A Nanostructured Lipid System as a Strategy to Improve the in Vitro Antibacterial Activity of Copper(II) Complexes

Exploiting thiol-functionalized benzosiloxaboroles for achieving diverse substitution patterns - synthesis, characterization and biological evaluation of promising antibacterial agents

Benzosiloxaboroles are an emerging class of medicinal agents possessing promising antimicrobial activity. Herein, the expedient synthesis of two novel thiol-functionalized benzosiloxaboroles 1e and 2e is reported. The presence of the SH group allowed for diverse structural modifications involving the thiol-Michael addition, oxidation, as well as nucleophilic substitution giving rise to a series of 27 new benzosiloxaboroles containing various polar functional groups, e.g., carbonyl, ester, amide, imide, nitrile, sulfonyl and sulfonamide, and pendant heterocyclic rings. The activity of the obtained compounds against selected bacterial and yeast strains, including multidrug-resistant clinical strains, was investigated. Compounds 6, 12, 20 and 22-24 show high activity against Staphylococcus aureus, including both methicillin-sensitive (MSSA) and methicillin-resistant (MRSA) strains, with MIC values in the range of 1.56-12.5 μg mL-1, while their cytotoxicity is relatively low. The in vitro assay performed with 2-(phenylsulfonyl)ethylthio derivative 20 revealed that, in contrast to the majority of known antibacterial oxaboroles, the plausible mechanism of antibacterial action, involving inhibition of the leucyl-tRNA synthetase enzyme, is not responsible for the antibacterial activity. Structural bioinformatic analysis involving molecular dynamics simulations provided a possible explanation for this finding.

Nanoencapsulation of Ruthenium Complex Ru(ThySMet): A Strategy to Improve Selective Cytotoxicity against Breast Tumor Cells in 2D and 3D Culture Models

BACKGROUND

Ruthenium complexes have shown promise in treating many cancers, including breast cancer. Previous studies of our group have demonstrated the potential of the trans- [Ru(PPh3)2(N,N-dimethylN'-thiophenylthioureato-k2O,S)(bipy)]PF6 complex, the Ru(ThySMet), in the treatment of breast tumor cancers, both in 2D and 3D culture systems. Additionally, this complex presented low toxicity when tested in vivo.

AIMS

Improve the Ru(ThySMet) activity by incorporating the complex into a microemulsion (ME) and testing its in vitro effects.

METHODS

The ME-incorporated Ru(ThySMet) complex, Ru(ThySMet)ME, was tested for its biological effects in two- (2D) and three-dimensional (3D) cultures using different types of breast cells, MDAMB- 231, MCF-10A, 4T1.13ch5T1, HMT-3522 and Balb/C 3T3 fibroblasts.

RESULTS

An increased selective cytotoxicity of the Ru(ThySMet)ME for tumor cells was found in 2D cell culture, compared with the original complex. This novel compound also changed the shape of tumor cells and inhibited cell migration with more specificity. Additional 3D cell culture tests using the non-neoplastic S1 and the triple-negative invasive T4-2 breast cells have shown that Ru(ThySMet)ME presented increased selective cytotoxicity for tumor cells compared with the 2D results. The morphology assay performed in 3D also revealed its ability to reduce the size of the 3D structures and increase the circularity in T4-2 cells.

CONCLUSION

These results demonstrate that the Ru(ThySMet)ME is a promising strategy to increase its solubility, delivery, and bioaccumulation in target breast tumors.

Galleria mellonella for systemic assessment of anti-Candida auris using amphotericin B loaded in nanoemulsion

Galleria mellonella is a model that uses adult larvae to assess the prophylactic, therapeutic, and acute toxic potential of substances. Given their benefits, G. mellonella models are being employed in investigations of systemic infections caused by highly resistant microorganisms. Among the multiresistant microorganisms, we highlight Candida auris, a yeast with high mortality potential and resistance. Among the potential drugs, amphotericin B (AmB) stands out; however, microbial resistance episodes and side effects caused by low selectivity have been observed. The incorporation of AmB into a nanoemulsion (NE) can contribute to the control of C. auris infections and resistance as well as decrease the side effects of this drug. This study aimed to develop AmB-loaded NE (NEA) and evaluate its antifungal action against C. auris in G. mellonella. NEs were obtained by using sunflower oil and cholesterol as the oily phase, polyoxyethylene 20 cetyl ether (Brij® 58) and soy phosphatidylcholine as the surfactant system, and PBS buffer as the aqueous phase. An alternative in vivo assay with G. mellonella for acute toxicity and infection was performed using adult stage larvae (200 mg to 400 mg). According to the obtained results, NE and NEA exhibited sizes of 43 and 48 nm, respectively. The PDI was 0.285 and 0.389 for NE and NEA, respectively. The ZP showed electronegativity for both systems, with -3.77 mV and -3.80 mV for NE and NEA, respectively. Acute toxicity showed that free AmB had greater acute toxicity potential than NEA. The survival assay showed high larval viability. NEA had a better antifungal profile against systemic infection in G. mellonella. It is concluded that the alternative model proved to be an efficient in vivo assay to determine the toxicity and evaluate the therapeutic property of free AmB and NEA in systemic infections caused by C. auris.

