Discovery of BP3 as an efficacious proteolysis targeting chimera (PROTAC) degrader of HSP90 for treating breast cancer

Advances in the structures, mechanisms and targeting of molecular chaperones

Molecular chaperones, a class of complex client regulatory systems, play significant roles in the prevention of protein misfolding and abnormal aggregation, the modulation of protein homeostasis, and the protection of cells from damage under constantly changing environmental conditions. As the understanding of the biological mechanisms of molecular chaperones has increased, their link with the occurrence and progression of disease has suggested that these proteins are promising targets for therapeutic intervention, drawing intensive interest. Here, we review recent advances in determining the structures of molecular chaperones and heat shock protein 90 (HSP90) chaperone system complexes. We also describe the features of molecular chaperones and shed light on the complicated regulatory mechanism that operates through interactions with various co-chaperones in molecular chaperone cycles. In addition, how molecular chaperones affect diseases by regulating pathogenic proteins has been thoroughly analyzed. Furthermore, we focus on molecular chaperones to systematically discuss recent clinical advances and various drug design strategies in the preclinical stage. Recent studies have identified a variety of novel regulatory strategies targeting molecular chaperone systems with compounds that act through different mechanisms from those of traditional inhibitors. Therefore, as more novel design strategies are developed, targeting molecular chaperones will significantly contribute to the discovery of new potential drugs.

Ligand-based pharmacophore modelling, structure optimisation, and biological evaluation for the identification of 2-heteroarylthio-N-arylacetamides as novel HSP90 C-terminal inhibitors

Targeting Heat shock protein 90 (HSP90) C-terminus is an important strategy to develop HSP90 inhibitors without inducing heat shock response. The development of C-terminal inhibitors, however, is hampered by a lack of understanding regarding the interaction between the HSP90 C-terminus and the present inhibitors. We collected seven classical and structurally diverse HSP90 C-terminal inhibitors and constructed a ligand-based pharmacophore model. The subsequent virtual screening and structural optimisation led to the identification of 2-heteroarylthio-N-arylacetamides as novel HSP90 C-terminal inhibitors. 9 and 27 exhibited strong antitumour activity in vitro by inhibiting proliferation and inducing apoptosis in multiple cancer cell lines. These compounds disrupted the interaction between HSP90 C-terminus and peptidylprolyl isomerase D, exerting a stronger inhibitory effect than novobiocin. 27 significantly induced the degradation of HSP90 clients without triggering heat shock response. In an in vivo study using 4T1 mice breast cancer models, 9 showed a potent antitumour effect without obvious toxicity.

TRAP1 drives smooth muscle cell senescence and promotes atherosclerosis via HDAC3-primed histone H4 lysine 12 lactylation

BACKGROUND AND AIMS

Vascular smooth muscle cell (VSMC) senescence is crucial for the development of atherosclerosis, characterized by metabolic abnormalities. Tumour necrosis factor receptor-associated protein 1 (TRAP1), a metabolic regulator associated with ageing, might be implicated in atherosclerosis. As the role of TRAP1 in atherosclerosis remains elusive, this study aimed to examine the function of TRAP1 in VSMC senescence and atherosclerosis.

METHODS

TRAP1 expression was measured in the aortic tissues of patients and mice with atherosclerosis using western blot and RT-qPCR. Senescent VSMC models were established by oncogenic Ras, and cellular senescence was evaluated by measuring senescence-associated β-galactosidase expression and other senescence markers. Chromatin immunoprecipitation (ChIP) analysis was performed to explore the potential role of TRAP1 in atherosclerosis.

RESULTS

VSMC-specific TRAP1 deficiency mitigated VSMC senescence and atherosclerosis via metabolic reprogramming. Mechanistically, TRAP1 significantly increased aerobic glycolysis, leading to elevated lactate production. Accumulated lactate promoted histone H4 lysine 12 lactylation (H4K12la) by down-regulating the unique histone lysine delactylase HDAC3. H4K12la was enriched in the senescence-associated secretory phenotype (SASP) promoter, activating SASP transcription and exacerbating VSMC senescence. In VSMC-specific Trap1 knockout ApoeKO mice (ApoeKOTrap1SMCKO), the plaque area, senescence markers, H4K12la, and SASP were reduced. Additionally, pharmacological inhibition and proteolysis-targeting chimera (PROTAC)-mediated TRAP1 degradation effectively attenuated atherosclerosis in vivo.

