Novel antiacanthamoebic compounds belonging to quinazolinones

Nutrition, phytochemical profiling, in vitro biological activities, and in silico studies of South Chinese white pitaya (Hylocereus undatus)

Background

White pitaya, a popular tropical fruit, is known for its high nutritional value. It is commercially cultivated worldwide for its potential use in the food and pharmaceutical industries. This study aims to assess the nutritional and phytochemical contents and biological potential of the South Chinese White Pitaya (SCWP) peel, flesh, and seed extracts.

Methods

Extract fractions with increasing polarity (ethyl acetate < acetone < ethanol < methanol < aqueous) were prepared. Antibacterial potential was tested against multidrug-resistant (MDR) bacteria, and antioxidant activity was determined using, 2-diphenyl-1-picrylhydrazyl (DPPH) and 2,2'-Azino-bis(3-ethylbenzothiazoline-6-sulphonic acid) (ABTS) radical scavenging assays, and cytotoxic activity against human keratinocyte cells using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-2H-tetrazolium bromide (MTT) assay. Pharmacological screening and molecular docking simulations were conducted to identify potential antibacterial compounds with druggable characteristics. Molecular dynamics simulation (MDS) was employed to validate the binding stability of the promising ligand-protein complexes.

Results

All parts of the fruit exhibited a substantial amount of crucial nutrients (minerals, sugars, proteins, vitamins, and fatty acids). The ethanol (ET) and acetone (AC) fractions of all samples demonstrated notable inhibitory effects against tested MDR bacteria, with MIC50 ranges of 74-925 μg/mL. Both ET and AC fractions also displayed remarkable antioxidant activity, with MIC50 ranges of 3-39 μg/mL. Cytotoxicity assays on HaCaT cells revealed no adverse effects from the crude extract fractions. LC-MS/MS analyses identified a diverse array of compounds, known and unknown, with antibacterial and antioxidant activities. Molecular docking simulations and pharmacological property screening highlighted two active compounds, baicalein (BCN) and lenticin (LTN), showing strong binding affinity with selected target proteins and adhering to pharmacological parameters. MDS indicated a stable interaction between the ligands (BCN and LTN) and the receptor proteins over a 100-ns simulation period.

Conclusion

Our study provides essential information on the nutritional profile and pharmacological potential of the peel, flesh, and seeds of SCWP. Furthermore, our findings contribute to the identification of novel antioxidants and antibacterial agents that could be capable of overcoming the resistance barrier posed by MDR bacteria.

Potential anti-amoebic effects of synthetic 1,4-benzothiazine derivatives against Acanthamoeba castellanii

A rare but lethal central nervous system disease known as granulomatous amoebic encephalitis (GAE) and potentially blinding Acanthamoeba keratitis are diseases caused by free-living Acanthamoeba. Currently, no therapeutic agent can completely eradicate or prevent GAE. Synthetic compounds are a likely source of bioactive compounds for developing new drugs. This study synthesized seventeen 1,4-benzothiazine derivatives (I -XVII) by a base-catalyzed one-pot reaction of 2-amino thiophenol with substituted bromo acetophenones. Different spectroscopic techniques, such as EI-MS, 1H-, and 13C NMR (only for the new compounds), were used for the structural characterization and conformation of compounds. These compounds were assessed for the first time against Acanthamoeba castellanii. All compounds showed anti-amoebic potential in vitro against A. castellanii, reducing its ability to encyst and excyst at 100 μM. Compounds IX, X, and XVI showed the most potent activities among all derivatives and significantly reduced the viability to 5.3 × 104 (p < 0.0003), 2 × 105 (p < 0.006), and 2.4 × 105 (p < 0.002) cells/mL, respectively. The cytotoxicity profile revealed that these molecules showed lower to moderate cytotoxicity, i.e., 36 %, 2 %, and 21 %, respectively, against human keratinocytes in vitro. These results indicate that 1,4-benzothiazines showed potent in vitro activity against trophozoites and cysts of A. castellanii. Hence, these 1,4-benzothiazine derivatives should be considered to develop new potential therapeutic agents against Acanthamoeba infections.

