Non-aggregated and water soluble non-peripherally octa substituted Co(II) and Cu(II) phthalocyanines: Synthesis and α-glucosidase inhibitory effects.

Type 2 diabetes (T2DM) is a progressive metabolic disease associated with high blood sugar levels that affects 537 million people worldwide. This study aim is to investigate the potential for use in the treatment of T2DM by examining the in vitro glucosidase inhibitory effects of novel synthesized metallophthalocyanines. For this reason, we have synthesized cobalt(II), copper(II) phthalocyanines (3PY-ON-CoQ, 3PY-ON-CuQ) that are both water-soluble and do not aggregate in water. These compounds were characterized by using various spectroscopic methods. The α-glucosidase inhibitory properties of 3PY-ON-CoQ and 3PY-ON-CuQ were carried out using the spectrophotometric method. Then, Lineweaver-Burk and Dixon plots were examined to determine the inhibitory type and constant (Ki). The IC50 values of 3PY-ON-CoQ and 3PY-ON-CuQ were 6.85 ± 1.25 µM and 55.09 ± 2.64 µM, respectively. Both compounds displayed mixed inhibitory effects on α-glucosidase according to Lineweaver-Burk plots. The Ki values of 3PY-ON-CoQ and 3PY-ON-CuQ were calculated as 6.30 ± 1.55 µM and 54.25 ± 1.20 µM, respectively. The results of this work may lead to the discovery of new compounds for the treatment of T2DM.

In vitro and in silico investigation of FDA-approved drugs to be repurposed against Alzheimer's disease.

Alzheimer's disease (AD), one of the main causes of dementia, is a neurodegenerative disorder. Cholinesterase inhibitors are used in the treatment of AD, but prolonged use of these drugs can lead to serious side effects. Drug repurposing is an approach that aims to reveal the effectiveness of drugs in different diseases beyond their clinical uses. In this work, we investigated in vitro and in silico inhibitory effects of 11 different drugs on cholinesterases. The results showed that trimebutine, theophylline, and levamisole had the highest acetylcholinesterase inhibitory actions among the tested drugs, and these drugs inhibited by 68.70 ± 0.46, 53.25 ± 3.40, and 44.03 ± 1.20%, respectively at 1000 µM. In addition, these drugs are bound to acetylcholinesterase via competitive manner. Molecular modeling predicted good fitness in acetylcholinesterase active site for these drugs and possible central nervous system action for trimebutine. All of these results demonstrated that trimebutine was determined to be the drug with the highest potential for use in AD.

Effective α-glycosidase inhibitors based on polyphenolic benzothiazole heterocycles.

α-Glycosidase inhibition is one of the main approaches to treat Diabetes mellitus. Polyphenolic moieties are known to be responsible for yielding exhibit potent α-glycosidase inhibitory effects. In addition, compounds containing benzothiazole and Schiff base functionalities were previously reported to show α-glycosidase inhibition. In this paper, the synthesis of seven new phloroglucinol-containing benzothiazole Schiff base derivatives through the reaction of 6-substituted-2-aminobenzothiazole compounds with 2,4,6-trihydroxybenzaldehyde using acetic acid as a catalyst was reported. The synthesized compounds were characterized using spectroscopic methods such as FT-IR, 1H NMR, 13C NMR, and elemental analysis. The synthesized compounds were evaluated for their inhibitory effects on α-glycosidase, compounds 3f and 3g were found to show significant inhibitory properties when compared to the positive control. The IC50 values of 3f and 3g were calculated as 24.05 ± 2.28 and 18.51 ± 1.19 µM, respectively. Kinetic studies revealed that compounds 3f and 3g exhibited uncompetitive mode of inhibition against α-glycosidase. Molecular modeling predicted druglikeness for the title compounds and underpinned the importance of phloroglucinol hydroxyls for interacting with the key residues of α-glycosidase.

Insights into the Biological Activity and Cytotoxic Mechanism of Epimedium pubigerum.

