Abstract 3353: Effect of erlotinib on the pharmacokinetics of irinotecan and its metabolites: A drug-drug interaction study.
Authors: Sanematsu Emiko , Toyooka Issei , Takashima Yuki , Okimoto Tamio , Tsubata Yukari , Saito Hideyuki , Isobe Takeshi , Hamada Akinobu 
Published: August 2014

Abstract
Purpose:
Since irinotecan and erlotinib are used in treatment for non-small cell lung cancer (NSCLC), co-administration of these drugs might be an effective treatment for NSCLC. However, drug-drug interaction should be concerned because these drugs are metabolized by CYP3A4 and excreted into bile by ABC transporters. To clarify the drug-drug interaction when these drugs are co-administered, we examined the effect of this co-administration on the pharmacokinetics of irinotecan, its active metabolite 7-ethyl-10-hydroxycamptothecin (SN-38), SN-38 glucuronide (SN-38G) in animal model.
Methods:
Cytotoxicity of irinotecan and SN-38 with erlotinib against NSCLC cell line (A549) was assessed. To elucidate the effect of drug-drug interaction between irinotecan and erlotinib, male Sprague-Dawley rats were treated with 10 mg/kg irinotecan and 25 mg/kg erlotinib. The concentrations of irinotecan, SN-38, SN-38G and erlotinib in plasma, bile, and tissues were analyzed by high-performance liquid chromatography. Pharmacokinetic parameters were calculated by non-compartmental model methods.
Results:
Co-exposured erlotinib enhanced the cytotoxicity of SN-38 in a dose-dependent manner, however it did not significantly affect the cytotoxicity of irinotecan against A549 that is resistant to erlotinib. Additionally, co-administration of erlotinib resulted in a significant increase of plasma concentration of irinotecan, SN-38 and SN-38G compared to irinotecan alone, but decrease in the biliary excretion. Erlotinib significantly increased the concentration of irinotecan and SN-38G in kidney and that of SN-38 in lung and jejunum. On the other hand, co-administration of irinotecan intended to decrease the plasma concentration of erlotinib but significant differences of pharmacokinetic parameters were not observed. Also, levels of erlotinib in tissues were not affected by co-administration of irinotecan.
Conclusions:
We proposed the possibility of combination therapy of irinotecan with erlotinib because the plasma concentration of irinotecan and its active metabolite SN-38 significantly increased in vivo and the cytotoxicity of SN-38 against NSCLC cell line enhanced. New effective salvage chemotherapy regimens are needed in patients with NSCLC. We conducted a phase I/II clinical study of combination chemotherapy with irinotecan and erlotinib for recurrent NSCLC because our data have shown synergistic/additive effects between irinotecan and epidermal growth factor receptor-tyrosine kinase inhibitor.
Citation Format: Emiko Sanematsu, Issei Toyooka, Yuki Takashima, Tamio Okimoto, Yukari Tsubata, Hideyuki Saito, Takeshi Isobe, Akinobu Hamada. Effect of erlotinib on the pharmacokinetics of irinotecan and its metabolites: A drug-drug interaction study. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 3353. doi:10.1158/1538-7445.AM2013-3353