Fluoroquinolones tackling antimicrobial resistance: Rational design, mechanistic insights and comparative analysis of norfloxacin vs ciprofloxacin derivatives

Antimicrobial resistance poses a global health concern and develops a need to discover novel antimicrobial agents or targets to tackle this problem. Fluoroquinolone (FN), a DNA gyrase and topoisomerase IV inhibitor, has helped to conquer antimicrobial resistance as it provides flexibility to researchers to rationally modify its structure to increase potency and efficacy. This review provides insights into the rational modification of FNs, the causes of resistance to FNs, and the mechanism of action of FNs. Herein, we have explored the latest advancements in antimicrobial activities of FN analogues and the effect of various substitutions with a focus on utilizing the FN nucleus to search for novel potential antimicrobial candidates. Moreover, this review also provides a comparative analysis of two widely prescribed FNs that are ciprofloxacin and norfloxacin, explaining their rationale for their design, structure-activity relationships (SAR), causes of resistance, and mechanistic studies. These insights will prove advantageous for new researchers by aiding them in designing novel and effective FN-based compounds to combat antimicrobial resistance.

Unraveling environmental effects in the absorption and fluorescence spectra of p-methoxyphenylpiperazine derivatives

The p-methoxyphenylpiperazine motif can be found in many biologically active molecules, including approved drugs. It is characterized by a relatively weak fluorescence, which can be employed in different types of studies involving molecules with this motif. In this work, a thorough analysis of the absorption, excitation and emission spectra of the diphenyl(aminomethyl)phosphine and tris(aminomethyl)phosphine derivatives of p-methoxyphenylpiperazine, supported by the DFT calculations (ωB97XD/6-311++G(d,p)) with NBO and QTAIM analysis also for different model molecules (e.g. 1-(4-methoxyphenyl)-4-methylpiperazine) enabled determination of the mechanisms underlying beneath the electronic transitions and allowed to rationalize mixed solvent effects observed in electronic spectra of the studied compounds. Electronic transition from the ground state to the first excited state can be regarded as the n,π → π* transition with no solvatochromic effects, however the hydrogen bonds between the HBD solvent molecules and the nitrogen atom bound directly to the aromatic ring (N(4)) are shifting strongly the 1st absorption or excitation band maxima to the higher energies. Fluorescence band, as a result of the electron transition from the equilibrated 1st excited state to the ground state, can be described as the π*→π with positive solvatochromism. N(4) in the excited states adopts a sp2 hybridization and is no longer able to form HBs. On the other hand, increased electron density on the aromatic ring makes the emission processes vulnerable to its direct environment.

Anticandidal Cu(I) complexes with neocuproine and 1-(4-methoxyphenyl)piperazine based diphenylaminomethylphosphine: Is Cu-diimine moiety a pharmacophore?

The studies on metal complexes as potential antifungals are of growing interest because they may be the answer to increasingly effective defense mechanisms. Herein we present two new copper(I) iodide or thiocyanide complexes with 2,9-dimethyl-1,10-phenanthroline (dmp) and diphenylphosphine derivative of 1-(4-methoxyphenyl)piperazine (4MP): [CuI(dmp)4MP] (1-4MP) and [CuNCS(dmp)4MP] (2-4MP) - their synthesis, as well as structural and spectroscopic characteristics. Interestingly, while 4MP and its oxide derivative (4MOP) show a very low or no activity against all tested Candida albicans strains (MIC50 ≥ 200 μM against CAF2-1 - laboratory control strain, DSY1050 - mutant without transporters Cdr1, Cdr2, Mdr1; isogenic for CAF2-1, and fluconazole resistant clinical isolates), for 1-4MP and 2-4MP MIC50 values were 0.4 μM, independently on the complex and strain tested. Determination of the viability of NHDF-Ad (Normal Adult Human Dermal Fibroblasts) cell line treated with 1-4MP and 2-4MP showed that for both complexes there was only a 20% reduction in the concentration range ¼ to 2 × MIC50 and the 70% at 4 × MIC50. Subsequently, the MLCT based luminescence of the complexes in aqueous media allowed to record the confocal micrographs of 1-4MP in the cells. The results show that it is situated most likely in the vacuoles (C. albicans) or lysosomes (NHDF-Ad).

