Targeting Excessive EZH1 and EZH2 Activities for Abnormal Histone Methylation and Transcription Network in Malignant Lymphomas

Although global H3K27me3 reprogramming is a hallmark of cancer, no effective therapeutic strategy for H3K27me3-high malignancies harboring EZH2WT/WT has yet been established. We explore epigenome and transcriptome in EZH2WT/WT and EZH2WT/Mu aggressive lymphomas and show that mutual interference and compensatory function of co-expressed EZH1 and EZH2 rearrange their own genome-wide distribution, thereby establishing restricted chromatin and gene expression signatures. Direct comparison of leading compounds introduces potency and a mechanism of action of the EZH1/2 dual inhibitor (valemetostat). The synthetic lethality is observed in all lymphoma models and primary adult T cell leukemia-lymphoma (ATL) cells. Opposing actions of EZH1/2-polycomb and SWI/SNF complexes are required for facultative heterochromatin formation. Inactivation of chromatin-associated genes (ARID1A, SMARCA4/BRG1, SMARCB1/SNF5, KDM6A/UTX, BAP1, KMT2D/MLL2) and oncovirus infection (HTLV-1, EBV) trigger EZH1/2 perturbation and H3K27me3 deposition. Our study provides the mechanism-based rationale for chemical dual targeting of EZH1/2 in cancer epigenome. [Display omitted] •Lymphoma transcriptome is under control of global H3K27me3 accumulation•EZH1 and EZH2 are druggable targets in EZH2WT/WT and EZH2WT/Mu malignancies•Inactivation of chromatin-associated genes triggers EZH1/2 perturbation•Targeting epigenome for pre-cancerous states is achieved by EZH1/2 inhibition A mechanism-based, effective strategy for controlling oncogenic H3K27me3 remains an open question. Yamagishi et al. provide the scientific rationale for dual targeting of EZH1+EZH2 in malignancies overexpressing EZH2, such as ATL, PTCL, and DLBCL, or harboring mutations in histone-modifying genes, as well as in pre-cancerous cells epigenomically perturbed by oncovirus infection.