Study of antimycobacterial, cytotoxic, and mutagenic potential of polymeric nanoparticles of copper (II) complex

This study aimed to encapsulate and characterize a potential anti-tuberculosis copper complex (CuCl₂(INH)₂.H₂O:I1) into polymeric nanoparticles (PNs) of polymethacrylate copolymers (Eudragit®, Eu) developed by nanoprecipitation method. NE30D, S100 and, E100 polymers were tested. The physicochemical characterizations were performed by DLS, TEM, FTIR, encapsulation efficiency and, in vitro release studies. Encapsulation of I1 in PN-NE30D, PN-E100, and PN-S100 was 26.3%, 94.5%, 22.6%, respectively. The particle size and zeta potential were 82.3 nm and -24.5 mV for PNs-NE30D, 304.4 nm and +18.7 mV for PNs-E100, and 517.9 nm and -6.9 mV for PNs-S100, respectively. All PDIs were under 0.5. The formulations showed a I1 controlled release at alkaline pH with 29.7% from PNs-NE30D, 7.9% from PNs-E100 and, 28.1% from PNs-S100 at 1 h incubation. PNs were stable for at least 3 months. Particularly, PNs-NE30D demonstrated moderate inhibition of M. tuberculosis and low cytotoxic activity. None of the PNs induced mutagenicity.

Application of Lipid-Based Nanocarriers for Antitubercular Drug Delivery: A Review

The antimicrobial drugs currently used for the management of tuberculosis (TB) exhibit poor bioavailability that necessitates prolonged treatment regimens and high dosing frequency to achieve optimal therapeutic outcomes. In addition, these agents cause severe adverse effects, as well as having detrimental interactions with other drugs used in the treatment of comorbid conditions such as HIV/AIDS. The challenges associated with the current TB regimens contribute to low levels of patient adherence and, consequently, the development of multidrug-resistant TB strains. This has led to the urgent need to develop newer drug delivery systems to improve the treatment of TB. Targeted drug delivery systems provide higher drug concentrations at the infection site, thus leading to reduced incidences of adverse effects. Lipid-based nanocarriers have proven to be effective in improving the solubility and bioavailability of antimicrobials whilst decreasing the incidence of adverse effects through targeted delivery. The potential application of lipid-based carriers such as liposomes, niosomes, solid lipid nanoparticles, nanostructured lipid carriers, nano and microemulsions, and self-emulsifying drug delivery systems for the treatment of TB is reviewed herein. The composition of the investigated lipid-based carriers, their characteristics, and their influence on bioavailability, toxicity, and sustained drug delivery are also discussed. Overall, lipid-based systems have shown great promise in anti-TB drug delivery applications. The summary of the reviewed data encourages future efforts to boost the translational development of lipid-based nanocarriers to improve TB therapy.

Improvement in the Pharmacological Profile of Copper Biological Active Complexes by Their Incorporation into Organic or Inorganic Matrix

Every year, more Cu(II) complexes are proven to be biologically active species, but very few are developed as drugs or entered in clinical trials. This is due to their poor water solubility and lipophilicity, low stability as well as in vivo inactivation. The possibility to improve their pharmacological and/or oral administration profile by incorporation into inorganic or organic matrix was studied. Most of them are either physically encapsulated or conjugated to the matrix via a moiety able to coordinate Cu(II). As a result, a large variety of species were developed as delivery carriers. The organic carriers include liposomes, synthetic or natural polymers or dendrimers, while the inorganic ones are based on carbon nanotubes, hydrotalcite and silica. Some hybrid organic-inorganic materials based on alginate-carbonate, gold-PEG and magnetic mesoporous silica-Schiff base were also developed for this purpose.

