Related Experiment Videos
Unusual oxygen concentration dependence of toxicity of SR-4233, a hypoxic cell toxin
1Radiation Oncology, University of Pennsylvania, Philadelphia 19104-6072.
Abstract:
Toxicity from drugs activated by bioreductive metabolism has been suggested as a means to eliminate the treatment resistance caused by hypoxic tumor cells. In general, drugs have been selected to maximize the hypoxic cytotoxicity ratio [exposure (drug concentration x time) in air:exposure in nitrogen] to cause equal toxicity. On this basis, two recently developed drugs have very similar characteristics; an aziridine derivative of misonidazole (RSU1069) and a benzotriazine di-N-oxide (SR4233). The oxygen dependence of the toxic response has not previously been characterized. This report shows that the toxicity from SR4233 extends over a much greater range of oxygen concentrations than does that of RSU1069. Furthermore, unlike all previous drugs studied, the toxicity of SR4233 does not level off at high oxygen concentrations, but continues to decrease as the oxygen concentration increases. For 1 mM oxygen (the solubility of oxygen in medium at 37 degrees C equilibrated with 100% oxygen and water vapor) the toxicity from SR4233 is at least 2000-fold less than that for hypoxia. Modeling the effect of oxygen on combined radiation and toxicity shows that radiation plus SR4233 should be much more effective in eliminating hypoxic cells than radiation plus RSU1069. The unusual oxygen dependence of toxicity by SR4233 may indicate a unique biochemical activation process.
Insights
Bioreductive drugs combat hypoxic tumor cells. SR4233 shows unique oxygen-dependent toxicity, decreasing with higher oxygen, making it more effective with radiation than RSU1069 for eliminating resistant cells.
Area of Science:
- Biochemistry
- Pharmacology
- Radiation Oncology
Background:
- Hypoxic tumor cells are resistant to cancer treatments.
- Bioreductive drugs activated by metabolism offer a strategy to overcome this resistance.
- Previous drug selection focused on maximizing hypoxic cytotoxicity ratio.
Purpose of the Study:
- To characterize the oxygen dependence of toxicity for bioreductive drugs RSU1069 and SR4233.
- To compare the efficacy of SR4233 and RSU1069 in combination with radiation for eliminating hypoxic cells.
Main Methods:
- Investigated the toxicity of SR4233 and RSU1069 across a range of oxygen concentrations.
- Compared the oxygen dependence of toxicity between the two drugs.
- Modeled the combined effect of radiation and each drug on hypoxic cell elimination.
Main Results:
- SR4233's toxicity spans a wider oxygen range than RSU1069.
- Unlike other drugs, SR4233 toxicity decreases with increasing oxygen concentration.
- SR4233 toxicity is significantly lower than RSU1069 at high oxygen levels.
- Radiation combined with SR4233 is predicted to be more effective than with RSU1069 against hypoxic cells.
Conclusions:
- SR4233 exhibits an unusual oxygen-dependent toxicity profile, suggesting a unique activation mechanism.
- The distinct oxygen sensitivity of SR4233 enhances its potential as a radiosensitizer for hypoxic tumors.
- SR4233 represents a promising therapeutic agent for overcoming treatment resistance in hypoxic cancers.