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Penetration of AF-2 and 4NQO into multicell spheroids
Abstract:
The mutagenicity of 4NQO and AF-2 was evaluated in a multicell system, Chinese hamster V79 spheroids, in order to determine the effects of drug delivery and metabolism on toxicity and mutagenicity. Both 4NQO and AF-2 undergo metabolic reduction of the nitro group to produce toxic intermediates. However, 4NQO is metabolized under oxic as well as hypoxic conditions, while AF-2 is reduced predominantly under hypoxia. This difference is apparently responsible for the observed pattern of toxicity and mutagenicity towards cells of large spheroids. Fluorescence microscopy revealed that 4NQO fluorescence localizes primarily in external (oxic) cells while AF-2 can penetrate further into the hypoxic region of spheroids. Although 4NQO is a far more potent single cell mutagen than AF-2 for equimolar exposures of single cells, the internal cells of spheroids exposed to 7.5 micrograms/ml of either agent under hypoxia were more readily mutated by AF-2 than by 4NQO.
Insights
The study investigated 4-nitroquinoline-1-oxide (4NQO) and AF-2 mutagenicity in Chinese hamster V79 spheroids. AF-2 showed higher mutagenicity in hypoxic spheroid cores compared to 4NQO, despite 4NQO
Area of Science:
- Toxicology
- Cell Biology
- Pharmacology
Background:
- 4-nitroquinoline-1-oxide (4NQO) and AF-2 are mutagens requiring metabolic reduction.
- Cellular metabolism and drug delivery influence mutagenicity and toxicity.
- Chinese hamster V79 spheroids model multicellular drug effects.
Purpose of the Study:
- Evaluate 4NQO and AF-2 mutagenicity in a multicellular spheroid system.
- Determine the impact of metabolic reduction and oxygen levels on mutagenicity.
- Compare the differential toxicity and mutagenicity of 4NQO and AF-2 in spheroids.
Main Methods:
- Utilized Chinese hamster V79 spheroids as a multicell system.
- Assessed mutagenicity under both oxic and hypoxic conditions.
- Employed fluorescence microscopy to track drug localization within spheroids.
Main Results:
- Both 4NQO and AF-2 produce toxic intermediates via nitro group reduction.
- 4NQO is metabolized under both oxic and hypoxic conditions; AF-2 is primarily reduced under hypoxia.
- AF-2 exhibited greater mutagenicity in the hypoxic core of spheroids compared to 4NQO, despite 4NQO's higher single-cell mutagenicity.
Conclusions:
- Metabolic pathways and oxygen availability significantly affect 4NQO and AF-2 mutagenicity in spheroids.
- Differential drug penetration and metabolism explain observed toxicity patterns in multicellular systems.
- AF-2 is a more potent mutagen than 4NQO within the hypoxic regions of V79 spheroids.