Design and synthesis of amphiphilic 2-hydroxybenzylphosphonium salts with antimicrobial and antitumor dual action

Harvesting phosphorus-containing moieties for their antibacterial effects

Clinically manifested resistance of bacteria to antibiotics has emerged as a global threat to society and there is an urgent need for the development of novel classes of antibacterial agents. Recently, the use of phosphorus in antibacterial agents has been explored in quite an unprecedent manner. In this comprehensive review, we summarize the use of phosphorus-containing moieties (phosphonates, phosphonamidates, phosphonopeptides, phosphates, phosphoramidates, phosphinates, phosphine oxides, and phosphoniums) in compounds with antibacterial effect, including their use as β-lactamase inhibitors and antibacterial disinfectants. We show that phosphorus-containing moieties can serve as novel pharmacophores, bioisosteres, and prodrugs to modify pharmacodynamic and pharmacokinetic properties. We further discuss the mechanisms of action, biological activities, clinical use and highlight possible future prospects.

Antimicrobial potential of quaternary phosphonium salt compounds: a review

Given that mitochondrial dysregulation is a biomarker of many cancers, cationic quaternary phosphonium salt (QPS) conjugation is a widely utilized strategy for anticancer drug design. QPS-conjugated compounds exhibit greater cell permeation and accumulation in negatively charged mitochondria, and thus, show enhanced activity. Phylogenetic similarities between mitochondria and bacteria have provided a rationale for exploring the antibacterial properties of mitochondria-targeted compounds. Additionally, due to the importance of mitochondria in the survival of pathogenic microbes, including fungi and parasites, this strategy can be extended to these organisms as well. This review examines recent literature on the antimicrobial activities of various QPS-conjugated compounds and provides future directions for exploring the medicinal chemistry of these compounds.

Novel triphenylphosphonium amphiphilic conjugates of glycerolipid type: synthesis, cytotoxic and antibacterial activity, and targeted cancer cell delivery

This work deals with the creation of new cationic triphenylphosphonium amphiphilic conjugates of glycerolipid type (TPP-conjugates), bearing a pharmacophore terpenoid fragment (abietic acid and betulin) and a fatty acid residue in one hybrid molecule as a new generation of antitumor agents with high activity and selectivity. The TPP-conjugates showed high mitochondriotropy leading to the development of mitochondriotropic delivery systems such as TPP-pharmacosomes and TPP-solid lipid particles. Introducing the betulin fragment into the structure of a TPP-conjugate (compound 10) increases the cytotoxicity 3 times towards tumor cells of prostate adenocarcinoma DU-145 and 4 times towards breast carcinoma MCF-7 compared to TPP-conjugate 4a in the absence of betulin. TPP-hybrid conjugate 10 with two pharmacophore fragments, betulin and oleic acid, has significant cytotoxicity toward a wide range of tumor cells. The lowest IC50 of 10 is 0.3 μM toward HuTu-80. This is at the level of the reference drug doxorubicin. TPP-pharmacosomes (10/PC) increased the cytotoxic effect approximately 3 times toward HuTu-80 cells, providing high selectivity (SI = 480) compared to the normal liver cell line Chang liver.

Repurposing of MitoTam: Novel Anti-Cancer Drug Candidate Exhibits Potent Activity against Major Protozoan and Fungal Pathogens

