Abstract B263: Mechanistic, functional, and in vivo efficacy of inhibiting ETK/BMX in cancer models

Abstract

Abstract Epithelial and endothelial tyrosine kinase (ETK), also known as bone marrow tyrosine kinase gene in chromosome X (BMX), belongs to the Burton's Tyrosine Kinase (BTK) family. ETK is a nonreceptor tyrosine kinases involved in tumorigenicity, adhesion, motility, angiogenesis, proliferation, and differentiation. It is overexpressed in metastatic breast and prostate cancers and is implicated in the neuroendocrine transformation of prostate cells. Significant oncogenes such as Src, focal adhesion kinase (FAK), and phosphatidyl-inositol (PI)-3 kinase are upstream regulators of ETK while several hub proteins, also critical for cancer development and progression, such as AKT, STAT3, and p21 activated kinase 1 (PAK1), are downstream of ETK. Cell-based validation studies also demonstrate that inhibition of ETK diminishes cellular transformation, proliferation, and migration. Such evidence provides substantial reasoning for developing new small molecule inhibitors against ETK. Applying SuperGen's proprietary small molecule drug discovery process, CLIMB™ a series of lead compounds were effectively developed to potently and selectively inhibit ETK. Biochemical data from kinase screens against ETK demonstrated nanomolar potency of SuperGen's inhibitors and good selectivity toward ETK from a panel of 75 kinases. To mechanistically demonstrate ETK inhibition in cell-based models, immunoprecipitations were carried out and phospho-ETK levels were detected. These compounds exhibited a dose-dependent response against phospho-ETK. Functionally, the inhibition of ETK will produce changes in phospho-AKT (S473) levels as well as phospho-STAT3 (Y705) levels downstream of EGF stimulation. Using Luminex bead-based technology and western blot techniques respectively, SuperGen's lead ETK compounds also yielded concentration-dependent responses with EC50 values in the nanomolar region. Given ETK's reported angiogenic role in endothelial cell migration and proliferation, these compounds were evaluated in an in vitro tube formation assay. Likewise, these ETK inhibitors demonstrated potent nanomolar inhibition of endothelial tube formation. Finally, having shown mechanistically and functionally the efficacy of ETK inhibitors through in vitro assays, the compounds were tested with in vivo solid tumor efficacy models in nude mice. All five lead inhibitors effectively decreased tumor burden volume relative to the vehicle treatment group in an AN3CA xenograft model. Taken together, these data suggest SuperGen's small molecule ETK inhibitors represent a potentially new therapeutic avenue for treating patients with solid tumor malignancies in the future. Citation Information: Mol Cancer Ther 2009;8(12 Suppl):B263.