Epacadostat, a highly selective oral inhibitor of the indoleamine 2,3-dioxygenase 1 (IDO1) enzyme, was well tolerated when combined with pembrolizumab and demonstrated encouraging antitumor activity in multiple types of advanced solid tumors, according to the results of a phase l/ll trial.
Tumors may evade immunosurveillance through upregulation of the IDO1 enzyme, and thus there is a great interest in developing combination therapies that can target various immune evasion pathways to improve therapeutic response and outcomes. In this study, the authors evaluated the investigational agent epacadostat combined with pembrolizumab in 62 patients with advanced solid tumors.
In the dose escalation phase, patents received increasing doses of oral epacadostat (25, 50, 100, or 300 mg) twice per day plus intravenous pembrolizumab 2 mg/kg or 200 mg every 3 weeks. During the safety expansion, epacadostat at 50, 100, or 300 mg was given twice per day, plus pembrolizumab 200 mg every 3 weeks. The maximum tolerated dose of epacadostat in combination with pembrolizumab was not reached.
Objective responses (per Response Evaluation Criteria in Solid Tumors [RECIST] version 1.1) occurred in 12 (55%) of 22 patients with melanoma and in patients with non–small-cell lung cancer, renal cell carcinoma, endometrial adenocarcinoma, urothelial carcinoma, and squamous cell carcinoma of the head and neck, reported Tara C. Mitchell, MD, of the Abramson Cancer Center, University of Pennsylvania, Philadelphia, and her colleagues. The report is in the Journal of Clinical Oncology.
The authors observed that there was antitumor activity at all epacadostat doses and in several tumor types. A complete response was achieved by 8 patients (treatment naive melanoma [5 patients] and previously treated for advanced/ metastatic melanoma, endometrial adenocarcinoma [EA], or urothelial carcinoma [UC] [1 patient each]), while 17 patients achieved a partial response (treatment-naive melanoma [6 patients], non–small cell lung cancer [NSCLC] [5 patients], renal cell carcinoma [RCC] and UC [2 patients each], and EA and squamous cell carcinoma of the head and neck [1 patient each]).
Most patients (n = 52, 84%) experienced treatment-related adverse events (TRAEs), the most frequently observed being fatigue (36%), rash (36%), arthralgia (24%), pruritus (23%), and nausea (21%). Grade 3/4 TRAEs occurred in 24% of patients, and 7 patients (11%) discontinued their treatment because of TRAEs. There were no deaths associated with TRAEs.
“The safety profile observed with epacadostat plus pembrolizumab compares favorably with studies of other combination immunotherapies,” wrote Dr. Mitchell and her colleagues. “Although not powered to evaluate efficacy, the phase I portion of this study showed that epacadostat plus pembrolizumab had encouraging and durable antitumor activity,” they said.
SOURCE: Mitchell TC et al. J Clin Oncol. 2018 Sep 28. doi: 10.1200/JCO.2018.78.9602.