COVID-19 therapy: What weapons do we bring into battle?

Urgent treatments, in any modality, to fight SARS-CoV-2 infections are desired by society in general, by health professionals, by Estate-leaders and, mainly, by the scientific community, because one thing is certain amidst the numerous uncertainties regarding COVID-19: knowledge is the means to discover or to produce an effective treatment against this global disease. Scientists from several areas in the world are still committed to this mission, as shown by the accelerated scientific production in the first half of 2020 with over 25,000 published articles related to the new coronavirus. Three great lines of publications related to COVID-19 were identified for building this article: The first refers to knowledge production concerning the virus and pathophysiology of COVID-19; the second regards efforts to produce vaccines against SARS-CoV-2 at a speed without precedent in the history of science; the third comprehends the attempts to find a marketed drug that can be used to treat COVID-19 by drug repurposing. In this review, the drugs that have been repurposed so far are grouped according to their chemical class. Their structures will be presented to provide better understanding of their structural similarities and possible correlations with mechanisms of actions. This can help identifying anti-SARS-CoV-2 promising therapeutic agents.

Thermodynamic Characterization of Mixed Monolayers of a Novel Oxazolidine Derivative and Phospholipids.

Oxazolidine derivatives (OxD) are five ring-membered compounds that contain at least one oxygen and nitrogen in their molecular structure. OxD are known due to several therapeutic activities such as anticancer and antibiotic properties. In this paper, we performed a thermodynamic analysis of the mixed films composed by dipalmitoylphosphatidylglycerol (DPPG), dipalmitoylphosphoethanolamine (DPPE), dipalmitoyl phosphatidylcholine (DPPC) or L-α phosphatidylcholine (PC) with a novel oxazolidine derivate (OxD). Relevant thermodynamic parameters such as excess areas (ΔAE), excess free energies (ΔG), and Gibbs free energy of mixing (AGmix) were derived from the surface pressure data. The topographical analysis was performed using atomic force microscopy. Based on the calculated values of the thermodynamic parameters, we observed that the miscibility of the mixed films was directly dependent on their composition. DPPG/OxD and DPPE/OxD systems present the best-mixed character at low pressures at OxD molar fraction equivalent to 0.25.

Anticancer properties of thiophene derivatives in breast cancer MCF-7 cells.

Substitutions in thiophene structure give rise to new derivatives with different biological and pharmacological activities. The present study investigated the cytotoxicity activity of some thiophene derivatives in breast cancer cells maintained in two-dimensional (2D) or in three-dimensional (3D) culture and evaluated the anticancer mechanism of these compounds. Cytotoxicity assays were performed against untransformed cells and against breast cancer cell MCF-7. Apoptosis analysis and in-vitro migration assay were also performed to evaluate the mechanism of induction of cell death. All thiophene derivatives reduced the cell viability in breast cancer cells, showing cytotoxic activity (IC50<30 µmol/l), and SB-200 compound showed the best selectivity index in MCF-7 cells compared with doxorubicin in 2D culture. All thiophene derivatives significantly induced G0/G1 phase cell cycle arrest. However, only SB-83 treatment was effective against motility of MCF-7 cells in 2D culture (P=0.0059). The SB-200 derivative treatment induced an increased proportion of acridine orange/Hoechst double-stained cells (35.35 vs. 3.14%, P=0.0002) compared with nontreated cells, with apoptosis morphological alterations independent of caspase 7 activation (P>0.05). MCF-7 cells became less responsive to SB-200 and to doxorubicin in 3D culture compared with cells in 2D culture (higher IC50 values); however, SB-200 showed a better cytotoxic effect compared with doxorubicin in 3D culture. Therefore, the current study provides an insight into anticancer potential of thiophene derivatives, and further studies should be conducted to understand the mechanism by which thiophene derivatives act on cancer cells.

Synthesis, DNA and protein interactions and human topoisomerase inhibition of novel Spiroacridine derivatives.

