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The role of glutathione peroxidases (GPx) in cancer and their influence on tumor prognosisand the development of anticancer drug resistance has been extensively and controversially discussed.The aim of this study was to evaluate the influence of GPx1 expression on anticancer drug cytotoxicity.For this purpose, a GPx1 knockout of the near-haploid human cancer cell line HAP-1 was generatedand compared to the native cell line with regards to morphology, growth and metabolic rates,and oxidative stress defenses. Furthermore, the IC50values of two peroxides and 16 widely usedanticancer drugs were determined in both cell lines. Here we report that the knockout of GPx1 in HAP-1cells has no significant effect on cell size, viability, growth and metabolic rates. Significant increasesin the cytotoxic potency of hydrogen peroxide andtert-butylhydroperoxide, the anticancer drugscisplatin and carboplatin as well as the alkylating agents lomustine and temozolomide were found.While a concentration dependent increases in intracellular reactive oxygen species (ROS) levelswere observed for both HAP-1 cell lines treated with either cisplatin, lomustine or temozolamide,no significant enhancement in ROS levels was observed in the GPx1 knockout compared to the nativecell line except at the highest concentration of temozolamide. On the other hand, a ca. 50% decreasein glutathione levels was noted in the GPx1 knockout relative to the native line, suggesting thatfactors other than ROS levels alone play a role in the increased cytotoxic activity of these drugs in theGPx1 knockout cells.
Pentathiepins are polysulfur-containing compounds that exert antiproliferative and cytotoxic activity in cancer cells, induce oxidative stress and apoptosis, and inhibit glutathione peroxidase (GPx1). This renders them promising candidates for anticancer drug development. However, the biological effects and how they intertwine have not yet been systematically assessed in diverse cancer cell lines. In this study, six novel pentathiepins were synthesized to suit particular requirements such as fluorescent properties or improved water solubility. Structural elucidation by X-ray crystallography was successful for three derivatives. All six underwent extensive biological evaluation in 14 human cancer cell lines. These studies included investigating the inhibition of GPx1 and cell proliferation, cytotoxicity, and the induction of ROS and DNA strand breaks. Furthermore, selected hallmarks of apoptosis and the impact on cell cycle progression were studied. All six pentathiepins exerted high cytotoxic and antiproliferative activity, while five also strongly inhibited GPx1. There is a clear connection between the potential to provoke oxidative stress and damage to DNA in the form of single- and double-strand breaks. Additionally, these studies support apoptosis but not ferroptosis as the mechanism of cell death in some of the cell lines. As the various pentathiepins give rise to different biological responses, modulation of the biological effects depends on the distinct chemical structures fused to the sulfur ring. This may allow for an optimization of the anticancer activity of pentathiepins in the future.