Hydrophobic tag-based protein degradation: Development, opportunity and challenge

Targeting Tau Protein with Proximity Inducing Modulators: A New Frontier to Combat Tauopathies

Dysregulation of correct protein tau homeostasis represents the seed for the development of several devastating central nervous system disorders, known as tauopathies, that affect millions of people worldwide. Despite massive public and private support to research funding, these diseases still represent unmet medical needs. In fact, the tau-targeting tools developed to date have failed to translate into the clinic. Recently, taking advantage of the modes that nature uses to mediate the flow of information in cells, researchers have developed a new class of molecules, called proximity-inducing modulators, which exploit spatial proximity to modulate protein function(s) and redirect cellular processes. In this perspective, after a brief discussion about tau protein and the classic tau-targeting approaches, we will discuss the different classes of proximity-inducing modulators developed so far and highlight the applications to modulate tau protein's function and tau-induced toxicity.

Targeted Protein Degradation in Cancer Therapy via Hydrophobic Polymer-Tagged Nanoparticles

Targeted protein degradation (TPD) strategies offer a significant advantage over traditional small molecule inhibitors by selectively degrading disease-causing proteins. While small molecules can lead to recurrence and resistance due to compensatory pathway activation, TPD addresses this limitation by promoting protein degradation, thereby reducing the likelihood of recurrence and resistance over the long-term. Despite these benefits, bifunctional TPD molecules face challenges such as low solubility, poor bioavailability, and limited tumor specificity. In this study, we developed polymer-based nanoparticles that combine TPD strategies with nanotechnology through a hydrophobic tagging method. Hydrophobic polymer-tagged nanoparticles facilitate targeted protein degradation by incorporating hydrophobic polymers that mimic hydrophobic residues in misfolded proteins. This system combines degradation and delivery capabilities within a polymer-based platform, inducing protein degradation while improving solubility, stability, and tumor targeting. These nanoparticles consist of a block copolymer composed of an androgen receptor ligand (ARL)-conjugated hydrophobic polylactic acid (PLA) and a hydrophilic polyethylene glycol (PEG), connected by a GSH-cleavable disulfide bond. In aqueous solutions, this block copolymer (ARL-PLA-SS-PEG) forms micelles that degrade in reducible cellular environments. The micelles demonstrated significant in vitro degradation of the target androgen receptor (AR). Furthermore, they achieved substantial tumor accumulation and significantly inhibited tumor growth in a tumor-bearing mouse model. A mechanistic study revealed that the micelle-mediated TPD follows a dual pathway involving both proteasome and autophagosome. This approach has the potential to serve as a universal platform for protein degradation, eliminating the need to develop disease-specific TPD molecules.

Recent advances in regulating the cell cycle through inhibiting CDKs for cancer treatment

The inhibition of cyclin-dependent kinases (CDKs) is considered a promising strategy for cancer treatment due to their role in cell cycle regulation. However, CDK inhibitors with no selectivity among CDK families have not been approved. A CDK inhibitor with high selectivity for CDK4/6 exhibited significant treatment effects on breast cancer and has become a heavy bomb on the market. Subsequently, resistance gradually decreased the efficacy of selective CDK4/6 inhibitors in breast cancer treatment. In this review, we first introduce the development of selective CDK4/6 inhibitors and then explain the role of CDK2 activation in inducing resistance to CDK4/6 inhibitors. Moreover, we focused on the development of CDK2/4/6 inhibitors and selective CDK2 inhibitors, which will aid in the discovery of novel CDK inhibitors targeting the cell cycle in the future.

A two-in-one expression construct for biophysical and structural studies of the human pregnane X receptor ligand-binding domain, a pharmaceutical and environmental target

The ligand-binding domain (LBD) of the human nuclear receptor pregnane X receptor (PXR) is known to crystallize in two different crystal forms, P212121 or P43212, depending on the construct and the strategy used for protein production, as well as the presence or absence of the coactivator-derived peptide SRC-1. In order to facilitate biophysical and structural studies, a versatile construct was designed that allows access to both forms. This was achieved by introducing a thrombin cleavage site between the PXRLBD and the SRC-1 peptide fused to its C-terminus. Here, we describe the expression, purification and crystallization processes of this novel construct and report two new structures of PXRLBD that were obtained thanks to this strategy.

