LAUSR

Chromatin remodeling is a crucial process for transcriptional regulation, of which dysregulation is often observed in various human cancers. The enhancer of zeste homology 2 (EZH2) and its homolog EZH1 are catalytic subunits of polycomb repressive complex 2 (PRC2), which trimethylate histone H3 at lysine 27 (H3K27me3) to repress transcription of its target genes. Although methlytransferase activity of PRC2 is mainly contributed by EZH2, EZH1 also conducts a compensatory role to maintain tri-methylation of H3K27. EZH1 also directly binds to chromatin and modulates its condensation. Recent studies have suggested that EZH1 as well as EZH2 played a critical role in T-cell lymphoma such as ATL/L and PTCL, which had high innate EZH1 and increased EZH2 expression upon acquisition of their malignancy. Consequently, dual inhibition of EZH1/2 might induce higher expression of downstream tumor suppressor genes than blocking EZH2 alone, expecting greater activity as an anti-cancer therapy. Herein, we presented a novel and potent EZH1/2 dual inhibitor, HM97662, which simultaneously inhibited the methyltransferase activity of both EZH1 and EZH2 with 2.1 and 16 nM of IC50, respectively. Surface plasmon resonance (SPR) assay verified that HM97662 had great binding affinity on EZH1-EED-SUZ12 complex as well as EZH2-EED-SUZ12 complex than competitors. HM97662 also showed broad and strong antiproliferative activity against various T-cell lymphoma cell lines. Representatively in HH cells, HM97662 not only suppressed global tri-methylation of H3K27, but also dose-dependently increased protein expression levels that modulate cell cycle or cancer cell apoptosis. HM97662 exhibited increment of CDKN1A (p21) proteins involved in cell cycle arrest and induced protein levels of cleaved caspase-3 as well as PARP. Additionally, resulting induction of apoptosis by HM97662 in HH cells was confirmed by TUNEL staining. Mechanistically, HM97662 increased mRNA expression of several target genes inducing cell cycle arrest and apoptosis in gene panel assay performed in HH cells. Two cell cycle repressor, CDKN2A (p16) and CDKN1C (p57), and a pro-apoptotic marker, BTG-2, were dose-dependently increased by HM97662. We further conducted chromatin accessibility assay and identified that the chromatin structures of them were loosened and highly transcribed after the treatment of HM97662. Based our in vitro pharmacology data, we evaluated an antitumor activity of HM97662 in EZH1/2 co-expressed HuT-102 T-cell lymphoma cell mouse xenograft model, and daily oral dosing of HM97662 showed potent tumor growth inhibition. In conclusion, the present studies demonstrated that HM97662 has promising prospective for the treatment of patients with T-cell lymphoma. Given that the necessity of new treatment options on T-cell lymphoma, it is urgent to assess the effectiveness of HM97662 in further clinical trials. Citation Format: Jooyun Byun, Seung Hyun Jung, Yu-Yon Kim, Miyoung Lee, Gunwoo Lee, Heesun Moon, Eun Young Lee, Junghwa Park, Seon Yeong Han, Young Gil Ahn, Young Hoon Kim, Kwee Hyun Suh. A novel and potent EZH1/2 dual inhibitor, HM97662 demonstrates antitumor activity in T-cell lymphoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 6267.