In this work, the phytochemical characterization, biological activity, and cytotoxic mechanism of aerial and rhizome methanol extracts (SME and RME) of Epimedium pubigerum were investigated to demonstrate its potential usage in the treatment of lung cancer. LC-HRMS analysis, total phenolic/flavonoid content assay, DPPH radical scavenging assay, DNA interaction, cytotoxicity, and western blotting were investigated using different methods. Fumaric acid was found to be the most abundant compound in both extracts. SME and RME were cytotoxic on A549 cells concentration-dependently. Also, in vitro scratch assay showed that SME and RME led to a significant anti-migratory effect at 1 mg/mL. Cytochrome c, p53, and caspase 3 expression significantly increased in the presence of RME compared to the control. All of these results claimed that RME might be suggested as a theoretically more effective phytotherapeutic agent for lung cancer compared to the effect seen with the SME.

Design, synthesis, and enzyme inhibition evaluation of some novel Mono- and Di-O-ß-D-Glycopyranosyl Chalcone analogues with molecular docking studies.

In this study, some novel mono- and di-O-ß-D-glycopyranosyl chalcone analogs were designed, synthesized, and characterized. The chalcone derivatives were synthesized with good yields by base-catalyzed Claisen-Schmidt condensation in EtOH solution. Then these chalcones were reacted with TAGBr (2,3,4,6-tetra-O-acetyl-α-D-glucopyranosylbromide) in dry acetone under the anhydrous condition at 0-5 °C. Deacylated was carried out by the Zemplen's method with NaOCH3 in dry methanol results in substituted chalcone-O-glycosides (mono- and di-O-ß-D-glycopyranosyl chalcone analogs). The chemical structures of all synthesized compounds were elucidated based on IR, NMR spectral data, and mass spectrometry. Further, the compounds (7a-c, 8a-c, 12a-c, 16a-c, and 17a-c) were tested for their enzyme inhibition activity against α-glycosidase, tyrosinase, and AChE with in vitro and in silico analysis. Amongst them, compounds 12a-c, 16a-c, and 17a-c displayed moderate or less enzyme inhibition activity against α-glycosidase while other compounds 7a-c and 8a-c) were not active. Remarkably interesting enzyme inhibition effects, with IC50 values below 30.59 ± 0.30 µM were recorded with 7c (IC50=11.07 ± 0.55 µM) against tyrosinase.

In vitro tyrosinase inhibitory, DNA interaction studies, and LC-HRMS analysis of Ficus carica leaves.

Turkey is the world's leading producer of figs, a typical Mediterranean fruit. The fig, Ficus carica L. (Moraceae), has been widely cultivated since ancient times due to the nutritional value of its fruits. It was aimed to investigate the phytochemical characterization and biological properties of F. carica leaf extracts in order to determine their potential for use in the treatment of various diseases. F. carica leaves were extracted in 70% methanol at 40 °C under reflux. To obtain extracts of different polarities, the crude extract was fractionated with n-hexane, dichloromethane, and n-butanol. Phenolic content was determined using liquid chromatography-high resolution mass spectrometry (LC-HRMS). 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging and antityrosinase activities of all extracts were investigated using spectrophotometric methods. Furthermore, the DNA-damage protective properties of extracts were investigated using electrophoretic methods. The n-butanol extract was found to have the highest total phenolic content, with 72.58 ± 4.52 mg GAE/g dry weight. According to LC-HRMS analysis, rutin (40.13 g/kg) was the most abundant compound in the n-butanol extract. The n-butanol extract, which was found to have the highest tyrosinase inhibitory effects among the extracts, demonstrated radical scavenging activity of 37.01 ± 1.15% and 82.57 ± 0.88% at 80 and 200 µg/mL, respectively. The n-butanol extract had the highest protective effects against Fenton's reagent, UV radiation, and singlet oxygen. Given these findings, it is possible to argue that F. carica leaves can be evaluated for developing products that could be used to treat various diseases.

Azole derivatives inhibit wildtype butyrylcholinesterase and its common mutants.

