Development of a Novel ¹⁸F-Labeled Radioligand for Imaging Cholesterol 24-Hydroxylase with Positron Emission Tomography

Cholesterol 24-hydroxylase (CYP46A1), also known as CH24H, is a brain-specific monooxygenase responsible for the elimination of cholesterol from the central nervous system (CNS). It catalyzes the conversion of cholesterol to 24(<i>S</i>)-hydroxycholesterol, the primary pathway for CNS cholesterol clearance. Dysregulation of cholesterol homeostasis has been implicated in neurodegenerative diseases, such as Alzheimer's disease (AD) and Parkinson's disease (PD). This study presents the synthesis and evaluation of [¹⁸F]<b>5</b> ([¹⁸F]CHL2310) as a novel radioligand for imaging CYP46A1 and cholesterol metabolism in the brain by positron emission tomography (PET). CHL2310 was identified as a potent inhibitor of CYP46A1 and subsequently labeled with fluorine-18 in a radiochemical yield of 13% and a high molar activity of 93 GBq/μmol. [¹⁸F]CHL2310 was evaluated in rats using in vitro autoradiography and PET imaging, demonstrating high brain uptake, heterogeneous brain distribution, favorable binding specificity, and suitable clearance kinetic profiles within the CNS. In all, [¹⁸F]<b>5</b> ([¹⁸F]CHL2310) represents a promising tool for noninvasive quantification of cholesterol metabolism by imaging CYP46A1.