The antibacterial potential of ciprofloxacin hybrids against Staphylococcus aureus

Staphylococcus aureus (S. aureus), an important pathogen of both humans and animals, is able to cause a variety of infections at any site of the body. The evolution of S. aureus resistance is notorious, and the widespread of drug-resistant S. aureus, especially methicillin-resistant S. aureus (MRSA), has made the treatment difficult in recent decades. Nowadays, S. aureus is among the leading causes of bacterial infections, creating an urgent need for the development of novel antibacterial agents. Ciprofloxacin, characterized by high clinical efficacy, is a broad-spectrum antibacterial agent with frequency of prescription for various Gram-positive and Gram-negative pathogens, many of which are resistant to a wide range of antibiotics. However, the long-term and widespread use of this antibiotic has led to the emergence of ciprofloxacin-resistant pathogens, and ciprofloxacin-resistant S. aureus has been noted in clinical practice. Ciprofloxacin hybrids have been recognized as advanced chemical entities to simultaneously modulate multiple drug targets in bacteria, so ciprofloxacin hybrids have the potential to overcome drug resistance. The present review provides an overview of ciprofloxacin hybrids with anti-S. aureus potential that have been reported in the last decade with emphasis on their structure-activity relationships and mechanisms of action.

Interaction between DNA, Albumin and Apo-Transferrin and Iridium(III) Complexes with Phosphines Derived from Fluoroquinolones as a Potent Anticancer Drug

A group of cytotoxic half-sandwich iridium(III) complexes with aminomethyl(diphenyl)phosphine derived from fluoroquinolone antibiotics exhibit the ability to (i) accumulate in the nucleus, (ii) induce apoptosis, (iii) activate caspase-3/7 activity, (iv) induce the changes in cell cycle leading to G2/M phase arrest, and (v) radicals generation. Herein, to elucidate the cytotoxic effects, we investigated the interaction of these complexes with DNA and serum proteins by gel electrophoresis, fluorescence spectroscopy, circular dichroism, and molecular docking studies. DNA binding experiments established that the complexes interact with DNA by moderate intercalation and predominance of minor groove binding without the capability to cause a double-strand cleavage. The molecular docking study confirmed two binding modes: minor groove binding and threading intercalation with the fluoroquinolone part of the molecule involved in pi stacking interactions and the Ir(III)-containing region positioned within the major or minor groove. Fluorescence spectroscopic data (HSA and apo-Tf titration), together with molecular docking, provided evidence that Ir(III) complexes can bind to the proteins in order to be transferred. All the compounds considered herein were found to bind to the tryptophan residues of HSA within site I (subdomain II A). Furthermore, Ir(III) complexes were found to dock within the apo-Tf binding site, including nearby tyrosine residues.

Antibacterial activity and action mode of Cu(I) and Cu(II) complexes with phosphines derived from fluoroquinolone against clinical and multidrug-resistant bacterial strains

Biological activity against reference and multi-drug resistant (MDR) clinical strains of fluoroquinolones (FQs): ciprofloxacin (HCp), norfloxacin (HNr), lomefloxacin (HLm) and sparfloxacin (HSf), phosphine ligands derived from those antibiotics and 14 phosphino copper(I) and copper(II) complexes with 2,9-dimethyl-1,10-phenanthroline, 1,10-phenanthroline or 2,2'-biquinoline have been determined. Almost all phosphines showed excellent antibacterial activity relative to reference strains (S. aureus ATCC 6538, E. coli ATCC 25922, K. pneumoniae ATCC 4352, and P. aeruginosa ATCC 27853). In rare cases P. aeruginosa rods showed natural insensitivity to oxides, and their copper(II) complexes. Most of the studied compounds showed weak antibacterial activity against clinical multi-drug resistant strains (MDR P. aeruginosa 16, 46, 325, 355, MRD A. baumanii 483 and MDR S. aureus 177). However, phosphines Ph₂PCH₂Sf (PSf), Ph₂PCH₂Lm (PLm) and their copper(I) complexes were characterized by the best antibacterial activity. In addition, PSf compounds, in which the activities relative to P. aeruginosa MDRs were relatively diverse, paid particular attention in our studies. Genetic and phenotypic studies of these strains showed significant differences between the strains, indicating different profiles of FQs resistance mechanisms. This may prove that a change in the spatial conformation of the PSf derivatives relative to the native form of HSf increased its affinity for the target site of action in gyrase, leading to selective inhibition of the multiplication of MDR strains. In conclusion, differences in PSf activity within closely related P. aeruginosa strains may indicate its diagnostic and therapeutic potential.

