Intrinsically Disordered Regions in the Transcription Factor MYC:MAX Modulate DNA Binding via Intramolecular Interactions.

The basic helix-loop-helix leucine zipper (bHLH-LZ) transcription factor (TF) MYC is in large part an intrinsically disordered oncoprotein. In complex with its obligate heterodimerization partner MAX, MYC preferentially binds E-Box DNA sequences (CANNTG). At promoters containing these sequence motifs, MYC controls fundamental cellular processes such as cell cycle progression, metabolism, and apoptosis. A vast network of proteins in turn regulates MYC function via intermolecular interactions. In this work, we establish another layer of MYC regulation by intramolecular interactions. We used nuclear magnetic resonance (NMR) spectroscopy to identify and map multiple binding sites for the C-terminal MYC:MAX DNA-binding domain (DBD) on the intrinsically disordered regions (IDRs) in the MYC N-terminus. We find that these binding events in trans are driven by electrostatic attraction, that they have distinct affinities, and that they are competitive with DNA binding. Thereby, we observe the strongest effects for the N-terminal MYC box 0 (Mb0), a conserved motif involved in MYC transactivation and target gene induction. We prepared recombinant full-length MYC:MAX complex and demonstrate that the interactions identified in this work are also relevant in cis, i.e., as intramolecular interactions. These findings are supported by surface plasmon resonance (SPR) experiments, which revealed that intramolecular IDR:DBD interactions in MYC decelerate the association of MYC:MAX complexes to DNA. Our work offers new insights into how bHLH-LZ TFs are regulated by intramolecular interactions, which open up new possibilities for drug discovery.

Fragment-to-Lead Medicinal Chemistry Publications in 2022.

This Perspective is the eighth in an annual series that summarizes successful fragment-to-lead (F2L) case studies published each year. A tabulated summary of relevant articles published in 2022 is provided, and features such as target class, screening methods, and ligand efficiency are discussed both for the 2022 examples and for the combined examples over the years 2015-2022. In addition, trends and new developments in the field are summarized. In 2022, 18 publications described successful fragment-to-lead studies, including the development of three clinical compounds (MTRX1719, MK-8189, and BI-823911).

Fragment-to-Lead Medicinal Chemistry Publications in 2021.

This Perspective is the seventh in an annual series that summarizes successful Fragment-to-Lead (F2L) case studies published in a given year. A tabulated summary of relevant articles published in 2021 is provided, and features such as target class, screening methods, and ligand efficiency are discussed, both for the 2021 examples and for the combined examples over the years 2015-2021. In addition, trends and new developments in the field are summarized. In particular, the use of structural information in fragment-based drug discovery is discussed.

Correspondence on "Synergy and Antagonism between Allosteric and Active-Site Inhibitors of Abl Tyrosine Kinase".

Soellner published on the interplay between allosteric and adenosine triphosphate (ATP)-competitive inhibitors of ABL kinase, showing that the latter preferably binds to different conformational states of ABL compared to allosteric agents that specifically target the ABL myristate pocket (STAMP) and deducing that asciminib cannot bind to ABL simultaneously with ATP-competitive drugs. These results are to some extent in line with ours, although our analyses of dose-response matrices from combinations of asciminib with imatinib, nilotinib or dasatinib, show neither synergy nor antagonism, but suggest additive antiproliferative effects on BCR-ABL-dependent KCL22 cells. Furthermore, our X-ray crystallographic, solution nuclear magnetic resonance (NMR), and isothermal titration calorimetry studies show that asciminib can bind ABL concomitantly with type-1 or -2 ATP-competitive inhibitors to form ternary complexes. Concomitant binding of asciminib with imatinib, nilotinib, or dasatinib might translate to benefit some chronic myeloid leukaemia patients.

The Disordered MAX N-terminus Modulates DNA Binding of the Transcription Factor MYC:MAX.

