Design, synthesis, and biological evaluation of a bioavailable EZH2 PROTAC with a 2,8-diazaspiro[4.5]decane linker.

Enhancer of zeste homolog 2 (EZH2) serves as a oncoprotein through catalyzing the methylation of substrates dependent on PRC2 complex, or driving gene transcription independent on enzymatic activities. Given that EZH2 is an important therapeutic target for cancer, protein degradation is an effective strategy to completely suppress its catalytic and non-catalytic functions. Herein, we designed a new class of CRBN-based EZH2 PROTACs by taking advantage of rigid linkers. Structure-activity relationship study identified compound 5g as an EZH2 PROTAC that degraded target protein and subunits of PRC2 complex in different cancer cell lines, with inhibition of H3K27me3, while it was selective over GSPT1 and IKZF1/3. Additionally, the degradation effect of 5g was dependent on the ubiquitin-proteasome system. Moreover, 5g showed antiproliferative activities against different cancer cell lines, while acute myeloid leukemia (AML) cells were more sensitive. In MV4-11 cells, 5g altered genes related to cell cycle and apoptosis in transcriptomic analysis, which was consistent with the G0/G1 phase arrest, increased cell apoptosis and changes in mRNA levels of downstream target genes after treatment with 5g. Furthermore, 5g exhibited acceptable predicted ADMET properties and had an oral bioavailability of 8.91 %. These findings indicated that compound 5g was a promising starting point for the further development of EZH2 PROTACs to treat AML.