Azoles, which have been used for antifungal chemotherapy for decades, have recently been of interest for their efficacy against acetylcholinesterase (AChE) and butyrylcholinesterase (BChE). There is little known about the potential of azoles against BChE, however there is none regarding their inhibitory effects against mutants of BChE. In the current study, an azole library of 1-aryl-2-(1H-imidazol-1-yl)ethanol/ethanone oxime esters were tested against AChE and BChE, which yielded derivates more potent than the positive control, galantamine, against both isoforms. Kinetic analyses were performed for wildtype and mutant (A328F and A328Y) inhibition for the two most potent BChE inhibitors, pivalic and 3-bezoylpropanoic acid esters of 2-(1H-imidazol-1-yl)-1-(2-naphthyl)ethanol, which were found to have great affinity to the wildtype and mutant BChE types with Ki values as low as 0.173 ± 0.012 µM. The compounds were identified to show linear competitive or mixed type inhibition. Molecular modeling confirmed these kinetic data and provided further insights regarding molecular basis of BChE inhibition by the active derivatives. Thus, current study suggests new azole derivatives with promising cholinesterase inhibitory effects and reveals the first set of information to promote our understanding for the inhibitory behavior of this class against the mutant BChE forms.

Synthesis and evaluation of the antioxidant and anti-tyrosinase activities of thiazolyl hydrazone derivatives and their application in the anti-browning of fresh-cut potato.

Tyrosinase is a key enzyme in the biosynthesis of melanin, which is responsible for the browning of foods as well as many skin disorders. In order to develop new anti-browning agents with dual antioxidant and anti-tyrosinase capacities, a series of 30 thiazolyl hydrazone derivatives were synthesized. Among the molecules prepared, 6 and 30 were found to be the most potent tyrosinase inhibitors with IC50 values ​​comparable to that of kojic acid. Interestingly, 6 also has the highest radical scavenging activity among the prepared molecules. The inhibition kinetics study indicated that 6 is a non-competitive inhibitor while 30 inhibits tyrosinase competitively. The anti-browning assay of fresh-cut potato slices revealed that 6 and 30 are potent anti-browning agents with a capacity as high as kojic acid. The mechanisms of free radical scavenging and tyrosinase inhibition have been fully investigated in silico using computational kinetics, molecular docking, and molecular dynamics simulations.

In Vitro and in Silico Investigation of DNA Interaction, Topoisomerase I and II Inhibitory Properties of Polydatin.

Polydatin or piceid, is the 3-O-glucoside of resveratrol and is found abundantly in grapes, peanuts, wine, beer, and cacao products. Although anticancer activity of polydatin was reported before, and potential antiproliferative mechanisms of polydatin have been proposed, its direct effects on DNA and inhibitory potential against topoisomerase enzymes have remained unknown. In this study we aimed to reveal the link between polydatin's effects on DNA and DNA-topoisomerases and its antiproliferative promise. For this purpose, we evaluated the effects of polydatin on DNA and DNA topoisomerase using in vitro and in silico techniques. Polydatin was found to protect DNA against Fenton reaction-induced damage while not showing any hydrolytic nuclease effect. Further, polydatin inhibited topoisomerase II but not topoisomerase I. According to molecular docking studies, polydatin preferably showed minor groove binding to DNA where the stilbene moiety was important for binding to the DNA-topoisomerase II complex. As a result, topoisomerase II inhibition might be another anticancer mechanism of polydatin.

Antifungal Azole Derivatives Featuring Naphthalene Prove Potent and Competitive Cholinesterase Inhibitors with Potential CNS Penetration According to the in Vitro and in Silico Studies.

