Enhancement of radiation-induced tumor cell killing by the hypoxic cell toxin SR 4233

Summary In this work tumour hypoxia is induced by physically occluding the tumour vascular supply by clamping, or by giving mice 5 mg kg-' hydralazine. These methods have previously been shown to increase the radiobiological hypoxic fraction in tumours close to 100%. Their effectiveness in potentiating the bioreductive toxicity of: misonidazole (800 mg kg-'), RSU1069 (80 mg kg-'), mitomycin C (5 mg kg-') and SR4233 (50 mg kg-') is assessed in the RIF-1 and KHT tumours using regrowth delay as an assay. Clamping alone for 120 min gives little or no response, but when RSU1069 is administered 15 min before clamping, large growth delays result. RIF-1 tumours clamped for 90 or 120 min with RSU1069 give cure rates of 12.5% and 37.5% respectively. Less effect with clamping is seen for the other bioreductive agents. The effect of hydralazine with RSU1069 although significant in the RIF-1 tumour, is modest compared to that for clamping. Small enhancements of toxicity are seen with hydralazine in combination with misonidazole in the RIF-1 tumour and mitomycin C in both tumours. The varying effectiveness of these treatments is attributed to several factors which include the level and duration of hypoxia, concentration and contact time of the bioreductive drugs, the microenvironment of the tumour and the nature of the reductive metabolic pathways available in the different tumour cell types.

Section: Discussionmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Bioreductive drugs and the selective induction of tumour hypoxia

Bremner

Stratford²,

Bowler³

et al. 1990

“…The bioreductive drug tirapazamine (SR4233, WIN 59075) has been investigated in vitro and in vivo for its cytotoxic and/or radiosensitising activity against tumour cells in air and in hypoxia (Zeman et al, 1986(Zeman et al, , 1988(Zeman et al, , 1990Brown, 1993;Koch, 1993). A higher aerobic-hypoxic ratio (concentration in air -concentration in nitrogen to obtain the same cytotoxicity) have been found in murine than in human tumours (Zeman et al, 1986).…”

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confidence: 99%

The effect of tirapazamine (SR-4233) alone or combined with chemotherapeutic agents on xenografted human tumours

Lartigau

Guichard²

1996

S_ary Recent data have shown that the in vitro and in vivo cytotoxicity of bioreductive drugs could be significantly increased when combined with chemotherapy drugs such as cisplatinum, depending on the timing of administration. The aim of this study was to define the toxicity (animal lethaity) and the activity (growth delay assay, excision assay) of a bioreductive drug, tirapazamine, alone and combined with chemotherapy agents (5-FU, VP16, bleo, DTIC and c-DDP) on nude mice bearing xenografted human tumours: a rectal carcinoma (HRT18) and a melanoma (Nal I +). Animal lethality was markedly increased when tirapazamine at the lethal dose 10% was combined with the other drugs. For the HRT18 tumour the combination of tirapazamine and bleomycin significantly increased the delay of regrowth compared with bleomycin alone (P=0.04) and was more cytotoxic than tirapazamine alone (P=0.04). For the Nall+ tumours the combination of tirapazamine with VP16 significantly increased tumour doubling time compared with the controls (P=0.001) or VP16 alone. The combination of tirapazamine and VP16 was more cytotoxic than VP16 alone (P=0.0001). When compared with c-DDP or tirapazamine alone, there was a significant decrease in plating efficiency when tirapazamine and c-DDP were given at the same time (P=0.04), but not when tirapazamine was given 3 h before c-DDP. In conclusion, tirapazamine was shown to be cytotoxic against clonogenic human tumour cells. Its efficacy in vivo may depend on its combination with already active chemotherapy drugs on the tumour model used. The timing of administration may be less important than previously thought.

“…Tirapazamine exhibits high hypoxia-selective cytotoxicity in the order of 50 to 200-fold in most rodent and human cell lines (Zeman et al, 1986(Zeman et al, , 1988Stratford and Stephens, 1989). Tirapazamine also kills hypoxic cells in transplanted tumours in mice (Zeman et al, 1988;Kim and Brown, 1994;Durand, 1994) and has been shown to potentiate the effects of modalities that are more toxic towards aerobic tumour cells.…”

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confidence: 99%

“…Tirapazamine also kills hypoxic cells in transplanted tumours in mice (Zeman et al, 1988;Kim and Brown, 1994;Durand, 1994) and has been shown to potentiate the effects of modalities that are more toxic towards aerobic tumour cells. In particular, a large potentiation of tumour cell kill has been observed with fractionated radiation (Brown andLemmon, 1990, 1991) and with some chemotherapeutic agents, particularly cisplatin (Dorie and Brown, 1993).…”

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confidence: 99%

Tirapazamine-induced DNA damage measured using the comet assay correlates with cytotoxicity towards hypoxic tumour cells in vitro

Siim

Zijl²,

Brown³

1996

Summary Tirapazamine (SR 4233), a bioreductive drug selectively toxic towards hypoxic cells, is presently in phase II clinical trials. Since it would not be expected that all tumours would respond equally to the drug, we are exploring ways of predicting the response of individual tumours. In this study we have tested whether the comet assay, which measures DNA damage in individual cells, can provide a simple, surrogate end point for cell killing by tirapazamine. We examined the relationship between the cytotoxicity of tirapazamine under hypoxic conditions and tirapazamine-induced DNA strand breaks in murine (SCCVII, EMT6, RIF-1) and human (HT1080, A549, HT29) tumour cell lines. These results were compared with the relationship between tirapazamine cytotoxicity and another measure of the ability of cells to metabolise tirapazamine; highperformance liquid chromatography (HPLC) analysis of tirapazamine loss or formation of the two electron reduction product SR 4317. The correlation between the hypoxic cytotoxic potency of tirapazamine and DNA damage was highly significant (r=0.905, P=0.013). A similar correlation was observed for hypoxic potency and tirapazamine loss (r=0.812, P=0.050), while the correlation between hypoxic potency and SR 4317 formation was not significant (r=0.634, P=0.171). The hypoxic cytotoxicity of tirapazamine in vitro can therefore be predicted by measuring tirapazamine-induced DNA damage using the comet assay. This approach holds promise for predicting the response of individual tumours to tirapazamine in the clinic.