Abstract 1931: Investigating the PK/PD/efficacy relationship of PI3K inhibitors in vitro, enabled by a microfluidic addition and removal device
Authors: Kostrzewski Tomasz M. , Singh Dharaminder , Golby Paul , Bray Alysha , Hughes David 
Published: August 2019

Abstract
Characterizing the relationship between pharmacokinetics (PK), pharmacodynamics (PD) and efficacy is critical in the discovery and development of new drugs, schedules and combinations. The PK/PD/efficacy relationship has historically been characterized in xenograft models, owing to an absence of viable alternatives. The study of this relationship in vitro, has to date been problematic as the generation of time varying concentrations in multi-well plates has not been possible.
We have explored an in vitro methodology utilizing a device (Microformulator, Viibre, Vanderbilt University) capable of precision addition and removal of medium from the wells of a microtiter cell culture plate. Through stepwise addition and removal of medium the device was able to recapitulate PK-like, time varying concentration profiles of one, or more drugs in individual wells. We used this approach to explore the effects of PI3K pathway inhibitors, on p-AKT levels, and viability in a number of cancer lines. The PI3K/mTOR pathway is a central oncogenic pathway deregulated in cancer and p-AKT is a marker of PI3K pathway activity.
BYL719 and PI-103, are PI3K inhibitors with varying PK profiles and varying target coverage against PI3K isoforms. The compounds were tested on a pair of cell lines, T47D (breast, sensitive) and Colo205 (gut, insensitive). Both compounds were potent in a bolus dose 72hr assay with BYL719 having an IC50 of 0.63 µM for T47D and 15.8 µM for Colo205. Whilst PI-103 gave IC50 of 0.72 µM for T47D and 4.16 µM for Colo205. Both compounds also reduced, p-AKT in a dose-dependent manner after 2 hours. Using the microfluidic device, we generated PK-like dosing profiles for the two compounds, (BYL719 - t1/2 6 hours) (PI-103 - t1/2 3 hours) which mimicked their in vivo clearance profiles over a 24-hour period. p-AKT levels were initially reduced by both compounds but recovered at 24 hours as the concentration of the compound in the well declined. This replicates findings in xenograph models. The shorter t1/2 of PI-103, resulted in a more rapid recovery of p-AKT than observed for BYL719. Efficacy tests were conducted in which a 24 hour PK-like profile was applied for 3 consecutive days, mimicking daily dosing. For both compounds in T47D cells, the inhibition of cell growth was reduced as compared to a bolus addition at the Cmax concentration. These data demonstrate how PI-103 initially appeared to be an efficacious molecule but its rapid in vivo metabolism meant it could not be progressed in clinical studies.
In conclusion, this study demonstrates the microfluidic addition and removal device can be used to recapitulate PK-like profiles in vitro and allow exploration of the PK/PD/efficacy relationship. The availability of an in vitro method will enable these important parameters to be determined at an earlier stage of the drug discovery process.
Citation Format: Tomasz M. Kostrzewski, Dharaminder Singh, Paul Golby, Alysha Bray, David Hughes. Investigating the PK/PD/efficacy relationship of PI3K inhibitors in vitro, enabled by a microfluidic addition and removal device [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 1931.