Design, Synthesis, Antibacterial Evaluation, Three-Dimensional Quantitative Structure-Activity Relationship, and Mechanism of Novel Quinazolinone Derivatives

Plant bacterial illnesses are common and cause dramatic damage to agricultural goods all over the world, yet there are few efficient bactericides to alleviate them at present. To discover novel antibacterial agents, two series of quinazolinone derivatives with novel structures were synthesized and their bioactivity against plant bacteria was tested. Combining CoMFA model search and the antibacterial bioactivity assay, D32 was identified as a potent antibacterial inhibitor against Xanthomonas oryzae pv. Oryzae (Xoo), with an EC₅₀ value of 1.5 μg/mL, much better in inhibitory capacity compared to bismerthiazol (BT) and thiodiazole copper (TC) (31.9 and 74.2 μg/mL). The activities of compound D32 against rice bacterial leaf blight in vivo were 46.7% (protective activities) and 43.9% (curative activities), better than commercial drug thiodiazole copper (29.3% protective activities and 30.6% curative activities). Flow cytometry, proteomics, reactive oxygen species, and key defense enzymes were used to further investigate the relevant mechanisms of action of D32. The identification of D32 as an antibacterial inhibitor and revelation of its recognition mechanism not only open the possibility of developing new therapeutic strategies for treatment of Xoo but also provide clues for elucidation of the acting mechanism of quinazolinone derivative D32, which is a possible clinical candidate worth in-depth study.

Applications of Polyaniline-Based Molybdenum Disulfide Nanoparticles against Brain-Eating Amoebae

Primary amoebic meningoencephalitis and granulomatous amoebic encephalitis are distressing infections of the central nervous system caused by brain-eating amoebae, namely, Naegleria fowleri and Acanthamoeba spp., respectively, and present mortality rates of over 90%. No single drug has been approved for use against these infections, and current therapy is met with an array of obstacles including high toxicity and limited specificity. Thus, the development of alternative effective chemotherapeutic agents for the management of infections due to brain-eating amoebae is a crucial requirement to avert future mortalities. In this paper, we synthesized a conducting polymer-based nanocomposite entailing polyaniline (PANI) and molybdenum disulfide (MoS₂) and explored its anti-trophozoite and anti-cyst potentials against Acanthamoeba castellanii and Naegleria fowleri. The intracellular generation of reactive oxygen species (ROS) and ultrastructural appearances of amoeba were also evaluated with treatment. Throughout, treatment with the 1:2 and 1:5 ratios of PANI/MoS₂ at 100 μg/mL demonstrated significant anti-amoebic effects toward A. castellanii as well as N. fowleri, appraised to be ROS mediated and effectuate physical alterations to amoeba morphology. Further, cytocompatibility toward human keratinocyte skin cells (HaCaT) and primary human corneal epithelial cells (pHCEC) was noted. For the first time, polymer-based nanocomposites such as PANI/MoS₂ are reported in this study as appealing options in the drug discovery for brain-eating amoebae infections.

Potential anti-acanthamoebic effects through inhibition of CYP51 by novel quinazolinones