CONCLUSIONS

This study reveals a novel mechanism by which mitonuclear communication orchestrates gene expression in VSMC senescence and atherosclerosis. TRAP1-mediated metabolic reprogramming increases lactate-dependent H4K12la via HDAC3, promoting SASP expression and offering a new therapeutic direction for VSMC senescence and atherosclerosis.

Targeting HSP90 for Cancer Therapy: Current Progress and Emerging Prospects

Heat shock protein 90 (HSP90), a highly conserved member of the heat shock protein family, regulates various proteins and signaling pathways involved in cancer, making it a promising target for cancer therapy. Traditional HSP90 inhibitors have demonstrated significant antitumor potential in preclinical trials, with over 20 compounds advancing to clinical trials and showing promising results. However, the limited clinical efficacy and shared toxicity of these inhibitors restrict their further clinical use. Encouragingly, developing novel inhibitors using conventional medicinal chemistry approaches─such as selective inhibitors, dual inhibitors, protein-protein interaction inhibitors, and proteolysis-targeting chimeras─is expected to address these challenges. Notably, the selective inhibitor TAS-116 has already been successfully marketed. In this Perspective, we summarize the structure, biological functions, and roles of HSP90 in cancer, analyze the clinical status of HSP90 inhibitors, and highlight the latest advancements in novel strategies, offering insights into their future development.

Application and challenges of nitrogen heterocycles in PROTAC linker

The absence of effective active pockets makes traditional molecularly targeted drug strategies ineffective against 80 % of human disease-related proteins. The PROTAC technology effectively makes up for the deficiency of traditional molecular targeted drugs, which produces drug activity by degrading rather than inhibiting the target protein. The degradation of PROTAC is not only affected by POI ligand and E3 ligand, but by the selection of suitable linker which can play an important role in the efficiency and selectivity of the degradation. In the early exploring stage of the PROTAC, flexible chains were priorly applied as the linker of PROTAC. Although PROTAC with flexible chains as linkers sometimes perform well in vitro bioactivity evaluations, the introduction of lipophilic flexible chains reduces the hydrophilicity of these molecules, resulting in generally poor pharmacokinetic characteristics and pharmacological activities in vivo. In addition, recent reports have also shown that some PROTAC with flexible chains have some risks to causing hemolysis in vivo. Therefore, PROTAC with flexible chains show less druggability and large difficulty to entering the clinical trial stage. On the other hand, the application of nitrogen heterocycles in the design of PROTAC linkers has been widely reported in recent years. More and more reports have shown that the introduction of nitrogen heterocycles in the linker not only can effectively improves the metabolism of PROTAC in vivo, but also can enhance the degradation efficiency and selectivity of PROTAC. These PROTAC with nitrogen heterocycle linkers have attracted much attention of pharmaceutical chemists. The introduction of nitrogen heterocycles in the linker deserves priority consideration in the primary design of the PROTAC based on various druggabilities including pharmacokinetic characteristics and pharmacological activity. In this work, we summarized the optimization process and progress of nitrogen heterocyclic rings as the PROTAC linker in recent years. However, there were still limited understanding of how to discover, design and optimize PROTAC. For example, the selection of the types of nitrogen heterocycles and the optimization sites of this linker are challenges for researchers, choosing between four to six-membered nitrogen heterocycles, selecting from saturated to unsaturated ones, and even optimizing the length and extension angle of the linker. There is a truly need for theoretical explanation and elucidation of the PROTAC to guide the developing of more effective and valuable PROTAC.

PROTAC: Novel degradable approach for different targets to treat breast cancer

The revolutionary Proteolysis Targeting Chimera (PROTACs) have the exciting potential to reshape the pharmaceutical industry landscape by leveraging the ubiquitin-proteasome system for targeted protein degradation. Breast cancer, the most prevalent cancer in women, could be treated using PROTAC therapy. Although substantial work has been conducted, there is not yet a comprehensive overview or progress update on PROTAC therapy for breast cancer. Hence, in this article, we've compiled recent research progress focusing on different breast cancer target proteins, such as estrogen receptor (ER), BET, CDK, HER2, PARP, EZH2, etc. This resource aims to serve as a guide for future PROTAC-based breast cancer treatment design.

