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Tox21_202591
Also known as: 6-mercaptopurine, 50-44-2, Purinethol, Mercapurin, 6-thiopurine, Leukerin
Molecular Formula
C5H4N4S
Molecular Weight
152.18  g/mol
InChI Key
GLVAUDGFNGKCSF-UHFFFAOYSA-N
FDA UNII
PKK6MUZ20G

An antimetabolite antineoplastic agent with immunosuppressant properties. It interferes with nucleic acid synthesis by inhibiting purine metabolism and is used, usually in combination with other drugs, in the treatment of or in remission maintenance programs for leukemia.
Mercaptopurine anhydrous is a Nucleoside Metabolic Inhibitor. The mechanism of action of mercaptopurine anhydrous is as a Nucleic Acid Synthesis Inhibitor.
1 2D Structure

Tox21_202591

2 Identification
2.1 Computed Descriptors
2.1.1 IUPAC Name
3,7-dihydropurine-6-thione
2.1.2 InChI
InChI=1S/C5H4N4S/c10-5-3-4(7-1-6-3)8-2-9-5/h1-2H,(H2,6,7,8,9,10)
2.1.3 InChI Key
GLVAUDGFNGKCSF-UHFFFAOYSA-N
2.1.4 Canonical SMILES
C1=NC2=C(N1)C(=S)N=CN2
2.2 Other Identifiers
2.2.1 UNII
PKK6MUZ20G
2.3 Synonyms
2.3.1 MeSH Synonyms

1. 1,7-dihydro-6h-purine-6-thione

2. 6 Mercaptopurine

3. 6 Mercaptopurine Monohydrate

4. 6 Thiohypoxanthine

5. 6 Thiopurine

6. 6-mercaptopurine

7. 6-mercaptopurine Monohydrate

8. 6-thiohypoxanthine

9. 6-thiopurine

10. 6h-purine-6-thione, 1,7-dihydro-

11. Bw 57 323h

12. Bw 57-323h

13. Bw 57323h

14. Leupurin

15. Mecaptopurine Anhydrous

16. Mercaptopurina Wellcome

17. Puri-nethol

18. Purimethol

19. Purinethol

2.3.2 Depositor-Supplied Synonyms

1. 6-mercaptopurine

2. 50-44-2

3. Purinethol

4. Mercapurin

5. 6-thiopurine

6. Leukerin

7. Leupurin

8. Mercaleukin

9. 7h-purine-6-thiol

10. 6-thioxopurine

11. Puri-nethol

12. Purinethiol

13. Ismipur

14. Mern

15. 6-thiohypoxanthine

16. 6-mercaptopurin

17. 6-purinethiol

18. 1,9-dihydro-6h-purine-6-thione

19. Purimethol

20. 6-mp

21. Purine-6-thiol

22. 3h-purine-6-thiol

23. 6 Mp

24. 9h-purine-6-thiol

25. Mercaleukim

26. 3,7-dihydropurine-6-thione

27. 1,7-dihydro-6h-purine-6-thione

28. Hypoxanthine, Thio-

29. Mercaptopurine (6-mp)

30. Mercaptopurine Anhydrous

31. Mercaptopurin

32. Mercaptopurina

33. Mercaptopurinum

34. Merkaptopuryna

35. 6h-purine-6-thione, 1,7-dihydro-

36. Xaluprine

37. 6-merkaptopurin

38. Purine, 6-mercapto-

39. 9h-purine-6(1h)-thione

40. Purine-6(1h)-thione

41. Nci-c04886

42. 7-mercapto-1,3,4,6-tetrazaindene

43. 1h-purine, 6-mercapto-

44. Nsc 755

45. U-4748

46. 1,9-dihydropurine-6-thione

47. Purixan

48. Mercaptopurine;6-mp

49. Nsc755

50. Nsc-755

51. Mercaptopurine (inn)

52. 3,7-dihydro-6h-purine-6-thione

53. Purinethol (tn)

54. Pkk6muz20g

55. 1h-purine-6(7h)-thione.

