Effect of P-glycoprotein inhibitor, verapamil, on oral bioavailability and pharmacokinetics of irinotecan in rats

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Abstract

The objective of present investigation was to study the effect of verapamil on the pharmacokinetics of irinotecan in order to evaluate the role of P-glycoprotein (P-gp) in irinotecan disposition. An in vitro study using Caco-2 intestinal cell monolayer was first carried out to determine the effect of verapamil on the function of intestinal P-gp. Verapamil (25 mg/kg) was administered orally 2 h before irinotecan oral (80 mg/kg) or intravenous (20 mg/kg) dosing in female Wistar rats. Plasma and biliary samples were collected at specified time points from control and treated animals to determine irinotecan and its metabolite, SN-38 concentrations. Bi-directional transport and inhibition studies in Caco-2 cells indicated irinotecan to be a P-gp substrate and the function of intestinal P-gp was significantly inhibited in presence of verapamil. After oral irinotecan dosing, the mean area under the plasma concentration–time curve (AUC) was found to be 14.03 ± 2.18 μg h/ml which was increased significantly, i.e. 61.71 ± 15.0 μg h/ml when verapamil was co-administered (P < 0.05). Similarly, the mean maximum plasma concentration of irinotecan increased from 2.93 ± 0.37 μg/ml (without verapamil) to 10.75 ± 1.0 μg/ml (with verapamil) (P < 0.05). There was approximately 4–5-folds increase in apparent bioavailability. On the other hand, the intravenous irinotecan administration with verapamil resulted in small but statistically significant effect on AUC (10.76 ± 2.0 to 23.3 ± 3.8 μg h/ml; P < 0.05) and systemic clearance (1206.4 ± 159.7 to 713.5 ± 78.2 ml/(h kg)). In addition, SN-38 showed significant change in oral pharmacokinetic parameters and minor changes in intravenous pharmacokinetic profile. Biliary excretion curves of both irinotecan and SN-38 were lowered by verapamil. The mean percent of irinotecan excreted into bile over 5 h following intravenous and oral administration was found to be 8% and 1%, respectively, which was further reduced to half when treated with verapamil. These results are quite stimulating for further development of a clinically useful oral formulation of irinotecan based on P-gp inhibition.

Introduction

Irinotecan (CPT-11), a water-soluble camptothecin, is the agent of choice for treatment of metastatic carcinomas of colon and rectum. It exerts anti-tumor activity by inhibiting the intranuclear enzyme topoisomerase I. Irinotecan itself is a prodrug and gets converted in vivo to 100–1000 times more potent active metabolite, 7-ethyl-10-hydroxy camptothecin (SN-38) by carboxylesterase enzyme. Majority of the studies performed with irinotecan are using intravenous administration (Chu et al., 1997, de Forni et al., 1994, Gupta et al., 1996, Iyer et al., 2002). However, it has been given orally in early clinical studies and its pharmacokinetic profile is characterized by relatively poor and highly variable oral bioavailability (Drengler et al., 1999, Schoemaker et al., 2005, Soepenberg et al., 2005, Zamboni et al., 1998). The main adverse effects of irinotecan in humans are gastrointestinal toxicity and myelosuppression which limits its usage and administration (Mathijssen et al., 2001, Yang et al., 2005). Since biliary excretion of irinotecan and its metabolites is a major elimination pathway, accounting for about 60% of the administered dose, several hypotheses for its toxicity directly involve the biliary excretion of these compounds (Chu et al., 1998).

The involvement of active transporters particularly P-glycoprotein (P-gp) in the transport of both irinotecan and SN-38 is demonstrated by various researchers (Itoh et al., 2005, Iyer et al., 2002, Luo et al., 2002, Takemoto et al., 2006, Yamamoto et al., 2001). P-gp is the major efflux transporter protein responsible for poor absorption of many drugs. Presence of P-gp transporter in intestinal epithelial membrane and biliary canalicular membrane makes its inhibition a logical strategy to enhance irinotecan oral bioavailability and ameliorating diarrhoeal toxicities. Verapamil is the most extensively characterized P-gp inhibitor and multi-drug resistance (MDR) reversal agent that has entered clinical trials (Perez-Tomas, 2006). It is also reported that verapamil has increased the AUC of doxorubicin and paclitaxel in rodents (Candussio et al., 2002, Choi and Li, 2005). Therefore, the effect of co-administration of verapamil on the oral bioavailability and pharmacokinetics of irinotecan is the subject of current investigation. Cyclosporin, PSC-833, ketoconazole, loperamide, probenecid and imatinib as the inhibitors of active transporters and cytochrome enzymes have modulated pharmacokinetics of irinotecan (Arimori et al., 2003, Gupta et al., 1996, Horikawa et al., 2002, Iyer et al., 2002, Kehrer et al., 2002, Liu et al., 1996, Stewart et al., 2004, Tobin et al., 2005). The main objective of the study is to evaluate the scope of improvement in oral delivery of irinotecan via co-treatment with oral P-gp inhibitor. P-gp inhibitors are generally administered intravenously and no suggestion is made regarding their oral intake. Parenteral administration of P-gp inhibitors in therapeutic doses into humans may cause severe clinical consequences. This is because in addition to intestine, P-gp is present in hepatocytes, bile canaliculi, brain and kidney suggesting its role in distribution, metabolism and excretion. Consequently, clinical pharmacokinetic interactions could be anticipated when P-gp inhibitors are co-administered. An ideal P-gp inhibitor should give nearly maximal inhibition of P-gp transport locally at intestine with a minimal systemic effect and whole body burden (Dantzig et al., 2003, Varma et al., 2003).

