Digoxin Derivatives Sensitize a Saccharomyces cerevisiae Mutant Strain to Fluconazole by Inhibiting Pdr5p.

The poor outcome of treatments for fungal infections is a consequence of the increasing incidence of resistance to antifungal agents, mainly due to the overexpression of efflux pumps. To surpass this mechanism of resistance, a substance able to inhibit these pumps could be administered in association with antifungals. Saccharomyces cerevisiae possesses an efflux pump (Pdr5p) homologue to those found in pathogenic yeast. Digoxin is a natural product that inhibits Na+, K+-ATPase. The aim of this study was to evaluate whether digoxin and its derivatives (i.e., DGB, digoxin benzylidene) can inhibit Pdr5p, reversing the resistance to fluconazole in yeasts. An S. cerevisiae mutant strain that overexpresses Pdr5p was used in the assays. The effects of the compounds on yeast growth, efflux activity, and Pdr5p ATPase activity were measured. All derivatives enhanced the antifungal activity of fluconazole against S. cerevisiae, in comparison to fluconazole alone, with FICI values ranging from 0.031 to 0.500. DGB 1 and DGB 3 presented combined effects with fluconazole against a Candida albicans strain, with fractional inhibitory concentration index (FICI) values of 0.625 and 0.281, respectively The compounds also inhibited the efflux of rhodamine 6G and Pdr5p ATPase activity, with IC50 values ranging from 0.41 µM to 3.72 µM. The results suggest that digoxin derivatives impair Pdr5p activity. Considering the homology between Pdr5p and efflux pumps from pathogenic fungi, these compounds are potential candidates to be used in association with fluconazole to treat resistant fungal infections.

Insecticidal activity of the essential oil of Piper corcovadensis leaves and its major compound (1-butyl-3,4-methylenedioxybenzene) against the maize weevil, Sitophilus zeamais.

BACKGROUND: Sitophilus zeamais is one of the most economically impactful pests, attacking various grains and processed foods. Control of this insect has been achieved using synthetic insecticides, exacerbated and careless use of which has led to the development of resistant insect populations, toxicity to non-target organisms and environmental contamination. In this study, Piper corcovadensis leaf essential oil (PcLEO) and its major compound, 1-butyl-3,4-methylenedioxybenzene (BMDB), were investigated as alternative insecticidal agents against S. zeamais. RESULTS: Characterization of PcLEO showed the presence of 40 compounds. The major components were the phenylpropanoid BMDB (35.77%) and the monoterpenes α-pinene (14.95%) and terpinolene (6.23%). PcLEO and BMDB were toxic by fumigation (half-maximal lethal concentration [LC50 ]: 9.46 and 0.85 µl L-1 of air, respectively), by contact (half-maximal lethal dose [LD50 ]: 9.38 and 6.16 µg g-1 of insect, respectively) and ingestion (LC50 : 16.04 and 14.30 mg g-1 , respectively). In the ingestion test, both PcLEO and BMDB promoted the loss of insect biomass and had a strong deterrent effect. In addition, both were able to inhibit trypsin and α-amylase activities. CONCLUSION: PcLEO and BMDB exhibited insecticidal activity against S. zeamais, with a toxic effect by fumigation, contact and ingestion, in addition to food deterrence and inhibiting trypsin and α-amylase activities, suggesting their potential for use in the control of this pest.

Streptomyces hygroscopicus UFPEDA 3370: A valuable source of the potent cytotoxic agent nigericin and its evaluation against human colorectal cancer cells.

Streptomyces hygroscopicus UFPEDA 3370 was fermented in submerged cultivation and the biomass extract was partitioned, obtaining a fraction purified named EB1. After purification of EB1 fraction, nigericin free acid was obtained and identified. Nigericin presented cytotoxic activity against several cancer cell lines, being most active against HL-60 (human leukemia) and HCT-116 (human colon carcinoma) cell lines, presenting IC50 and (IS) values: 0.0014 µM, (30.0) and 0.0138 µM (3.0), respectively. On HCT-116, nigericin caused apoptosis and autophagy. In this study, nigericin was also screened both in vitro and in silico against a panel of cancer-related kinases. Nigericin was able to inhibit both JAK3 and GSK-3ß kinases in vitro and its binding affinities were mapped through the intermolecular interactions with each target in silico.

Furan inhibitory activity against tyrosinase and impact on B16F10 cell toxicity.

Many skin disorders and diseases are related to tyrosinase activity, in particular, due to the vital role played by this enzyme in the melanogenic process. Although numerous natural and synthetic tyrosinase inhibitors have been published, substantial efforts have been made to understand the influence of tyrosinase inhibition on the viability of melanoma cells. Here, we assess the impact of two keto-derivatives: 2-acetyl-furan (F1), furfural-acetone (F2), and two carboxyl-derivatives: 2-furan-acrylic acid (F3), 5-methyl-2-furan-acrylic acid (F4), on the mushroom tyrosinase (mTYR) activity, by applying spectroscopic, kinetic and theoretical techniques. From an exploratory and theoretical point of view, results indicated that albeit all furans bind tightly to and inhibit mTYR very efficient, carboxyl-furan derivatives presented best inhibitory activities than keto- derivatives and performed the inhibition competitively and reversible. Moreover, we examined the influence of carboxyl derivative on the viability of melanoma cells. Results expose differential toxicity of these furan derivatives, which indicates a piece of evidence that furan inhibition activity may be related to its toxicity against B16F10 cells.