56. Chebi:2208

57. Mercaptopurine (van)

58. Dsstox_cid_810

59. Mercaptopurin [german]

60. Merkaptopuryna [polish]

61. 6-merkaptopurin [czech]

62. Dsstox_rid_75801

63. Mercaptopurine [inn]

64. Dsstox_gsid_20810

65. Mercaptopurine (anhydrous)

66. Mercaptopurinum [inn-latin]

67. Mercaptopurina [inn-spanish]

68. Thiohypoxanthine

69. Purine-6-thiol, Monohydrate

70. Cas-50-44-2

71. 157930-11-5

72. Smr000544948

73. Mercaptopurine, 6-

74. Ccris 2761

75. Hsdb 3235

76. Sr-05000001925

77. 1194-62-3

78. Einecs 200-037-4

79. Unii-pkk6muz20g

80. Ncimech_000025

81. 9h-purin-6-yl Hydrosulfide

82. A Thiopurine

83. Mercaptopurine [usan:usp:inn]

84. 157930-13-7

85. Spectrum_000921

86. Spectrum2_000060

87. Spectrum3_000491

88. Spectrum4_000857

89. Spectrum5_000950

90. M0063

91. H-purine-6(1h)-thione

92. Azathioprine Ep Impurity B

93. Schembl3893

94. Chembl1425

95. Bspbio_001981

96. Kbiogr_001493

97. Kbiogr_002363

98. Kbioss_001401

99. Kbioss_002366

100. Mercaptopurine [hsdb]

101. Ag-670/31547064

102. Mls001066623

103. Mls001304020

104. Mls001304953

105. Mls006011869

106. Divk1c_000493

107. Spectrum1500387

108. Spbio_000219

109. 6-mercaptopurine [mi]

110. Gtpl7226

111. Schembl2790086

112. 7h-purin-6-yl Hydrosulfide #

113. 6-mercaptopurine [iarc]

