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Enhancer of zests homologous (EZH)1 and its close homolog EZH2 are component of polycomb repressive complex (PRC) 2 protein complex, and play redundant and crucial role for the maintenance of transcriptional repression by tri-methylating histone H3 lysine 27 (H3K27). Hyper tri-methylation of H3K27 has been associated with lymphoma and myeloma progression, suggesting that PRC2 is a therapeutic target for hematological malignancies. Selective EZH2 inhibitors induce compensatory activation of EZH1 which in turn re-activates PRC2 function. We hypothesized that dual inhibition of EZH1 and EZH2 is more effective than selective EZH2 inhibition as anti-tumor therapy. We have developed a novel EZH1 and EZH2 dual inhibitor DS-3201, which simultaneously inhibited the enzymatic activity of EZH1 and EZH2 in nano-molar concentration. DS-3201 showed anti-proliferative effect against various NHL cells, such as diffuse large B-cell lymphoma (DLBCL), mantle cell lymphoma, and peripheral T-cell lymphoma, with GI50 values less than 100 nM regardless of EZH2 gain-of-function mutations. DS-3201 also induced differentiation of undifferentiated NHL cells with increment of cell lineage specific markers and which induced cell death in vitro. DS-3201 also showed synergistic effect with the standard of care agents for NHL in vitro and in vivo. An open-label phase 1 clinical study was initiated to examine the safety and pharmacokinetics of multiple-dose monotherapy of DS-3201b which is the salt form of DS-3201 in patients with NHL (ClinicalTrials.gov Identifier: NCT02732275). Eighteen patients with relapsed or refractory NHL were enrolled. The patients received oral administration of DS-3201b once daily in a 28-day cycle at dose of 150, 200 and 300 mg. Preliminary efficacy results (D. Maruyama, et al. ASH 2017), showed that the overall response rate was 58.8% (10/17) with 1 complete response and 9 partial responses (PR). Thirteen NHL patients including five follicular lymphoma (FL) and one DLBCL were analyzed for gene mutation status by targeted gene sequencing. EZH2 mutation was detected only in one FL patient, who achieved PR. It was suggested that DS-3201b has clinical activity against NHL, regardless of the mutation status of EZH2. Disclosures Honma: Daiichi Sankyo: Employment. Nosaka:Daiichi Sankyo: Employment. Shiroishi:Daiichi Sankyo: Employment. Takata:Daiichi Sankyo: Employment. Hama:Daiichi Sankyo: Employment. Yamamoto:Daiichi Sankyo RD Novare: Employment. Adachi:Daiichi Sankyo: Employment. Maruyama:Mundipharma International: Honoraria, Research Funding; MSD: Honoraria, Research Funding; Chugai Pharma: Honoraria, Research Funding; Dai-ichi-Sankyo: Honoraria; Bristol-Myers Squibb: Honoraria; Biomedis International: Honoraria, Research Funding; Celgene: Honoraria, Research Funding; Kyowa Hakko Kirin: Honoraria, Research Funding; Fujifilm: Honoraria, Research Funding; Ono Pharmaceutical: Honoraria, Research Funding; Takeda: Honoraria, Research Funding; Janssen: Honoraria, Research Funding; Eisai: Honoraria, Research Funding; Dai-Nippon-Sumitomo: Honoraria; Asahi Kasei Pharma: Honoraria; AstraZeneca: Research Funding; Solasia Pharma: Research Funding; Pfizer: Research Funding; Nippon Boehringer Ingelheim: Research Funding; Novartis: Research Funding; Otsuka: Research Funding; Amgen Astellas BioPharma: Research Funding; Astellas Pharma: Research Funding; Abbvie: Research Funding; GlaxoSmithKline: Research Funding; Zenyaku Kogyo: Honoraria, Research Funding. Tobinai:Chugai Pharma: Honoraria, Research Funding; Kyowa Hakko Kirin: Honoraria, Research Funding; Ono Pharmaceutical: Honoraria, Research Funding; Janssen: Honoraria, Research Funding; GlaxoSmithKline: Research Funding; Eisai: Honoraria, Research Funding; Mundipharma: Honoraria, Research Funding; Takeda: Honoraria, Research Funding; SERVIER: Research Funding; Abbvie: Research Funding; Celgene: Consultancy, Honoraria, Research Funding; Zenyaku Kogyo: Consultancy, Honoraria; HUYA Bioscience International: Consultancy, Honoraria. Ishida:Kyowa Hakko Kirin Co.Ltd: Honoraria, Research Funding; Celgene K.K: Honoraria, Research Funding; Bayer AG: Research Funding; Mundiparma K: Honoraria. Kusumoto:Bristol-Myers Squibb: Honoraria, Research Funding; Chugai Pharmaceutical Co. Ltd: Honoraria, Research Funding; Kyowa Hakko Kirin: Honoraria, Research Funding. Tsukasaki:Daiich-Sankyo: Consultancy; Ono Pharma: Consultancy; HUYA: Consultancy, Research Funding; Chugai Pharma: Honoraria, Research Funding; Eisai: Research Funding; Celgene: Honoraria; Mundy Pharma: Honoraria; Kyowa-hakko/Kirin: Honoraria; Seattle Genetics: Research Funding. Fujioka:Daiichi Sankyo: Employment. Watanabe:Daiichi Sankyo: Employment. Kanno:Daiichi Sankyo: Employment. Kumazawa:Daiichi Sankyo RD Novare: Employment. Fujitani:Daiichi Sankyo: Employment. Araki:Daiichi Sankyo: Employment. Fujiwara:Daiichi Sankyo: Employment.

