Melanogenesis inhibits respiration in B16-F10 melanoma cells whereas enhances mitochondrial cell content.

Melanoma is a rare and aggressive skin tumor; the survival of patients diagnosed late is fairly low. This high mortality rate is due to the characteristics of the cells that allow them to be resistant to radiotherapy and conventional chemotherapy, besides of being able to evade the immune system. Melanin, the pigment responsible for skin, hair and eye color, seems to be involved in this resistance. The main function of melanin is to protect the cells against ultraviolet (UV) light by absorbing this radiation and reactive oxygen species (ROS) scavenging. But this pigment may have also a role as photosensitizer, because when it is irradiated with UVA light (320-400 nm), the generation of ROS was detected. Besides, the melanogenesis stimulation on B16-F10 cells resulted in cell cycle arrest, induction of a quiescent state, change in the expression of several proteins and alterations on ADP/ATP ratio. The present study aimed to investigate the influence of melanogenesis stimulation in mitochondrial function of B16-F10 melanoma cells. Therefore, we analyzed cells respiration, mitochondrial membrane potential (Δψm) and mitochondria mass in B16-F10 melanoma cells stimulated with 0.4mML-tyrosine and 10mM NH4Cl. Our results showed that the induction of melanin synthesis was able to reduce significantly the oxygen consumption after 48h of stimulation, without changes of mitochondrial membrane potential when compared to non-stimulated cells. Despite of respiration inhibition, the mitochondria mass was higher in cells with melanogenesis stimulation. We suggest that the stimulation in the melanin synthesis might be promoting the inhibition of electrons transport chain by some intermediate compound from the synthesis of the pigment and this effect could contribute to explain the entry in the quiescent state.

A series of mononuclear Co(III) complexes using tridentate N,O-donor ligands: chemical properties and cytotoxicity activity.

Continuing our interest in tridentate ligands to develop new prototypes of cobalt-based metallodrugs for combating cancer, modifications in the backbone of HL1, [(2-hydroxybenzyl)(2-(pyridil-2-yl)ethyl]amine) were proposed in order to modulate the redox potential of new Co(III) complexes. Three ligands with electron withdrawing groups were synthesized: HL2: [(2-hydroxy-5-nitrobenzyl)(2-(pyridil-2-yl)ethyl]amine); HL3: [(2-hydroxybenzyl)(2-(pyridil-2-yl)ethyl]imine) and HL4: [(2-hydroxy-5-nitrobenzyl)(2-(pyridil-2-yl)ethyl]imine). They were used to obtain the respective mononuclear complexes 2, 3 and 4, which are discussed compared to the previous reported complex 1 (obtained from HL1). The new complexes were characterized and studied by several techniques including X-ray crystallography, elemental and conductimetric analysis, IR, UV-vis and (1)H NMR spectroscopies, and electrochemistry. The substitutions of the group in the para position of the phenol (HL1 and HL2) and the imine instead of the amine (HL3 and HL4), promote anodic shifts in the complexes reduction potentials. The influence of these substitutions in the biological activities of the Co(III) complexes against the murine melanoma cell line (B16F10) was also evaluated. Little effect was observed on cellular viability decrease for all free ligands, however the coordination to Co(III) enhances their activities in the following range: 1>4≈2>3. The data suggest that no straight correlation can be addressed between the reduction potential of the Co(III) center and the cell viability.

6-Mercaptopurine complexes with silver and gold ions: anti-tuberculosis and anti-cancer activities.

Synthesis, characterization and biological studies of silver and gold complexes with 6-mercaptopurine (H2MP) are described. The Ag(I) and Au(I) complexes with HMP-, AgHMP and AuIHMP, were obtained by mixing an acidified H2MP aqueous solution with an equimolar aqueous solution of AgNO3 or Au(CN)2. The Au(III) complex with HMP-, AuIIIHMP, was obtained by adding an aqueous solution of K(AuCl4) to an acidified H2MP aqueous solution (1:1 molar ratio) and the final solution was acidified with HCl to pH=1.0. The Au(III)MP complex, KAu(MP)2, was obtained by adding an aqueous solution of K(AuCl4) to a basic H2MP solution (M:L - 1:2 molar ratio). Formulas for the complexes are: (Ag[C5H3N4S])*½H2O for AgHMP, (Au[C5H3N4S]) for AuIHMP, (Au[C5H3N4S][Cl]2)*2H2O for AuIIIHMP and K(Au[C5H2N4S]2)·2H2O for KAu(MP)2. The AuIHMP and KAu(MP)2 complexes decreased cell viability of HeLa cancer cells in vitro. The IC50 values for AuIHMP and KAu(MP)2 are 3.0 and 30.0 µM, respectively. Anti-M.tuberculosis assays showed a MIC value of 2.24 µM for AuIHMP and 5.12 µM for free MP while AgHMP is active at the concentration 93.2 µM.