Melanoma is the most aggressive type of skin cancer, the incidence of which has been increasing annually worldwide.
1. Introduction
The past decades have marked important advances in the traditional view of many roles that metals and their compounds play in biological systems. In fact, metals, inorganic compounds and/or metals-organic frameworks show a diversity of properties that allowed them to present several and distinct biological, environmental and health applications [
1,
2,
3,
4,
5,
6,
7,
8,
9,
10,
11,
12,
13,
14,
15,
16,
17,
18,
19]. Recent insights into metals applications includes for instance, zinc nanoparticles as feed additives showing more efficiency than zinc salts, increasing growth not only in fish [
1] but also in plants [
2], besides preventing metal contaminants accumulation [
2] and normalizing antioxidant biomarkers [
1,
2]. Very recently, zinc salts have been referred with a potential use in medicine such for the prevention and treatment of SARS-CoV-2 infection [
3,
4]. Polyoxotungstates (POTs), such as decatungstate (W
10O
324−), have shown, by photocatalytic activity, to decompose antibiotics namely sulfasalazine and sulfapyridine with different specificities and rates [
5]. Besides green biotechnology applications, it was suggested that some POTs hamper melanoma cancer cells growth through inhibition of aquaporin-3 activity [
6], whereas others POTs as well as gold compounds showed specific inhibitory activities for P-type ATPases [
7,
8].
Removal of metal contaminants, such as for example cadmium, lead, arsenic and uranium from the environmental is still a problem to overcome in the 21st century. Recent studies highlighted the importance of uranyl speciation and the choice of specific chelating ligands for uranium removal and recovery from wastewater using electrocoagulation, being alizarin and iron electrode the most efficient combination [
9]. On the other hand, metals contaminants such as cadmium are known to induce changes in biochemical parameters in brain causing neurological dysfunction that were proposed to be prevent by tomato and/or garlic extracts, in a rat model [
10]. In humans, cadmium levels in urine were also found to be associated with an increase of LDL (low density lipoprotein)-cholesterol and a decrease of HDL (high density lipoprotein)-cholesterol, leading to an increased cardiovascular risk [
11].
Lithium, the well-known benefic metal and used in treatment of bipolar disease, has been recently described to partially prevent the increase of Na
+/K
+-ATPase activity induced by sleep privation, as observed in rats [
12]. In humans, lithium showed to be a Na
+/K
+-ATPase regulator once it was verified that impede the decreased of the Na
+/K
+-ATPase activity observed in chorea-acanthocytosis patients [
13]. Essential elements such as cobalt could be a good choice in hip prosthesis [
14]. However, it was described that cobalt is accumulated and affects differently astrocytes and neurons, inducing cytotoxicity in brain cells [
14], whereas functionalized cobalt nanoflakes were described with anticancer activities [
15]. Finally, a large number of different vanadium salts and complexes have been investigated and reported to have insulin enhancing, as well as anticancer properties [
16,
17]. Regarding vanadium and cancer, the number of articles found are higher for lung (n = 80), breast (n = 73) and liver (n = 70) cancer, medium for colon (n = 32), leukemia (n = 26) and bone (n = 21), whereas lower numbers of studies were found for brain (n = 10) and skin (n = 8), after a research in the Web of Science.
Although vanadium studies in skin cancer have being scarce, melanoma is the most aggressive type of skin cancer, and its incidence has been increasing annually worldwide at a faster rate compared to any other type of malignant tumor [
20,
21]. Usually, this pathology is diagnosed early and treated by surgery. On the other hand, its ability to metastasize makes this pathology dangerous [
21], which along with patients’ relapse driven by the acquisition of therapy resistance [
22], makes the search for novel therapeutic targets and options for melanoma treatment a priority [
23].
This disease develops from melanocytes, cells found predominantly in the basal layer of the epidermis [
20,
24,
25]. Melanocytes derive embryologically from pluripotent neural crest stem cells, which have high migratory potential [
25,
26]. This migratory embryonic origin of the melanocytes explains why melanoma is a type of cancer with a high capacity for metastasis [
25]. The homeostasis of these melanocytes is controlled by epidermal keratinocytes. These last cells produce a hormone called MSH (melanocyte stimulating hormone), which allows the binding between MC1R (melanocortin 1 receptor) and melanocytes, controlling melanocytes proliferation and preventing the appearance of changes in DNA, through the production of melanin [
20]. When skin cells are exposed to excessive ultraviolet (UV) radiation, the formation of malignant melanocytes can be induced through two different mechanisms: direct transformation of normal melanocytes into cancerous melanocytes and the transformation of melanocytes into benign nevi, which subsequently become malignant (). Direct targeting of melanocytes normally occurs when mutations in proto-oncogenes and tumor suppressor genes emergence (TP53, NF1, PTEN, etc.). When melanocytes are turned into benign nevi, these can stay that way for decades. However, UV rays can cause the appearance of genetic mutations in the TERT genes (reverse transcriptase of telomerase II) and CDKN2A (cyclin 2A-dependent kinase inhibitor) for example, which lead to malignant transformation of the nevi () [
20].
This entry is adapted from the peer-reviewed paper 10.3390/met11050828