Pharmacokinetic study of Tdp1 inhibitor resulted in a significant increase in antitumor effect in the treatment of Lewis lung carcinoma in mice by its combination with topotecan

We have previously shown that the Tdp1 inhibitor, enamine derivative of usnic acid, the agent OL9-116, enhances the antitumor activity of topotecan. In the present study, we developed and validated LC-MS/MS method for the quantification of OL9-116 in mouse whole blood and studied pharmacokinetics of the agent. The substance OL9-116 was shown to be stable in the whole blood in vitro. Sample preparation included two steps: mixing 10 µL of a blood sample with 10 µL of 0.2 M ZnSO4 aqueous solution, followed by protein precipitation with 100 µL of acetonitrile containing internal standard. Quantification of the compound was performed using SCIEX 6500 QTRAP mass spectrometer in MRM mode following chromatographic separation on a C8 reversed-phase column. The method was validated in terms of selectivity, linearity, accuracy, precision, recovery, and stability of the prepared sample. When the agent OL9-116 was administered intragastrically at a dose of 150 mg/kg, the maximum concentration in the blood (about 5000 ng/mL) was reached after 2-4 h followed by the distribution and elimination of the compound. A study of the antitumor activity of a combination of OL9-116 and topotecan against Lewis lung carcinoma revealed that administration of topotecan 3 h after OL9-116 resulted in the most pronounced antitumor effect compared to simultaneous or individual administration of both compounds.

Usnic Acid Derivatives Inhibit DNA Repair Enzymes Tyrosyl-DNA Phosphodiesterases 1 and 2 and Act as Potential Anticancer Agents

Tyrosyl-DNA phosphodiesterase 1 and 2 (Tdp1 and Tdp2) are DNA repair enzymes that repair DNA damage caused by various agents, including anticancer drugs. Thus, these enzymes resist anticancer therapy and could be the reason for resistance to such widely used drugs such as topotecan and etoposide. In the present work, we found compounds capable of inhibiting both enzymes among derivatives of (-)-usnic acid. Both (+)- and (-)-enantiomers of compounds act equally effectively against Tdp1 with IC50 values in the range of 0.02-0.2 μM; only (-)-enantiomers inhibited Tdp2 with IC50 values in the range of 6-9 μM. Surprisingly, the compounds protect HEK293FT wild type cells from the cytotoxic effect of etoposide (CC50 3.0-3.9 μM in the presence of compounds and 2.4 μM the presence of DMSO) but potentiate it against Tdp2 knockout cells (CC50 1.2-1.6 μM in the presence of compounds against 2.3 μM in the presence of DMSO). We assume that the sensitizing effect of the compounds in the absence of Tdp2 is associated with the effective inhibition of Tdp1, which could take over the functions of Tdp2.

The pyrazole derivative of usnic acid inhibits the proliferation of pancreatic cancer cells in vitro and in vivo

BACKGROUND

Pancreatic cancer is one of the leading causes of cancer death in Western societies. Its late diagnosis and resistance to chemotherapies result in a high mortality rate; thus, the development of more effective therapies for the treatment of pancreatic cancer is strongly warranted. Usnic acid (UA) is a secondary metabolite of lichens that shows modest antiproliferative activity toward cancer cells. Recently, we reported the synthesis of a UA pyrazole derivative, named 5, which was more active than the parent compound toward cervical cancer cells. Here, its anticancer potential has been evaluated in detail in other cancer cells, particularly pancreatic cancer cells.

METHODS

The impact of UA and derivative 5 on cell viability, morphology, cell cycle, and death was assessed using the MTT test, electron microscopy, flow cytometry, and immunoblotting, respectively. The calcium ions level was detected fluorometrically. In vivo, the anticancer activity of 5 was evaluated in a murine xenograft model.

RESULTS

Derivative 5 inhibited the viability of different cancer cells. Noncancerous cells were less sensitive. It induced the release of calcium ions from the endoplasmic reticulum (ER) and ER stress, which was manifested by cell vacuolization. It was accompanied by G0/G1 cell cycle arrest and cell death of pancreatic cancer cells. When applied to nude mice with xenografted pancreatic cancer cells, 5 inhibited tumor growth, with no signs of kidney or liver toxicity.

CONCLUSIONS

UA derivative 5 is superior to UA inhibiting the growth and proliferation of pancreatic cancer cells. ER stress exaggeration is a mechanism underlying the activity of derivative 5.

