Toward optimization of a BMAP-derived antimicrobial peptide for the treatment of pulmonary infections caused by Pseudomonas aeruginosa in cystic fibrosis patients.

Introduction: BMAP-271-18 is a shortened form of the α-helical bovine myeloid antimicrobial peptide BMAP-27. It is active against P. aeruginosa strains from cystic fibrosis (CF) patients (MIC90: 16 μg/ml, on 15 strains), and it is well tolerated when intra-tracheally administered to healthy mice1. Aim of this study was to evaluate the potential of BMAP-271-18 for the development of novel drugs to treat CF lung infections. Materials and Methods: In vivo efficacy of BMAP-271-18 was evaluated in C57BL/6NCrl mice by single intratracheal administration of different concentrations of the peptide immediately after exposure to P. aeruginosa RP73 strain. Peptide stability in murine bronchoalveolar lavage (BAL) was evaluated by SDS-PAGE. Peptide synthesis was performed using solid-phase Fmoc chemistry method, followed by purification by reversed phase HPLC. MICs were determined according to EUCAST guidelines. Results: BMAP-271-18 showed no significant protection against P. aeruginosa lung infection, regardless of doses used. This is likely due to the fact that it was rapidly degraded (within 10 minutes) when exposed to BAL. To overcome this problem an all-D isomer of BMAP271-18 was synthesized. This peptide resulted to be significantly more resistant to pulmonary proteases, being not degraded in BAL even after one week, and showed an antimicrobial activity against P. aeruginosa (strain RP73; MIC: 4 μg/ml) comparable to the all-L isomer. Discussion and Conclusions: Despite its relevant in vitro antimicrobial activity, BMAP271-18 does not show protective effect in a murine model of lung infection because it is rapidly degraded by pulmonary host proteases. The D-BMAP-271-18 represents a promising improvement of the original peptide, since it is resistant to proteolytic cleavage although preserving in vitro antimicrobial activity. Further in vitro and in vivo studies are now ongoing to evaluate the protective effect and the safety of D-BMAP-271-18.