The  research programme coordinated by Marco  Scocchi  is focused on the study of biology and on the biotechnological use of natural bioactive peptides with antimicrobial properties. The “host defense peptides” (HDPs) or antimicrobial peptides (AMPs) are part of the innate immune system of eukaryotes and participate in the eradication/prevention of infections by killing pathogens and/or stimulating the immune system.

The objectives of the research’s team are: 

• To investigate the molecular mechanism of AMPs action. Differently to antibiotics, AMPs target bacteria by multiple modes of action. Research is aimed at clarifying these mechanisms and understanding the route of internalization of AMPs into the bacteria. 
• To develop AMPs as novel drugs. AMPs show attractive characteristics as antimicrobials. Aim of the research group is to optimize them, combining high antibacterial activity with low toxicity and a reliable route of administration. 

1) Characterization and optimization of proline-rich antimicrobial peptides (PR-AMPs)

Most antimicrobial peptides (AMPs) inactivate target bacteria through pore formation or membrane barrier disruption, while others, including PR-AMPs, cross the membrane without damages and act inside the cells affecting vital processes. Most PrAMPs act by interacting with the bacterial ribosomes, thereby interfering with protein translation.

This research group  has isolated and studied two mammalian PrAMPs of 5 and 7 KDa called Bac5 and Bac7 respectively, that are stored in neutrophil granules and kill a number of gram-negative bacteria; these peptides are internalized through the bacterial membrane transporter SbmA and then kill bacteria intracellularly, targeting the ribosome and hinibiting the translational apparatus.

We characterized some short fragments of Bac5 and Bac7, showing that these shorter peptides retained the mechanism of action of the full-length PrAMPs.The shortest Bac 5 and Bac7 fragments with significant antimicrobial activity and low cytotoxicity were chosen to  be optimized by introducing mutations in the sequence of the Bac fragments and/or attaching diverse non-peptidic moieties to the peptides. Our lab is currently characterizing libraries of peptide mutants in vitro aiming to i) find short molecules derived from Bac5 and Bac7, with optimal combinations of antimicrobial activity, low cytotoxicity and stability in biological fluids, and ii) test the resulting best candidate molecules in mouse models of infection.

The aims of this project are: i) to unravel the precise molecular mechanism by which this PR-AMP kills bacteria identifying the ribosomal proteins/RNA  involved in the interaction with the peptide, and ii) to study the regulation of the expression of SbmA as a tool to modulate the sensitivity of the bacterial cell to AMPs.  Results will allow us to optimize this AMP as a potential new antimicrobial drug against Gram-negative bacteria.

(Researchers involved: M. Scocchi, M. Benincasa, G. Runti, M. Mardirossian)

2) Development of AMPs for biomedical applications

The increasing emergence of multidrug-resistant (MDR) microorganisms is one of the greatest challenges in the clinical management of infectious diseases. Therefore, novel antimicrobial agents are urgently required to address this issue. The problem is exacerbated by the capability of most bacteria to form biofilms, which are present in up to 60% of infections and are intrinsically resistant to antibiotics.

In this context, our research is focused on three different topics:

AMPs for the treatment of pulmonary infections - Pulmonary 80% of  cystic fibrosis  patients (CF)  succumb to respiratory failure due to chronic bacterial infection. We have showed that BMAPs are AMPs that are in vitro and in vivo active against P. aeruginosa and S. maltophilia strains and their in vitro biofilm forms which cause most pulmonary chronic complications in CF patients. Our team is investigating the potential of the synthetic all-D derivative D-BMAP18 against these antibiotic-resistant and/or biofilm producing pathogens and how to enhance its activity in CF pulmonary environment. Ultimate aim of this research is to optimize the all-D 18-amino acid long peptide by combining  high antimicrobial activity with low cytotoxicity and a feasible route of  in vivo administration, in order to maximize its efficacy as novel antibacterial for the treatment of CF-associated pulmonary infections. For this reason we are working on a pro-drug derived form of D-BMAP18 which would  be activated only at the site of infection.

AMPs evaluation against emerging pathogens - A. baumannii and K. pneumoniae colonize medical devices causing up to 50% of ventilator-associated pneumonia infections. Our team is investigating the potential of AMPs against these antibiotic-resistant and/or biofilm producing pathogens and their use to prevent colonization of abiotic surfaces on medical devices.

Numerous studies indicate AMPs as advisable candidates in the fight against MDR microorganisms, although  literature about these compounds does not report their effects against susceptible bacteria when they are used at sub-inhibitory concentrations. In this context, a study on  sub toxic effects of  the PrAMP Bac7(1-35) on biofilm formation and twitching motility of A. baumannii clinical isolates is ongoing.

(Researchers involved: M. Scocchi, S. Pacor, M. Benincasa, M. Mardirossian)