Marta RodrÃguez Jiménez 1,2, Alejandro Serrano Alcaide 1,2, Ainara Salgado 1,2, I.F. Troconiz 1,2,3, M.J. Garrido 1,2
1 Universidad De Navarra (Pamplona, Spain), 2 Navarra Institute for Health Research (IdiSNA) (Pamplona, Spain), 3 Institute of Data Science and Artificial Intelligence (DATAI) (Pamplona, Spain)
Objectives
Targeting regulatory T cells (Tregs) is a promising approach to overcome tumor-driven immunosuppression. For this purpose, P60 peptide shows strong anti‑Treg activity. Nevertheless, its translation is constrained by rapid systemic clearance and limited selectivity for Tregs. To address these limitations, a liposomal nanocarrier encapsulating P60 was developed and functionalized with an anti‑CD25 Fab. Encapsulation enhances peptide stability and tumor deposition, whereas CD25 Fab functionalization promotes preferential delivery to Tregs. In parallel, computational modeling can help explain the in vivo disposition of these therapeutics and link tumor exposure to oncolytic response, informing rational design optimization. Therefore, we aimed to develop a PBPK/PD model that characterizes the oncolytic effects of P60 delivered via targeted nanoparticles in tumor‑bearing mice.
Methods
Two types of experiments were conducted.
For nanoparticle distribution, two consecutive studies were performed in C57BL/6J mice bearing MC38 tumors (approximately 50 mm³ at dosing), using ILDIT CF‑P60 (anti‑CD25 Fab‑targeted nanoparticles). In the first (terminal) study, four mice per time point (50% female) were sampled at 15 min, 1, 3, 6, 24, and 48 h; fluorescence was quantified (i) in blood after centrifugation using a plate reader and (ii) ex vivo in lungs, heart, liver, spleen, thymus, kidneys, and tumor using IVIS. This study included 24 treated mice plus 2 saline controls. In the second study, four mice underwent longitudinal IVIS in vivo imaging of the subcutaneous tumor at 15 min, 1, 2, 6, 24, 48, 72, 96, 144, 168, and 256 h, plus 2 controls.
For tumor volume time course, measurements were obtained from forty‑eight female C57BL/6J mice bearing MC38 tumors, randomized to saline (n=16) or multiple once‑daily doses of free P60 (5 mg/kg) or targeted nanoparticles (P60‑equivalent dose of 0.25 mg/kg).
A semi-mechanistic multiscale model integrating the available data was developed. Analyses were performed in NONMEM 7.5 using a population approach when animals contributed more than one observation and naïve pooling otherwise. Model selection prioritized acceptable parameter estimates and adequate simulation‑based diagnostic performance.
Results
A joint PBPK/PD model was established to simultaneously describe organ exposure to the targeted nanoparticles and P60 effect. Tumor exposure to P60 was derived by coupling the PBPK model with peptide release kinetics from the carrier. The tumor growth‑inhibition component combined a disease‑progression term with a tumor‑cell killing effect.
Nanoparticle organ disposition was influenced by anti‑CD25 Fab functionalization, exhibiting higher distribution to Treg‑rich tissues such as spleen and thymus. Because of tumor fluorescence kinetics, inclusion of extended follow up and longitudinal tumor imaging to capture the late phase decline was required. The model incorporated (i) size‑restricted endothelial extravasation, (ii) CD25‑mediated cellular uptake with immune cell driven redistribution, and (iii) EPR mediated tumor retention.
Tumor volume analysis indicated that encapsulated P60 markedly outperformed free P60 (37.5% vs 18.75% cured).
Conclusions
A PBPK/PD model describing the biodistribution and antitumor dynamics of P60‑loaded, Treg‑targeted nanoparticles in tumor‑bearing mice was developed, providing a semi-mechanistic foundation for future optimization of Treg‑directed nanotherapies.
References:
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Kumar, M., Kulkarni, P., Liu, S., Chemuturi, N., & Shah, D. K. (2023). Nanoparticle biodistribution coefficients: A quantitative approach for understanding the tissue distribution of nanoparticles. Advanced drug delivery reviews, 194, 114708. https://doi.org/10.1016/j.addr.2023.114708
Cao, X., Li, K., Wang, J., Xie, X., & Sun, L. (2025). PBPK model of pegylated liposomal doxorubicin to simultaneously predict the concentration-time profile of encapsulated and free doxorubicin in tissues. Drug delivery and translational research, 15(4), 1342–1362. https://doi.org/10.1007/s13346-024-01680-0
Serrano, A., Casares, N., Trocóniz, I. F., Lozano, T., Lasarte, J. J., Zalba, S., & Garrido, M. J. (2025). Foxp3 inhibitory peptide encapsulated in a novel CD25-targeted nanoliposome promotes efficient tumor regression in mice. Acta pharmacologica Sinica, 46(1), 171–183. https://doi.org/10.1038/s41401-024-01338-0
Reference: PAGE 34 (2026) Abstr 11976 [www.page-meeting.org/?abstract=11976]
Poster: Drug/Disease Modelling - Absorption & PBPK