The synthesis and structural requirements for measuring glucocorticoid receptor expression in vivo with (±)-¹¹C-YJH08 PET

Abstract

Non-invasive methods to study glucocorticoid receptor (GR) signaling are urgently needed to reveal 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 (named as (±)-[¹¹C]YJH08), a radioligand for positron emission tomography (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 with PET/CT and autoradiography. A library of analogues were 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). An analysis of the (±)-YJH08 structure-activity relationship with molecular dynamics simulations showed that (R)- and (S)-enantiomers occupy the ligand binding domain on GR with different binding modes and have indistinguishable patterns of biodistribution in vivo. Moreover, a focused chemical screen of analogues revealed that the aryl fluoride motif on YJH08 is essential for high affinity GR binding in vitro, high tissue uptake in vivo, and passage across the blood brain barrier. Lastly, we performed dosimetry studies in rodents, from which we showed estimated human equivalent doses of (±)-[¹¹C]YJH08 to be commensurate with widely used carbon-11 and fluorine-18 tracers. Conclusion: In summary, these studies reveal the molecular determinants of a high affinity and selectivity ligand-receptor interaction and support the use of (±)-[¹¹C]YJH08 PET to make the first measurements of GR expression in human subjects.