Discovery of selective protein arginine methyltransferase 5 inhibitors and biological evaluations

Protein arginine methyltransferase 5 (PRMT5) is an important protein arginine methyltransferase that catalyzes the symmetric dimethylation of arginine resides on histones or non-histone substrate proteins. It has been thought as a promising target for many diseases, particularly cancer. Despite the potential applications of PRMT5 inhibitors in cancer treatment, very few of PRMT5i have been publicly reported. In this investigation, virtual screening and structure-activity relationship studies were carried out to discover novel PRMT5i, which finally led to the identification of a number of new PRMT5i. The most active compound, P5i-6, exhibited a considerable inhibitory potency against PRMT5 with an IC₅₀ value of 0.57 μm, and a high selectivity for PRMT5 against other tested PRMTs. It displayed a very good antiviability activity against two colorectal cancer cell lines, HT-29 and DLD-1, and one hepatic cancer cell line, HepG2, in a sensitivity assay against 36 different cancer cell lines. Western blot assays indicated that P5i-6 selectively inhibited the symmetric dimethylations of H4R3 and H3R8 in DLD-1 cells. Overall, P5i-6 could be used as a chemical probe to investigate new functions of PRMT5 in biology and also served as a good lead compound for the development of new PRMT5-targeting therapeutic agents.