Abstract
BackgroundMetals including iron, copper and zinc are essential for physiological processes yet can be toxic at high concentrations. However the role of these metals in the progression of cancer is not well defined. Here we study the anti-tumor activity of the metal chelator, TPEN, and define its mechanism of action.MethodsMultiple approaches were employed, including cell viability, cell cycle analysis, multiple measurements of apoptosis, and mitochondrial function. In addition we measured cellular metal contents and employed EPR to record redox cycling of TPEN–metal complexes. Mouse xenografts were also performed to test the efficacy of TPEN in vivo.ResultsWe show that metal chelation using TPEN (5μM) selectively induces cell death in HCT116 colon cancer cells without affecting the viability of non-cancerous colon or intestinal cells. Cell death was associated with increased levels of reactive oxygen species (ROS) and was inhibited by antioxidants and by prior chelation of copper. Interestingly, HCT116 cells accumulate copper to 7-folds higher levels than normal colon cells, and the TPEN-copper complex engages in redox cycling to generate hydroxyl radicals. Consistently, TPEN exhibits robust anti-tumor activity in vivo in colon cancer mouse xenografts.ConclusionOur data show that TPEN induces cell death by chelating copper to produce TPEN-copper complexes that engage in redox cycling to selectively eliminate colon cancer cells.
Highlights
Metals including iron, copper and zinc are essential for physiological processes yet can be toxic at high concentrations
The TPEN-copper complex undergoes redox cycling reactions. These results suggest that TPEN chelates accumulated copper in HCT116 cells making it available for redox cycling leading to cell toxicity and death
No obvious cell cycle arrest was associated with the TPEN treatment (Figure 1C), indicating that the primary effect of TPEN on HCT116 cells is to induce cell death
Summary
Copper and zinc are essential for physiological processes yet can be toxic at high concentrations. The etiology of cancer varies greatly between different types of neoplasms, a hallmark finding is a defect in cell cycle regulation [1,2] Such cell cycle disruption is associated with genomic instability, due to mutations and chromosomal aberrations that disrupt critical housekeeping. TPEN-induced meiotic arrest is due to the lack of activation of Cdc25C, a dual specificity phosphatase in oocytes that represents the rate limiting step in activating the master regulator of the G2-M transition cyclin-dependent kinase 1 (Cdk1) [5]. This is because Cdc25C is a Zn2+-binding protein and removal of Zn2+ inhibits its ability to interact with and dephosphorylate Cdk1 [3]. TPEN treatment results in meiosis arrest in mouse oocytes [6]
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