@article {1705, title = {Genetic polymorphism of inosine-triphosphate-pyrophosphatase influences mercaptopurine metabolism and toxicity during treatment of acute lymphoblastic leukemia individualized for thiopurine-S-methyl-transferase status.}, journal = {Expert Opin Drug Saf}, volume = {9}, year = {2010}, month = {2010 Jan}, pages = {23-37}, abstract = {

IMPORTANCE OF THE FIELD: Although genetic polymorphisms in the gene encoding human thiopurine methyltransferase (TPMT) are known to have a marked effect on mercaptopurine metabolism and toxicity, there are many patients with wild-type TPMT who develop toxicity. Furthermore, when mercaptopurine dosages are adjusted in patients who are heterozygous at the TPMT locus, there are still some patients who develop toxicity for reasons that are not fully understood. Therefore, we recently studied the effects of a common polymorphism in another gene encoding an enzyme involved in mercaptopurine metabolism (SNP rs1127354 in inosine-triphospate-pyrophosphatase, ITPA), showing that genetic polymorphism of ITPA is a significant determinant of mercaptopurine metabolism and of febrile neutropenia following combination chemotherapy of acute lymphoblastic leukemia (ALL) in which mercaptopurine doses are individualized based on TPMT genotype.

AREA COVERED IN THIS REVIEW: In this review, we summarize the knowledge available about the effect and clinical relevance of TPMT and ITPA on mercaptopurine pharmacogenomics, with a particular focus on the use of this medication in pediatric patients with ALL.

WHAT THE READER WILL GAIN: Reader will gain insights into: i) the effects of pharmacogenomic traits on mercaptopurine toxicity and efficacy for the treatment of ALL and ii) individualization strategies that can be used to mitigate toxicity without compromising efficacy in pediatric patients with ALL.

TAKE HOME MESSAGE: Mercaptopurine dose can be adjusted on the basis of TPMT genotype to mitigate toxicity in pediatric patients with ALL. As treatment is individualized in this way for the most relevant genetic determinant of drug response (i.e., for mercaptopurine, TPMT), the importance of other genetic polymorphisms emerges (e.g., ITPA).

}, keywords = {6-Mercaptopurine, Antineoplastic Combined Chemotherapy Protocols, Child, Humans, Individualized Medicine, Methyltransferases, Models, Biological, Neutropenia, Nucleotide Transport Proteins, Polymorphism, Genetic, Precursor Cell Lymphoblastic Leukemia-Lymphoma, Pyrophosphatases}, issn = {1744-764X}, doi = {10.1517/14740330903426151}, author = {Stocco, Gabriele and Crews, Kristine R and Evans, William E} } @article {1686, title = {Pharmacogenomics in pediatric leukemia.}, journal = {Curr Opin Pediatr}, volume = {22}, year = {2010}, month = {2010 Dec}, pages = {703-10}, abstract = {

PURPOSE OF REVIEW: The therapeutic index of many medications, especially in children, is very narrow with substantial risk for toxicity at doses required for therapeutic effects. This is particularly relevant to cancer chemotherapy, when the risk of toxicity must be balanced against potential suboptimal (low) systemic exposure that can be less effective in patients with higher rates of drug clearance. The purpose of this review is to discuss genetic factors that lead to interpatient differences in the pharmacokinetics and pharmacodynamics of these medications.

RECENT FINDINGS: Genome-wide agonistic studies of pediatric patient populations are revealing genome variations that may affect susceptibility to specific diseases and that influence the pharmacokinetic and pharmacodynamic characteristics of medications. Several genetic factors with relatively small effect may be combined in the determination of a pharmacogenomic phenotype and considering these polygenic models may be mandatory in order to predict the related drug response phenotypes. These findings have potential to yield new insights into disease pathogenesis, and lead to molecular diagnostics that can be used to optimize the treatment of childhood cancers.

SUMMARY: Advances in genome technology, and their comprehensive and systematic deployment to elucidate the genomic basis of interpatient differences in drug response and disease risk, hold great promise to ultimately enhance the efficacy and reduce the toxicity of drug therapy in children.

}, keywords = {Antineoplastic Agents, Child, Genetic Predisposition to Disease, Genetic Testing, Humans, Individualized Medicine, Pharmacogenetics, Phenotype, Precursor Cell Lymphoblastic Leukemia-Lymphoma}, issn = {1531-698X}, doi = {10.1097/MOP.0b013e32833fde85}, author = {Paugh, Steven W and Stocco, Gabriele and Evans, William E} }