Safety lead-in of the MEK inhibitor trametinib in combination with GSK2141795, an AKT inhibitor, in patients with recurrent endometrial cancer: An NRG Oncology/GOG study

Abstract Objective We sought to determine safety and efficacy of the AKT inhibitor, GSK2141795, combined with the MEK inhibitor, trametinib, in endometrial cancer. Methods Patients with measurable recurrent endometrial cancer were eligible. One to two prior cytotoxic regimens were allowed; prior use of a MEK or PI3K pathway inhibitor was excluded. Initial trial design consisted of a KRAS mutation stratified randomized phase II with a safety lead-in evaluating the combination. For the safety lead in, the previously recommended phase 2 dose (RP2D; trametinib 1.5 mg, GSK2141795 50 mg) was chosen for Dose Level 1 (DL1). Results Of 26 enrolled patients, 14 were treated on DL1 and 12 were treated on DL-1 (trametinib 1.5 mg, GSK2141795 25 mg). Most common histologies were endometrioid (58%) and serous (27%). Four of 25 (16%) patients were KRAS mutant. Dose limiting toxicities (DLTs) were assessed during cycle 1. DL1 had 8 DLTs (hypertension (n = 2), mucositis (2), rash (2), dehydration, stroke/acute kidney injury). DL1 was deemed non-tolerable so DL-1 was explored. DL-1 had no DLTs. Sixty-five percent of patients had ≥ grade 3 toxicity. There were no responses in DL1 (0%, 90%CI 0–15%) and 1 response in DL-1 (8.3%, 90%CI 0.4–33.9%). Proportion PFS at 6 months for DL1 is 14%, and 25% for DL-1. Conclusion The combination of trametinib and GSK2141795 had high levels of toxicity in endometrial cancer at the previously RP2D but was tolerable at a reduced dose. Due to insufficient preliminary efficacy at a tolerable dose, the Phase II study was not initiated.