The Influence of CYP2C9 and CYP2C19 Gene Polymorphism On Metabolism of Drugs Used in Therapy of Acute Leukemia in Children.

Gene polymorphism coding for drug-metabolizing enzymes may cause individual differences in effectiveness and toxicity of many medications, including cytostatics. Although intensified treatment resulted recently in better prognosis of leukemia, many adverse effects are still observed during therapy resulting from nonspecific activity and narrow therapeutic index of anti-cancer drugs. The objectives of the study: 1. Determining the frequency of selected allele variants: CYP2C9, CYP2C19 in population of Polish children treated for acute leukemia. 2. Analysis of the role of CYP2C9 and CYP2C19 in cyclophosphamide metabolism. 3. Determininig the influence of carrying selected CYP2C9 and C19 polymorphism on cyclophosphamide metabolism in form of increased adverse reaction risk (according to WHO score), relapse and other infringements in treatment protocols and procedures following the use of standard doses of alkylating agents. Patients: 184 patients (106 boys, 78 girls) were examined, age between 1 and 18 (median age 7 years, average age 7.64 years, SD=5.3) treated for acute leukemia (ALL:167, AML:17) at various time points: on diagnosis, during cytostatic treatment and after therapy cessation. All patients were treated with current uniform treatment protocols and procedures. Adverse reactions in each child was recorded according to WHO toxicity scale, during the entire length of observation period and in particular stages (6 periods).

Either bone marrow or peripheral blood samples were used for the analyses. DNA isolation procedure was carried out with the use of standard tests. CYP2C9*2,*3 and CYP2C19*2 allelic variant determination was carried out with real-time PCR with double-marked probe hydrolysis with the use of Pre-Developed TaqMan Assay Reagents for Allelic Discrimination sets. PCR products fluorescence was carried out on 7900HT Fast Real-Time PCR device.

1. For CYP2C9, IM phenotype was present in 22.3% patients (n=41) and PM phenotype in 7.6% cases (n=14), the most frequently detected polymorphic variant being CYP2C9*2 (75.3%). In case of CYP2C19, IM phenotype occurred in 22.3% patients (n=41) and PM phenotype in 7.1% (n=13). 2. Toxicity risk analysis in patients with acute leukemia did not reveal statistically significant differences depending on CYP2C9 genotype. In patients with CYP2C19*2 allelic variant, statistically lower level of alkaline phosphatase (p=0.013) was observed during the entire treatment and in particular stages (I: p=0.0096; II: p=0.022; III: p=0.038; IV:p=0.0024; V:p=0.044). Lower alkaline phosphatase levels were observed only in patients with ALL (p=0.026). Lower transaminase levels after completion of intensive treatment phase were observed in patients with CYP2C19 mutations (GOT, p=0.044). In patients with CYP2C19 and CYP2C9 polymorphic variants no dependence of risk of adverse reactions with correlation to cyclophosphamide and its dose was observed. 3. In patients with CYP2C9 and CYP2C19 polymorphism no significant relation was discovered. 4. Death risk was not relevant to CYP2C9 or CYP2C19 genotype. Conclusions 1. Occurrence of slow metaboliser phenotype for CYP2C9 and CYP2C19 is more frequent in patients with acute leukemia than in the untreated population. 2. CYP2C9 and CYP2C19 cytochromes are involved in cyclophosphamide metabolism but do not play a major role in drug metabolism. 3. CYP2C9 and CYP2C19 single nucleotide polymorphism is correlated neither with an increased risk of adverse reactions or death during therapy, nor with a relapse of acute leukemia in children.

No relevant conflicts of interest to declare.