114. Dtxsid0020810

115. Schembl12683725

116. Chebi:50667

117. Chebi:94796

118. Hms501i15

119. Kbio1_000493

120. Kbio2_001401

121. Kbio2_002363

122. Kbio2_003969

123. Kbio2_004931

124. Kbio2_006537

125. Kbio2_007499

126. Kbio3_001481

127. Kbio3_002842

128. 7-mercapto-1,4,6-tetrazaindene

129. Cmap_000033

130. Ninds_000493

131. 6,7-dihydro-3h-purine-6-thione

132. Hms1920l07

133. Hms2091b20

134. Hms2236l06

135. Hms3259n03

136. Hms3369m05

137. Hms3651g07

138. Hms3713n10

139. Hms3747a17

140. Hms3872n13

141. Pharmakon1600-01500387

142. Act11542

143. Discontinued, See M225450

144. Zinc4658290

145. Tox21_111158

146. Tox21_202591

147. Bdbm50423778

148. Ccg-35344

149. Ccg-39915

150. Mfcd00233552

151. Nsc759614

152. Nsc817004

153. S1305

154. Sk5357

155. Stk727062

156. Stl257085

157. 6-mercaptopurine, Analytical Standard

158. Wln: T56 Bm Dn Fn Hnj Ish

159. Akos000170222

160. Akos000275858

161. Akos005224624

162. Akos008901311

163. Akos016903205

164. Tox21_111158_1

165. Am81386

166. Ccg-266232

167. Cs-1499

168. Db01033

169. Nc00613

170. Nsc-817004

171. Idi1_000493

172. Mercaptopurine Anhydrous [who-dd]

173. Ncgc00091641-02

174. Ncgc00091641-03

175. Ncgc00091641-04

176. Ncgc00091641-16

177. Ncgc00094717-01

178. Ncgc00094717-02

179. Ncgc00094717-03

180. Ncgc00094717-05

181. Ncgc00094717-06

182. Ncgc00188973-01

183. Ncgc00188973-02

184. Ncgc00260139-01

185. Ac-11464

186. As-13109

187. Hy-13677

188. Nci60_041653

189. Smr004703503

190. Sbi-0051437.p004

191. Db-026398

192. Azathioprine Impurity B [ep Impurity]

193. Bb 0241023

194. Ft-0621175

195. Sw199090-2

196. En300-61517

197. 50m442

198. C01756

199. C02380

200. D04931

201. Ab00171799_05

202. Ab00641894-03

203. Ab00641894-04

204. Ab00641894_05

205. Ab00876276-13

206. 233d552

207. 462m721

208. 599m524

209. A828129

210. Q418529

211. Sr-05000001925-1

212. Sr-05000001925-2

213. W-105961

214. Purine Antimetabolite: Inhibits Nucleic Acid Replication

215. 1,9-dihydropurine-6-thione Discontinued, See M225450

216. Mercaptopurine; 7h-purine-6-thiol; Azathioprine Bp Impurity B

2.4 Create Date
2004-09-16
3 Chemical and Physical Properties
Molecular Weight 152.18 g/mol
Molecular Formula C5H4N4S
XLogP30
Hydrogen Bond Donor Count2
Hydrogen Bond Acceptor Count2
Rotatable Bond Count0
Exact Mass152.01566732 g/mol
Monoisotopic Mass152.01566732 g/mol
Topological Polar Surface Area85.2 Ų
Heavy Atom Count10
Formal Charge0
Complexity190
Isotope Atom Count0
Defined Atom Stereocenter Count0
Undefined Atom Stereocenter Count0
Defined Bond Stereocenter Count0
Undefined Bond Stereocenter Count0
Covalently Bonded Unit Count1
4 Drug and Medication Information
4.1 Drug Information
1 of 4  
Drug NameMercaptopurine
PubMed HealthMercaptopurine (By mouth)
Drug ClassesAntineoplastic Agent, Antirheumatic, Cytotoxic, Gastrointestinal Agent
Drug LabelMercaptopurine was synthesized and developed by Hitchings, Elion, and associates at the Wellcome Research Laboratories.Mercaptopurine, known chemically as 6H-purine-6-thione, 1,7-dihydro-, monohydrate, is an analogue of the purine bases adenine and h...
Active IngredientMercaptopurine
Dosage FormTablet
RouteOral
Strength50mg
Market StatusPrescription
CompanyRoxane; Prometheus Labs; Mylan

2 of 4  
Drug NamePurinethol
PubMed HealthMercaptopurine (By mouth)
Drug ClassesAntineoplastic Agent, Antirheumatic, Cytotoxic, Gastrointestinal Agent
Drug LabelPURINETHOL (mercaptopurine) was synthesized and developed by Hitchings, Elion, and associates at the Wellcome Research Laboratories.Mercaptopurine, known chemically as 1,7-dihydro-6H-purine-6-thione monohydrate, is an analogue of the purine bases ade...
Active IngredientMercaptopurine
Dosage FormTablet
RouteOral
Strength50mg
Market StatusPrescription
CompanyTeva

3 of 4  
Drug NameMercaptopurine
PubMed HealthMercaptopurine (By mouth)
Drug ClassesAntineoplastic Agent, Antirheumatic, Cytotoxic, Gastrointestinal Agent
Drug LabelMercaptopurine was synthesized and developed by Hitchings, Elion, and associates at the Wellcome Research Laboratories.Mercaptopurine, known chemically as 6H-purine-6-thione, 1,7-dihydro-, monohydrate, is an analogue of the purine bases adenine and h...
Active IngredientMercaptopurine
Dosage FormTablet
RouteOral
Strength50mg
Market StatusPrescription
CompanyRoxane; Prometheus Labs; Mylan

4 of 4  
Drug NamePurinethol
PubMed HealthMercaptopurine (By mouth)
Drug ClassesAntineoplastic Agent, Antirheumatic, Cytotoxic, Gastrointestinal Agent
Drug LabelPURINETHOL (mercaptopurine) was synthesized and developed by Hitchings, Elion, and associates at the Wellcome Research Laboratories.Mercaptopurine, known chemically as 1,7-dihydro-6H-purine-6-thione monohydrate, is an analogue of the purine bases ade...
Active IngredientMercaptopurine
Dosage FormTablet
RouteOral
Strength50mg
Market StatusPrescription
CompanyTeva

4.2 Therapeutic Uses

Antimetabolites; Antimetabolites, Antineoplastic; Immunosuppressive Agents; Nucleic Acid Synthesis Inhibitors

National Library of Medicine's Medical Subject Headings. Mercaptopurine. Online file (MeSH, 2016). Available from, as of December 5, 2016: https://www.nlm.nih.gov/mesh/2016/mesh_browser/MBrowser.html


/CLINICAL TRIALS/ ClinicalTrials.gov is a registry and results database of publicly and privately supported clinical studies of human participants conducted around the world. The Web site is maintained by the National Library of Medicine (NLM) and the National Institutes of Health (NIH). Each ClinicalTrials.gov record presents summary information about a study protocol and includes the following: Disease or condition; Intervention (for example, the medical product, behavior, or procedure being studied); Title, description, and design of the study; Requirements for participation (eligibility criteria); Locations where the study is being conducted; Contact information for the study locations; and Links to relevant information on other health Web sites, such as NLM's MedlinePlus for patient health information and PubMed for citations and abstracts for scholarly articles in the field of medicine. Mercaptopurine is included in the database.