Cholinesterase inhibition is of great importance in the fight against neurodegenerative disorders such as Alzheimer's disease. Azole antifungals have come under the spotlight with recent discoveries that underline the efficacy and potential of miconazole and its derivatives against cholinesterase enzymes. In this study, we evaluated a library of azoles against acetylcholinesterase and butyrylcholinesterase using in vitro and in silico methods to identify potent inhibitors. Low micromolar IC50 values were obtained for imidazole derivatives, which were further tested and found potent competitive cholinesterase inhibitors via enzyme kinetics study. The active derivatives showed negligible toxicity in in vitro cytotoxicity tests. Molecular modeling studies predicted that these derivatives were druglike, could penetrate blood-brain barrier, and tightly bind to cholinesterase active site making key interactions via the imidazole moiety at protonated state. Thus, current study identifies potent and competitive cholinesterase inhibitor azoles with minor toxicity and potential to pass into the central nervous system.

Multiple biological effects of secondary metabolites of Ziziphus jujuba: isolation and mechanistic insights through in vitro and in silico studies.

In this study, we tested tyrosinase and α-glucosidase effects of different extracts of Ziziphus jujuba fruits. The n-BuOH subextract inhibited both tyrosinase and α-glucosidase (IC50 = 18.82 ± 1.13 and 25.03 ± 0.77 µg/mL, respectively) better than the positive controls kojic acid and acarbose (IC50 = 58.26 ± 0.25 and 46.10 ± 2.3 µg/mL, respectively). Thus, the n-BuOH extract was selected for further phytochemical studies. Indole-3-lactic acid methylester, catechin, magnoflorine, kaempferol 3-O-α-rhamnopyranosyl-(1 → 6)-ß-galactopyranoside, quercetin 3-O-α-rhamnopyranosyl-(1 → 6)-ß-galactopyranoside, and procyanidin B4 were isolated from the extract. We tested α-glucosidase and tyrosinase inhibitory effects, as well as DNA nuclease effects of the isolated compounds. Procyanidin B4 exhibited the best activity against both tyrosinase and α-glucosidase (IC50 = 60.25 ± 0.88 and 170.18 ± 5.60 µg/mL, respectively). The isolates did not show any nuclease effect at increasing concentrations. Molecular docking studies provided insights into inhibition mechanisms of the isolates against tyrosinase and α-glucosidase at the molecular level. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1007/s00217-021-03946-0.

Synthesis and in vitro α-glucosidase and cholinesterases inhibitory actions of water-soluble metallophthalocyanines bearing ({6-[3-(diethylamino)phenoxy]hexyl}oxy groups.

In this paper, we have prepared peripherally tetra-({6-[3-(diethylamino)phenoxy]hexyl}oxy substituted cobalt(II), copper(II), manganese(III) phthalocyanines (3, 4, 5) and their water-soluble derivatives (3a, 4a, 5a). Then, in vitro α-glucosidase and cholinesterases inhibitory actions of the water-soluble 3a, 4a, 5a were examined using spectrophotometric methods. 4a had the highest inhibitory effects among the tested compounds against α-glucosidase due to IC50 values. 4a and 5a had 40 fold higher inhibitory effects than the positive control. For cholinesterases, the compounds showed significant inhibitory actions that of galantamine which was used as a positive control. According to the SI value, 3a inhibited acetylcholinesterase enzyme selectively. In kinetic studies, 4a was a mixed inhibitor for α-glucosidase, 3a was a competitive inhibitor for AChE, and 4a was a mixed inhibitor for BuChE. The therapeutic potential of these compounds has been demonstrated by in vitro studies, but these data should be supported by further studies.

Potential of nafimidone derivatives against co-morbidities of epilepsy: In vitro, in vivo, and in silico investigations.

