Séminaire CIRI (29.11.2023) : Dr. Maisem LAABEI & Dr. Serena BETTONI

Dr. Maisem LAABEI: University of Bath;  « Developing small molecule inhibitors of Lipoteichoic acid synthesis »

Abstract: The lipoteichoic acid (LTA) biosynthesis pathway has emerged as a promising antimicrobial therapeutic target. Previous studies identified the 1,3,4 oxadiazole compound 1771 as an LTA
inhibitor with activity against Gram-positive pathogens. We have succeeded in making multiple 1771 derivatives and, through subsequent hit validation, identified the incorporation of a pentafluorosulfanyl substituent as central in enhancing activity. Our newly described derivative, compound 13, showed a 16- to 32-fold increase in activity compared to 1771 when tested against a cohort of multidrug-resistant Staphylococcus aureus strains while simultaneously exhibiting an improved toxicity profile against mammalian cells. Molecular techniques were employed in which the assumed target, lipoteichoic acid synthase
(LtaS), was both deleted and overexpressed. Neither deletion nor
overexpression of LtaS altered 1771 or compound 13 susceptibility; however, overexpression of LtaS increased the MIC of Congo red, a previously identified LtaS inhibitor. These data were further supported by comparing the docking poses of 1771 and derivatives in the LtaS active site, which indicated the possibility of an additional target(s). Finally, we show that both 1771 and compound 13 have activity that is independent of LtaS, extending to cover Gram-negative species if the outer membrane is first permeabilized, challenging the classification that these compounds are strict LtaS inhibitors.

Dr. Serena BETTONI: PostDoc, University of Bath: « Group A streptococcus and inflammasomes: role of C4BP »

Abstract: Group A streptococcus (GAS) is a pathogen responsible for over half a million deaths worldwide each year, and currently, there is no available vaccine. In response to GAS infection, human immune cells activate the NLRP3 inflammasome, leading to the secretion of pro-inflammatory cytokines and cell death to eliminate the bacteria.
To evade immune recognition, GAS recruits the complement inhibitor C4b-binding protein (C4BP) to its surface, preventing complement deposition and limiting phagocytosis. Previous research has shown that C4BP can attenuate NLRP3 inflammasome activation in response to various stimuli, such as amyloid fibrils common in type 2 diabetes and insoluble particles responsible for conditions like silicosis and gout. In this study, we investigated the role of C4BP in the inflammasome response to GAS infection.
Using primary peripheral blood mononuclear cells and GMCSF-differentiated macrophages, and the reference strain GAS-AP1, we observed that plasma-purified C4BP reduced the IL-1β response, with no effect on cell priming. C4BP was engulfed by cells along with bacteria but excluded from low-pH vesicles. Intracellularly, C4BP localized within the cytosol and near the inflammasome complex but did not inhibit its assembly or activation. The observation that gasderminD cleavage were reduced in the presence of C4BP suggested that NLRP3 inflammasome inhibition by C4BP was due to its interference with caspase-1 activity.
Given that the severity of GAS infection is influenced by the amount of IL-1β, our results provide new insights into the effect of C4BP as a potential therapeutic target for controlling the inflammasome response to GAS infection.