Many of the currently available anti-parasitic and anti-fungal frontline drugs have severe limitations, including adverse side effects, complex administration, and increasing occurrence of resistance. The discovery and development of new therapeutic agents is a costly and lengthy process. Therefore, repurposing drugs with already established clinical application offers an attractive, fast-track approach for novel treatment options. In this study, we show that the anti-cancer drug candidate MitoTam, a mitochondria-targeted analog of tamoxifen, efficiently eliminates a wide range of evolutionarily distinct pathogens in vitro, including pathogenic fungi, Plasmodium falciparum, and several species of trypanosomatid parasites, causative agents of debilitating neglected tropical diseases. MitoTam treatment was also effective in vivo and significantly reduced parasitemia of two medically important parasites, Leishmania mexicana and Trypanosoma brucei, in their respective animal infection models. Functional analysis in the bloodstream form of T. brucei showed that MitoTam rapidly altered mitochondrial functions, particularly affecting cellular respiration, lowering ATP levels, and dissipating mitochondrial membrane potential. Our data suggest that the mode of action of MitoTam involves disruption of the inner mitochondrial membrane, leading to rapid organelle depolarization and cell death. Altogether, MitoTam is an excellent candidate drug against several important pathogens, for which there are no efficient therapies and for which drug development is not a priority.

Synthesis, biological evaluation and structure-activity relationship of 2-(2-hydroxyaryl)alkenylphosphonium salts with potency as anti-MRSA agents

Here we report the synthesis, in vitro antimicrobial activity, preliminary toxicity and mechanism study of a new series of 2-(2-hydroxyaryl)alkenylphosphonium salts with the variation of phosphonium moiety obtained by a two-step synthetic method from phosphine oxides. The salts showed pronounced activity against Gram-positive bacteria, including MRSA strains, and some fungi. Mechanism of action against S. aureus was studied by CV test, TEM and proteomic assay. No cell wall integrity loss was observed while proteomic assay results suggested interference in different metabolic processes of S. aureus. For this series, lipophilicity was determined as a key factor for the inhibition of Gram-positive bacteria growth and S. aureus killing. Biological properties of methylated derivatives were notably different with manifested action against Gram-negative bacteria.

Rigidity-Activity Relationships of bisQPC Scaffolds Against Pathogenic Bacteria

Biscationic quaternary phosphonium compounds (bisQPCs) represent a promising class of antimicrobials, displaying potent activity against both Gram-negative and Gram-positive bacteria. In this study, we explored the effects of structural rigidity on the antimicrobial activity of QPC structures bearing a two-carbon linker between phosphonium groups, testing against a panel of six bacteria, including multiple strains harboring known disinfectant resistance mechanisms. Using simple alkylation reactions, 21 novel compounds were prepared, although alkene isomerization as well as an alkyne reduction were observed during the respective syntheses. The resulting bisQPC compounds showed strong biological activity, but were hampered by diminished solubility of their iodide salts. One compound (P2P-10,10 I) showed single digit micromolar activity against the entire panel of bacteria. Overall, intriguing biological activity was observed, with more rigid structures displaying better efficacy against Gram-negative strains and less rigid structures demonstrating slightly increased efficacy against S. aureus strains.

Cationic Imidazolium Amphiphiles Bearing a Methoxyphenyl Fragment: Synthesis, Self-Assembly Behavior, and Antimicrobial Activity

Novel cationic amphiphiles of the 3-alkyl-1-(4-methoxyphenyl)-1H-imidazol-3-ium bromide series bearing methoxyphenyl fragments (MPI-n) have been synthesized. Their aggregation properties in aqueous solutions, solubilization capacity, and hemolytic and antimicrobial activities have been investigated by a number of physicochemical methods. Using tensiometry, conductometry, and fluorescence spectroscopy, it was shown that the MPI-n have lower CMCs than their nonfunctionalized counterparts. The unusual alkyl-chain-length-dependent morphology of aggregates is testified for this homological series. Amphiphiles with 12, 14, and 16 alkyl tails are characterized by the formation of micellar aggregates, while a surfactant with a decyl tail is characterized by the formation of larger aggregates with lower surface curvature. The MPI-10 aggregate morphology was rationalized in terms of the packing parameter consideration and was supported by size measurements and the fluorescence probe techniques, which showed that vesicle-like aggregates in close-packing mode probably occur. MPI-n aggregates have exhibited a high solubilization capacity toward hydrophobic azo dye Orange OT. Importantly, amphiphiles studied showed (i) high bacteriostatic activity at the level of ciprofloxacin; (ii) high bactericidal action against all Gram-positive bacteria, including methicillin-resistant strains; (iii) bactericidal properties against Gram-negative bacteria; and (iv) low hemolytic activity.