Overcoming drug resistance in castrate-resistant prostate cancer: current mechanisms and emerging therapeutic approaches

Metastatic castration-resistant prostate cancer (mCRPC) is driven by a complex network of resistance mechanisms against standard-of-care therapies, resulting in poor long-term outcomes. This review offers a uniquely comprehensive and integrative perspective on these resistance pathways, systematically examining both androgen receptor (AR)-dependent factors (including AR overexpression, point mutations, glucocorticoid receptor signaling, splice variants, post-translational modifications, altered coregulators, and intratumoral hormone biosynthesis) and AR-independent pathways (such as neuroendocrine differentiation, lineage plasticity, and alternative growth factor signaling). We also highlight resistance mechanisms influencing immunotherapy, chemotherapy, radiopharmaceutical therapy and targeted therapy. By synthesizing emerging insights across these domains, this review not only clarifies the underlying biology of mCRPC resistance but also identifies key leverage points for more effective interventions. Building on this foundation, we propose a forward-looking framework for overcoming mCRPC drug resistance, emphasizing the importance of biomarker-guided patient selection, combination strategies that simultaneously target multiple resistance mechanisms, and novel therapies under investigation. These recommendations are intended to guide future clinical trial designs and research priorities that move beyond incremental improvements. Ultimately, this comprehensive synthesis aims to serve as a resource for clinicians and researchers to accelerate the development of durable, precision-based treatment strategies in mCRPC.

Recent advances in developing targeted protein degraders

Targeted protein degradation (TPD) represents a promising therapeutic approach, encompassing several innovative strategies, including but not limited to proteolysis targeting chimeras (PROTACs), molecular glues, hydrophobic tag tethering degraders (HyTTD), and lysosome-targeted chimeras (LYTACs). Central to TPD are small molecule ligands, which play a critical role in mediating the degradation of target proteins. This review summarizes the current landscape of small molecule ligands for TPD molecules. These small molecule ligands can utilize the proteasome, lysosome, autophagy, or hydrophobic-tagging system to achieve the degradation of target proteins. The article mainly focuses on introducing their design principles, application advantages, and potential limitations. A brief discussion on the development prospects and future directions of TPD technology was also provided.

Small molecule targeted protein degradation via the UPS: venturing beyond E3 substrate receptors

The ubiquitin proteasome system (UPS) has been successfully hi-jacked by both bifunctional and monovalent small molecules to affect the degradation of proteins that were once considered undruggable. This field has primarily focused on the targeted recruitment of proteins to substrate receptors on E3 ubiquitin ligases, which are only one part of the UPS. More recently, the field has begun to explore recruitment to other types of UPS proteins including E2 ubiquitin-conjugating enzymes, substrate adaptor proteins within the E3 complex, chaperone proteins that associate with E3s, proteasomal subunits, and proteasome-associated proteins. While these approaches are relatively nascent compared to more traditional E3 substrate receptor-based degradation, these approaches are starting to show promise and could offer unique advantages. This review will cover key findings in small molecule UPS-mediated targeted protein degradation (TPD) affected by co-opting proteins beyond traditional E3 substrate receptors.

Versatile One-Pot Synthesis of Hydrophobic Tags by Multicomponent Reactions

Among the various strategies being developed in the field of protein degraders, HyTags remain relatively underexplored, despite their advantages over PROTACs. Their synthesis typically involves multistep procedures, including the use of coupling reagents and protection/deprotection steps. To develop a more sustainable and streamlined approach, we designed a versatile multicomponent platform that generates HyTags with diverse linkers and hydrophobic moieties in high yields. Using (+)-JQ1 as the POI ligand, we synthesized a series of BRD4-targeting HyTags and discovered that compound 23 induces degradation of BRD4 via the autophagy-lysosome pathway through ER stress. This finding further supports the valuable application of this synthetic methodology in the search for effective degraders.

