TOPO IIα inhibitor with broad-spectrum in vitro antitumor effects (IC50 values 4.3 µM, 11.5 µM, and 4.6 µM for inhibition of proliferation of breast cancer MDA-MB-231, human lung cancer A549 and human cervical cancer HeLa cell lines, respectively). CS1 functions as a Topo II poison to stabilize Topo II/DNA complex, which leads to DNA damage, cell cycle arrest at G2/M phase and apoptosis, and is 6–10-fold less cytotoxic against HL7702 and HUVEC cells compared with etoposide.