Nine new spiroacridine derivatives were synthetized by introducing cyano-N-acylhydrazone group between the acridine and phenyl-substituted rings followed by spontaneous cyclization. The new compounds were assayed for their DNA binding properties, human topoisomerase IIα inhibition and bovine serum albumin (BSA) interaction. Besides, docking analysis were performed in order to better understanding the biomolecule-compounds interactions. All compounds interacted with BSA which was demonstrated by the fluorescence suppression constant of 104 M-1. Compounds with chloro and NO2 substituents at that para-position on phenyl ring demonstrated the best results for BSA interaction. DNA binding constant determined by UV-vis data demonstrated high values for AMTAC-11 and AMTAC-14, 1.1 × 108 M-1 and 4.8 × 106 M-1, respectively, and all others presented constant values of 105 M-1. AMTAC-06 with chloro at para-position on phenyl ring presented a topoisomerase II inhibition of 84.34% in comparison to the positive controls used. Docking studies indicated that AMTAC-06 is able to intercalate the DNA base pairs at topoisomerase IIα active site, preventing DNA connection after break, in a process known as poisoning. Topoisomerase enzyme inhibition result was correlated to BSA interaction profile, since AMTAC-06 showed the best results in both analysis. The findings obtained here proved that methoxy or chloro substitution on phenyl ring at para-position is fundamental for in vitro activity of new spiroacridine derivatives, and indicates that AMTAC-06 is a promising entity and should serve as a lead compound in the development of new DNA and protein binders, as well as human topoisomerase II inhibitors.

PPARγ partial agonist GQ-16 strongly represses a subset of genes in 3T3-L1 adipocytes.

Thiazolidinediones (TZDs) are peroxisome proliferator-activated receptor gamma (PPARγ) agonists that improve insulin resistance but trigger side effects such as weight gain, edema, congestive heart failure and bone loss. GQ-16 is a PPARγ partial agonist that improves glucose tolerance and insulin sensitivity in mouse models of obesity and diabetes without inducing weight gain or edema. It is not clear whether GQ-16 acts as a partial agonist at all PPARγ target genes, or whether it displays gene-selective actions. To determine how GQ-16 influences PPARγ activity on a gene by gene basis, we compared effects of rosiglitazone (Rosi) and GQ-16 in mature 3T3-L1 adipocytes using microarray and qRT-PCR. Rosi changed expression of 1156 genes in 3T3-L1, but GQ-16 only changed 89 genes. GQ-16 generally showed weak effects upon Rosi induced genes, consistent with partial agonist actions, but a subset of modestly Rosi induced and strongly repressed genes displayed disproportionately strong GQ-16 responses. PPARγ partial agonists MLR24 and SR1664 also exhibit disproportionately strong effects on transcriptional repression. We conclude that GQ-16 displays a continuum of weak partial agonist effects but efficiently represses some negatively regulated PPARγ responsive genes. Strong repressive effects could contribute to physiologic actions of GQ-16.

Synthesis, DNA Binding, and Antiproliferative Activity of Novel Acridine-Thiosemicarbazone Derivatives.

In this work, the acridine nucleus was used as a lead-compound for structural modification by adding different substituted thiosemicarbazide moieties. Eight new (Z)-2-(acridin-9-ylmethylene)-N-phenylhydrazinecarbothioamide derivatives (3a-h) were synthesized, their antiproliferative activities were evaluated, and DNA binding properties were performed with calf thymus DNA (ctDNA) by electronic absorption and fluorescence spectroscopies. Both hyperchromic and hypochromic effects, as well as red or blue shifts were demonstrated by addition of ctDNA to the derivatives. The calculated binding constants ranged from 1.74 × 10(4) to 1.0 × 10(6) M(-1) and quenching constants from -0.2 × 10(4) to 2.18 × 10(4) M(-1) indicating high affinity to ctDNA base pairs. The most efficient compound in binding to ctDNA in vitro was (Z)-2-(acridin-9-ylmethylene)-N- (4-chlorophenyl) hydrazinecarbothioamide (3f), while the most active compound in antiproliferative assay was (Z)-2-(acridin-9-ylmethylene)-N-phenylhydrazinecarbothioamide (3a). There was no correlation between DNA-binding and in vitro antiproliferative activity, but the results suggest that DNA binding can be involved in the biological activity mechanism. This study may guide the choice of the size and shape of the intercalating part of the ligand and the strategic selection of substituents that increase DNA-binding or antiproliferative properties.

