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Abdominal aortic aneurysm (AAA) lacks effective pharmacotherapy. This study examines whether proprotein convertase subtilisin/kexin type 9 (PCSK9) drives ferroptosis in vascular smooth muscle cells (VSMCs) and whether its pharmacological degradation mitigates disease progression. PCSK9 is enriched in VSMCs of human AAA and in murine models induced by PPE or Ang II. SMC-specific PCSK9 overexpression (PCSK9 ) increases aortic diameter, aggravates elastin fragmentation and collagen deposition and elevates MMP2/9 expression. Within aortic lesions, PCSK9 enhances iron accumulation and lipid peroxidation while reducing glutathione GPX4, consistent with ferroptosis. In primary VSMCs, PCSK9 overexpression suppresses GPX4 and glutathione, increases malondialdehyde and Fe levels and impairs viability, whereas PCSK9 knockdown attenuates Ang II-induced ferroptosis. Mechanistically, PCSK9 triggers ferritinophagy, as shown by decreased ferritin heavy chain-1 (FTH1) and nuclear receptor coactivator-4 (NCOA4), an increased LC3-II/I ratio and enhanced FTH1-LAMP1 colocalisation. Autophagy inhibition with bafilomycin A1 blocks Fe accumulation and rescues ferroptotic indices. The cell-permeable peptide Cadd4 promotes PCSK9 degradation, restores FTH1 and NCOA4 and suppresses ferroptosis in VSMCs. In PPE and Ang II models, Cadd4 reduces aortic dilation, preserves medial structure and normalises ferroptosis and ferritinophagy markers. PCSK9 drives ferritinophagy-dependent ferroptosis in VSMCs, and Cadd4 represents a promising therapeutic strategy for AAA.

Proteolysis-targeting chimeras (PROTACs) are engineered techniques for targeted protein degradation. A bifunctional PROTAC molecule with two covalently-linked ligands recruits target protein and E3 ubiquitin ligase together to trigger proteasomal degradation of target protein by the ubiquitin-proteasome system. PROTAC has emerged as a promising approach for targeted therapy in various diseases, particularly in cancers. In this review, we introduce the principle and development of PROTAC technology, as well as the advantages of PROTACs over traditional anti-cancer therapies. Moreover, we summarize the application of PROTACs in targeting critical oncoproteins, provide the guidelines for the molecular design of PROTACs and discuss the challenges in the targeted degradation by PROTACs.

Target protein degradation has emerged as a promising strategy for the discovery of novel therapeutics during the last decade. Proteolysis-targeting chimera (PROTAC) harnesses a cellular ubiquitin-dependent proteolysis system for the efficient degradation of a protein of interest. PROTAC consists of a target protein ligand and an E3 ligase ligand so that it enables the target protein degradation owing to the induced proximity with ubiquitin ligases. Although a great number of PROTACs has been developed so far using previously reported ligands of proteins for their degradation, E3 ligase ligands have been mostly limited to either CRBN or VHL ligands. Those PROTACs showed their limitation due to the cell type specific expression of E3 ligases and recently reported resistance toward PROTACs with CRBN ligands or VHL ligands. To overcome these hurdles, the discovery of various E3 ligase ligands has been spotlighted to improve the current PROTAC technology. This review focuses on currently reported E3 ligase ligands and their application in the development of PROTACs.

