Abstract 1443: Pharmacokinetics and pharmacogenetics of Actinomycin D in an animal model and pediatric patient population

ATP binding cassette (ABC) transporters, such as ABCB1 (MDR1/P-gp), are expressed throughout the body to protect against exogenous toxins. ABC transporters control removal from the body of anti-cancer drugs such as doxorubicin and etoposide via biliary or renal excretion. 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 >80% currently observed. Although Act D is generally well tolerated, severe hepatic toxicity has been associated with treatment. It has previously been demonstrated that Act D exposure is associated with a large degree of inter-patient variability in children with cancer. As common single nucleotide polymorphisms (SNPs) in ABC transporters have previously been shown to alter clinical exposure to various anti-cancer agents, we have carried out translational and clinical studies to investigate the transport of Act D using well established cell line and animal models. Growth inhibition (GI) and intracellular accumulation studies, over a range of Act D concentrations (0-10µM), were initially carried out to determine the role of ABC transporter expression in MDCKII-WT and ABCB1, ABCC1, ABCC2 and ABCG2 over-expressing cell lines. To assess the importance of ABCB1 and ABCC2 transporter expression in vivo, Act D pharmacokinetics and exposure were determined in Abcb1a/1b and Abcc2 knockout mice over 6 hours. In addition, liver, kidney and brain tissue samples were analysed to assess Act D tissue accumulation. Further pharmacokinetic sampling has also been carried out from children receiving Act D as part of their standard treatment, with analysis using a validated LC/MS method. Blood samples were obtained from all patients for pharmacogenetic analysis. Following treatment with Act D, a 59-fold decrease in Act D sensitivity was observed in ABCB1 over-expressing cells (GI50: 745nM), a 2-fold decrease in ABCC1 (GI50: 25.7nM) and a 3-fold decrease (GI50: 40.4nM) in ABCC2, as compared to the parental cell line (GI50: 12.7nM). Intracellular accumulation of Act D was lower in ABCB1 cells compared to the parental cell line, following incubation with Act D for 6 hours. This effect was abrogated by use of the ABCB1 inhibitor verapamil. In vivo pharmacokinetic analysis revealed a 64% higher AUC0-6h in mice with no Abcb1a/1b expression and a 22% lower AUC0-6h in Abcc2-/- mice compared to WT. Pharmacokinetic analysis of samples obtained from 71 patients indicated a large inter-patient variability in Act D exposure (AUC0-24h range: 1.7 - 19.4 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 haplotypes and Act D exposure in children with cancer. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 1443. doi:1538-7445.AM2012-1443