IDH1 mutant inhibitor targets gliomas, chondrosarcomas




BOSTON – An investigational agent targeted against tumors carrying mutant forms of the metabolic protein IDH1 has shown clinical activity against advanced solid tumors, including gliomas and chondrosarcomas, investigators reported.

In a phase I trial in 62 patients with advanced IDH1 mutation-positive solid tumors that had recurred or progressed on a median three prior lines of therapy, 7 of 11 patients with chondrosarcomas treated with AG-120 had stable disease, with five of the responses maintained beyond 6 months, and 10 of 20 patients with glioma had stable disease, with 4 having responses longer than 6 months, reported Dr. Howard A. Burris III, chief medical officer and executive director, drug development program, at the Sarah Cannon Research Institute, Nashville, Tenn.

Dr. Howard A. Burris III

Dr. Howard A. Burris III

“These tumors don’t respond to any of our systemic therapies, so it’s pretty remarkable that you get patients who don’t have treatment options that do so well for so long. We’ve just not seen that in the past,” commented Dr. Lee J. Helman, a sarcoma specialist at the National Cancer Institute in Bethesda, Md., who was not involved in the study.

A related compound, AG-221, which inhibits IDH2, has previously been shown to produce durable objective responses in 30%-50% of patients with acute myeloid leukemia. Here at the AACR–NCI–EORTC International Conference on Molecular Targets and Cancer Therapeutics, Dr. Burris presented the first clinical results with the IHD1-inhibiting compound in solid tumors.

IDH1 is normally involved in regulation of the Krebs cycle, the central metabolic pathway. IDH1 mutations produce the metabolite 2-hydroxyglutarate (2-HG), which causes genetic and epigenetic dysregulation, leading to oncogenesis via unchecked cell proliferation. AG-120 blocks the accumulation of 2-HG, thereby allowing cells to differentiate and undergo apoptosis as normal, thereby restoring homeostasis.

Dr. Lee J. Helman

Dr. Lee J. Helman

IDH1 mutations are found in an estimated 68%-74% of gliomas, 11%-24% of intrahepatic cholangiocarcinomas (IHCC), and in 40%-52% of chondrosarcomas, Dr. Burris said.

Early efficacy promising

He reported early safety and clinical data from a single-arm, dose escalation study of single-agent AG-210 dosed orally once or twice daily in 28-day cycles in one of eight dose levels. The dose escalation phase has been completed and a 500-mg q.i.d. dose has been selected.

There were no dose-limiting toxicities, and the maximum tolerated dose was not reached. Serious adverse events, occurring in one patient each (18 of 62 patients) were acute kidney injury, acute respiratory failure, anemia, ataxia, brain herniation, confusional state, cystitis, urinary tract infection, headache, hyponatremia, joint effusion, esophageal varices hemorrhage, partial seizures, seizure, bacteremia, superior vena cava syndrome, vertebral fracture, and urosepsis. There were no deaths judged to be treatment related.

Data on 55 patients were available for the efficacy analysis. Among 11 patients with chondrosarcoma, 7 had stable disease, 2 had progressive disease, and 2 had unknown status. Among 20 patients with IHCC, there was 1 partial response, 11 cases of stable disease, 6 of progressive disease, and 2 unknown. Among patients with glioma, 10 had stable disease, and 10 had progressive disease.

Of four remaining patients (with adenocarcinoma and colitis-associated neuroendocrine, small intestine, and ovarian cancers), one had stable disease, and three had progression.

The patient with IHCC who had a partial response was a 65-year-old woman who had previously been treated with multiple lines of chemotherapy, including combinations of cisplatin and gemcitabine, gemcitabine and oxaliplatin, and cisplatin and docetaxel. Following treatment with AG-120, she had a 98.7% reduction in 2-HG level, and an 81% reduction in Ki-67 staining, indicating marked tumor reduction.

“This patient in fact was on the trial for more than 9 months. By protocol criteria, she had to come off study for development of a solitary new, small lesion that was felt to be a new metastatic spot, but had no change – no further regrowth of the tumor that had shrunk,” Dr. Burris said in a briefing following his presentation of the data in a plenary session.

In a 38-year-old man with grade II glioma, investigators saw volumetric changes consistent with 2-HG reduction on magnetic resonance spectroscopy, he added.

For the expansion phase, investigators are currently enrolling four cohorts each of 25 patients with low-grade glioma (with at least 6 months of prior scans), IHCC following progression on first-line therapy, high-grade metastatic chondrosarcoma, and patients with other solid tumors with IDH1 mutations. They are also planning a randomized phase II study in patients with IHCC beginning in 2016.

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