Modulares PROTAC-Design zum Abbau von onkogenem BCR-ABL

A beginner's guide to current synthetic linker strategies towards VHL-recruiting PROTACs

Over the last two decades, proteolysis targeting chimeras (PROTACs) have been revolutionary in drug development rendering targeted protein degradation (TPD) as an emerging therapeutic modality. These heterobifunctional molecules are comprised of three units: a ligand for the protein of interest (POI), a ligand for an E3 ubiquitin ligase, and a linker that tethers the two motifs together. Von Hippel-Lindau (VHL) is one of the most widely employed E3 ligases in PROTACs development due to its prevalent expression across tissue types and well-characterised ligands. Linker composition and length has proven to play an important role in determining the physicochemical properties and spatial orientation of the POI-PROTAC-E3 ternary complex, thus influencing the bioactivity of degraders. Numerous articles and reports have been published showcasing the medicinal chemistry aspects of the linker design, but few have focused on the chemistry around tethering linkers to E3 ligase ligands. In this review, we focus on the current synthetic linker strategies employed in the assembly of VHL-recruiting PROTACs. We aim to cover a range of fundamental chemistries used to incorporate linkers of varying length, composition and functionality.

Recent Developments in PROTAC-Mediated Protein Degradation: From Bench to Clinic

Proteolysis-targeting chimeras (PROTACs), an emerging paradigm-shifting technology, hijacks the ubiquitin-proteasome system for targeted protein degradation. PROTACs induce ternary complexes between an E3 ligase and POI, and this induced proximity leads to polyUb chain formation on substrates and eventual proteasomal-mediated POI degradation. PROTACs have shown great therapeutic potential by degrading many disease-causing proteins, such as the androgen receptor and BRD4. The PROTAC technology has advanced significantly in the last two decades, with the repertoire of PROTAC targets increased tremendously. Herein, we describe recent developments of PROTAC technology, focusing on mechanistic and kinetic studies, pharmacokinetic study, spatiotemporal control of PROTACs, covalent PROTACs, resistance to PROTACs, and new E3 ligands.

Selective degradation-inducing probes for studying cereblon (CRBN) biology

Targeted protein degradation represents a rapidly growing area in drug discovery and development. Moreover, small molecules that induce the targeted degradation of a given protein also represent an important addition to the chemical probes toolbox as these compounds can achieve selective protein knockdown, thus providing an approach that is orthogonal to genetic knockdowns. In order to develop degradation-inducing chemical probes for studying cereblon (CRBN) biology, we generated six CRBN-CRBN (homo-PROTAC) degraders and six CRBN-VHL (hetero-PROTAC) degraders. From these compounds we identified two potent and selective CRBN degraders (ZXH-4-130 and ZXH-4-137), both of which are CRBN-VHL compounds. We characterized these lead degraders by quantitative proteomics in five cell lines (MM1.S, Kelly, SK-N-DZ, HEK293T, and MOLT-4) and observed high selectivity for CRBN in all cell lines. Furthermore, we directly compared our compounds to current lead CRBN degraders and demonstrated how these probes can be used as chemical knockdown reagents for studying CRBN-dependent processes. Overall, our work provides a roadmap for thorough degrader characterization by combination western and proteomic analysis, as illustrated by the identification of ZXH-4-130 and ZXH-4-137 as CRBN-knockdown tool compounds suitable for cell-based studies.

Advances in Strategies and Tools Available for Interrogation of Protein O-GlcNAcylation

The attachment of a single O-linked β-N-acetylglucosamine (O-GlcNAc) to serine and threonine residues of numerous proteins in the nucleus, cytoplasm, and mitochondria is a reversible post-translational modification (PTM) and plays an important role as a regulator of various cellular processes in both healthy and disease states. Advances in strategies and tools that allow for the detection of dynamic O-GlcNAcylation on cellular proteins have helped to enhance our initial and ongoing understanding of its dynamic effects on cellular stimuli and given insights into its link to the pathogenesis of several chronic diseases. Furthermore, chemical genetic strategies and related tools have been successfully applied to a myriad of biological systems with a new level of spatiotemporal and molecular precision. These strategies have started to be used in studying and controlling O-GlcNAcylation both in vivo and in vitro. In this minireview, overviews of recent advances in molecular tools being applied to the detection and identification of O-GlcNAcylation on cellular proteins as well as on individual proteins are provided. In addition, chemical genetic strategies that have already been applied or are potentially usable in O-GlcNAc functional are also discussed.

