Covalent Conjugates of Allylbenzenes and Terpenoids as Antibiotics Enhancers with the Function of Prolonged Action

Abstract

The drug resistance of pathogenic bacteria is often due efflux pumps—specific proteins that remove foreign compounds from bacterial cells. To overcome drug resistance, adjuvants are often used that can inhibit efflux pumps or other systems that ensure the resistance of bacteria to the action of antibiotics. We assumed that a new level of effectiveness with the use of an antibiotic + an adjuvant pair could be achieved by their joint delivery into the pathogen. To test this hypothesis, we constructed a series of molecular carriers based on poly-(olygo-, dendry)mers based on cyclodextrin-grafted PEI or mannan, as well as glycol chitosan, covalently bound to antibiotic, adjuvant, and the oligosaccharide ligand to the macrophage mannose receptor (CD206), which we studied earlier and showed high efficiency and selectivity of delivery of a therapeutic “cargo” to macrophages. Moxifloxacin was used as an antibiotic, and terpenoid and allylbenzene compounds were used as adjuvants, for which we previously discovered the ability to inhibit bacterial efflux pumps. We show that: (a) the resulting structures were stable in vitro for a long time (up to 10 days); (b) they were adsorbed on bacterial cells, providing a local increase in the concentration of the antibiotic and adjuvant in pathogen cells; (c) they were internalized by bacterial cells, ensuring the accumulation of both antibiotic and adjuvant inside bacterial cells; (d) the adjuvant, after entering the bacterial cell, provided inhibition of the efflux pumps; (e) due to this action of the adjuvant, combined with the targeted delivery by the carrier, the antibiotic’s half-life in rats increased by more than 2 times, the effective concentration of the drug in the blood plasma (AUC) increased up to 8–10 times; (f) a significant increase in the effectiveness of the antibacterial action against Gram+ and Gram- cells was achieved (up to 3 times). Potentially, such an approach would significantly increase the effectiveness of therapies for a number of infectious and other diseases, reduce the dosage of antibiotics, shorten the duration of treatment, and reduce the risk of developing bacterial resistance. Moreover, the use of a polymer carrier with covalently bound organic molecules of different structures will avoid problems linked to different (suboptimal) solubility and bio-distribution of the administered molecules, which would be almost inevitable when using the same compounds separately. It would be very difficult to find antibiotic/adjuvant pairs that simultaneously achieve optimal concentrations in the same target cells. In our case, terpenoids and alkylbenzenes used as adjuvants are practically insoluble as individual compounds, and their unacceptable pharmacological properties would not allow them to be used as efflux pump inhibitors.