S516 (Compound 22) is an active metabolite of CKD-516 and a potent tubulin polymerization inhibitor with an IC50 of 4.29 μM. S516 has marked antitumor activity. IC50 & Target: IC50: 4.29 μM (tubulin polymerization)In Vitro: S516 has potent cytotoxicity with IC50s of 4.8 nM, 42.8 nM and 24.9 nM for HL-60, HCT116 and HCT15 cells, respectively. S516 (Compound 22; 30 nM; 16 hours; HL60 cells) treatmemt causes significant arrest of cells at the G2/M phase, resulting in apoptosis with concomitant loss of G0/G1 phase. In Vivo: S516 (Compound 22; 5-10 mg/kg; intraperitoneal injection; mice) treatment has promising antitumor activity (inhibition ratio (IR)> 63%) in human LX-1 lung cancer and CX-1 colon cancer mouse xenografts.