Additionally, the structurally related and recently approved anti-Parkinson drug istradefylline emerged as a potent TLX modulator with low nanomolar potency. Mutagenesis studies defined a molecular epitope of TLX modulation by this class of TLX ligands to a region inside the ligand binding domain (LBD) involving interaction with helix 5. We observed also heterodimerization of TLX with retinoid X receptor (RXR) as well as recruitment of the nuclear receptor co-repressor 2 (SMRT). We demonstrated that istradefylline robustly displaced this repressor from TLX and modulated dimerization aligning with its effects on cellular TLX activity. This observation also suggests unprecedentedly a role of TLX as a direct repressor for other nuclear receptors. Overall, our results provide potent TLX modulators to study the receptor's role in health and disease and as a chemical starting point to facilitate future TLX ligand discovery.