Gene Expression Patterns Associated with Cytarabine Pharmacology and Outcome in Pediatric Acute Myeloid Leukemia.

Abstract 114

To identify genes that influence responses to cytarabine (ara-C) treatment, we explored the association of gene expression in leukemic cells at diagnosis with multiple pharmacological and clinical end-points in children with acute myeloid leukemia (AML) treated with ara-C on the St. Jude AML97 clinical trial. We applied a novel statistical procedure, PRojection Onto the Most Interesting Statistical Evidence (PROMISE; PR), to identify genes with expression levels associated with clinical and pharmacological endpoints. To do this, we first defined the following values of the clinical and pharmacological variables as “therapeutically beneficial” :higher leukemic cell ara-C triphosphate levels, lower DNA synthesis values on days 1 and 2 of treatment relative to baseline, decreases in leukocyte counts on day 2 of treatment, improved response and decreased risk of relapse, death, or second malignancy. We considered a gene to show a therapeutically beneficial pattern of association if its expression was positively correlated with ara-CTP levels, negatively correlated with DNA synthesis levels, negatively correlated with decrease in leukocyte counts on day 2, positively correlated with better treatment response, and negativelycorrelated with the risk of relapse or death. A gene showed a therapeutically detrimental pattern of association if its expression had the opposite correlations with the clinical and pharmacological variables. We performed five variable (PR5 using early pharmacologically interesting phenotype measures) or seven variable (PR7 all the above indicated phenotypes) PROMISE analyses. PR5 identified 275 beneficial probe sets and 69 detrimental probe sets (p ≤ 0.005). PR7 analysis identified 112 beneficial probe sets and 115 detrimental probe sets (p ≤ 0.005). To confirm these results, we performed a PROMISE for a cohort of patients treated with ara-C and other agents on the AML02 protocol. Gene expression in leukemic cells at diagnosis was analyzed for a beneficial or detrimental pattern of association with three phenotypes (PR-3); diagnostic blast ara-C cytotoxicity, minimal residual disease (MRD) and event-free survival (EFS). Eighty-one probe sets identified by PR5 or PR7 analyses in the initial cohort were confirmed in the PR-3 analysis of AML02 data. Genes identified in the present study may serve as predictive markers of response and candidates for future drug development.