Synthesis, DNA binding and topoisomerase I inhibition activity of thiazacridine and imidazacridine derivatives.

Thiazacridine and imidazacridine derivatives have shown promising results as tumors suppressors in some cancer cell lines. For a better understanding of the mechanism of action of these compounds, binding studies of 5-acridin-9-ylmethylidene-3-amino-2-thioxo-thiazolidin-4-one, 5-acridin-9-ylmethylidene-2-thioxo-thiazolidin-4-one, 5-acridin-9-ylmethylidene-2-thioxo-imidazolidin-4-one and 3-acridin-9-ylmethyl-thiazolidin-2,4-dione with calf thymus DNA (ctDNA) by electronic absorption and fluorescence spectroscopy and circular dichroism spectroscopy were performed. The binding constants ranged from 1.46 × 10(4) to 6.01 × 10(4) M(-1). UV-Vis, fluorescence and circular dichroism measurements indicated that the compounds interact effectively with ctDNA, both by intercalation or external binding. They demonstrated inhibitory activities to human topoisomerase I, except for 5-acridin-9-ylmethylidene-2-thioxo-1,3-thiazolidin-4-one. These results provide insight into the DNA binding mechanism of imidazacridines and thiazacridines.

Evaluation of the hydroalcoholic extract of Clarisia racemosa as an antiparasitic agent: an in vitro approach.

Clarisia racemosa Ruiz & Pav is a neotropical species found in humid forests from southern Mexico to southern Brazil. There are few studies related to the ethnopharmacological use of C. racemosa. Our objective was to evaluate the hydroalcoholic extract of C. racemosa as a potential antiparasitic agent. For this, we performed in vitro assays against strains of Leishmania amazonensis, Trypanosoma cruzi, Plasmodium falciparum, and Schistosoma mansoni. At the same time, immunomodulatory activity tests were carried out. The results demonstrated that the extract was able to stimulate and activate immune cells. In preliminary antiparasitic tests, structural modifications were observed in the promastigote form of L. amazonensis and in adult worms of S. mansoni. The extract was able to inhibit the growth of trypomastigote form of T. cruzi and finally showed low antiparasitic activity against strains of P. falciparum. It is pioneering work and these results demonstrate that C. racemosa extract is a promising alternative and contributes to the arsenal of possible forms of treatment to combat parasites. Supplementary Information: The online version contains supplementary material available at 10.1007/s13205-023-03799-2.

Pectin-like polysaccharide extracted from leaves Crataeva tapia promotes antioxidant, immunomodulatory and emulsifiers applied in therapeutic formulations.

The objective of this work was to isolate a polysaccharide similar to pectin from Crataeva tapia leaves, not yet reported in the literature, and to evaluate its antioxidant, cytotoxic and immunomodulatory profile. Pectin was extracted from the leaves in three stages, organic solvent followed by acidified water and ethanol precipitation. With the pectin obtained, the physicochemical characterization of the molecule was carried out using high-performance liquid chromatography, Fourier-transform infrared spectroscopy, nuclear magnetic resonance (13C and 1H) and different thermal and elemental analysis. Furthermore, the antioxidant activities were evaluated in vitro, and using human peripheral blood mononuclear cell culture, cytotoxicity and immunostimulatory actions were investigated. Physical and chemical analyses showed characteristic signs of pectin. Antioxidant activity tests showed that pectin had moderate to low antioxidant activity. Furthermore, pectin did not affect the viability of erythrocytes and PBMC and induced an immunostimulatory state when it promoted the production of cytokines IL-6, IL-10 and TNF-α and increased the activation of CD8 + T lymphocytes. This study showed that pectin from Crataeva tapia is not cytotoxic and promoted a pro-inflammatory profile in peripheral blood mononuclear cell with application as an immunostimulating and emulsifying compound.

ACW-02 an Acridine Triazolidine Derivative Presents Antileishmanial Activity Mediated by DNA Interaction and Immunomodulation.

