Tasidotin hydrochloride, a peptide analog of the antimitotic depsipeptide dolastatin 15, is an inhibitor of microtubule assembly and microtubule dynamics.

The greatest difference in sensitivity to Tasidotin is between the more sensitive MDA-MB-435 line and the less sensitive HS 578-T line of the remaining lines. The IC50 values in the two lines are 4 and 200 nM, respectively. The IC50 in Ewing's sarcoma, rhabdomyosarcoma, osteosarcoma, and synovial sarcoma lines ranges from 2 to 320 nM. Tasidotin induces a G2-M arrest that persists for 48 h after Tasidotin is washed from the cells in the SK-ES1 and RH30 cell lines. In vitro, more than half the cells are in the early or late phase of apoptosis 48 h after treatment with Tasidotin. Following treatment for 24 h with 160 nM Tasidotin, the RH30 line, and SK-ES1 line each shows an accumulation of cells in the G2-M phase. At hour 24, nearly all the RH30 cells are in the G2-M phase [1][2].

Tasidotin (90 mg/kg/d, mice) treatment has a mean weight loss of <16% following each 5-day treatment of Tasidotin. In vivo, a significant increase in apoptotic nuclei is apparent in xenograft tumors harvested within 24 h after a 5-day course of Tasidotin. Mice treated with 100 mg/kg have a mean weight loss of >20% with no return to their baseline starting weight, and one mouse dies before the second treatment course [2].