Implications of Synthetic Modifications of the Cardiotonic Steroid Lactone Ring on Cytotoxicity.

Na,K-ATPase (NKA) and cardiotonic steroids (CTS) have shown potent cytotoxic and anticancer effects. Here, we have synthesized a series of CTS digoxin derivatives (γ-benzylidene) with substitutions in the lactone ring and evaluated the cytotoxicity caused by digoxin derivatives in tumor and non-tumor cells lines, as well as their effects on NKA. The cytotoxicity assay was determined in HeLa, A549, and WI-26 VA4 after they were treated for 48 h with increased concentrations of CTS. The effects of CTS on NKA activity and immunoblotting of α1 and ß1 isoforms were evaluated at IC50 concentrations in A549 cell membrane. NKA activity from mouse brain cortex was also measured. The majority of CTS exhibited low cytotoxicity in tumor and non-tumor cells, presenting IC50 values at micromolar concentrations, while digoxin showed cytotoxicity at nanomolar concentrations. BD-15 presented the lowest IC50 value (8 µM) in A549 and reduced its NKA activity in 28%. In contrast, BD-7 was the compound that most inhibited NKA (56% inhibition) and presented high IC50 value for A549. In mouse cortex, only BD-15 modulated the enzyme activity in a concentration-dependent inhibition curve. These results demonstrate that the cytotoxicity of these compounds is not related to NKA inhibition. The substitutions in the lactone ring of digoxin led to an increase in the cytotoxic concentration in tumor cells, which may not be interesting for cancer, but it has the advantage of increasing the therapeutic margin of these molecules when compared to classic CTS, and can be used safely in research for other diseases.

Pharmacologic potential of new nitro-compounds as antimicrobial agents against nosocomial pathogens: design, synthesis, and in vitro effectiveness.

Nosocomial infections are an important cause of morbi-mortality worldwide. The increase in the rate of resistance to conventional drugs in these microorganisms has stimulated the search for new therapeutic options. The nitro moiety (NO2) is an important pharmacophore of molecules with high anti-infective activity. We aimed to synthesize new nitro-derivates and to evaluate their antibacterial and anti-Candida potential in vitro. Five compounds [3-nitro-2-phenylchroman-4-ol (3); 3-nitro-2-phenyl-2H-chromene (4a); 3-nitro-2-(4-chlorophenyl)-2H-chromene (4b); 3-nitro-2-(4-fluorophenyl)-2H-chromene (4c), and 3-Nitro-2-(2,3-dichlorophenyl)-2H-chromene (4d)] were efficiently synthesized by Michael-aldol reaction of 2-hydroxybenzaldehyde with nitrostyrene, resulting in one ß-nitro-alcohol (3) and four nitro-olefins (4a-4d). The antibacterial and anti-Candida potentials were evaluated by assaying minimal inhibitory concentration (MIC), minimum fungicidal concentration (MFC), and minimum bactericidal concentration (MBC). Mono-halogenated nitro-compounds (4b and 4c) showed anti-staphylococcal activity with MIC values of 15.6-62.5 µg/mL and MBC of 62.5 µg/mL. However, the activity against Gram-negative strains was showed to be considerably lower and our data suggests that this effect was associated with the outer membrane. Furthermore, nitro-compounds 4c and 4d presented activity against Candida spp. with MIC values ranging from 7.8-31.25 µg/mL and MFC of 15.6-500 µg/mL. In addition, these compounds were able to induce damage in fungal cells increasing the release of intracellular material, which was associated with actions on the cell wall independent of quantitative changes in chitin and ß-glucan. Together, these findings show that nitro-compounds can be exploited as anti-staphylococcal and anti-Candida prototypes.