Prof. Dr. Daniel Ricklin

Current estimates suggest that nearly 1.3 million lives are lost annually to antibiotic-resistant infections, with this number rising to 10 million by 2050. Antibiotic resistance results in failed treatment, prolonged hospital stays, and increases the financial burden placed on medical systems and society. Therefore, novel approaches to antibiotic use are urgently needed.

Recently, a novel class of anti-virulence compounds based on mucosal glycans were discovered, which are active against a range of pathogenic cross-kingdom species, including fungal, Gram-positive, and Gram-negative bacterial pathogens. These mucin O-glycans do not directly affect pathogen survival but instead repress virulence, thereby increasing susceptibility to host immune pathways and indirectly reducing infection load. By exerting their activity through virulence attenuation instead of broad-spectrum elimination, these compounds can promote the reestablishment of a healthy microbiome and are expected to be at a reduced risk of developing drug resistance. Although this exciting new class of compounds has demonstrated broad activity, the mechanism(s) by which these glycans act has not yet been elucidated. By identifying their discrete molecular target(s), specific binding interactions can be analyzed and more drug-like glycomimetic therapies can be developed.

Mucins contain hundreds of different O-glycans which are not commercially available, cannot be purified as single structures from native sources, and are not readily amenable to solid-phase synthesis. Therefore, in ongoing work we have been developing a platform to generate individual mucin glycan structures and evaluate their ability to regulate pathogen virulence. In the further development and application of this platform, specific aims of the current proposal are focused on: (i) the recombinant expression of predicted virulence-regulating proteins; (ii) the investigation of mucin glycan binding to virulence-regulating proteins through parallel techniques; and (iii) further expansion of the mucin glycan library and the development of next-generation glycomimetic molecules.

The proposed project will improve our understanding of mucus–pathogen relationships, provide insights into virulence-attenuating mechanism(s), and provide the next steps to development of an innovative therapeutic.

The complement system plays an essential role in host immunity, assisting in the recognition and clearance of pathogens and damaged cells. However, dysregulation of the complement system can lead to tissue damage, contributing to a variety of inflammatory diseases. Over recent years, the therapeutic modulation of complement activity has emerged as a promising clinical intervention, creating an urgent need for new modes of complement regulation and therapeutic candidates. This proposal takes inspiration from nature to investigate the development of a new class of complement regulators.

Evolved to avoid innate immune responses, the giant Amazon leech secretes gigastasin, a protein capable of blocking the proteases responsible for initiating the complement cascade. However, the application of gigastasin as a therapeutic candidate is hampered by the complexity in its recombinant production, and the potential for triggering undesired immunogenicity. An alternative approach is to utilize the structural and mechanistic information of protease inhibition by gigastasin, to derive new molecules capable of mimicking the key target interactions. Peptides are attractive candidates as they can maintain the critical protein-target interactions, but can be accessed by scalable and modular chemical synthesis, while also minimizing immunogenicity.  

In this proposal, peptides will be derived from distinct portions of gigastasin that bind to the active center and exosite of the protease, and covalently linked together to create bivalent peptide inhibitors. The resulting peptides will be assessed for target affinity, protease inhibition, and subsequently, the impairment of complement activation in vitro. Furthermore, gigastasin, from which the peptides will be derived, exhibits multi-target protease inhibition, including those involved in both complement and coagulation pathways. Taking advantage of the highly modular chemical synthesis, structure guided optimization of the peptides towards each of the target proteases will be conducted by employing both canonical and unnatural amino acids, going beyond the current state-of-the-art in host defense protease regulation. Finally, the translational potential of the resulting peptide candidates will be evaluated, testing for complement modulation in physiologically relevant models, such as hemolytic assays, and complement inhibition in human and non-human serum samples.  

The development of leech-derived bivalent peptide inhibitors in this proposal will provide critical insights into complement protease regulation, not only providing tools for selective pathway modulation in research, but also improving our understanding of target selectivity tuning employed by parasites. Motivated by the growing success of peptides in clinical complement modulation (pegcetacoplan, Empaveli/Syfovre, Apellis; Zilucoplan, Zilbrysq, UCB, inc.), the resulting peptide candidates may also provide a platform for future therapeutic evaluation and development.