Synthesis of charged cyclodextrins for encapsulation of antibiotics

Antimicrobial resistance is a contemporary serious threat to public health due to theworldwide spread of resistant bacterial strains that severely disempower the effectivenessof existing antibiotics. Apart from the discovery of new drugs, the elaboration of methodsto suppress resistance and repotentiate drugs is a much desired solution to this severeproblem. The employment of cyclodextrins as nanosized host molecules to protectantibiotics from resistance-conferring bacterial enzymes could be proposed as ananotechnological approach towards this end. Cyclodextrins (CDs) consist of 6, 7 or 8 α-1,4-linked D-glucopyranose units to form macrocyclic oligosaccharides (α-, β- or γ-CD,respectively) which are used as pharmaceutical excipients, thanks to their ability toenhance the water solubility and stability of hydrophobic drugs upon formation ofsupramolecular host : guest complexes. In this dissertation, multifunctional CD-basednanocarriers have been designed, synthesized and studied in detail towards protection andrepotentiation of antibiotics against resistant infections. In a first approach,comprehensive NMR and ITC studies were undertaken to screen four β-lactam antibioticswith a panel of natural and specifically synthesized CDs, in order to investigate theeffects of host size, flexibility and end-group charges on the binding with the drugs. Thestudy has completely defined the structural requirements and the associated strengths andlimitations regarding CD : penicillin complexation. Therefore, the results showed that ofall CDs studied, the engineered cysteamine-appended γ-CD (GCYS) forms the strongestinclusion complex with oxacillin (OXA, an antistaphylococcal penicillin) during anenthalpically and entropically favored process resulting in ΔGb = -18.5 kJ mol-1 and Kb ≈1700 M-1 at 37 oC. Moreover, GCYS protects OXA from hydrolysis by a specific oxa-1β-lactamase enzyme produced by E. coli, reducing the corresponding rate by 2.3-fold.Finally, GCYS is also able to penetrate the cell walls of macrophages, thus it can beproposed as an effective delivery system for OXA to mammalian cells. The findings mayhave important implications since phagocytosis of invading infectious bacteria plays akey role in host immune defense. It is then plausible to propose that increasedconcentrations of antibiotics within macrophages via entry of GCYS/antibioticcomplexes may enhance bacterial killing. In another approach, a combination of detailedNMR and UV-Vis spectroscopic investigations highlighted the ability of heptakis(2,6-di-O-methyl)-βCD (DIMEB), among different methylated CD derivatives, to formcomplexes with rifampicin, an ansamycin antibiotic used as first-line treatment oftuberculosis. Enhanced water solubility and long-term stability of rifampicin wasachieved upon complexation with DIMEB in neutral conditions via formation of a strong,2 : 1 complex (Kb1 ≈ 3000 M-1, Kb2 ≈ 10 M-1) at the piperazine site of the drug,accompanied by two more binding sites responsible for weaker bindings. A decreasedhost : guest affinity (Kb ≈ 400 M-1) was…