Abstract C112: Debrisoquine as a model substrate of the organic cation transporter OCT1.

Organic cation transporters are involved in the cellular uptake of chemotherapeutic drugs like cisplatin, oxaliplatin and imatinib. We have also shown that genetic polymorphisms in the liver-specific organic cation transporter OCT1 may affect pharmacokinetics and efficacy of supportive care drugs like the antiemetics ondansetron and tropisetron or the opioid tramadol. Here we tested whether debrisoquine, a model drug used to phenotype CYP2D6 activity, is a substrate of the liver-specific organic cation transporter OCT1 and whether genetic polymorphisms in OCT1 affect debrisoquine cellular uptake. We measured the inhibition of OCT1 by debrisoquine and OCT1-mediated uptake of debrisoquine using HEK293 cells genetically engineered to overexpress wild type or loss-of-function OCT1 isoforms. We overexpressed OCT1 isoforms carrying the common loss-of-function amino acids substitutions in Caucasians Arg61Cys, Cys88Arg, Gly401Ser, Gly465Arg or deletion of Met420. Debrisoquine inhibited the uptake of the model OCT1 substrate MPP+ with IC50 below 10 μM. Debrisoquine uptake was significantly increased both in time and in concentration dependent manner in cells overexpressing wild-type OCT1 (KM of 5.9 ×1.5 μM and vMAX of 41.9 ×4.5 pmol/min/mg protein). OCT1-mediated uptake of debrisoquine was reduced or missing in cells expressing the common loss-of-function isoforms. The deletion of Met420 and the substitutions of Arg61Cys and Gly401Ser reduced vMAX by 48, 63 and 91%, respectively, but did not affect the Km of the OCT1-mediated debrisoquine uptake. The OCT1 isoforms carrying Cys88Arg or Gly465Arg substitutions completely lacked OCT1-mediated debrisoquine uptake. In conclusion, debrisoquine is a substrate of OCT1 and common loss-of-function OCT1 polymorphisms affect debrisoquine uptake. Debrisoquine has a potential to be used as phenotyping marker for OCT1 activity. Moreover, known in vivo variations in debrisoquine pharmacokinetic and their relation to development of lung and bladder cancer may be related to variation not only in CYP2D6, but also in OCT1 activity. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2011 Nov 12-16; San Francisco, CA. Philadelphia (PA): AACR; Mol Cancer Ther 2011;10(11 Suppl):Abstract nr C112.