A Novel CYP11B2-Specific Imaging Agent for Detection of Unilateral Subtypes of Primary Aldosteronism

Context: Although adrenal vein sampling is the standard method to distinguish unilateral from bilateral forms of primary aldosteronism, it is an invasive and technically difficult procedure. C-11-metomidate (MTO)-positron emission tomography was reported as a potential replacement for adrenal vein sampling. However, MTO has low selectivity for CYP11B2 over CYP11B1. Objective: This study aimed to determine the selectivity of F-18-CDP2230, a new imaging agent, for CYP11B2 over CYP11B1 and determine whether the biodistribution profile of F-18-CDP2230 is favorable for imaging CYP11B2. Methods: The IC50 of CDP2230 for the enzymatic activities of CYP11B2 and CYP11B1 was determined using cells with stable expression of either enzyme. In vitro autoradiography of human adrenal sections with aldosterone-producing adenomas was performed to confirm the specific binding ability of F-18-CDP2230 to CYP11B2-expressing regions. Furthermore, positron emission tomography and magnetic resonance imaging were performed to evaluate the biodistribution of F-18-CDP2230 in rats. Results: Although CDP2230 showed a significantly lower affinity for CYP11B2 and CYP11B1 than did MTO analogues, its selectivity for CYP11B2 over CYP11B1 was higher than that of MTO analogues. In vitro autoradiography revealed that the binding of F-18-CDP2230 to CYP11B2-expressing regions in the adrenal gland was more specific than that of I-123-IMTO. Moreover, the biodistribution study showed that F-18-CDP2230 accumulated in adrenal glands with low background uptake. Conclusions: Our study showed a high selectivity of F-18-CDP2230 for CYP11B2 over CYP11B1 with a favorable biodistribution for imaging CYP11B2. F-18-CDP2230 is a promising imaging agent for detecting unilateral subtypes of primary aldosteronism.