Rapid solid-phase extraction method to quantify [11C]-verapamil, and its [11C]-metabolites, in human and macaque plasma

Unadkat, Jashvant D.; Chung, Francisco; Sasongko, Lucy; Whittington, Dale; Eyal, Sara; Mankoff, David; Collier, Ann C.; Muzi, Mark; Link, Jeanne

doi:10.1016/j.nucmedbio.2008.08.001

« Previous Next »Nuclear Medicine and Biology
Volume 35, Issue 8 , Pages 911-917, November 2008

Rapid solid-phase extraction method to quantify [¹¹C]-verapamil, and its [¹¹C]-metabolites, in human and macaque plasma☆

Jashvant D. Unadkat
- Department of Pharmaceutics, University of Washington, Box 357610, Seattle, WA 98195, USA
- Corresponding author. Department of Pharmaceutics, School of Pharmacy, University of Washington, Box 357610, Seattle, WA 98195, USA. Tel.: +1 206 543 9434; fax: +1 206 543 3204.
Francisco Chung
- Department of Pharmaceutics, University of Washington, Box 357610, Seattle, WA 98195, USA
Lucy Sasongko
- Department of Pharmaceutics, University of Washington, Box 357610, Seattle, WA 98195, USA
Dale Whittington
- Department of Pharmaceutics, University of Washington, Box 357610, Seattle, WA 98195, USA
Sara Eyal
- Department of Pharmaceutics, University of Washington, Box 357610, Seattle, WA 98195, USA
David Mankoff
- Department of Radiology, University of Washington, Box 356004, Seattle, WA 98195, USA
Ann C. Collier
- Department of Medicine, University of Washington, Box 359929, Seattle, WA 98195, USA
Mark Muzi
- Department of Radiology, University of Washington, Box 356004, Seattle, WA 98195, USA
Jeanne Link
- Department of Radiology, University of Washington, Box 356004, Seattle, WA 98195, USA

Received 5 June 2008; received in revised form 24 July 2008; accepted 9 August 2008. published online 29 September 2008.

Abstract

Introduction

P-glycoprotein (P-gp), an efflux transporter, is a significant barrier to drug entry into the brain and the fetus. The positron emission tomography (PET) ligand, [¹¹C]-verapamil, has been used to measure in vivo P-gp activity at various tissue–blood barriers of humans and animals. Since verapamil is extensively metabolized in vivo, it is important to quantify the extent of verapamil metabolism in order to interpret such P-gp activity. Therefore, we developed a rapid solid-phase extraction (SPE) method to separate, and then quantify, verapamil and its radiolabeled metabolites in plasma.

Methods

Using high-performance liquid chromatography (HPLC), we established that the major identifiable circulating radioactive metabolite of [¹¹C]-verapamil in plasma of humans and the nonhuman primate, Macaca nemestrina, was [¹¹C]-D-617/717. Using sequential and differential pH elution on C₈ SPE cartridges, we developed a rapid method to separate [¹¹C]-verapamil and [¹¹C]-D-617/717. Recovery was measured by spiking the samples with the corresponding nonradioactive compounds and assaying these compounds by HPLC.

Results

Verapamil and D-617/717 recovery with the SPE method was >85%. When the method was applied to PET studies in humans and nonhuman primates, significant plasma concentration of D-617/717 and unknown polar metabolite(s) were observed. The SPE and the HPLC methods were not significantly different in the quantification of verapamil and D-617/717.

Conclusions

The SPE method simultaneously processes multiple samples in less than 5 min. Given the short half-life of [¹¹C], this method provides a valuable tool to rapidly determine the concentration of [¹¹C]-verapamil and its [¹¹C]-metabolites in human and nonhuman primate plasma.

Keywords: P-Glycoprotein, PET, SPE, Human, M. nemestrina, [¹¹C]-Verapamil, Metabolites, Macaque