Immune Targeting of Mycobacteria through Cell Surface Glycan Engineering

Redirecting the host immune response to bacterial infection with antibody-recruiting molecules (ARMs)

The increasing prevalence of antibiotic resistance, the stagnation of antibiotic development, and the adaptive capacity of bacteria to subvert the host immune response combine to pose significant global health concerns. Consequently, there is an urgent need to develop alternative therapeutic approaches to combat bacterial infections. Antibody-recruiting molecules (ARMs), which are bispecific small molecules that recruit endogenous antibodies to pathogenic cells or viruses, offer a promising avenue to harness the host immune system to target various diseases. In this review, we cover ARM strategies that have been developed for bacterial pathogens, including Gram-positive bacteria, Gram-negative bacteria, and mycobacteria, and we discuss the prospects and challenges of utilizing ARMs as alternatives to traditional antibiotic therapies.

Siderophore-based targeted antibody recruitment for promoting immune responses towards Gram-negative pathogens

Antibody-recruiting molecules (ARMs) have emerged as a promising strategy for enhancing immune responses against pathogens and cancer cells. In this study, we developed a novel class of antibacterial ARMs utilizing siderophores, small iron-chelating compounds, as targeting motifs. Siderophores naturally exhibit high specificity for bacterial pathogens due to their role in iron acquisition, making them ideal candidates for selective targeting. We identified a potent ARM, GNP3, comprising MECAM, a siderophore mimetic, and 2,4-dinitrophenyl (DNP), a motif recognized by endogenous antibodies, connected via a flexible linker. GNP3 binds simultaneously to both anti-DNP antibody and the siderophore receptor, FepA, facilitating the targeted deposition of antibodies on the surface of FepA-expressing bacterial cells, such as Escherichia coli and Pseudomonas aeruginosa. This GNP3-induced opsonization promoted robust immune responses, including complement-dependent cytotoxicity (CDC) in the presence of serum and macrophage-mediated phagocytosis. Moreover, GNP3 effectively triggered CDC activity against serum-resistant uropathogenic E. coli. The results suggest that siderophore-based ARMs, by harnessing the immune defense system, represent a promising complementary approach to traditional antibiotics for overcoming recalcitrant bacterial infections.

Chemical biology tools to probe bacterial glycans

Bacterial cells are covered by a complex carbohydrate coat of armor that allows bacteria to thrive in a range of environments. As a testament to the importance of bacterial glycans, effective and heavily utilized antibiotics including penicillin and vancomycin target and disrupt the bacterial glycocalyx. Despite their importance, the study of bacterial glycans lags far behind their eukaryotic counterparts. Bacterial cells use a large palette of monosaccharides to craft glycans, leading to molecules that are significantly more complex than eukaryotic glycans and that are refractory to study. Fortunately, chemical tools designed to probe bacterial glycans have yielded insights into these molecules, their structures, their biosynthesis, and their functions.

Chemical remodeling of the mycomembrane with chain-truncated lipids sensitizes mycobacteria to rifampicin

The outer mycomembrane of Mycobacterium tuberculosis and related pathogens is a robust permeability barrier that protects against antibiotic treatment. Here, we demonstrate that synthetic analogues of the mycomembrane biosynthetic precursor trehalose monomycolate bearing truncated lipid chains increase permeability of Mycobacterium smegmatis cells and sensitize them to treatment with the first-line anti-tubercular drug rifampicin. The reported strategy may be useful for enhancing entry of drugs and other molecules to mycobacterial cells, and represents a new way to study mycomembrane structure and function.