Acanthamoeba spp. are free living amoebae which can give rise to Acanthamoeba keratitis and granulomatous amoebic encephalitis. The surface of Acanthamoeba contains ergosterol which is an important target for drug development against eukaryotic microorganisms. A library of ten functionally diverse quinazolinone derivatives (Q1-Q10) were synthesised to assess their activity against Acanthamoeba castellanii T4. The in-vitro effectiveness of these quinazolinones were investigated against Acanthamoeba castellanii by amoebicidal, excystation, host cell cytopathogenicity, and NADPH-cytochrome c reductase assays. Furthermore, wound healing capability was assessed at different time durations. Maximum inhibition at 50 μg/mL was recorded for compounds Q5, Q6 and Q8, while the compound Q3 did not exhibit amoebicidal effects at tested concentrations. Moreover, LDH assay was conducted to assess the cytotoxicity of quinazolinones against HaCaT cell line. The results of wound healing assay revealed that all compounds are not cytotoxic and are likely to promote wound healing at 10 μg/mL. The excystation assays revealed that these compounds significantly inhibit the morphological transformation of A. castellanii. Compound Q3, Q7 and Q8 elevated the level of NADPH-cytochrome c reductase up to five folds. Sterol 14alpha-demethylase (CYP51) a reference enzyme in ergosterol pathway was used as a potential target for anti-amoebic drugs. In this study using i-Tasser, the protein structure of Acanthamoeba castellanii (AcCYP51) was developed in comparison with Naegleria fowleri protein (NfCYP51) structure. The sequence alignment of both proteins has shown 42.72% identity. Compounds Q1-Q10 were then molecularly docked with the predicted AcCYP51. Out of ten quinazolinones, three compounds (Q3, Q7 and Q8) showed good binding activity within 3 Å of TYR 114. The in-silico study confirmed that these compounds are the inhibitor of CYP51 target site. This report presents several potential lead compounds belonging to quinazolinone derivatives for drug discovery against Acanthamoeba infections.

Polyaniline (PANI)-conjugated tungsten disulphide (WS2) nanoparticles as potential therapeutics against brain-eating amoebae

Brain-eating amoebae, including Acanthamoeba castellanii and Naegleria fowleri, are the causative agents of devastating central nervous system infections with extreme mortality rates. There is an indisputable urgency for the development of effective chemotherapeutic agents for the control of these diseases that are increasing in incidence. Here, we evaluated the anti-amoebic potential of polyaniline:tungsten disulphide (PANI:WS₂) nanocomposite against the infective trophozoite and cyst stages of N. fowleri and A. castellanii. Throughout these evaluations, significant viability inhibition was noted when 100 µg/mL of PANI:WS₂ was employed at its 1:5 formulation. These effects were studied to be due to increased levels of reactive oxygen species (ROS) as visualised through fluorescence microscopy. Furthermore, field emission scanning electron microscopy (FE-SEM) analysis pictured disruption to amoeba morphology. The host-cell cytotoxicity of the nanocomposite (PANI:WS₂) was studied to be negligible, making it an attractive avenue in the pursuit for effective treatments for brain-eating amoeba infections. KEY POINTS: • Synthesis of polyaniline:tungsten disulphide (PANI:WS₂) nanocomposite. • Anti-amoebic potential of PANI:WS₂ nanocomposite. • PANI:WS₂ nanocomposites are promising anti-amoebic agents in vitro.

Crystal structure of 5-nitroquinazolin-4(3H)-one, C8H5N3O3

C8H5N3O3, monoclinic, P21/c (no. 14), a = 9.1778(16) Å, b = 7.0270(10) Å, c = 12.518(2) Å, β = 92.930(6)°, V = 806.3(2) Å3, Z = 4, R gt(F 2) = 0.0469, wR ref (F 2) = 0.1353, T = 298 K.

Novel Tetrazoles against Acanthamoeba castellanii Belonging to the T4 Genotype

BACKGROUND

Acanthamoeba castellanii is a pathogenic free-living amoeba responsible for blinding keratitis and fatal granulomatous amoebic encephalitis. However, treatments are not standardized but can involve the use of amidines, biguanides, and azoles.

OBJECTIVES

The aim of this study was to synthesize a variety of synthetic tetrazole derivatives and test their activities against A. castellanii.

METHODS

A series of novel tetrazole compounds were synthesized by one-pot method and characterized by NMR and mass spectroscopy. These compounds were subjected to amoebicidal, and cytotoxicity assays against A. castellanii belonging to the T4 genotype and human keratinocyte skin cells respectively. Additionally, reactive oxygen species determination and electron microscopy studies were carried out. Furthermore, two of the seven compounds were conjugated with silver nanoparticles to study their antiamoebic potential.

