Effects of one 150R x-ray exposure on DMBA-DNA adduct formation in Syrian hamster cheek pouch epithelium in vivo

The authors' prior studies showed enhancement of DMBA carcinogenesis in hamster buccal pouch epithelium by repeated 20R head and neck x-ray exposures. Possible mechanisms included radiation-induced increases in covalent binding of DMBA to epithelial cell DNA. This pilot study assessed, at one time period, the effect of a single modest x-ray exposure on in vivo DMBA-DNA adduct formation in the cheek pouch. Hamsters received one 0.05ml topical application of 5.0μg 3H-DMBA (900μCi) in DMSO to the right pouch. Two hours later, 1/2 of the hamsters received a single 150R head and neck x-ray exposure. 24 hours after DMBA treatments, pouches were exercised and epithelium was isolated. Epithelial DNA was extracted and purified using homogenization, phenol-chloroform-isoamyl alcohol extraction, and spermine precipitation. DMBA-DNA adducts were calculated via scintillation spectrometry of radioactivity and fluorometry of DNA, and were expressed as μg DMBA bound / mg DNA. There was no significant difference between irradiated and non-irradiated groups in DMBA bound. This may reflect a true lack of radiation effect on DMBA binding, a temporal displacement of increased binding not detectable at 24 hours, or too small a binding increase from one x-ray exposure to detect. Ongoing studies are addressing these possibilities