Enhanced Antibacterial Activity of a Cationic Macromolecule by Its Complexation with a Weakly Active Pyrazole Derivative

Abstract

Molecules containing the pyrazole nucleus are widely reported as promising candidates to develop new antimicrobial compounds against multidrug-resistant (MDR) bacteria, where available antibiotics may fail. Recently, aiming at improving the too-high minimum inhibitory concentrations (MICs) of a pyrazole hydrochloride salt (CB1H), CB1H-loaded nanoparticles (CB1H-P7 NPs) were developed using a potent cationic bactericidal macromolecule (P7) as polymer matrix. Here, CB1H-P7 NPs have been successfully tested on several clinical isolates of Gram-positive and Gram-negative species, including relevant MDR strains. CB1H-P7 NPs displayed very low MICs (0.6–4.8 µM), often two-fold lower than those of P7, on 34 out of 36 isolates tested. Upon complexation, the antibacterial effects of pristine CB1H were improved by 2–16.4-fold, and, unexpectedly, also the already potent antibacterial effects of P7 were 2–8 times improved against most of bacteria tested when complexed with CB1H. Time-killing experiments performed on selected species established that CB1H-P7 NPs were bactericidal against Staphylococcus aureus, Escherichia coli and Pseudomonas aeruginosa. Selectivity indices values up to 2.4, determined by cytotoxicity experiments on human keratinocytes, suggested that CB1H-P7 NPs could be promising for counteracting serious infections sustained by most of the isolates tested in this study.

Pyrazole-Enriched Cationic Nanoparticles Induced Early- and Late-Stage Apoptosis in Neuroblastoma Cells at Sub-Micromolar Concentrations

“…In cytotoxicity experiments at 24 h of exposure which were carried out by treating HaCaT cells with CB1H, CB1H-P7 and P7 NPs, we observed that NPs caused a significant reduction in cell viability only over concentrations of 1.43 µM [ 23 ]. So, in this case, the cytotoxic activity of the CB1H as a function of its concentrations was investigated using a wider concentration range (1–100 µM).…”

“…The selectivity of the cytotoxic activity of the tested compounds against tumor cells (cytotoxic properties) was estimated by selectivity indices (SI). The SI values were determined using the IC 50 , as was previously reported for the same compounds against normal human keratinocytes (HaCaT) [ 23 ] and according to Equation (1). …”

“…In light of this, aiming at developing new antitumor agents to counteract NB cells, pyrazole-based nanocomposites (namely BBB4-G4K and CB1H-P7 NPs) have recently been reported to have remarkable antibacterial activity, mainly towards Staphylococci (BBB4-G4K NPs) [ 22 ], and broad-spectrum bactericidal effects [ 23 ]; here, we assayed them against two NB cell lines (IMR-32 and SHSY 5Y). Particularly, we carried out dose- and time-dependent cytotoxicity experiments using the pristine pyrazoles BBB4 and CB1H ( Figure S1 , Section S1 in Supplementary Materials (SM) ), the empty cationic NPs G4K and P7 ( Figure S2, Section S1, (SM) ) and the pyrazole-enriched nanocomposites BBB4-G4K and CB1H-P7 ( Figure S3, Section S1 (SM) ) [ 24 , 25 ] to assess their efficiency in inhibiting NB cells, and to assess which compound/s could be worthy of further investigations.…”

“…The scope of a previous piece of research by us [ 22 , 23 , 24 , 25 ] was to develop new pyrazole-based antibacterial agents using pyrazole BBB4 ( Figure S1a ), found active against several human diseases [ 24 ], and the free pyrazole amine (CB1) of the pyrazole hydrochloride salt (CB1H), as shown in Figure S1b .…”

“…Therefore, we solved the drawbacks of BBB4 related to water-solubility through its nano formulation, using the highly hydrophilic and water-soluble cationic dendrimer G4K and obtaining water-soluble NPs (BBB4-G4K NPs) [ 24 ] which demonstrated remarkable and improved antibacterial properties and high values of selectivity indices (SIs) [ 22 ]. As for CB1, its poor water-solubility was solved in advance by preparing it in the form of ammonium hydrochloride salt (CB1H) [ 25 ], while its nano formulation using broad-spectrum bactericidal NPs, namely P7 [ 21 ], was carried out to improve the weak antibacterial properties observed for CB1H [ 23 ]. The obtained CB1H-P7 NPs demonstrated potent broad-spectrum bactericidal effects even higher than those of P7 [ 21 ].…”