A Study on the Effect of Quaternization of Polyene Antibiotics' Structures on Their Activity, Toxicity, and Impact on Membrane Models.

Polyene antibiotics have been used in antifungal therapy since the mid-twentieth century. They are highly valued for their broad spectrum of activity and the rarity of pathogen resistance to their action. However, their use in the treatment of systemic mycoses often results in serious side-effects. Recently, there has been a renewed interest in the development of new antifungal drugs based on polyenes, particularly due to the emergence of highly dangerous pathogenic strains of fungi, such as Candida auris, and the increased incidence of mucormycosis. Considerable understanding has been established regarding the structure-biological activity relationships of polyene antifungals. Yet, no previous studies have examined the effect of introducing quaternized fragments into their molecular structure. In this study, we present a series of amides of amphotericin B, nystatin, and natamycin bearing a quaternized group in the side chain, and discuss their biological properties: antifungal activity, cytotoxicity, and effects on lipid bilayers that mimic fungal and mammalian cell membranes. Our research findings suggest that the nature of the introduced quaternized residue plays a more significant role than merely the introduction of a constant positive charge. Among the tested polyenes, derivatives 4b, 5b, and 6b, which contain a fragment of N-methyl-4-(aminomethyl)pyridinium in their structure, are particularly noteworthy due to their biological activity.

Antiproliferative activity and apoptosis-inducing mechanism of Amaryllidaceae alkaloid montanine on A549 and MOLT-4 human cancer cells.

The isoquinoline alkaloids found in Amaryllidaceae are attracting attention due to attributes that can be harnessed for the development of new drugs. The possible molecular mechanisms by which montanine exerts its inhibitory effects against cancer cells have not been documented. In the present study, montanine, manthine and a series of 15 semisynthetic montanine analogues originating from the parent alkaloid montanine were screened at a single test dose of 10 µM to explore their cytotoxic activities against a panel of eight cancer cell lines and one non-cancer cell line. Among montanine and its analogues, montanine and its derivatives 12 and 14 showed the highest cytostatic activity in the initial single-dose screening. However, the native montanine exhibited the greatest antiproliferative activity against cancer cells, with a lower mean IC50 value of 1.39 µM, compared to the displayed mean IC50 values of 2.08 µM for 12 and 3.57 µM for 14. Montanine exhibited the most potent antiproliferative activity with IC50 values of 1.04 µM and 1.09 µM against Jurkat and A549 cell lines, respectively. We also evaluated montanine's cytotoxicity and cell death mechanisms. Our results revealed that montanine triggered apoptosis of MOLT-4 cells via caspase activation, mitochondrial depolarisation and Annexin V/PI double staining. The Western blot results of MOLT-4 cells showed that the protein levels of phosphorylated Chk1 Ser345 were upregulated with increased montanine concentrations. Our findings provide new insights into the mechanisms underlying the cytostatic, cytotoxic and pro-apoptotic activities of montanine alkaloids in lung adenocarcinoma A549 and leukemic MOLT-4 cancer cell types.

Semisynthetic Amides of Amphotericin B and Nystatin A1: A Comparative Study of In Vitro Activity/Toxicity Ratio in Relation to Selectivity to Ergosterol Membranes.

Polyene antifungal amphotericin B (AmB) has been used for over 60 years, and remains a valuable clinical treatment for systemic mycoses, due to its broad antifungal activity and low rate of emerging resistance. There is no consensus on how exactly it kills fungal cells but it is certain that AmB and the closely-related nystatin (Nys) can form pores in membranes and have a higher affinity towards ergosterol than cholesterol. Notably, the high nephro- and hemolytic toxicity of polyenes and their low solubility in water have led to efforts to improve their properties. We present the synthesis of new amphotericin and nystatin amides and a comparative study of the effects of identical modifications of AmB and Nys on the relationship between their structure and properties. Generally, increases in the activity/toxicity ratio were in good agreement with increasing ratios of selective permeabilization of ergosterol- vs. cholesterol-containing membranes. We also show that the introduced modifications had an effect on the sensitivity of mutant yeast strains with alterations in ergosterol biosynthesis to the studied polyenes, suggesting a varying affinity towards intermediate ergosterol precursors. Three new water-soluble nystatin derivatives showed a prominent improvement in safety and were selected as promising candidates for drug development.

