Bacillus anthracis, a rod shaped, spore forming, gram positive bacteria, is the etiological
agent of anthrax. B. anthracis virulence is partly attributable to two secreted bipartite protein toxins,
which act inside host cells to disrupt signaling pathways important for host defense against infection.
These toxins may also directly contribute to mortality in late stage infection. The zinc-dependent metalloproteinase
anthrax lethal factor (LF) is a critical component of one of these protein toxins and a
prime target for inhibitor development to produce anthrax therapeutics. Here, we describe recent efforts
to identify specific and potent LF inhibitors. Derivatization of peptide substrate analogs bearing
zinc-binding groups has produced potent and specific LF inhibitors, and X-ray crystallography of LFinhibitor
complexes has provided insight into features required for high affinity binding. Novel inhibitor scaffolds have
been identified through several approaches, including fragment-based drug discovery, virtual screening, and highthroughput
screening of diverse compound libraries. Lastly, efforts to discover LF inhibitors have led to the development
of new screening strategies, such as the use of full-length proteins as substrates, that may prove useful for other proteases
as well. Overall, these efforts have led to a collection of chemically and mechanistically diverse molecules capable of inhibiting
LF activity in vitro and in cells, as well as in animal models of anthrax infection.