Recent developments of HSP90 inhibitors: an updated patent review (2020-present)

INTRODUCTION

The 90-kDa heat shock protein (HSP90) functions as a molecular chaperone, it assumes a significant role in diseases such as cancer, inflammation, neurodegeneration, and infection. Therefore, the research and development of HSP90 inhibitors have garnered considerable attention.

AREAS COVERED

The primary references source for this review is patents obtained from SciFinder, encompassing patents on HSP90 inhibitors from the period of 2020 to 2023.This review includes a thorough analysis of their structural attributes, pharmacological properties, and potential clinical utilities.

EXPERT OPINION

In the past few years, HSP90 inhibitors targeting ATP binding pocket are still predominate and one of them has been launched, besides, novel drug design strategies like C-terminal targeting, isoform selective inhibiting and bifunctional molecules are booming, aiming to improve the efficacy and safety. With expanded drug types and applications, HSP90 inhibitors may gradually becoming a sagacious option for treating various diseases.

Discovery of X10g as a selective PROTAC degrader of Hsp90α protein for treating breast cancer

Heat shock protein 90 (Hsp90), a highly conserved and widely expressed molecular chaperone, is mainly responsible for maintaining the correct folding of client proteins and is closely related to the stability and activation of tumour-related proteins. Hsp90α, the major isoform of Hsp90, can promote tumour cell migration and metastasis, and is abundantly secreted in highly invasive tumours. To date, most pan-Hsp90 inhibitors have been limited in their applications due to high toxicity. Herein, we described the candidate compound X10g based on a proteolysis-targeting chimaera (PROTAC) strategy that potently and selectively degraded Hsp90α. The results showed that X10g inhibited tumours better with lower toxicity in vivo. These findings demonstrate that synthesized selective Hsp90α degrader X10g provides a new strategy for breast cancer therapy.

Target protein degradation by protacs: A budding cancer treatment strategy

Cancer is one of the most common causes of death. So, its lethal effect increases with time. Near about hundreds of cancers are known in humans. Cancer treatment is done to cure or prolonged remission, and shrinkage of the tumor. Cytotoxic agents, biological agents/targeted drugs, hormonal drugs, surgery, radiotherapy/proton therapy, chemotherapy, immunotherapy, and gene therapy are currently used in the treatment of cancer but their cost is high and cause various side effects. Seeing this, some new targeted strategies such as PROTACs are the need of the time. Proteolysis targeting chimera (PROTAC) has become one of the most discussed topics regarding cancer treatment. Few of the PROTAC molecules are in the trial phases. PROTACs have many advantages over other strategies such as modularity, compatibility, sub-stoichiometric activity, acting on undruggable targets, molecular design, and acts on intracellular targets, selectivity and specificity can be recruited for any cancer, versatility, and others. PROTACs are having some unclear questions on their pharmacokinetics, heavy-molecular weight, etc. PROTACs are anticipated to bring about a conversion in current healthcare and will emerge as booming treatments. In this review article we summarize PROTACs, their mechanism of action, uses, advantages, disadvantages, challenges, and future aspects for the successful development of potent PROTACs as a drug strategy.

Development of the first geldanamycin-based HSP90 degraders

Despite the early clinical promise, adverse events such as acquired resistance and dose-limiting toxicities have barred the widespread use of HSP90 inhibitors as anticancer drugs. A new approach involving proteolysis-targeting chimeras (PROTACs) to degrade the protein instead of inhibiting it may overcome these problems. In this work, we describe the design, synthesis, and evaluation of cereblon-recruiting geldanamycin-based HSP90 degraders based on the PROTAC technology. Our best degrader, 3a, effectively decreased HSP90α and HSP90β levels in cells utilizing the ubiquitin-proteasome pathway.

E3 ubiquitin ligases in cancer stem cells: key regulators of cancer hallmarks and novel therapeutic opportunities

BACKGROUND

Human malignancies are composed of heterogeneous subpopulations of cancer cells with phenotypic and functional diversity. Among them, a unique subset of cancer stem cells (CSCs) has both the capacity for self-renewal and the potential to differentiate and contribute to multiple tumor properties. As such, CSCs are promising cellular targets for effective cancer therapy. At the molecular level, hyper-activation of multiple stemness regulatory signaling pathways and downstream transcription factors play critical roles in controlling CSCs establishment and maintenance. To regulate CSC properties, these stemness pathways are controlled by post-translational modifications including, but not limited to phosphorylation, acetylation, methylation, and ubiquitination.

