The induction of senescence, an irreversible growth arrest, in cancer cells is regarded as a mean to halt tumor progression. The phytoalexin resveratrol (RV) is known to possess a variety of cancer-preventive, -therapeutic, and -chemosensitizing properties. We report here that chronic treatment with RV in a subapoptotic concentration induces senescence-like growth arrest in tumor cells. In contrast to the widely accepted antioxidant property of RV, we demonstrate that one causative stimulus for senescence induction by chronic RV is an increased level of reactive oxygen species (ROS). The ROS formed upon RV exposure include hydrogen peroxide and superoxide and originate largely from mitochondria. Consistently, co-incubation with the antioxidant N-acetyl cysteine interfered with RV-mediated reactivation of the senescence program. Molecular mediators on the way from increased ROS levels to the observed growth arrest include p38 MAPK, p53, and p21. Moreover, we provide evidence that RV-initiated replication stress, apparent by activation of the ataxia telangiectasia-mutated kinase pathway, is associated with increased ROS levels and senescence induction. This is the first report linking cell cycle effects with a pro-oxidant and pro-senescent effect of RV in cancer cells.Normal cells possess a finite mitotically active life span. After an inherent number of cell divisions, the so-called Hayflick number, they enter the state of senescence, an irreversible proliferation arrest despite intact metabolic activity (1). There are several forms and triggers of senescence. Replicative senescence is caused by redox stress and/or telomere erosion below a certain threshold (2-5). A second form of senescence is triggered by DNA-damaging agents. Both forms are reported to depend on the DNA damage checkpoint kinases ataxia telangiectasia-mutated (ATM) 2 and Chk (checkpoint kinase) (6 -8).ATM is a protein that is well known as a central mediator of responses to DNA double strand breaks and subsequent replication stress. Oncogene activation has been identified as a third trigger for senescence (9, 10) and is also associated with signs of replicative stress (11-13). Downstream mediators of senescence include the tumor suppressor networks around p53 and retinoblastoma protein/p16 (9,14,15). If the senescence program fails in transformed cells, mostly due to inactivation of tumor suppressor genes, the cells continue to divide and may proceed to malignancy. Reactivation of senescence in these cells could therefore represent an attractive complementary way to prevent or halt cancer progression (16,17). Resveratrol (RV), a polyphenol found in berries, nuts, and red wine, has been assigned a variety of cancer chemopreventive activities including anti-inflammatory, pro-apoptotic, anti-angiogenic, and chemosensitizing properties, in a variety of cell culture and in vivo systems (18 -21). As a polyphenol, RV is redox-active and has been claimed to be an antioxidant (22, 23). However, there are also reports showing a pro-oxidant capacity of RV ...
