ATLANTA – Combination entinostat and pembrolizumab showed promising activity in a phase 2 study of non–small cell lung cancer patients who progressed on or after anti-programmed death-ligand 1 (PD-L1) therapy, and new analyses have identified gene signatures associated with treatment response.
Gene set analysis in tumors from 43 of the patients – 4 responders and 39 nonresponders – who participated in the open-label ENCORE-601 study revealed that Myc gene signaling was enriched in responders vs. nonresponders,, said at the annual meeting of the American Association for Cancer Research.
High Myc gene activity is known from previous studies to be associated with response to immune checkpoint inhibition, and this has been attributed to high PD-L1 expression, decrease in interferon signatures, and exclusion of lymphocytes, he noted.
“And we know from other publications that entinostat is known to decrease Myc activity,” he said. “Therefore, our putative hypothesis at this time – albeit on a small set of patients – is that for patients with baseline high Myc activity, when they have developed resistance to PD-1 or PD-L1 inhibition ... giving them entinostat drives down the Myc activity and results in a change in the tumor microenvironment to one where immune checkpoint inhibition could be rendered effective.”
Patients from ENCORE-601 also were evaluated by baseline circulating classical monocyte levels as prior findings showed improved overall survival and progression-free survival (PFS) in melanoma patients with higher vs. lower counts, Dr. Ramalingam explained.
The overall response rate (ORR) in those with baseline levels above the median (MHi, 11 patients) was 21.1% vs. 6.5% in those with levels below the median (MLo, 32 patients); median PFS was 4.7 vs. 2.7 months in the MHi and MLo groups, respectively, said Dr. Ramalingam of Winship Cancer Institute, Emory University, Atlanta.
ENCORE-601 included 76 subjects who received entinostat at a dose of 5 mg per week plus intravenous pembrolizumab at 200 mg every 3 weeks. The confirmed ORR with treatment in 72 efficacy-evaluable patients was 10%, with an additional 50% of patients having stable disease. The median duration of response was 8 months, and median PFS was 2.8 months.
Top-line results from the study, which was undertaken based in part on preclinical data showing synergy between the oral class 1-selective histone deacetylase inhibitor entinostat and anti-PD-1 inhibition, were presented at the 2018 World Conference on Lung Cancer, and the current findings represent secondary outcome measures involving analyses in pretreatment tumor samples from patients with sufficient RNA yield for analysis.
The data may provide a mechanistic basis for the responses seen with entinostat and pembrolizumab in ENCORE-601, Dr. Ramalingam said.
“Now we acknowledge that this is a relatively small dataset, and therefore further studies are warranted using these biomarkers to further understand whether they can be used as predictive biomarkers for treatment,” he said, noting that one such clinical trial is currently in the discussion phase.
The ENCORE-601 findings are important given that “with the movement of checkpoint inhibitors to the front-line setting, there is now an unmet need in the second-line [setting] where patients have already received a checkpoint inhibitor and have developed disease progression,” he noted, adding that “while chemotherapy remains central to this group of patients, development of novel agents is an unmet need.”
Dr. Ramalingam disclosed ties to AbbVie, Advaxis, Amgen, Astra Zeneca, Bristol-Myers Squibb, Genentech/Roche, Loxo, Merck, Nektar, Takeda, and Syndax.
SOURCE: Ramalingam S et al. AACR 2019, .