pharmacogenomic of tpmt which affected to plasma level of thiopurine drugs
TRANSCRIPT
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Nin Prapongsena, MPh.Faculty of pharmacy
Huachiew chalermprakiet University
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Outline
• Introduction of thiopurines• Thiopurine metabolism and their mechanism of actions• ADR of thiopurines• How thiopurine treatment failure ???• Polymorphisms of thiopurine methyltransferase
(TPMT) gene and their clinical effects of TPMT activity• Correlation of TPMT genotype and phenotype• Limitation of TPMT genotype and phenotype
assessment• Conclusion• Pharmacist’s role
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Thiopurine drugs
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Azathioprine (AZA)
Pharmacological category: ImmunosuppressantIndication:
- Rheumatoid arthitis (RA)- Inflammatory bowel disease (IBD)- Psoriasis- Prevent graft rejection
ADR: - N/V- Hepatotoxicity- Leukopenia & thrombocytopenia- Cutaneous ADR
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6-Mercaptopurine (6-MP): 50 mg/m2
Pharmacologic category: Antineoplastic agent & immunosuppressant
Indication: - Acute myelogenous leukemia (AML)
in induction & maintenance phase (remission ≈ 80%)
- Inflammatory bowel disease (IBD)ADR:
- Myelosuppression(onset 7 d, nadir 14-16 d, recovery 21-28 d)
- Hepatotoxicity- Cutaneous ADR
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6-Thioguanine (6-TG): 40 mg/m2
Pharmacologic category: Antineoplastic agent
Indication: - Acute lymphoblastic leukemia (ALL)- Acute myelogenous leukemia (AML)
ADR: - Myelosuppression
(onset 7-10 d, nadir 14 d, recovery 21 d)- Hepatotoxicity- Cutaneous ADR
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Metabolism of thiopurines
Azathioprine (AZA)
6-Mercaptopurine (6-MP)
Glutathione S- transferase (GST)
Xanthine oxidase(XO)
Thiouric acid(inactive)
*Thiopurinemethyltransferase
(TPMT)
6-Methyl mercaptopurine(antiangiogenesis)
Hypoxanthine phosphoribosyl
transferase(HPRT)
Thioinosine monophosphate(TIMP)
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Metabolism of thiopurines (continue)
TIMP
*TPMT
6-Methyl thioinosinemonophosphate
(MeTIMP)
Hepatotoxicity
Inosine monophosphateDehydrogenase (IMPDH)
6-Thioguanine monophosphate
(TGMP)
Guanosine monophosphateSynthetase
Purinebiosynthesis
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Metabolism of thiopurines (continue)
TGMP
6-MP 6-Thioguanine (6-TG)
HPRT
*TPMT
6-Methylthioguanine Monophosphate (MeTGMP)
Phosphokinase
Deoxythioguaninetriphosphate (TGN)
Purinebiosynthesis
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Deoxythioguanine triphosphate effect
Deoxythioguaninetriphosphate (TGN)
Caused cell death& myelosuppression
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ADR of thiopurines
• Found ADR 25.9% in patients who taking thiopurines
ADR of thiopurine drugs Liver abnormalities
Allergy
Pancreatitis
Bonemarrowsuppression
N/V
Other
34 %
6%9 %
***7 %
25 %
7 %
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Related to dose and durationof 6-MP & 6-TG treatment in acute leukemia
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How thiopurine treatment failure ? ? ?
• Drug interactions• Food interactions• Pharmacogenomics
Changed active metabolites level
Treatment failure• ADR (especially neutropenia)
• Too low dose
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Thiopurine methyltransferase (TPMT) gene
• Located at chromosome 6 (6p22)
• 3.4 kb (composed of 10 exon)
• TPMT found in liver, renal, RBC, etc.
• TPMT expression α TPMT activity α 1/TGN
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Weinshilboum RM., and Sladek SL
Am J Hum Genet. 1980; 32: 651-652.
