The competence regulon of Streptococcus pneumoniae (pneumococcus) is a quorum-sensing circuitry that regulates the ability of this pathogen to acquire antibiotic resistance or perform serotype switching, leading to vaccine-escape serotypes, via horizontal gene transfer, as well as initiate virulence. Induction of the competence regulon is centered on binding of the competence-stimulating peptide (CSP) to its cognate receptor, ComD. We have recently synthesized multiple dominant-negative peptide analogs capable of inhibiting competence induction and virulence in S. pneumoniae. However, the pharmacodynamics and safety profiles of these peptide drug leads have not been characterized. Therefore, in this study, we compared the biostability of cyanine-7.5-labeled wild-type CSPs versus dominant-negative peptide analogs (dnCSPs) spatiotemporally by using an IVIS Spectrum in vivo imaging system. Moreover, in vitro cytotoxicity and in vivo toxicity were evaluated. We conclude that our best peptide analog, CSP1-E1A-cyc(Dap6E10), is an attractive therapeutic agent against pneumococcal infection with superior safety and pharmacokinetics profiles.
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