Bioactive Lichen Secondary Metabolites and Their Presence in Species from Chile

Lichens are symbiotic organisms composed of at least one fungal and one algal species. They are found in different environments around the world, even in the poles and deserts. Some species can withstand extreme abiotic conditions, including radiation and the vacuum of space. Their chemistry is mainly due to the fungal metabolism and the production of several secondary metabolites with biological activity, which have been isolated due to an increasing interest from the pharmaceutical community. However, beyond the experimental data, little is known about their mechanisms of action and the potential pharmaceutical use of these kinds of molecules, especially the ones isolated from lesser-known species and/or lesser-studied countries. The main objective of this review is to analyze the bibliographical data of the biological activity of secondary metabolites from lichens, identifying the possible mechanisms of action and lichen species from Chile. We carried out a bibliographic revision of different scientific articles in order to collect all necessary information on the biological activity of the metabolites of these lichen species. For this, validated databases were used. We found the most recent reports where in vitro and in vivo studies have demonstrated the biological properties of these metabolites. The biological activity, namely anticancer, antioxidant, and anti-inflammatory activity, of 26 secondary metabolites are described, as well as their reported molecular mechanisms. The most notable metabolites found in this review were usnic acid, atranorin, protolichesterinic acid, and lobaric acid. Usnic acid was the most investigated metabolite, in addition to undergoing toxicological and pharmacological studies, where a hepatotoxicity effect was reported due to uncoupling oxidative phosphorylation. Additionally, no major studies have been made to validate the pharmacological application of these metabolites, and few advancements have been made in their artificial growth in bioreactors. Despite the described biological activities, there is little support to consider these metabolites in pharmaceutical formulations or to evaluate them in clinical trials. Nevertheless, it is important to carry out further studies regarding their possible human health effects. These lichen secondary metabolites present a promising research opportunity to find new pharmaceutical molecules due to their bioactive properties.

Natural Products and Their Derivatives as Inhibitors of the DNA Repair Enzyme Tyrosyl-DNA Phosphodiesterase 1

Tyrosyl-DNA phosphodiesterase 1 (TDP1) is an important repair enzyme that removes various covalent adducts from the 3' end of DNA. Particularly, covalent complexes of topoisomerase 1 (TOP1) with DNA stabilized by DNA damage or by various chemical agents are an examples of such adducts. Anticancer drugs such as the TOP1 poisons topotecan and irinotecan are responsible for the stabilization of these complexes. TDP1 neutralizes the effect of these anticancer drugs, eliminating the DNA adducts. Therefore, the inhibition of TDP1 can sensitize tumor cells to the action of TOP1 poisons. This review contains information about methods for determining the TDP1 activity, as well as describing the inhibitors of these enzyme derivatives of natural biologically active substances, such as aminoglycosides, nucleosides, polyphenolic compounds, and terpenoids. Data on the efficiency of combined inhibition of TOP1 and TDP1 in vitro and in vivo are presented.

Divergent reactivity of usnic acid and evaluation of its derivatives for antiproliferative activity against cancer cells

Natural products continue to be an inspiration for new drugs to treat debilitating diseases such as cancer. Usnic acid is a secondary metabolite isolated predominately from lichen species and has been shown to exhibit antiproliferative properties, however its application is limited by poor drug-like properties and low specificity. We report our work on investigating the reactivity of usnic acid for incorporating heterocyclic rings and the divergent reactivity that can be obtained by simply altering the reaction solvent and temperature. The synthesised derivatives were then tested against HeLa cancer cells for their antiproliferative properties. A number of promising compounds were obtained including 4, 5 and 9 that showed an IC₅₀ of 878, 311 and 116 nM, respectively, against HeLa cancer cells after 48 h of treatment.

Usnic Acid-Mediated Exchange of Protons for Divalent Metal Cations across Lipid Membranes: Relevance to Mitochondrial Uncoupling

Usnic acid (UA), a unique lichen metabolite, is a protonophoric uncoupler of oxidative phosphorylation, widely known as a weight-loss dietary supplement. In contrast to conventional proton-shuttling mitochondrial uncouplers, UA was found to carry protons across lipid membranes via the induction of an electrogenic proton exchange for calcium or magnesium cations. Here, we evaluated the ability of various divalent metal cations to stimulate a proton transport through both planar and vesicular bilayer lipid membranes by measuring the transmembrane electrical current and fluorescence-detected pH gradient dissipation in pyranine-loaded liposomes, respectively. Thus, we obtained the following selectivity series of calcium, magnesium, zinc, manganese and copper cations: Zn2+ > Mn2+ > Mg2+ > Ca2+ >> Cu2+. Remarkably, Cu2+ appeared to suppress the UA-mediated proton transport in both lipid membrane systems. The data on the divalent metal cation/proton exchange were supported by circular dichroism spectroscopy of UA in the presence of the corresponding cations.