The design of present study includes an initial in vitro investigation on Caco-2 cells to evaluate the effect of verapamil on the function of intestinal P-gp. This was followed by determination of irinotecan pharmacokinetics (plasma concentrations and biliary excretion) following oral and intravenous (i.v.) administration with and without co-administration of verapamil in female Wistar rats. Based on these studies, it might be feasible to develop an oral irinotecan formulation which is much more convenient than the i.v. dosage forms.

Section snippets

Chemicals and apparatus

Irinotecan (>99%), SN-38 (>96%) and topotecan (>98%) originated from Dabur Pharma Limited (U.P., India). Verapamil, disodium ethylene diamine tetra acetic acid and non-essential amino acids were purchased from Sigma–Aldrich (St. Louis, MO, USA). Acetonitrile of HPLC grade was obtained from J.T. Baker (USA). O-phosphoric acid and DMSO were from Merck Ltd. (India). Ketamine (Aneket) and xylazine HCl (Xylaxin) were obtained from Neon Labs Ltd. (Mumbai, India) and Indian Immunologicals Ltd. (A.P.,

Bi-directional transport of irinotecan in Caco-2 cells

No significant change was observed in the TEER value (>400 Ω cm2) measured before (0 h) and after (2 h) completion of transport studies. The transport rate of lucifer yellow was also not changed in the presence of various P-gp modulators. The results obtained with rhodamine 123 indicated its polarized transport (PappB–A: 128 ± 12 nm s−1; PappA–B: 5 ± 2 nm s−1) similar to that reported earlier (Troutman and Thakker, 2003), enabling the complete standardisation of Caco-2 cell monolayer (Irvine et al., 1999).

Discussion

Irinotecan, a FDA approved anti-cancer agent, is widely indicated for the treatment of various malignancies. It is currently marketed for intravenous use although few reports of its oral drug administration exist (Drengler et al., 1999, Schoemaker et al., 2005, Soepenberg et al., 2005, Stewart et al., 1997). Data available on its absorption and disposition showed encouraging results with variable absorption, poor efficacy and toxicity profiles. As a result novel formulations of irinotecan

Conclusions

The simultaneous administration of verapamil significantly modulates the oral bioavailability and pharmacokinetics of irinotecan. Oral absorption and bioavailability of irinotecan are markedly increased (4.3-fold) suggesting that its low systemic exposure after oral administration is, at least in part, due to its high affinity for P-gp efflux pump. P-gp in the gastro-intestinal mucosa limits the absorption of orally administered xenobiotics and mediates its excretion into the bile. The effect

Acknowledgements

One of the authors (T.B.) is grateful to the Council of Scientific & Industrial Research (CSIR), New Delhi, India for providing senior research fellowship.

References (40)

  • Bansal, T., Awasthi, A., Jaggi, M., Khar, R.K., Talegaonkar, S., in press a. Development and validation of reversed...
  • Bansal, T., Awasthi, A., Jaggi, M., Khar, R.K., Talegaonkar, S., in press b. Pre-clinical evidence for altered...
  • X.Y. Chu et al.

    Multispecific organic anion transporter is responsible for the biliary excretion of the camptothecin derivative irinotecan and its metabolites in rats

    J. Pharmacol. Exp. Ther.

    (1997)
  • X.Y. Chu et al.

    Biliary excretion mechanism of CPT-11 and its metabolites in humans: involvement of primary active transporters

    Cancer Res.

    (1998)
  • M. de Forni et al.

    Phase I and pharmacokinetic study of the camptothecin derivative irinotecan, administered on a weekly schedule in cancer patients

    Cancer Res.

    (1994)
  • R.L. Drengler et al.

    Phase I and pharmacokinetic trial of oral irinotecan administered daily for 5 days every 3 weeks in patients with solid tumors

    J. Clin. Oncol.

    (1999)
  • E. Gupta et al.

    Metabolic fate of irinotecan in humans: correlation of glucuronidation with diarrhea

    Cancer Res.

    (1994)
  • E. Gupta et al.

    Pharmacokinetic modulation of irinotecan and metabolites by cyclosporin A

    Cancer Res.

    (1996)
  • T. Itoh et al.

    Uptake of irinotecan metabolite SN-38 by the human intestinal cell line Caco-2

    Cancer Chemother. Pharmacol.

    (2005)
  • L. Iyer et al.

    Biliary transport of irinotecan and metabolites in normal and P-glycoprotein-deficient mice

    Cancer Chemother. Pharmacol.

    (2002)
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