Quaternary Phosphonium Compounds: An Examination of Non-Nitrogenous Cationic Amphiphiles That Evade Disinfectant Resistance

Quaternary ammonium compounds (QACs) serve as mainstays in the formulation of disinfectants and antiseptics. However, an over-reliance and misuse of our limited QAC arsenal has driven the development and spread of resistance to these compounds, as well as co-resistance to common antibiotics. Extensive use of these compounds throughout the COVID-19 pandemic thus raises concern for the accelerated proliferation of antimicrobial resistance and demands for next-generation antimicrobials with divergent architectures that may evade resistance. To this end, we endeavored to expand beyond canonical ammonium scaffolds and examine quaternary phosphonium compounds (QPCs). Accordingly, a synthetic and biological investigation into a library of novel QPCs unveiled biscationic QPCs to be effective antimicrobial scaffolds with improved broad-spectrum activities compared to commercial QACs. Notably, a subset of these compounds was found to be less effective against a known QAC-resistant strain of MRSA. Bioinformatic analysis revealed the unique presence of a family of small multiresistant transporter proteins, hypothesized to enable efflux-mediated resistance to QACs and QPCs. Further investigation of this resistance mechanism through efflux-pump inhibition and membrane depolarization assays illustrated the superior ability of P6P-10,10 to perturb the cell membrane and exert the observed broad-spectrum potency compared to its commercial counterparts. Collectively, this work highlights the promise of biscationic phosphonium compounds as next-generation disinfectant molecules with potent bioactivities, thereby laying the foundation for future studies into the synthesis and biological investigation of this nascent antimicrobial class.

Isatin-3-acylhydrazones with enhanced lipophilicity: synthesis, antimicrobial activity evaluation and the influence on hemostasis system

Water-soluble trialkylammonium isatin-3-hydrazone derivatives bearing hydroxybenzyl substituent were easily synthesized with high yields. XRD studies confirmed the presence of these compounds as trans-( Z )-isomers in a crystal. It was shown that an increase in the lipophilicity of the cationic center leads to an increase in activity against Gram-positive bacteria Staphylococcus aureus and Bacillus cereus, including methicillin-resistant (MRSA) strains. The MIC values of the leading compounds turned out to be 2-100 times higher than the MIC of norfloxacin against the MRSA strains in the absence of hemo- and cytotoxicity. Antiaggregation and anticoagulation properties were in vitro better than for acetylsalicylic acid and sodium heparin drugs. It has been shown by UV spectroscopy and fluorescence microscopy that the mechanism of antimicrobial action of new acylhydrazones is associated with their ability to destroy the bacterial cell membrane.

Synthesis, antimicrobial activity and cytotoxicity of triphenylphosphonium (TPP) conjugates of 1,2,3-triazolyl nucleoside analogues

