The Synthesis and Structural Requirements for Measuring Glucocorticoid Receptor Expression In Vivo with (±)-¹¹C-YJH08 PET

Noninvasive methods to study glucocorticoid receptor (GR) signaling are urgently needed to elaborate the complexity of GR signaling in normal physiology and human disorders, as well as to identify selective GR modulators to treat diseases. Here, we report evidence supporting translational studies with (±)-¹¹C-5-(4-fluorobenzyl)-10-methoxy-2,2,4-trimethyl-2,5-dihydro-1H-chromeno[3,4-f]-quinoline ((±)-¹¹C-YJH08), a radioligand for PET that engages the ligand binding domain on GR. Methods: (±)-¹¹C-YJH08 was synthesized by reacting the phenol precursor with ¹¹C-methyl iodide. The biodistribution was studied in vivo. Specific binding was tested in vivo with adrenalectomy and ligand competition. A library of analogs was synthesized and studied in vitro and in vivo to understand the (±)-¹¹C-YJH08 structure-activity relationship. Rodent dosimetry studies were performed to estimate the human-equivalent doses of (±)-¹¹C-YJH08. Results: (±)-¹¹C-YJH08 was synthesized by reaction of the phenolic precursor with ¹¹C-methyl iodide, giving a radiochemical yield of 51.7% ± 4.7% (decay-corrected to starting ¹¹C-methyl iodide). Specific binding was observed in many tissues, including the brain. An analysis of the (±)-YJH08 structure-activity relationship showed that (R)- and (S)-enantiomers are equally avid for GR by occupying discrete binding modes. A focused chemical screen revealed that the aryl fluoride motif on YJH08 is essential for high-affinity GR binding in vitro, high tissue uptake in vivo, and efficient passage across the blood-brain barrier. Lastly, we performed dosimetry studies on rodents, from which we estimated the human-equivalent doses of (±)-¹¹C-YJH08 to be commensurate with the widely used ¹¹C and ¹⁸F tracers. Conclusion: These studies reveal the molecular determinants of a high-affinity and high-selectivity ligand-receptor interaction and support the use of (±)-¹¹C-YJH08 PET to make the first measurements of GR expression in human subjects.