Semisynthetic Amides of Polyene Antibiotic Natamycin.

Natamycin is a macrolide polyene antibiotic, characterized by a potent broad spectrum antifungal activity and low toxicity. However, it is not used for the treatment of systemic mycoses due to its low bioavailability and low solubility in aqueous solutions. In order to create new semisynthetic antifungal agents for treatment of mycoses, a series of water-soluble amides of natamycin were synthesized. Antifungal activities of natamycin derivatives were investigated against Candida spp., including a panel of Candida auris clinical isolates and filamentous fungi. Toxicity for mammalian cells was assayed by monitoring antiproliferative activity against human postnatal fibroblasts (HPF) and human embryonic kidney cells (HEK293). By comparing leakage of contents from ergosterol versus cholesterol containing vesicles, a ratio that characterizes the efficacy and safety of natamycin and its derivatives was determined (EI, efficiency index). Ability of all tested semisynthetic natamycines to prevent proliferation of the yeast Candida spp. cells was comparable or even slightly higher to those of parent antibiotic. Interestingly, amide 8 was more potent than natamycin (1) against all tested C. auris strains (MIC values 2 µg/mL vs 8 µg/mL, respectively). Among 7 derivatives, amide 10 with long lipophilic side chains showed the highest EI and strong antifungal activity in vitro but was more toxic against HPF. In vivo experiments with amide 8 showed in vivo efficacy on a mouse candidemia model with a larger LD50/ED50 ratio in comparison to amphotericin B.

Gentiopicroside-An Insight into Its Pharmacological Significance and Future Perspectives.

Gentiopicroside (GPS) is a leading component of several plant species from the Gentianaceae botanical family. As a compound with plenty of biological activities and a component of herbal drugs, GPS has an important role in the regulation of physiological processes in humans. The results of recently published scientific studies underline a meaningful role of this molecule as an active factor in metabolic pathways and mechanisms, which may have an influence in the treatment of different diseases, including digestive tract disorders, malignant changes, neurological disorders, microbial infections, bone formation disorders, inflammatory conditions, and others. This review aims to collect previously published reports on the biological properties of GPS as a single compound that were confirmed by in vitro and in vivo studies, and to draw attention to the newly discovered role of this bitter-tasting secoiridoid. Thanks to these properties, the research on this substance could be revisited.

Comparative Cytotoxic Activity of Hydroxytyrosol and Its Semisynthetic Lipophilic Derivatives in Prostate Cancer Cells.

A high adherence to a Mediterranean diet has been related to numerous beneficial effects in human health, including a lower incidence and mortality of prostate cancer (PCa). Olive oil is an important source of phenolic bioactive compounds, mainly hydroxytyrosol (HT), of this diet. Because of the growing interest of this compound and its derivatives as a cancer chemopreventive agent, we aimed to compare the in vitro effect of HT isolated from olive mill wastewaters and five semisynthetic alkyl ether, ester, and nitro-derivatives against prostate cancer (PCa) cell lines. The effect in cell proliferation was determined in RWPE-1, LNCaP, 22Rv1, and PC-3 cells by resazurin assay, the effect in cell migration by wound healing assay, and tumorsphere and colony formation were evaluated. The changes in key signaling pathways involved in carcinogenesis were assessed by using a phosphorylation pathway profiling array and by Western blotting. Antiproliferative effects of HT and two lipophilic derivatives [hydroxytyrosyl acetate (HT-Ac)/ethyl hydroxytyrosyl ether (HT-Et)] were significantly higher in cancerous PC-3 and 22Rv1 cells than in non-malignant RWPE-1 cells. HT/HT-Ac/HT-Et significantly reduced migration capacity in RWPE-1 and PC-3 and prostatosphere size and colony formation in 22Rv1, whereas only HT-Ac and HT-Et reduced these functional parameters in PC-3. The cytotoxic effect in 22Rv1 cells was correlated with modifications in the phosphorylation pattern of key proteins, including ERK1/2 and AKT. Consistently, HT-Ac and HT-Et decreased p-AKT levels in PC-3. In sum, our results suggest that HT and its lipophilic derivatives could be considered as potential therapeutic tools in PCa.