Ramos M, Toledo LGD, Rodero CF, Hilário F, dos Santos LC, Chorilli M, Bauab TM. Syngonanthus nitens (Bong.) Ruhland Derivatives Loaded into a Lipid Nanoemulsion for Enhanced Antifungal Activity Against Candida parapsilosis

Background:

Vaginal infections caused by non-albicans species have become common in women of all age groups. The resistance of species such as Candida parapsilosis to the various antifungal agents is a risk factor attributed to these types of infections, which instigates the search for new sources of active compounds in vulvovaginal candidiasis (VCC) therapy.

Objective:

This study evaluated the antifungal activity of Syngonanthus nitens Bong. (Ruhland) derivatives and employed a lipid nanoemulsion as a delivery system.

Methods:

In this study, a lipid nanoemulsion was employed as a delivery system composed of Cholesterol (10%), soybean phosphatidylcholine: Brij 58 (1: 2) and PBS (pH 7.4) with the addition of 0.5% of a chitosan dispersion (80%), and evaluated the antifungal activity of S. nitens Bong. (Ruhland) derivatives against planktonic cells and biofilms of Candida parapsilosis. By a biomonitoring fractionation, the crude extract (EXT) and one fraction (F2) were selected and incorporated into a lipid nanoemulsion (NL) composed of cholesterol (10%), a 1:2 mixture of soybean phosphatidylcholine:polyoxyethylene -20- cetyl ether (10%), and phosphate buffer solution (pH 7.4) with a 0.5% chitosan dispersion (80%). The NL presented a diameter size between 50-200 nm, pseudoplastic behavior, and positive charge. The EXT and five fractions were active against planktonic cells.

Results and Discussion:

The incorporation of EXT and F2 into the NL increased antifungal activity and enhanced the anti-biofilm potential. This study classified the use of an NL as an important tool for the administration of S. nitens derivatives in cases of infections caused by this C. parapsisilosis.

Conclusion:

This work concluded that S. nitens derivatives were important sources of active molecules against C. parapsilosis and the use of a lipid nanoemulsion was an important tool to promote more effective F2 release and to improve the antifungal activity aiming the control of C. parapsilosis infections.

Antibacterial Activity of 7-Epiclusianone and Its Novel Copper Metal Complex on Streptococcus spp. Isolated from Bovine Mastitis and Their Cytotoxicity in MAC-T Cells

Mastitis is an inflammation of mammary gland parenchyma that adversely affects bovine health and dairy production worldwide despite significant efforts to eradicate it. The aim of this work was to characterize the antimicrobial activity of 7-epiclusianone (7-epi), a compound extracted from the Rheedia brasiliensis fruit, its complex with copper against Streptococcus spp. isolated from bovine mastitis, and to assess their cytotoxicity to bovine mammary alveolar cells (MAC-T). The complex 7-epiclusianone-Cu (7-epi-Cu) was an amorphous green solid with optical activity. Its vibrational spectrum in the infrared region showed absorption bands in the high-frequency region, as well as bands that can be attributed to the unconjugated and conjugated stretching of the free ligand. The complex was anhydrous. One of the tested bacterial strains was not sensitive to the compounds, while the other three had MIC values of 7.8 µg mL^-1 and minimum bactericidal concentration (MBC) values between 15.6 and 31.3 µg mL^-1. These two compounds are bacteriostatic, did not cause damage to the cell wall and, at sub-inhibitory concentrations, did not induce bacterial adhesion. The compounds were not cytotoxic. Based on these results, 7-epi and 7-epi-Cu exhibited desirable antimicrobial properties and could potentially be used in bovine mastitis treatment.

Nanostructured lipid carriers for incorporation of copper(II) complexes to be used against Mycobacterium tuberculosis