Usnic Acid Isolated from Usnea antarctica (Du Rietz) Reduced In Vitro Angiogenesis in VEGF- and bFGF-Stimulated HUVECs and Ex Ovo in Quail Chorioallantoic Membrane (CAM) Assay

Simple Summary

Anti-angiogenic therapy, a promising strategy against cancer progression, is limited by drug resistance. Natural plants, such as secondary metabolites of lichens, may represent an appropriate strategy to increase the effectiveness of conventional therapies and overcome resistance to anti-angiogenic therapy if combined with existing chemotherapy. Accordingly, our study was designed to determine the potential anti-angiogenic effect of usnic acid, a secondary metabolite of lichens, on VEGF- and bFGF-stimulated HUVECs as well as in quail chorioallantoic membrane assays, which were supplemented by histological sections of CAM-affected layers.

Abstract

Natural products include a diverse set of compounds of drug discovery that are currently being actively used to target tumor angiogenesis. In the present study, we evaluated the anti-angiogenic activities of secondary metabolite usnic acid isolated from Usena antarctica. We investigated the in vitro effects on proliferation, migration, and tube formation of VEGF- and bFGF-stimulated HUVECs. Ex ovo anti-angiogenic activity was evaluated using the CAM assay. Our findings demonstrated that usnic acid in the concentration of 33.57 µM inhibited VEGF (25 ng/mL) and bFGF (30 ng/mL)-induced HUVECs proliferation, migration, and tube formation. The ex ovo CAM model was used to confirm the results obtained from in vitro studies. VEGF- and bFGF-induced vessel formation was inhibited by usnic acid after 72 h in over 2-fold higher concentrations compared to in vitro. Subsequently, histological sections of affected chorioallantoic membranes were stained with hematoxylin–eosin and alcian blue to determine the number and diameter of vessels as well as the thickness of the individual CAM layers (ectoderm, mesoderm, endoderm). Usnic acid was able to suppress the formation of VEGF- and bFGF-induced vessels with a diameter of less than 100 μm, which was demonstrated by the reduction of mesoderm thickness as well.

Ribosome-Directed Therapies in Cancer

The human ribosomes are the cellular machines that participate in protein synthesis, which is deeply affected during cancer transformation by different oncoproteins and is shown to provide cancer cell proliferation and therefore biomass. Cancer diseases are associated with an increase in ribosome biogenesis and mutation of ribosomal proteins. The ribosome represents an attractive anti-cancer therapy target and several strategies are used to identify specific drugs. Here we review the role of different drugs that may decrease ribosome biogenesis and cancer cell proliferation.

The Isoxazole Derivative of Usnic Acid Induces an ER Stress Response in Breast Cancer Cells That Leads to Paraptosis-like Cell Death

Derivatives of usnic acid (UA), a secondary metabolite from lichens, were synthesized to improve its anticancer activity and selectivity. Recently we reported the synthesis and activity of an UA isoxazole derivative, named 2b, against cancer cells of different origins. Herein, the molecular mechanisms underlying its activity and efficacy in vivo were tested. The viability of breast cancer or normal cells has been tested using an MTT assay. Cell and organelle morphology was analyzed using light, electron and fluorescence microscopy. Gene expression was evaluated by RNAseq and protein levels were evaluated by Western blotting. In vivo anticancer activity was evaluated in a mice xenograft model. We found that 2b induced massive vacuolization which originated from the endoplasmic reticulum (ER). ER stress markers were upregulated both at the mRNA and protein levels. ER stress was caused by the release of Ca²⁺ ions from the ER by IP3R channels which was mediated, at least partly, by phospholipase C (PLC)-synthetized 1,4,5-inositol triphosphate (IP3). ER stress led to cell death with features of apoptosis and paraptosis. When applied to nude mice with xenografted breast cancer cells, 2b stopped tumour growth. In mice treated with 2b, vacuolization was observed in tumour cells, but not in other organs. This study shows that the antiproliferative activity of 2b relates to the induction of ER stress in cancer, not in healthy, cells and it leads to breast cancer cell death in vitro and in vivo.

The influence of an enamine usnic acid derivative (a tyrosyl-DNA phosphodiesterase 1 inhibitor) on the therapeutic effect of topotecan against transplanted tumors in vivo

Tyrosyl-DNA phosphodiesterase 1 (Tdp1) is a repair enzyme for 3'-end DNA lesions, predominantly stalled DNA-topoisomerase 1 (Top1) cleavage complexes. Tdp1 is a promising target for anticancer therapy based on DNA damage caused by Top1 poisoning. Earlier, we have reported about usnic acid enamine derivatives that are Tdp1 inhibitors sensitizing tumor cells to the action of Top1 poison (Zakharenko in J Nat Prod 79:2961-2967, 2016). In the present work, we showed a sensitizing effect of an enamine derivative of usnic acid (when administered intragastrically) on Lewis lung carcinoma in mice in combination with topotecan (TPT, Top1 poison used in the clinic). In the presence of the usnic acid derivative, both the volume of the primary tumor and the number of metastases significantly diminished. The absence of acute toxicity of this compound was demonstrated, as was the importance of the method of its administration for the manifestation of the sensitizing properties.