Mercaptopurine pharmacogenetics: monogenic inheritance of erythrocyte thiopurine methyltransferase activity
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Undetected(0.3%)
Intermediate or LowActivity (11%)
Normal activity (89%)
X-axis: RBC TPMT activity (U/mL)6-mp 4mM
Y-a
xis:
% o
f su
bje
cts
RBC TPMT activity
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Polymorphisms of thiopurinemethyltransferase (TPMT) gene
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Proc. Natl. Acad. Sci. USAVol. 94, pp. 6444–6449, June 1997Medical Sciences
Enhanced proteolysis of thiopurine S-transferase(TPMT) encoded by mutant alleles in human TPMT*3A, TPMT*2): mechanisms for the genetic polymorphism of TPMT activity
Tai HL., Krynetski EY., Yanishevski Y., and Evans WE
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mRNA of TPMT
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RBC TPMT activity
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Stability of TPMT
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Polymorphisms of thiopurinemethyltransferase (TPMT) gene
Normal actvityT1/2: 18 h
Low TPMT activityT1/2: 15 min
Low TPMT activity
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Polymorphism of TPMT gene in Thailand
200 unrelated samples
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Clinical effects of TPMT activity
• High TPMT activity (If TPMT level > 65 U/mL):
- High meTIMP level
- Low TGN level
Inhibited purine synthesis
Hepatotoxicity
Risk to failure in ALL treatment
• How to solve this problems ?
Recommend increasing dose of 6-MP or 6-TG thanusual dose and closely hepatic enzymes monitoring
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Clinical effects of TPMT activity
• Intermediate TPMT activity (25 U/mL > TPMT level < 45 U/mL):
- High TGN level Myelosuppression
Increased risk of 2nd malignancy
• How to solve this problems ?
Recommend reducing dose to 50-80 % of standard dose
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Clinical effects of TPMT activity
• Low TPMT activity or TPMT deficiency (If TPMT level < 25 U/mL):
- Very high TGN level Severe myelosuppression
High risk of 2nd malignancy
• How to solve this problems ?
Recommend reducing dose to 10-20 % of standard dose
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Correlation of TPMT genotype and phenotype
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Assessment of Thiopurine S-MethyltransferaseActivity in Patients Prescribed Thiopurines: A Systematic Review
Ann Intern Med. 2011;154:814-823.
Ronald A. Booth, PhD; Mohammed T. Ansari, MBBS, MMedSc, MPhil; Evelin Loit, PhD; Andrea C. Tricco, PhD; Laura Weeks, PhD; Steve Doucette, MSc; Becky Skidmore, MLS; Margaret Sears, PhD; Richmond Sy, MD; and Jacob Karsh, MDCM
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Have False positive(Specificity is not 100%): cause low dose of 6-MP/6-TG usage
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Limitation of TPMT phenotype and genotype testing
Genotype testing
Missed target:pseudogene onchromosome 18
Phenotype testing
• Factors affected to TPMT activity:
- Age- Blood transfusion
• Loss sample between testing
Investigated both genotype and phenotypeof TPMT are more utility
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Cost effective for screening TPMT mutation
J Am Acad Dermatol 2000;42: 628-632
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Cost effective for screening TPMT mutation
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Conclusion• TPMT gene mutation affected to TPMT level, activity
and stability• TPMT expression α TPMT activity α 1/TGN level,
TGN level α myelosuppression & 2nd malignancy • Only TPMT*3C found in Thais (≈ 9%)• Dose adjustment:
- High TPMT (> 65 U/mL): dose- Intermediate TPMT (25-45 U/mL): dose 20-50%- Low or absence TPMT (< 25 U/mL): dose 80-90%
•TPMT genotype correlated with phenotype but not100% (Many factors affected to TPMT activity)
• There are limitation of genotype and phenotype testing, then investigated both are more utility.
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Case report
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Cutaneous ADR occured
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Pharmacist’s role
Prevented
Screening TPMT genotype Testing TPMT activity
Considered appropriate initial dose
Monitor CBC and hepatic enzymes
Toxicity or ADR occurred:Adjusted dose or delayed dose± antibiotic (NCCN guideline)
± myelosuppressive treatment (NCCN guideline)and closely liver enzymes monitoring
Corrected
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