleen exhibited faster initial sequestration than other organs, consistent with sinusoidal and intravascular capture, and spleen exhibited greater total accumulation and slower washout.
Inter-phage differences in early plasma decline and tissue accumulation were captured by adjustments in transcytosis exchange and MPS uptake parameters, consistent with restricted extravasation and enhanced sequestration for larger or tailed phages relative to the smaller podovirus, without asserting a unique quantitative size-parameter relationship. GMFE values were 5.25 (PA_LZ7), 6.54 (AB_SZ6), and 2.61 (SE_SZW1) calculated across plasma and available organs at all sampled time points.
Conclusions:
A whole-body PBPK model integrating transcytosis, lymphatic convection, and capacity-limited MPS uptake described systemic and organ-level phage disposition within a unified structure. Phage-specific differences were primarily captured by plasma clearance and distribution/MPS-uptake parameters that are plausibly influenced by particle size and morphology. The framework supports quantitative comparison of candidate phages under consistent physiological assumptions.
References:
[1]. Echterhof A, Dharmaraj T, Blankenberg P, Targ B, Nguyen TD, Bollyky PL, Smith NM, Blankenberg FG. 2026. Whole-body distribution of three Pseudomonas phages characterized by a translational physiologically based pharmacokinetic model. Antimicrob Agents Chemother 70:e01506-25.
[2]. Tan X, Chen K, Jiang Z, Liu Z, Wang S, Ying Y, Zhang J, Yuan S, Huang Z, Gao R, Zhao M, Weng A, Yang Y, Luo H, Zhang D, Ma Y. 2024. Evaluation of the impact of repeated intravenous phage doses on mammalian host–phage interactions. J Virol 98:e01359-23.
Reference: PAGE 34 (2026) Abstr 12162 [www.page-meeting.org/?abstract=12162]
Poster: Drug/Disease Modelling - Absorption & PBPK