Bispecific Aptamer Chimeras Enable Targeted Protein Degradation on Cell Membranes

The ability to regulate membrane protein abundance offers great opportunities for developing therapeutic sites for various diseases. Herein, we describe a platform for the targeted degradation of membrane-associated proteins using bispecific aptamer chimeras that bind both the cell-surface lysosome-shuttling receptor (IGFIIR) and the targeted membrane-bound proteins of interest. We demonstrate that the aptamer chimeras can efficiently and quickly shuttle the therapeutically relevant membrane proteins of Met and PTK-7 to lysosomes and degrade them through the lysosomal protein degradation machinery. We anticipate that our method will provide a universal platform for the use of readily synthesized aptamer materials for biochemical research and potential therapeutics.

PROTACs and Other Chemical Protein Degradation Technologies for the Treatment of Neurodegenerative Disorders

Neurodegenerative disorders (NDs) are a group of diseases that cause neural cell damage, leading to motility and/or cognitive dysfunctions. One of the causative agents is misfolded protein aggregates, which are considered as undruggable in terms of conventional tools, such as inhibitors and agonists/antagonists. Indeed, there is currently no FDA-approved drug for the causal treatment of NDs. However, emerging technologies for chemical protein degradation are opening up the possibility of selective elimination of target proteins through physiological protein degradation machineries, which do not depend on the functions of the target proteins. Here, we review recent efforts towards the treatment of NDs using chemical protein degradation technologies, and we briefly discuss the challenges and prospects.

Bifunctional Small-Molecule Ligands of K-Ras Induce Its Association with Immunophilin Proteins

Here we report the design, synthesis, and characterization of bifunctional chemical ligands that induce the association of Ras with ubiquitously expressed immunophilin proteins such as FKBP12 and cyclophilin A. We show this approach is applicable to two distinct Ras ligand scaffolds, and that both the identity of the immunophilin ligand and the linker chemistry affect compound efficacy in biochemical and cellular contexts. These ligands bind to Ras in an immunophilin-dependent fashion and mediate the formation of tripartite complexes of Ras, immunophilin, and the ligand. The recruitment of cyclophilin A to GTP-bound Ras blocks its interaction with B-Raf in biochemical assays. Our study demonstrates the feasibility of ligand-induced association of Ras with intracellular proteins and suggests it as a promising therapeutic strategy for Ras-driven cancers.

Breaking the Fourth Wall: Modulating Quaternary Associations for Protein Regulation and Drug Discovery

Protein-protein interactions (PPIs) are an effective means to orchestrate intricate biological processes required to sustain life. Approximately 650 000 PPIs underlie the human interactome; thus underscoring its complexity and the manifold signaling outputs altered in response to changes in specific PPIs. This minireview illustrates the growing arsenal of PPI assemblies and offers insights into how these varied PPI regulatory modalities are relevant to customized drug discovery, with a focus on cancer. First, known and emerging PPIs and PPI-targeted drugs of both natural and synthetic origin are categorized. Building on these discussions, the merits of PPI-guided therapeutics over traditional drug design are discussed. Finally, a compare-and-contrast section for different PPI blockers, with gain-of-function PPI interventions, such as PROTACS, is provided.

Efficient Synthesis of Immunomodulatory Drug Analogues Enables Exploration of Structure-Degradation Relationships

The immunomodulatory drugs (IMiDs) thalidomide, pomalidomide, and lenalidomide have been approved for the treatment of multiple myeloma for many years. Recently, their use as E3 ligase recruiting elements for small-molecule-induced protein degradation has led to a resurgence in interest in IMiD synthesis and functionalization. Traditional IMiD synthesis follows a stepwise route with multiple purification steps. Herein we describe a novel one-pot synthesis without purification that provides rapid access to a multitude of IMiD analogues. Binding studies with the IMiD target protein cereblon (CRBN) reveals a narrow structure-activity relationship with only a few compounds showing sub-micromolar binding affinity in the range of pomalidomide and lenalidomide. However, anti-proliferative activity as well as Aiolos degradation could be identified for two IMiD analogues. This study provides useful insight into the structure-degradation relationships for molecules of this type as well as a rapid and robust method for IMiD synthesis.