In Vitro Anticancer Activity and Oxidative Stress Biomarkers Status Determined by Usnea barbata (L.) F.H. Wigg. Dry Extracts

Lichens represent an important resource for common traditional medicines due to their numerous metabolites that can exert diverse pharmacological activities including anticancer effects. To find new anticancer compounds with fewer side effects and low tumor resistance, a bioprospective study of Usnea barbata (L.) F.H. Wigg. (U. barbata), a lichen from the Călimani Mountains (Suceava county, Romania) was performed. The aim of this research was to investigate the anticancer potential, morphologic changes, wound healing property, clonogenesis, and oxidative stress biomarker status of four extracts of U. barbata in different solvents (methanol, ethanol, acetone, and ethyl acetate), and also of usnic acid (UA) as a positive control on the CAL-27 (ATCC^® CRL-2095™) oral squamous carcinoma (OSCC) cell line and V79 (ATCC^® CCL-93™) lung fibroblasts as normal cells. Using the MTT assay and according to IC₅₀ values, it was found that the most potent anticancer property was displayed by acetone and ethyl acetate extracts. All U. barbata extracts determined morphological modifications (losing adhesion capacity, membrane shrinkage, formation of abnormal cellular wrinkles, and vacuolization) with higher intensity in tumor cells than in normal ones. The most intense anti-migration effect was established in the acetone extract treatment. The clonogenic assay showed that some U. barbata extracts decreased the ability of cancer cells to form colonies compared to untreated cells, suggesting a potential anti-tumorigenic property of the tested extracts. Therefore, all the U. barbata extracts manifest anticancer activity of different intensity, based, at least partially, on an imbalance in antioxidant defense mechanisms, causing oxidative stress.

New Hybrid Compounds Combining Fragments of Usnic Acid and Monoterpenoids for Effective Tyrosyl-DNA Phosphodiesterase 1 Inhibition

Usnic acid (UA) is a secondary metabolite of lichens that exhibits a wide range of biological activities. Previously, we found that UA derivatives are effective inhibitors of tyrosyl-DNA phosphodiesterase 1 (TDP1). It can remove covalent complex DNA-topoisomerase 1 (TOP1) stabilized by the TOP1 inhibitor topotecan, neutralizing the effect of the drugs. TDP1 removes damage at the 3′ end of DNA caused by other anticancer agents. Thus, TDP1 is a promising therapeutic target for the development of drug combinations with topotecan, as well as other drugs for cancer treatment. Ten new UA enamino derivatives with variation in the terpene fragment and substituent of the UA backbone were synthesized and tested as TDP1 inhibitors. Four compounds, 11a-d, had IC₅₀ values in the 0.23–0.40 μM range. Molecular modelling showed that 11a-d, with relatively short aliphatic chains, fit to the important binding domains. The intrinsic cytotoxicity of 11a-d was tested on two human cell lines. The compounds had low cytotoxicity with CC₅₀ ≥ 60 μM for both cell lines. 11a and 11c had high inhibition efficacy and low cytotoxicity, and they enhanced topotecan’s cytotoxicity in cancerous HeLa cells but reduced it in the non-cancerous HEK293A cells. This “protective” effect from topotecan on non-cancerous cells requires further investigation.

Application of enzyme probiotic drug developed based on microorganisms of the rumen of reindeer (Rangifer tarandus) in feeding cows

In the current conditions of intense technologies of milk production, the feeding of dairy cows is aimed at providing fast rates of growth and maximum productivity over a short period. However, such systems of diets often have negative effects on the health of the animals as a result of metabolism malfunctioning. The present study was conducted to assess the influence of the enzyme probiotic preparation Rumit, developed based on cellulolytic bacteria isolated from the rumen of reindeer, on dairy activity, food intake, density of ciliate fauna of the rumen, feeding activity, and also metabolic profile and the level of natural resistance of newly-calved heifers. To conduct the experiment, we composed two groups (control and experimental) of first-calf heifers with 12 individuals in their first 100 days of lactation after calving. The first-calf heifers of the experimental group, in addition to the main diet, received the preparation in the amount of 50 g per individual daily in the lunch time feeding for 90 days. Inclusion of the probiotic increased the dairy productivity, particularly a 3.1 kg increase in the average yield of daily 4%-fat milk, 9.6 kg in the butterfat output, and 7.7 kg in that of dairy protein. With increase in dairy productivity, a 0.09 EFU (energy fodder units, equals 10 MJ) decrease was observed in energy expenditure for 1 kg of milk. Intake of the probiotic led to increase in the index of nutritional activity by 0.03 units and increase in the density of ciliates by 155, 900 individuals/mL. Use of the biopreparation had a positive effect on the metabolic processes in the organism of heifers. The animals of the experimental group were observed to have an increase in the content of the total protein in the blood, 12.5% decrease in the urea, and glucose concentration reached the normative values. In the first-calf heifers that had received the food supplement in addition to their diet, the physiological parameters of health normalized and the protective abilities of the organism activated, the pulse and respiration frequencies increased (by 3.8% and 6.6%), the phagocytic index grew by 30.2%, and the absorptive ability of neutrophils increased by 40%. Thus, enzyme probiotic preparation Rumit confirmed its efficiency when fed to newly-calved heifers.