NIH/NLM; ClinicalTrials.Gov. Available from, as of February 1, 2017: https://clinicaltrials.gov/ct2/results?term=MERCAPTOPURINE&Search=Search


Mercaptopurine tablets are indicated for maintenance therapy of acute lymphatic (lymphocytic, lymophoblastic) leukemia as part of a combination regimen. The response to this agent depends upon the particular subclassification of acute lymphatic leukemia and the age of the patient (pediatric or adult). Mercaptopurine is not effective prophylaxis or treatment of central nervous system leukemia. Mercaptopurine is not effective in acute myelogenous leukemia, chronic lymphatic leukemia, the lymphomas (including Hodgkins Disease), or solid tumors. /Included in US product label/

NIH; DailyMed. Current Medication Information for Mercaptopurine (Updated: October 2016). Available from, as of February 6, 2017: https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=c3b5b8b0-bc5c-4ce9-bbdc-febba60c2658


MEDICATION (VET): Rarely used in veterinary medicine. Veterinary uses of mercaptopurine have included adjunctive therapy of lymphosarcoma, acute leukemias, and severe rheumatoid arthritis. It may have potential benefit in treating other autoimmune conditions (eg, unresponsive ulcerative colitis) as well.

Plumb D.C. Veterinary Drug Handbook. 8th ed. (pocket). Ames, IA: Wiley-Blackwell, 2015., p. 928


For more Therapeutic Uses (Complete) data for Mercaptopurine (9 total), please visit the HSDB record page.


4.3 Drug Warning

Tumor lysis syndrome with hyperuricemia and/or hyperuricosuria may occur as a result of rapid cell lysis in patients receiving mercaptopurine as antineoplastic therapy. Prophylactic use of a xanthine oxidase inhibitor such as allopurinol may be used to minimize these adverse effects, but reduction of mercaptopurine dosage is required.

American Society of Health-System Pharmacists 2016; Drug Information 2016. Bethesda, MD. 2016, p. 1176


VET: Like azathioprine, mercaptopurine is best avoided in cats. Additionally, with with caution in dog breeds that potentially have a low thiopurine methyltransferase (TPMT) activity (eg, giant Schnauzers).

Plumb D.C. Veterinary Drug Handbook. 8th ed. (pocket). Ames, IA: Wiley-Blackwell, 2015., p. 929


VET: At usual doses, GI effects (nausea, anorexia, vomiting, diarrhea) are most likely seen in small animals. However, bone marrow suppression, hepatotoxicity, pancreatitis, GI (including oral) ulceration, and dermatologic reactions are, potentially, possible.

Plumb D.C. Veterinary Drug Handbook. 8th ed. (pocket). Ames, IA: Wiley-Blackwell, 2015., p. 929


Drug fever rarely has been reported in patients receiving mercaptopurine. Other causes of pyrexia, such as sepsis, should be ruled out before attributing the effect to the drug in patients with acute leukemia.103 Other infrequently occurring adverse effects of mercaptopurine include fever, headache, and excessive weakness. Oligospermia has been reported.

American Society of Health-System Pharmacists 2016; Drug Information 2016. Bethesda, MD. 2016, p. 1177


For more Drug Warnings (Complete) data for Mercaptopurine (20 total), please visit the HSDB record page.


4.4 Drug Indication

For remission induction and maintenance therapy of acute lymphatic leukemia.


FDA Label


Xaluprine is indicated for the treatment of acute lymphoblastic leukaemia (ALL) in adults, adolescents and children.


5 Pharmacology and Biochemistry
5.1 Pharmacology

Mercaptopurine is one of a large series of purine analogues which interfere with nucleic acid biosynthesis and has been found active against human leukemias. It is an analogue of the purine bases adenine and hypoxanthine. It is not known exactly which of any one or more of the biochemical effects of mercaptopurine and its metabolites are directly or predominantly responsible for cell death.


5.2 MeSH Pharmacological Classification

Antimetabolites

Drugs that are chemically similar to naturally occurring metabolites, but differ enough to interfere with normal metabolic pathways. (From AMA Drug Evaluations Annual, 1994, p2033) (See all compounds classified as Antimetabolites.)


Antimetabolites, Antineoplastic

Antimetabolites that are useful in cancer chemotherapy. (See all compounds classified as Antimetabolites, Antineoplastic.)