Enhancer of zeste homolog (EZH) 1 and its close homolog EZH2 are component of polycomb repressive complex 2 (PRC2), and play a partially redundant and crucial role for the maintenance of transcriptional repression by tri-methylating histone H3 lysine 27 (H3K27). Hyper tri-methylation of H3K27 have been associated with lymphoma and myeloma progression, suggesting PRC2 is a therapeutic target for hematological malignancies. We have developed a novel EZH1 and EZH2 dual inhibitor valemetostat (DS-3201b), which simultaneously inhibited the enzymatic activity of EZH1 and EZH2 in nano-molar concentration. Valemetostat demonstrated anti-proliferative activities against the Activated B-cell-like (ABC) and Germinal Center B-cell-like (GCB) subtypes of Diffuse Large B-cell Lymphoma (DLBCL) cells. Furthermore, valemetostat induced apoptosis in DLBCL cell lines, regardless of subtype. We revealed that the pleiotropic effects of valemetostat on the expression levels of B-cell receptor signaling molecules by western blotting analysis. In particular, valemetostat suppressed the expression level of BCL6 protein, a key oncogene in B cell lymphoma. Transcriptome analysis of 16 DLBCL cell lines using RNA sequencing suggested that tumor suppressor genes, DNA damage response related genes and cell cycle related genes were affected by valemetostat treatment. In particular, valemetostat down regulated c-myc signaling in valemetostat-sensitive cells. Valemetostat also demonstrated synergistic anti-tumor activity with standard of care therapy against a DLBCL cell line KARPAS-422 xenografted model. In conclusion, our results suggested that valemetostat has therapeutic activity in DLBCL cells by inhibiting B-cell receptor signaling and c-myc signaling pathway. A phase 1 clinical study of valemetostat mono-therapy is now ongoing in patients with non-Hodgkin lymphoma including DLBCL (Clinical trial information: NCT02732275). Disclosures Hama: Daiichi Sankyo Co., Ltd.: Employment. Banjo:Daiichi Sankyo Co., Ltd.: Employment. Honma:Daiichi Sankyo Co., Ltd.: Employment. Takata:Daiichi Sankyo Co., Ltd.: Employment. Nosaka:Daiichi Sankyo Co., Ltd.: Employment. Shiroishi:Daiichi Sankyo Co., Ltd.: Employment. Watanabe:Daiichi Sankyo Co., Ltd.: Employment. Yamamoto:Daiichi Sankyo RD Novare Co., Ltd.: Employment. Hirata:Daiichi Sankyo RD Novare Co., Ltd.: Employment. Nakano:Daiichi Sankyo RD Novare Co., Ltd.: Employment. Inaki:Daiichi Sankyo Co., Ltd.: Employment. Goto:Daiichi Sankyo RD Novare Co., Ltd.: Employment. Totoki:Daiichi Sankyo RD Novare Co., Ltd.: Employment. Kataoka:Daiichi Sankyo RD Novare Co., Ltd.: Employment. Lim:Daiichi Sankyo RD Novare Co., Ltd.: Employment. Wada:Daiichi Sankyo RD Novare Co., Ltd.: Employment. Kumazawa:Daiichi Sankyo RD Novare Co., Ltd.: Employment. Tsutsumi:Daiichi Sankyo Co., Ltd.: Employment.

Abstract. We have previously demonstrated an important role of influx of Cl − rather than Ca 2+in acute excitotoxicity in adult rat retina. As p53 has been implicated in delayed apoptotic cell death, here we examined the appearance of p53 immunoreactivity in a rat eyecup preparation. Kainate induced p53 expression in a subpopulation of ganglion cells and other cells in the ganglion cell layer. Application of a calpain inhibitor, but not reduction of extracellular Cl − , markedly inhibited kainate-induced p53 expression. The results suggest that, in contrast to acute excitotoxicity, delayed excitotoxicity in retinal neurons is mediated by Ca 2+-dependent processes, including calpain activation.