Abstract 5447: Investigating the relationship between pharmacogenetic variation in ABCB1 and ABCC2 tagSNPs and actinomycin D pharmacokinetics in children
Authors: Hill Christopher R. , Brown Colin D A , Boddy Alan V. , Veal Gareth J. 
Published: June 2012

Abstract
Actinomycin D (Act D) has been used successfully to treat adult and childhood cancers for over 30 years. It continues to play a key role in the treatment of Wilms tumour patients, with 5-year survival rates &gt;80% currently observed. While treatment is generally well tolerated, veno-occlusive disease (VOD) is a potentially life-threatening side effect observed in 1.7-13.5% of patients. Dose-intensity of Act D treatment has been highlighted as a possible risk-factor for VOD in paediatric patient populations.
ATP binding cassette (ABC) transporters are expressed throughout the body to protect against exogenous compounds. In the liver and kidney, ABC transporters facilitate the removal of compounds via biliary or renal excretion and have previously been shown to play a major role in the transport of anti-cancer agents such as doxorubicin and irinotecan. Common single nucleotide polymorphisms (SNPs) for these transporters have been shown to alter clinical exposure to various anti-cancer agents. We have therefore carried out translational and clinical studies focusing on Act D pharmacokinetics in Wilms tumour patients and pharmacogenetic variation in key ABC transporters.
Initial experiments were carried out to determine the potential importance of ABC transporter expression on the in vitro activity and transport of Act D, using MDCKII-WT alongside ABCB1, ABCG2 and ABCC2 over-expressing cell lines. Growth inhibition (GI) and intracellular accumulation experiments were carried out over a range of Act D concentrations (0-10µM). Pharmacokinetic analysis of samples obtained from patients receiving Act D was carried out using a validated LC/MS method and blood samples were obtained from all patients for pharmacogenetic analysis. Finally, the International HapMap database was used to determine tagSNPs for ABCB1 and ABCC2 with minor allele frequencies of greater than 0.1 in a Caucasian population, allowing the link between ABCB1 and ABCC2 haplotypes and Act D exposure to be investigated.
GI experiments indicated a 40-fold decrease in Act D sensitivity in cells over-expressing ABCB1 (GI50: 0.85µM) and a 3-fold decrease in cells over-expressing ABCC2 (GI50: 0.06µM) compared to the control cell line (GI50: 0.02µM). Higher intracellular levels of Act D (normalized per mg protein) were observed in the WT parental cell line (650nM) as compared to those over-expressing ABCB1 (215nM), following a 6h incubation with 2µM Act D. This effect was abrogated by use of the ABCB1 inhibitor verapamil. Pharmacokinetic analysis of samples obtained from 56 patients indicated a large inter-patient variability in Act D exposure (AUC0-24h range: 1.6 – 11.4 µg/ml.min). Ongoing investigations into pharmacogenetic variation in ABCB1 and ABCC2 tagSNPs in these patients provide novel preliminary data relating to links between ABCB1 and ABCC2 haplotypes and Act D exposure in children with cancer.
Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 5447. doi:10.1158/1538-7445.AM2011-5447