Immunosuppressive Agents

Agents that suppress immune function by one of several mechanisms of action. Classical cytotoxic immunosuppressants act by inhibiting DNA synthesis. Others may act through activation of T-CELLS or by inhibiting the activation of HELPER CELLS. While immunosuppression has been brought about in the past primarily to prevent rejection of transplanted organs, new applications involving mediation of the effects of INTERLEUKINS and other CYTOKINES are emerging. (See all compounds classified as Immunosuppressive Agents.)


Nucleic Acid Synthesis Inhibitors

Compounds that inhibit cell production of DNA or RNA. (See all compounds classified as Nucleic Acid Synthesis Inhibitors.)


5.3 FDA Pharmacological Classification
5.3.1 Active Moiety
MERCAPTOPURINE ANHYDROUS
5.3.2 FDA UNII
PKK6MUZ20G
5.3.3 Pharmacological Classes
Nucleoside Metabolic Inhibitor [EPC]; Nucleic Acid Synthesis Inhibitors [MoA]
5.4 ATC Code

L01BB02


L01BB02

S76 | LUXPHARMA | Pharmaceuticals Marketed in Luxembourg | Pharmaceuticals marketed in Luxembourg, as published by d'Gesondheetskeess (CNS, la caisse nationale de sante, www.cns.lu), mapped by name to structures using CompTox by R. Singh et al. (in prep.). List downloaded from https://cns.public.lu/en/legislations/textes-coordonnes/liste-med-comm.html. Dataset DOI:10.5281/zenodo.4587355


L - Antineoplastic and immunomodulating agents

L01 - Antineoplastic agents

L01B - Antimetabolites

L01BB - Purine analogues

L01BB02 - Mercaptopurine


5.5 Absorption, Distribution and Excretion

Absorption

Clinical studies have shown that the absorption of an oral dose of mercaptopurine in humans is incomplete and variable, averaging approximately 50% of the administered dose. The factors influencing absorption are unknown.


Volume of Distribution

The volume of distribution exceeded that of the total body water.


/MILK/ It is not known whether mercaptopurine is distributed into milk.

American Society of Health-System Pharmacists 2016; Drug Information 2016. Bethesda, MD. 2016, p. 1178


Mercaptopurine and its metabolites are distributed throughout total body water. The volume of distribution of mercaptopurine usually exceeds total body water content. Although the drug reportedly crosses the blood-brain barrier, CSF concentrations are not sufficient for the treatment of meningeal leukemia.

American Society of Health-System Pharmacists 2016; Drug Information 2016. Bethesda, MD. 2016, p. 1178


Mercaptopurine is excreted in urine as unchanged drug and metabolites. In one study in adults with normal renal function, about 11% of an oral dose was recovered in the urine within 6 hours.

American Society of Health-System Pharmacists 2016; Drug Information 2016. Bethesda, MD. 2016, p. 1179


The immunosuppressant azathioprine is increasingly being used in pregnancy. The human placenta is considered a relative barrier to the major metabolite, 6-mercaptopurine (6-MP), and likely explains the lack of proven teratogenicity in humans. The aim of this study was to determine how the human placenta restricts 6-MP transfer using the human placental perfusion model. After addition of 50 ng/mL (n=4) and 500 ng/mL (n=3) 6-MP into the maternal circulation, there was a biphasic decline in its concentration and a delay in fetal circulation appearance. Under equilibrative conditions, the fetal-to-maternal concentration ratio was >1.0 as a result of ion trapping. Binding to placental tissue and maternal pharmacokinetic parameters are the main factors that restrict placental transfer of 6-MP. Active transport is unlikely to play a significant role and drug interactions involving, or polymorphisms in, placental drug efflux transporters are not likely to put the fetus at risk of higher 6-MP exposure.

PMID:21903160 Hutson JR et al; Reprod Toxicol 32 (3): 349-53 (2011)


For more Absorption, Distribution and Excretion (Complete) data for Mercaptopurine (9 total), please visit the HSDB record page.


5.6 Metabolism/Metabolites

Hepatic. Degradation primarily by xanthine oxidase. The catabolism of mercaptopurine and its metabolites is complex. In humans, after oral administration of 35S-6-mercaptopurine, urine contains intact mercaptopurine, thiouric acid (formed by direct oxidation by xanthine oxidase, probably via 6-mercapto-8-hydroxypurine), and a number of 6-methylated thiopurines. The methylthiopurines yield appreciable amounts of inorganic sulfate.


