Design and synthesis of cell selective α/β-diastereomeric peptidomimetic with potent in vivo antibacterial activity against methicillin resistant S. Aureus.

Design of therapeutically viable antimicrobial peptides with cell selectivity against microorganisms is an important step towards the development of new antimicrobial agents. Here, we report four de novo designed, short amphipathic sequences based on a α-helical template comprising of Lys, Trp and Leu or their corresponding D-and/or β-amino acids. Sequence A-12 was protease susceptible whereas its α/β-diastereomeric analogue UNA-12 was resistant to trypsin and proteinase K up to 24 h. A-12 and UNA-12 exhibited broad-spectrum antibacterial activity (MIC: 2-32 µg/mL) against pathogens including methicillin resistant S. aureus (MRSA) and methicillin-resistant S. epidermidis (MRSE). Interestingly, A-12 was found to be most toxic (>50% haemolytic at 250 µg/mL) whereas UNA-12 was found to be non cytotoxic among the all analogues against hRBCs and human keratinocytes. Interaction studies with artificial membranes by tryptophan fluorescence and acrylamide quenching assay demonstrated A-12 interacted equally in bacterial as well as mammalian mimic membrane whereas UNA-12 was found to be more selective towards bacterial mimic membrane. Further microscopic tool has revealed membrane damaging ability of A-12 and UNA-12 with bactericidal mode of action against MRSA. Encouragingly, peptidomimetics analogue UNA-12 showed remarkable safety and efficacy against MRSA in in-vivo neutropenic mice thigh infection model. In summary, simultaneous replacement of the natural amino acids with D-/β-congeners is a promising strategy for designing of potent, cell selective and protease stable peptide based antibiotics.