Nafimidone is known for its clinical antiepileptic effects and alcohol derivatives of nafimidone were reported be potent anticonvulsants. These compounds are structurally similar to miconazole, which is known to inhibit cholinesterases, protect neurons, and ameliorate cognitive decline. Herein, we aimed to reveal the potential of three nafimidone alcohol esters (5 g, 5i, and 5 k), which were previously reported for their anticonvulsant effects, against co-morbidities of epilepsy such as inflammatory and neuropathic pain, cognitive and behavioral deficits, and neuron death, and understand their roles in related pathways such as γ-butyric acid type A (GABAA ) receptor and cholinesterases using in vitro, in vivo and in silico methods. 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) test was used for cytotoxicity evaluation, hippocampal slice culture assay for neuroprotection, formalin test for acute and inflammatory pain, sciatic ligation for neuropathic pain, Morris water maze and open field locomotor tasks for cognitive and behavioral deficits, radioligand binding for GABAA receptor affinity, spectrophotometric methods for cholinesterase inhibition in vitro, and molecular docking in silico. The compounds were non-toxic to fibroblast cells. 5 k was neuroprotective against kainic acid-induced neuron death. 5i reduced pain response of mice in both the acute and the inflammatory phases. 5i improved survival upon status epilepticus. The compounds showed no affinity to GABAA receptor but inhibited acetylcholinesterase, 5 k also inhibited butyrylcholinesterase. The compounds were predicted to interact mainly with the peripheric anionic site of cholinesterase enzymes. The title compounds showed neuroprotective, analgesic, and cholinesterase inhibitory effects, thus they bear promise against certain co-morbidities of epilepsy with neurological insults.

Pyridine substituted BODIPYs: synthesis, characterization and cholinesterease, α-glucosidase inhibitory, DNA hydrolytic cleavage effects.

In this study, the synthesis of new monostyryl (BDPY-2) and distyryl BODIPY dyes (BDPY-4, BDPY-5) containing pyridine groups has been reported for the first time. The acetylcholinesterase from Electrophorus electricus (AChE), butyrylcholinesterase from equine serum (BuChE), α-glucosidase from Saccharomyces cerevisiae and DNA hydrolytic cleavage actions of BDPY-2, BDPY-4, BDPY-5 were investigated using various techniques. The results indicated that the compounds had varying inhibition properties against AChE, BuChE, and α-glucosidase. BDPY-4 was the most potent compound on AChE with IC50 of 54.78 ± 4.51 µM, and Lineweaver-Burk plots indicated that the compound is bound to a site other than the active site as a noncompetitive inhibitor. The compound-protein binding experiment showed that BDPY-4 changed the microenvironment around AChE. On the other hand, the compounds showed lower α-glucosidase inhibition than the positive control. The DNA hydrolytic cleavage effects were not observed on supercoiled plasmid DNA in the presence of the compounds as compared to negative controls. These findings suggested that BDPY-4 might be a promising compound to treat Alzheimer's diseases.

Design, synthesis and biological evaluation of water soluble and non-aggregated silicon phthalocyanines, naphthalocyanines against A549, SNU-398, SK-MEL128, DU-145, BT-20 and HFC cell lines as potential anticancer agents.

Cancer has become an important public problem in worldwide since cancer incidence and mortality are growing rapidly. In this study, water soluble and non-aggregated silicon (IV) phthalocyanines and naphthalocyanines containing (3,5-bis{3-[3-(diethylamino)phenoxy]propoxy}phenyl)methoxy groups have been synthesized and characterized to investigate their anticancer potential. Their DNA binding/nuclease, topoisomerases inhibition were investigated using UV-Vis absorption, thermal denaturation and agarose gel electrophoresis. The in vitro cytotoxic properties of the compounds on human lung (A549), breast (BT-20), liver (SNU-398), prostate (DU-145), melanoma (SK-Mel 128) carcinoma and human fibroblast (HFC) normal cell lines were evaluated by using MTT assay. In order to determine the mechanism of cancer cell growth suppression, cell cycle analysis was carried out using flow cytometer on A549 cell line. The Kb values of SiPc1a and SiNc2a were 6.85 ± (0.35) × 106 and 1.72 ± (0.16) × 104 M-1 and Tm values of ct-DNA were calculated as 82.02 °C and 78.07 °C, respectively in the presence of both compounds. The ΔTm values of SiPc1a and SiNc2a were calculated as 6.45 and 2.50 °C, respectively. The nuclease effects of SiPc1a and SiNc2a with supercoiled plasmid pBR322 DNA demonstrated that both compounds did not trigger any DNA nuclease effects at the lowest concentrations without irradiation whereas both compounds in the presence of activating agent (H2O2) showed significant plasmid DNA nuclease actions under irradiation (22.5 J/cm2). SiPc1a and SiNc2a inhibited to topoisomerase I on increasing concentrations whilst they had lower inhibition action toward topoisomerase II that of topoisomerase I. The in vitro cytotoxicity studies displayed that SiPc1a had the highest cytotoxic effects among the tested compounds against A549, SNU-398, SK-MEL128, DU-145, BT-20 and HFC cell lines with CC50 values ranged from 0.49 to 2.99 µM. Furthermore, SiPc1a inhibited cell proliferation by cell cycle arrest in G0/G1 phase. All of these results suggested that SiPc1a is a promising candidate as an anticancer agent.

