Development of a High-throughput NanoBRET Screening Platform to Identify Modulators of the RAS/RAF Interaction

Discovery of a Novel and Potent LCK Inhibitor for Leukemia Treatment via Deep Learning and Molecular Docking

The lymphocyte-specific protein tyrosine kinase (LCK) plays a crucial role in both T-cell development and activation. Dysregulation of LCK signaling has been demonstrated to drive the oncogenesis of T-cell acute lymphoblastic leukemia (T-ALL), thus providing a therapeutic target for leukemia treatment. In this study, we introduced a sophisticated virtual screening strategy combined with biological evaluations to discover potent LCK inhibitors. Our initial approach involved utilizing the PLANET algorithm to assess and contrast various scoring methodologies suitable for LCK inhibitor screening. After effectively evaluating PLANET, we progressed to devise a virtual screening workflow that synergistically combines the strengths of PLANET with the capabilities of Schrödinger's suite. This integrative strategy led to the efficient identification of four potential LCK inhibitors. Among them, compound 1232030-35-1 stood out as the most promising candidate with an IC50 of 0.43 nM. Further in vitro bioassays revealed that 1232030-35-1 exhibited robust antiproliferative effects on T-ALL cells, which was attributed to its ability to suppress the phosphorylations of key molecules in the LCK signaling pathway. More importantly, 1232030-35-1 treatment demonstrated profound in vivo antileukemia efficacy in a human T-ALL xenograft model. In addition, complementary molecular dynamics simulations provided deeper insight into the binding kinetics between 1232030-35-1 and LCK, highlighting the formation of a hydrogen bond with Met319. Collectively, our study established a robust and effective screening strategy that integrates AI-driven and conventional methodologies for the identification of LCK inhibitors, positioning 1232030-35-1 as a highly promising and novel drug-like candidate for potential applications in treating T-ALL.

Studying RAS Interactions in Live Cells with BRET

Bioluminescence resonance energy transfer (BRET) is a valuable technique for studying protein-protein interactions (PPIs) within live cells (Pfleger and Eidne, Nat Methods 3:165-174, 2006). Among the various BRET methodologies, a recent addition called NanoBRET has emerged, leveraging advancements in donor and acceptor technologies (Machleidt and Woodroofe, ACS Chem Biol 10:1797-1804, 2015). In this study, we present a developed methodology designed to measure PPIs involving the RAS protein family and their effectors and interactors at the plasma membrane. By utilizing the NanoLuc and HaloTag BRET pair, we provide evidence of a saturable interaction between KRAS4b-G12D and full-length RAF1. Conversely, the RAF1 R89L mutant, known to impede RAF1 binding to active RAS, exhibits nonspecific interactions. The assay exhibits remarkable signal-to-background ratios and is highly suitable for investigating the interactions of RAS with effectors, as well as for high-throughput screening assays.

Targeting the RAS/RAF/MAPK pathway for cancer therapy: from mechanism to clinical studies

Metastatic dissemination of solid tumors, a leading cause of cancer-related mortality, underscores the urgent need for enhanced insights into the molecular and cellular mechanisms underlying metastasis, chemoresistance, and the mechanistic backgrounds of individuals whose cancers are prone to migration. The most prevalent signaling cascade governed by multi-kinase inhibitors is the mitogen-activated protein kinase (MAPK) pathway, encompassing the RAS-RAF-MAPK kinase (MEK)-extracellular signal-related kinase (ERK) pathway. RAF kinase is a primary mediator of the MAPK pathway, responsible for the sequential activation of downstream targets, such as MEK and the transcription factor ERK, which control numerous cellular and physiological processes, including organism development, cell cycle control, cell proliferation and differentiation, cell survival, and death. Defects in this signaling cascade are associated with diseases such as cancer. RAF inhibitors (RAFi) combined with MEK blockers represent an FDA-approved therapeutic strategy for numerous RAF-mutant cancers, including melanoma, non-small cell lung carcinoma, and thyroid cancer. However, the development of therapy resistance by cancer cells remains an important barrier. Autophagy, an intracellular lysosome-dependent catabolic recycling process, plays a critical role in the development of RAFi resistance in cancer. Thus, targeting RAF and autophagy could be novel treatment strategies for RAF-mutant cancers. In this review, we delve deeper into the mechanistic insights surrounding RAF kinase signaling in tumorigenesis and RAFi-resistance. Furthermore, we explore and discuss the ongoing development of next-generation RAF inhibitors with enhanced therapeutic profiles. Additionally, this review sheds light on the functional interplay between RAF-targeted therapies and autophagy in cancer.

Analysis of RAS and drug induced homo- and heterodimerization of RAF and KSR1 proteins in living cells using split Nanoluc luciferase