Chemically Induced Degradation of Anaplastic Lymphoma Kinase (ALK)

We present the development of the first small molecule degraders that can induce anaplastic lymphoma kinase (ALK) degradation, including in non-small-cell lung cancer (NSCLC), anaplastic large-cell lymphoma (ALCL), and neuroblastoma (NB) cell lines. These degraders were developed through conjugation of known pyrimidine-based ALK inhibitors, TAE684 or LDK378, and the cereblon ligand pomalidomide. We demonstrate that in some cell types degrader potency is compromised by expression of drug transporter ABCB1. In addition, proteomic profiling demonstrated that these compounds also promote the degradation of additional kinases including PTK2 (FAK), Aurora A, FER, and RPS6KA1 (RSK1).

New Modalities for Challenging Targets in Drug Discovery

Our ever-increasing understanding of biological systems is providing a range of exciting novel biological targets, whose modulation may enable novel therapeutic options for many diseases. These targets include protein-protein and protein-nucleic acid interactions, which are, however, often refractory to classical small-molecule approaches. Other types of molecules, or modalities, are therefore required to address these targets, which has led several academic research groups and pharmaceutical companies to increasingly use the concept of so-called "new modalities". This Review defines for the first time the scope of this term, which includes novel peptidic scaffolds, oligonucleotides, hybrids, molecular conjugates, as well as new uses of classical small molecules. We provide the most representative examples of these modalities to target large binding surface areas such as those found in protein-protein interactions and for biological processes at the center of cell regulation.

Synthetic Biology-The Synthesis of Biology

Synthetic biology concerns the engineering of man-made living biomachines from standardized components that can perform predefined functions in a (self-)controlled manner. Different research strategies and interdisciplinary efforts are pursued to implement engineering principles to biology. The "top-down" strategy exploits nature's incredible diversity of existing, natural parts to construct synthetic compositions of genetic, metabolic, or signaling networks with predictable and controllable properties. This mainly application-driven approach results in living factories that produce drugs, biofuels, biomaterials, and fine chemicals, and results in living pills that are based on engineered cells with the capacity to autonomously detect and treat disease states in vivo. In contrast, the "bottom-up" strategy seeks to be independent of existing living systems by designing biological systems from scratch and synthesizing artificial biological entities not found in nature. This more knowledge-driven approach investigates the reconstruction of minimal biological systems that are capable of performing basic biological phenomena, such as self-organization, self-replication, and self-sustainability. Moreover, the syntheses of artificial biological units, such as synthetic nucleotides or amino acids, and their implementation into polymers inside living cells currently set the boundaries between natural and artificial biological systems. In particular, the in vitro design, synthesis, and transfer of complete genomes into host cells point to the future of synthetic biology: the creation of designer cells with tailored desirable properties for biomedicine and biotechnology.

Degradation of the BAF Complex Factor BRD9 by Heterobifunctional Ligands

The bromodomain-containing protein BRD9, a subunit of the human BAF (SWI/SNF) nucleosome remodeling complex, has emerged as an attractive therapeutic target in cancer. Despite the development of chemical probes targeting the BRD9 bromodomain, there is a limited understanding of BRD9 function beyond acetyl-lysine recognition. We have therefore created the first BRD9-directed chemical degraders, through iterative design and testing of heterobifunctional ligands that bridge the BRD9 bromodomain and the cereblon E3 ubiquitin ligase complex. Degraders of BRD9 exhibit markedly enhanced potency compared to parental ligands (10- to 100-fold). Parallel study of degraders with divergent BRD9-binding chemotypes in models of acute myeloid leukemia resolves bromodomain polypharmacology in this emerging drug class. Together, these findings reveal the tractability of non-BET bromodomain containing proteins to chemical degradation, and highlight lead compound dBRD9 as a tool for the study of BRD9.