Discovery of potent α-glucosidase inhibitors through structure-based virtual screening of an in-house azole collection.

Diabetes mellitus, a chronic disorder characterized by hyperglycemia, is considered a pandemic of modern times. α-Glucosidase inhibitors emerged as a promising class of antidiabetic drugs with better tolerability compared with its alternatives. Azoles, although widely preferred in drug design, have scarcely been investigated for their potential against α-glucosidase. In this study, we evaluated α-glucosidase inhibitory effects 20 azole derivatives selected out of an in-house collection via structure-based virtual screening (VS) with consensus scoring approach. Seven compounds were identified with better IC50 values than acarbose (IC50  = 68.18 ± 1.01 µM), a well-known α-glucosidase inhibitor drug, which meant 35% success for our VS methodology. Compound 52, 54, 56, 59, and 81 proved highly potent with IC50 values in the range of 40-60 µM. According to the enzyme kinetics study, four of them were competitive, 56 was non-competitive inhibitor. Structure-activity relationships, quantum mechanical, and docking analyses showed that azole rings at ionized state may be key to the potency observed for the active compounds and modifications to shift the balance between the neutral and ionized states further to the latter could yield more potent derivatives.

Photodynamic therapy effect of morpholinium containing silicon (IV) phthalocyanine on HCT-116 cells.

In this study, we investigated the in vitro potential of axially 1-morpholiniumpropan-2-ol disubstituted silicon (IV) phthalocyanine (SiPc) which was synthesized previously, on HCT-116 cells as a photodynamic therapy (PDT) agent. The singlet oxygen and photodegradation quantum yields of SiPc were calculated using UV-vis spectrophotometer. The cytotoxic and phototoxic effects of SiPc were evaluated by 3-[4,5-dimethylthiazol-2-yl]-2,5 diphenyl tetrazolium bromide (MTT) assay. Annexin V-FITC/PI double staining kit, cell cycle kit, and mitochondria membrane potential (ΔΨm) assay kit with JC-1 were used to indicate the cell death pathway. Caspase-3 and ß-catenin protein expressions were evaluated by western blotting. The singlet oxygen and photodegradation quantum yields of SiPc were calculated as 0.73 and 3.64 × 10-4 in DMSO. The cell viability assays showed that IC50 value of SiPc did not reach to 100 µM without irradiation. However, excellent phototoxicity was observed in the presence of SiPc upon light irradiation. The cells undergoing early/late apoptosis significantly increased in the presence SiPc at 5 µM upon light irradiation. Besides, the proportion of cells at S and G2/M phase increased. Moreover, mitochondria membrane potentials significantly decreased at 1 and 5 µM of SiPc with light irradiation. While caspase-3 expression increased, ß-catenin expression significantly decreased on HCT-116 in the presence of SiPc (p < 0.01). The results indicated that the PDT could be related to apoptosis and Wnt/ß-catenin signaling pathway. Based on our findings, SiPc exhibited a significant PDT effect on HCT-116 cells therefore, worthy of more detailed study.

In vitro and in silico assessment of DNA interaction, topoisomerase I and II inhibition properties of chrysosplenetin.