CONCLUSION

In this review, we focus on E3 ubiquitin ligases and their roles and mechanisms in regulating essential hallmarks of CSCs, such as self-renewal, invasion and metastasis, metabolic reprogramming, immune evasion, and therapeutic resistance. Moreover, we discuss emerging therapeutic approaches to eliminate CSCs through targeting E3 ubiquitin ligases by chemical inhibitors and proteolysis-targeting chimera (PROTACs) which are currently under development at the discovery, preclinical, and clinical stages. Several outstanding issues such as roles for E3 ubiquitin ligases in heterogeneity and phenotypical/functional evolution of CSCs remain to be studied under pathologically and clinically relevant conditions. With the rapid application of functional genomic and proteomic approaches at single cell, spatiotemporal, and even single molecule levels, we anticipate that more specific and precise functions of E3 ubiquitin ligases will be delineated in dictating CSC properties. Rational design and proper translation of these mechanistic understandings may lead to novel therapeutic modalities for cancer procession medicine.

Albumin-encapsulated HSP90-PROTAC BP3 nanoparticles not only retain protein degradation ability but also enhance the antitumour activity of BP3 in vivo

Proteolysis-targeting chimaera (PROTAC) has received extensive attention in industry. However, there are still some limitations that hinder its further development. In a previous study, our group first demonstrated that the HSP90 degrader BP3 synthesised by the principle of PROTACs showed therapeutic potential for cancer. However, its application was hindered by its high molecular weight and water insolubility. Herein, we aimed to improve these properties of HSP90-PROTAC BP3 by encapsulating it into human serum albumin nanoparticles (BP3@HSA NPs). The results demonstrated that BP3@HSA NPs showed a uniform spherical shape with a size of 141.01 ± 1.07 nm and polydispersity index < 0.2; moreover, BP3@HSA NPs were more readily taken up by breast cancer cells and had a stronger inhibitory effect in vitro than free BP3. BP3@HSA NPs also demonstrated the ability to degrade HSP90. Mechanistically, the improved inhibitory effect of BP3@HSA NPs on breast cancer cells was related to its stronger ability to induce cell cycle arrest and apoptosis. Furthermore, BP3@HSA NPs improved PK properties and showed stronger tumour suppression in mice. Taken together, this study demonstrated that hydrophobic HSP90-PROTAC BP3 nanoparticles encapsulated by human serum albumin could improve the safety and antitumour efficacy of BP3.

Following the design path of isoform-selective Hsp90 inhibitors: Small differences, great opportunities

The heat shock protein 90 (Hsp90) family consists of four highly conserved isoforms: the mitochondrial TRAP-1, the endoplasmic reticulum-localised Grp94, and the cytoplasmic Hsp90α and Hsp90β. Since the late 1990s, this family has been extensively studied as a potential target for the treatment of cancer, neurological disorders, and infectious diseases. The initial approach was to develop non-selective, so-called pan-Hsp90 ATP-competitive inhibitors of the N-terminal domain. Many of these agents were tested in clinical trials, mainly for the treatment of cancer, but none of them succeeded in the clinic. This was mainly due to the lack of efficacy and various toxicities associated with the induction of heat shock response (HSR). This lack of success has prompted a turn to new approaches of Hsp90 inhibition. Thus, inhibitors selective for a particular isoform of Hsp90 have been developed. These isoform-selective inhibitors do not induce HSR and have a more targeted effect because not all client proteins are equally dependent on all four paralogues of Hsp90. However, it is extremely difficult to develop such selective compounds because the family is highly conserved. Hsp90α and Hsp90β have an amazing 95% identity of the N-terminal ATP binding site, differing only in two amino acid residues. Therefore, the focus of this review is to fully elucidate the key structural features of the selective inhibitor classes in terms of binding site dissimilarities. In addition to a methodological characterisation of the structure-activity relationships, the main advantages of selective inhibition of the TRAP-1, Grp94, Hsp90α and Hsp90β isoforms are discussed.

