Vaccines and Therapeutics for Anthrax

National Institute Of Allergy And Infectious Diseases

Investigators

Linked publications, trials & patents

Abstract

Anthrax lethal toxin (LT) and edema toxin (ET) are made of three protein components: protective antigen (PA), lethal factor (LF) and edema factor (EF). PA is the cell binding moiety which binds to cellular receptors, is proteolytically cleaved to form an oligomer which allows binding of the two enzymatic moieties, LF and EF, and their transport into the cell cytosol. LF is a zinc-dependent protease which cleaves several mitogen-activated protein kinase kinases (MEKs), shutting down ERK and p38 signaling with extreme consequences for almost all cell types. This protease also cleaves the rodent inflammasome sensor Nlrp1. EF is an adenylate cyclase which converts ATP to cAMP and activates signaling pathways which lead to edema in the host. Because these two toxins are the major virulence determinants of anthrax, vaccine and therapeutic development against this disease primarily targets these proteins. During 2018 our laboratory continued work on further development of anti-toxin vaccines and therapeutics. We tested new small molecular inhibitors of EF developed at Hawaii Biotech to determine relative efficacy based on structural modifications. The small molecule 5'-fluoro-sulfonylbenzoyl-5'-adenosine (FSBA) was found to react irreversibly with EF and block the toxins enzymatic activity. Modifications of the adenosine group of this drug was identified that yield drugs which had >1000-fold greater inhibition of EF activity. We also further characterized previously identified LF inhibitors developed by Hawaii Biotech for their ability to inhibit substrate cleavage in mice at various time points after anthrax spore infection. In collaborative studies with the NIH Clinical Center, an anti-PA antibody preparation, anthrax immune globulin (AIG), was tested in canines challenged with LT and ET infusions. The antibody was found to improve hemodynamics, blood pressure and survival in this animal model. In a different collaboration with the same group, arterial function in rats infused with ET or LT was studied. We found that ET but not LT depresses arterial function in rats, and that the drug adefovir can inhibit ET effects on hypotension to improve survival in this model. In collaboration with the FDA, we started in vivo studies on the role of anthrax toxin receptors in immunization efficacy against PA using tissue-specific receptor knockout mice developed in our laboratory. These studies are underway. In collaboration with the University at Buffalo, we tested novel liposome delivery systems for improving immunization against anthrax in the mouse model. These studies are ongoing.