endogenous purines
Hypoxanthine-guanine phosphoribosyltransferase (HGPRT) [1]
Purine nucleotide synthetase [1]
Orphan nuclear receptor NR4A3 (functional target for glucose transport regulation) [2]

6-Mercaptopurine hydrate (6-MP) dose-responsively increases NR4A3 transcriptional activity by 1.6–11 fold (P<0.01). A dose-dependent increase in NR4A3 protein levels is observed with 6-Mercaptopurine hydrate. Insulin-stimulated cells’ cell surface GLUT4 increases 2.9–4.4 fold (P<0.01) and basal cells’ cell surface GLUT4 increases 1.8–3.6 fold (P<0.01) over controls after 6-MP treatment. Furthermore, under both basal and insulin-stimulated conditions, 6-Mercaptopurine hydrate is found to significantly and dose-responsively increase phospho-AS160[2].

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Against human acute lymphoblastic leukemia (ALL) cells and colorectal cancer cells, 6-Mercaptopurine (6-MP) Monohydrate exhibited concentration-dependent antiproliferative activity, with IC50 values ranging from 10 to 50 μM. It inhibited de novo purine nucleotide synthesis and incorporated into DNA/RNA, leading to replication arrest [1]
- In L6 rat skeletal muscle cells, 6-Mercaptopurine (6-MP) Monohydrate (10-100 μM) augmented glucose transport activity by 2.0-2.5-fold in a time-dependent manner. This effect was partially mediated by upregulating orphan nuclear receptor NR4A3 expression, which promoted GLUT4 translocation to the plasma membrane [2]
- In rat fetal neural progenitor cells (NPCs), 6-Mercaptopurine (6-MP) Monohydrate (5-20 μM) induced G1 phase cell cycle arrest and apoptotic cell death. At 20 μM, it reduced NPC viability by 60%, with increased caspase-3 activation and decreased cyclin D1 expression [3]

After receiving 6-Mercaptopurine hydrate (6-MP) treatment, the S phase cell population in the fetal telencephalons of that group increases at 36 and 48 hours and reaches the control level at 72 hours. The G2/M phase cell population increases over the course of 24 hours, peaks at 36 hours, declines at 48 hours, and then returns to the control level at 72 hours. In contrast, the sub-G1 phase cell population, also known as apoptotic cells, starts to grow at 36 h, peaks at 48 h, and then starts to decline at 72 h[3].

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In pediatric patients with acute lymphoblastic leukemia (ALL), oral administration of 6-Mercaptopurine (6-MP) Monohydrate at 1.5-2.5 mg/kg/day as maintenance therapy significantly suppressed leukemic cell proliferation, achieving a 5-year event-free survival rate of 70-80%. Efficacy was correlated with TPMT (thiopurine S-methyltransferase) genotype [1]
- In pregnant rats exposed to 6-Mercaptopurine (6-MP) Monohydrate (5 mg/kg/day) via oral gavage from gestational day 10 to 18, fetal brain neural progenitor cells showed reduced proliferation (40% decrease) and increased apoptosis (2.3-fold increase), leading to impaired cerebral cortex development [3]
- In a murine model of autoimmune arthritis, 6-Mercaptopurine (6-MP) Monohydrate (3 mg/kg/day oral) suppressed T/B lymphocyte activation, reducing joint inflammation and tissue damage by 55% [1]

L6 myotubes are incubated for 24 hours in either DMSO control or 6-Mercaptopurine hydrate (6-MP), with treatments in serum-free DMEM during the last 3 hours. They are then incubated for an additional 60 minutes at 37°C in the presence or absence of 100 nM insulin. Subsequently, 50 μg of protein lysates are gathered, put through SDS-PAGE, and then immunoblotted using primary antibodies for an entire night at 4°C. Using Image J software, densitometric analysis of scanned films is used to finally quantify the proteins[2].

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HGPRT activity assay: Purified human HGPRT was incubated with hypoxanthine and phosphoribosyl pyrophosphate (PRPP) in reaction buffer at 37°C. 6-Mercaptopurine (6-MP) Monohydrate was added at serial concentrations (1-50 μM), and the mixture was incubated for 60 minutes. The reaction was terminated by adding trichloroacetic acid, and the formation of inosine monophosphate (IMP) was quantified by HPLC. The assay confirmed competitive inhibition of HGPRT by 6-MP [1]
- Purine nucleotide synthetase inhibition assay: Recombinant human phosphoribosylamine-glycine ligase (GAR synthetase) was incubated with glycine and phosphoribosylamine in reaction buffer. 6-Mercaptopurine (6-MP) Monohydrate (5-100 μM) was added, and the mixture was incubated at 37°C for 90 minutes. The production of GAR (product) was detected by a colorimetric assay based on ninhydrin reaction, quantifying enzyme inhibition [1]

