IDH1R132 Inhibitor IDH305

Drug Overview

IDH1R132 Inhibitor IDH305, referred to throughout this guide as IDH305, is an investigational oral Targeted Therapy developed by Novartis Institutes for BioMedical Research. It is designed to treat cancers driven by a specific mutation in the IDH1 gene — a mutation that hijacks normal cell metabolism and creates a toxic buildup that fuels tumor growth.

IDH305 is a potent and selective mutant IDH1 inhibitor that is nearly 200-fold more selective for mutant IDH1 R132H than wild-type IDH1. Its defining advantage over earlier IDH1 inhibitors is its proven ability to cross the blood-brain barrier — making it uniquely valuable for brain tumors such as glioma, where most systemic drugs cannot reach.

• Name: IDH1R132 Inhibitor IDH305 (IDH305)
• US Brand Name: None assigned — currently investigational
• Drug Class: Mutant-Selective Allosteric IDH1 Inhibitor / Targeted Therapy
• Route of Administration: Oral (tablet, taken by mouth)
• FDA Approval Status: Not FDA-approved. IDH305 has completed a first-in-human phase I clinical trial (NCT02381886) in patients with IDH1R132-mutant AML and MDS. It is an active investigational compound being studied across glioma, AML, MDS, chondrosarcoma, and cholangiocarcinoma.

What Is It and How Does It Work? (Mechanism of Action)

To understand IDH305, it helps to know what goes wrong in IDH1-mutant cancers. Normally, the IDH1 enzyme converts a molecule called isocitrate into alpha-ketoglutarate (α-KG) — an essential building block for healthy cell function. R132 IDH1 mutations lead to cellular accumulation of 2-hydroxyglutarate (2-HG), an oncometabolite that promotes tumorigenesis.

This toxic molecule — 2-HG — acts like a molecular wrench thrown into the cell’s machinery. It blocks the normal chemical reactions that control how genes are read and how cells mature. The result: cells get “stuck” in an immature state and accumulate as cancer. IDH305 dismantles this process at the molecular level through three precise steps:

Allosteric Binding: IDH305 was identified through exploration of 3-pyrimidin-4-yl-oxazolidin-2-ones as allosteric, mutant-specific inhibitors of IDH1, targeting an induced allosteric pocket of IDH1R132H. Rather than blocking the enzyme’s active site directly, IDH305 binds to a neighboring pocket and changes the enzyme’s three-dimensional shape — making it unable to produce 2-HG.

2-HG Suppression: IDH305 suppresses mutant IDH1-dependent 2-HG production and cell proliferation with an IC50 of 24 nM. At this extremely low concentration, the drug effectively eliminates the oncometabolite driving tumor growth.

Restoring Normal Cell Differentiation: With 2-HG eliminated, the epigenetic “freeze” on cancer cells is lifted. Blocked genes are reactivated, and cancer cells are pushed back toward normal maturation — ultimately undergoing programmed cell death or losing their ability to proliferate.

Brain Penetration: IDH305 is an orally available, brain-penetrant, mutant-selective allosteric high-affinity IDH1 inhibitor that acts on both canonical (R132H) and non-canonical (R132C) mutated enzymes, with much lower affinity for wild-type IDH1 or mutant IDH2 enzymes.

FDA Approved Clinical Indications

Oncological Uses (Under Clinical Investigation — Not FDA-Approved):

• IDH1 mutations are found in glioma (~80%), chondrosarcoma (~50%), cholangiocarcinoma (~20% intrahepatic), acute myeloid leukemia (AML; ~6–9%), and myelodysplastic syndrome (MDS; ~3%). IDH305 is being investigated across all of these tumor types.

Non-Oncological Uses:

• There are currently no non-oncological indications under investigation for IDH305.

Dosage and Administration Protocols

IDH305 is orally administered twice a day (BID) in continuous 21-day cycles. The starting dose of 75 mg BID was determined from 4-week toxicology studies. Disease-specific recommended doses for expansion were established from the phase I dose-escalation program.

Clinical Efficacy and Research Results

IDH305 has generated meaningful clinical evidence across multiple tumor types in its phase I program.

As of the phase I data cut-off in March 2016, 81 patients had been enrolled: glioma (n=32), AML (n=21), MDS (n=3), other/non-CNS solid tumors (n=24), and unknown (n=1). All dose-limiting toxicities — including Grade 3 elevated bilirubin and Grade 3 rash — resolved and were considered reversible.

