Taurolidine: cytotoxic and mechanistic evaluation of a novel antineoplastic agent

Bis-(1,1-dioxoperhydro-1,2,4-thiadiazinyl-4)methane (taurolidine) is a synthetic broad-spectrum antibiotic that reacts with bacterial cell membrane components to prevent adhesion to epithelial cell surfaces. Reflecting the key role of adhesion in the growth and development of human solid tumors, studies were initiated to assess the antiproliferative activity of this agent in selected human and murine tumor cell lines. A 3-day exposure to Taurolidine inhibited the growth of all of the cell lines evaluated with IC(50)s ranging from 9.6-34.2 microM. Studies to identify the mechanism responsible for this effect were conducted in NIH-3T3 murine fibroblasts and the PA-1 and SKOV-3 human ovarian tumor cells. These studies revealed that a 48-h exposure to taurolidine had little effect on cell cycle distribution in PA-1 and SKOV-3 cells but significantly increased the appearance of DNA debris in the sub-G(0)/G(1) region, an effect consistent with an induction of apoptosis. In contrast, in NIH-3T3 cells, taurolidine exposure did not increase DNA debris in the sub-G(0)/G(1) region. Additional studies assessed phosphotidylserine externalization after a 24-h exposure to taurolidine using annexin-V binding as a cell surface marker. These studies revealed that taurolidine increased the percentage of annexin-V-positive cells by 4-fold and 3-fold in PA-1 and SKOV-3 cells, respectively. In NIH-3T3 cells, taurolidine exposure slightly increased ( approximately 5%) annexin-V binding. Parallel studies revealed that exposure to taurolidine also resulted in poly(ADP-ribose) polymerase cleavage in both ovarian tumor cell lines but not in NIH-3T3 cells. Finally, murine-based studies were conducted to assess the antineoplastic activity of three consecutive daily i.p. bolus injections of taurolidine at doses ranging from 5-mg injection/mouse to 30-mg injection/mouse. The 20-mg injection dose produced approximately 10% mortality and was identified as the maximally tolerated dose in this model. Administration of this regimen to nude mice bearing i.p. human ovarian tumor xenografts significantly inhibited both tumor formation and growth. These findings are discussed in light of their clinical implications.