Razvoj fizioloških farmakokinetičnih modelov za monoklonsko protitelo trastuzumab in njegove fragmente s programsko opremo PK-SIM

Šircelj, Kaja (author), Grabnar, Iztok (mentor)

Farmakokinetika predstavlja pomemben del razvoja in uporabe zdravil, saj nam pomaga oceniti časovni potek koncentracije zdravilne učinkovine v telesu po aplikaciji. Zato so razvili farmakokinetične modele, ki jih delimo na prostorske in fiziološke. Slednji so kompleksnejši in opisujejo porazdelitev zdravilne učinkovine po celotnem telesu. Pri razvoju modelov pa moramo upoštevati, da se farmakokinetika majhnih molekul razlikuje od farmakokinetike makromolekul. Za protitelesa je značilen fenomen nelinearne farmakokinetike, ker je ta tarčno pogojena. Opisujemo jo z modelom tarčno pogojene farmakokinetike, v katerega vključimo specifično vezavo na farmakološko tarčo, kar pri nizkih koncentracijah predstavlja večji del očistka protiteles. Pri višjih koncentracijah, ko so tarče zasičene, je na voljo več nevezane frakcije in ima velik vpliv na očistek vezava na neonatalni Fc receptor. Cilj magistrske naloge je bil razviti fiziološke farmakokinetične modele s programsko opremo PK-Sim na primeru protitelesa trastuzumab in njegovih fragmentov (IgG brez vezavnega mesta za FcRn, F(ab)2, Fab, scFv in nanotelo) ter ovrednotiti uporabnost PK-Sim za razvoj farmakokinetičnih modelov, oceniti vpliv različnih parametrov in ovrednotiti točnost napovedi modelov. S programom smo naredili simulacije s prednastavljenimi parametri, nato pa smo prilagajali parametre, specifične za molekulo (od teh tudi samo konstanto disociacije) in specifične za organizem (od teh tudi samo porazdelitvene koeficiente), ter ovrednotili izboljšanje ujemanja odzivov modelov z eksperimentalnimi vrednostmi. Ugotovili smo, da modeli s prednastavljenimi parametri slabo sledijo eksperimentalnim vrednostim. Po prilagajanju parametrov, specifičnih za molekulo, se je ujemanje izboljšalo samo pri protitelesu IgG. Razlog za to je prilagajanje konstante disociacije za vezavo na FcRn, saj se IgG veže na FcRn, ostali fragmenti pa nimajo vezavnega mesta za vezavo na FcRn. Po prilagajanju parametrov, specifičnih za organizem, se je ujemanje izboljšalo pri vseh molekulah, najmanj pri protitelesu IgG. Ugotovili smo, da na protitelo IgG vpliva konstanta disociacije za vezavo na FcRn, na fragmente pa v večji meri porazdelitveni koeficienti med intersticijem in plazmo ter znotrajcelično tekočino in plazmo. Kljub prilagajanju parametrov, specifičnih za molekulo in specifičnih za organizem, je ujemanje modelov z eksperimentalnimi vrednostmi še vedno slabo. Razviti modeli so zato primerni za vrednotenje in napovedovanje farmakokinetike trastuzumaba, za fragmente trastuzumaba pa so neprimerni.

• Language: Slovenian
• Keywords: fiziološki farmakokinetični model, fragmenti protitelesa, konstanta disociacije, neonatalni Fc receptor, porazdelitveni koeficient, trastuzumab
• Work type: Master's thesis/paper
• Organization: FFA - Faculty of Pharmacy
• Year: 2025
• PID: 20.500.12556/RUL-174980
• Publication date in RUL: 11.10.2025

Secondary language

• Language: English
• Title: Development of physiologically-based pharmacokinetic models of trastuzumab monoclonal antibody and its fragments using PK-SIM software

Abstract

Pharmacokinetics plays an important role in the development and therapeutic use of medicines by facilitating the assessment of time course of the concentration of drug in the body following application. To that end, pharmacokinetic models, divided into compartmental and physiological, have been developed. The latter are more complex and describe the distribution throughout the body. The model development has to consider that the pharmacokinetics of small molecules differs from the pharmacokinetics of macromolecules. Antibodies are characterised by the phenomenon of non-linear pharmacokinetics, known as the model of target-mediated drug disposition, entailing a specific binding to the pharmacological target which at low concentrations represents a major portion of the clearance of antibodies. More of the free fraction is available at higher concentrations when targets are saturated, with the binding on the neonatal Fc receptor having a large impact on clearance. The aim of the master’s thesis was the development of physiological pharmacokinetic models using the PK-Sim software on the example of the trastuzumab antibody and its fragments (IgG without the binding site for FcRn, F(ab)2, Fab, scFv and nanobody), the evaluation of the utility of PK-Sim for the development of pharmacokinetic models, the assessment of the impact of various parameters, and the evaluation of model prediction. Simulations using preset parameters were performed with the software, followed by adjustments of the molecule-specific (including the dissociation constant) and organism-specific (including distribution coefficients) parameters and an evaluation of the improvement in the matching of model results with experimental values. It has been determined that the models with preset parameters are poorly matched to experimental values. The adjustment of molecule-specific parameters has improved prediction only for the IgG antibody. The reason is the adjustment of the dissociation constant for binding to FcRn since IgG binds to FcRn whereas other fragments have no binding site for binding to FcRn. The adjustment of organism-specific parameters has improved matching for all molecules with the least improvement noted for the IgG antibody. It was established that the dissociation constant for binding to FcRn impacts the IgG antibody whereas fragments were largely affected by coefficients of distribution between interstitium and plasma and between intracellular fluid and plasma. The agreement of model predictions with experimental values has remained poor even after the adjustment of molecule-specific and organism-specific parameters. The developed models are therefore suitable for the evaluation and forecasts of pharmacokinetics of trastuzumab but not suited for trastuzumab fragments.

• Keywords: physiological pharmacokinetic model, antibody fragments, dissociation constant, neonatal Fc receptor, distribution coefficient, trastuzumab