Steuerung der intrazellulären Proteinmenge durch niedermolekulare Modulatoren des Ubiquitin-Proteasom-Systems

Discovery of Norbornene as a Novel Hydrophobic Tag Applied in Protein Degradation

Hydrophobic tagging (HyT) is a potential therapeutic strategy for targeted protein degradation (TPD). Norbornene was discovered as an unprecedented hydrophobic tag in this study and was used to degrade the anaplastic lymphoma kinase (ALK) fusion protein by linking it to ALK inhibitors. The most promising degrader, Hyt-9, potently reduced ALK levels through Hsp70 and the ubiquitin-proteasome system (UPS) in vitro without compensatory upregulation of ALK. Furthermore, Hyt-9 exhibited a significant tumor-inhibiting effect in vivo with moderate oral bioavailability. More importantly, norbornene can also be used to degrade the intractable enhancer of zeste homolog 2 (EZH2) when tagged with the EZH2 inhibitor tazemetostat. Thus, the discovery of novel hydrophobic norbornene tags shows promise for the future development of TPD technology.

Applications and Limitations of Oxime-Linked "Split PROTACs"

Proteolysis targeting chimeras are of keen interest as probe molecules and drug leads. Their activity is highly sensitive to the length and nature of the linker connecting the E3 Ubiquitin Ligase (E3 Ubl) and target protein (TP) ligands, which therefore requires tedious optimization. The creation of "split PROTACs" from E3 Ubl and TP ligands modified with residues suitable for them to couple when simply mixed together would allow various combinations to be assessed in a combinatorial fashion, thus greatly easing the workload relative to a one-by-one synthesis of many different PROTACs (proteolysis targeting chimeras). We explore oxime chemistry here for this purpose. We show that PROTAC assembly occurs efficiently when the components are mixed at a high concentration, then added to cells. However, in situ coupling of the TP and E3 Ubl ligands is inefficient when these units are added to cells at lower concentrations.

Targeting TRIM Proteins: A Quest towards Drugging an Emerging Protein Class

The ubiquitylation machinery regulates several fundamental biological processes from protein homeostasis to a wide variety of cellular signaling pathways. As a consequence, its dysregulation is linked to diseases including cancer, neurodegeneration, and autoimmunity. With this review, we aim to highlight the therapeutic potential of targeting E3 ligases, with a special focus on an emerging class of RING ligases, named tri-partite motif (TRIM) proteins, whose role as targets for drug development is currently gaining pharmaceutical attention. TRIM proteins exert their catalytic activity as scaffolds involved in many protein-protein interactions, whose multidomains and adapter-like nature make their druggability very challenging. Herein, we give an overview of the current understanding of this class of single polypeptide RING E3 ligases and discuss potential targeting options.

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.

Identification of the Biosynthetic Gene Cluster for Himeic Acid A: A Ubiquitin-Activating Enzyme (E1) Inhibitor in Aspergillus japonicus MF275

Himeic acid A, which is produced by the marine fungus Aspergillus japonicus MF275, is a specific inhibitor of the ubiquitin-activating enzyme E1 in the ubiquitin-proteasome system. To elucidate the mechanism of himeic acid biosynthesis, feeding experiments with labeled precursors have been performed. The long fatty acyl side chain attached to the pyrone ring is of polyketide origin, whereas the amide substituent is derived from leucine. These results suggest that a polyketide synthase-nonribosomal peptide synthase (PKS-NRPS) is involved in himeic acid biosynthesis. A candidate gene cluster was selected from the results of genome sequencing analysis. Disruption of the PKS-NRPS gene by Agrobacterium-mediated transformation confirms that HimA PKS-NRPS is involved in himeic acid biosynthesis. Thus, the him biosynthetic gene cluster for himeic acid in A. japonicus MF275 has been identified.

Small-Molecule-Mediated Degradation of the Androgen Receptor through Hydrophobic Tagging

Androgen receptor (AR)-dependent transcription is a major driver of prostate tumor cell proliferation. Consequently, it is the target of several antitumor chemotherapeutic agents, including the AR antagonist MDV3100/enzalutamide. Recent studies have shown that a single AR mutation (F876L) converts MDV3100 action from an antagonist to an agonist. Here we describe the generation of a novel class of selective androgen receptor degraders (SARDs) to address this resistance mechanism. Molecules containing hydrophobic degrons linked to small-molecule AR ligands induce AR degradation, reduce expression of AR target genes and inhibit proliferation in androgen-dependent prostate cancer cell lines. These results suggest that selective AR degradation may be an effective therapeutic prostate tumor strategy in the context of AR mutations that confer resistance to second-generation AR antagonists.