Selenium is an essential trace element that is crucial for cellular antioxidant defense against reactive oxygen species (ROS). Recently, many selenium-containing compounds have exhibited a wide spectrum of biological activities that make them promising scaffolds in Medicinal Chemistry, and, in particular, in the search for novel compounds with anticancer activity. Similarly, certain tellurium-containing compounds have also exhibited substantial biological activities. Here we provide an overview of the biological activities of seleno- and tellurocompounds including chemopreventive activity, antioxidant or pro-oxidant activity, modulation of the inflammatory processes, induction of apoptosis, modulation of autophagy, inhibition of multidrug efflux pumps such as P-gp, inhibition of cancer metastasis, selective targeting of tumors and enhancement of the cytotoxic activity of chemotherapeutic drugs, as well as overcoming tumor drug resistance. A review of the chemistry of the most relevant seleno- or tellurocompounds with activity against resistant cancers is also presented, paying attention to the synthesis of these compounds and to the preparation of bioactive selenium or tellurium nanoparticles. Based on these data, the use of these seleno- and tellurocompounds is a promising approach in the development of strategies that can drive forward the search for novel therapies or adjuvants of current therapies against drug-resistant cancers.

Department of Biochemistry and Microbiology Faculty of Food and Biochemical Technology University of Chemistry and Technology Prague Technická 3 166 28 Prague 6 Czech Republic

Department of Medical Microbiology Albert Szent Györgyi Health Center Albert Szent Györgyi Medical School University of Szeged Semmelweis utca 6 6725 Szeged Hungary

Division of Bioorganic Chemistry School of Pharmacy Saarland University D 66123 Saarbruecken Germany

Instituto de Química Orgánica General CSIC Juan de la Cierva 3 28006 Madrid Spain

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