SNO summary, episode 2: AG-120 phase 1 trial for IDH1-mutant glioma

AG-120, a first-in-class mutant IDH1 inhibitor in patients with recurrent or progressive IDH1 mutant glioma: updated results from the phase 1 non-enhancing glioma population.

Summary by SW who attended the presentation and took photos of the slides.

Ingo Mellinghoff of Memorial Sloan Kettering Cancer Center presented results of a phase 1 trial of AG-120 (ivosidenib), a mutant IDH1 inhibitor, for IDH1-mutant cancers.  The presentation specifically focused on a subset of patients in the phase 1 trial: those with non-enhancing (no contrast enhancement on MRI images) IDH1-mutant gliomas.  This analysis included 11 patients in the dose escalation phase, and an additional 24 patients from the dose expansion phase, a total of 35 patients.  The primary study objective was to evaluate safety and tolerability of AG-120, and determine the maximum-tolerated dose and/or the recommended phase 2 dose.

28 out of 35 patients (80%) of patients in this analysis were treated with 500 mg of AG-120 daily.  The majority (24/35, or 69%) of patients in this non-enhancing glioma cohort were WHO grade 2 gliomas.  An additional 23% were WHO grade 3.  Only one grade IV glioma (3%) was included.

Most patients in this analysis had been previously treated with either radiation (57%) or chemotherapy (69%) and the median number of prior systemic therapies was 2.

AG-120 was well tolerated, and the maximum tolerated dose was not reached. The majority of adverse events were low grade, and only 20% of patients experienced a grade 3 or higher adverse event. 

Pharmacodynamic analysis of tumor tissue in two patients revealed that AG-120 treatment strongly suppressed 2-hydroxyglutarate levels in the tumors.  2-hydroxyglutarate is the oncometabolite produced by the mutant IDH1 enzyme.

By far the most common response to AG-120 treatment in this cohort was stable disease, which was achieved in 83% of patients. Only two patients (5.7%) achieved a minor response, including one grade 2 and one grade 3 glioma. Only four out of the 35 patients (11%) had progressive disease with neither stabilization or response.  

More important is the duration of stable disease without progression.  Median duration of AG-120 treatment for all 35 patients is 16 months. For the grade 2 gliomas, representing nearly 70% of the population of this study, median progression-free survival has not yet been reached, and looks to be at least 19 months at the time of the analysis (data cutoff May 12 2017).

When volumetric growth rates pre- and post AG-120 treatment were calculated by imaging studies for the 24 patients in the dose expansion group, the mean percentage change in tumor volume per six months was found to be 24% prior to treatment, and 11% after AG-120 treatment.  In the 1p/19q intact (that is, the astrocytoma) subgroup of 15 patients, before and after AG-120 growth rates per six months were 38% and 14%.  This confirms that the primary effect of AG-120 in this group of non-enhancing (mostly) lower grade gliomas is to significantly slow tumor progression, which was deemed to be a disease stabilization in the majority of cases.

A different drug by Agios Pharmaceuticals, called AG-881, is a dual inhibitor of mutant IDH1 and IDH2, is more brain penetrant than AG-120, and is also being studied in clinical trials for IDH mutant gliomas.