The present study proposed the synthesis of a novel acridine derivative not yet described in the literature, chemical characterization by NMR, MS, and IR, followed by investigations of its antileishmanial potential. In vitro assays were performed to assess its antileishmanial activity against L. amazonensis strains and cytotoxicity against macrophages through MTT assay and annexin V-FITC/PI, and the ability to perform an immunomodulatory action using CBA. To investigate possible molecular targets, its interaction with DNA in vitro and in silico targets were evaluated. As results, the compound showed good antileishmanial activity, with IC50 of 6.57 (amastigotes) and 94.97 (promastigotes) µg mL-1, associated with non-cytotoxicity to macrophages (CC50 > 256.00 µg mL-1). When assessed by flow cytometry, 99.8% of macrophages remained viable. The compound induced an antileishmanial effect in infected macrophages and altered TNF-α, IL-10 and IL-6 expression, suggesting a slight immunomodulatory activity. DNA assay showed an interaction with the minor grooves due to the hyperchromic effect of 47.53% and Kb 1.17 × 106 M-1, and was sustained by docking studies. Molecular dynamics simulations and MM-PBSA calculations propose cysteine protease B as a possible target. Therefore, this study demonstrates that the new compound is a promising molecule and contributes as a model for future works.

Synthesis and cytotoxic activity of new acridine-thiazolidine derivatives.

Although their exact role in controlling tumour growth and apoptosis in humans remains undefined, acridine and thiazolidine compounds have been shown to act as tumour suppressors in most cancers. Based on this finding, a series of novel hybrid 5-acridin-9-ylmethylene-3-benzyl-thiazolidine-2,4-diones were synthesised via N-alkylation and Michael reaction. The cell viability was analysed using a 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay, and DNA interaction assays were performed using electrochemical techniques.

New imidazolidine derivatives as anti-Trypanosoma cruzi agents: structure-activity relationships.

Imidazolidine derivatives are key components for the development of bioactive compounds for the treatment of many diseases, especially Chagas. In fact, others studies showed that the imidazolidine-2,4-dione has stood out by presenting a wide spectrum of pharmacological activities including anticonvulsants, antiarrhythmic, and antiparasitic. In the present study, we investigated the morphological alterations induced by imidazolidine derivates LPSF/NN-52 and LPSF/NN-100 on trypomastigotes forms of Trypanosoma cruzi through ultrastructural analysis by electron microscopy. Many concentrations were used to measure the antiparasitic propriety promoted by imidazolidine derivatives, and our study indicates that parasites treated with 13 µg mL(-1) of the imidazolidine derivates for 24 h revealed severe damage to the parasite's mitochondrial complex. Beyond that, also observed in treated parasites were the following: myelin bodies, enlargement of cytoplasm vacuole, fragmentation of endoplasmic reticulum, and some treated samples clearly showed signs of necrosis. To confirm the ultrastructural results, some assays were performed for knowledge cellular death induction promoted by imidazolidine derivates against immune spleen cells. The induction of the necrotic process through derivatives LPSF/NN-52 and LPSF/NN-100 showed similar results in relation to nifurtimox and benznidazole. In the last assays, it was demonstrated that NN-100 was efficient against epimastigotes and trypomastigotes forms and these results reinforce the mechanisms of action of both new imidazolidine derivatives against T. cruzi.

Study of the activity of 3-benzyl-5-(4-chloro-arylazo)-4-thioxo-imidazolidin-2-one against Schistosomiasis mansoni in mice.

