CARM1-IN-4 (compound 11f) is a potent CARM1 inhibitor with IC 50 s of 9 nM and 56 nM for CARM1 and PRMT1 , respectively. CARM1-IN-4 displays significant anti-proliferative effects on colorectal cancer cell lines. CARM1-IN-4 effectively inhibits the methyltransferase activity of CARM1 and prevents methylation of downstream proteins. CARM1-IN-4 induces apoptosis and shows antitumor activity.