An overview of GPX4-targeting TPDs for cancer therapy

Ferroptosis is a newly identified form of regulated, non-apoptotic cell death caused by iron-dependent phospholipid peroxidation. Glutathione peroxidase 4 (GPX4) inactivation-induced ferroptosis is an efficient antitumor treatment. Currently, several GPX4 inhibitors have been identified. However, these inhibitors exhibit low selectivity and poor pharmacokinetic properties that preclude their clinical use. Targeted protein degradation (TPD) is an efficient strategy for discovering drugs and has unique advantages over target protein inhibition. Given GPX4's antitumor effects and the potential of TPD, researchers have explored GPX4-targeting TPDs, which outperform conventional inhibitors in several aspects, such as increased selectivity, strong anti-proliferative effects, overcoming drug resistance, and enhancing drug-like properties. In this review, we comprehensively summarize the progress in GPX4-targeting TPDs. In addition, we reviewed the changes and challenges related to the development of GPX4-targeting TPDs for cancer therapy.

Identification of inhibitors targeting the FLT3-ITD mutation through 4D-QSAR, in vitro, and in silico

The FMS-like tyrosine kinase 3-internal tandem duplication (FLT3-ITD) mutation is a key target for acute myeloid leukemia (AML) treatment. The second-generation inhibitors such as Gilteritinib still present off-target effects and associated side effects. Therefore, identifying novel FLT3-ITD inhibitors has become a promising strategy for AML treatment. In this study, a 4D-QSAR model was developed based on Gilteritinib and its analogues, and it was found that introducing hydrophobic bulky groups at the piperazine or piperidine of Gilteritinib would enhance the binding affinity to FLT3-ITD. So, three series of targeted compounds (A1-A5, B1-B5 and C1-C5) were designed and synthesized. The antiproliferative activity against MOLM-13 cells was evaluated in vitro. Compound A1 (IC50 = 25.65 nM), with a cubane group at the piperazine position; Compounds B2 (IC50 = 63.38 nM) and C2 (IC50 = 54.96 nM), with a norbornene group at the piperidine position, showed the strongest inhibition in their series. Their IC50 values were comparable to that of the positive control Gilteritinib (IC50 = 22.37 nM). FLT3-ITD was confirmed as the degradation target through a kinase inhibition assay, where the IC50 values were 2.12 nM (Compound A1), 1.29 nM (Compound B2), and 3.06 nM (Compound C2), which were comparable to that of Gilteritinib (IC50 = 0.43 nM). Additionally, molecular docking and molecular dynamics (MD) simulations showed that Compounds A1, B2, and C2 had similar binding modes to that of Gilteritinib with more stable affinities. Overall, these results demonstrated that Compounds A1, B2, and C2 were promising inhibitors for targeting AML with FLT3-ITD mutation.

Exploring oncogenic roles and clinical significance of EZH2: focus on non-canonical activities

The enhancer of zeste homolog 2 (EZH2) is a catalytic component of Polycomb repressive complex 2 (PRC2) mediating the methylation of histone 3 lysine 27 (H3K27me3) and hence the epigenetic repression of target genes, known as canonical function. Growing evidence indicates that EZH2 has non-canonical roles that are exerted as PRC2-dependent and PRC2-independent methylation of non-histone proteins, and methyltransferase-independent interactions of EZH2 with various proteins contributing to gene expression regulation and alterations in the protein stability. EZH2 is frequently mutated and/or its expression is deregulated in various cancer types. The cancer sensitivity to inhibitors of EZH2 enzymatic activity and state-of-the-art approaches to deplete EZH2 with chemical degraders are discussed. This review also presents the clinical trials in various phases that evaluate the use of EZH2 inhibitors, both as monotherapy and in combination with other agents for the treatment of patients with diverse types of cancers.

Development of Novel Silicon-Based Hydrophobic Tags (SiHyT) for Targeted Proteins Degradation

Recent advances in targeted protein degradation (TPD) have propelled it to the forefront of small molecular drug discovery. Among these, hydrophobic tagging (HyT) strategies have garnered significant interest. Carbon-based hydrophobic tags have been recognized as effective Hyts for degrading a variety of target proteins. In this study, we introduce a novel class of potential EGFR degraders for the first time, which combine Gefitinib with silicon-based hydrophobic tags (SiHyT). The most promising candidate, degrader 7, which links Gefitinib to a simple TBDPS silyl ether, has shown efficacy in degrading mutant EGFRs via the ubiquitin-proteosome system (UPS) both in vitro and in vivo. Notably, degrader 7 exhibits enhanced oral bioavailability owing to its superior metabolic stability compared to traditional carbon-based Hyts. Mechanistically, it was revealed that degrader 7 disrupts EGFR stability by dissociating the EGFR-HSP90 complex and recruiting E3 ligase, RNF149. More importantly, the potent and selective PD-L1 and BTK degraders were discovered successfully by utilizing the SiHyT strategy. The development of these innovative SiHyT compounds could broaden the repertoire of HyTs, enhancing the future design of TPD agents.

