Pre-clinical development of oxidative DNA adducts as biomarkers for the chemoprevention of prostate cancer.

Reactive oxygen species (ROS) are mechanistically implicated in the development and progression of prostate cancer. Intracellular ROS may cause oxidative DNA damage, resulting in the formation of adducts, such as 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxo-dG) and the cyclic pyrimidopurinone N-1, N-2 malondialdehyde-2'-deoxyguanosine (M1dG). These adducts have been associated with carcinogenesis, genomic instability and clonal evolution. It has previously been shown in vitro that testosterone and dihydrotestosterone (DHT) increase ROS levels in the androgen-sensitive, human prostate cancer cell line, LNCaP. We tested two hypotheses using human prostate cancer cells grown in vitro and in a xenograft nude mouse model. 1) Levels of oxidative DNA adducts increase in LNCaP cells treated with DHT. 2) Flutamide, a competitive androgen receptor antagonist, prevents DHT-induced changes. The levels of M1dG and 8-oxo-dG adducts were determined by immunoslot blot and liquid chromatography-tandem mass spectrometry, respectively. M1dG and 8-oxo-dG adduct levels were significantly higher than control levels in LNCaP cells exposed to physiological levels of DHT. This effect was also concentration-dependent. Pre-treatment with flutamide completely prevented increases in oxidative DNA adducts. In the athymic nude mouse LNCaP xenograft, tumour levels of M1dG were decreased by 46% in flutamide-treated animals compared with controls. Flutamide also inhibited the growth of LNCaP tumours and this correlated with a reduction in serum Prostate Specific Antigen (PSA) levels. The changes in oxidative DNA adduct levels in vitro and in vivo suggest that oxidative DNA adducts may serve as potential biomarkers of the efficacy of androgen manipulation in chemoprevention trials. Furthermore, a secondary finding of the study suggests that flutamide may be considered as a chemopreventive agent for prostate cancer. These adducts may serve as biomarkers of such a trial.