Abstract 2452: Deorphanizing TLX: Implications for treatment of glioblastomas

Abstract Nuclear receptors (NRs) are important ligand-dependent transcriptional factors. Presently, no natural or synthetic ligand has been identified for a large group of so- called “orphan” NRs. The orphan NR tailless (TLX, NR2E1), a transcriptional repressor, is a major player in neurogenesis and emerging evidence indicates that it is an excellent target to treat Neural Stem Cell (NSC) derived brain tumors and glioblastomas. Indeed, several groups hypothesized that small molecules de-repressing TLX activity in glioblastoma cells should slow tumor progression and invasiveness by inducing the cyclin-dependent kinase inhibitor p21 and the tumor suppressor pten. Until recently, no chemical probes to modulate TLX activity to test this hypothesis were available, and it was not clear whether TLX was druggable. Our homology models of the TLX ligand binding domain (LBD) suggest that TLX belongs to an emerging class of NRs that lack two LBD helices and fold into an auto-repressed conformation. While our models suggests that TLX could harbor a ligand binding pocket, the consequences of its unusual organization for small molecule development were unknown. We used a medium throughput screening strategy to assess TLX ligand binding capacity. We investigated direct binding of 20,000 compounds to purified human TLX protein and verified interactions with a secondary (orthogonal) assay. We then assessed effects of verified binders on TLX activity. As a result, we reported three compounds that bind to TLX with affinities in the high nanomolar to low micromolar range and enhance TLX transcriptional repressive activity. Based on this study, we could conclude that TLX is druggable. We are now investigating how to de-repress TLX transcriptional activity using derivatives of these small molecules. We are imaging the mode of binding of the three identified ligands and discovering surfaces which bind coregulators of TLX in glioblastomas. This knowledge will allow us to devise strategies to chemically modify novel TLX ligands to disrupt coregulator interactions and to obtain the desirable biological activities. A first generation of novel analogues is currently being tested. In this presentation we will describe ongoing Structure-Activity Relationship studies to identify new specific TLX ligands able to de-repress TLX transcriptional activity. Citation Format: Cindy C. Benod, Rosa Villagomez, Paul Webb. Deorphanizing TLX: Implications for treatment of glioblastomas. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 2452. doi:10.1158/1538-7445.AM2015-2452