Overview of the PRMT6 modulators in cancer treatment: Current progress and emerged opportunity

Protein Arginine Methyltransferase 6 (PRMT6) is a Type I PRMT enzyme that plays a role in the epigenetic regulation of gene expression by methylating histone and non-histone proteins. It is also involved in various cellular processes, including alternative splicing, DNA repair, and cell signaling. Furthermore, PRMT6 exerts multiple effects on cellular processes such as growth, migration, invasion, apoptosis, and drug resistance in various cancers, positioning it as a promising target for anti-tumor therapeutics. In this review, we initially provide an overview of the structure and biological functions of PRMT6, along with its association with cancer. Subsequently, we focus on recent progress in the design and development of modulators targeting PRMT6. This includes a comprehensive review of PRMT6 inhibitors (isoform-selective and non-selective), dual-target inhibitors based on PRMT6, PRMT6 covalent inhibitors, and PRMT6-targeting hydrophobic tagging (HyT) degraders, from the perspectives of rational design, pharmacodynamics, pharmacokinetics, and the clinical status of these modulators. Finally, we also provided the challenges and prospective directions for PRMT6 targeting drug discovery in cancer therapy.

Development of natural product-based targeted protein degraders as anticancer agents

Targeted protein degradation (TPD) has emerged as a powerful approach for eliminating cancer-causing proteins through an "event-driven" pharmacological mode. Proteolysis-targeting chimeras (PROTACs), molecular glues (MGs), and hydrophobic tagging (HyTing) have evolved into three major classes of TPD technologies. Natural products (NPs) are a primary source of anticancer drugs and have played important roles in the development of TPD technology. NPs potentially expand the toolbox of TPD by providing a variety of E3 ligase ligands, protein of interest (POI) warheads, and hydrophobic tags (HyTs). As a promising direction in the TPD field, NP-based degraders have shown great potential for anticancer therapy. In this review, we summarize recent advances in the development of NP-based degraders (PROTACs, MGs and HyTing) with anticancer applications. Moreover, we put forward the challenges while presenting potential opportunities for the advancement of future targeted protein degraders derived from NPs.

Design, synthesis, and biological evaluation of RSL3-based GPX4 degraders with hydrophobic tags

Ferroptosis is a new type of programmed cell death characterized by iron-dependent lipid peroxidation, during which glutathione peroxidase 4 (GPX4) plays an essential role and is well-recognized as a promising therapeutic target for cancer treatment. Although some GPX4 degradation molecules have been developed to induce ferroptosis, the discovery of GPX4 degraders with hydrophobic tagging (HyT) as an innovative approach is more challenging. Herein, we designed and synthesized a series of HyT degraders by linking the GPX4 inhibitor RSL3 with a hydrophobic and bulky group of adamantane. Among them, compound R8 is a potent degrader (DC50, 24h = 0.019 μM) which can effectively degrade GPX4 in a dose- and time-dependent manner. Furthermore, compound R8 exhibited superior in vitro antitumor potency against HT1080 and MDA-MB-231 cell lines with IC50 values of 24 nM and 32 nM respectively, which are 4 times more potent than parental compound RSL3. Mechanistic investigation evidenced that R8 consumes GPX4 protein mainly through the ubiquitin proteasome (UPS) and enables to induce the accumulation of LPO, thereby triggering ferroptosis. Our work presented the novel GPX4 degrader of R8 by HyT strategy, and provided a promising pathway of degradation agents for the treatment of ferroptosis relevant diseases.

