Molecular mechanisms and novel biological-based therapies for anthrax lethal toxin-induced mortality

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Abstract Bacillus anthracis, the causative agent of anthrax disease, has remained as a top bioterrorism concern since the 2001 anthrax attack. B. anthracis causes anthrax through a combination of bacterial infection and toxemia. As a major virulence factor, the anthrax lethal toxin (LT) plays an essential role during multiple steps of the disease. Due to the rapid course of anthrax disease, in particular, the non-specific, flu-like symptoms of inhalational anthrax, patients usually seek medical assistance when the disease is already in the middle/late stages, making the clinical management of anthrax patients an extremely challenging task. Current treatments include antibiotics and anti-toxin antibodies that respectively eliminate the pathogen and neutralize the toxin. However, there is no therapy available to deal with the cellular/tissue damage caused by LT already having reached its molecular targets inside cells. Mortality usually follows when the host fails to repair this damage, the so called “point-of-no- return” for current therapy. Thus, even with intensive medical care, the mortality rate of systemic anthrax is high, reaching > 50%. Therefore, there is an urgent unmet clinical need to develop better targeted therapies to avert anthrax -induced mortality. Our goal in this application is to discover the molecular mechanisms underlying LT- induced lethality and to develop potential targeted therapeutics to treat patients beyond the “point-of-no-return”. Here, we set out to determine the specific roles of disrupting each of the ERK, p38, and JNK pathways in anthrax- induced lethality, discover the underlying molecular mechanisms, and develop the concept of reactivation /mobilization of these pathways as a targeted therapy for anthrax-induced mortality. In Aim 1, we will determine the role of specifically disrupting the ERK pathway in anthrax-induced lethality and explore ERK pathway reactivation as a targeted therapy. Among the three core MAPK pathways targeted by LT, the ERK pathway is fundamental to many biological processes, including cell proliferation and survival. Thus, we hypothesize that disrupting the ERK pathway is the major cause of anthrax-induced lethality. We will generate and use novel mouse models containing MEK1 and MEK2 alleles that are resistant to LT-cleavage to understand the precise role of ERK pathway inactivation in anthrax pathogenesis. We will further test this hypothesis and explore ERK pathway reactivation as a targeted therapy for anthrax-induced tissue damage. Importantly, our preliminary data demonstrate that the LT-disrupted ERK pathway can be reactivated by the addition of potent mitogens, such as epidermal growth factor. In Aim 2, we will further determine the roles of disrupting the p38 and JNK pathways in anthrax pathogenesis and explore the feasibility of mobilizing these pathways in anthrax-targeted therapy. Upon completion of these studies, it is our expectation that we will provide significant conceptual advances in our understanding of the underlying molecular mechanisms of anthrax LT and offer an evidence-based framework for developing anthrax-targeted therapies, which will complement the current therapies with antibiotics and anti-toxin antibodies, to prevent anthrax mortality, even at advanced stages of anthrax infection.