Recognition of antibiotics by calixarene-based micellar aggregates in aqueous solution: binding features and driving forces

The search for novel drug delivery systems (DDSs) able to improve the performance of old-generation antibiotics is a topic of great interest due to overcoming problems associated with antibiotic resistance [1]. Polycationic calixarene derivatives able to self-assemble in nanoaggregates are promising novel nanocontainers for delivering antibiotics to bacteria due to their ability to establish electrostatic interactions with the negatively charged bacterial membranes [2]. In particular, a polycationic amphiphilic calix[4]arene, bearing choline groups and dodecyl aliphatic chains at the cavity upper and lower rim respectively, proved to be a promising nanocarrier for drug delivery [3]. The determination of the strength and nature of drug-micelle interactions is crucial for the design of novel medicines and the modification or selection of suitable shuttles for target-oriented drug delivery. However, despite the wide interest in the examination of these interactions, a quantitative analysis of the species, binding constants and thermodynamic parameters for the recognition/inclusion of a drug with(in) micellar assemblies has rarely been addressed. The present work deals with the study of the binding features of polycationic calix[4]arene derivatives (CholineC4dod, MedeaC4dod and MedeaC4prop) with ofloxacin, chloramphenicol or tetracycline in neutral aqueous solution for investigating the capability of micellar aggregates to recognize and host three old generation antibiotics. These molecules were selected as models of antibiotics affected by the onset of resistance phenomena with the aim of contributing to the design and development of effective DDSs for the repurposing of old-fashioned drugs. The study of the solution equilibria and the determination of the binding parameters in neutral aqueous solution were carried out using nano-isothermal titration calorimetry, that allows obtaining both stability constant and enthalpy change values for host-guest complex formation [4] and/or selforganization of surfactants into micelles by a single experiment [5,6]. ITC measurements showed that the formation of the chloramphenicol-micelle adduct is always an enthalpically driven process while the adducts with ofloxacin and tetracycline are always entropically driven and enthalpically unfavored. NMR experiments confirmed the picture on the positioning of the antibiotics within the micellar backbone provided by the ITC data [7]. [1] R. K. Kobayashi, G. Nakazato, Front. Microbiol. 2020, 11, 1421. [2] I. Di Bari, R. Picciotto, G. Granata, A. R. Blanco, G. M. L. Consoli, S. Sortino, Org. Biomol. Chem. 2016, 14(34), 8047. [3] G. Granata, S. Petralia, G. Forte, S. Conoci, G. M. L. Consoli, Mater. Sci. Eng. C 2020, 111, 110842. [4] C. Bonaccorso, R. Migliore, M. A. Volkova, G. Arena, C. Sgarlata, Thermochim. Acta 2017, 656, 47. [5] W. Loh, C. Brinatti, K. C. Tam, Biochim. Biophys. Acta 2016, 1860(5), 999. [6] R. Migliore, PhD Thesis, University of Catania, 2019. [7] R. Migliore, G. Granata, A. Rivoli, G. M. L. Consoli, C. Sgarlata, Front. Chem. 2021, 8, 626467.