In vitro activity: (±)-10-Hydroxycamptothecin (10-OH-camptothecin or 10-HCPT) is an inhibitor of topo I. (±)-10-Hydroxycamptothecin (10-HCPT, 5-20 nM) markedly inhibits the proliferation of Colo 205 cells in a dose-dependent manner. (±)-10-Hydroxycamptothecin (5-20 nM) arrests Colo 205 cells in the G2 phase of the cell cycle and triggers apoptosis through a caspase-3-dependent pathway. (±)-10-Hydroxycamptothecin (HPT, 0.01-10 μg/mL) causes cell shrinage, nuclear fragmentation and condensed chromosomes and induces apoptosis of human urinary bladder cancer cell line (T24).

Cell Assay: Colo 205 cells (5×105) (ATCC:CCL-222) are seeded in 25T flasks overnight and then treated without (control) and with 5, 10, 15 or 20 nM of HCPT, respectively. After treatment for 24-120 h, cells are harvested by trypsin-EDTA and then centrifuged at 1,500 rpm for 5 min at 4?C. The cell pellet is resuspended in culture medium containing 0.04% trypan blue and the viable cells are enumerated by a hemocytometer.