Influence of OATPs on Hepatic Disposition of Erlotinib Measured With Positron Emission Tomography

Abstract

To assess the hepatic disposition of erlotinib, we performed positron emission tomography (PET) scans with [¹¹ C]erlotinib in healthy volunteers without and with oral pretreatment with a therapeutic erlotinib dose (300 mg). Erlotinib pretreatment significantly decreased the liver exposure to [¹¹ C]erlotinib with a concomitant increase in blood exposure, pointing to the involvement of a carrier-mediated hepatic uptake mechanism. Using cell lines overexpressing human organic anion-transporting polypeptides (OATPs) 1B1, 1B3, or 2B1, we show that [¹¹ C]erlotinib is selectively transported by OATP2B1. Our data suggest that at PET microdoses hepatic uptake of [¹¹ C]erlotinib is mediated by OATP2B1, whereas at therapeutic doses OATP2B1 transport is saturated and hepatic uptake occurs mainly by passive diffusion. We propose that [¹¹ C]erlotinib may be used as a hepatic OATP2B1 probe substrate and erlotinib as an OATP2B1 inhibitor in clinical drug-drug interaction studies, allowing the contribution of OATP2B1 to the hepatic uptake of drugs to be revealed.

Figure 1

Representative PET images (subject 4) of the abdominal region for baseline scan (scan 1) and scan after oral intake of erlotinib (scan 2) recorded at 3.5, 17.5, 42.5, 67.5, and 87.5 min after radiotracer injection. Radioactivity concentration is expressed as percent of the injected dose per mL (%ID/mL) and radiation scale is set from 0 to 0.04. Anatomical structures are labeled with arrows (L, liver; GB, gall bladder; BD, bile duct; C, colon; S, spleen).

Figure 2

Mean time–activity curves (%ID/mL or %ID ± SD, n = 6) in arterial blood (a), liver (b) and bile duct and gall bladder (c) for baseline scan (scan 1) and scan after oral intake of erlotinib (scan 2). In d, the liver‐to‐blood concentration ratio (K _b,liver) over time is shown for the two scans.

Figure 3

Diagram of the liver model. C _blood is the concentration of [¹¹C]erlotinib in arterial blood, C _liver the concentration of [¹¹C]erlotinib in the liver, and X _bile the total amount of [¹¹C]erlotinib in the bile duct and gall bladder. V _d and V _liver denote volume of distribution and physiological liver volume, respectively. K _influx (min⁻¹) is the influx rate constant from blood into liver, k _backflux (min⁻¹) the backflux rate constant from liver into blood, k _bile (min⁻¹) the rate constant for biliary excretion, and k _el (min⁻¹) the rate constant for elimination of [¹¹C]erlotinib from blood. K _influx/k _backflux defines the apparent [¹¹C]erlotinib influx into the liver at steady state. Hepatic uptake clearance (CL _uptake, mL min⁻¹) is defined as k _influx × V _d.

Figure 4

CL _uptake (a), k _backflux (b), k _influx/k _backflux (c), and k _bile (d) in individual subjects for baseline scan (scan 1) and scan after oral intake of erlotinib (scan 2). ns, not significant, *P < 0.05, Wilcoxon matched‐pairs signed rank test.

Figure 5

(a) Mean uptake of [¹¹C]erlotinib (<0.1 μM) after 5‐min incubation time (% of vector control ± SD) in OATP1B1, OATP1B3, and OATP2B1 overexpressing cells treated with vehicle, cyclosporine A (CsA, 10 μM), rifampicin (100 μM), or unlabeled erlotinib (1 μM). (b) Time dependency of [¹¹C]erlotinib (<0.1 μM) uptake (percent of applied dose per 10⁶ cells, %AD/10⁶ cells ± SD) in cells overexpressing OATP1B1, OATP1B3, or OATP2B1 or transfected with the empty vector (vector control). (c) Concentration dependency of the OATP2B1‐specific uptake of [¹¹C]erlotinib determined at 7.5 min at various erlotinib concentrations (0.05–2.05 μM). Black solid line represents model fit and broken red and blue lines represent fits for saturable and nonsaturable components, respectively. Kinetic parameters ± standard error are shown in the graph. Details of the fitting are described in the Supplementary Methods. Data shown in a are from two experiments performed with three technical replicates each and data shown in b and c are from one experiment performed with three technical replicates each. ns, not significant, ***P < 0.001, two‐way ANOVA with Bonferroni posttest.