A first-in-class potent EZH2 degrader, AXT-1003, exhibits robust anti-tumor activity across multiple lymphomas and solid tumors

Enhancer of Zeste Homolog 2 (EZH2) acts as the core enzymatic component of the Polycomb Repressive Complex 2 (PRC2), which mediates trimethylation of histone H3 lysine 27 (H3K27Me3) to maintain the epigenetic repression of target genes. Mutated and/or dysregulated EZH2 expression is a hallmark of various cancers and is frequently correlated with poor patient prognosis. Several S-adenosylmethionine (SAM)-competitive EZH2 inhibitors, which suppress methyltransferase activity of EZH2, have clinically shown promising results in treating sarcoma and lymphoma, including the FDA-approved tazemetostat (EPZ-6438). However, monotherapy with these EZH2 inhibitors has limited efficacy in most solid tumors, even though they effectively reduce the H3K27Me3. Growing evidence suggests that EZH2 commonly functions noncanonically, in a methyltransferase-independent manner, as a transcriptional coactivator through associating with oncogenic transcription factors in solid tumors. Therefore, targeting EZH2 with degradation can be advantageous for the treatment of EZH2-dependent cancers.​ Herein, we reported the development of a first-in-class, oral, and potent EZH2 degrader, AXT-1003. Across multiple in vitro and in vivo tumor models, this degrader promoted a dose- and time-dependent reduction of EZH2 protein, which led to significant inhibition of H3K27Me3. Meanwhile, AXT-1003 had no significant effect on EZH2 at transcriptional levels, and its protein expression was restored by MG-132 (proteasome inhibitor). Our ubiquitinomics and proteomics studies demonstrated that AXT-1003 simultaneously triggered ubiquitination and degradation of EZH2 protein, suggesting AXT-1003 serves as an EZH2-targeting degrader via the ubiquitin-proteasome pathway. Additionally, AXT-1003 effectively inhibited enzymatic activity of wild-type EZH2 and its mutants at nanomolar concentrations in a non-SAM-competitive manner and exhibited greater selectivity for EZH2 inhibition than EPZ-6438. AXT-1003 exhibited broader and stronger anti-proliferative activities against various lymphoma cell lines with wild-type or mutated EZH2 as well as solid tumor cell lines. Notably, in the patient-derived organoid (PDO) models from ovarian clear cell carcinoma (OCCC) samples, AXT-1003 displayed superior efficacy compared with cisplatin or mevrometostat (PF-06821497), regardless of ARID1A status. AXT-1003 suppressed tumor growth more effectively than EPZ-6438 in several cancer cell-derived xenograft (CDX) mice models. Furthermore, the in vivo combination treatment of AXT-1003 with enzalutamide showed synergistic efficacy in a prostate cancer (LNCaP) CDX mice model. In conclusion, our preclinical data highlight the therapeutic potential of AXT-1003 and support its ongoing clinical evaluation in patients with EZH2-driven cancers.