Potent and Broad-Spectrum Bactericidal Activity of a Nanotechnologically Manipulated Novel Pyrazole

Abstract

The antimicrobial potency of the pyrazole nucleus is widely reported these days, and pyrazole derivatives represent excellent candidates for meeting the worldwide need for new antimicrobial compounds against multidrug-resistant (MDR) bacteria. Consequently, 3-(4-chlorophenyl)-5-(4-nitrophenylamino)-1H-pyrazole-4-carbonitrile (CR232), recently reported as a weak antiproliferative agent, was considered to this end. To overcome the CR232 water solubility issue and allow for the determination of reliable minimum inhibitory concentration values (MICs), we initially prepared water-soluble and clinically applicable CR232-loaded nanoparticles (CR232-G5K NPs), as previously reported. Here, CR232-G5K NPs have been tested on several clinically isolates of Gram-positive and Gram-negative species, including MDR strains. While for CR232 MICs ≥ 128 µg/mL (376.8 µM) were obtained, very low MICs (0.36–2.89 µM) were observed for CR232-G5K NPs against all of the considered isolates, including colistin-resistant isolates of MDR Pseudomonas aeruginosa and Klebsiella pneumoniae carbapenemases (KPCs)-producing K. pneumoniae (0.72 µM). Additionally, in time–kill experiments, CR232-G5K NPs displayed a rapid bactericidal activity with no significant regrowth after 24 h on all isolates tested, regardless of their difficult-to-treat resistance. Conjecturing a clinical use of CR232-G5K NPs, cytotoxicity experiments on human keratinocytes were performed, determining very favorable selectivity indices. Collectively, due to its physicochemical and biological properties, CR232-G5K NPs could represent a new potent weapon to treat infections sustained by broad spectrum MDR bacteria.

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

“…With this strategy, we obtained pyrazole-loaded water-soluble NPs which were easily evaluated for their antibacterial effects and cytotoxicity on eukaryotic cells [6,22]. Although the dendrimers used as solubilizing agents were free of any antibacterial effect, following the encapsulation, the antibacterial properties of pristine pyrazoles were significantly improved and their cytotoxicity reduced, achieving pyrazole-based NPs endowed with potent antibacterial/bactericidal activity against several species of MDR bacteria [6,22]. Now, we first synthetized a new highly substituted pyrazole derivative, in the form of ammonium hydrochloride salt (CB1H), to resolve the poor water solubility of the free amine in advance [23].…”

“…MIC values of CB1H-P7 NPs and those of P7 and CB1H in the complex against bacteria of Gram-negative species, obtained from experiments carried out in triplicate, and those of reference antibiotics expressed as µM and µg/mL. To date, as far as we know, except for CR232-G5K NPs that we have recently developed [22], no other pyrazole-containing macromolecule has been reported for its bactericidal effects. On the contrary, bactericidal effects have been demonstrated by one hydroxy-coumarin-substituted pyrazole-derived hydrazone derivative against an ATCC strain of MRSA [37].…”

“…In addition to having available a library of pyrazoles, also including previously synthetized molecules, to meet the desired low economic inputs required for the development of new antimicrobial agents and to exploit the promising antibacterial characteristics of pyrazoles, we recently developed a new one-pot, low-cost synthetic strategy for the preparation of highly functionalized pyrazole derivatives [19]. Furthermore, we recently synthetized pyrazole-based dendrimer nanoparticles, developed to address the solubility disadvantages of the pristine CR232 and BBB4 pyrazoles showed in Figure 1 The obtained water-soluble and clinically applicable BBB4-G4K and CR232-G5K NPs, realized using dendrimers (G4K and G5K) free of any antibacterial effects, demonstrated potent specific or broad-spectrum antibacterial activity also against MDR bacteria, low level of cytotoxicity on eukaryotic cells and high selectivity indices [6,[20][21][22]. Interestingly, CR232-G5K NPs were effective also against isolates of P. aeruginosa and K. pneumoniae resistant to colistin, on which all other clinically approved antibiotics failed The obtained water-soluble and clinically applicable BBB4-G4K and CR232-G5K NPs, realized using dendrimers (G4K and G5K) free of any antibacterial effects, demonstrated potent specific or broad-spectrum antibacterial activity also against MDR bacteria, low level of cytotoxicity on eukaryotic cells and high selectivity indices [6,[20][21][22].…”

“…Furthermore, we recently synthetized pyrazole-based dendrimer nanoparticles, developed to address the solubility disadvantages of the pristine CR232 and BBB4 pyrazoles showed in Figure 1 The obtained water-soluble and clinically applicable BBB4-G4K and CR232-G5K NPs, realized using dendrimers (G4K and G5K) free of any antibacterial effects, demonstrated potent specific or broad-spectrum antibacterial activity also against MDR bacteria, low level of cytotoxicity on eukaryotic cells and high selectivity indices [6,[20][21][22]. Interestingly, CR232-G5K NPs were effective also against isolates of P. aeruginosa and K. pneumoniae resistant to colistin, on which all other clinically approved antibiotics failed The obtained water-soluble and clinically applicable BBB4-G4K and CR232-G5K NPs, realized using dendrimers (G4K and G5K) free of any antibacterial effects, demonstrated potent specific or broad-spectrum antibacterial activity also against MDR bacteria, low level of cytotoxicity on eukaryotic cells and high selectivity indices [6,[20][21][22]. Interestingly, CR232-G5K NPs were effective also against isolates of P. aeruginosa and K. pneumoniae resistant to colistin, on which all other clinically approved antibiotics failed and against NDMs, thus being more efficacious than ceftolozane [22].…”

“…and against NDMs, thus being more efficacious than ceftolozane [22]. More recently, aiming at improving the weak antibacterial activity (MICs = 128 µg/mL and > 256 µg/mL on selected Gram-positive and Gram-negative isolates respectively) of a new pyrazole hydrochloride salt (CB1H) (Figure 2a), CB1H-loaded nanoparticles (CB1H-P7 NPs) were developed by using a cationic copolymer (P7) (Figure 2b) [23].…”