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EXPLORING ANTIBIOTIC CONJUGATION TO CATIONIC AMPHIPHILIC POLYPROLINE HELICES
Pathogenic bacteria present a critical threat to modern medicine. Therapeutic strategies to target and eliminate resilient bacteria are not advancing at the same rate as the emergence of bacterial resistance. An associated urgent concern regarding antibiotic resistance is the existence and proliferation of intracellular bacteria, which find refuge from bactericidal mechanisms by hiding within mammalian cells. Therefore, many once-successful antibiotics become ineffective through the development of resistance, or through failure to reach intracellular locations in therapeutic concentration. To overcome these challenges, the covalent combination of a conventional antibiotic with an antibiotic, cell-penetrating peptide was explored to develop dual-action antibiotic conjugates.
Herein, we utilized a strategy in conjugating the antibiotics by a cleavable linkage to cationic amphiphilic polyproline helices (CAPHs) to improve vancomycin and linezolid antibiotics. This approach enables the conjugate to penetrate cells and deliver two potent monomeric antimicrobial drugs. The vancomycin-CAPH conjugate, VanP14S, showed enhanced mammalian cell uptake compared to vancomycin, a poor mammalian cell-penetrating agent; and VanP14S was capable of cleaving and releasing two antibiotics under mimicked physiological conditions. Enhanced antibacterial activity was observed against a spectrum of Gram-positive and Gram-negative pathogens, including drug-resistant strains. Further investigation revealed that this conjugate’s bactericidal activity was not entirely the result of significant membrane perturbation such as a lytic mode of action. Mammalian cell toxicity and red blood cell lysis were insignificant at relevant bactericidal concentrations below 20 µM. The current results suggest an enhanced binding to the peptidoglycan of bacteria, the target of vancomycin, although more work is needed to justify this claim. Preliminary results on VanP14GAPS, a conjugate with a more rigid CAPH, convey similar activity to VanP14S; however, moderate increases in red blood cell lysis and cytotoxicity were observed.
Regarding the LnzP14 conjugate, preliminary data reveal that the conjugate has Gram-negative activity against Escherichia coli, whereas linezolid is ineffective in killing Gram-negative bacteria. This conjugate showed significant enhancement in cellular uptake compared to the CAPH, and the release of linezolid and CAPH in physiological conditions was confirmed. Overall, arming a conventional antibiotic with an antimicrobial, cell-penetrating peptide appears to be a powerful strategy in providing novel antibiotic conjugates with the propensity to overcome the limitations in treating challenging pathogens.