Previous studies conducted with the imidazolidinic derivative 3-benzyl-5-(4-chloro-arylazo)-4-thioxo-imidazolidin-2-one (LPSF-PT05) show outstanding activity against adult Schistosoma mansoni worms in vitro. In the first phase of this study, S. mansoni-infected mice were treated, orally, with 100 mg/Kg of the LPSF-PT05 in three formulations: Tween 80 and saline solution, oil/water (70 : 30) emulsion, and solid dispersion with polyethylene glycol (PEG). In the second phase, three other doses of the LPSF-PT05 in PEG were tested: 3, 10, 30 mg/kg. These treatment regimens significantly reduced the number of recovered worms due to increases in the solubility of the compound in this formulation; the greatest reduction (70.5%) was observed at the dose of 100 mg/kg. There was no changes in the pattern of mature egg compared to immature eggs; however there was a significant increase in the number of dead eggs. Histopathological analysis of liver tissue showed changes in morphological aspects of the hepatic parenchyma with decrease exudative-productive hepatic granuloma stages, although we found no significant differences in IFN-γ, IL-4, IL-10, or NO production in response to the specific antigen SEA. The results show the derivative LPSF-PT05 to be a potential candidate in the etiological treatment of schistosomiasis with a possible dampening effect of the granulomatous process.

Neurolocomotor Behavior and Oxidative Stress Markers of Thiazole and Thiazolidinedione Derivatives against Nauphoeta cinerea.

Thiazolidine compounds NJ20 {(E)-2-(2-(5-bromo-2-methoxybenzylidene)hydrazinyl)-4-(4-nitrophenyl)thiazole} and NW05 [(2-(benzo (d) (1,3) dioxol-4-ylmethylene)-N-(4-bromophenyl)-thiosemicarbazone] potentiated the effect of norfloxacin in resistant bacteria; however, there are no reports on their effects on Nauphoeta cinerea in the literature. The objective of this work was to evaluate the behavioral effects and oxidative markers of NW05 and NJ20 in lobster cockroach N. cinerea. To evaluate the behavioral study, a video tracking software was used to evaluate the locomotor points and the exploratory profile of cockroaches in the horizontal and vertical regions of a new environment. The total concentration of thiol and reduced glutathione (GSH), substances reactive to thiobarbituric acid (TBARS), free iron (II) content and mitochondrial viability were determined. The antioxidant potential was evaluated by the DPPH method. Both substances induced changes in the behavior of cockroaches, showing a significant reduction in the total distance covered and in the speed. In the cell viability test (MTT), there was a significant reduction for NJ20 (1 mM). NJ20 caused a significant increase in total levels of thiol and non-protein thiol (NPSH), although it also slightly increased the content of malondialdehyde (MDA). Both compounds (NW05 and NJ20) caused a significant reduction in the content of free iron at a concentration of 10 mM. In conclusion, the compound NJ20 caused moderate neurotoxicity (1 mM), but had good antioxidant action, while NW05 did not show toxicity or significant antioxidant activity in the model organism tested. It is desirable to carry out complementary tests related to the antioxidant prospection of these same compounds, evaluating them at different concentrations.

Antischistosomal action of thioxo-imidazolidine compounds: an ultrastructural and cytotoxicity study.

Schistosomiasis is a disease caused by helminthes of the genus Schistosoma, which threatens approximately 207 million people worldwide. Recently, strains of Schistosoma mansoni appear to be developing tolerance and resistance against Praziquantel, the most commonly available drug on the market used in the treatment of disease. This worrisome development justifies studies that seek alternatives for the prevention, treatment and cure of this disease. This study aimed to evaluate the in vitro activity of new imidazolidine compounds 1-benzyl-4-[(4-chloro-phenyl)-hydrazono]-5-thioxo-imidazolidin-2-one (LPSF/PT-5) and 1-(4-chloro-benzyl)-4-[(4-fluoro-phenyl)-hydrazono]-5-thioxo-imidazolidin-2-one (LPSF/PT-11) against adult worms of S. mansoni. LPSF/PT-5 and LPSF/PT-11 imidazolidine derivatives showed relevant schistosomicidal activity in vitro and induced significant ultrastructural alterations in worms and cell death: results similar to praziquantel. Thus, it is possible that these imidazolidine derivatives can be future candidates as schistosomotic drugs, but further studies are needed to elucidate the induced mechanisms behind this response.

Biological and immunological activity of new imidazolidines against adult worms of Schistosoma mansoni.

