Novel antibacterial nanoconstructs based on carbon dots or calixarene derivatives incorporating natural bioactive compounds and ciprofloxacin for combined effect.

Introduction. An appealing strategy to counteract the increasing antimicrobial resistance is represented by combinations of natural and conventional antimicrobial molecules and their entrapment into nanocarriers for simultaneous delivery. The present study aims to develop novel antimicrobial drug delivery systems by co-loading natural hydrophobic compounds, namely carvacrol (CAR) and curcumin (CUR), and conventional ciprofloxacin (CPX) in nanocarriers for multidrug treatment of antibiotic resistant infections. Materials and Methods. Two classes of nanocarriers were prepared and their physicochemical properties were characterized. Specifically, a nanocarrier composed of a carbonaceous core (carbon-dot) covered by β-cyclodextrin units (Cdots-βCD) and nanocarriers generated by the self-assembling of amphiphilic calixarene derivatives were studied. The drug loading capacity percentage of the nanocarriers was calculated. The carrier-drugs interactions were investigated by molecular dynamics simulations, the HOMO energy (nπ* transition) for Cdots-βCD/CPX complex was calculated, and the UV-Vis spectra simulated. The in vitro antibacterial and antibiofilm activities were investigated by broth microdilution and biofilm biomass measurement against methicillin resistant Staphylococcus aureus, ESBLs producing Escherichia coli, Acinetobacter baumannii, and VIM-2 producing Pseudomonas aeruginosa. The antioxidant activity was evaluated by 2,2-diphenyl-1-picrylhydrazyl (DPPH) assay. Results. The carrier-drug nanoconstructs showed good dispersibility in aqueous solution, high chemical stability, biocompatibility and optical properties including luminescence and photothermal effect at 405 nm. The Cdots-βCD/CAR nanosystem and the micellar sulfonate-calixarene co-loading CUR and CPX demonstrated antibacterial efficacy comparable or even better than that of the individual bioactive compounds. Notably, Cdots-βCD/CAR exhibited MIC values ranging from 17.5 to 70 µg/mL and more than 50% inhibition of S. aureus biofilm formation at sub-MIC concentrations. Interestingly, the sulfonate-calixarene/CPX/CUR nanoconstruct was found to possess antioxidant activity. Discussion and Conclusions. The designed nanocarriers appear as promising candidates for improving solubility, stability, and bioavailability of the selected bioactive compounds. The presence of multiple sites of complexation also allows their co-delivery for additive or synergistic effects. Our findings suggest that the novel nanoconstructs could be favorable delivery systems for the treatments of antibiotic resistant infections. Acknowledgments All the authors acknowledge financial support: Project PRIN 2022 PNRR (P20229ZLSA_002) “BIONANOF” funded by the European Union – Next Generation EU”.