Antiproliferative effect of oxidative stress induced by tellurite in breast carcinoma cells Ayesha Noreen, Abdul Rehman, Saira Aftab, Abdul Rauf Shakoori Journal of Cancer Research and Practice 2019 6(2):68-75 Background: Recent studies have revealed that tellurium (Te) compounds have pharmacological and/or antioxidant properties against tumors as they have antitumor and chemoprotective properties. The toxic nature of tellurium compounds and their beneficial effects as antitumor agents have led to an increasing number of studies on their toxicological and pharmacological modes of action. Materials and Methods: The breast cancer cell line, MDA-MB-231, was cultured in the absence or presence of tellurite for biochemical and morphological analysis to measure the extent of cell death. The roles of antioxidant compounds 3-methyladenine, N-acetylcysteine, and 1,2-bis (2-aminophenoxy) ethane-N, N, N′, N′-tetra acetic acid (acetoxymethyl ester) in supporting proliferation in the presence of tellurite were investigated. Results: There was significant oxidative stress in the tellurite-exposed cells, which curtailed cell Adenosine triphosphate (ATP) levels. Tellurite-induced cytotoxicity substantially increased lactate dehydrogenase leakage, lipid peroxidation, and DNA damage, as analyzed by micronuclei and comet formation. Conclusions: Tellurite-induced damage led to cell cycle arrest, resulting in cell death by activating apoptotic machinery by increasing p21 gene expression in tellurite-treated cells.