The only drug available for treating schistosomiasis is praziquantel, however there are already reports of resistance to its use in treatment, making it necessary to search and develop new compounds to combat schistosomiasis. We tested, in vitro, two new products, Laboratório de Planejamento de Síntese de Fármacos (LPSF)/5-(4-chloro-benzylidene-3-(4-nitrebenzyl)-4-thioxo-imidazolidin-2-one (RZS-2) and LPSF/5-(4-fluoride-benzylidene-3-(4-nitrebenzyl)-4-thioxo-imidazolidin-2-one (RZS-5) imidazolidines, against adult worms of Schistosoma mansoni. Efficacy and safety of these compounds were analyzed through IC50 cytotoxicity, immune response and cell viability tests. At different concentrations ranging from 40-640 microM, the imidazolidines produced motor abnormalities, inhibition of pairing and oviposition and mortality within 24 h at the higher concentrations. Although not triggering changes in IFN-gamma and IL-10, LPSF/RZS-2 and LPSF/RZS-5 induced production of nitric oxide and showed similar behavior to praziquantel in the cell death test.

Novel indol-3-yl-thiosemicarbazone derivatives: Obtaining, evaluation of in vitro leishmanicidal activity and ultrastructural studies.

Parasitic diseases still represent serious public health problems, since the high and steady emergence of resistant strains is evident. Because parasitic infections are distributed predominantly in developing countries, less toxic, more efficient, safer and more accessible drugs have become desirable in the treatment of the infected population. This is the case of leishmaniasis, an infectious disease caused by a protozoan of the genus Leishmania sp., responsible for triggering pathological processes from the simplest to the most severe forms leading to high rates of morbidity and mortality throughout the world. In the search for new leishmanicidal drugs, the thiosemicarbazones and the indole fragments have been identified as promising structures for leishmanicidal activity. The present study proposes the synthesis and structural characterization of new indole-thiosemicarbazone derivatives (2a-j), in addition to performing in vitro evaluations through cytotoxicity assays using macrophages (J774) activity against forms of Leishmania infantum and Leishmania amazonensis promastigote as well as ultrastructural analyzes in promastigotes of L. infantum. Results show that the indole-thiosemicarbazone derivatives were obtained with yield values varying from 32.09 to 94.64%. In the evaluation of cytotoxicity, the indole-thiosemicarbazone compounds presented CC50 values between 53.23 and 357.97 µM. Concerning the evaluation against L. amazonensis promastigote forms, IC50 values ranged between 12.31 and  > 481.52 µM, while the activity against L. infantum promastigotes obtained IC50 values between 4.36 and 23.35 µM. The compounds 2d and 2i tested against L. infantum were the most promising in the series, as they showed the lowest IC50 values: 5.60 and 4.36 respectively. The parasites treated with the compounds 2d and 2i showed several structural alterations, such as shrinkage of the cell body, shortening and loss of the flagellum, intense mitochondrial swelling and vacuolization of the cytoplasm leading the parasite to cellular unviability. Therefore, the indole-thiosemicarbazone compounds are promising because they yield considerable synthesis, have low cytotoxicity to mammalian cells and act as leishmanicidal agents.

Thiophene-thiosemicarbazone derivative (L10) exerts antifungal activity mediated by oxidative stress and apoptosis in C. albicans.

Reactive oxygen species (ROS) cause cell damage and death. To reverse these effects, cells produce substances such as reduced glutathione (GSH) that serve as substrates for antioxidant enzymes. One way to combat microbial resistance includes nullifying the effect of glutathione in microbial cells, causing them to die from oxidative stress. The compound 2-((5-nitrothiophen-2-yl)methylene)-N-(pyridin-3-yl) hydrazine carbothioamide (L10) is a new thiophene-thiosemicarbazone derivative with promising antifungal activity. The aim of this study was to evaluate its mechanism of action against Candida albicans using assays that evaluate its effects on redox balance. Treatment with L10 promoted significant changes in the minimum inhibitory concentration (MIC) values in ascorbic acid and GSH protection tests, the latter increasing up to 64-fold of the MIC. Using nuclear magnetic resonance, we demonstrated interaction of L10 and GSH. At concentrations of 4.0 and 8.0 µg/mL, significant changes were observed in ROS production and mitochondrial membrane potential. The cell death profile showed characteristics of initial apoptosis at inhibitory concentrations (4.0 µg/mL). Transmission electron microscopy data corroborated these results and indicated signs of apoptosis, damage to plasma and nuclear membranes, and to mitochondria. Taken together, these results suggest a possible mechanism of action for L10 antifungal activity, involving changes in cellular redox balance, ROS production, and apoptosis-compatible cellular changes.