Chrysosplenetin is a methoxyflavone with reported anti-cancer effect. We tested its cytotoxic effect on the MCF-7 breast cancer cell line, and determined its effect on DNA intercalation and on the activity of topoisomerases I and II. The compound inhibited proliferation MCF-7 with an IC50 value of 0.29 µM. Chrysosplenetin did not initiate plasmid DNA cleavage but, in a concentration-dependent manner, protected plasmid DNA against damage induced by Fenton reagents. Furthermore, it possessed dual Topoisomerase I and II inhibitory properties. Especially, it inhibited topoisomerase II by 83-96% between the range 12.5-100 µM. In the light of these experimental findings, molecular docking studies were performed to understand binding mode, interactions and affinity of chrysosplenetin with DNA, and with topoisomerases I and II. These studies showed that of 4-chromone core and the hydroxyl and methoxy groups important for both intercalation with DNA and topoisomerase I and II inhibition.

Synthesis of axially disubstituted quaternized silicon phthalocyanines as a promising photosensitizer for the photodynamic treatment of HCT-116, A549 and SH-SY5Y cancer cell lines.

In this study, novel silicon(iv) phthalocyanines axially disubstituted with bis[(4-{3-[3-(dimethylamino)phenoxy]propoxy}phenyl)methoxy] and bis[(4-{3-[3-(diethylamino)phenoxy]propoxy}phenyl)methoxy] groups and their quaternized derivatives were synthesized and characterized. Then, their supercoiled pBR322 plasmid DNA cleavage properties were investigated using agarose gel electrophoresis. The in vitro PDT effects of Si-3a and Si-4a were investigated using the MTT cell viability assay against HCT-116, A549 and SH-SY5Y cell lines. Si-3a and Si-4a did not show cleavage effects upon increasing concentrations in the dark but both compounds showed cleavage activities upon irradiation for 30 and 60 min, respectively. The MTT cell viability assay indicated that Si-4a had a cytotoxic effect in a concentration-dependent manner on the HCT-116 cell line but it did not show any statistical difference with regard to phototoxicity. Otherwise, Si-3a and Si-4a had significant phototoxic effects when compared to cytotoxic effects against A549 and SH-SY5Y. The results suggested that Si-3a and Si-4a showed better cell death against SH-SY5Y than other cell lines with irradiation.

Flavones as tyrosinase inhibitors: kinetic studies in vitro and in silico.

INTRODUCTION: Tyrosinase is a multifunctional copper-containing oxidase enzyme that catalyses the first steps in the formation of melanin pigments. Identification of tyrosinase inhibitors is of value for applications in cosmetics, medicine and agriculture. OBJECTIVE: To develop an analytical method that allows identification of drug-like natural products that can be further developed as tyrosinase inhibitors. Results of in vitro and in silico studies will be compared in order to gain a deeper insight into the mechanism of action of enzyme inhibition. METHOD: Using an in vitro assay we tested tyrosinase inhibitor effects of five structurally related flavones, i.e. luteolin (1), eupafolin (2), genkwanin (3), nobiletin (4), and chrysosplenetin (5). The strongest inhibitors were further investigated in silico, using enzyme docking simulations. RESULTS: All compounds tested showed modest tyrosinase inhibitory effect compared to the positive control, kojic acid. The polymethoxy flavones 4 and 5 exhibited the strongest tyrosinase inhibitory effect with the half maximal inhibitory concentration (IC50 ) values of 131.92 ± 1.75 µM and 99.87 ± 2.38 µM respectively. According to kinetic analysis 2, 4 and 5 were competitive inhibitors, whereas 1 and 3 were non-competitive inhibitors of tyrosinase. Docking studies indicated that methoxy groups on 4 and 5 caused steric hindrance which prevented alternative binding modes in the tyrosinase; the methoxy groups on the B-ring of these flavones faced the catalytic site in the enzyme. CONCLUSIONS: The docking simulations nicely complemented the in vitro kinetic studies, opening the way for the development of predictive models for use in drug design.