RESEARCH ARTICLE – Pharmacokinetics, Pharmacodynamics and Drug Transport and MetabolismSaturable Hepatic Extraction of Gemcitabine Involves Biphasic Uptake Mediated by Nucleoside Transporters Equilibrative Nucleoside Transporter 1 and 2
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INTRODUCTION
Pancreatic cancer is a major cause of cancer-related death globally, and has a 5-year survival rate of only about 5% for all stages combined.1 Surgical treatment offers the best possibility for cure, but pancreatic cancer is likely to become metastatic,1 especially to the liver (60%).2 Even patients who receive surgery experience a 50%–80% local recurrence rate and a 25%–50% risk of developing distant metastases,3 and the 5-year survival rate after recurrence is less than 30%.4., 5. Therefore,
Chemicals
[3H]GEM (16.3 Ci/mmol) and [14C]inulin (16 mCi/mmol) were purchased from Moravek Biochemicals, Inc. (Brea, California) and American Radiolabeled Chemicals, Inc. (St. Louis, Missouri), respectively. Nonlabeled GEM was purchased from Tokyo Chemical Industry Company, Ltd. (Tokyo, Japan). Collagenase Type I from Clostridium histolyticum was obtained from Sigma–Aldrich (St. Louis, Missouri). All other chemicals were commercial products of analytical or cell-culture grade. S
Time Course of [3H]GEM Uptake in Rat Hepatocytes
[3H]GEM uptake by rat hepatocytes increased time-dependently up to 30 min. Initial uptake (cell-to-medium ratio) was approximately linear up to 5 min and the uptake clearance at 5 min was 18 μ L/mg protein (Fig. 1). [3H]GEM uptake was markedly inhibited by 77% of initial uptake at 30 min in the presence of 10 mM nonlabeled GEM (Fig. 1). Therefore, the uptake time was fixed at 5 min for subsequent studies.
Kinetic Analysis of [3H]GEM Uptake in Rat and Human Hepatocytes
Initial uptake rate of GEM in rat hepatocytes followed Michaelis–Menten kinetics (Fig. 2a). The
DISCUSSION
We have confirmed the effectiveness and safety of GEM HAI in a previous phase I clinical study,18., 19., 20., 21. but nevertheless, dose selection remains a critical issue, because saturation of hepatic extraction in HAI would lead to increased systemic exposure, resulting in potentially severe toxicity. Therefore, in this study, we examined the saturability of hepatic extraction of GEM at clinically relevant concentrations in normal hepatocytes to provide a rational basis for dose selection
CONCLUSION
Our results indicate that hepatic extraction of GEM is predominantly mediated by hENT2, and at clinically relevant dose levels, hENT2-mediated uptake is not completely saturated. This is critical for HAI, because saturation of hepatic uptake would result in a marked increase of GEM concentration in the peripheral circulation, abrogating the advantage of HAI over i.v. administration in terms of the likelihood of severe adverse events. Thus, expression of ENT2 in hepatic tissue may be a key
ACKNOWLEDGMENT
This study was supported in part by JSPS KAKENHI grant number 23590173.
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