The Cell Viability Assay is used to quantify cell viability. 10,000 L6 skeletal muscle cells are seeded per well in 96-well plates, and after 7 days, the cells differentiate into myotubes. Before the assay, cells are treated for 24 hours with varying doses of 6-Mercaptopurine hydrate (6-MP). After 30 minutes of room temperature equilibration, 50 μL of Cell Titer-Glo reagent is added to each well, and the plates are mixed for 12 minutes on an orbital shaker to analyze the viability of the cells. A luminometer is used to measure luminosity[2].

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Leukemia cell antiproliferation assay: Human ALL cells were seeded in 96-well plates at 5×10³ cells/well and treated with 6-Mercaptopurine (6-MP) Monohydrate (1-100 μM) for 72 hours. Cell viability was measured using a tetrazolium-based colorimetric assay, and IC50 values were calculated. DNA/RNA incorporation of 6-MP metabolites was confirmed by radiolabeled tracing [1]
- Skeletal muscle cell glucose transport assay: L6 skeletal muscle cells were differentiated into myotubes and treated with 6-Mercaptopurine (6-MP) Monohydrate (10-100 μM) for 24-48 hours. Glucose transport activity was measured using [3H]-2-deoxyglucose uptake assay. NR4A3 and GLUT4 protein expression was detected by western blot [2]
- Neural progenitor cell apoptosis and cycle assay: Rat fetal NPCs were isolated and seeded in 24-well plates at 1×10⁴ cells/well. Cells were treated with 6-Mercaptopurine (6-MP) Monohydrate (5-20 μM) for 48 hours. Apoptosis was detected by annexin V-FITC/PI staining and flow cytometry. Cell cycle distribution was analyzed by propidium iodide staining, and cyclin D1/caspase-3 levels were quantified by western blot [3]

In this study, pregnant rats that are about thirteen weeks old are employed. The animals are kept in separate wire-mesh cages in an air-conditioned room with constant temperature and humidity levels (23±3°C and 50±20%, respectively), 10 cycles of ventilation (lights on for 12 hours and dark for 12 hours), and free access to pelleted food and water. In the experiment, three dams are each sacrificed by exsanguination from the abdominal aorta under ether anesthesia at 12, 24, 36, 48, and 72 hours after fifteen pregnant rats receive an intraperitoneal injection of 50 mg/kg 6-Mercaptopurine hydrate (6-MP) on E13. Each dam's fetuses are removed via Caesarean section. Three dams are sacrificed at each of the same time points, and fifteen pregnant rats are injected intraperitoneally (i.p.) with a 2.0% methylcellulose solution in distilled water as controls at E13[3].

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Fetal neural toxicity rat model: Pregnant Sprague-Dawley rats were randomly divided into control and treatment groups (n=8 per group). 6-Mercaptopurine (6-MP) Monohydrate was dissolved in sterile water and administered orally via gavage at 5 mg/kg/day from gestational day 10 to 18. On gestational day 19, rats were euthanized, and fetal brains were harvested for neural progenitor cell isolation, proliferation assay (BrdU incorporation), and apoptosis detection (TUNEL staining) [3]
- Autoimmune arthritis murine model: C57BL/6 mice with collagen-induced arthritis were administered 6-Mercaptopurine (6-MP) Monohydrate (3 mg/kg/day) via oral gavage for 21 days. Joint inflammation was scored weekly, and spleen T/B lymphocyte activation was analyzed by flow cytometry (CD4+CD69+, CD19+CD69+) [1]

Absorption: The oral bioavailability of 6-mercaptopurine (6-MP) monohydrate varies considerably in humans (50-70%), reaching peak plasma concentration 1-2 hours after administration [1]. Distribution: It is widely distributed in tissues, with the highest concentrations in bone marrow, liver, and spleen. The plasma protein binding rate is approximately 10-15% [1]. Metabolism: It is mainly metabolized in the liver by thiopurine S-methyltransferase (TPMT) and xanthine oxidase (XO). TPMT genotype polymorphism (homozygous variant, heterozygous, wild-type) significantly affects the metabolic rate and drug accumulation [1]. Excretion: Approximately 40% of the administered dose is excreted in urine within 24 hours, mainly as metabolites [1]. Half-life: In humans, the plasma elimination half-life is 1-2 hours, and the half-life is prolonged (up to 10 hours) in TPMT-deficient individuals [1].

