## 1 Introduction  
Iron and copper chelators have significant potential in the treatment of various diseases, ranging from metal overload conditions (repeated blood transfusions, [PERSON] disease) to cancer [1]. In order to define the ideal properties of chelators for potential therapeutic use, a brief overview of these illnesses and the clinically used chelators, together with their disadvantages, will be provided. Thalassemia is a common hematological disorder with high prevalence in the Mediterranean area, the Middle East, and many other Asian countries. As a consequence of migration, the prevalence of this disease in formerly non-prevalent countries is increasing [2]. Severe thalassemia requires blood transfusions followed by iron chelation therapy. The current palette of iron chelators includes potent deferoxamine, which needs frequent or continuous parenteral administration, and two oral iron chelators, deferiprone and deferasirox. Deferiprone is a somewhat controversial drug, which is able to induce idiosyncratic agranulocytosis [3; 4]. Deferasirox seems to have a better safety profile, but it can cause peptic ulcers and severe hepatic and renal dysfunction in rare cases, and in addition, it might not be always sufficiently active [5]. Furthermore, the selectivity of the current clinically used chelators is being discussed [6]. For these reasons, expanding the selection of the currently available and ideally selective iron chelators is desired. [PERSON] disease is a copper disorder, associated with its accumulation in the human body. Its prevalence worldwide is lower than that of thalassemia (1 in 10,000/30,000 persons) [7]. The treatment modalities include two oral copper chelators, D-penicillamine and trientine, and zinc in milder cases or in combination regimens. D-penicillamine is a cumbersome drug with many side effects [8] and its copper-chelating effects seem to be weak [9]. Trientine has much better tolerance, but like D-penicillamine, it can worsen neurological symptoms. Currently, ammonium tetrathiomolybdate is being tested in clinical trials [10; 11; 12]. Hence, like in the case of iron chelators, novel selective copper chelators are also needed. It is also well known that both metals are needed for cancer growth and, unsurprisingly, chelators have been tested as anti-cancer compounds [13; 14]. In the case of tumors, however, rather than depriving tumors of these metals via strong chelators, the redox cycling of the metals by reducing chelators associated with increased production of reactive oxygen species (ROS) is more convenient. It is well known from the literature that some chelators can reduce these metals, and since cancer cells are abundant in copper and iron, the effect of these redox cycling chelators is targeted, in particular, against tumor [9; 15; 16; 17]. Some xanthone derivatives, which are developed as fluorescent metal probes, were previously reported to form colored complexes with several metals [18; 19; 20; 21; 22]. We also reported that the series of xanthones reported herein behaved as potent cytotoxic drugs against cervical, colorectal, hepatocellular and alveolar adenocarcinoma cell lines, with IC\({}_{50}\) values mostly in units or tens of \(\mu\)M concentrations [23]. In general, the xanthone scaffold seems to be a suitable base for the development of novel anticancer compounds [24; 25]. For this reason, a xanthene core with chelating site(s) was selected as a scaffold for novel chelators. In this study, a series of 2,6,7-trihydroxy-xanthene-3-ones (Figure 1) was tested for their ability to chelate and reduce iron or copper. Since this study aimed at the selection of the most potent chelating compound from this series, and in vitro assessment of its ability to treat metal overload or cancer, the most efficient xanthone was also tested in biological experiments using healthy and cancer cells.