Androgen receptor splice variant‐7 (AR‐V7), one of the major driving factors, is the most attractive drug target in castration‐resistant prostate cancer (CRPC). Currently, no available drugs efficiently target AR‐V7 in clinical practice. The DNA binding domain (DBD) is indispensable for the transcriptional activity of AR full length and AR splice variants, including AR‐V7. Based on the homodimerization structure of the AR DBD, a novel peptide‐based proteolysis‐targeting chimera (PROTAC) drug is designed to induce AR and AR‐V7 degradation in a DBD and MDM2‐dependent manner, without showing any activity on other hormone receptors. To overcome the short half‐life and poor cell penetrability of peptide PROTAC drugs, an ultrasmall gold (Au)‐peptide complex platform to deliver the AR DBD PROTAC in vivo is developed. The obtained Au‐AR pep‐PROTAC effectively degrades AR and AR‐V7 in prostate cancer cell lines, particularly in CWR22Rv1 cells with DC50 values 48.8 and 79.2 nM, respectively. Au‐AR pep‐PROTAC results in suppression of AR levels and induces tumor regression in both enzalutamide sensitive and resistant prostate cancer animal models. Further optimization of the Au‐AR pep‐PROTAC can ultimately lead to a new therapy for AR‐V7‐positive CRPC. A novel peptide PROTAC targeting androgen receptor DNA binding domain via AI‐Rosetta assisted design for castration‐resistant prostate cancer therapy is presented.

Proteolysis targeting chimeras (PROTACs) are heterobifunctional small molecules that simultaneously bind to a target protein and an E3 ligase, thereby leading to ubiquitination and subsequent degradation of the target. They present an exciting opportunity to modulate proteins in a manner independent of enzymatic or signaling activity. As such, they have recently emerged as an attractive mechanism to explore previously “undruggable” targets. Despite this interest, fundamental questions remain regarding the parameters most critical for achieving potency and selectivity. Here we employ a series of biochemical and cellular techniques to investigate requirements for efficient knockdown of Bruton’s tyrosine kinase (BTK), a nonreceptor tyrosine kinase essential for B cell maturation. Members of an 11-compound PROTAC library were investigated for their ability to form binary and ternary complexes with BTK and cereblon (CRBN, an E3 ligase component). Results were extended to measure effects on BTK–CRBN cooperative interactions as well as in vitro and in vivo BTK degradation. Our data show that alleviation of steric clashes between BTK and CRBN by modulating PROTAC linker length within this chemical series allows potent BTK degradation in the absence of thermodynamic cooperativity.

Proteolysis targeting chimeric (PROTAC) technology is an effective endogenous protein degradation tool developed in recent years that can ubiquitinate the target proteins through the ubiquitin-proteasome system (UPS) to achieve an effect on tumor growth. A number of literature studies on PROTAC technology have proved an insight into the feasibility of PROTAC technology to degrade target proteins. Additionally, the first oral PROTACs (ARV-110 and ARV-471) have shown encouraging results in clinical trials for prostate and breast cancer treatment, which inspires a greater enthusiasm for PROTAC research. Here we focus on the structures and mechanisms of PROTACs and describe several classes of effective PROTAC degraders based on E3 ligases.

Targeting “undruggable” targets with intrinsically disordered structures is of great significance for the treatment of disease. The transcription factor c‐Myc controls global gene expression and is an attractive therapeutic target for multiple types of cancers. However, due to the lack of defined ligand binding pockets, targeted c‐Myc have thus far been unsuccessful. Herein, to address the dilemma of lacking ligands, an efficient and high throughput aptamer screening strategy is established, named polystyrene microwell plate‐based systematic evolution of ligands by exponential enrichment (microwell‐SELEX), and identify the specific aptamer (MA9C1) against c‐Myc. The multifunctional aptamer‐based Proteolysis Targeting Chimeras (PROTAC) for proteolysis of the c‐Myc (ProMyc) is developed using the aptamer MA9C1 as the ligand. ProMyc not only significantly degrades c‐Myc by the ubiquitin‐proteasome system, but also reduces the Max protein, synergistically inhibiting c‐Myc transcriptional activity. Combination of the artificial cyclization and anti‐PD‐L1 aptamer (PA1)‐based delivery system, circular PA1‐ProMyc chimeras achieve tumor regression in the xenograft tumor model, laying a solid foundation for the development of efficacious c‐Myc degrader for the clinic. Therefore, this aptamer‐based degrader provides an invaluable potential degrader in drug discovery and anti‐tumor therapy, offering a promising degrader to overcome the challenge of targeting intractable targets. The drugs against “Undruggable” targets remain an enormous challenge in drug discovery. Aptamers are used to address the ligand deficiency and isolate the anti‐c‐Myc aptamer. The aptamer‐based PROTAC that efficiently degrades c‐Myc (ProMyc) is developed. Based on the aptamer (PA1) delivery system, circular PA1‐ProMyc displays powerful antitumor activity in the tumor model, offering a potential degrader for intractable targets.