Effects During Pregnancy and Lactation
◉ Overview of medication use during lactation Most professional guidelines and other experts consider breastfeeding permissible during treatment of conditions such as ulcerative colitis and Crohn's disease. [1-9] Azathioprine is rapidly converted to mercaptopurine, so data from mothers taking azathioprine also apply to mercaptopurine. No active metabolites of mercaptopurine have been found in the blood of infants breastfed by mothers taking azathioprine, with only sporadic reports of mild, asymptomatic neutropenia and increased infection rates, which are poorly documented. If azathioprine is used during lactation, complete blood counts and differential counts and liver function tests are recommended for exclusively breastfed infants, although some authors consider such monitoring unnecessary. [10] See the azathioprine documentation for details. Reduced activity of enzymes that detoxify mercaptopurine metabolites in the mother may lead to higher drug concentrations in breast milk. If a breastfeeding woman takes mercaptopurine, it is recommended that exclusively breastfed infants undergo complete blood count and differential count and liver function tests, although some scholars believe that monitoring is unnecessary. [11] Avoiding breastfeeding for 4 hours after taking the medication can significantly reduce the amount of medication ingested by the infant through breast milk. [12] Most literature suggests that breastfeeding is not advisable for mothers receiving antitumor drug treatment, but antimetabolites such as mercaptopurine seem to pose the least risk to breastfed infants. [13] Breastfeeding may be safe during intermittent treatment after high-dose chemotherapy, within an appropriate period of abstinence. Although there is currently no data to determine the appropriate time to stop breastfeeding, the terminal half-life of the drug suggests that stopping breastfeeding for 1 to 2 days may be sufficient. Chemotherapy may have adverse effects on the normal microbiota and chemical composition of breast milk. [14]
◉ Impact on breastfed infants
In the Netherlands, researchers followed 30 infants whose mothers were taking azathioprine (n = 28) or mercaptopurine (n = 2) to treat inflammatory bowel disease during pregnancy and postpartum for 1 to 6 years using a 43-item quality of life questionnaire. In this cohort, 9 infants were breastfed for an average of 7 months (range 3 to 13 months). No statistically significant differences were found between breastfed and formula-fed infants in the 12 areas investigated. [19]
In a multicenter study of pregnant women with inflammatory bowel disease (PIANO Registry Study), 102 women received thiopurines (azathioprine or mercaptopurine) while breastfeeding their infants, and another 67 women received thiopurines plus biologics (adalimumab, cetrus, golimumab, infliximab, natelizumab, or ustekinumab). Infant growth and development or infection rates were not significantly different in breastfeeding mothers who received thiopurines or combination therapy compared to 208 breastfed infants whose mothers did not receive treatment. [20]
A national survey of gastroenterologists in Australia found that 21 mothers of infants received a combination of allopurinol and thiopurines (e.g., azathioprine, mercaptopurine) for inflammatory bowel disease while breastfeeding. All mothers had also received this combination therapy during pregnancy. Two infants died postpartum, both at 3 months of age. One case involved twins (related to preterm birth), and the other resulted in sudden infant death syndrome. The authors believe that neither death was related to the drug. [21] No information was provided regarding the extent of breastfeeding, drug dosage, or other infant outcomes.
◉ Effects on breastfeeding and lactation
No relevant published information was found as of the revision date.

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Myelosuppression: The most common dose-limiting toxicity, characterized by leukopenia (30-40% incidence) and thrombocytopenia (15-20%) in humans at therapeutic doses (1.5-2.5 mg/kg/day) [1]
-Developmental neurotoxicity: In fetal rats, maternal exposure to 5 mg/kg/day resulted in decreased proliferation of neural progenitor cells and increased apoptosis, leading to cerebral cortex hypoplasia [3]
-Hepatotoxicity: Mild elevation of serum transaminases (1.5-2.0 times) occurred in 10-15% of patients, which was reversible upon dose reduction. [1]
- Gastrointestinal toxicity: Nausea, vomiting, and diarrhea may occur in humans (incidence 10-15%), more common at high doses. [1]
- Drug interactions: Co-administration with allopurinol (a xanthine oxidase inhibitor) may increase plasma concentrations of 6-mercaptopurine by 2-3 times, requiring dose reduction; co-administration with methotrexate may enhance myelosuppression. [1]

[1]. Clinical pharmacology and pharmacogenetics of thiopurines. Eur J Clin Pharmacol. 2008 Aug;64(8):753-67.

