Complexos de In(III) com tiossemicarbazonas como candidatos a fármacos antineoplásicos e antimicrobianos

Abstract

The investigation on indium-based drug candidates remains practically unexplored. In order to study the pharmacological profile of In(III) complexes with bioactive 2acetylpyridine-derived thiosemicarbazones, complexes [In(2Ac4oClPh)Cl2(MeOH)] (In1), [In(2Ac4pClPh)Cl2(MeOH)] (In2), [In(2Ac4pFPh)Cl2(MeOH)] (In3), [In(2Ac4pIPh)Cl2(MeOH)] (In4), [In(2Ac4Ph)2]NO3·H2O (In5), [In(2Ac4oClPh)2]NO3 (In6), [In(2Ac4mClPh)2]NO3·1.5H2O (In7), [In(2Ac4pClPh)2]NO3·2H2O (In8), [In(2Ac4pFPh)2]NO3·1.5H2O (In9) and [In(2Ac4pIPh)2]NO3·H2O (In10) were obtained with 2-acetylpyridine-N(4)-phenylthiosemicarbazone (H2Ac4Ph) and its N(4)-orthochlorophenyl (H2Ac4oClPh), N(4)-meta-chlorophenyl (H2Ac4mClPh), N(4)-parachlorophenyl (H2Ac4pClPh), N(4)-para-fluorophenyl (H2Ac4pFPh) and N(4)-paraiodophenyl (H2Ac4pIPh) derivatives (HL). In all complexes the thiosemicarbazone ligand coordinates to the metal center through the Npy-Nimine-S chelating system. Crystallographic structures were determined for In1-In8. The compounds were evaluated for their ability to inhibit the viability of human leukemia (HL-60, Jurkat and THP-1) and solid tumor (MDA-MB 231, MCF-7 and HCT116) cells, as well as against non-malignant Vero cells. The cytotoxicity and selectivity indexes (SI = IC50 Vero / IC50 tumor cell) increased in several cases for the In(III) complexes in comparison with the free thiosemicarbazones. Some compounds showed IC50 values in the nanomolar range with high selectivity indexes, such as In3 (IC50 = 137 nM, SI = 373), In5 (IC50 = 20 nM, SI = 144) and In9 (IC50 = 11 nM, SI = 420) on HCT-116 cells. The antimicrobial action of In1-In10 and the parent thiosemicarbazones was evaluated against Gram-positive and Gram-negative bacterial species and against yeast strains of the genus Candida. Complexes [In(L)Cl2(MeOH)] (In1-In4) and their precursor thiosemicarbazones presented a considerably superior antifungal action when compared to the antibacterial action. These compounds showed IC50 values lower than 3.80 mol/L against Candida lusitaniae and Candida dubliniensis, being more active than the antifungal agent nystatin in most cases. The [InL2]NO3 compounds (In5-In10) were inactive. Although devoid of fused aromatic rings, the [In(L)Cl2(MeOH)] compounds (In1In4) interact with deoxyribonucleic acid (DNA), at least partially, by an atypical intercalation mechanism. It was also observed that Van der Walls forces and hydrogen bonds played a major role in the interactions between In1-In4 and human serum albumin (HSA), indicating that these compounds could be transported in the blood. Theoretical studies suggested that the coordinated methanol molecule in In1-In4 can be easily replaced by DMSO used in the preparation of stock solutions, with the formation of [In(L)Cl2(DMSO)]. The following substitution of DMSO by water in aqueous solution is unfavorable, but the displacement of one or two chloride ligands by water is extremely favorable, suggesting that the [In(L)Cl(H2O)(DMSO)]+ or [In(L)(H2O)2(DMSO)]2+ species might be responsible for the biological activities of In1In4. Structure-activity relationship (SAR) studies were carried out to identify the physicochemical properties that might be involved in the antifungal action, as well as in the cytotoxic effect of In1-In4 against HL-60 cells. In both cases, correlations between the bioactivity and physicochemical properties did not appreciably change when the chloride ligands in [In(L)Cl2(DMSO)] were replaced by water molecules. In relation to the cytotoxic activity, reasonable correlations were found between the IC50 values and the HOMO energy, the dipole moment and the molecular volume. In relation to the antimicrobial activity, it was observed that the stereoelectronic parameters correlate differently for each yeast of the genus Candida, so that different mechanisms of action may be involved. Neutron activation of complexes In1, In3, In6 and In9 was carried out producing the radioactive 114mIn analogs *In1, *In3, *In6 and *In9. The cytotoxic activities of the compounds were investigated on MCF-7 breast cancer cells, as well as against nonmalignant MRC-5 fibroblast cells. While both non-radioactive and radioactive In(III) salts were inactive against MCF-7 cells, the radioactive complexes proved to be 102 to 104 times more potent than the non-radioactive analogues against MCF-7 cells. The selectivity indexes (SI = IC50 MRC-5 / IC50 MCF-7) for the radioactive In(III) complexes were SI = 46 - 4716, indicating that irradiation represented an interesting strategy for increasing selectivity. Radioactive complexes induced higher levels of intracellular reactive oxygen species (ROS) in MCF-7 cells in comparison to the parent compounds, which partially explains the more potent cytotoxic action of these compounds. In addition, morphological changes of the nucleus and cells membrane treated with the non-radioactive and radioactive compounds suggest occurrence of cell death by apoptosis.