Population Pharmacokinetic Modeling of Etoposide Free Concentrations in Solid Tumor

Abstract

Purpose: This study aimed to determine free etoposide (ETO) concentrations in two regions of Walker-256 (W256) solid tumor using microdialysis and to establish a population pharmacokinetic (popPK) model to describe simultaneously free tumor and total plasma concentrations.

Methods: W256 tumor-bearing Wistar rats received ETO 10 or 20 mg/kg i.v. bolus. Free ETO concentrations were sampled from central and peripheral regions of the tumor via CMA/20 probes for up to 7 h, whereas blood samples were collected via carotid artery cannulation. Total plasma and free tumor concentration-time profiles were analyzed by non-compartmental approach using WinNonlin® v. 5.3. PopPK modeling was conducted using MONOLIX v.4.3.3.

Results: ETO penetration was higher in the periphery (61 ± 15% and 61 ± 29%) than in tumor center (34 ± 6% and 28 ± 11%) following 10 and 20 mg/kg doses, respectively (ANOVA, α = 0.05). A 4-compartment model fitted ETO concentration-time profiles in all sampling compartments.

Conclusions: The popPK model allowed the simultaneous fitting of plasma and tumor concentrations and a better understanding of ETO distribution in solid tumors. ETO plasma concentrations are not a good surrogate for tumoral exposure, emphasizing the importance of knowing intratumoral concentrations to predict drug response.

Keywords: anticancer; drug tumor penetration; etoposide; microdialysis; population pharmacokinetics.