Sphaeropsidin A: A Pimarane Diterpene with Interesting Biological Activities and Promising Practical Applications.

Sphaeropsidin A (SphA) is a tetracyclic pimarane diterpene, first isolated as the main phytotoxin produced by Diplodia cupressi the causal agent of a severe canker disease of Italian cypress (Cupressus sempervirens L.). It was also produced, together with several analogues, by different pathogenic Diplodia species and other fungi and showed a broad array of biological activities suggesting its promising application in agriculture and medicine. The anticancer activity of SphA is very potent and cell specific. Recent studies have revealed its unique mode of action. This minireview reports the structures of SphA and its family of natural analogues, their biosynthetic origins, their fungal sources, and biological activities. The preparation of various SphA derivatives is also described as well as the results of structure-activity relationship (SAR) studies and on their potential practical applications.

Effects of Structural Manipulation on the Bioactivity of some Coumarin-Based Products.

Coumarin (2H-1-benzopyran-2-one) is a plant-derived natural product known for its pharmacological properties, such as anti-inflammatory, anticoagulant, antibacterial, antifungal, antiviral, anticancer, antihypertensive, antitubercular, anticonvulsant, antiadipogenic, antihyperglycemic, antioxidant, and neuroprotective. Two coumarin-based products were identified in the seeds of two apple phenotypes commonly known as Granny Smith and Red Delicious. This study aimed to evaluate the chemical manipulation of these coumarin-based products to more lipophilic semisynthetic compounds and trace the role of the phenolic hydroxyl group in the bioactivity of the parent natural products. The bioactivity evaluation included studying the potentials of the natural- and semisynthetic-coumarins as antioxidant, antineoplastic, antifungal, and antibacterial agents. At the first step, the antiradical potential of these products was evaluated versus the free radicals of hydroxyl and DPPH. The second potential was investigated utilizing an MTT-based photo assay versus several cancer-line cells,including SK-OV-3, MCF-7, KYSE-30, LC540, HeLa, AR42J, AB12, and AMN3. The third and fourth potentials were recognized by conducting a disc-diffusion method against six infective bacterial strains and three fungal strains. The test bacteria were Shigella dysenteriae, Klebsiella pneumonia, Escherichia coli, Haemophilus influenzae, Salmonella typhi, and Pseudomonas aeruginosa. On the other hand, the test fungi included Aspergillus flavus, Candida albicans, and Aspergillus niger. The results arising from these biopotentials revealed that the investigated functional group exerted a positive impact on the antiradical and antineoplastic potentials of the natural derivatives; however, they had a negative consequence on their antimicrobial potentials.

Antiproliferative Phenanthrenes from Juncus tenuis: Isolation and Diversity-Oriented Semisynthetic Modification.

The occurrence of phenanthrenes is limited in nature, with such compounds identified only in some plant families. Phenanthrenes were described to have a wide range of pharmacological activities, and numerous research programs have targeted semisynthetic derivatives of the phenanthrene skeleton. The aims of this study were the phytochemical investigation of Juncus tenuis, focusing on the isolation of phenanthrenes, and the preparation of semisynthetic derivatives of the isolated compounds. From the methanolic extract of J. tenuis, three phenanthrenes (juncusol, effusol, and 2,7-dihydroxy-1,8-dimethyl-5-vinyl-9,10-dihydrophenanthrene) were isolated. Juncusol and effusol were transformed by hypervalent iodine(III) reagent, using a diversity-oriented approach. Four racemic semisynthetic compounds possessing an alkyl-substituted p-quinol ring (1-4) were produced. Isolation and purification of the compounds were carried out by different chromatographic techniques, and their structures were elucidated by means of 1D and 2D NMR, and HRMS spectroscopic methods. The isolated secondary metabolites and their semisynthetic analogues were tested on seven human tumor cell lines (A2780, A2780cis, KCR, MCF-7, HeLa, HTB-26, and T47D) and on one normal cell line (MRC-5), using the MTT assay. The effusol derivative 3, substituted with two methoxy groups, showed promising antiproliferative activity on MCF-7, T47D, and A2780 cell lines with IC50 values of 5.8, 7.0, and 8.6 µM, respectively.

