Peptide-conjugates derived from bacterial ParE toxin: synthesis and biological studies

Antimicrobial resistance represents the major public health problem of the 21st century.New therapeutic agents, with innovative modes of action, are urgently needed given the seriousness of the problem.Peptides derived from bacterial toxins could be considered as a way to avoid this global health threat.ParELC3, a peptide derived from bacterial toxin ParE was reported to be a good inhibitor of bacterial topoisomerases in vitro and therefore a potential antibacterial agent [1].However, a permeability limitation prevents its use as a new therapeutic agent.For circumvent this permeability limitation and promote a dual inhibitory targeting, we decided to design and synthesize molecular structures resulting from the conjugation of a ParELC3 analog with quinolone and coumarin groups to permeate the bacterial membrane and act synergistically in the inhibition of different topoisomerases.The peptide ParELC3M and respective conjugates CJHOAc, CJCOQ, CJCFX and CJNCFX (Figure 1b) were chemically synthesized by Solid Phase methodology, purified by RP-HPLC and characterized by mass spectrometry.(ESI-MS).The obtained peptide-conjugates were evaluated for their ability to inhibit topoisomerases activity and prevent the bacterial growth.In standard supercoiling and relaxation assays, the peptide ParELC3M and its conjugates did not inhibit the E. coli and S. pneumoniae DNA gyrase activity.On the other hand, all conjugates were able to inhibit completely the M. tuberculosis DNA gyrase activity and relaxation reaction of E. coli and S. pneumoniae topo IV with expressive IC 100 values.In addition, CJCFX and CJNCFX conjugates inhibited E. coli topo IA with IC 100 smaller than 6.25 mol.L -1 .For yeast topoisomerase II, the inhibition was even more effective.The conjugates were effective against E. coli and S. aureus with MIC values of 25 mol.L -1 .The results also showed low cytotoxicity for both peptide and peptide-conjugates with a cell viability greater than 75% even under the highest tested concentration.The results showed that the insertion of coumarin and fluoroquinolones groups to a peptide chain increase its capacity to permeate the bacterial plasma membrane and reach the cytoplasm, where can exert its activity.