Vaccines and Therapeutics for Anthrax

National Institute Of Allergy And Infectious Diseases

Investigators

Linked publications, trials & patents

Abstract

Mutational activation of the Raf-MEK-ERK pathway is a frequent cause of the uncontrolled cell growth that defines malignancy, so the proteins in this pathway have long been targets of drug development. While FDA-approved small molecule MEK inhibitors have demonstrated efficacy in patients with metastatic melanomas, these "targeted" therapeutics typically have a low therapeutic index since these agents affect normal cells, causing undesirable side effects. The lethal factor (LF) component of anthrax toxin is a protease which selectively cleaves members of the MEK family of kinases. For this reason, LF was early on recognized as an alternative, potentially useful MEK inhibitor having therapeutic potential. Our continuing work has sought to characterize the mechanism of the anti-tumor action of LF. Our LF-based anti-tumor agents achieve cell entry following binding to the cell surface capillary morphogenesis protein-2 (CMG2) toxin receptor. During 2023, we used our previously generated mice expressing CMG2 on individual types of cells. This system allows us to define the roles of individual tumor stromal cell types in tumor development. In the most recent work, we established mice with CMG2 expressed only in tumor endothelial cells (ECs). These mice were as sensitive to our LF-based agent as were fully wild type mice expressing CMG2 throughout their bodies. Thus, we have shown that disruption of the MEK-ERK signaling only within tumor ECs is sufficient to halt tumor growth. Furthermore, we found that c-Myc is a downstream effector of ERK signaling, with c-Myc levels greatly depressed following LF treatment. This established that the MEKERKc-Myc central metabolic axis in tumor ECs is essential for tumor progression. As such, disruption of ERKc-Myc signaling in host-derived tumor ECs by our tumor-selective anthrax toxins explains their high efficacy in solid tumor therapy. In other work during CY 2023, we began reexamination of the basis for the selective cleavage by LF of six of the seven members of the MEK family of protein kinases. Previous work showed that specificity resulted in part from binding of LF to a MEK exosite far from the bond that is cleaved. While mutagenesis and other techniques might provide some characterization of the regions on LF and MEK that interact, a full understanding of the interaction requires that the 3D structure of the putative complex be determined. With that goal, we are purifying several members of the MEK family and will be measuring their binding to LF by several biophysical techniques. Provided there is good affinity, we will then attempt structural determination.