Topoisomerase 1B poisons: Over a half-century of drug leads, clinical candidates, and serendipitous discoveries.

Topoisomerases are DNA processing enzymes that relieve supercoiling (torsional strain) in DNA, are necessary for normal cellular division, and act by nicking (and then religating) DNA strands. Type 1B topoisomerase (Top1) is overexpressed in certain tumors, and the enzyme has been extensively investigated as a target for cancer chemotherapy. Various chemical agents can act as "poisons" of the enzyme's religation step, leading to Top1-DNA lesions, DNA breakage, and eventual cellular death. In this review, agents that poison Top1 (and have thus been investigated for their anticancer properties) are surveyed, including natural products (such as camptothecins and indolocarbazoles), semisynthetic camptothecin and luotonin derivatives, and synthetic compounds (such as benzonaphthyridines, aromathecins, and indenoisoquinolines), as well as targeted therapies and conjugates. Top1 has also been investigated as a therapeutic target in certain viral and parasitic infections, as well as autoimmune, inflammatory, and neurological disorders, and a summary of literature describing alternative indications is also provided. This review should provide both a reference for the medicinal chemist and potentially offer clues to aid in the development of new Top1 poisons.

Antioxidant activity of oleuropein and semisynthetic acetyl-derivatives determined by measuring malondialdehyde in rat brain.

OBJECTIVES: The purpose of this study was the evaluation of the antioxidant activity of natural and semisynthetic polyphenol derivatives from Olea europea L., by assessing malondialdehyde (MDA), an important marker of oxidative stress. METHODS: Polyphenol as hydroxytyrosol, oleuropein, oleuropein aglycone as mix of four tautomeric forms and their respective acetyl-derivatives were obtained from olive leaves using semisynthetic protocols. These compounds were administered intraperitoneally to Wistar rats treated with paraquat, an herbicide which is able to cause oxidative stress after central administration. Malondialdehyde was derivatized with 2,4-dinitrophenylhydrazine to produce hydrazone that was purified by solid-phase extraction. Using high-performance liquid chromatography coupled with a diode array, free and total MDA was measured on homogenate rat brain as marker of lipid peroxidation. The analytical method was fully validated and showed linearity in the tested concentration range, with detection limit of 5 ng/ml. Recovery ranged from 94.1 to 105.8%. KEY FINDINGS: Both natural and semisynthetic polyphenol derivatives from a natural source as olive leaves were able to reduce MDA detection. The more lipophilic acetyl-derivatives showed an antioxidant activity greater than parent compounds. This potency seems to put in evidence a strict correlation between lipophilicity and bioavailability.

Oleanane-, ursane-, and quinone methide friedelane-type triterpenoid derivatives: Recent advances in cancer treatment.

Natural pentacyclic triterpenoids (PTs) have been often reported to exhibit a wide range of biological activities. Among them, the anticancer and anti-inflammatory activities are the most studied. Over the last two decades, the number of publications reporting the anticancer effects of PTs has risen exponentially, reflecting the increasing interest in these natural products for the development of new antineoplastic drugs. Among of the most investigated PTs regarding their anticancer properties are oleanane-, ursane and friedelane-types, including oleanolic, glycyrrhetinic, ursolic and asiatic acids, and celastrol, among others. The extensive research in this field shows that the anticancer effects of PTs are mediated by several mechanisms, as they modulate a diverse range of molecular targets and signaling pathways, involved in cancer cell proliferation and survival. Considering the anticancer potential of this class of compounds, a number of semisynthetic derivatives has been synthetized aiming to improve their therapeutic activity and pharmacokinetic properties, and decrease their toxicity. Some of these new semisynthetic derivatives have shown improved anticancer activity in various cancer cell lines and animal models compared with the parent compound. Moreover, some of these compounds have been assessed in clinical trials, proving to be safe for human use. This review updates the most recent findings on the semisynthetic derivatives of oleanane-, ursane- and quinone methide friedelane-type PTs with anticancer activity. A brief introduction concerning the PTs and their anticancer activity is given, and the main semisynthetic modifications that have been performed between 2012 and early 2017 are reviewed and discussed.

