Mercaptopurine
| Evidence Level: L3 | Predicted Indications: 8 |
Table of Contents
Mercaptopurine: Myeloid leukemia
One-Sentence Summary
Mercaptopurine is an oral thiopurine antimetabolite that is currently marketed in Canada. The TxGNN model predicts it may be useful for myeloid leukemia (prediction score 0.9994). The data compiled for this report include 15 registered clinical trials and 20 publications. Most trials are regimen-level studies in which mercaptopurine is not tested on its own, and only a few publications examine it directly in this disease.
Quick Overview
| Item | Content |
|---|---|
| Original Indication | Not recorded in the local data |
| Predicted New Indication | Myeloid leukemia |
| TxGNN Prediction Score | 0.9994 |
| Evidence Level | L3 |
| Canada Market Status | Marketed (marketed DINs: 2 of 2) |
| Number of DINs | 2 (marketed: 2) |
| Recommended Decision | Hold |
Why is This Prediction Reasonable?
Detailed mechanism-of-action data were not available in the compiled data. Mercaptopurine is a purine analogue. Its active thioguanine nucleotides are incorporated into DNA and RNA and inhibit de novo purine synthesis. This is cytotoxic to rapidly dividing leukemic cells, including myeloid cells.
The same mechanism could apply to myeloid leukemia. Mercaptopurine appears in published multi-agent regimens and as oral maintenance therapy, usually together with methotrexate. It has been tested this way in acute myeloid leukemia (AML) and acute promyelocytic leukemia (APL).
The evidence comes mostly from combination protocols. The contribution of mercaptopurine alone cannot be separated out. Evidence level L3 reflects a cohort study (PMID 26425037) and a prospective pilot study (PMID 27275453) of oral mercaptopurine in AML. No randomized trial tests mercaptopurine itself in this disease.
Clinical Trial Evidence
| Trial Number | Phase | Status | Enrollment | Key Findings |
|---|---|---|---|---|
| NCT02521493 | Phase 3 | Active, not recruiting | 280 | Response-based, risk-stratified chemotherapy for AML in Down syndrome. Regimen-level evidence. |
| NCT06199557 | Phase 1/2 | Recruiting | 48 | Safety and early efficacy of 6-mercaptopurine plus valproic acid, or hydroxyurea plus valproic acid, in AML or high-risk MDS patients unfit for standard therapy. |
| NCT05506332 | Phase 1 | Recruiting | 10 | Venetoclax plus 6-mercaptopurine in relapsed or refractory AML. Very small and early-stage. |
| NCT00492856 | Phase 3 | Completed | 105 | SWOG S0521: maintenance versus observation in low- and intermediate-risk APL. Maintenance commonly includes mercaptopurine. |
| NCT00003934 | Phase 3 | Completed | 420 | Tretinoin-based maintenance, intermittent tretinoin versus tretinoin plus mercaptopurine and methotrexate, in untreated APL. |
| NCT00002701 | Phase 3 | Unknown | 750 | ATRA plus idarubicin and intensive consolidation, then randomized maintenance in APL. |
| NCT02688140 | Phase 3 | Completed | 133 | Arsenic trioxide plus ATRA and idarubicin versus the AIDA regimen in high-risk APL. Mercaptopurine is at most a maintenance component. |
| NCT00482833 | Phase 3 | Completed | 276 | Arsenic trioxide plus ATRA versus the AIDA regimen in non-high-risk APL. |
| NCT00866918 | Phase 3 | Completed | 106 | Risk-adapted treatment of childhood APL with arsenic trioxide during consolidation. |
| NCT00136084 | Phase 3 | Completed | 238 | Two multi-agent regimens with different cytarabine doses in newly diagnosed AML or myelodysplasia. Mercaptopurine’s role is not evident. |
Literature Evidence
| PMID | Year | Type | Journal | Key Findings |
|---|---|---|---|---|
| 26425037 | 2015 | Cohort | J Korean Med Sci | Two years of oral maintenance with daily 6-mercaptopurine and weekly methotrexate in AML patients ineligible for transplantation. |
| 27275453 | 2016 | Prospective pilot | South Asian J Cancer | Metronomic oral 6-mercaptopurine as palliative therapy in elderly AML. |
| 38828002 | 2024 | Cohort | Ther Adv Hematol | Multicentre report from China on intensive chemotherapy with dual induction and lymphoid-style consolidation for childhood AML. |
| 32459546 | 2020 | Retrospective | Pediatr Hematol Oncol | Outcomes of juvenile myelomonocytic leukemia after sequential cytarabine and 6-mercaptopurine. |
| 3513537 | 1986 | Clinical study | Am J Clin Oncol | Hydroxyurea alone versus hydroxyurea plus 6-mercaptopurine in chronic granulocytic leukemia. |
| 12057059 | 2000 | Review | Curr Treat Options Oncol | Overview of APL treatment, including ATRA and consolidation chemotherapy. |
| 33183436 | 2021 | Review | J Nanosci Nanotechnol | 6-MP nano-delivery systems intended to overcome poor solubility and toxicity in leukemia treatment. |
| 34442422 | 2021 | Review | J Pers Med | NUDT15 and TPMT polymorphisms predict thiopurine toxicity such as bone marrow suppression. |
| 2676034 | 1989 | Review | Blood Rev | Purine metabolism as a target for leukemia chemotherapy, including 6-mercaptopurine. |
Canada Market Information
Health Canada records show two valid single-ingredient licences for mercaptopurine. The local data do not record the approved indication text or dosage form for these products.
| DIN | Product Name | Dosage Form | Approved Indication |
|---|---|---|---|
| 02415275 | MERCAPTOPURINE TABLETS USP | Not specified | Not specified |
| 00004723 | PURINETHOL | Not specified | Not specified |
Cytotoxicity
| Item | Content |
|---|---|
| Cytotoxicity Classification | Conventional cytotoxic (purine antimetabolite) |
| Myelosuppression Risk | Medium to high. Bone marrow suppression is a recognized effect, and TPMT and NUDT15 variants increase the risk. |
| Emetogenicity Classification | Low |
| Monitoring Items | Complete blood count with differential, liver function, renal function. Consider TPMT/NUDT15 genotyping. |
| Handling Protection | Follow cytotoxic drug handling regulations. Please refer to the package insert for details. |
Safety Considerations
- Drug Interactions: The interaction database lists 100 interacting drugs. Those rated Moderate include mesalazine, balsalazide, olsalazine, sulfasalazine and naltrexone. Levofloxacin is rated Minor. Several others, such as prednisone, omeprazole and metformin, have an unknown severity level.
- Please refer to the package insert for warnings and contraindications.
Conclusion and Next Steps
Decision: Hold
Rationale: Mercaptopurine has a plausible mechanism and a history of use in leukemia regimens. The Phase 3 trials in the compiled data are regimen-level, however, and mercaptopurine itself is supported only by cohort and pilot data in AML. Moving beyond a research question needs clearer evidence of its own contribution.
To proceed, the following is needed:
- Trials or analyses that isolate mercaptopurine’s contribution within AML and APL maintenance regimens
- Mechanism-of-action data for myeloid leukemia
- The Health Canada product monograph warnings and contraindications, for safety screening
- A myelosuppression monitoring plan, including TPMT/NUDT15 testing
Disclaimer
This content is for research purposes only and does not constitute medical advice. Clinical validation is required before any clinical application.