Abstract
Individualized Therapy: Role of Thiopurine S-Methyltransferase Protein and Genetic VariantsThiopurine S-methyltransferase (TPMT: EC 2.1.1.67) is an enzyme that metabolizes immunosuppressive thiopurine medications, used in the treatment of autoimmune diseases, cancer and in transplantation medicine. In some individuals, TPMT enzyme activity is significantly increased or decreased compared to the normal TPMT activity level. Structural and biochemical analyses of the TPMT protein revealed the existence of certain protein variants with altered activity. It has been shown that certain TPMT gene polymorphisms exist, that define different TPMT allozymes. Decreased TPMT enzyme activity can also be a consequence of lower protein synthesis, which depends on the promoter transcription activity. Promoter polymorphisms, such as variable number of tandem repeats (VNTR), can modulate the transcription. Administering thiopurine drugs in patients with certain genetic TPMT variants leads to severe hematologic toxicity. To avoid toxicity, therapy is being modified according to the TPMT genotype (pharmacogenetics). We investigated the polymorphisms in exons and regulatory elements (promoter) of the TPMT gene which affect TPMT enzyme activity in the Serbian population. We used PCR-based methodology and sequencing in the detection of genetic variants on TPMT gene. We showed that genetic variants in exons account for 7.5% of all TPMT variants with decreased enzyme activity. The therapy for patients with these pharmacogenetic markers was modified, which contributed to the efficiency of treatment. Functional assaysin vitroshowed that the TPMT promoter activity and, therefore, the quantity of TPMT protein synthesized, depended on the architecture of VNTRs (i.e. number and type) in the promoter. Promoter of the TPMT gene specifically responds to mercaptopurine treatment of K562 cells in a VNTR-dependent manner. Study of DNA-protein interactions revealed that Sp1 and Sp3 transcription factors interact with VNTRs. Our research pointed out that the VNTR promoter region of the TPMT gene could become a new pharmacogenetic marker, clinically significant for the individualization of thiopurine therapy.
Highlights
We investigated the polymorphisms in exons and regulatory elements of the TPMT gene which affect TPMT enzyme activity in the Serbian population
We investigated polymorphisms in the exons of the TPMT gene which affect TPMT enzyme activity in the Serbian population in 100 unrelated blood donors and 100 children with acute lymphoblastic leukemia
Our study showed that the application of pharmacogenetics principles in clinical practice is needed and indispensable even for the heterozygous carriers of TPMT polymorphisms
Summary
Thiopurine S-methyltransferase (TPMT; EC 2.1.1.67) represents one of the true examples of how pharmacogenetics can be applied to individualize drug therapy. Some patients do not tolerate standard doses of thiopurine drugs and develop myelotoxicity [5,6,7], as a consequence of inherited TPMT deficiency. 90% of individuals inherit two functional TPMT alleles resulting in high TPMT activity. These individuals are referred to as high methylators. Intermediate TPMT activity is seen in carriers of one nonfunctional TPMT allele. These intermediate methylators represent approximately 10% of the population. Low or undetectable TPMT activity is reported in 0.3% individuals who inherit two nonfunctional TPMT alleles [8]. Knowledge of the level of TPMT enzyme activity is essential for the balance of therapeutic and toxic effects of thiopurine drug dose
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