Synthesis, Properties, and Mechanism of Action of New Generation of Polycyclic Glycopeptide Antibiotics.

INTRODUCTION: The increased resistance of glycopeptide based antibiotics has become a serious problem for the chemotherapy of infections triggered by resistant Gram-positive bacteria. This has motivated the urgent sincere efforts to develop potent glycopeptide-based antibiotics in both academy and industry research laboratories. Understanding of the mechanism of action of natural and modified glycopeptides is considered as the basis for the rational design of compounds with valuable properties to achieve the fundamental results. Several hydrophobic glycopeptide analogues active against resistant strains were developed during the last two decades. Three drugs, namely, oritavancin, telavancin and dalbavancin were approved by FDA in 2013-2014. It was found that hydrophobic derivatives act through different mechanisms without binding with the modified target of resistant bacteria. Types: Different types of chemical modifications led to several glycopeptide analogues active against Gram-negative bacteria as advocated by in vitro studies or demonstrating potent antiviral activity in the cell models. CONCLUSION: A new class of glycopeptide antibiotics with potent activity against sensitive and resistant bacterial strains has been recently reported with the aim to overcome the resistance, however, there are a lot of obscure problems in the complete understanding of their mechanisms of actions. In this review, we summarized the achievements of synthetic methods devoted to the construction of new polycyclic glycopeptide antibiotics and described the studies related to their mechanism of actions.

Modulation of Tumour-Related Signaling Pathways by Natural Pentacyclic Triterpenoids and their Semisynthetic Derivatives.

Pentacyclic triterpenoids are a large class of natural isoprenoids that are widely biosynthesized in higher plants. These compounds are potent anticancer agents that exhibit antiproliferative, antiangiogenic, antiinflammatory and proapoptotic activities. Although their effects on multiple pathways have been reported, unifying mechanisms of action have not yet been established. To date, a huge number of semisynthetic derivatives have been synthesized in different laboratories on the basis of triterpenoid scaffolds, and many have been assayed for their biological activities. The present review focuses on natural triterpenoids of the oleanane-, ursane- and lupane-types and their semisynthetic derivatives. Here, we summarize the diverse cellular and molecular targets of these compounds and the signal pathways involved in the performance of their antitumour actions. Among the most relevant mechanisms involved are cell cycle arrest, apoptosis and autophagy triggered by the effect of triterpenoids on TGF-ß and HER cell surface receptors and the downstream PI3KAkt- mTOR and IKK/NF-kB signaling axis, STAT3 pathway and MAPK cascades.

Anti-Trichomonas vaginalis activity of betulinic acid derivatives.

Caused by Trichomonas vaginalis, trichomoniasis is the most common non-viral STD worldwide. Currently, metronidazole and tinidazole are the only drugs approved for treatment of the condition. However, problems such as metronidazole-resistant T. vaginalis isolates and allergic reactions have been reported. Based on data previously published by our group, structural changes in betulinic acid (1) were performed, generating three new compounds that were tested for in vitro anti-T.vaginalis activity in this study. Whereas derivative 2 did not demonstrate anti-T. vaginalis activity, derivatives 3 and 4 reduced trophozoite viability by 100%, with MIC values of 50µM. The structural difference of two compounds was performed only on the C-28 position. Derivative 3 showed low cytotoxicity against Vero cells in 24h; however, derivative 4 was highly cytotoxic, but efficient when associated with metronidazole in the synergism assay. ROS production by neutrophils was reduced, and derivative 3 showed anti-inflammatory effect. Collectively, the results of this study provide in vitro evidence that betulinic acid derivatives 3 and 4 are potential compounds with anti-T. vaginalis activity.

