The microtubules act as an attractive target for anticancer drug discovery nowadays. Disruption of microtubules can induce cell cycle arrest in the G2-M phase and formation of abnormal mitotic spindles. The tubulin polymerization inhibitors have emerged as one of promising anticancer therapeutics because of their dual mechanism of action, i.e. apoptosis by cell-cycle arrest and vascular disrupting agent (VDA). VDAs are more efficient and less toxic.

Tubulin inhibitors possess potent cytotoxicity and strong inhibition of tubulin polymerization as well as potent in vivo antitumor efficacy.

S516 has potent cytotoxicity against several cancer cells including P-gp overexpressing MDR positive cell line (HCT15). Indeed, S516 also induces cell cycle arrest at the G2/M phase. Moreover, S516 has promising antitumor activity (inhibition ratio of 65%). Especially, S516 inhibits tubulin polymerization in a concentration-dependent manner with an IC₅₀ of 4.3 μM.

Researches measured the effect of S516 on the cell cycle by flow cytometry against HL60 cells after 16 h. At 30 nM, S516 causes the significant arrest of cells at the G2/M phase relative to the untreated control (70% with 22 vs 12% with control), resulting in apoptosis with concomitant loss of G0/G1 phase.

S516 has potent cytotoxicity against several cancer cell lines (HL60 and HCT116) including P-gp overexpressing MDR positive cell lines (HCT15) with concomitant inhibition of tubulin polymerization. Valecobulin (CKD-516; HY-13598) is the L-valine prodrug of S516. In the murine model, CKD-516 induces significant tumor growth inhibition against both CT26 colon cancer (IR = 55% at 10 mg/kg) and 3LL lung cancer (IR = 68% at 10 mg/kg). Moreover, Valecobulin (CKD-516) is an antivascular agent in nude mice bearing HCT116.