Usnic Acid Conjugates with Monoterpenoids as Potent Tyrosyl-DNA Phosphodiesterase 1 Inhibitors

Hybrid molecules created from different pharmacophores of natural and synthetic equivalents are successfully used in pharmaceutical practice. One promising target for anticancer therapy is tyrosyl-DNA phosphodiesterase 1 (Tdp1) because it can repair DNA lesions caused by DNA-topoisomerase 1 (Top1) inhibitors, resulting in drug resistance. In this study, new hybrid compounds were synthesized by combining the pharmacophoric moiety of a set of natural compounds with inhibitory properties against Tdp1, particularly, phenolic usnic acid and a set of different monoterpenoid fragments. These fragments were connected through a hydrazinothiazole linker. The inhibitory properties of the new compounds mainly depended on the structure of the terpenoid moieties. The two most potent compounds, 9a and 9b, were synthesized from citral and citronellal, which contain acyclic fragments with IC₅₀ values in the range of 10-16 nM. Some synthesized derivatives showed low cytotoxicity against HeLa cells and increased the effect of the Top1 inhibitor topotecan in vitro by three to seven times. These derivatives may be considered as potential agents for the development of anticancer therapies when combined with Top1 inhibitors.

Synthesis and antiproliferative activity of novel (+)- usnic acid analogues

Twenty one novel (+)- usnic acid-based analogues belonging to three classes such as enamines, imines, and pyrazoles were synthesized. All the synthesized compounds were characterized by their spectral data (¹H NMR, ¹³C NMR, IR, and HRMS). The synthesized compounds were evaluated for their antiproliferative activity against a panel of four human cancer cell lines including HeLa (cervix), MDA-MB-231 (breast), A549 (lung), and MiaPaca (pancreas) by employing SRB cell proliferation assay. Screening results indicated that all synthesized compounds showed enhanced activity than the parent compound. Most significantly, compounds 2e and 4a showed potent antiproliferative activity against all the cancer cell lines tested. Compounds 2e and 4a arrested the cell cycle in G2/M phase and induced apoptosis in HeLa cells. In view of significant antiproliferative activity, compounds 2e and 4a can be considered as lead molecules for further development.[Formula: see text].

New Hydrazinothiazole Derivatives of Usnic Acid as Potent Tdp1 Inhibitors

Tyrosyl-DNA phosphodiesterase 1 (Tdp1) is a promising therapeutic target in cancer therapy. Combination chemotherapy using Tdp1 inhibitors as a component can potentially improve therapeutic response to many chemotherapeutic regimes. A new set of usnic acid derivatives with hydrazonothiazole pharmacophore moieties were synthesized and evaluated as Tdp1 inhibitors. Most of these compounds were found to be potent inhibitors with IC₅₀ values in the low nanomolar range. The activity of the compounds was verified by binding experiments and supported by molecular modeling. The ability of the most effective inhibitors, used at non-toxic concentrations, to sensitize tumors to the anticancer drug topotecan was also demonstrated. The order of administration of the inhibitor and topotecan on their synergistic effect was studied, suggesting that prior or simultaneous introduction of the inhibitor with topotecan is the most effective.

Synthesis of Usnic Acid Derivatives and Evaluation of Their Antiproliferative Activity against Cancer Cells

Usnic acid is a secondary metabolite abundantly found in lichens, for which promising cytotoxic and antitumor potential has been shown. However, knowledge concerning activities of its derivatives is limited. Herein, a series of usnic acid derivatives were synthesized and their antiproliferative potency against cancer cells of different origin was assessed. Some of the synthesized compounds were more active than usnic acid. Compounds 2a and 2b inhibited survival of all tested cancer cell lines in a dose- and time-dependent manner. Their IC₅₀ values after 48 h of treatment were ca. 3 μM for MCF-7 and PC-3 cells and 1 μM for HeLa cells, while 3a and 3b revealed antiproliferative activity only against HeLa cells. All active usnic acid derivatives induced G0/G1 arrest and a drop in the fraction of HeLa cells in the S and G2/M phases. Compounds 2a and 2b decreased the clonogenic potential of the cancer cells evaluated and induced cell cycle arrest at the G0/G1 phase and apoptosis in MCF-7 cells. Moreover, they induced massive cytoplasmic vacuolization, which was associated with elevated dynein-dependent endocytosis, a process that has not been reported for usnic acid and indicates a novel mechanism of action of its synthetic derivatives. This work also shows that naturally occurring usnic acids are promising lead compounds for the synthesis of derivatives with more favorable properties against cancer cells.

