An open-label, single-arm phase 2 trial of valemetostat for relapsed or refractory adult T-cell leukemia/lymphoma.

Adult T-cell leukemia/lymphoma (ATL) is an aggressive non-Hodgkin lymphoma with poor prognosis and few treatment options for patients with relapsed, recurrent, or refractory disease. We evaluated the efficacy and safety of valemetostat, a potent enhancer of zeste homolog 2 (EZH2) and EZH1 inhibitor, in treating relapsed or refractory (R/R) ATL. This multicenter phase 2 trial enrolled patients with R/R aggressive ATL (acute, lymphoma, unfavorable chronic type). Patients received valemetostat 200 mg/day orally until progressive disease or unacceptable toxicity. The primary end point was overall response rate (ORR) centrally assessed by an independent efficacy assessment committee (IEAC). Secondary end points included best response in disease compartments, duration of response (DOR), pharmacokinetics, and safety. Twenty-five patients (median age, 69.0 years) with a median of 3 prior lines of therapy were enrolled; 24 had prior mogamulizumab treatment. The primary end point was met with a centrally reviewed ORR of 48.0% (90% confidence interval [CI], 30.5-65.9), including 5 complete and 7 partial remissions. Patients pretreated with mogamulizumab had an ORR of 45.8% (4 complete and 7 partial remissions). IEAC-assessed median DOR was not reached (NR) (95% CI, 1.87 to NR; months). Treatment-emergent adverse events (TEAEs) were manageable. TEAEs that occurred in ≥20% of patients included thrombocytopenia, anemia, alopecia, dysgeusia, neutropenia, lymphopenia, leukopenia, decreased appetite, and pyrexia. Grade ≥3 TEAEs included thrombocytopenia, anemia, lymphopenia, leukopenia, and neutropenia. Valemetostat demonstrated promising efficacy and tolerability in heavily pretreated patients, warranting further investigation in treating R/R ATL. This trial was registered at www.clinicaltrials.gov as #NCT04102150.

CDKN1C-mediated growth inhibition by an EZH1/2 dual inhibitor overcomes resistance of mantle cell lymphoma to ibrutinib.

Mantle cell lymphoma (MCL) is a rare subtype of non-Hodgkin's lymphoma, which is characterized by overexpression of cyclin D1. Although novel drugs, such as ibrutinib, show promising clinical outcomes, relapsed MCL often acquires drug resistance. Therefore, alternative approaches for refractory and relapsed MCL are needed. Here, we examined whether a novel inhibitor of enhancer of zeste homologs 1 and 2 (EZH1/2), OR-S1 (a close analog of the clinical-stage compound valemetostat), had an antitumor effect on MCL cells. In an ibrutinib-resistant MCL patient-derived xenograft (PDX) mouse model, OR-S1 treatment by oral administration significantly inhibited MCL tumor growth, whereas ibrutinib did not. In vitro growth assays showed that compared with an established EZH2-specific inhibitor GSK126, OR-S1 had a marked antitumor effect on MCL cell lines. Furthermore, comprehensive gene expression analysis was performed using OR-S1-sensitive or insensitive MCL cell lines and showed that OR-S1 treatment modulated B-cell activation, differentiation, and cell cycle. In addition, we identified Cyclin Dependent Kinase Inhibitor 1C (CDKN1C, also known as p57, KIP2), which contributes to cell cycle arrest, as a direct target of EZH1/2 and showed that its expression influenced MCL cell proliferation. These results suggest that EZH1/2 may be a potential novel target for the treatment of aggressive ibrutinib-resistant MCL via CDKN1C-mediated cell cycle arrest.

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.

Novel orally bioavailable EZH1/2 dual inhibitors with greater antitumor efficacy than an EZH2 selective inhibitor.

Polycomb repressive complex 2 (PRC2) methylates histone H3 lysine 27 and represses gene expression to regulate cell proliferation and differentiation. Enhancer of zeste homolog 2 (EZH2) or its close homolog EZH1 functions as a catalytic subunit of PRC2, so there are two PRC2 complexes containing either EZH2 or EZH1. Tumorigenic functions of EZH2 and its synthetic lethality with some subunits of SWItch/Sucrose Non-Fermentable (SWI/SNF) chromatin remodeling complexes have been observed. However, little is known about the function of EZH1 in tumorigenesis. Herein, we developed novel, orally bioavailable EZH1/2 dual inhibitors that strongly and selectively inhibited methyltransferase activity of both EZH2 and EZH1. EZH1/2 dual inhibitors suppressed trimethylation of histone H3 lysine 27 in cells more than EZH2 selective inhibitors. They also showed greater antitumor efficacy than EZH2 selective inhibitor in vitro and in vivo against diffuse large B-cell lymphoma cells harboring gain-of-function mutation in EZH2. A hematological cancer panel assay indicated that EZH1/2 dual inhibitor has efficacy against some lymphomas, multiple myeloma, and leukemia with fusion genes such as MLL-AF9, MLL-AF4, and AML1-ETO. A solid cancer panel assay demonstrated that some cancer cell lines are sensitive to EZH1/2 dual inhibitor in vitro and in vivo. No clear correlation was detected between sensitivity to EZH1/2 dual inhibitor and SWI/SNF mutations, with a few exceptions. Severe toxicity was not seen in rats treated with EZH1/2 dual inhibitor for 14 days at drug levels higher than those used in the antitumor study. Our results indicate the possibility of EZH1/2 dual inhibitors for clinical applications.

Cleavage, but not read-through, stimulation activity is responsible for three biologic functions of transcription elongation factor S-II.

Transcription elongation factor S-II stimulates cleavage of nascent transcripts generated by RNA polymerase II stalled at transcription arrest sites. In vitro experiments have shown that this action promotes RNA polymerase II to read through these transcription arrest sites. This S-II-mediated cleavage is thought to be necessary, but not sufficient, to promote read-through in the in vitro systems. Therefore, Saccharomyces cerevisiae strains expressing S-II mutant proteins with different in vitro activities were used to study both the cleavage and the read-through stimulation activities of S-II to determine which S-II functions are responsible for its biologic functions. Strains expressing mutant S-II proteins active in both cleavage and read-through stimulation were as resistant as wild type strains to 6-azauracil and mycophenolic acid. 6-Azauracil also induced IMD2 gene expression in both these mutant strains and the wild type. Furthermore, strains having a genotype consisting of one of these S-II mutations and the spt4 null mutation grew as well as the spt4 null mutant at 37 degrees C, a restrictive temperature for a strain bearing double null mutations of spt4 and S-II. In contrast, strains bearing S-II mutations defective in both cleavage and read-through stimulation had phenotypes similar to those of an S-II null mutant. However, one strain expressing a mutant S-II protein active only in cleavage stimulation had a phenotype similar to that of the wild type strain. These results suggest that cleavage, but not read-through, stimulation activity is responsible for all three biologic functions of S-II (i.e. suppression of 6-azauracil sensitivity, induction of the IMD2 gene, and suppression of temperature sensitivity of spt4 null mutant).