After oral administration of 35(S)-6-mercaptopurine, urine contains intact mercaptopurine, thiouric acid (formed by direct oxidation by xanthine oxidase, probably via 6-mercapto-8-hydroxypurine), and a number of 6-methylated thiopurines.

NIH; DailyMed. Current Medication Information for Mercaptopurine (Updated: October 2016). Available from, as of February 6, 2017: https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=c3b5b8b0-bc5c-4ce9-bbdc-febba60c2658


Mercaptopurine is metabolized via 2 major pathways. Mercaptopurine is rapidly and extensively oxidized to 6-thiouric acid in the liver by the enzyme xanthine oxidase. Because xanthine oxidase is inhibited by allopurinol, concomitant use of this drug decreases the metabolism of mercaptopurine and its active metabolites and leads to toxicity. If allopurinol and mercaptopurine are used concomitantly, the dosage of mercaptopurine must be reduced to avoid toxicity. Another major catabolic pathway is thiol methylation of mercaptopurine to form the inactive metabolite methyl-6-MP. This reaction is catalyzed by the enzyme thiopurine S-methyltransferase (TPMT). Variability in TPMT activity in patients because of a genetic polymorphism in the TPMT gene causes interindividual differences in the metabolism of mercaptopurine and resulting systemic exposure to the drug and its active metabolites. Dethiolation can also occur, with large portions of the sulfur being excreted as inorganic sulfate.

American Society of Health-System Pharmacists 2016; Drug Information 2016. Bethesda, MD. 2016, p. 1179


... In this study, we investigated the in vitro metabolism of 6-mercaptopurine (6MP) to 6-thiouric acid (6TUA) in pooled human liver cytosol. We discovered that 6MP is metabolized to 6TUA through sequential metabolism via the 6-thioxanthine (6TX) intermediate. The role of human AO and XO in the metabolism of 6MP was established using the specific inhibitors raloxifene and febuxostat. Both AO and XO were involved in the metabolism of the 6TX intermediate, whereas only XO was responsible for the conversion of 6TX to 6TUA. These findings were further confirmed using purified human AO and Escherichia coli lysate containing expressed recombinant human XO. Xanthine dehydrogenase (XDH), which belongs to the family of xanthine oxidoreductases and preferentially reduces nicotinamide adenine dinucleotide (NAD(+)), was shown to contribute to the overall production of the 6TX intermediate as well as the final product 6TUA in the presence of NAD(+) in human liver cytosol. In conclusion, we present evidence that three enzymes, AO, XO, and XDH, contribute to the production of 6TX intermediate, whereas only XO and XDH are involved in the conversion of 6TX to 6TUA in pooled HLC.

PMID:24824603 Full text: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4109211 Choughule KV et al; Drug Metab Dispos 42 (8): 1334-40 (2014)


The thiopurine antimetabolites, 6-mercaptopurine (6-MP) and 6-thioguanine (6-TG) are inactive pro-drugs that require intracellular metabolism for activation to cytotoxic metabolites. Thiopurine methyltransferase (TPMT) is one of the most important enzymes in this process metabolizing both 6-MP and 6-TG to different methylated metabolites including methylthioinosine monophosphate (meTIMP) and methylthioguanosine monophosphate (meTGMP), respectively, with different suggested pharmacological and cytotoxic properties. While meTIMP is a potent inhibitor of de novo purine synthesis (DNPS) and significantly contributes to the cytotoxic effects of 6-MP, meTGMP, does not add much to the effects of 6-TG, and the cytotoxicity of 6-TG seems to be more dependent on incorporation of thioguanine nucleotides (TGNs) into DNA rather than inhibition of DNPS. In order to investigate the role of TPMT in metabolism and thus, cytotoxic effects of 6-MP and 6-TG, we knocked down the expression of the gene encoding the TPMT enzyme using specifically designed small interference RNA (siRNA) in human MOLT4 leukemia cells. The knock-down was confirmed at RNA, protein, and enzyme function levels. Apoptosis was determined using annexin V and propidium iodide staining and FACS analysis. The results showed a 34% increase in sensitivity of MOLT4 cells to 1 uM 6-TG after treatment with TPMT-targeting siRNA, as compared to cells transfected with non-targeting siRNA, while the sensitivity of the cells toward 6-MP was not affected significantly by down-regulation of the TPMT gene. This differential contribution of the enzyme TPMT to the cytotoxicity of the two thiopurines is probably due to its role in formation of the meTIMP, the cytotoxic methylated metabolite of 6-MP, while in case of 6-TG methylation by TPMT substantially deactivates the drug.