Inhibiting eukaryotic ribosome biogenesis

BACKGROUND

Ribosome biogenesis is a central process in every growing cell. In eukaryotes, it requires more than 250 non-ribosomal assembly factors, most of which are essential. Despite this large repertoire of potential targets, only very few chemical inhibitors of ribosome biogenesis are known so far. Such inhibitors are valuable tools to study this highly dynamic process and elucidate mechanistic details of individual maturation steps. Moreover, ribosome biogenesis is of particular importance for fast proliferating cells, suggesting its inhibition could be a valid strategy for treatment of tumors or infections.

RESULTS

We systematically screened ~ 1000 substances for inhibitory effects on ribosome biogenesis using a microscopy-based screen scoring ribosomal subunit export defects. We identified 128 compounds inhibiting maturation of either the small or the large ribosomal subunit or both. Northern blot analysis demonstrates that these inhibitors cause a broad spectrum of different rRNA processing defects.

CONCLUSIONS

Our findings show that the individual inhibitors affect a wide range of different maturation steps within the ribosome biogenesis pathway. Our results provide for the first time a comprehensive set of inhibitors to study ribosome biogenesis by chemical inhibition of individual maturation steps and establish the process as promising druggable pathway for chemical intervention.

Dual DNA topoisomerase 1 and tyrosyl-DNA phosphodiesterase 1 inhibition for improved anticancer activity

Tyrosyl-DNA phosphodiesterase 1 (Tdp1) is a DNA repair enzyme that catalyzes the hydrolysis of the phosphodiester bond in the DNA-topoisomerase 1 (Top1) covalent complex and repairs some other 3'-end DNA adducts. Currently, Tdp1 functions as an important target in cancer drug design owing to its ability to break down various DNA adducts induced by chemotherapeutics. Tdp1 inhibitors may sensitize tumor cells to the action of Top1 poisons, thereby potentiating their effects. This mini-review summarizes findings from studies reporting the combined inhibition of Top1 and Tdp1. Two different approaches have been considered for developing such drug precursors.

Novel tyrosyl-DNA phosphodiesterase 1 inhibitors enhance the therapeutic impact of topoteсan on in vivo tumor models

The druggability of the tyrosyl-DNA phosphodiesterase 1 (Tdp1) enzyme was investigated in conjunction with topoisomerase 1 inhibition. A novel class of thiazole, aminothiazole and hydrazonothiazole usnic acid derivatives was synthesized and evaluated as Tdp1 inhibitors and their ability to sensitize tumors to topotecan, a topoisomerase inhibitor in clinical use. Of all the compounds tested, four hydrazinothiazole derivatives, 20c, 20d, 20h and 20i, inhibited the enzyme in the nanomolar range. The activity of the compounds was verified by affinity experiments as well as supported by molecular modelling. The most effective Tdp1 inhibitor, 20d, was ton-toxic and increased the effect of topotecan both in vitro and in vivo in the Lewis lung carcinoma model. Furthermore, 20d showed significant increase in the antitumor and antimetastatic effect of topotecan in mice. The results presented here justify compound 20d to be considered as a drug lead for antitumor therapy.

Biogenic fabrication and characterization of silver nanoparticles using aqueous-ethanolic extract of lichen (Usnea longissima) and their antimicrobial activity

Background

Biogenic fabrication of silver nanoparticles from naturally occurring biomaterials provides an alternative, eco-friendly and cost-effective means of obtaining nanoparticles. It is a favourite pursuit of all scientists and has gained popularity because it prevents the environment from pollution. Our main objective to take up this project is to fabricate silver nanoparticles from lichen, Usnea longissima and explore their properties. In the present study, we report a benign method of biosynthesis of silver nanoparticles from aqueous-ethanolic extract of Usnea longissima and their characterization by ultraviolet–visible (UV-vis), Fourier transform infrared (FTIR) spectroscopy, transmission electron microscopy (TEM) and scanning electron microscopy (SEM) analyses. Silver nanoparticles thus obtained were tested for antimicrobial activity against gram positive bacteria and gram negative bacteria.

