Mercaptopurine
| Evidence Level: L5 | Predicted Indications: 10 |
Table of Contents
Mercaptopurine: From Acute Lymphoblastic Leukaemia to Myeloid Leukaemia
One-Sentence Summary
Mercaptopurine is a purine antimetabolite, originally used to treat acute lymphoblastic leukaemia (ALL) and related leukaemias. The TxGNN model predicts it may be effective for myeloid leukaemia, with 15 clinical trials and 20 publications retrieved for this direction. However, most of these trials are multi-agent regimens in which mercaptopurine's individual contribution cannot be isolated.
Quick Overview
| Item | Content |
|---|---|
| Original Indication | Acute lymphoblastic leukaemia (the Singapore licence record contains no approved-indication text; the original indication is taken from the TxGNN knowledge graph) |
| Predicted New Indication | Myeloid leukaemia |
| TxGNN Prediction Score | 99.94% |
| Evidence Level | L1 (formally; see the caveat below) |
| Singapore Market Status | ✓ Marketed |
| Number of Registrations | 1 |
| Recommended Decision | Proceed with Guardrails |
Why is This Prediction Reasonable?
Detailed mechanism-of-action data is not available in the data compiled for this report. Based on known pharmacology, mercaptopurine is a purine antimetabolite. Its thioguanine nucleotide metabolites are incorporated into DNA and RNA and inhibit de novo purine synthesis. This is cytotoxic to rapidly dividing leukaemic blasts.
ALL and myeloid leukaemia are both haematological malignancies of rapidly dividing blood cells, so an antimetabolite that works in ALL could plausibly act in myeloid disease. The strongest support is mercaptopurine's use as a maintenance component (6-MP plus methotrexate) in acute promyelocytic leukaemia regimens and in some AML maintenance settings. A Korean cohort study of oral 6-MP and methotrexate maintenance in transplant-ineligible AML patients is consistent with this use.
Important caveat: The Phase 3 trials found are in the leukaemia space, but the data do not show that mercaptopurine was an independently randomised variable in them. The evidence therefore supports the regimen context, not an isolated mercaptopurine effect. The L1 grade should be read with this limitation in mind.
Clinical Trial Evidence
| Trial Number | Phase | Status | Enrollment | Key Findings |
|---|---|---|---|---|
| NCT00003934 | Phase 3 | Completed | 420 | Tretinoin plus chemotherapy with or without arsenic trioxide, then maintenance with tretinoin versus tretinoin plus mercaptopurine and methotrexate in untreated APL. This is the trial that names mercaptopurine directly. |
| NCT00492856 | Phase 3 | Completed | 105 | S0521: maintenance versus observation in low/intermediate-risk APL. A mercaptopurine-containing maintenance regimen is plausible but not confirmed from the title. |
| NCT00002701 | Phase 3 | Unknown | 750 | ATRA plus idarubicin with intensive consolidation and randomised maintenance in APL. Mercaptopurine is a standard APL maintenance component, though this is not confirmed. |
| NCT02521493 | Phase 3 | Active, not recruiting | 280 | Risk-stratified therapy for AML in Down syndrome. Mercaptopurine's contribution is not isolated. |
| NCT00136084 | Phase 3 | Completed | 238 | Two multi-agent regimens with different cytarabine doses in newly diagnosed AML or myelodysplasia. Mercaptopurine's role is unclear. |
| NCT02688140 | Phase 3 | Completed | 133 | Arsenic trioxide plus ATRA and idarubicin versus AIDA in high-risk APL. Mercaptopurine involvement is indirect. |
| NCT00482833 | Phase 3 | Completed | 276 | Arsenic trioxide plus ATRA versus AIDA in non-high-risk APL. |
| NCT00866918 | Phase 3 | Completed | 106 | Risk-adapted treatment of childhood APL using arsenic trioxide in consolidation. |
| NCT05506332 | Phase 1 | Recruiting | 10 | Venetoclax plus 6-mercaptopurine in relapsed/refractory AML. Mechanistically relevant but early-phase and very small. |
| NCT06199557 | Phase 1/2 | Recruiting | 48 | Hydroxyurea plus valproic acid, or 6-mercaptopurine plus valproic acid, in AML or high-risk MDS patients unfit for standard therapy. |
Literature Evidence
| PMID | Year | Type | Journal | Key Findings |
|---|---|---|---|---|
| 26425037 | 2015 | Cohort | Journal of Korean Medical Science | Oral 6-MP plus methotrexate maintenance in transplant-ineligible AML patients, evaluating leukaemia-free and overall survival. |
| 27275453 | 2016 | Prospective pilot | South Asian Journal of Cancer | Metronomic oral 6-MP in elderly AML. |
| 32459546 | 2020 | Retrospective | Pediatric Hematology and Oncology | Outcomes of juvenile myelomonocytic leukaemia after sequential cytarabine and 6-MP. |
