AT-101 is an inhibitor of the enzyme called protein arginine methyltransferase 5 (PRMT5). AT-101 is a small molecule, which can be taken orally. It selectively binds to PRMT5, and inhibits its function. This blocks the gene expression pathway that is required by cancer cells for their growth and proliferation.  

It is believed that AT-101 could find utility in treating tumours with currently unmet clinical need, such as liver, bowel, or pancreatic cancer. 

Cell replication is regulated by the transcription factor E2F1. In tumour cells, E2F1 exists in a liberated methylated state, where it drives uncontrolled cell proliferation. However, E2F1 can also promote cell suicide (apoptosis). This dual role of E2F1 in regulating cell proliferation and apoptosis is controlled by arginine methylation status.  Inhibition of PRMT5-mediated arginine methylation by AT-101 switches E2F1 from its growth-promoting mode into cell death mode.