Abstract LB-102: Extranodal natural killer/T cell lymphoma (ENKTL) exhibits an unprecedented degree of global DNA hypermethylation, providing a potent targeted therapy in vivo

Extranodal natural killer/T cell lymphoma (ENKTL) is a rare aggressive form of non-Hodgkin lymphoma that is uniformly EBV-positive. Despite the implementation of combinatorial chemotherapies, almost all patients with advanced ENKTL die of their disease. The rational identification of potential novel therapeutic targets in ENKTL would be greatly aided by a more complete understanding of its molecular pathogenesis. We have identified atypical NK cell populations in untreated ENKTL patient samples. These atypical NK cells consistently showed an undifferentiated immunophenotype reminiscent of immature NK developmental stages. As cellular differentiation depends on epigenetic modifications and EBV is known to disrupt epigenetic patterns, we performed genome-wide DNA methylation profiling of ENKTL tumors (n=31 patients) using Illumina MethylationEPIC BeadChip arrays. We uncovered an unprecedented degree of epigenetic dysregulation in ENKTL, primarily involving extensive DNA hypermethylation. In the majority of ENKTL cases, greater than 50% of all CpG islands were hypermethylated, thus representing the most hypermethylated tumor type identified relative to available pan-cancer data (TCGA). In order to explore strategies to target the aberrant DNA hypermethylation in ENKTL, we exposed ENKTL cell lines YT and NK-92 to the demethylating agent 5-azacytidine (5-aza). We observed an unusually high sensitivity of ENKTL cell lines to 5-aza when compared to various other hematologic cancer cell lines, including several EBV-positive lymphoma lines. Hypomethylating agents altered DNA methylation at gene promoters and led to re-expression of epigenetically-silenced tumor suppressor genes in ENKTL cells. We also found synergistic inhibition of in vitro cell growth when combining 5-aza with the standard-of-care chemotherapeutic agents oxaliplatin and gemcitabine. Finally, through engraftment of primary ENKTL patient tumor cells, we have established a patient-derived xenograft (PDX) ENKTL mouse model. In this model, treatment with 5-aza resulted in profound cytoreduction, phenotypic and molecular differentiation of ENKTL cells, as well as significantly prolonged survival. In summary, we report massive, widespread DNA hypermethylation in ENKTL that exceeds the degree of hypermethylation found in other profiled cancers, including other EBV-positive malignancies. We hypothesize that epigenetic dysregulation plays a central role in ENKTL and rational targeting with epigenetic therapies may provide therapeutic benefit to patients. Our ongoing studies aim to identify the optimal epigenetic therapy and potential synergy with chemotherapy in preclinical models, thus providing the basis for novel treatments for ENKTL. Citation Format: Christoph Weigel, Bethany L. Mundy-Bosse, Yue-Zhong Wu, Kathleen McConnell, Anjali Mishra, Michael A. Caligiuri, Robert A. Baiocchi, Yaso Natkunam, Pierluigi Porcu, Jonathan Brammer, Aharon G. Freud, Christopher C. Oakes. Extranodal natural killer/T cell lymphoma (ENKTL) exhibits an unprecedented degree of global DNA hypermethylation, providing a potent targeted therapy in vivo [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr LB-102.