Rebamipide and Derivatives are Potent, Selective Inhibitors of Histidine Phosphatase Activity of the Suppressor of T Cell Receptor Signaling Proteins.

The suppressor of T cell receptor signaling (Sts) proteins are negative regulators of immune signaling. Genetic inactivation of these proteins leads to significant resistance to infection. From a 590,000 compound high-throughput screen, we identified the 2-(1H)-quinolinone derivative, rebamipide, as a putative inhibitor of Sts phosphatase activity. Rebamipide, and a small library of derivatives, are competitive, selective inhibitors of Sts-1 with IC50 values from low to submicromolar. SAR analysis indicates that the quinolinone, the acid, and the amide moieties are all essential for activity. A crystal structure confirmed the SAR and reveals key interactions between this class of compound and the protein. Although rebamipide has poor cell permeability, we demonstrated that a liposomal preparation can inactivate the phosphatase activity of Sts-1 in cells. These studies demonstrate that Sts-1 enzyme activity can be pharmacologically inactivated and provide foundational tools and insights for the development of immune-enhancing therapies that target the Sts proteins.

Protocol for 3D screening of lung cancer spheroids using natural products.

Non-small cell lung cancer (NSCLC) is the most common type of lung cancer and accounts for ∼84% of all lung cancer cases. NSCLC remains one of the leading causes of cancer-associated death, with a 5-year survival rate less than 25%. This type of cancer begins with healthy cells that change and start growing out of control, leading to the formation of lesions or tumors. Understanding the dynamics of how the tumor microenvironment promotes cancer initiation and progression that leads to cancer metastasis is crucial to help identify new molecular therapies. 3D primary cell tumor models have received renewed recognition due to their ability to better mimic the complexity of in vivo tumors and as a potential bridge between traditional 2D culture and in vivo studies. Vast improvements in 3D cell culture technologies make them much more cost effective and efficient largely because of the use of a cell-repellent surfaces and a novel angle plate adaptor technology. To exploit this technology, we accessed the Natural Products Library (NPL) at UF Scripps, which consists of crude extracts, partially purified fractions, and pure natural products (NPs). NPs generally are not very well represented in most drug discovery libraries and thus provide new insights to discover leads that could potentially emerge as novel molecular therapies. Herein we describe how we combined these technologies for 3D screening in 1536 well format using a panel of ten NSCLC cells lines (5 wild type and 5 mutant) against ∼1280 selected members of the NPL. After further evaluation, the selected active hits were prioritized to be screened against all 10 NSCLC cell lines as concentration response curves to determine the efficacy and selectivity of the compounds between wild type and mutant 3D cell models. Here, we demonstrate the methods needed for automated 3D screening using microbial NPs, exemplified by crude extracts, partially purified fractions, and pure NPs, that may lead to future use targeting human cancer.