Preclinical pharmacokinetic and pharmacodynamic evaluation of thiazolidinone PG15: an anti-inflammatory candidate.

OBJECTIVES: Novel 5-benzilidene thiazolidinones have been synthesized and exhibited anti-inflammatory activity. In this work one of the compounds of the thiazolidinone chemical series, (5Z,E)-3-[2-(4-chlorophenyl)-2-oxoethyl]-5-(1H-indol-3-ylmethylene)-thiazolidine-2,4-dione (PG15) was investigated aiming to determine the drug's anti-inflammatory potential in pre-clinical studies. METHODS: Methods used included the in-vitro inhibition of cyclooxygenase-1 and -2, in-vivo evaluation of anti-inflammatory activity by air pouch and peritonitis models and the pharmacokinetic profile after intravenous (3 mg/kg) and oral (3 and 6 mg/kg) dosing to rats. KEY FINDINGS: A two-compartment model with a fast distribution and an elimination half-life of 5.9 +/- 3.8 h described the PG15 plasma profile after intravenous dosing. PG15 showed an erratic and rapid absorption following oral administration with peak concentrations between 0.5 and 1 h. PG15 0.1 microM inhibited more than 30% and 13% of purified cyclooxygenase-1 and -2 activity in vitro, respectively. A lack of dose dependency was observed for the anti-inflammatory effect in the dose range investigated (0.8-50 mg/kg), with a maximum of 67.2 +/- 4.6% inhibition of leucocyte migration in the carrageenan-induced air pouch model obtained with the 3 mg/kg dose, similar to that observed for indometacin 10 mg/kg. CONCLUSIONS: The erratic absorption of PG15 observed after oral dosing could explain the lack of anti-inflammatory dose dependency.

Spiro-acridine inhibiting tyrosinase enzyme: Kinetic, protein-ligand interaction and molecular docking studies.

Here, we evaluate spiroacridines as inhibitors of tyrosinase, a key enzyme to melanogenesis. For this purpose, the spiroacridines 3-(acridin-9-yl)-N-benzylidene-2-cyanoacrylohydrazide (AMTAC-01) and 3-(acridin-9-yl)-2-cyano-N-(4-metoxybenzylidene)-acrylohydrazide (AMTAC-02) were synthesized and their enzymatic inhibition types and mechanisms were investigated. In addition, the interaction of these compounds with the enzyme were studied by UV-Vis spectroscopy, spectrofluorimetry, 1H NMR titration as well as molecular docking. Spectroscopic results reveals that the acridine derivatives interact strongly (Ka ≅ 104 - 105 M-1) with the mushroom tyrosinase and the enzyme undergoes small structural modifications due to the interaction with AMTAC-01 compound. The interaction studies support the enzymatic inhibition results, which suggests that AMTAC-01 compounds inhibit the enzyme reversibly and follows a noncompetitive type (AMTAC-01) and mixed type (AMTAC-02) of inhibition. Nevertheless, AMTAC-02 (IC50 = 96.29 µM) inhibits the enzyme more effectively than AMTAC-01 (IC50 = 189.40 µM), which suggests a highly relevant role of AMTAC-02's methoxy group to the inhibition activity, which is confirmed by docking studies to mushroom tyrosinase. Docking also indicates this interaction to be absent in human tyrosinase. SIGNIFICANCE: Based on previous results which evidenced the relevant activity of two spiroacridinic compounds for cell growth inhibition against melanoma cells, here we improve our understanding about the spiroacridines in the biological media by exploring the molecular mechanism that govern the activities of these two compounds using mushroom tyrosinase (mTYR) enzyme as molecular target. The paper not only will have a major impact upon molecular mechanism that regulates melanin inhibition by spiroacridinic compounds, but also by guiding the search for enzyme inhibitors and the development of new anti-melanoma prophylaxis.