[11C]glyburide PET imaging for quantitative determination of the importance of Organic Anion-Transporting Polypeptide transporter function in the human liver and whole-body

Abstract

Organic Anion-Transporting Polypeptides (OATPs) are known to control the liver uptake of many drugs. Non-hepatic expression of OATPs has been reported although functional importance for whole-body pharmacokinetics (WBPK) remains unknown. Glyburide is a well described substrate of several hepatic and non-hepatic OATPs. Dynamic whole-body positron emission tomography (DWB-PET) with [¹¹C]glyburide was performed in humans for determination of the importance of OATPs for liver uptake and WBPK. Seven healthy male subjects (24.7 ± 3.2 years) underwent [¹¹C]glyburide PET scan with concomitant blood sampling. All subjects underwent baseline [¹¹C]glyburide PET scan. Five subjects underwent a subsequent [¹¹C]glyburide PET scan after infusion of the potent OATP inhibitor rifampicin (9 mg/kg i.v.). The transfer constant (k_uptake) of [¹¹C]glyburide from blood to the liver was estimated using the integration plot method. The tissue exposure of [¹¹C]glyburide was described by the area under the time-activity curve (AUC) and corresponding tissue/blood ratio (AUCR). [¹¹C]glyburide was barely metabolized in both the baseline and rifampicin conditions. Parent (unmetabolized) [¹¹C]glyburide accounted for > 90 % of the plasma radioactivity. Excellent correlation was found between radioactive counting in arterial blood samples and in the image-derived input function, in both the baseline and rifampicin conditions (R² = 97.9 %, p < 0.01). [¹¹C]glyburide predominantly accumulated in the liver. Rifampicin decreased liver k_uptake by 77.3 ± 7.3 %, which increased exposure in blood, kidneys, spleen, myocardium and brain (p < 0.05). No significant change in AUCR was observed except in the liver (p < 0.01). [¹¹C]glyburide benefits from metabolic stability and high sensitivity to OATP inhibition which enables quantitative determination of OATP function. DWB-PET suggests negligible role for non-hepatic OATPs in controlling the tissue distribution of [¹¹C]glyburide.

Keywords: Hepatocyte; Liver; PET; Pharmacokinetics; Positron emission tomography; Transporters; [(11)C]glyburide.