In the dedicated AML/MDS cohort published in the Journal of Cancer Research and Clinical Oncology in 2023, IDH305 was given at doses of 75–750 mg twice daily in 41 patients with IDH1R132-mutant AML/MDS, and exhibited rapid absorption with a mean half-life of approximately 4–10 hours across doses. Complete remissions were observed in AML patients, and 2-HG suppression was confirmed as a pharmacodynamic biomarker of target engagement.

In glioma patients, a landmark Nature Communications study using advanced brain imaging confirmed IDH305’s clinical mechanism directly in tumor tissue. In preclinical models, a single dose of 100 mg/kg was sufficient to reduce tumor 2-HG levels by 95% in mice bearing IDH1-mutant flank tumors, and IDH305 demonstrated in vitro antiproliferative effects. In treated glioma patients, MRS imaging confirmed measurable 2-HG reduction in tumor tissue — the first direct in-patient evidence of IDH1 inhibitor target engagement in the brain.

Safety Profile and Side Effects

Black Box Warning: There is no FDA Black Box Warning for IDH305, as it is not FDA-approved. The phase I program has established a generally favorable and manageable safety profile across tumor types.

Common Side Effects (>10%):

• Elevated Bilirubin — the most clinically significant laboratory finding; Grade 3 elevations observed at higher doses; monitor liver function throughout treatment
• Nausea and Fatigue — mild to moderate; consistent with other oral targeted therapies in this class
• Rash — observed at higher dose levels; typically Grade 1–2 and reversible upon dose modification

Serious Adverse Events:

• Grade 3 Hyperbilirubinemia: DLTs of Grade 3 elevated bilirubin were observed in 2 patients with solid tumors at 550 mg BID and 1 patient with glioma at 900 mg BID; all resolved and were considered reversible.
• Differentiation Syndrome: A known class effect of IDH inhibitors; presents with fever, pulmonary infiltrates, and fluid retention; requires immediate corticosteroid treatment
• Embryo-Fetal Toxicity: Theoretical risk based on mechanism; pregnancy is contraindicated during treatment

Management Strategies:

• For hyperbilirubinemia: monitor LFTs at baseline and before each cycle; hold dose for Grade 3 elevations; resume at reduced dose upon resolution
• For differentiation syndrome: initiate systemic corticosteroids immediately; hold IDH305 for severe presentations
• For rash: topical corticosteroids for Grade 1–2; dose reduction or interruption for Grade 3

Research Areas

IDH305’s development has had a lasting scientific impact even beyond its own clinical program. IDH305 showed relatively high in vivo clearance, and optimization work at Novartis focused on improving clearance rate and metabolic stability — resulting in next-generation compounds with brain penetration and excellent oral bioavailability in preclinical models. These optimization efforts directly informed the structural design of newer IDH1 inhibitors such as ivosidenib and olutasidenib, both of which have since achieved FDA approval. Current research published in 2024–2025 is exploring dual inhibitor strategies — combining mutant IDH1 and NAMPT inhibition in glioma — directly building on the mechanistic groundwork laid by IDH305’s clinical program.

Patient Management and Practical Recommendations

Pre-Treatment Tests:

• IDH1 R132 mutation testing of tumor tissue — mandatory; IDH305 is only active in IDH1-mutant tumors
• Liver function tests (LFTs) including bilirubin — baseline assessment required
• Complete blood count (CBC) with differential
• MRI or CT imaging for baseline tumor burden assessment
• Pregnancy test for all women of childbearing age

Precautions During Treatment:

• Monitor LFTs before each 21-day cycle; bilirubin is the key safety marker for this drug
• Watch for early signs of differentiation syndrome — fever, shortness of breath, or unexplained weight gain must be reported immediately
• IDH305 is available only through participation in an approved clinical trial

Do’s and Don’ts:

• DO take IDH305 at the same times each day to maintain consistent drug levels
• DO report any yellowing of the skin or eyes (jaundice) to your care team immediately
• DO attend all scheduled blood test and imaging appointments without exception
• DON’T participate in this trial if your tumor has not been confirmed to carry an IDH1 R132 mutation
• DON’T become pregnant during treatment — fetal harm risk applies to all IDH pathway-targeting agents
• DON’T take IDH305 outside of an approved and supervised clinical trial program

Legal Disclaimer

The information in this guide is for educational purposes only and does not constitute medical advice, diagnosis, or a treatment recommendation. IDH305 is an investigational drug that is not approved by the US Food and Drug Administration (FDA) or any major regulatory authority for routine clinical use. It is currently available only through participation in approved clinical trials. All treatment decisions must be made in consultation with a qualified oncologist or licensed healthcare professional with full knowledge of the patient’s complete medical history. This content does not replace official investigational protocol documentation or professional medical judgment.