Propranolol Activates the Orphan Nuclear Receptor TLX to Counteract Proliferation and Migration of Glioblastoma Cells

Abstract

The ligand-sensing transcription factor tailless homologue (TLX, NR2E1) is an essential regulator of neuronal stem cell homeostasis with appealing therapeutic potential in neurodegenerative diseases and central nervous system tumors. However, knowledge on TLX ligands is scarce, providing an obstacle to target validation and medicinal chemistry. To discover TLX ligands, we have profiled a drug fragment collection for TLX modulation and identified several structurally diverse agonists and inverse agonists of the nuclear receptor. Propranolol evolved as the strongest TLX agonist and promoted TLX-regulated gene expression in human glioblastoma cells. Structure−activity relationship elucidation of propranolol as a TLX ligand yielded a structurally related negative control compound. In functional cellular experiments, we observed an ability of propranolol to counteract glioblastoma cell proliferation and migration, while the negative control had no effect. Our results provide a collection of TLX modulators as initial chemical tools and set of lead compounds and support therapeutic potential of TLX modulation in glioblastoma.

Druggability Evaluation of the Neuron Derived Orphan Receptor (NOR‐1) Reveals Inverse NOR‐1 Agonists

“…Compared to previous screening campaigns of the same chemically diverse fragment library on nuclear receptors [20–22] and enzymes, [23] the hit‐rate on NOR‐1 was low. This aligns with the fact that almost no NOR‐1 modulators have been reported to date and suggests that NOR‐1 is particularly restrictive in terms of ligand binding.…”

The Transcriptional Repressor Orphan Nuclear Receptor TLX Is Responsive to Xanthines

“…Using the VP16/TLX reporter gene assay, we have screened a drug fragment library comprising 480 small organic molecules (MW range: 80–300 g/mol) for TLX modulatory activity . Therein, we have discovered 1-methylxanthine ( 1 ) as a TLX modulator that diminished TLX-mediated transcriptional repression with an IC 50 value of 9 ± 3 μM (Table ).…”

“…Together with the few available TLX ligands, − the xanthines will be a valuable tool to study the mechanisms of TLX modulation in cell-free systems and may also be useful as an early tool for experiments in a cellular contextparticularly the TLX preferential xanthine 19 . In addition, TLX modulation by xanthines may have pharmacological relevance.…”

“…Beyond these roles in neuronal homeostasis and brain function, recent reports have suggested a potential tumorigenic activity of the orphan NR due to marked overexpression in glioblastoma and neuroblastoma cell lines. , These lines of evidence suggest TLX as an attractive drug target for neurodegenerative diseases and malignant brain tumors. However, endogenous TLX ligands, forming an essential part of the NR function, remain elusive, and only few synthetic TLX modulators have been described to date. − In light of its obvious therapeutic potential, further evaluation of the receptor’s function and the discovery of potent TLX ligands are imperative.…”

Oleic acid is an endogenous ligand of TLX/NR2E1 that triggers hippocampal neurogenesis

“…Nuclear receptors are transcription factors whose functions are modulated through the binding of endogenous small molecules. TLX is considered an orphan nuclear receptor since its endogenous ligand has not yet been discovered [exogenous and synthetic ligands have been reported but without physiological function in vivo ( 16 – 19 )]. The identification of such a functional endogenous ligand would help validate TLX as a therapeutic target for promoting neurogenesis for a variety of human diseases ( 10 – 12 ) and potentially also suggest approaches to modulate ligand abundance or availability.…”