Discovery of novel cereblon-recruiting PRMT5 degraders with in vivo efficacy against triple-negative breast cancer.

The epigenetic regulator protein arginine methyltransferase 5 (PRMT5) is aberrantly overexpressed in triple-negative breast cancer (TNBC) and represents a promising therapeutic target. Currently reported PRMT5-targeting PROTAC degraders (MS4322 and MS115) are both derived from a tetrahydroisoquinoline scaffold. These compounds require treatment for more than five days to exert effective antiproliferative activities, and no in vivo antitumor efficacy has been reported. To address these limitations, we adopted the carbazole-based PRMT5 inhibitor PJ-68, which features a lower molecular weight and a more accessible linker attachment site. Herein, we reported a series of novel PRMT5 degraders with carbazole scaffold. The representative compound YZ-17 degraded PRMT5 (DC50 = 2.2 μM in HCC1806 and 3.3 μM in HCC1937 cells) and its adaptor protein MEP50 (DC50 = 2.0 μM and 2.9 μM, respectively) within 24 h. YZ-17 also suppressed PRMT5-mediated symmetric dimethylarginine (sDMA) modification and colony formation, induced G1 phase cell cycle arrest, and displayed favorable antiproliferative activities across several TNBC cell lines (IC50 = 2.6 - 3.7 μM). Importantly, YZ-17 showed in vivo efficacy in an HCC1806 xenograft model, achieving a tumor growth inhibition (TGI) of 44.12% at 30 mg/kg (i.p., every other day) without obvious toxicity. Collectively, YZ-17 represents a structurally novel PRMT5 degrader with rapid onset of action, effective in vitro and in vivo anti-TNBC activity, offering a distinct chemical tool for further functional studies of PRMT5.