IDH Mutations (Isocitrate Dehydrogenase 1 & 2)
Normal Function
- IDH1 (cytoplasmic/peroxisomal) and IDH2 (mitochondrial) are enzymes in the citric acid (TCA) cycle.
- They normally convert isocitrate → α-ketoglutarate (α-KG).
- Mutations in IDH1 (R132) or IDH2 (R140, R172) confer a neomorphic enzymatic activity.
- Instead of producing α-KG, mutant IDH produces 2-hydroxyglutarate (2-HG), an oncometabolite.
- 2-HG interferes with DNA/histone methylation → epigenetic dysregulation, impaired differentiation, and oncogenesis.
Clinical Relevance
- Acute Myeloid Leukemia (AML): ~15–20% harbor IDH1/2 mutations.
- Gliomas (astrocytomas, oligodendrogliomas): IDH mutations common, associated with better prognosis compared to IDH-wildtype glioblastomas.
- Also reported in cholangiocarcinoma and other solid tumors.
Targeted Therapies (IDH Inhibitors)
- Ivosidenib (Tibsovo) → oral IDH1 inhibitor
- Indications: IDH1-mutant AML, IDH1-mutant cholangiocarcinoma.
- Enasidenib (Idhifa) → oral IDH2 inhibitor
- Indication: IDH2-mutant relapsed/refractory AML.
- Olutasidenib (Rezlidhia) → another IDH1 inhibitor (for R/R AML).
- These drugs restore normal cellular differentiation by reducing 2-HG levels.
Key Toxicity
- Differentiation syndrome (similar to ATRA/arsenic in APL):
- Fever, pulmonary infiltrates, hypoxia, edema, hypotension.
- Can be life-threatening; treat with high-dose corticosteroids (e.g., dexamethasone) and supportive care.
Pharmacist Pearls
- Always check for IDH1/2 mutation testing in AML and cholangiocarcinoma before therapy.
- Oral targeted agents (ivosidenib, enasidenib, olutasidenib) are major advances in precision oncology.
- Monitor closely for differentiation syndrome, QT prolongation, leukocytosis, and drug–drug interactions (CYP3A4).
- In gliomas, IDH status is part of the WHO 2021 CNS tumor classification and affects prognosis and management.
In short:
- IDH mutation = metabolic driver → produces 2-HG → epigenetic dysregulation.
- Important biomarker in AML, gliomas, cholangiocarcinoma.
- Targeted therapies (IDH inhibitors) available, with differentiation syndrome as key toxicity.