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Selective toxicity of nitracrine to hypoxic mammalian cells
Abstract:
Hypoxic cells in solid tumours are resistant to ionizing radiation and may be refractory to treatment by many chemotherapeutic agents. For these reasons the identification of drugs with selective toxicity towards hypoxic cells is an important objective in cancer chemotherapy. Nitroimidazoles such as misonidazole demonstrate such hypoxia-selective toxicity but have very low dose potency. The 1-nitroacridine derivative 1-nitro-9-(dimethylaminopropylamino)acridine (nitracrine) binds reversibly to DNA but also forms covalent adducts with DNA in vivo. We have found nitracrine to be selectively toxic to the Chinese hamster ovary cell line AA8 under hypoxic conditions in culture, with a potency approximately 100,000 times higher than that of misonidazole. The effect of oxygen is not a simple dose-modifying one in this system, probably in part because of rapid metabolic inactivation of nitracrine under hypoxic conditions. Viscometric studies with the mini col E1 plasmid PML-21 confirmed that nitracrine binds to DNA by intercalation, and provided an unwinding angle of 16 degrees (relative to 26 degrees for ethidium). It is proposed that the cytotoxicity of nitracrine under hypoxia is due to reductive metabolism to form an alkylating species, but that intercalation of the chromophore may enhance reactivity towards DNA and hence contribute to the marked enhancement of potency with respect to simple nitroheteroaromatic drugs.
Insights
Nitracrine, a novel drug, shows significantly higher toxicity against hypoxic cancer cells than existing treatments. This discovery offers a promising new avenue for developing more effective cancer chemotherapy targeting resistant tumor cells.
Area of Science:
- Cancer Research
- Medicinal Chemistry
- Molecular Biology
Background:
- Hypoxic tumor cells exhibit resistance to radiation and chemotherapy.
- Developing drugs with selective toxicity towards hypoxic cells is crucial for cancer treatment.
- Nitroimidazoles show hypoxia-selective toxicity but lack potency.
Purpose of the Study:
- To investigate the selective toxicity of the 1-nitroacridine derivative, nitracrine, against hypoxic cancer cells.
- To compare the potency of nitracrine with existing hypoxia-targeting drugs like misonidazole.
- To elucidate the mechanism of nitracrine's action on DNA.
Main Methods:
- Culturing Chinese hamster ovary cell line AA8 under hypoxic and normoxic conditions.
- Assessing nitracrine's cytotoxicity and potency.
- Conducting viscometric studies with mini col E1 plasmid PML-21 to analyze DNA binding.
- Comparing nitracrine's DNA intercalation with ethidium.
Main Results:
- Nitracrine demonstrated selective toxicity towards hypoxic cells, with approximately 100,000 times higher potency than misonidazole.
- Nitracrine binds to DNA via intercalation, confirmed by viscometric studies.
- The oxygen effect on nitracrine's toxicity is complex, potentially due to metabolic inactivation.
Conclusions:
- Nitracrine is a potent and selectively toxic agent against hypoxic cancer cells.
- Its cytotoxicity under hypoxia is likely due to reductive metabolism forming an alkylating species.
- DNA intercalation by nitracrine may enhance its reactivity and contribute to its high potency.