Antimicrobial and anti-biofilm properties of new taxodione derivative from hairy roots of Salvia austriaca

Microbial biofilm: formation, architecture, antibiotic resistance, and control strategies

The assembly of microorganisms over a surface and their ability to develop resistance against available antibiotics are major concerns of interest. To survive against harsh environmental conditions including known antibiotics, the microorganisms form a unique structure, referred to as biofilm. The mechanism of biofilm formation is triggered and regulated by quorum sensing, hostile environmental conditions, nutrient availability, hydrodynamic conditions, cell-to-cell communication, signaling cascades, and secondary messengers. Antibiotic resistance, escape of microbes from the body's immune system, recalcitrant infections, biofilm-associated deaths, and food spoilage are some of the problems associated with microbial biofilms which pose a threat to humans, veterinary, and food processing sectors. In this review, we focus in detail on biofilm formation, its architecture, composition, genes and signaling cascades involved, and multifold antibiotic resistance exhibited by microorganisms dwelling within biofilms. We also highlight different physical, chemical, and biological biofilm control strategies including those based on plant products. So, this review aims at providing researchers the knowledge regarding recent advances on the mechanisms involved in biofilm formation at the molecular level as well as the emergent method used to get rid of antibiotic-resistant and life-threatening biofilms.

[The mechanisms of taxodione-induced apoptosis in BCR-ABL-positive leukemia cells]

Chronic myeloid leukemia (CML) and acute lymphoblastic leukemia (ALL) are caused by a fusion protein, BCR-ABL, which induces cellular transformation by activating the signaling molecules, STAT5 and Akt. The specific BCR-ABL inhibitors including imatinib, nilotinib, and dasatinib, are clinically utilized in the treatment with CML and ALL patients. Although these BCR-ABL inhibitors are initially successful in the treatment of leukemia, many patients develop drug resistance due to the appearance of the gatekeeper mutation of BCR-ABL, T315I. Recently, we found that taxodione, a quinone methide diterpene isolated from a conifer, Taxodium distichum, significantly induced apoptosis in human myelogenous leukemia-derived K562 cells, which is positive for the bcr-abl gene. Taxodione reduced the activities of mitochondrial respiratory chain complex III, leading to the production of reactive oxygen species (ROS). An antioxidant agent, N-acetylcysteine (NAC), canceled taxodione-induced ROS production and apoptotic cell death, suggesting that taxodione induced apoptosis through ROS accumulation. Furthermore, in K562 cells treated with taxodione, BCR-ABL, STAT5 and Akt were sequestered in mitochondrial fraction, and their localization changes decrease their abilities to stimulate cell proliferation. Strikingly, NAC canceled these taxodione-caused inhibition of BCR-ABL, STAT5 and Akt. In addition, taxodione significantly induced apoptosis in transformed Ba/F3 cells by not only BCR-ABL but also T315I-mutated BCR-ABL through the generation of ROS, suggesting that taxodione has potential as anti-tumor drug with high efficacy to overcome BCR-ABL T315I mutation-mediated resistance in leukemia cells. It's also expected that these knowledge becomes an important clue in the development of anti-cancer drugs against the broad range of tumors.

Fine-tuning of the hydrophobicity of caffeic acid: studies on the antimicrobial activity against Staphylococcus aureus and Escherichia coli

Caffeic acid derivatives are proposed to act as cell permeabilizers, inducing membrane alterations, causing rupture with potassium leakage, particularly on the Gram positive bacterium, and consequent cell death.

Saponins of Trifolium spp. aerial parts as modulators of Candida albicans virulence attributes

The aim was to provide the insight into the biology of C. albicans influenced by undescribed yet properties of saponin-rich (80%–98%) fractions (SAPFs), isolated from extracts of Trifolium alexandrinum, T. incarnatum, T. resupinatum var. resupinatum aerial parts. Their concentrations below 0.5 mg/mL were arbitrarily considered as subMICs for C. albicans ATCC 10231 and were further used. SAPFs affected yeast enzymatic activity, lowered tolerance to the oxidative stress, to the osmotic stress and to the action of the cell wall disrupting agent. In their presence, germ tubes formation was significantly and irreversibly inhibited, as well as Candida invasive capacity. The evaluation of SAPFs interactions with anti-mycotics showed synergistic activity, mainly with azoles. Fluconazole MIC was lowered—susceptible C. albicans ATCC 10231 was more susceptible, and resistant C. glabrata (clinical strain) become more susceptible (eightfold). Moreover, the tested samples showed no hemolytic activity and at the concentrations up to 0.5 mg/mL did not reduce viability of fibroblasts L929. This study provided the original evidence that SAPFs of Trifolium spp. aerial part exhibit significant antimicrobial activity, by reduce the expression/quantity of important Candida virulence factors and have good potential for the development of novel antifungal products supporting classic drugs.

Taxodione and arenarone inhibit farnesyl diphosphate synthase by binding to the isopentenyl diphosphate site

We used in silico methods to screen a library of 1,013 compounds for possible binding to the allosteric site in farnesyl diphosphate synthase (FPPS). Two of the 50 predicted hits had activity against either human FPPS (HsFPPS) or Trypanosoma brucei FPPS (TbFPPS), the most active being the quinone methide celastrol (IC50 versus TbFPPS ∼ 20 µM). Two rounds of similarity searching and activity testing then resulted in three leads that were active against HsFPPS with IC50 values in the range of ∼ 1-3 µM (as compared with ∼ 0.5 µM for the bisphosphonate inhibitor, zoledronate). The three leads were the quinone methides taxodone and taxodione and the quinone arenarone, compounds with known antibacterial and/or antitumor activity. We then obtained X-ray crystal structures of HsFPPS with taxodione+zoledronate, arenarone+zoledronate, and taxodione alone. In the zoledronate-containing structures, taxodione and arenarone bound solely to the homoallylic (isopentenyl diphosphate, IPP) site, not to the allosteric site, whereas zoledronate bound via Mg(2+) to the same site as seen in other bisphosphonate-containing structures. In the taxodione-alone structure, one taxodione bound to the same site as seen in the taxodione+zoledronate structure, but the second located to a more surface-exposed site. In differential scanning calorimetry experiments, taxodione and arenarone broadened the native-to-unfolded thermal transition (Tm), quite different to the large increases in ΔTm seen with biphosphonate inhibitors. The results identify new classes of FPPS inhibitors, diterpenoids and sesquiterpenoids, that bind to the IPP site and may be of interest as anticancer and antiinfective drug leads.