A study of using epigenetic modulators to enhance response to pembrolizumab (MK-3475) in microsatellite stable advanced colorectal cancer

Approximately 95% of advanced colorectal cancer patients (CRC) have mismatch repair MMR-proficient (MMRp) tumors, which do not respond to PD1 blockade alone. Preclinical studies have shown that combined histone deacetylases (HDAC) and/or DNA methyltransferases (DNMT) inhibition can induce susceptibility to immune checkpoint therapy and inhibit tumor growth. We conducted a pilot trial evaluating PD-1 immune checkpoint inhibitor therapy in combination with DNMT and HDAC inhibitors in MMRp CRC. The study was designed with a biological endpoint of change in immune cell infiltration, to determine the optimal epigenetic combination that optimizes the tumor microenvironment. This trial was designed to test that hypothesis. From January 2016 to November 2018, 27 patients were enrolled with median age of 57 (range 40-69) years. Median progression-free survival and overall survival were 2.79 months and 9.17, respectively. One patient in Arm C achieved a durable partial response by RECIST criteria, lasting for approximately 19 months. The most common treatment-related hematological adverse events in all arms were anemia (62%), lymphopenia (54%) and thrombocytopenia (35%), and non-hematological AEs were anorexia (65%), nausea (77%), and vomiting (73%). The combination of 5-azacitidine and romidepsin with pembrolizumab was safe and tolerable in patients with advanced MMRp CRC, but with a minimal activity. Further mechanistic investigations are needed to understand epigenetic-induced immunologic shift and to expand the potential applicability of checkpoint inhibitors in this setting.