PMID:23811272 Karim H et al; Biochem Biophys Res Commun 437 (2): 280-6 (2013)


6-Thiouric acid is the major metabolite of 6-mercaptopurine and is formed from this drug by the action of xanthine oxidase.

IARC. Monographs on the Evaluation of the Carcinogenic Risk of Chemicals to Humans. Geneva: World Health Organization, International Agency for Research on Cancer, 1972-PRESENT. (Multivolume work). Available at: https://monographs.iarc.fr/ENG/Classification/index.php, p. V26 257 (1981)


5.7 Biological Half-Life

Triphasic: 45 minutes, 2.5 hours, and 10 hours.


Following IV administration of mercaptopurine (an IV preparation of the drug currently is not commercially available in the US), the elimination half-life of the drug is reportedly 21 minutes in pediatric patients and 47 minutes in adults.

American Society of Health-System Pharmacists 2016; Drug Information 2016. Bethesda, MD. 2016, p. 1178


After an intravenous dose, the half-life of the drug in plasma is relatively short (about 50 minutes) due to uptake by cells, renal excretion, and rapid metabolic degradation.

Gilman, A.G., T.W. Rall, A.S. Nies and P. Taylor (eds.). Goodman and Gilman's The Pharmacological Basis of Therapeutics. 8th ed. New York, NY. Pergamon Press, 1990., p. 1235


After iv administration of 6-mercaptopurine, the half-Iie for disappearance from the blood was about 9 min in rats and 14 min in mice.

IARC. Monographs on the Evaluation of the Carcinogenic Risk of Chemicals to Humans. Geneva: World Health Organization, International Agency for Research on Cancer, 1972-PRESENT. (Multivolume work). Available at: https://monographs.iarc.fr/ENG/Classification/index.php, p. V26 257 (1981)


5.8 Mechanism of Action

Mercaptopurine competes with hypoxanthine and guanine for the enzyme hypoxanthine-guanine phosphoribosyltransferase (HGPRTase) and is itself converted to thioinosinic acid (TIMP). TIMP inhibits several reactions that involve inosinic acid (IMP), such as the conversion of IMP to xanthylic acid (XMP) and the conversion of IMP to adenylic acid (AMP) via adenylosuccinate (SAMP). Upon methylation, TIMP forms 6-methylthioinosinate (MTIMP) which inhibits glutamine-5-phosphoribosylpyrophosphate amidotransferase in addition to TIMP. Glutamine-5-phosphoribosylpyrophosphate amidotransferase is the first enzyme unique to the _de novo_ pathway for purine ribonucleotide synthesis. According to experimental findings using radiolabeled mercaptopurine, mercaptopurine may be recovered from the DNA in the form of deoxythioguanosine. In comparison, some mercaptopurine may be converted to nucleotide derivatives of 6-thioguanine (6-TG) via actions of inosinate (IMP) dehydrogenase and xanthylate (XMP) aminase that convert TIMP to thioguanylic acid (TGMP).


The pathogenesis of several neurodegenerative diseases often involves the microglial activation and associated inflammatory processes. Activated microglia release pro-inflammatory factors that may be neurotoxic. 6-Mercaptopurine (6-MP) is a well-established immunosuppressive drug. Common understanding of their immunosuppressive properties is largely limited to peripheral immune cells. However, the effect of 6-MP in the central nervous system, especially in microglia in the context of neuroinflammation is, as yet, unclear. Tumor necrosis factor-alpha (TNF-a) is a key cytokine of the immune system that initiates and promotes neuroinflammation. The present study aimed to investigate the effect of 6-MP on TNF-a production by microglia to discern the molecular mechanisms of this modulation. Lipopolysaccharide (LPS) was used to induce an inflammatory response in cultured primary microglia or murine BV-2 microglial cells. Released TNF-a was measured by enzyme-linked immunosorbent assay (ELISA). Gene expression was determined by real-time reverse transcription polymerase chain reaction (RT-PCR). Signaling molecules were analyzed by western blotting, and activation of NF-kB was measured by ELISA-based DNA binding analysis and luciferase reporter assay. Chromatin immunoprecipitation (ChIP) analysis was performed to examine NF-kB p65 and coactivator p300 enrichments and histone modifications at the endogenous TNF-a promoter. Treatment of LPS-activated microglia with 6-MP significantly attenuated TNF-a production. In 6-MP pretreated microglia, LPS-induced MAPK signaling, I?B-a degradation, NF-kB p65 nuclear translocation, and in vitro p65 DNA binding activity were not impaired. However, 6-MP suppressed transactivation activity of NF-?B and TNF-a promoter by inhibiting phosphorylation and acetylation of p65 on Ser276 and Lys310, respectively. ChIP analyses revealed that 6-MP dampened LPS-induced histone H3 acetylation of chromatin surrounding the TNF-a promoter, ultimately leading to a decrease in p65/coactivator-mediated transcription of TNF-a gene. Furthermore, 6-MP enhanced orphan nuclear receptor Nur77 expression. Using RNA interference approach, we further demonstrated that Nur77 upregulation contribute to 6-MP-mediated inhibitory effect on TNF-a production. Additionally, 6-MP also impeded TNF-a mRNA translation through prevention of LPS-activated PI3K/Akt/mTOR signaling cascades. These results suggest that 6-MP might have a therapeutic potential in neuroinflammation-related neurodegenerative disorders through downregulation of microglia-mediated inflammatory processes.