DNA topoisomerase IIIβ promotes cyst generation by inducing cyst wall protein gene expression in Giardia lamblia

Giardia lamblia causes waterborne diarrhoea by transmission of infective cysts. Three cyst wall proteins are highly expressed in a concerted manner during encystation of trophozoites into cysts. However, their gene regulatory mechanism is still largely unknown. DNA topoisomerases control topological homeostasis of genomic DNA during replication, transcription and chromosome segregation. They are involved in a variety of cellular processes including cell cycle, cell proliferation and differentiation, so they may be valuable drug targets. Giardia lamblia possesses a type IA DNA topoisomerase (TOP3β) with similarity to the mammalian topoisomerase IIIβ. We found that TOP3β was upregulated during encystation and it possessed DNA-binding and cleavage activity. TOP3β can bind to the cwp promoters in vivo using norfloxacin-mediated topoisomerase immunoprecipitation assays. We also found TOP3β can interact with MYB2, a transcription factor involved in the coordinate expression of cwp1-3 genes during encystation. Interestingly, overexpression of TOP3β increased expression of cwp1-3 and myb2 genes and cyst formation. Microarray analysis confirmed upregulation of cwp1-3 and myb2 genes by TOP3β. Mutation of the catalytically important Tyr residue, deletion of C-terminal zinc ribbon domain or further deletion of partial catalytic core domain reduced the levels of cleavage activity, cwp1-3 and myb2 gene expression, and cyst formation. Interestingly, some of these mutant proteins were mis-localized to cytoplasm. Using a CRISPR/Cas9 system for targeted disruption of top3β gene, we found a significant decrease in cwp1-3 and myb2 gene expression and cyst number. Our results suggest that TOP3β may be functionally conserved, and involved in inducing Giardia cyst formation.

New anticandidal Cu(i) complexes with neocuproine and ketoconazole derived diphenyl(aminomethyl)phosphane: luminescence properties for detection in fungal cells

Anticandidal activity and a complex luminescence in water solutions of the new copper(i) complexes with a ketoconazole derived phosphane ligand.

Anticancer potency of novel organometallic Ir(iii) complexes with phosphine derivatives of fluoroquinolones encapsulated in polymeric micelles

A 3D model of cell culturing (spheroids) was explored and the anticancer potential of the selected novel organometallic Ir(iii) complex encapsulated in Pluronic p-123 micelles was clearly proved.

New diphenylphosphane derivatives of ketoconazole are promising antifungal agents

Four new derivatives of ketoconazole (Ke) were synthesized: diphenylphosphane (KeP), and phosphane chalcogenides: oxide (KeOP), sulphide (KeSP) and selenide (KeSeP). These compounds proved to be promising antifungal compounds towards Saccharomyces cerevisiae and Candida albicans, especially in synergy with fluconazole. Simulations of docking to the cytochrome P450 14α-demethylase (azoles’ primary molecular target) proved that the new Ke derivatives are capable of inhibiting this enzyme by binding to the active site. Cytotoxicity towards hACSs (human adipose-derived stromal cells) of the individual compounds was studied and the IC₅₀ values were higher than the MIC₅₀ for C. albicans and S. cerevisiae. KeP and KeOP increased the level of the p21 gene transcript but did not change the level of p53 gene transcript, a major regulator of apoptosis, and decreased the mitochondrial membrane potential. Taken together, the results advocate that the new ketoconazole derivatives have a similar mechanism of action and block the lanosterol 14α-demethylase and thus inhibit the production of ergosterol in C. albicans membranes.

Repositioning of fluoroquinolones from antibiotic to anti-cancer agents: An underestimated truth

Increasing development costs and higher failure rate in clinical trials has reduced the repertoire of newer drugs in the market for clinical use. The most appropriate approach to end the search for newer drugs is "Repositioning", as it requires less time and money to explore new indication of existing drug or failed drug. In the past, several drugs have been repositioned for different indication but the full potential remains unharnessed. With rise in cancer prevalence and treatment costs, it is imperative to search for newer drugs and the use of repositioning approach may help us. Fluoroquinolones has been used as antibiotics for over four decades now, but recent research highlighted their use as pharmacological compounds with multifaceted implication. Repositioning of fluoroquinolones into anti-cancer molecule seems to be a highly plausible option owing to their profound immunomodulatory, pro-apoptotic, anti-proliferative and anti-metastatic potential. The present review provides a comprehensive account of the recent and past explorations pertaining to the anti-cancer activity of fluoroquinolones and also discusses the various approaches that are being considered to remodel them for the treatment of cancer.

Ciprofloxacin derivatives and their antibacterial activities

Bacterial infections represent a significant health threat globally, and are responsible for the majority of hospital-acquired infections, leading to extensive mortality and burden on global healthcare systems. The second generation fluoroquinolone ciprofloxacin which exhibits excellent antimicrobial activity and pharmacokinetic properties as well as few side effects is introduced into clinical practice for the treatment of various bacterial infections for around 3 decades. The emergency and widely spread of drug-resistant pathogens making ciprofloxacin more and more ineffective, so it's imperative to develop novel antibacterials. Numerous of ciprofloxacin derivatives have been synthesized for seeking for new antibacterials, and some of them exhibited promising potency. This review aims to summarize the recent advances made towards the discovery of ciprofloxacin derivatives as antibacterial agents and the structure-activity relationship of these derivatives was also discussed.