The intrinsically disordered protein MYC belongs to the family of basic helix-loop-helix leucine zipper (bHLH-LZ) transcription factors (TFs). In complex with its cognate binding partner MAX, MYC preferentially binds to E-Box promotor sequences where it controls fundamental cellular processes such as cell cycle progression, metabolism, and apoptosis. Intramolecular regulation of MYC:MAX has not yet been investigated in detail. In this work, we use Nuclear Magnetic Resonance (NMR) spectroscopy to identify and map interactions between the disordered MAX N-terminus and the MYC:MAX DNA binding domain (DBD). We find that this binding event is mainly driven by electrostatic interactions and that it is competitive with DNA binding. Using NMR spectroscopy and Surface Plasmon Resonance (SPR), we demonstrate that the MAX N-terminus serves to accelerate DNA binding kinetics of MYC:MAX and MAX:MAX dimers, while it simultaneously provides specificity for E-Box DNA. We also establish that these effects are further enhanced by Casein Kinase 2-mediated phosphorylation of two serine residues in the MAX N-terminus. Our work provides new insights how bHLH-LZ TFs are regulated by intramolecular interactions between disordered regions and the folded DNA binding domain.

Fragment-to-Lead Medicinal Chemistry Publications in 2020.

Fragment-based drug discovery (FBDD) continues to evolve and make an impact in the pharmaceutical sciences. We summarize successful fragment-to-lead studies that were published in 2020. Having systematically analyzed annual scientific outputs since 2015, we discuss trends and best practices in terms of fragment libraries, target proteins, screening technologies, hit-optimization strategies, and the properties of hit fragments and the leads resulting from them. As well as the tabulated Fragment-to-Lead (F2L) programs, our 2020 literature review identifies several trends and innovations that promise to further increase the success of FBDD. These include developing structurally novel screening fragments, improving fragment-screening technologies, using new computer-aided design and virtual screening approaches, and combining FBDD with other innovative drug-discovery technologies.

The 2nd Alpine Winter Conference on Medicinal and Synthetic Chemistry.

The second biannual Alpine Winter Conference on Medicinal and Synthetic Chemistry (short: Alpine Winter Conference) took place January 19-23, 2020, in St. Anton in western Austria. There were roughly 180 attendees from around the globe, making this mid-sized conference particularly conducive to networking and exchanging ideas over the course of four and a half days. This report summarizes the key events and presentations given by researchers working in both industry and academia.

Fragment-to-Lead Medicinal Chemistry Publications in 2019.

Fragment-based drug discovery (FBDD) has grown and matured to a point where it is valuable to keep track of its extent and details of application. This Perspective summarizes successful fragment-to-lead stories published in 2019. It is the fifth in a series that started with literature published in 2015. The analysis of screening methods, optimization strategies, and molecular properties of hits and leads are presented in the hope of informing best practices for FBDD. Moreover, FBDD is constantly evolving, and the latest technologies and emerging trends are summarized. These include covalent FBDD, FBDD for the stabilization of proteins or protein-protein interactions, FBDD for enzyme activators, new screening technologies, and advances in library design and chemical synthesis.

Correction to: NMR in pharmaceutical discovery and development.

The article "Boeszoermenyi A, Ogórek B, Jain A, Arthanari H, Wagner G (2020) The precious fluorine on the ring: fluorine NMR for biological systems. J Biomol NMR. https ://doi.org/10.1007/s10858-020-00331-z" was written for the "Special Issue: NMR in Pharmaceutical Discovery and Development". However, unfortunately, it was published in an earlier issue of this journal owing to a publisher error. Further, the ORCID ID of author Wolfgang Jahnke is updated in the article. The original article has been corrected.

Discovery of Roblitinib (FGF401) as a Reversible-Covalent Inhibitor of the Kinase Activity of Fibroblast Growth Factor Receptor 4.

FGF19 signaling through the FGFR4/ß-klotho receptor complex has been shown to be a key driver of growth and survival in a subset of hepatocellular carcinomas, making selective FGFR4 inhibition an attractive treatment opportunity. A kinome-wide sequence alignment highlighted a poorly conserved cysteine residue within the FGFR4 ATP-binding site at position 552, two positions beyond the gate-keeper residue. Several strategies for targeting this cysteine to identify FGFR4 selective inhibitor starting points are summarized which made use of both rational and unbiased screening approaches. The optimization of a 2-formylquinoline amide hit series is described in which the aldehyde makes a hemithioacetal reversible-covalent interaction with cysteine 552. Key challenges addressed during the optimization are improving the FGFR4 potency, metabolic stability, and solubility leading ultimately to the highly selective first-in-class clinical candidate roblitinib.