Indoleamine 2,3-dioxygenase 1 (IDO1) is a heme enzyme that catalyzes the oxidation of L -tryptophan. Functionally, IDO1 has played a pivotal role in cancer immune escape via catalyzing the initial step of the kynurenine pathway, and overexpression of IDO1 is also associated with poor prognosis in various cancers. Currently, several small-molecule candidates and peptide vaccines are currently being assessed in clinical trials. Furthermore, the “proteolysis targeting chimera” (PROTAC) technology has also been successfully used in the development of IDO1 degraders, providing novel therapeutics for cancers. Herein, we review the biological functions of IDO1, structural biology and also extensively summarize medicinal chemistry strategies for the development of IDO1 inhibitors in clinical trials. The emerging PROTAC-based IDO1 degraders are also highlighted. This review may provide a comprehensive and updated overview on IDO1 inhibitors and their therapeutic potentials.

Proteolysis targeting chimeras (PROTACs) technology has emerged as a novel therapeutic paradigm in recent years. PROTACs are heterobifunctional molecules that degrade target proteins by hijacking the ubiquitin–proteasome system. Currently, about 20–25% of all protein targets are being studied, and most works focus on their enzymatic functions. Unlike small molecules, PROTACs inhibit the whole biological function of the target protein by binding to the target protein and inducing subsequent proteasomal degradation. PROTACs compensate for limitations that transcription factors, nuclear proteins, and other scaffolding proteins are difficult to handle with traditional small-molecule inhibitors. Currently, PROTACs have successfully degraded diverse proteins, such as BTK, BRD4, AR, ER, STAT3, IRAK4, tau, etc. And ARV-110 and ARV-471 exhibited excellent efficacy in clinical II trials. However, what targets are appropriate for PROTAC technology to achieve better benefits than small-molecule inhibitors are not fully understood. And how to rationally design an efficient PROTACs and optimize it to be orally effective poses big challenges for researchers. In this review, we summarize the features of PROTAC technology, analyze the detail of general principles for designing efficient PROTACs, and discuss the typical application of PROTACs targeting different protein categories. In addition, we also introduce the progress of relevant clinical trial results of representative PROTACs and assess the challenges and limitations that PROTACs may face. Collectively, our studies provide references for further application of PROTACs.

The evolution of targeted protein degradation (TPD) has been significantly propelled by the advent of proteolysis-targeting chimeras (PROTACs), which utilize heterobifunctional molecules to facilitate the ubiquitination-mediated degradation of previously “undruggable” proteins. Mouse double minute 2 (MDM2), which is often overexpressed in various diseases and plays a crucial role in regulating key pathways like p53, emerges as an exemplary candidate for therapeutic exploitation within the TPD realm, serving both as an intrinsic E3 ligase and as a direct protein of interest (POI). By harnessing MDM2’s inherent E3 ligase activity, PROTACs have been designed to efficiently degrade specific POIs, achieving substantial success in both in vitro and in vivo studies. Alternatively, PROTACs have been developed to directly target MDM2 itself, offering new approaches for therapeutic intervention. Recent research has yielded valuable strategies for optimizing MDM2-harnessing and MDM2-targeted PROTAC designs, concentrating on warhead selection of POI, linker length and composition optimization, and the choice among various E3 ligases and their corresponding recruiters. These advancements not only broaden the scope of PROTAC technologies but also expedite the development of MDM2-based therapies, inspiring approaches for disease treatment.