Antibacterial activity of (-)-cubebin isolated from Piper cubeba and its semisynthetic derivatives against microorganisms that cause endodontic infections

Abstract Recent publications have highlighted the numerous biological activities attributed to the lignan (-)-cubebin (1), Piper cubeba L. f., Piperaceae, and ongoing studies have focused on its structural optimization, in order to obtain derivatives with greater pharmacological potential. The aim of this study was the obtainment of (1), its semisynthetic derivatives and evaluation of antibacterial activity. The extract of the seeds of P. cubeba was chromatographed, subjected to recrystallization and was analyzed by HPLC and spectrometric techniques. It was used for the synthesis of: (-)-O-methylcubebin (2), (-)-O-benzylcubebin (3), (-)-O-acetylcubebin (4), (-)-O-(N, N-dimethylamino-ethyl)-cubebin (5), (-)-hinokinin (6) and (-)-6.6'-dinitrohinokinin (7). The evaluation of the antibacterial activity has been done by broth microdilution technique for determination of the minimum inhibitory concentration and the minimum bactericidal concentration against Porphyromonas gingivalis, Prevotella nigrescens, Actinomyces naeslundii, Bacteroides fragilis and Fusobacterium nucleatum. It was possible to make an analysis regarding the relationship between structure and antimicrobial activity of derivatives against microorganisms that cause endodontic infections. The most promising were minimum inhibitory concentration =50 µg/ml against P. gingivalis by (2) and (3), and minimum inhibitory concentration =100 µg/ml against B. fragilis by (6). Cytotoxicity assays demonstrated that (1) and its derivatives do not display toxicity.

Synergy Potential of Indole Alkaloids and Its Derivative against Drug-resistant Escherichia coli.

Antibacterial and synergy potential of naturally occurring indole alkaloids (IA): 10-methoxy tetrahydroalstonine (1), isoreserpiline (2), 10 and 11 demethoxyreserpiline (3), reserpiline (4), serpentine (5), ajmaline (6), ajmalicine (7), yohimbine (8), and α-yohimbine (9) was evaluated using microbroth dilution assay. Further, α-yohimbine (9) was chemically transformed into six semisynthetic derivatives (9A-9F), and their antibacterial and synergy potential in combination with nalidixic acid (NAL) against E. coli strains CA8000 and DH5α were also evaluated. The IA 1, 2, 4, 5, 9 and the derivative 9F showed eightfold reduction in the MIC of NAL against the DH5α and four- to eightfold reduction against CA8000. These alkaloids also reduced MIC of another antibiotic, tetracycline up to 8folds, against the MDREC-KG4, a multidrug-resistant clinical isolate of E. coli. Mode of action study of these alkaloids showed efflux pumps inhibitory potential, which was supported by their in silico binding affinity and downregulation of efflux pump genes. These results may be of great help in the development of cost-effective antibacterial combinations for treating patients infected with multidrug-resistant Gram-negative infections.

Gastroprotective activity of ent-beyerene derivatives in mice: Effects on gastric secretion, endogenous prostaglandins and non-protein sulfhydryls.

Seventeen compounds (2-18) synthetized from the diterpenoid ent-beyer-15-en-18-ol (1) isolated from aerial part of Baccharis tola were tested for their gastroprotective activity on the model of HCl/EtOH-induced gastric lesions in mice. Furthermore cytotoxicity test toward fibroblasts and AGS cells were performed. The results showed that compound 1 (ED50=50 mg/kg), 2, 6 and 13 were the most active regarding gastroprotective activity. Compounds 8-10 and 17-18 showed the lowest cytotoxicity toward fibroblasts and AGS cells. Regarding to mode of gastroprotective action, the effect elicited by 6 (50 mg/kg) was reversed by Indomethacin but not by N-ethylmaleimide, N(G)-nitro-L-arginine methyl ester or ruthenium red, which suggests that prostaglandins are involved in the mode of gastroprotective action of 6.