CuI and CuII complexes with phosphine derivatives of fluoroquinolone antibiotics - A comparative study on the cytotoxic mode of action

In this paper, we present a comparative study on the cytotoxic mode of action of copper(I) and copper(II) complexes with phosphine derivatives of fluoroquinolone antibiotics (ciprofloxacin HCp and norfloxacin HNr). The in vitro cytotoxic activity of four new compounds was tested against two selected cancer cell lines. All complexes exhibited much better cytotoxicity against both cell lines than unmodified fluoroquinolone antibiotics, their phosphines (PCp, PNr), chalcogenide derivatives (oxides: OPCp, OPNr; sulfides: SPCp, SPNr and selenides: SePCp, SePNr) and previously described by us complexes with phosphines derived from different fluoroquinolones: lomefloxacin (HLm) and sparfloxacin (HSf) as well as cisplatin. Apoptosis, observed at a great predominance, was induced by all studied complexes. Importantly, it was concluded that coordination compounds with Cu(I) ion ([Cu^I-PNr] and [Cu^I-PCp]) were much more active than those with Cu(II) ion ([OPNr-Cu^II], [OPCp-Cu^II]), even though the highest efficacy to produce reactive oxygen species, participating in overall cytotoxicity, was proved for copper(II) complexes among all studied compounds. Herein, we discuss not only results obtained for copper(I)/(II) complexes with phosphines derived from HNr and HCp but we also compare them to previously described data for complexes with HLm and HSf derivatives. This is the first insight into a structure-activity relationship of copper complexes with phosphine derivatives of fluoroquinolone antibiotics.

Ruthenium(II) piano stool coordination compounds with aminomethylphosphanes: Synthesis, characterisation and preliminary biological study in vitro

Reaction of {[Ru(η⁶-p-cymene)Cl]₂(μ-Cl)₂} (1) with aminomethylphosphane derived from morpholine (P{CH₂N(CH₂CH₂)₂O}₃ (A), PPh₂{CH₂N(CH₂CH₂)₂O} (B)) or piperazine (P{CH₂N(CH₂CH₂)₂NCH₂CH₃}₃ (C), PPh₂{CH₂N(CH₂CH₂)₂NCH₂CH₃} (D)) results in four new piano stool ruthenium(II) coordination compounds: [Ru(η⁶-p-cymene)Cl₂(A)] (2A), [Ru(η⁶-p-cymene)Cl₂(B)] (2B), [Ru(η⁶-p-cymene)Cl₂(C)] (2C) and [Ru(η⁶-p-cymene)Cl₂(D)] (2D). Every complex was fully characterized using spectroscopic methods (¹H, ¹³C{¹H}, ³¹P{¹H} NMR and ESI-MS), elemental analysis, X-ray single crystal diffraction and DFT calculations. Preliminary studies of in vitro cytotoxicity on the A549 (human lung adenocarcinoma) and MCF7 (human breast adenocarcinoma) cell lines revealed 2A-2D activity in the same order of magnitude as in the case of cisplatin. Additionally, the study confirmed the ability of 2A-2D to interact with DNA helix and transferrin.

A potent synthetic inorganic antibiotic with activity against drug-resistant pathogens

The acronymously named “ESKAPE” pathogens represent a group of bacteria that continue to pose a serious threat to human health, not only due to their propensity for repeated emergence, but also due to their ability to “eskape” antibiotic treatment12. The evolution of multi-drug resistance in these pathogens alone has greatly outpaced the development of new therapeutics, necessitating an alternative strategy for antibiotic development that considers the evolutionary mechanisms driving antibiotic resistance. In this study, we synthesize a novel inorganic antibiotic, phosphopyricin, which has antibiotic activity against the Gram-positive methicillin-resistant Staphylococcus aureus (MRSA) and vancomycin-resistant Enterococcus faecium (VRE). We show that this potent antibiotic is bactericidal, and exhibits low toxicity in an acute dose assay in mice. As a synthetic compound that does not occur naturally, phosphopyricin would be evolutionarily foreign to microbes, thereby slowing the evolution of resistance. In addition, it loses antibiotic activity upon exposure to light, meaning that the active antibiotic will not accumulate in the general environment where strong selective pressures imposed by antibiotic residuals are known to accelerate resistance. Phosphopyricin represents an innovation in antimicrobials, having a synthetic core, and a photosensitive chemical architecture that would reduce accumulation in the environment.

Coordination versatility of phosphine derivatives of fluoroquinolones. New CuI and CuII complexes and their interactions with DNA

This paper describes syntheses and interactions with DNA of copper(i) and copper(ii) complexes with phosphine derivatives of fluoroquinolone antibiotics (ciprofloxacin and norfloxacin).