PMID:27075886 Full text: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4831152 Huang HY et al; J Neuroinflammation 13 (1): 78 (2016)


Mercaptopurine (6-MP) competes with hypoxanthine and guanine for the enzyme hyphoxanthine-guanine phosphoribosyltransferase (HGPRTase) and is itself converted to thioinosinic acid (TIMP). This intracellular nucleotide inhibits several reactions involving inosinic acid (IMP), including the conversion of IMP to xanthylic acid (XMP) and the conversion of IMP to adenylic acid (AMP) via adenylosuccinate (SAMP). In addition, 6-methylthioinosinate (MTIMP) is formed by the methylation of TIMP. Both TIMP and MTIMP have been reported to inhibit glutamine-5-phosphoribosylpyrophosphate amidotransferase, the first enzyme unique to the de novo pathway for purine ribonucleotide synthesis. Experiments indicate that radiolabeled mercaptopurine may be recovered from the DNA in the form of deoxythioguanosine. Some mercaptopurine is converted to nucleotide derivatives of 6-thioguanine (6-TG) by the sequential actions of inosinate (IMP) dehydrogenase and xanthylate (XMP) aminase, converting TIMP to thioguanylic acid (TGMP). Animal tumors that are resistant to mercaptopurine often have lost the ability to convert mercaptopurine to TIMP. However, it is clear that resistance to mercaptopurine may be acquired by other means as well, particularly in human leukemias. It is not known exactly which of any one or more of the biochemical effects of mercaptopurine and its metabolites are directly or predominantly responsible for cell death.

NIH; DailyMed. Current Medication Information for Mercaptopurine (Updated: October 2016). Available from, as of February 6, 2017: https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=c3b5b8b0-bc5c-4ce9-bbdc-febba60c2658


Inflammatory bowel disease is characterized by chronic intestinal inflammation. Azathioprine and its metabolite 6-mercaptopurine (6-MP) are effective immunosuppressive drugs that are widely used in patients with inflammatory bowel disease. ... Azathioprine and 6-MP have been shown to affect small GTPase Rac1 in T cells and endothelial cells, whereas the effect on macrophages and gut epithelial cells is unknown. Macrophages (RAW cells) and gut epithelial cells (Caco-2 cells) were activated by cytokines and the effect on Rac1 signaling was assessed in the presence or absence of 6-MP. Rac1 is activated in macrophages and epithelial cells, and treatment with 6-MP resulted in Rac1 inhibition. In macrophages, interferon-gamma induced downstream signaling through c-Jun-N-terminal Kinase (JNK) resulting in inducible nitric oxide synthase (iNOS) expression. iNOS expression was reduced by 6-MP in a Rac1-dependent manner. In epithelial cells, 6-MP efficiently inhibited tumor necrosis factor-a-induced expression of the chemokines CCL2 and interleukin-8, although only interleukin-8 expression was inhibited in a Rac1-dependent manner. In addition, activation of the transcription factor STAT3 was suppressed in a Rac1-dependent fashion by 6-MP, resulting in reduced proliferation of the epithelial cells due to diminished cyclin D1 expression. These data demonstrate that 6-MP affects macrophages and gut epithelial cells beneficially, in addition to T cells and endothelial cells. Furthermore, mechanistic insight is provided to support development of Rac1-specific inhibitors for clinical use in inflammatory bowel disease.

PMID:25029617 Marinkovic G et al; Inflamm Bowel Dis 20 (9): 1487-95 (2014)


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