Four new triphenylphosphonium (TPP) conjugates of 1,2,3-triazolyl nucleoside analogues were synthesized by coupling with 8-bromoctyl- or 10- bromdecyltriphenylphosphonium bromide and evaluated for the in vitro antibacterial activity against S. aureus, B. cereus, E. faecalis, two MRSA strains isolated from patients and resistant to fluoroquinolone antibiotic ciprofloxacin and β-lactam antibiotic amoxicillin, E. coli, antifungal activity against T. mentagrophytes C. albicans and cytotoxicity against human cancer cell lines M-HeLa, MCF-7, A549, HuTu-80, PC3, PANC-1 and normal cell line Wi-38. In these compounds a TPP cation was attached via an octyl or a decyl linker to the N 3 atom of the heterocycle moiety (thymine, 6-methyluracil, quinazoline-2,4-dione) which was bonded with 2',3',5'-tri- O - acetyl-greek beta-d-ribofuranose residue by the (1,2,3-triazol-4-il)methyl bridge. All synthesized compounds showed high antibacterial activity against S. aureus within the range of MIC values 1.2-4.3 greek muM, and three of them appeared to be bactericidal with respect to tis bacterium at MBC values 4.1-4.3 greek muM. Two lead compounds showed both high antibacterial activity against the MRSA strains resistant to Ciprofloxacin and Amoxicillin within the range of MIC values 1.0-4.3 greek muM and high cytotoxicity against human cancer cell lines HuTu-80 and MCF-7 within the range of IC₅₀ values 6.4-10.2 greek muM. This is one of the few examples when phosphonium salts exhibited both antibacterial activity and cytotoxicity against human cancer cell lines. According to the results obtained the bactericidal effect of the lead compounds, unlike classical surfactants, was not caused by a violation of the integrity of the cytoplasmic membrane of bacteria and their cytotoxic activity is most likely associated both with the induction of apoptosis along the mitochondrial pathway and the arrest of the cell cycle in the G0/G1 phase.

Trialkyl(vinyl)phosphonium Chlorophenol Derivatives as Potent Mitochondrial Uncouplers and Antibacterial Agents

Trialkyl phosphonium derivatives of vinyl-substituted p-chlorophenol were synthesized here by a recently developed method of preparing quaternary phosphonium salts from phosphine oxides using Grignard reagents. All the derivatives with a number (n) of carbon atoms in phosphonium alkyl substituents varying from 4 to 7 showed pronounced uncoupling activity in isolated rat liver mitochondria at micromolar concentrations, with a tripentyl derivative being the most effective both in accelerating respiration and causing membrane potential collapse, as well as in provoking mitochondrial swelling in a potassium-acetate medium. Remarkably, the trialkyl phosphonium derivatives with n from 4 to 7 also proved to be rather potent antibacterial agents. Methylation of the chlorophenol hydroxyl group suppressed the effects of P₅₅₅ and P₄₄₄ on the respiration and membrane potential of mitochondria but not those of P₆₆₆, thereby suggesting a mechanistic difference in the mitochondrial uncoupling by these derivatives, which was predominantly protonophoric (carrier-like) in the case of P₅₅₅ and P₄₄₄ but detergent-like with P₆₆₆. The latter was confirmed by the carboxyfluorescein leakage assay on model liposomal membranes.

Trivalent sulfonium compounds (TSCs): Tetrahydrothiophene-based amphiphiles exhibit similar antimicrobial activity to analogous ammonium-based amphiphiles

Recent advances in the development of quaternary ammonium compounds (QACs) have focused on new structural motifs to increase bioactivity, but significantly less studied has been the change from ammonium- to sulfonium-based disinfectants. Herein, we report the synthesis of structurally analogous series of quaternary ammonium and trivalent sulfonium compounds (TSCs). The bioactivity profiles of these compounds generally mirror each other, and the antibacterial activity of sulfonium-based THT-18 was found to be comparable to the commercial disinfectant, BAC. The development of these compounds presents a new avenue for further study of disinfectants to combat the growing threat of bacterial resistance.

Advancements in the Development of Non-Nitrogen-Based Amphiphilic Antiseptics to Overcome Pathogenic Bacterial Resistance

The prevalence of quaternary ammonium compounds (QACs) as common disinfecting agents for the past century has led bacteria to develop resistance to such compounds. Given the alarming increase in resistant strains, new strategies are required to combat this rise in resistance. Recent efforts to probe and combat bacterial resistance have focused on studies of multiQACs. Relatively unexplored, however, have been changes to the primary atom bearing positive charge in these antiseptics. Here we review the current state of the field of both phosphonium and sulfonium amphiphilic antiseptics, both of which hold promise as novel means to address bacterial resistance.