Abstract LB-316: Pharmacokinetic modeling optimizes direct inhibition of the ‘undruggable’ target EWS-FLI1 of Ewing Sarcoma

Abstract

Abstract Chimeric transcription factors have long been considered ideal anti-cancer targets since they are only present in tumor cells, however, their lack of enzymatic activity has placed them in a category of ‘undruggable’ proteins. The EWS-FLI1 fusion protein of Ewing Sarcoma (ES) has been validated as an anticancer target both alone and as a partner of RNA Helicase A (RHA). Our prior work identified the small molecule YK-4-279 as a specific inhibitor of EWS-FLI1 by blocking the interaction with RHA. Blocking this interaction leads to apoptosis. Data suggests that relatively long exposures of drug are necessary to keep EWS-FLI1 and RHA apart. We have modeled YK-4-279 treatment using cell lines (TC71, TC32, A4573, SK-ES, and RD-ES) to establish the duration of YK-4-279 exposure that leads to apoptosis. Apoptosis was measured by caspase-3 cleavage. A validated plasma detection method allows for HPLC measurement of YK-4-279. Pharmacokinetic (PK) models of YK-4-279 for both intraperitoneal (IP) and intravenous (IV) administration were developed in SD rats and BL6 mice. ES cell lines were exposed to YK-4-279 over a time-course, followed by a caspase-3 activity assay that demonstrated a minimum of 16 hours exposure was necessary to achieve maximal apoptosis using either 3 or 10 microM compound. A dose-dependency assay demonstrated that while apoptosis could be achieved with 30 - 80 microM YK-4-279 after 4 hours of treatment, caspase-3 activity was less than or equal to 3 microM for 16 hours. Rat PK modeling demonstrated a t1/2 of 30 minutes following IV administration. BL6 mice demonstrated similar kinetics to the rat. SCID/bg mice, which are necessary for tumor efficacy studies, demonstrated approximately 50% faster clearance than either rat or BL6 mice. Absolute bioavailability for IP administration was 41%. Models that use cell culture based targets for plasma levels and duration of exposure will be created to optimize IP dosing regimen. The optimized IP dosage and dosing intervals will be evaluated in tumor bearing animals in order to advance development of YK-4-279. The results of these studies will be used to guide toxicology studies in animals. In addition, pharmacodynamics models are being developed to compare YK-4-279 levels with functional activity. The combined results of these investigations will lead to human clinical trials for this first-in-chemical class, first-in-mechanism drug candidate. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr LB-316. doi:1538-7445.AM2012-LB-316