Mercaptopurine (6-MP)

Inhibitor of de novo purine synthesis through interference with DNA and RNA synthesis. Immunosuppressive and antileukemic drug; reduces the anticoagulation elicited by warfarin. Active metabolite of azathioprine.

Time-course changes in neural cell apoptosis in the rat fetal brain from dams treated with 6-mercaptopurine (6-MP).[Pubmed:19130401]

Histol Histopathol. 2009 Mar;24(3):317-24.

6-Mercaptopurine (6-MP), one of the major drugs for the therapy of acute lymphoblastic leukemia and autoimmune diseases, is incorporated as thioguanine in nucleic acid and it induces cytotoxicity and fetotoxicity. In the present study, pregnant rats were treated with 50 mg/kg of 6-MP on 13 embryonic days (E), and fetuses were collected from 12 to 96 h after the treatment to examine the mechanism and time-course changes in neural cell death in the developing brain. The weights of fetal telencephalon and the thickness of the dorsal telencephalic wall of the fetuses were significantly reduced at 96 h. The number of pyknotic neural cells in the fetal telencephalon began to increase at 24 h, peaked at 36 h, and then gradually decreased toward 72 h. The nuclei of most of these pyknotic cells were stained positively by TUNEL method, which detects DNA fragmentation. Moreover, pyknotic cells were immunohistochemically positive for cleaved caspase-3, one of the key executioners of apoptosis, and the increased expression of the protein from 30 to 48 h was confirmed by using Western blot analysis. Also, electron microscopical features of the pyknotic cells showed ultrastructural characteristics of apoptosis. On the other hand, the number of mitotic and BrdU-positive neural cells in the telencephalon decreased from 30 to 72 h. These results suggest that 6-MP induced apoptotic cell death in neural cells in the rat fetal brain is probably due to cytotoxic action of 6-MP.

6-mercaptopurine (6-MP) induces p53-mediated apoptosis of neural progenitor cells in the developing fetal rodent brain.[Pubmed:19281843]

Neurotoxicol Teratol. 2009 Jul-Aug;31(4):198-202.

6-Mercaptopurine (6-MP), a DNA-damaging agent, induces apoptosis of neural progenitor cells, and causes malformation in the fetal brain. The aim of the present study is to clarify the molecular pathway of 6-MP-induced apoptosis of neural progenitor cells in the fetal telencephalon of rats and mice. p53 protein is activated by DNA damage and induces apoptosis through either the intrinsic pathway involving the mitochondria or the extrinsic pathway triggered by death receptors. In this study, the expression of puma and cleaved caspase-9 proteins, which are specific intrinsic pathway factors, increased in the rat telencephalon after 6-MP treatment. 6-MP-induced apoptosis of neural progenitor cells was completely absent in p53-deficient mice. On the other hand, the expression of Fas protein, an extrinsic pathway factor, did not change throughout the experimental period in the rat telencephalon treated with 6-MP. The number of apoptotic neural progenitor cells was similar among Fas-mutated lpr/lpr and wild-type mice, suggesting that the Fas pathway does not play a significant role in 6-MP-induced apoptosis of neural progenitor cells. These results may suggest that the p53-mediated intrinsic pathway is essential for 6-MP-induced apoptosis of neural progenitor cells in the developing telencephalon of rats and mice.

6-Mercaptopurine (6-MP) induces cell cycle arrest and apoptosis of neural progenitor cells in the developing fetal rat brain.[Pubmed:18951973]

Neurotoxicol Teratol. 2009 Mar-Apr;31(2):104-9.

6-Mercaptopurine (6-MP), an analogue of hypoxanthine, is used in the therapy of acute lymphoblastic leukemia and causes fetal neurotoxicity. To clarify the mechanisms of 6-MP-induced fetal neurotoxicity leading to the cell cycle arrest and apoptosis of neural progenitor cells, pregnant rats were treated with 50 mg/kg 6-MP on embryonic day (E) 13, and the fetal telencephalons were examined at 12 to 72 h (h) after treatment. Flow-cytometric analysis confirmed an accumulation of cells at G2/M, S, and sub-G1 (apoptotic cells) phases from 24 to 72 h. The number of phosphorylated histone H3-positive cells (mitotic cells) decreased from 36 to 72 h, and the phosphorylated (active) form of p53 protein, which is a mediator of apoptosis and cell cycle arrest, increased from 24 to 48 h. An executor of p53-mediated cell cycle arrest, p21, showed intense overexpression at both the mRNA and protein levels from 24 to 72 h. Cdc25A protein, which is needed for the progression of S phase, decreased at 36 and 48 h. In addition, phosphorylated cdc2 protein, which is an inactive form of cdc2 necessary for G2/M progression, increased from 24 to 48 h. These results suggest that 6-MP induced G2/M arrest, delayed S-phase progression, and finally induced apoptosis of neural progenitor cells mediated by p53 in the fetal rat telencephalon.

The study of oxidization fluorescence sensor with molecular imprinting polymer and its application for 6-mercaptopurine (6-MP) determination.[Pubmed:18656656]

Talanta. 2008 Aug 15;76(4):768-71.

This paper developed optical fiber sensor based on molecular imprinted polymer as artificial recognition element for the determination of 6-Mercaptopurine (6-MP) in human serum. This approach displayed high sensitivity by oxidizing 6-MP to a strong fluorescent compound with H(2)O(2) in the alkaline media. It offered a relatively nice selectivity for 6-MP detection by molecular imprinted polymer's recognition. The relative standard deviation (R.S.D.) was 5% for a same sensor (n=5) when 6-MP concentration was 1.0 x 10(-7)gm L(-1) in serum. The developed method was satisfactorily applied to the determination of 6-MP in human serum without any necessity for sample treatment or time-consuming extraction steps prior to the analysis.

Clinical pharmacology and pharmacogenetics of thiopurines.[Pubmed:18506437]

Eur J Clin Pharmacol. 2008 Aug;64(8):753-67.

The thiopurine drugs-azathioprine (AZA), 6-Mercaptopurine (6-MP), and thioguanine-are widely used to treat malignancies, rheumatic diseases, dermatologic conditions, inflammatory bowel disease, and solid organ transplant rejection. However, thiopurine drugs have a relatively narrow therapeutic index and are capable of causing life-threatening toxicity, most often myelosuppression. Thiopurine S-methyltransferase (TPMT; EC 2.1.1.67), an enzyme that catalyzes S-methylation of these drugs, exhibits a genetic polymorphism in 10% of Caucasians, with 1/300 individuals having complete deficiency. Patients with intermediate or deficient TPMT activity are at risk for excessive toxicity after receiving standard doses of thiopurine medications. This report reviews the recent advances in the knowledge of the mechanism of action as well as the molecular basis and interethnic variations of TPMT and inosine triphosphate pyrophosphatase (ITPase; EC 3.6.1.19), another enzyme implicated in thiopurine toxicity. In addition, an update on pharmacokinetics, metabolism, drug-drug interactions, safety, and tolerability of thiopurine drugs is provided.

6-Mercaptopurine is a purine analogue which acts as an antagonist of the endogenous purines and has been widely used as antileukemic agent and immunosuppressive drug.

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