Definition

An orally available small molecule inhibitor of protein arginine methyltransferase 5 (PRMT5), with potential antiproliferative and antineoplastic activities. Upon oral administration, PRMT5 inhibitor AMG 193 selectively binds to PRMT5 and inhibits its function. By inhibiting its methyltransferase activity, levels of both monomethylated and dimethylated arginine residues in histones H2A, H3 and H4 are decreased. This modulates the expression of genes involved in several cellular processes, including cellular proliferation. This may increase the expression of antiproliferative genes and/or decrease the expression of genes that promote cell proliferation, which may lead to decreased growth of rapidly proliferating cells, including cancer cells. PRMT5, a type II methyltransferase that catalyzes the formation of both omega-N monomethylarginine (MMA) and symmetric dimethylarginine (sDMA) on histones and a variety of other protein substrates involved in signal transduction and cellular transcription, is overexpressed in several neoplasms. Elevated levels are associated with decreased patient survival. Methylthioadenosine phosphorylase (MTAP) is deleted in certain cancer cells leading to an accumulation of methylthioadenosine (MTA). As MTA inhibits PRMT5, MTAP-null cancer cells are specifically sensitive to PRMT5 inhibitors.