Differential Involvement of Reactive Oxygen Species and Nucleoside Transporters in Cytotoxicity Induced by Two Adenosine Analogues in Human Prostate Cancer Cells

BACKGROUND. Elevated levels of cellular oxidative stress represent a specific vulnerability of malignant cells and exposure to cytotoxic drugs is known to induce oxidative stress in cancer cells. The effects of two adenosine analogues, 2-chloroadenosine and 2-chlorodeoxyadenosine, were investigated to assess their mechanism of action in prostate cancer cells. METHODS. Androgen-independent and -sensitive (PC3 and LNCaP) prostate cancer cells and mouse primary prostate cultures were used in the study. Proliferation and cell cycle progression were analyzed in the presence of 2-chloroadenosine and 2-chlorodeoxyadenosine. Adenosine receptors and nucleoside transporters expression were determined by RT-PCR. GSH and reactive oxygen species levels were determined by DTNB and DCFH-DA, respectively. Nuclear translocation of Nrf2 was assessed by Western blotting. RESULTS. 2-Chloroadenosine marginally affected primary prostate cells viability whereas it was more potent than 2-chlorodeoxyadenosine in reducing viability and increasing apoptosis in both prostate cancer cell lines. Moreover, ROS levels and GSH content were markedly affected in PC3 whereas only ROS production was increased in LNCaP cells. The antioxidant butylated hydroxytoluene protected PC3 cells from GSH depletion and reduction in cell viability induced by 2-chloroadenosine. CONCLUSIONS. 2-Chloroadenosine, but not 2-chlorodeoxyadenosine is capable of inducing apoptosis in prostate cancer cells, an effect which may be explained at least partially by the capacity of the nucleoside analogue to modify ROS and GSH levels. These observations may offer a rationale for the use of 2-chloroadenosine to improve the clinical efficacy of GSH-dependent antitumor drugs. Prostate 69: 538-547, 2009. (C) 2008 Wiley-Liss, Inc.