Abstract B19: Population pharmacokinetic-pharmacodynamic (PKPD) modeling of ibrutinib in patients with B-cell malignancies.

Abstract

Abstract Ibrutinib (IBRU) is an oral Bruton's tyrosine kinase (BTK) inhibitor, approved by US FDA for the treatment of chronic lymphocytic leukemia (CLL/SLL) and mantle cell lymphoma (MCL) patients having received at least one prior therapy. A nonlinear mixed-effects population model was developed to describe the PK of IBRU in patients with B-Cell malignancies and to establish the effect of pathophysiological covariates on its PK behavior. The relationship between PK and BTK engagement in peripheral blood mononuclear cells (PBMC) was also explored. IBRU PK data (3477 observations in 245 patients) were available in patients with MCL, CLL/SLL and recurrent B-cell malignancies at dose levels from 1.25 to 12.5 mg/kg and at fixed doses from 420 to 840 mg once daily. An additional phase 2 study in 119 patients with MCL (772 observations) treated at 560 mg once daily was used to validate the PK model. BTK occupancy was assessed (694 observations in 127 patients) in PBMCs using a fluorescent affinity probe. Various models were tested on the data using the first-order conditional estimation method as implemented in NONMEM version 7.1. A 2-compartment linear model with sequential zero-first order absorption and first order elimination was able to accommodate available PK data, including those of the validation dataset (prediction errors <15%). PK was dose- and time- independent. IBRU was rapidly absorbed, extensively distributed (volume of distribution at steady-state ~ 10,000 L) and cleared (apparent oral clearance ~1000 L/h). Relative bioavailability in the fasting state was about one third lower compared to the fed condition used in the clinical trials. No significant effect of other pathophysiological covariates on the PK was found (including sex, age or indication) except for body weight and coadministration of antacids, which had a marginal effect on the volume of distribution and duration of absorption, respectively. Analysis of PK-BTK engagement suggested that IBRU is a potent inhibitor of the BTK activity and that its interaction with BTK is rapid and durable. Citation Format: Italo Poggesi, Maria Luisa Sardu, Eleonora Marostica, Juthamas Sukbuntherng, Betty Y. Chang, Jan de Jong, Xavier Woot de Trixhe, An Vermeulen, Giuseppe De Nicolao, Susan Mary O'Brien, John C Byrd, Ranjana H Advani, Danelle Frances James, William Deraedt, Darrin Beaupre, Michael Wang. Population pharmacokinetic-pharmacodynamic (PKPD) modeling of ibrutinib in patients with B-cell malignancies. [abstract]. In: Proceedings of the AACR Special Conference on Hematologic Malignancies: Translating Discoveries to Novel Therapies; Sep 20-23, 2014; Philadelphia, PA. Philadelphia (PA): AACR; Clin Cancer Res 2015;21(17 Suppl):Abstract nr B19.