Genetic Polymorphisms In Candidate Genes Predict Increased Toxicity With Methotrexate Therapy In Children With Acute Lymphoblastic Leukemia In Lebanon

Acute Lymphoblastic Leukemia (ALL) is the most common cancer in childhood accounting for almost 30% of pediatric cancer cases in Lebanon. Polymorphisms in genes involved in methotrexate (MTX) metabolism have been associated with toxicity but with controversial results. The aim of this study was to analyze polymorphisms in genes involved in MTX metabolism including ABCB1 (or MDR1), ABCC2, SLC19-A (or RFC19),SLCO1B1; and MTX effect mainly MTHFR and TYMS; as well as measure the frequency of polymorphisms in TPMT involved in 6MP detoxification; and to assess whether these polymorphisms are predictors of treatment toxicity and/or MTX clearance.

This is a retrospective cohort study whereby all patients (pts) diagnosed with ALL and followed up and treated at the AUB CCCL as per the St. Jude TOTAL XV protocol between 2009 and 2012 were recruited. The study was approved by the IRB. Informed consents were obtained. Medical records were reviewed for baseline data at the time of diagnosis and treatment and toxicity details during the consolidation and continuation phase. Whole peripheral blood for DNA was collected after completion of the induction phase and documentation of remission.

Genotyping was performed using real time PCR or RFLP. MTX levels were measured by a polarization fluorescence assay from Roche (Basel, Switzerland). MTX clearance was estimated based on all available MTX levels measured after HDMTX treatment during consolidation phase, using 2-compartmental linear pharmacokinetic model with 2 doses (10% of the total dose infused in the first hour and 90% infused in the next 23 hours) via WinNonlin software version 6.3 (Pharsight Corporation, St. Louis, USA). Data were analyzes using SPSS version 19.

This study included 127 ALL pts. Table 1  shows the genotype frequencies that were all in Hardy Weinberg Equilibrium and similar to Caucasian populations.

During the consolidation phase, a statistically significant association was found among neutropenia (ANC<300) and variant allele carriers of ABCB1 rs1045642 (OR=5.174; 95% CI: 1.674-15.989) and ABCB1 rs1128503 (OR=3.364; 95% CI: 1.257-9.004) respectively. ABCC2 rs717620 variant allele carriers needed significantly more prolonged time to reach a MTX level below 0.1µM. (Beta=5.122; 95% CI: 1.412-8.831). In addition, a clinically significant association was shown between MTHFRrs1801133 variant allele carriers and drop in hemoglobin levels (OR=3.057; 95% CI: 1.217, 7.680). No statistically significant associations were found with MTX clearance estimates.

During continuation phase, a statistically significant association was shown between ABCC2 rs717620 and TYMS 28 bp tandem repeats variant allele carriers with the need to decrease the weekly doses of methotrexate in order to maintain an ANC> 300 and be able to administer weekly chemotherapy (Beta=-5.770 95% CI: -10.138; -1.403 and Beta=-5.770; 95% CI: -10.138; -1.403) respectively. There was a close to significant association between ABCB1 rs1128503 variant allele carriers and development of febrile neutropenia P=0.046 but this was lost with regression analysis (OR=3.937; 95% CI: 0.847-18.309). The three pts with TPMT (*1/*3A) developed severe anemia and neutropenia necessitating a decrease in their chemotherapy doses.

Polymorphisms in ABCB1, ABCC2, and MTHFR were associated with increased toxicity during consolidation phase whereas polymorphisms in ABCC2 and TYMSwere associated with increased toxicity during the continuation phase of ALL therapy in Lebanese children. Genotyping for these polymorphisms may be helpful in identifying pts at risk of increased MTX toxicity and the need for dose optimization before treatment initiation.

Abboud:Novartis: Honoraria; Sangart: Membership on an entity’s Board of Directors or advisory committees, Research Funding; Pfizer: Research Funding; Hemaquest: Research Funding.