The
mutagen sensitivity assay is one of the approaches used to investigate individual DNA repair capacity. This method is based on the premise that after in vitro treatment with a test
mutagen,
DNA from subjects with defective repair will be more damaged than
DNA from those with an efficient repair system. However, very little is known about unmeasured processes that occur between cell treatment and final assessment of DNA damage. To develop a more precise assay, we modified the traditional
mutagen sensitivity assay to also include measurement of DNA damage after culturing cells in the absence of
mutagen. First, we treated apparently normal and
xeroderma pigmentosum lymphoblastoid cell lines with various doses of
benzo(a)pyrene diol
epoxide (
BPDE) and harvested cells at different time points. A polyclonal antiserum against
BPDE-DNA was used to quantitate levels of adducts by immunoslot-blot and immunohistochemistry. Selected conditions included treatment with 10 microM
BPDE, a 4-hr culture in
mutagen-free medium, and immunohistochemical measurement of
BPDE-DNA adducts. The method was then applied in a pilot study to 50 lymphoblastoid lines from sisters discordant for
breast cancer. There was no significant difference between cases and controls in the level of
BPDE-DNA adducts in lymphoblasts harvested immediately after
BPDE treatment. However, after a 4-hr culture in
mutagen-free medium, the level of adducts was significantly higher (P = 0.006) among cases than in controls. There was a two-fold increase in mean adduct removal in lines from nonaffected as compared to affected sisters (44% and 22% decrease, respectively). DNA repair capacity was predictive of case status (P = 0.04) in logistic regression analysis. This method, which can be easily applied to large numbers of samples, should be useful in studies to investigate the role of DNA repair in
cancer risk.