Results

Formation of silver nanoparticles was confirmed by the appearance of an absorption band at 400 nm in the UV-vis spectrum of the colloidal solution containing both the nanoparticles and U. longissima extract. Poly(ethylene glycol) coated silver nanoparticles showed additional absorption peaks at 424 and 450 nm. FTIR spectrum showed the involvement of amines, usnic acids, phenols, aldehydes and ketones in the reduction of silver ions to silver nanoparticles. Morphological studies showed three types of nanoparticles with an abundance of spherical shaped silver nanoparticles of 9.40–11.23 nm. Their average hydrodynamic diameter is 437.1 nm. Results of in vitro antibacterial activity of silver nanoparticles against Staphylococcus aureus, Streptococcus mutans, Streptococcus pyrogenes, Streptococcus viridans, Corynebacterium xerosis, Corynebacterium diphtheriae (gram positive bacteria) and Escherichia coli, Klebsiella pneuomoniae and Pseudomonas aeruginosa (gram negative bacteria) showed that it was effective against tested bacterial strains. However, S. mutans, C. diphtheriae and P. aeruginosa were resistant to silver nanoparticles.

Conclusion

Lichens are rarely exploited for the fabrication of silver nanoparticles. In the present work the lichen acts as reducing as well as capping agent. They can therefore, be used to synthesize metal nanoparticles and their size may be controlled by monitoring the concentration of extract and metal ions. Since they are antibacterial they may be used for the treatment of bacterial infections in man and animal. They can also be used in purification of water, in soaps and medicine. Their sustained release may be achieved by coating them with a suitable polymer. Silver nanoparticles fabricated from edible U. longissima are free from toxic chemicals and therefore they can be safely used in medicine and medical devices. These silver nanoparticles were stable for weeks therefore they can be stored for longer duration of time without decomposition.

Synthesis and evaluation of aryliden- and hetarylidenfuranone derivatives of usnic acid as highly potent Tdp1 inhibitors

Tyrosyl-DNA phosphodiesterase 1 (Tdp1) is a repair enzyme for stalled DNA-topoisomerase 1 (Top 1) cleavage complexes and other 3'-end DNA lesions. Tdp1 is a promising target for anticancer therapy, since it can repair DNA lesions caused by Top1 inhibitors leading to drug resistance. Hence, Tdp1 inhibition should result in synergistic effect with Top1 inhibitors. Twenty nine derivatives of (+)-usnic acid were tested for in vitro Tdp1 inhibitory activity using a fluorescent-based assay. Excellent activity was obtained, with derivative 6m demonstrating the lowest IC₅₀ value of 25 nM. The established efficacy was verified using a gel-based assay, which gave close results to that of the fluorescent assay. In addition, molecular modeling in the Tdp1 substrate binding pocket suggested plausible binding modes for the active analogues. The synergistic effect of the Tdp1 inhibitors with topotecan, a Top1 poison in clinical use, was tested in two human cell lines, A-549 and HEK-293. Compounds 6k and 6x gave very promising results. In particular, 6x has a low cytotoxicity and an IC₅₀ value of 63 nM, making it a valuable lead compound for the development of potent Tdp1 inhibitors for clinical use.

Comparative phytotoxicity of usnic acid, salicylic acid, cinnamic acid and benzoic acid on photosynthetic apparatus of Chlamydomonas reinhardtii

The effects of four phytotoxins usnic acid (UA), salicylic acid (SA), cinnamic acid (CA) and benzoic acid (BA) on photosynthesis of Chlamydomonas reinhardtii were studied in vivo to identify and localise their initial action sites on two photosystems. Our experimental evidence shows that the four phytotoxins have multiple targets in chloroplasts, which mainly lie in photosystem II (PSII), not photosystem I (PSI). They share an original action site by blocking electron transport beyond Q_A (primary plastoquinone acceptor) at PSII acceptor side since a fast increase of the J-step level is the greatest change in chlorophyll a fluorescence induction kinetics OJIP in C. reinhardtii cells treated with the phytotoxins. UA decreases photosynthetic activity by reducing O₂ evolution rate, interrupting PSII electron transport at both the donor and acceptor sides, inactivating the PSII reaction centers (RCs), reducing the content of chlorophylls and carotenoids, destroying the conformation of antenna pigment assemblies, and casuing the degradation of D1/D2 proteins. SA damage to photosynthetic machinery is mainly attributed to inhibition of PSII electron transport beyond Q_A at the acceptor side, inactivation of the PSII RCs, reduction of chlorophyll content, digestion of thylakoid ploypeptides and destabilization of thylakoid membranes. Both CA and BA affect the photosynthetic process by decreasing PSII electron transport efficiency at the acceptor side and the amount of active PSII RCs. Besides, the initial cause of BA-inhibiting photosynthesis is also assocaited with the O₂ evolution rate and the disconnection of some antenna molecules from PSII RCs.

