Functional characterization of 23 allelic variants of thiopurine S-methyltransferase gene (TPMT*2 - *24).

Abstract

OBJECTIVE:

Thiopurine S-methyltransferase (TPMT) is an enzyme responsible for the detoxification of the widely used thiopurine drugs. TPMT is genetically polymorphic and is associated with large interindividual variations in thiopurine drug toxicity and therapeutic efficacy. In this study, we performed an in-vitro analysis of TPMT variant alleles, namely, TPMT*2, *3A, *3B, *3C, *5, *6, *7, *8, *9, *10, *11, *12, *13, *14, *16, *17, *18, *19, *20, *21, *22, *23, and *24.

METHODS:

The wild-type TPMT proteins, TPMT.1 and 23 variants were heterologously expressed in COS-7 cells, and the kinetic parameters Km, Vmax, and intrinsic clearance (Vmax/Km) of 6-thioguanine S-methylation were determined.

RESULTS:

The expression levels of TPMT.2, TPMT.3A, TPMT.5, TPMT.12, TPMT.14, and TPMT.22 were considerably lower than that of TPMT.1 (P<0.005), and that of TPMT.18 was slightly reduced (P<0.05). The kinetic parameters of TPMT.3A, TPMT.3B, TPMT.5, TPMT.14, TPMT.18, TPMT.21, and TPMT.22 could not be accurately established because of no activity in 6-thioguanine S-methylation. The Vmax/Km values of TPMT.2, TPMT.7, TPMT.17, and TPMT.24 were displayed less than 10% of the wild-type.

CONCLUSION:

This functional analysis with respect to TPMT variants could provide useful information for individualization of thiopurine drugs therapy.

• Authors: Shuta Ujiie, Takamitsu Sasaki, Michinao Mizugaki, Masaaki Ishikawa, Masahiro Hiratsuka
• Journal: Pharmacogenetics and genomics (Pharmacogenet Genomics) Vol. 18 Issue 10 Pg. 887-93 (Oct 2008) ISSN: 1744-6872 [Print] United States
• PMID: 18708949 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't)

Chemical References

• Methyltransferases
• thiopurine methyltransferase
• Thioguanine

Topics

• Alleles
• Animals
• COS Cells
• Chlorocebus aethiops
• Genetic Variation
• Humans
• Kinetics
• Methylation
• Methyltransferases (genetics)
• Models, Genetic
• Mutagenesis, Site-Directed
• Open Reading Frames
• Pharmacogenetics (methods)
• Polymorphism, Genetic
• Thioguanine (chemistry)