Fragment-Based Discovery of Non-bisphosphonate Binders of Trypanosoma brucei Farnesyl Pyrophosphate Synthase.

Trypanosoma brucei is the causative agent of human African trypanosomiasis (HAT). Nitrogen-containing bisphosphonates, a current treatment for bone diseases, have been shown to block the growth of the T. brucei parasites by inhibiting farnesyl pyrophosphate synthase (FPPS); however, due to their poor pharmacokinetic properties, they are not well suited for antiparasitic therapy. Recently, an allosteric binding pocket was discovered on human FPPS, but its existence on trypanosomal FPPS was unclear. We applied NMR and X-ray fragment screening to T. brucei FPPS and report herein on four fragments bound to this previously unknown allosteric site. Surprisingly, non-bisphosphonate active-site binders were also identified. Moreover, fragment screening revealed a number of additional binding sites. In an early structure-activity relationship (SAR) study, an analogue of an active-site binder was unexpectedly shown to bind to the allosteric site. Overlaying identified fragment binders of a parallel T. cruzi FPPS fragment screen with the T. brucei FPPS structure, and medicinal chemistry optimisation based on two binders revealed another example of fragment "pocket hopping". The discovery of binders with new chemotypes sets the framework for developing advanced compounds with pharmacokinetic properties suitable for the treatment of parasitic infections by inhibition of FPPS in T. brucei parasites.

Fragment-to-Lead Medicinal Chemistry Publications in 2018.

This Perspective, the fourth in an annual series, summarizes fragment-to-lead (F2L) success stories published during 2018. Topics such as target class, screening methods, physicochemical properties, and ligand efficiency are discussed for the 2018 examples as well as for the combined 111 F2L examples covering 2015-2018. While the overall properties of fragments and leads have remained constant, a number of new trends are noted, for example, broadening of target class coverage and application of FBDD to covalent inhibitors. Moreover, several studies make use of fragment hits that were previously described in the literature, illustrating that fragments are versatile starting points that can be optimized to structurally diverse leads. By focusing on success stories, the hope is that this Perspective will identify and inform best practices in fragment-based drug discovery.

Site-Directed Fragment-Based Screening for the Discovery of Protein-Protein Interaction Stabilizers.

Modulation of protein-protein interactions (PPIs) by small molecules has emerged as a valuable approach in drug discovery. Compared to direct inhibition, PPI stabilization is vastly underexplored but has strong advantages, including the ability to gain selectivity by targeting an interface formed only upon association of proteins. Here, we present the application of a site-directed screening technique based on disulfide trapping (tethering) to select for fragments that enhance the affinity between protein partners. We target the phosphorylation-dependent interaction between the hub protein 14-3-3σ and a peptide derived from Estrogen Receptor α (ERα), an important breast cancer target that is negatively regulated by 14-3-3σ. We identify orthosteric stabilizers that increase 14-3-3/ERα affinity up to 40-fold and propose the mechanism of stabilization based on X-ray crystal structures. These fragments already display partial selectivity toward ERα-like motifs over other representative 14-3-3 clients. This first of its kind study illustrates the potential of the tethering approach to overcome the hurdles in systematic PPI stabilizer discovery.

Fragment-to-Lead Medicinal Chemistry Publications in 2017.

This Miniperspective is the third in a series reviewing fragment-to-lead publications from a given year. Following our reviews for 2015 and 2016, this Miniperspective provides tabulated summaries of relevant articles published in 2017 along with some general observations. In addition, we discuss insights obtained from analysis of the combined data set of 85 examples from all three years of publications.

Fragment-Based Drug Discovery: Advancing Fragments in the Absence of Crystal Structures.

