Effect of polymorphisms in transporter genes on dosing, efficacy and toxicity of maintenance therapy in children with acute lymphoblastic leukemia.

The aim of the present work was to assess whether polymorphisms in genes coding for drug transport proteins may influence dosing, efficacy and toxicity of maintenance therapy with methotrexate (MTX) and 6-mercaptopurine (6MP) in childhood acute lymphoblastic leukemia (ALL). A total of 41 children with ALL were screened for 10 SNPs in the SLC19A1, ABCB1, ABCC2, ABCC4 and ABCG2 transporter genes by means of direct sequencing. Carriers of the ABCC4 934CC and ABCB1 1236TT genotypes received a lower percentage of the protocol-recommended starting dose of MTX (62.1 vs. 81.3% for 934CA carriers, p=0.001) and 6MP (73.1 vs. 87.7% for 1236CC/CT carriers; p=0.026), respectively. The C1236T SNP also increased the efficiency of myelosuppression. Median (and interquartile) number of blood tests with leukocytes levels <3109 /L for the CC; CT and TT genotypes were 22 (13), 30.5 (11.75) and 33 (17.25), respectively (p=0.001). In addition, this SNP also correlated with the number of hematological adverse events (p=0.004 for the difference between same genotypes). The event more profoundly affected was neutropenia (p=0.004). In the same manner, the ABCC4 934CC genotype was also associated to more frequent hematological toxicity (p=0.041 vs. CT carriers) and raised LDH levels (p=0.004 vs. CT carriers); although only the latter association remained significant after correction by multiple testing. Overall, our findings indicate that variability in the ABCB1 and ABCC4 genes may confer higher sensitivity to maintenance chemotherapy of ALL, and therefore its determination may be helpful in individualizing this treatment.