Results of a first-in-human, dose-escalation phase 1 study of the ERK1/2 inhibitor ATG-017 in patients with advanced solid tumors.

e15114 Background: This open-label, first-in-human, phase 1 study evaluates the safety, pharmacokinetics, and maximum tolerated dose (MTD) of ATG-017, an oral, potent, and highly selective inhibitor of ERK1/2, in patients with refractory advanced solid tumors. Methods: Twenty-one patients with solid tumors harboring activating alterations in the RAS-MAPK pathway were enrolled in the 3+3 design dose-escalation phase for continuous dosing: 5 mg QD (n=1), 5 mg BID (3), 10 mg BID (3), 20 mg BID (7), 30 mg BID (4), and 40 mg BID (3). Results: Safety: All patients reported at least 1 treatment-emergent adverse event (TEAE). Fourteen patients (66.7%) experienced serious adverse events. At 40mg BID, 2 of 3 patients experienced a dose-limiting toxicity (DLT) (grade 3 diarrhea and grade 3 retinopathy). At 30mg BID, 2 of 4 patients experienced a DLT (grade 3 acneiform dermatitis and grade 2 blurred vision). All DLTs resolved with drug interruption. At 20mg BID, a potentially biologically active dose, 7 patients were treated with no DLTs observed. At all dose levels, the most commonly observed TEAEs were consistent with previously reported toxicities with other ERK pathway inhibitors (gastrointestinal, skin, and ocular adverse events). Pharmacokinetics: Between 5mg BID and 30mg BID, exposure increased proportionally. At doses 20mg BID or higher, the concentration in the whole dosing interval (≥ 328ng/mL, geometric mean) was higher than the target concentration (231 ng/mL) for effective ERK inhibition derived from preclinical PK/PD models. Efficacy: Of the 21 treated patients, one patient (4.8%) with mesonephric-like ovarian adenocarcinoma (KRAS G12V mutation) in the 30 mg BID cohort achieved a best response of partial response (sustained for six cycles of treatment), and 8 (38%) patients were assessed as having stable disease (sustained over an average of five cycles), based on RECIST v1.1. Conclusions: In patients with solid tumors, 20mg BID continuous dosing of ATG-017 was identified as the MTD and delivers exposure that is likely to be active in inhibiting ERK. This dose is currently being explored in a dose expansion phase. A combination regimen with nivolumab is also being investigated. Clinical trial information: NCT04305249 .