PRMT5 (protein arginine methyltransferase 5), MTA-cooperative

Class

PRMT5-MTA inhibitor

Pathway

Inhibits PRMT5 methyltransferase activity in a methylthioadenosine (MTA)-cooperative manner, exploited particularly in MTAP-deleted cancers

PRMT5 (protein arginine methyltransferase 5) is an enzyme that adds methyl groups to arginine residues on histones and other proteins, thereby influencing RNA splicing, transcription, and DNA repair. Because these processes are essential for cell survival, complete PRMT5 inhibition tends to be toxic to normal tissue as well as tumor tissue. A subset of cancers carries deletion of a neighboring gene, MTAP (methylthioadenosine phosphorylase), which normally breaks down the metabolite methylthioadenosine (MTA). When MTAP is lost, MTA accumulates inside the cell and partially suppresses PRMT5 activity on its own, leaving these tumor cells more dependent on the enzyme's remaining function and more vulnerable to further inhibition. MTA-cooperative PRMT5 inhibitors are designed to bind the enzyme preferentially when MTA is already present, so they act with much greater potency in MTAP-deleted cells than in normal cells, which retain low MTA levels. This approach aims to create a genetically defined therapeutic window, targeting a metabolic vulnerability specific to a molecularly defined subset of cancers, such as certain solid tumors with this deletion, rather than inhibiting PRMT5 uniformly throughout the body.