Fragment-based drug discovery typically requires an interplay between screening methods, structural methods, and medicinal chemistry. X-ray crystallography is generally the method of choice to obtain three-dimensional structures of the bound ligand/protein complex, but this can sometimes be difficult, particularly for early, low-affinity fragment hits. In this Perspective, we discuss strategies to advance and evolve fragments in the absence of crystal structures of protein-fragment complexes, although the structure of the unliganded protein may be available. The strategies can involve other structural techniques, such as NMR spectroscopy, molecular modeling, or a variety of chemical approaches. Often, these strategies are aimed at guiding evolution of initial fragment hits to a stage where crystal structures can be obtained for further structure-based optimization.

Discovery of Asciminib (ABL001), an Allosteric Inhibitor of the Tyrosine Kinase Activity of BCR-ABL1.

Chronic myelogenous leukemia (CML) arises from the constitutive activity of the BCR-ABL1 oncoprotein. Tyrosine kinase inhibitors (TKIs) that target the ATP-binding site have transformed CML into a chronic manageable disease. However, some patients develop drug resistance due to ATP-site mutations impeding drug binding. We describe the discovery of asciminib (ABL001), the first allosteric BCR-ABL1 inhibitor to reach the clinic. Asciminib binds to the myristate pocket of BCR-ABL1 and maintains activity against TKI-resistant ATP-site mutations. Although resistance can emerge due to myristate-site mutations, these are sensitive to ATP-competitive inhibitors so that combinations of asciminib with ATP-competitive TKIs suppress the emergence of resistance. Fragment-based screening using NMR and X-ray yielded ligands for the myristate pocket. An NMR-based conformational assay guided the transformation of these inactive ligands into ABL1 inhibitors. Further structure-based optimization for potency, physicochemical, pharmacokinetic, and drug-like properties, culminated in asciminib, which is currently undergoing clinical studies in CML patients.

Inhibition of K-RAS4B by a Unique Mechanism of Action: Stabilizing Membrane-Dependent Occlusion of the Effector-Binding Site.

KRAS is frequently mutated in several of the most lethal types of cancer; however, the KRAS protein has proven a challenging drug target. K-RAS4B must be localized to the plasma membrane by prenylation to activate oncogenic signaling, thus we endeavored to target the protein-membrane interface with small-molecule compounds. While all reported lead compounds have low affinity for KRAS in solution, the potency of Cmpd2 was strongly enhanced when prenylated K-RAS4B is associated with a lipid bilayer. We have elucidated a unique mechanism of action of Cmpd2, which simultaneously engages a shallow pocket on KRAS and associates with the lipid bilayer, thereby stabilizing KRAS in an orientation in which the membrane occludes its effector-binding site, reducing RAF binding and impairing activation of RAF. Furthermore, enrichment of Cmpd2 on the bilayer enhances potency by promoting interaction with KRAS. This insight reveals a novel approach to developing inhibitors of membrane-associated proteins.

Fragment-to-Lead Medicinal Chemistry Publications in 2016.

The popularity of fragment-based drug discovery (FBDD) is demonstrated by the number of recent successful fragment-to-lead (F2L) publications. This Miniperspective provides a tabulated summary of the F2L literature published in the year 2016, along with discussion of general trends. It uses the same format as our summary of the 2015 literature and is intended to be a resource for both FBDD practitioners and medicinal chemists in general.

Identification of Two Secondary Ligand Binding Sites in 14-3-3 Proteins Using Fragment Screening.

Proteins typically interact with multiple binding partners, and often different parts of their surfaces are employed to establish these protein-protein interactions (PPIs). Members of the class of 14-3-3 adapter proteins bind to several hundred other proteins in the cell. Multiple small molecules for the modulation of 14-3-3 PPIs have been disclosed; however, they all target the conserved phosphopeptide binding channel, so that selectivity is difficult to achieve. Here we report on the discovery of two individual secondary binding sites that have been identified by combining nuclear magnetic resonance-based fragment screening and X-ray crystallography. The two pockets that these fragments occupy are part of at least three physiologically relevant and structurally characterized 14-3-3 PPI interfaces, including those with serotonin N-acetyltransferase and plant transcription factor FT. In addition, the high degree of conservation of the two sites implies their relevance for 14-3-3 PPIs. This first identification of secondary sites on 14-3-3 proteins bound by small molecule ligands might facilitate the development of new chemical tool compounds for more selective PPI modulation.