RESULTS

A series of seven tetrazole derivatives were synthesized successfully. The selected tetrazoles showed anti-amoebic activities at 10µM concentration against A. castellanii in vitro. The compounds tested caused increased reactive oxygen species generation in A castellanii, and significant morphological damage to amoebal membranes. Moreover, conjugation of silver nanoparticles enhanced antiamoebic effects of two tetrazoles.

CONCLUSIONS

The results showed that azole compounds hold promise in the development of new formulations of anti-Acanthamoebic agents.

Polyaniline-Conjugated Boron Nitride Nanoparticles Exhibiting Potent Effects against Pathogenic Brain-Eating Amoebae

Free-living amoebae include Acanthamoeba castellanii and Naegleria fowleri that are opportunistic protozoa responsible for life-threatening central nervous system infections with mortality rates over 90%. The rising number of cases and high mortality rates are indicative of the critical unmet need for the development of efficient drugs in order to avert future deaths. In this study, we assess the anti-amoebic capacity of a conducting polymer nanocomposite comprising polyaniline (PANI) and hexagonal boron nitride (hBN) against A. castellanii and N. fowleri. We observed significant amoebicidal and cysticidal effects using 100 μg/mL PANI/hBN (P < 0.05). Further, the nanocomposite demonstrated negligible cytotoxicity toward HaCaT and primary human corneal epithelial cells (pHCECs). In evaluating the mode of inhibition of A. castellanii due to treatment with PANI/hBN, increased intracellular reactive oxygen species (ROS) was measured and scanning microscopy visualized the formation of pores in the amoebae. Overall, this study is suggestive of the potential of the PANI/hBN nanocomposite as a promising therapy for amoeba infections.

Applications of medicinal chemistry for drug discovery against Acanthamoeba infections

Acanthamoeba is a genus of free-living amoebae, pervasively found in the environment. Most of its pathogenic species are the causative agent of sight-threatening Acanthamoeba keratitis and fatal granulomatous amoebic encephalitis. Despite the advancements in the field of chemotherapy, treating Acanthamoeba infections is still challenging due to incomplete knowledge of the complicated pathophysiology. In case of infection, the treatment regimen for the patients is often ineffective due to delayed diagnosis, poor specificity, and side-effects. Besides the resistance of Acanthamoeba cysts to most of the drugs, the recurrence of infection further complicates the recovery. Thus, it is necessary to develop an effective treatment which can eradicate these rare, but serious infections. Based on various computational and in vitro studies, it has been established that the synthetic scaffolds such as heterocyclic compounds may act as potential drug leads for the development of antiamoebic drugs. In this review, we report different classes of synthetic compounds especially heterocyclic compounds which have shown promising results against Acanthamoeba. Moreover, the antiamoebic activities of synthetic compounds with their possible mode of actions against Acanthamoeba, have been summarized and discussed in this review.

Antimicrobial properties of multifunctional polypyrrole-cobalt oxide-silver nanocomposite against pathogenic bacteria and parasite

BACKGROUND

Conducting polymer based nanocomposites are known to be effective against pathogens. Herein, we report the antimicrobial properties of multifunctional polypyrrole-cobalt oxide-silver nanocomposite (PPy-Co₃O₄-AgNPs) for the first time. Antibacterial activities were tested against multi-drug-resistant Gram-negative Escherichia coli (E. coli) and Gram-positive methicillin-resistant Staphylococcus aureus (MRSA) bacteria, while antiamoebic effects were assessed against opportunistic protist Acanthamoeba castellanii (A. castellanii).

RESULTS

The ternary nanocomposite containing conducting polymer polypyrrole, cobalt oxide, and silver nanoparticles showed potent antimicrobial effects against these pathogens. The antibacterial assay showed that PPy-Co₃O₄-AgNPs exhibited significant bactericidal activity against neuropathogenic E. coli K1 at only 8 μg/mL as compared to individual components of the nanocomposite, whereas a 70 % inhibition of A. castellanii viability was observed at 50 μg/mL. Moreover, PPy-Co₃O₄-AgNPs were found to have minimal cytotoxicity against human keratinocytes HaCaT cells in vitro even at higher concentration (50 μg/mL), and also reduced the microbes-mediated cytopathogenicity against host cells.

