Monitoring and quantifying drug-target binding in a live-cell setting is important to bridging the gap between in vitro assay results and the phenotypic outcome, and therefore represents a crucial step in target validation and drug development (1). The NanoBRET™ Target Engagement (TE) assay is a biophysical technique that enables quantitative assessment of small molecule-target protein binding in live cells. This live-cell target engagement assay uses the bioluminescence resonance energy transfer (BRET) from a NanoLuc® luciferase-tagged target protein and a cell-permeable fluorescent tracer that reversibly binds the target protein of interest. In the presence of unlabeled test compound that engages the target protein, the tracer is displaced, and a loss of BRET signal is observed. Due to the tight distance constraints for BRET, the signal measured is specific to the target fused to NanoLuc® luciferase.
Promega offers over 400 ready-to-use assays for multiple target classes, including kinases, E3 ligases, RAS, and many others. For targets that do not have an existing NanoBRET™ TE assay, Promega offers NanoBRET™ dyes, NanoLuc® cloning vectors, and NanoBRET™ detection reagents to develop novel NanoBRET™ TE assays.
One critical component in the development of novel NanoBRET™ TE assay is the creation of the cell-permeable fluorescent tracers (NanoBRET™ tracers) against the target protein of interest. The tracers are bifunctional, consisting of a NanoBRET™-compatible fluorophore and a target-binding moiety connected by a linker. While the NanoBRET™ 590 dyes have demonstrated consistently robust cell permeability and optimal spectral overlap with NanoLuc® for BRET, a ligand capable of binding to the target protein of interest needs to be identified to generate a NanoBRET™ tracer.
What Are DNA-Encoded Libraries?
DNA-Encoded Libraries, (DELs), have emerged as powerful tools for discovering small molecule ligands to target proteins of interest at an unprecedented scale. . owing to the ability of a DEL to enable the synthesis of larger libraries of compounds and to target proteins without any prior structural knowledge of the proteins or their ligands (2). Because each member of a DEL contains a DNA barcode and a small molecule separated by a linker, DEL is primed for discovering leads within therapeutic modalities that rely on bifunctional chemistry, such as proteolysis targeting chimeras (PROTACs). Since NanoBRET™ tracers are also bifunctional, ligands identified from DEL selections could serve as ideal candidates for developing novel NanoBRET™ tracers that can enable NanoBRET™ TE assays for new targets.
Antibody-based immune checkpoint inhibitors remain a major focus of immuno-oncology drug research and development efforts because of their recent success in providing long-term anti-tumor responses. However, the range of response of different tumor types to these drugs is hugely varied. Small molecule kinase inhibitors that block signaling pathways involved in regulation of tumor immunity at multiple points in the “cancer immunity cycle” may provide alternate, effective therapeutics. One kinase that may be a target for such small molecule inhibitors is Hematopoietic Progenitor Kinase 1 or HPK1; the potential of this kinase as a therapeutic target was reviewed by Sawasdikosol and Burakoff (1). HPK1, also known as MAP4K1, is a member of the MAP kinase protein kinase family that negatively regulates signal transduction in T-cells, B-cells and dendritic cells of the immune system.
The Foundation for Food and Agriculture Research (FFAR) announced on November 30 that they are awarding $1M to a project based at the University of California, Davis, to study protein kinases of rice plants. The team is led by Dr. Pamela Ronald, a leading expert in plant genetics who has engineered disease- and flood-resistant rice. This project aims to address the growing agricultural problem of water scarcity by gaining a better understanding of the role kinases play in enabling drought-resistance. Promega will be supporting this research by providing NanoBRET™ products to help characterize kinase inhibitors.
The research team will begin by screening over 1,000 human kinase inhibitors to determine which ones do interact with the plant kinome and, if applicable, which kinase(s) they inhibit. Once the compound library has been established, the team will assess the inhibitors’ phenotypic effects on rice to identify kinases that, when inhibited, positively impact root growth and development. The long-term goal is to use these findings to engineer drought-resistant rice.
The first small-molecule kinase inhibitor approved as a cancer therapeutic, imatinib mesylate (Gleevec® treatment), has been amazingly successful. However, a thorough understanding of its molecular mechanism of action (MMOA) was not truly obtained until more than ten years after the molecule had been identified.
Understanding the MMOA for a small-molecule inhibitor can play a major role in optimizing a drug’s development. The way a drug actually works–the kinetics of binding to the target molecule and how it competes with endogenous substrates of that target–ultimately determines whether or not a a candidate therapeutic can be useful in the clinic. Drugs that fail late in development are extremely costly.
Drug research and discovery for neglected tropical diseases suffer from a lack of a large commercial market to absorb the costs of late-stage drug development failures. It becomes very important to know as much as possible, simply and quickly, about MMOA for candidate molecules for these diseases that are devastating to large populations.
Drug research and development is a complex and expensive process that begins with initial screening steps of candidate chemical compounds, and compounds that appear to have the desired potency against a specific cellular target or pathway are further evaluated. Candidate compounds that fail late in development or during clinical trials because of off-target effects are costly, and can be dangerous. Therefore drug developers not only need to ensure that a candidate compound is effective as a therapy, but also they need to predict any potential undesirable side effects due to off-target activities as early as possible in the drug discovery and development process. Continue reading “Making Drug Discovery More Efficient: Predicting Drug Side Effects in Early Screening Efforts”
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