The dimerization of RAF kinases represents a key event in their activation cycle and in RAS/ERK pathway activation. Genetic, biochemical and structural approaches provided key insights into this process defining RAF signaling output and the clinical efficacy of RAF inhibitors (RAFi). However, methods reporting the dynamics of RAF dimerization in living cells and in real time are still in their infancy. Recently, split luciferase systems have been developed for the detection of protein-protein-interactions (PPIs), incl. proof-of-concept studies demonstrating the heterodimerization of the BRAF and RAF1 isoforms. Due to their small size, the Nanoluc luciferase moieties LgBiT and SmBiT, which reconstitute a light emitting holoenzyme upon fusion partner promoted interaction, appear as well-suited to study RAF dimerization. Here, we provide an extensive analysis of the suitability of the Nanoluc system to study the homo- and heterodimerization of BRAF, RAF1 and the related KSR1 pseudokinase. We show that KRAS^G12V promotes the homo- and heterodimerization of BRAF, while considerable KSR1 homo- and KSR1/BRAF heterodimerization already occurs in the absence of this active GTPase and requires a salt bridge between the CC-SAM domain of KSR1 and the BRAF-specific region. We demonstrate that loss-of-function mutations impairing key steps of the RAF activation cycle can be used as calibrators to gauge the dynamics of heterodimerization. This approach identified the RAS-binding domains and the C-terminal 14-3-3 binding motifs as particularly critical for the reconstitution of RAF mediated LgBiT/SmBiT reconstitution, while the dimer interface was less important for dimerization but essential for downstream signaling. We show for the first time that BRAF^V600E, the most common BRAF oncoprotein whose dimerization status is controversially portrayed in the literature, forms homodimers in living cells more efficiently than its wildtype counterpart. Of note, Nanoluc activity reconstituted by BRAF^V600E homodimers is highly sensitive to the paradox-breaking RAFi PLX8394, indicating a dynamic and specific PPI. We report the effects of eleven ERK pathway inhibitors on RAF dimerization, incl. third-generation compounds that are less-defined in terms of their dimer promoting abilities. We identify Naporafenib as a potent and long-lasting dimerizer and show that the split Nanoluc approach discriminates between type I, I^1/2 and II RAFi. Video Abstract.

The Application of High-Throughput Approaches in Identifying Novel Therapeutic Targets and Agents to Treat Diabetes

During the past decades, unprecedented progress in technologies has revolutionized traditional research methodologies. Among these, advances in high-throughput drug screening approaches have permitted the rapid identification of potential therapeutic agents from drug libraries that contain thousands or millions of molecules. Moreover, high-throughput-based therapeutic target discovery strategies can comprehensively interrogate relationships between biomolecules (e.g., gene, RNA, and protein) and diseases and significantly increase the authors' knowledge of disease mechanisms. Diabetes is a chronic disease primarily characterized by the incapacity of the body to maintain normoglycemia. The prevalence of diabetes in modern society has become a severe public health issue that threatens the well-being of millions of patients. Although a number of pharmacological treatments are available, there is no permanent cure for diabetes, and discovering novel therapeutic targets and agents continues to be an urgent need. The present review discusses the technical details of high-throughput screening approaches in drug discovery, followed by introducing the applications of such approaches to diabetes research. This review aims to provide an example of the applicability of high-throughput technologies in facilitating different aspects of disease research.

Tolypocladamides A-G: Cytotoxic Peptaibols from Tolypocladium inflatum

Seven new peptaibols named tolypocladamides A-G have been isolated from an extract of the fungus Tolypocladium inflatum, which inhibits the interaction between Raf and oncogenic Ras in a cell-based high-throughput screening assay. Each peptaibol contains 11 amino acid residues, an octanoyl or decanoyl fatty acid chain at the N-terminus, and a leucinol moiety at the C-terminus. The peptaibol sequences were elucidated on the basis of 2D NMR and mass spectral fragmentation analyses. Amino acid configurations were determined by advanced Marfey's analyses. Tolypocladamides A-G caused significant inhibition of Ras/Raf interactions with IC50 values ranging from 0.5 to 5.0 μM in a nanobioluminescence resonance energy transfer (NanoBRET) assay; however, no interactions were observed in a surface plasmon resonance assay for binding of the compounds to wild type or G12D mutant Ras constructs or to the Ras binding domain of Raf. NCI 60 cell line testing was also conducted, and little panel selectivity was observed.

KRAS is vulnerable to reversible switch-II pocket engagement in cells

Current small-molecule inhibitors of KRAS(G12C) bind irreversibly in the switch-II pocket (SII-P), exploiting the strong nucleophilicity of the acquired cysteine as well as the preponderance of the GDP-bound form of this mutant. Nevertheless, many oncogenic KRAS mutants lack these two features, and it remains unknown whether targeting the SII-P is a practical therapeutic approach for KRAS mutants beyond G12C. Here we use NMR spectroscopy and a cellular KRAS engagement assay to address this question by examining a collection of SII-P ligands from the literature and from our own laboratory. We show that the SII-Ps of many KRAS hotspot (G12, G13, Q61) mutants are accessible using noncovalent ligands, and that this accessibility is not necessarily coupled to the GDP state of KRAS. The results we describe here emphasize the SII-P as a privileged drug-binding site on KRAS and unveil new therapeutic opportunities in RAS-driven cancer.

The use of NMR spectroscopy and development of a cellular BRET KRAS engagement assay revealed that noncovalent ligands can access the switch-II pocket of KRAS hotspot mutants.

Development of a biotin-streptavidin-enhanced enzyme-linked immunosorbent assay (BA-ELISA) for high-throughput screening of KRASG12C inhibitors

KRAS, the most frequently mutated oncogene in human cancers, was considered "undruggable" until the identification of small molecules that bind irreversibly to the mutant reactive cysteine at residue 12. Despite the encouraging anticancer activity of KRAS^G12C inhibitors in clinical trials, identification of more potent drugs is expected to achieve the maximal clinical benefit, which is hindered by the low sensitivity or throughput of current biochemical approaches. To overcome these limitations, a biotin-streptavidin-enhanced enzyme-linked immunosorbent assay (BA-ELISA) based on the competitive interaction of biotin-labeled probe and the test compound with KRAS^G12C was developed. Compared with reported assays, less protein was used in BA-ELISA, which significantly improves the resolution of inhibitor potency, thus contributing to the identification of highly potent inhibitors. Furthermore, BA-ELISA can also be expanded to determine the cellular potency of the inhibitors using KRAS^G12C mutant living cells. Using three previously disclosed compounds, ARS-1620, AMG 510, and MRTX849, we demonstrated that BA-ELISA is a highly sensitive, specific, and robust method for high-throughput screening of KRAS^G12C inhibitors.