| 38828002 | 2024 | Cohort | Therapeutic Advances in Hematology | Intensive chemotherapy with dual induction and ALL-like consolidation in childhood AML (multicentre, China). |
| 22715121 | 2012 | Clinical trial | Blood | ATRA, idarubicin and intravenous arsenic trioxide as initial APL therapy (APML4). |
| 12057059 | 2000 | Review | Current Treatment Options in Oncology | Overview of APL treatment: ATRA with chemotherapy and consolidation. |
| 3513537 | 1986 | Clinical study | American Journal of Clinical Oncology | Hydroxyurea and 6-MP in chronic granulocytic leukaemia. |
| 33183436 | 2021 | Review | Journal of Nanoscience and Nanotechnology | 6-MP nanomedicine in leukaemia. |
| 34442422 | 2021 | Review | Journal of Personalized Medicine | NUDT15 polymorphisms and thiopurine toxicity such as bone marrow suppression. |
| 2676034 | 1989 | Review | Blood Reviews | Purine metabolism as a target for leukaemia chemotherapy. |
Singapore Market Information
| Authorization Number | Product Name | Dosage Form | Approved Indication |
|---|---|---|---|
| SIN10810P | PURINETONE TABLETS 50 mg | Tablet | Not stated in the registration record |
Cytotoxicity
| Item | Content |
|---|---|
| Cytotoxicity Classification | Conventional cytotoxic (purine antimetabolite) |
| Myelosuppression Risk | High. Neutropenia, leukopenia and thrombocytopenia are among the conditions flagged for caution. Susceptibility is strongly influenced by TPMT and NUDT15 genotype. |
| Emetogenicity Classification | Low (general class information; not drawn from the compiled data) |
| Monitoring Items | Complete blood count with differential, liver function (including bilirubin), renal function, and pancreatic enzymes if symptoms arise |
| Handling Protection | Follow cytotoxic drug handling regulations |
Safety Considerations
- Conditions of concern (knowledge-graph contraindication links, not package-insert text): kidney disease, liver disease, gallbladder disease, pancreatitis, cholestasis (including benign recurrent and familial intrahepatic forms), hyperbilirubinaemia (including Gilbert syndrome), thrombocytopenia, neutropenia, leukopenia, agranulocytosis, anaemia (including macrocytic anaemia), pyoureter, and hepatosplenic T-cell lymphoma.
- Drug Interactions: 100 interactions were identified. Moderate-level interactions include mesalazine, balsalazide, olsalazine, sulfasalazine and naltrexone. Levofloxacin is rated minor. Others (e.g., prednisone, metformin, omeprazole, pantoprazole, vancomycin, amphotericin B) have no assigned severity. Literature also notes that allopurinol shifts thiopurine metabolite ratios and requires dose adjustment.
- Pharmacogenomics: The literature, including a study in Taiwanese children, links NUDT15 and TPMT variants to mercaptopurine intolerance and severe myelosuppression.
Package-insert warnings and contraindications have not been retrieved, so please refer to the package insert for authoritative safety information.
Conclusion and Next Steps
Decision: Proceed with Guardrails
Rationale: Mercaptopurine has biological plausibility in myeloid leukaemia, and several Phase 3 APL and AML trials exist, one of which (NCT00003934) names mercaptopurine in a maintenance arm. However, in most of these trials the drug's individual effect cannot be separated from the multi-agent regimen. The supporting AML literature is mostly small cohort or pilot studies, so the evidence is regimen-level, not drug-specific.
To proceed, the following is needed:
- Retrieval of the package insert (warnings, contraindications and approved indications) from the HSA website, since safety screening cannot be completed without it
- Mechanism-of-action data from DrugBank
- Confirmation of mercaptopurine's role in the cited Phase 3 protocols (especially NCT00492856, NCT00002701 and NCT02688140)
- A TPMT/NUDT15 genotyping plan, blood-count-guided dose titration, and an interaction check (e.g., allopurinol, aminosalicylates)
Other Predicted Indications (Brief Note)
Among the other predictions, precursor lymphoblastic lymphoma/leukaemia and acute lymphoblastic leukaemia reflect mercaptopurine's established on-label use rather than new repurposing. The other predictions have little or no supporting evidence:
- Small cell lung carcinoma: a 1985 Phase 2 study and preclinical work only (research question).
- Hodgkin lymphoma: only indirect lymphoid-malignancy data.
- Chronic lymphocytic leukaemia subtypes, pulmonary blastoma, primary pulmonary lymphoma and fetal adenocarcinoma of the lung: prediction signal only, so Hold.
Disclaimer
This content is for research purposes only and does not constitute medical advice. Clinical validation is required before any clinical application.