Using C. elegans to Identify Novel Targets Against Multidrug-Resistant Bacteria
Hummell, Nicholas Andrew
Kirienko, Natasha; Tao, Jane
Doctor of Philosophy
Antibiotic-resistant infections cause an average of 23,000 deaths per year. Due to dwindling commercial interest for antimicrobial discovery, novel methods for combating infection and developing new antimicrobials are desperately needed. Previously in our lab, we performed a high-throughput chemical screen to identify small molecules that rescued the nematode Caenorhabditis elegans from infection by P. aeruginosa. Of the hits identified, 5 (LK32, LK34, LK35, LK38 and LK56) were determined to be stimulators of host defense pathways while 5 additional hits (DMAQ-B1, CD437, carboplatin, oxaliplatin, and PSB-069) possessed a known target or bioactivity but had no previously reported antimicrobial activity against P. aeruginosa.. Using microarray analysis, RNAi knockdown of candidate pathways, transgene reporters, and infection assays with other pathogens, we made important observations concerning the mechanism of action and therapeutic repurposing potential for the compounds. Firstly, I identified a subunit of the Mediator complex, mdt-15, and the PMK-1/p38 MAPK pathway as necessary for rescue for LK56 and LK38 respectively, demonstrating that both pathways are amenable to immune stimulation. I have also found that some molecules can defend against E. faecalis and S. aureus as well as Pseudomonas while being largely non-toxic. Additionally, most molecules stimulated the activation of multiple innate immune pathways. These experiments showed the potential for development of broad-spectrum immune stimulants and identified promising pathways amenable to immune stimulation. They also highlighted potential for our LK molecules as tools for future studies of innate immune stimulation in C. elegans. For our bioactive compounds, I used similar C. elegans-based methods to generate a number of important conclusions: I confirmed the antimicrobial activity of CD437 against Gram-positive pathogens, observed a weakness of P. aeruginosa to platinum complexes, and established the naturally occurring insulin mimetic, DMAQ-B1, as a powerful antimicrobial agent. Although toxic, an existing non-toxic analog presents potential for further therapeutic optimization. Through these studies, I have utilized C. elegans as a powerful drug discovery tool to gain insight into mechanism and therapeutic utility of two groups of anti-infective molecules. I have shown the strength of our model in drug repurposing efforts as well as demonstrated therapeutic potential for immune stimulation as a promising approach to combatting the growing antimicrobial resistance crisis.
C. elegans; Drug discovery; Immune stimulation; Repurposing; Antimicrobial Resistance