Mechanistic and antineoplastic evaluation of taurolidine in the DU145 model of human prostate cancer

Abstract

Taurolidine (TRD) was designed in the 1970s as a broad-spectrum antibiotic and is used clinically at high doses without systemic toxicity. We have found that this agent possesses cytotoxic activity in human tumor cell lines and antineoplastic activity in mice bearing i.p. human tumor xenografts. We now report the mechanism by which TRD induces cell death in DU145 human prostate tumor cells. The IC50 (3 days) of TRD in this model was 16.8+/-1.1 microM. Cytotoxicity was associated with DNA debris and increased membrane phosphatidylserine externalization, both suggesting the induction of apoptosis. This was confirmed by the ability of TRD to induce PARP cleavage in these cells, an effect prevented by coexposure to the pan-caspase inhibitor zVAD-FMK. TRD exposure also resulted in the appearance of cytochrome c in the cytoplasm, procaspase 9 activation within 2 h of drug exposure and procaspase 8 activation 4 h after exposure. Parallel experiments revealed that cytochrome c appearance in the cytoplasm was not blocked by preexposure to zVAD-FMK, while activation of both procaspase 9 and procaspase 8 was prevented. Finally, antineoplastic activity was assessed in mice bearing subcutaneous xenografts of DU145 cells. Initial studies quantitated the toxicity of three i.p. injections of TRD, administered as one injection on three alternate days per week, at doses ranging from 500 to 700 mg/kg per injection. The 500 mg/kg dose produced about 7% mortality after three cycles and effectively inhibited tumor growth. Thus, TRD induced mitochondrial-mediated apoptosis in DU145 human prostate tumor cells and this effect could be exploited for therapeutic advantage.

Stat3 Cleavage by Caspases

“…In preliminary studies we have exposed purified Stat3 to individual caspases under cell-free conditions and have observed that Stat3 is not demolished with equal efficiency by all caspases (64). Interestingly, only caspases 2, 4, 5, and 10 appear capable of cleaving Stat3 and generating specific cleavage fragments, a finding consistent with data presented here (Fig.…”

Taurolidine: Mode of administration in mouse tumor models

“…[2][3][4] Despite this increase in dose, a significant promotion of lung and liver metastasis was still observed and the mortality was comparable to that in the Darnowski study. 3 Thus, even this higher dose, despite reaching the toxic range, did not inhibit tumor progression and metastasis. With regard to toxicity of chemotherapeutics, one also needs to keep in mind that well-established chemotherapeutics like cisplatin or doxorubicin are also used in doses that are toxic and cause severe side effects.…”

“…treatment regimens that were previously reported to be successful in three different mouse tumor models. [2][3][4] Braumann in his letter to the editor criticized that we did not determine the maximal tolerated dose (MTD) in our study and that the doses used were in the toxic range and the data therefore were not relevant in the context of a clinical application. However, Calabresi et al 2 and Darnowski et al 3 performed MTD-finding experiments in tumorfree nude mice with taurolidine doses ranging from 5 to 30 mg/mouse/injection ( 217-1,300 mg/kg/injection).…”

“…[2][3][4] Braumann in his letter to the editor criticized that we did not determine the maximal tolerated dose (MTD) in our study and that the doses used were in the toxic range and the data therefore were not relevant in the context of a clinical application. However, Calabresi et al 2 and Darnowski et al 3 performed MTD-finding experiments in tumorfree nude mice with taurolidine doses ranging from 5 to 30 mg/mouse/injection ( 217-1,300 mg/kg/injection). In the study of Calabresi et al, 2 a dose of 20 mg taurolidine/ mouse/injection (equivalent to 870 mg/kg) resulted in 13% mortality and was chosen as MTD for their subsequent treatment study in an ovarian carcinoma mouse model with i.p.…”

Taurolidine: Mode of administration in mouse tumor models

“…injection; 37.9% at 600 mg/kg and 50% at 700 mg/kg) (Ref. 5). It is uncommon that MTD was taken as the dose which associates with a 10% mortality rate.…”