PF-9366 is a potent and selective inhibitor of PRMT5 (protein arginine methyltransferase 5), an enzyme involved in epigenetic regulation of gene expression. It is primarily used in cancer research due to its ability to disrupt the methylation of arginine residues on histones and other proteins, which plays a key role in tumor cell proliferation and survival. This compound shows promising antitumor activity in hematological malignancies and certain solid tumors, especially those with MTAP deletion, a genetic alteration that increases cancer cell dependency on PRMT5. PF-9366 is widely utilized in preclinical studies to evaluate the therapeutic potential of PRMT5 inhibition, helping to establish pharmacodynamic markers and effective combination strategies with other anticancer agents. Its high selectivity and cellular potency make it a valuable tool compound in oncology drug discovery.