PHARMACOGENOMIC PROFILE ASSOCIATED WITH HIGH SENSITIVITY AND LOW TOXICITY TO A COMBINATION OF GEMTUZUMAB OZOGAMICIN PLUS FLUDARABINE, CYTARABINE, IDARUBICIN IN CD33-POSITIVE ACUTE MYELOID LEUKEMIA

Background: In acute myeloid leukemia (AML) the presence or absence of cytogenetic abnormalities allows the identification of favorable, intermediate and unfavorable subgroups. However, besides these specific subgroups, little it is known about the genetic variations influencing specific drug-related phenotypes. Aims: To perform an exploratory pharmacogenomic study that relates genetic variations in multidrug enzymes and transporters genes with the efficacy and toxicity to treatment. Patients and methods: We analyzed 94 CD33-positive AML patients younger than 65 previously untreated and enrolled in a phase III multicenter clinical trial combining low dose of Gemtuzumab-ozogamicin (GO) with FLAI regimen (Fludarabine, Cytarabine, Idarubicin) as Induction chemotherapy (eudract: 2007-005248-26; ClinicalTrials.gov NCT00909168). The induction regimen (GO-FLAI) included fludarabine (25 mg/sqm) and Ara-C (2 g/sqm) on days 1-5, idarubicin (10 mg/sqm) on days 1, 3, and 5 and GO (3 mg/sqm) on day 6. Hematopoietic stem cell transplant was planned for all high risk AML patients in first complete remission (CR) after consolidation with intermediate doses of Ara-C and idarubicin. Cytogenetics, multidrug-resistance phenotype, FLT3 and NPM mutation status, as well as WT1 quantitative expression analyses were performed at diagnosis in all patients. Furthermore, high-resolution single nucleotide polymorphism (SNP) array analysis (Affymetrix, Inc. Santa Clara, CA, USA) was also performed. The allele frequencies of 1936 genetic variations of 225 absorption, distribution, metabolism and excretion were assessed using the new Affymetrix drug-metabolizing enzyme and transport (DMET Plus) genotyping platform (Affymetrix). All statistical analyses were performed using the R package 2.11.1. Results: Of the 94 patients, genotype results were evaluable for 91 cases. The median call rate was 99.48 (range, 96.32-100). Three samples were run in duplicate and results with “passed call rate” were compared across all the polymorphic sites, showing a repeatability of 99.99%. In an initial screening procedure, we tested the association among SNPs and response to the induction cycle (FLAI + Gemtuzumab-Ozogamicin). Therefore, the genotyping profile of 80 patients in complete (85%) and partial (3%) remission was compared to that of patients (12%) with no response. We found a highly significant difference (p < 0.001) in the allele frequency of 2 variants, in complete linkage disequilibrium, in the alcohol dehydrogenase enzyme (ADH1A). These variants were not associated with high risk AML, FLT3 and NPM1 mutations, but strongly influenced response to the induction phase also in a multivariate analysis. Since genetic polymorphisms may influence the toxicity of chemotherapy drugs, we stratified SNPs according to liver toxicity and a significant difference in the allele frequency of a member of the cytochrome P450 family which is involved in the alcohol metabolism (CYP2E1) was found to be associated with a grade I/II liver toxicity. Conclusions: A pharmacogenomic panel made up of 1 gene (ADH1A) associated with clinical outcome and 1 gene (CYP2E1) associated with toxicity was for the first time identified in AML patients younger than 65 years treated with a combination of GO and FLAI regimen. Supported by European LeukemiaNet, AIL, AIRC, FIRB 2006, Ateneo RFO grants, Project of integrated program, PRIN 2008, Programma di Ricerca Regione – Università 2007 – 2009.