Design of pH-responsive Peptide Assembly for Acid-activatable Antimicrobial Therapy

Non-technical Summary

Bacteria can infect all body parts, including those with pH values below neutral, such as the urinary tract, oral cavity, respiratory epithelia, skin, and other soft tissues. While many antimicrobial agents have optimal bactericidal activity at a neutral pH, the unusual acidic pH can impair the bacteriostatic and bactericidal activities of pharmaceutical drugs and promote bacterial resistance.

Antimicrobial peptides (AMPs) have emerged as an alternative solution to conventional antibiotics to address the global problem of infectious diseases due to their broad-spectrum antimicrobial activity and less tendency for bacteria to develop resistance. Although AMPs are considered promising alternatives to conventional antibiotics, their widespread use and translation into clinical application is hampered by several intrinsic limitations, including their susceptibility to proteases and moderate to severe toxicity towards host cells.

It is generally believed that new design and engineering strategy is needed to overcome the intrinsic limitation of traditional AMPs for targeted antimicrobial therapy. The PI’s group recently developed a technology platform of self-assembling antimicrobial nanofibers (SAANs) to circumvent the shortcomings of both traditional antibiotics and AMPs.

SAANs are supramolecular assemblies of multidomain peptides (MDPs) that can undergo programmed self-assembly into nanostructured filaments. While killing broad-spectrum antibiotic-resistant bacteria, SAANs offer key advantages over traditional single chain AMPs in terms of improved stability, precisely controlled AMP loading capacity, minimal cytotoxicity and greatly improved hemocompatibility.

More recently, the PI’s group advance the fundamental design principles to develop a novel acid-activatable SAANs using pH-responsive MDPs as the molecular building block. The long-term goal is to apply SAANs as stable systemic nanocarriers for targeted AMP delivery. The research objectives of the present proposal are to expand the family of SAANs containing pH-responsive non-natural amino acids to further modulate materials stability and activity, and to develop more potent pH-dependent multicomponent SAANs with synergistic antimicrobial effect to eradicate bacteria at their preferred acidic environment without affecting healthy tissues and cells.

At the University of Texas at Arlington which is a Hispanic-serving institution, the PI contributes to education of increased diversity in STEM fields, particularly encouraging research participation from underrepresented students with weakly performing academic record along with her other outreach and education efforts.

Technical Summary

The NSF project is focused on the synthesis and self-assembly of pH-responsive peptides with non-natural amino acids that show triggered antimicrobial activity in the weakly acidic pH range. The project is driven by our recent discovery of Acid-Activatable Self-Assembled Antimicrobial Nanofibers (AA-SAANs), which is generated through the self-assembly of pH-responsive multidomain peptides (MDPs).

The MDPs are assembled into nanofibers at the physiological condition and being inactive. At the acidic infection site where the local pH decreases, AA-SAANs are triggered to dissemble and release the activated MDPs to interact with the bacterial cell membrane and kill bacteria. In this proposal we will validate and advance the fundamental design principle by using MDPs with expanded chemistry to develop more potent AA-SAANs.

The research objectives of this proposal are: 1) Establish AA-SAANs using new pH-responsive MDPs containing non-natural ionic amino acids; 2) Fabrication and evaluation of multicomponent AA-SAANs with synergistic antimicrobial activity; 3) Evaluate the pH-dependent biological activity of these materials in vitro. These efforts will provide critical insight into the fundamental molecular and supramolecular chemistry that govern the structure and antimicrobial activity of AA-SAANs.

Further, this strategy is highly transformative for the rational design and synthesis of functional materials with built-in pH-responsive properties to probe various complex biological processes in which pH gradient plays an important role.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.