Mutagenicity of Ochratoxin A: Role for a Carbon-Linked C8-Deoxyguanosine Adduct?

Ochratoxin A (OTA) is a fungal toxin that is considered to be a potent kidney carcinogen in rodent models. The toxin produces double strand breaks and has a propensity for deletions, single-base substitutions, and insertions. The toxin reacts covalently with DNA to afford a C8-2'-deoxyguanosine carbon-linked adduct (OT-dG) as the major lesion in animal tissues. Incorporation of model C-linked C8-aryl-dG adducts into the G3 site of the NarI sequence demonstrates a tendency to induce base substitutions and deletion mutations in primer extension assays using model polymerases. The degree of misincorporation induced by the C-linked C8-dG adducts correlates with an ability to adopt the promutagenic syn conformation within the NarI duplex as predicted by molecular dynamics (MD) simulations. MD simulations of the OT-dG adduct within the NarI duplex predict an even greater degree of conformational flexibility, suggesting enhanced in vitro mutagenicity compared to the simpler model C-linked C8-dG adducts. Together these findings support the role of OT-dG in promoting OTA-mediated mutagenicity and carcinogenicity in animal studies.