CONCLUSION

These results demonstrate that PPy-Co₃O₄-AgNPs hold promise in the development of novel antimicrobial nanomaterials for biomedical applications.

KEY POINTS

•Synthesis of polypyrrole-cobalt oxide-silver (PPy-Co₃O₄-AgNPs) nanocomposite. •Antimicrobial activity of nanocomposite. •PPy-Co₃O₄-AgNPs hold promise for biomedical applications.

Aryl Quinazolinone Derivatives as Novel Therapeutic Agents against Brain-Eating Amoebae

Naegleria fowleri and Balamuthia mandrillaris are protist pathogens that infect the central nervous system, causing primary amoebic meningoencephalitis and granulomatous amoebic encephalitis with mortality rates of over 95%. Quinazolinones and their derivatives possess a wide spectrum of biological properties, but their antiamoebic effects against brain-eating amoebae have never been tested before. In this study, we synthesized a variety of 34 novel arylquinazolinones derivatives (Q1-Q34) by altering both quinazolinone core and aryl substituents. To study the antiamoebic activity of these synthetic arylquinazolinones, amoebicidal and amoebistatic assays were performed against N. fowleri and B. mandrillaris. Moreover, amoebae-mediated host cells cytotopathogenicity and cytotoxicity assays were performed against human keratinocytes cells in vitro. The results revealed that selected arylquinazolinones derivatives decreased the viability of B. mandrillaris and N. fowleri significantly (P < 0.05) and reduced cytopathogenicity of both parasites. Furthermore, these compounds were also found to be least cytotoxic against HaCat cells. Considering that nanoparticle-based materials possess potent in vitro activity against brain-eating amoebae, we conjugated quinazolinones derivatives with silver nanoparticles and showed that activities of the drugs were enhanced successfully after conjugation. The current study suggests that quinazolinones alone as well as conjugated with silver nanoparticles may serve as potent therapeutics against brain-eating amoebae.

Antiamoebic activity of 3-aryl-6,7-dimethoxyquinazolin-4(3H)-one library against Acanthamoeba castellanii

Acanthamoeba castellanii is a free-living amoeba which can cause a blinding keratitis and fatal granulomatous amoebic encephalitis. The treatment of Acanthamoeba infections is challenging due to formation of cyst. Quinazolinones are medicinally important scaffold against parasitic diseases. A library of nineteen new 3-aryl-6,7-dimethoxyquinazolin-4(3H)-one derivatives was synthesized to evaluate their antiamoebic activity against Acanthamoeba castellanii. One-pot synthesis of 3-aryl-6,7-dimethoxyquinazolin-4(3H)-ones (1-19) was achieved by reaction of 2-amino-4,5-dimethoxybenzoic acid, trimethoxymethane, and different substituted anilines. These compounds were purified and characterized by standard chromatographic and spectroscopic techniques. Antiacanthamoebic activity of these compounds was determined by amoebicidal, encystation, excystation and host cell cytopathogenicity in vitro assays at concentrations of 50 and 100 μg/mL. The IC₅₀ was found to be between 100 and 50 μg/mL for all the compounds except compound 5 which did not exhibit amoebicidal effects at these concentrations. Furthermore, lactate dehydrogenase assay was also performed to evaluate the in vitro cytotoxicity of these compounds against human keratinocyte (HaCaT) cells. The results revealed that eighteen out of nineteen derivatives of quinazolinones significantly decreased the viability of A. castellanii. Furthermore, eighteen out of nineteen tested compounds inhibited the encystation and excystation, as well as significantly reduced the A. castellanii-mediated cytopathogenicity against human cells. Interestingly, while tested against human normal cell line HaCaT keratinocytes, all compounds did not exhibit any overt cytotoxicity. Furthermore, a detailed structure-activity relationship is also studied to optimize the most potent hit from these synthetic compounds. This report presents several potential lead compounds belonging to 3-aryl-6,7-dimethoxyquinazolin-4(3H)-one derivatives for drug discovery against infections caused by Acanthamoeba castellanii.