(697a) Inhibition of Bacterial Toxin Activity Using Receptor-Based Peptides

New approaches to the treatment of bacterial illnesses are desperately needed, as the number of antibiotic-resistant strains of bacteria increases and the pipeline of new antibiotics dries up. In addition, traditional antibiotics kill both pathogenic and commensal organisms, leading to detrimental effects to the microbiota. Our lab is interested in developing novel, targeted approaches to this problem; to do so, we focus on bacterial toxins, which are secreted by pathogenic bacteria to destroy host cells, thereby allowing the bacteria to colonize and survive within the host. Our goal is to understand the initial interaction of bacterial toxins with target cell membranes, with the objective of inhibiting the activity of the toxins to prevent bacterial survival.

In this project, we designed targeted receptor-based peptides to inhibit the activity of the leukotoxin (LtxA), secreted by the bacterium Aggregatibacter actinomycetemcomitans. This toxin is a member of the RTX (repeats-in-toxin) family of toxins and targets leukocytes through its recognition of the lymphocyte function-associated antigen-1 (LFA-1) integrin, which is only expressed by human white blood cells, as well as its strong affinity for cholesterol in the plasma membrane of the target cell. We designed a panel of small peptides, based on the b-propeller region of the CD11a subunit of LFA-1, which has been implicated in LtxA binding, and characterized their capability to inhibit LtxA binding to LFA-1 and subsequent cytotoxicity in human immune cells. We found that four of the five peptides, specifically those corresponding to sequential b-strands in the b-propeller domain, inhibited LtxA activity, demonstrating the effectiveness of this approach. These peptides specifically inhibit the ability of LtxA to bind LFA-1, thus preventing internalization and subsequent cytotoxicity. A panel of peptides based on the murine form of LFA-1, for which LtxA has no affinity, was used as a negative control. These peptides were less effective than the human-based peptides in inhibiting LtxA activity, demonstrating that this inhibition is specific to the LtxA-LFA-1 interaction. Together, these results demonstrate the possibility of using receptor-based peptides to inhibit LtxA activity. We expect that a similar approach could be used to hinder the activity of other RTX toxins.