Advancing targeted protein degradation for metabolic diseases therapy

The development and application of traditional drugs represented by small molecule chemical drugs and biological agents, especially inhibitors, have become the mainstream drug development. In recent years, targeted protein degradation (TPD) technology has become one of the most promising methods to remove specific disease-related proteins using cell self-destruction mechanisms. Many different TPD strategies are emerging based on the ubiquitin-proteasome system (UPS) and the autophagy-lysosomal pathway (ALP), including but not limited to proteolysis-targeting chimeras (PROTAC), molecular glues (MG), lysosome targeting chimeras (LYTAC), chaperone-mediated autophagy (CMA)-targeting chimeras, autophagy-targeting chimera (AUTAC), autophagosome-tethering compound (ATTEC), and autophagy-targeting chimera (AUTOTAC). The advent of targeted degradation technology can change most protein targets in human cells from undruggable to druggable, greatly expanding the therapeutic prospect of refractory diseases such as metabolic syndrome. Here, we summarize the latest progress of major TPD technologies, especially in metabolic syndrome and look forward to providing new insights for drug discovery.

Recent Advances in PROTAC-Based Antiviral Strategies

Numerous mysteries of cell and molecular biology have been resolved through extensive research into intracellular processes, which has also resulted in the development of innovative technologies for the treatment of infectious and non-infectious diseases. Some of the deadliest diseases, accounting for a staggering number of deaths, have been caused by viruses. Conventional antiviral therapies have been unable to achieve a feat in combating viral infections. As a result, the healthcare system has come under tremendous pressure globally. Therefore, there is an urgent need to discover and develop newer therapeutic approaches against viruses. One such innovative approach that has recently garnered attention in the research world and can be exploited for developing antiviral therapeutic strategies is the PROteolysis TArgeting Chimeras (PROTAC) technology, in which heterobifunctional compounds are employed for the selective degradation of target proteins by the intracellular protein degradation machinery. This review covers the most recent advancements in PROTAC technology, its diversity and mode of action, and how it can be applied to open up new possibilities for creating cutting-edge antiviral treatments and vaccines.

New class of fused [3,2-b][1,2,4]triazolothiazoles for targeting glioma in vitro

Glioma is aggressive malignant tumor with limited therapeutic interventions. Herein we report the synthesis of fused bicyclic 1,2,4-triazolothiazoles by a one-pot multi-component approach and their activity against C6 rat and LN18 human glioma cell lines. The target compounds 2-(6-phenylthiazolo[3,2-b][1,2,4]triazol-2-yl) isoindoline-1,3-diones and (E)-1-phenyl-N-(6-phenylthiazolo[3,2-b][1,2,4]triazol-2-yl) methanimines were obtained by the reaction of 5-amino-4H-1,2,4-triazole-3-thiol with substituted phenacyl bromide, phthalic anhydride, and different aromatic aldehydes in EtOH/HCl under reflux conditions. In C6 rat glioma cell lines, compounds 4g and 6i showed good cytotoxic activity with IC₅₀ values of 8.09 and 8.74 μM, respectively, resulting in G1 and G2-M phase arrest of the cell cycle and activation of apoptosis by modulating phosphorylation of ERK and AKT pathway.

Multi-Faceted Roles of DNAJB Protein in Cancer Metastasis and Clinical Implications

Heat shock proteins (HSPs) are highly conserved molecular chaperones with diverse cellular activities, including protein folding, assembly or disassembly of protein complexes, and maturation process under diverse stress conditions. HSPs also play essential roles in tumorigenesis, metastasis, and therapeutic resistance across cancers. Among them, HSP40s are widely accepted as regulators of HSP70/HSP90 chaperones and an accumulating number of biological functions as molecular chaperones dependent or independent of either of these chaperones. Despite large numbers of HSP40s, little is known about their physiologic roles, specifically in cancer progression. This article summarizes the multi-faceted role of DNAJB proteins as one subclass of the HSP40 family in cancer development and metastasis. Regulation and deregulation of DNAJB proteins at transcriptional, post-transcriptional, and post-translational levels contribute to tumor progression, particularly cancer metastasis. Furthermore, understanding differences in function and regulating mechanism between DNAJB proteins offers a new perspective on tumorigenesis and metastasis to improve therapeutic opportunities for malignant diseases.

Recent Advances in Natural Product-Based Hybrids as Anti-Cancer Agents

Cancer is one of the top leading causes of death worldwide. It is a heterogenous disease characterized by unregulated cell proliferation and invasiveness of abnormal cells. For the treatment of cancer, natural products have been widely used as a source of therapeutic ingredients since ancient times. Although natural compounds and their derivatives have demonstrated strong antitumor activity in many types of cancer, their poor pharmacokinetic properties, low cell selectivity, limited bioavailability and restricted efficacy against drug-resistant cancer cells hinder their wide clinical application. Conjugation of natural products with other bioactive molecules has given rise to a new field in drug discovery resulting to the development of novel, bifunctional and more potent drugs for cancer therapy to overcome the current drawbacks. This review discusses multiple categories of such bifunctional conjugates and highlights recent trends and advances in the development of natural product hybrids. Among them, ADCs, PDCs, ApDCs, PROTACs and AUTOTACs represent emerging therapeutic agents against cancer.