Usnic acid and its derivatives for pharmaceutical use: a patent review (2000-2017)

INTRODUCTION

Usnic acid (UA) is a lichen-derived secondary metabolite with a unique dibenzofuran skeleton and is commonly found in lichenized fungi of the genera Usnea and Cladonia. Usnic acid has been incorporated for years in cosmetics, perfumery, and traditional medicines. It has a wide range of bioactivities, including antimicrobial, antiviral, anticancer, anti-inflammatory properties.

AREAS COVERED

This review covers patents on therapeutic activities of UA and its synthetic derivatives published during the period 2000-2017.

EXPERT OPINION

UA demonstrates excellent anticancer and antimicrobial properties. However, its application was withdrawn due to acute liver toxicity reported with chronic consumption. The broad spectrum of its biological activity indicates high the variability of UA's binding preferences. The main idea to be addressed in the future should include the synthesis of UA derivatives because these might possess increased bioactivity, bioavailability and decreased toxicity. It is noteworthy that UA derivatives possessed better antibacterial, antitubercular, and anticancer activity than the parent compound . Most importantly, UA and its analogs (to a greater extent than UA) can be useful in cancer drug treatment. They have the potential for joint application with other anticancer drugs in order to overcome drug resistance.

Design, synthesis and antimicrobial activity of usnic acid derivatives

Usnic acid, a dibenzofuran, was originally isolated from lichens producing secondary metabolites, and is well known as an antibiotic, but is also endowed with several other interesting properties. Thus, the goal of this paper is the design of new usnic acid derivatives and evaluation of their antimicrobial activity. All newly synthesized compounds possess good antibacterial activity with MIC ranging from 1.02-50.93 × 10-2 mmol mL-1 and MBC from 2.05-70.57 × 10-2 mmol mL-1. The most sensitive bacterial species was Staphylococcus aureus, while Pseudomonas aeruginosa and Escherichia coli were the most resistant among the ATCC strains, and MRSA was the most resistant among all tested bacteria (ATCC and clinical isolates). Their antifungal activity was very strong (MIC = 0.35-7.53 × 10-2 mmol mL-1 and MFC = 0.70-15.05 × 10-2 mmol mL-1) - better than those of reference compounds and usnic acid itself. The most sensitive fungal species was Trichoderma viride, while Penicillium versicolor var. cyclopium appeared to be the most resistant. It should be mentioned that in general most of the compounds showed weaker antibacterial activity, but better antifungal properties than usnic acid itself. The results allow us to conclude that the title compounds are good lead compounds for novel more active antibacterial drugs. On the other hand, these compounds are very promising as antifungals.

Usnic Acid Benzylidene Analogues as Potent Mechanistic Target of Rapamycin Inhibitors for the Control of Breast Malignancies

(+)-Usnic acid (1) is a common bioactive lichen-derived secondary metabolite with a characteristic dibenzofuran scaffold. It displayed low micromolar antiproliferative activity levels and, notably, induced autophagy in a panel of diverse breast cancer cell lines, suggesting the mechanistic (formerly "mammalian") target of rapamycin (mTOR) as a potential macromolecular target. The cellular autophagic markers were significantly upregulated due to the inhibition of mTOR downstream effectors. Additionally, 1 showed an optimal binding pose at the mTOR kinase pocket aided by multiple interactions to critical amino acids. Rationally designed benzylidene analogues of 1 displayed excellent fitting into a targeted deep hydrophobic pocket at the core of the kinase cleft, through stacking with the phenolic side chain of the Tyr2225 residue. Several potent analogues were generated, including 52, that exhibited potent (nM concentrations) antiproliferative, antimigratory, and anti-invasive activities against cells from multiple breast cancer clonal lines, without affecting the nontumorigenic MCF-10A mammary epithelial cells. Analogue 52 also exhibited potent mTOR inhibition and autophagy induction. Furthermore, 52 showed potent in vivo antitumor activity in two athymic nude mice breast cancer xenograft models. Collectively, usnic acid and analogues are potential lead mTOR inhibitors appropriate for future use to control breast malignancies.

Tyrosyl-DNA Phosphodiesterase 1 Inhibitors: Usnic Acid Enamines Enhance the Cytotoxic Effect of Camptothecin

Tyrosyl-DNA phosphodiesterase 1 (TDP1) is a repair enzyme for stalled DNA-topoisomerase 1 (Top1) cleavage complexes and other 3'-end DNA lesions. TDP1 is a perspective target for anticancer therapy based on Top1-poison-mediated DNA damage. Several novel usnic acid derivatives with an enamine moiety have been synthesized and tested as inhibitors of TDP1. The enamines of usnic acid showed IC₅₀ values in the range of 0.16 to 2.0 μM. These compounds revealed moderate cytotoxicity against human tumor MCF-7 cells. These new compounds enhanced the cytotoxicity of the established Top1 poison camptothecin by an order of magnitude.