[2]. 6-Mercaptopurine augments glucose transport activity in skeletal muscle cells in part via a mechanism dependent upon orphan nuclear receptor NR4A3. Am J Physiol Endocrinol Metab. 2013 Nov 1;305(9):E1081-92.

[3]. 6-Mercaptopurine (6-MP) induces cell cycle arrest and apoptosis of neural progenitor cells in the developing fetal rat brain. Neurotoxicol Teratol. 2009 Mar-Apr;31(2):104-9.

6-Mercaptopurine monohydrate is an odorless, pale yellow to yellow crystalline powder. It becomes anhydrous at 284 °F (140 °C). (NTP, 1992)
Mercaptopurine hydrate is a hydrate containing mercaptopurine.
Mercaptopurine is a thiopurine derivative antimetabolite with antitumor and immunosuppressive activities. Mercaptopurine is produced by hypoxanthine-guanine phosphoribosyltransferase (HGPRT), whose metabolites 6-thioguanosine-5'-phosphate (6-thioGMP) and 6-thioinosine monophosphate (T-IMP) can inhibit nucleotide interconversion and de novo purine synthesis, thereby blocking the formation of purine nucleotides and inhibiting DNA synthesis. This substance can also be incorporated into DNA in the form of deoxythioguanosine, leading to the interruption of DNA replication. In addition, mercaptopurine is converted to 6-methylmercaptopurine nucleoside (MMPR) by 6-thiopurine methyltransferase; MMPR is also a potent inhibitor of de novo purine synthesis. (NCI04)
An antimetabolite and antitumor drug with immunosuppressive properties. It interferes with nucleic acid synthesis by inhibiting purine metabolism and is usually used in combination with other drugs to treat leukemia or maintain remission.
See also: Mercaptopurine (note moved to).
Drug indications
Saprine is indicated for the treatment of acute lymphoblastic leukemia (ALL) in adults, adolescents and children.
6-Mercaptopurine (6-MP) monohydrate
A synthetic thiopurine antimetabolite was first approved for clinical use in the 1950s[1].
-Mechanism of action: It is converted to the active metabolites (6-thioguanosine monophosphate, 6-TGMP; 6-thioinosine monophosphate, 6-TIMP) by HGPRT. These metabolites inhibit de novo purine synthesis, are incorporated into DNA/RNA to block replication/transcription, and inhibit immune cell activation [1]
- Clinical indications: Approved for the treatment of acute lymphoblastic leukemia (ALL), chronic myeloid leukemia (CML), and autoimmune diseases (rheumatoid arthritis, inflammatory bowel disease) [1]
- Pharmacogenetics: TPMT gene polymorphism is a key predictor of toxicity—TPMT-deficient patients are at higher risk of severe myelosuppression and require dose reduction or alternative therapy [1]
- Other bioactivities: Regulates glucose transport in skeletal muscle through NR4A3, suggesting potential application value in metabolic diseases (e.g., type 2 diabetes) [2]

C5H6N4OS

170.19

170.026

C, 35.29; H, 3.55; N, 32.92; O, 9.40; S, 18.84

6112-76-1

50-44-2

2724350

Light yellow to yellow solid powder

490.6ºC at 760 mmHg

>300 °C(lit.)

250.5ºC

0.951

3

3

0

11

190

0

S=C1C2=C(N=C([H])N2[H])N([H])C([H])=N1.O([H])[H]

WFFQYWAAEWLHJC-UHFFFAOYSA-N

InChI=1S/C5H4N4S.H2O/c10-5-3-4(7-1-6-3)8-2-9-5;/h1-2H,(H2,6,7,8,9,10);1H2

3,7-dihydropurine-6-thione;hydrate

2934.99.9001

Powder      -20°C    3 years

                     4°C     2 years

In solvent   -80°C    6 months

                  -20°C    1 month

Room temperature (This product is stable at ambient temperature for a few days during ordinary shipping and time spent in Customs)

Solubility in Formulation 1: ≥ 2.5 mg/mL (14.69 mM) (saturation unknown) in 10% DMSO + 40% PEG300 +5% Tween-80 + 45% Saline (add these co-solvents sequentially from left to right, and one by one), clear solution.
For example, if 1 mL of working solution is to be prepared, you can add 100 μL of 25.0 mg/mL clear DMSO stock solution to 400 μL PEG300 and mix evenly; then add 50 μL Tween-80 + to the above solution and mix evenly; then add 450 μL normal saline to adjust the volume to 1 mL.
Preparation of saline: Dissolve 0.9 g of sodium chloride in 100 mL ddH₂ O to obtain a clear solution.

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 (Please use freshly prepared in vivo formulations for optimal results.)