IDH Mutations

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).

Pathologic Mutation

• 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.