PIK-C98 is a potent and selective PI3K inhibitor, with IC 50 s of 0.59, 1.64, 3.65, and 0.74 μM for α , β , δ , and γ isoforms , respectively. PIK-C98 inhibits all class I PI3Ks but has no effects on AKT or mTOR activity. PIK-C98 interferes with the ATP-binding pockets of PI3Ks by forming H-bonds and arene-H interactions with specific amino acid residues. PIK-C98 induces apoptosis by inhibiting PI3K. PIK-C98 can be used for the research of multiple myeloma.