Developmental therapy for selectively targeting MEK-ERK pathway in cancer cells and tumor stromal compartment

Project Summary/Abstract Carcinogenic mutations in the RAS-RAF-MEK-ERK pathway are present in 46% of all human cancers. This has inspired the successful development of many small molecule BRAF and MEK pathway inhibitors. These agents are currently FDA approved for the treatment of metastatic melanomas containing BRAF mutations. Although

BRAF and MEK inhibitors have shown some benefits to patients, these “targeted” therapeutics have a very low therapeutic index, since these small molecules also target normal cells, causing undesirable, even fatal, side effects. Moreover, whether the clinical efficacy of these inhibitors is via direct effects on the tumor or through

modulation of the tumor stromal compartment remains elusive. In this application, we address the above critical unmet needs and will develop a potent and highly tumor-selective MEK inactivator by engineering an anthrax toxin-based protein delivery system. Through manipulating the expression of the toxin receptor on specific tumor

stromal cell types, we will also delineate how stromal MEK inhibition regulates tumor development. We propose two parallel, but independent Specific Aims to achieve these goals. In Aim 1, we will generate an anthrax toxin-based, highly tumor-selective MEK inactivator and evaluate its anti-tumor activity in a variety of

tumor models. This MEK inactivator specifically binds to the major toxin receptor CMG2 (capillary morphogenesis protein-2) on tumor cells and tumor stromal cells. Specificity is ensured through strict reliance on the simultaneous presence of two distinct tumor-associated proteases, MMPs and urokinase, to gain entry into tumor

cells and tumor stromal cells. Once inside, it inactivates MEK-ERK signaling, achieving potent selective targeting. In Aim 2, we will employ our unique tumor-host-toxin system to determine the roles of MEK-ERK signaling in tumor stromal cells in tumor development and in the toxin’s tumor targeting. We have previously established a

genetic system allowing CMG2 gain-of-function or loss-of-function in various specific cell types in the tumor microenvironment. Thus, we hypothesize that a genetic manipulation of CMG2 expression on cancer cells and various tumor stromal cells in the whole body of CMG2-/- mice will provide the first tractable genetic system to

delineate the role of specific cell types in the tumor microenvironment. Therefore, in this Aim 2, we will determine the roles of selected tumor stromal cell types including tumor endothelial cells (EC), tumor-associated macrophages (TAM), cancer-associated fibroblasts (CAF), B cells, and regulatory T cells (Treg), and the

molecular mechanisms of MEK-ERK inhibition in these cells in tumor development. Upon completion of these studies, we expect to have developed a highly potent, tumor-selective MEK inactivator as a novel tumor-targeted therapeutic. These studies will also unambiguously determine the role of MEK-ERK signaling in both the tumor

and the stroma, thereby validating and identifying specific tumor stromal cell types as targets for future therapeutics development.