Applications of Solution NMR in Drug Discovery

During the past decades, solution nuclear magnetic resonance (NMR) spectroscopy has demonstrated itself as a promising tool in drug discovery. Especially, fragment-based drug discovery (FBDD) has benefited a lot from the NMR development. Multiple candidate compounds and FDA-approved drugs derived from FBDD have been developed with the assistance of NMR techniques. NMR has broad applications in different stages of the FBDD process, which includes fragment library construction, hit generation and validation, hit-to-lead optimization and working mechanism elucidation, etc. In this manuscript, we reviewed the current progresses of NMR applications in fragment-based drug discovery, which were illustrated by multiple reported cases. Moreover, the NMR applications in protein-protein interaction (PPI) modulators development and the progress of in-cell NMR for drug discovery were also briefly summarized.

Discovery of betulinaldehyde as a natural RORγt agonist

Retinoic Acid Receptor-Related Orphan Receptor γt (RORγt) is a dual-functional therapeutic target. The agonists and inhibitors of RORγt are potential agents for tumor immunotherapy and autoimmune diseases, respectively, and sometimes share similar scaffolds. Although the widely distributed triterpenoid ursolic acid (UA) has been identified as a RORγt inhibitor, the report of a triterpenoid RORγt agonist is still absent. By screening an in-house triterpenoid library, we uncovered a novel RORγt agonist, betulinaldehyde (1), together with an inhibitor (2, 3β, 28-Dihydroxy-lupan-29-oic acid). Compound 1 showed a good RORγt activating effect with the EC₅₀ of 11.4 μM in Alpha Screen assay, and altered the thermal stability of RORγt by directly binding to the protein in vitro. Combined with the SPR assay, the Kd value of compound 1 was examined as 2.99 μM. The modulation mechanism of triterpenoid agonists and inhibitors were discussed by molecular docking. Herein, we firstly discovered compound 1 as a triterpenoid agonist of RORγt. The co-distribution of triterpenoid RORγt agonist and inhibitors in the same plant, might be related to the anti-inflammatory and anti-cancerous bioactivity of the plant extract.

Homogeneous Assay for Target Engagement Utilizing Bioluminescent Thermal Shift

Protein thermal shift assays (TSAs) provide a means for characterizing target engagement through ligand-induced thermal stabilization. Although these assays are widely utilized for screening libraries and validating hits in drug discovery programs, they can impose encumbering operational requirements, such as the availability of purified proteins or selective antibodies. Appending the target protein with a small luciferase (NanoLuc) allows coupling of thermal denaturation with luminescent output, providing a rapid and sensitive means for assessing target engagement in compositionally complex environments such as permeabilized cells. The intrinsic thermal stability of NanoLuc is greater than mammalian proteins, and our results indicate that the appended luciferase does not alter thermal denaturation of the target protein. We have successfully applied the NanoLuc luciferase thermal shift assay (NaLTSA) to several clinically relevant protein families, including kinases, bromodomains, and histone deacetylases. We have also demonstrated the suitability of this assay method for library screening and compound profiling.

Meltdown: A Tool to Help in the Interpretation of Thermal Melt Curves Acquired by Differential Scanning Fluorimetry

The output of a differential scanning fluorimetry (DSF) assay is a series of melt curves, which need to be interpreted to get value from the assay. An application that translates raw thermal melt curve data into more easily assimilated knowledge is described. This program, called "Meltdown," conducts four main activities--control checks, curve normalization, outlier rejection, and melt temperature (T(m)) estimation--and performs optimally in the presence of triplicate (or higher) sample data. The final output is a report that summarizes the results of a DSF experiment. The goal of Meltdown is not to replace human analysis of the raw fluorescence data but to provide a meaningful and comprehensive interpretation of the data to make this useful experimental technique accessible to inexperienced users, as well as providing a starting point for detailed analyses by more experienced users.