MDM2-Based Proteolysis-Targeting Chimeras (PROTACs): An Innovative Drug Strategy for Cancer Treatment

Proteolysis-targeting chimeras (PROTACs) are molecules that selectively degrade a protein of interest (POI). The incorporation of ligands that recruit mouse double minute 2 (MDM2) into PROTACs, forming the so-called MDM2-based PROTACs, has shown promise in cancer treatment due to its dual mechanism of action: a PROTAC that recruits MDM2 prevents its binding to p53, resulting not only in the degradation of POI but also in the increase of intracellular levels of the p53 suppressor, with the activation of a whole set of biological processes, such as cell cycle arrest or apoptosis. In addition, these PROTACs, in certain cases, allow for the degradation of the target, with nanomolar potency, in a rapid and sustained manner over time, with less susceptibility to the development of resistance and tolerance, without causing changes in protein expression, and with selectivity to the target, including the respective isoforms or mutations, and to the cell type, overcoming some limitations associated with the use of inhibitors for the same therapeutic target. Therefore, the aim of this review is to analyze and discuss the characteristics of MDM2-based PROTACs developed for the degradation of oncogenic proteins and to understand what potential they have as future anticancer drugs.

Design, synthesis, and biological evalution of bifunctional inhibitors against Hsp90-HDAC6 interplay

HDAC6 and Hsp90, existing as a cytosolic complex play an important role in maintaining the protein homeostasis. The interplay of HDAC6 and Hsp90 has attracted wide attention due to their important role and promise as therapeutic targets in malignant cancers. Therefore, the discovery of dual inhibitors targeting HDAC6 and Hsp90 is of high importance. In the present study, we describe the design, synthesis, and biological evaluation of bifunctional inhibitors against HDAC6 and Hsp90 interplay. In particular, compound 6e shows a significant inhibitory activity against both HDAC6 and Hsp90 with IC₅₀ values of 106 nM and 61 nM, respectively. Compound 6e promotes the acetylation of HDAC6 substrate proteins such as α-tubulin and Hsp90 via HDAC6 inhibition, and also induces the degradation of Hsp90 clients such as Her2, EGFR, Met, Akt, and HDAC6 via Hsp90 inhibition. Compound 6e consequently furnishes potent antiproliferative effect on gefitinib-resistant H1975 non-small cell lung cancer (NSCLC) with a GI₅₀ value of 1.7 μM. In addition, compound 6e successfully achieved significant tumor growth inhibition in H1975 NSCLC xenograft model without noticeable abnormal behavior, body weight changes, and apparent ocular toxicity. We conclude that compound 6e constitutes an excellent tool as well as a valuable lead for assessment of Hsp90 and HDAC6 dual inhibition with a single molecule.

PROTACs: great opportunities for academia and industry (an update from 2020 to 2021)

PROteolysis TArgeting Chimeras (PROTACs) technology is a new protein-degradation strategy that has emerged in recent years. It uses bifunctional small molecules to induce the ubiquitination and degradation of target proteins through the ubiquitin-proteasome system. PROTACs can not only be used as potential clinical treatments for diseases such as cancer, immune disorders, viral infections, and neurodegenerative diseases, but also provide unique chemical knockdown tools for biological research in a catalytic, reversible, and rapid manner. In 2019, our group published a review article "PROTACs: great opportunities for academia and industry" in the journal, summarizing the representative compounds of PROTACs reported before the end of 2019. In the past 2 years, the entire field of protein degradation has experienced rapid development, including not only a large increase in the number of research papers on protein-degradation technology but also a rapid increase in the number of small-molecule degraders that have entered the clinical and will enter the clinical stage. In addition to PROTAC and molecular glue technology, other new degradation technologies are also developing rapidly. In this article, we mainly summarize and review the representative PROTACs of related targets published in 2020-2021 to present to researchers the exciting developments in the field of protein degradation. The problems that need to be solved in this field will also be briefly introduced.