Tuberculosis (TB) is a disease caused by Mycobacterium tuberculosis. Cessation of treatment before the recommended conclusion may lead to the emergence of multidrug-resistant strains. The aim of this study was to develop nanostructured lipid carriers (NLCs) for use in the treatment of M. tuberculosis. The NLCs comprised the following lipid phase: 2.07% polyoxyethylene 40 stearate, 2.05% caprylic/capric triglyceride, and 0.88% polyoxyl 40 hydrogenated castor oil; the following aqueous phase: 3.50% poloxamer 407 (F1-F6), and 0.50% cetyltrimethylammonium bromide (F7-F12); and incorporated the copper(II) complexes [CuCl₂(INH)₂]·H₂O (1), [Cu(NCS)₂(INH)₂]·5H₂O (2), and [Cu(NCO)₂(INH)₂]·4H₂O (3) to form compounds F11.1, F11.2, and F11.3, respectively. The mean diameter of F11, F11.1, F11.2, and F11.3 ranged from 111.27±21.86 to 134.25±22.72 nm, 90.27±12.97 to 116.46±9.17 nm, 112.4±10.22 to 149.3±15.82 nm, and 78.65±6.00 to 122.00±8.70 nm, respectively. The polydispersity index values for the NLCs ranged from 0.13±0.01 to 0.30±0.09. The NLCs showed significant changes in zeta potential, except for F11.2, with F11, F11.1, F11.2, and F11.3 ranging from 18.87±4.04 to 23.25±1.13 mV, 17.03±1.77 to 21.42±1.87 mV, 20.51±1.88 to 22.60±3.44 mV, and 17.80±1.96 to 25.25±7.78 mV, respectively. Atomic force microscopy confirmed the formation of nanoscale spherical particle dispersions by the NLCs. Differential scanning calorimetry determined the melting points of the constituents of the NLCs. The in vitro activity of copper(II) complex-loaded NLCs against M. tuberculosis H₃₇R_v showed an improvement in the anti-TB activity of 55.4, 27.1, and 41.1 times the activity for complexes 1, 2, and 3, respectively. An in vivo acute toxicity study of complex-loaded NLCs demonstrated their reduced toxicity. The results suggest that NLCs may be a powerful tool to optimize the activity of copper(II) complexes against M. tuberculosis.

Targeting the molecular chaperone SlyD to inhibit bacterial growth with a small molecule

Molecular chaperones are essential molecules for cell growth, whereby they maintain protein homeostasis. Because of their central cellular function, bacterial chaperones might be potential candidates for drug targets. Antimicrobial resistance is currently one of the greatest threats to human health, with gram-negative bacteria being of major concern. We found that a Cu2+ complex readily crosses the bacterial cell wall and inhibits SlyD, which is a molecular chaperone, cis/trans peptidyl prolyl isomerise (PPIase) and involved in various other metabolic pathways. The Cu2+ complex binds to the active sites of SlyD, which suppresses its PPIase and chaperone activities. Significant cell growth retardation could be observed for pathogenic bacteria (e.g., Staphylococcus aureus and Pseudomonas aeruginosa). We anticipate that rational development of drugs targeting molecular chaperones might help in future control of pathogenic bacterial growth, in an era of rapidly increasing antibiotic resistance.

In Vitro Activity of Copper(II) Complexes, Loaded or Unloaded into a Nanostructured Lipid System, against Mycobacterium tuberculosis

Tuberculosis (TB) is an infectious disease caused mainly by the bacillus Mycobacterium tuberculosis (Mtb), presenting 9.5 million new cases and 1.5 million deaths in 2014. The aim of this study was to evaluate a nanostructured lipid system (NLS) composed of 10% phase oil (cholesterol), 10% surfactant (soy phosphatidylcholine, sodium oleate), and Eumulgin^® HRE 40 ([castor oil polyoxyl-40-hydrogenated] in a proportion of 3:6:8), and an 80% aqueous phase (phosphate buffer pH = 7.4) as a tactic to enhance the in vitro anti-Mtb activity of the copper(II) complexes [CuCl₂(INH)₂]·H₂O (1), [Cu(NCS)₂(INH)₂]·5H₂O (2) and [Cu(NCO)₂(INH)₂]·4H₂O (3). The Cu(II) complex-loaded NLS displayed sizes ranging from 169.5 ± 0.7095 to 211.1 ± 0.8963 nm, polydispersity index (PDI) varying from 0.135 ± 0.0130 to 0.236 ± 0.00100, and zeta potential ranging from −0.00690 ± 0.0896 to −8.43 ± 1.63 mV. Rheological analysis showed that the formulations behave as non-Newtonian fluids of the pseudoplastic and viscoelastic type. Antimycobacterial activities of the free complexes and NLS-loaded complexes against Mtb H₃₇Rv ATCC 27294 were evaluated by the REMA methodology, and the selectivity index (SI) was calculated using the cytotoxicity index (IC₅₀) against Vero (ATCC^® CCL-81), J774A.1 (ATCC^® TIB-67), and MRC-5 (ATCC^® CCL-171) cell lines. The data suggest that the incorporation of the complexes into NLS improved the inhibitory action against Mtb by 52-, 27-, and 4.7-fold and the SI values by 173-, 43-, and 7-fold for the compounds 1, 2 and 3, respectively. The incorporation of the complexes 1, 2 and 3 into the NLS also resulted in a significant decrease of toxicity towards an alternative model (Artemia salina L.). These findings suggest that the NLS may be considered as a platform for incorporation of metallic complexes aimed at the treatment of TB.