The increase in cancer incidence together with acquired resistance to conventional treatments, reinforces the urgent need for new therapeutic approaches. Skin cancer is the most common malignant neoplasm globally, and nucleic acid analogues like 5-fluorouracil (5-FU) have been used clinically to treat patients affected by this disease. At the same time, coordination chemistry has been consolidating itself as a promising strategy in the development of new antitumor agents. Among the metals of interest, cobalt(II) remains as a particularly attractive candidate, still largely unexplored, but with high therapeutic potential.

The present work is dedicated to the synthesis and characterization of a novel cobalt(II) complex containing a nucleobase derivative, besides the evaluation of the in vitro antiproliferative activity of the compound over melanoma (SK-MEL-28) cells.

The Co(II) complex was synthesised by deprotonation of the nucleobase analog (6-trifluoromethyluracil, Merck, 97% purity) in alkaline aqueous medium; In another flask, Co(II) bipyridine was prepared and then added to the nucleobase aqueous solution. The synthesis was stirred for 2h. Red crystals were obtained and collected. Elemental analyses (CHN) were performed using the CHNS/O Perkin Elmer 2400 analyzer. Antiproliferative activity of the complex was evaluated against melanoma (SK-MEL-28) and immortalized keratinocyte (HaCaT) cell lines using a colorimetric assay. Cells were treated with the complex. Cisplatin and the free nucleobase were used as positive controls. Cell growth inhibition was determined by absorbance at 540nm and IC50 values were calculated by sigmoidal regression.

Elemental analysis confirmed the composition of the complex as C20H12CoF6N6O4. The cobalt(II) complex showed moderate antiproliferative activity over SK-MEL-28 cells, with IC50 ranging from 20 µM to 200 µM, while cisplatin showed IC50 value of 13.5 µM. Free nucleobase did not show antiproliferative effect even at the highest concentration tested.

A new cobalt(II) complex with the nucleic acid analogue 6-trifluoromethyluracil with composition C20H12CoF6N6O4 was obtained. The cobalt(II) complex has presented modest antiproliferative activity against SK-MEL-28 cells, while the free ligand did not show activity even at the highest concentration. Further analyses are envisaged to determine the structural formula of the complex besides the evaluation of its antiproliferative activities over other skin cancer cells.