A novel hydrophobic tag leads to the efficient degradation of programmed death-ligand 1

The interaction of PD-L1 and PD-1 transmits the inhibitory signal to reduce the proliferation of antigen-specific T-cells in lymph nodes. The expression of PD-L1 confers a potential escaping mechanism of tumors from the host immune system. Blocking the interaction of PD-1 and PD-L1 enables tumor-reactive T cells to overcome regulatory mechanisms and induce an effective antitumor response. The hydrophobic tag tethering degrader (HyTTD) contains a hydrophobic moiety, binding to the protein of interest (POI) to mimic the misfolding state of the POI, thereby inducing the degradation of POI. In this work, using the HyTTD strategy, we selected the diphenylmethyl derivatives as the PD-L1 binding motif for PD-L1 to develop the degraders for PD-L1, and multiple hydrophobic tags were attached. As a result, two HyTTDs Z2d and Z3d efficiently decreased the protein level of PD-L1 in both NCI-H460 and HT-1080 cells with low cytotoxicity. Meanwhile, the reduction of PD-L1 protein levels by Z2d/Z3d was counteracted by MG132, which indicated that Z2d/Z3d degraded PD-L1 through the proteasome pathway. Moreover, the molecular modeling results indicated that the HyT group of Z2d or Z3d extended the surface of the protein to mimic the misfold. Importantly, our work also identified a novel HyT, which could be applied to develop the HyTTD for other target proteins.

Selective Protein Degradation through Tetrazine Ligation of Genetically Incorporated Unnatural Amino Acids

Small molecule-responsive tags for targeted protein degradation are valuable tools for fundamental research and drug target validation. Here, we show that genetically incorporated unnatural amino acids bearing a strained alkene or alkyne functionality can act as a minimalist tag for targeted protein degradation. Specifically, we observed the degradation of strained alkene- or alkyne-containing kinases and E2 ubiquitin-conjugating enzymes upon treatment with hydrophobic tetrazine conjugates. The extent of the induced protein degradation depends on the identity of the target protein, unnatural amino acid, and tetrazine conjugate, as well as the site of the unnatural amino acid in the target protein. Mechanistic studies revealed proteins undergo proteasomal degradation after tetrazine tethering, and the identity of tetrazine conjugates influences the dependence of ubiquitination on protein degradation. This work provides an alternative approach for targeted protein degradation and mechanistic insight, facilitating the future development of more effective targeted protein degradation strategies.

Targeting the STAT3 pathway with STAT3 degraders

Signal transducer and activator of transcription 3 (STAT3) has been widely considered as a therapeutic target for various diseases, especially tumors. Thus far, several STAT3 inhibitors have been advanced to clinical trials; however, the development of STAT3 inhibitors is hindered by numerous dilemmas. Fortunately, STAT3 degraders represent an alternative and promising strategy to block STAT3, attracting extensive research interest. Here, we analyze the recent advancements of STAT3 degraders, including proteolysis targeting chimeras (PROTACs) and small-molecule natural products, focusing on their structures, mechanisms, and biological activities. We discuss the potential opportunities and challenges for developing STAT3 degraders. It is hoped that this Review will provide insights into the discovery of potent STAT3-targeting drugs.

Discovery of Potent and Selective c-Met Degraders for Hepatocellular Carcinoma Treatment

Targeting c-Met is a clinical trend for the precise treatment of HCC, but the potential issue of acquired drug resistance cannot be ignored. Targeted protein degradation technology has demonstrated promising prospects in disease treatment and overcoming drug resistance due to its special mechanism of action. In this study, we designed and synthesized two series of novel c-Met degraders and conducted a systematic biological evaluation of the optimal compound H11. H11 exhibited good c-Met degradation activity and anti-HCC activity. Importantly, H11 also demonstrated more potent inhibitory activity against Ba/F3-TPR-MET-D1228N and Ba/F3-TPR-MET-Y1230H cell lines than did tepotinib. In summary, H11 displayed potent anti-HCC activity as a degrader and may overcome resistance to type Ib inhibitors, making it a new therapeutic strategy for HCC with MET alterations.

Discovery of a first-in-class degrader for the protein arginine methyltransferase 6 (PRMT6)

PRMT6 is a member of the protein arginine methyltransferase family, which participates in a variety of physical processes and plays an important role in the occurrence and development of tumors. Using small molecules to design and synthesize targeted protein degraders is a new strategy for drug development. Here, we report the first-in-class degrader SKLB-0124 for PRMT6 based on the hydrophobic tagging (HyT) method.Importantly, SKLB-0124 induced proteasome dependent degradation of PRMT6 and significantly inhibited the proliferation of HCC827 and MDA-MB-435 cells. Moreover, SKLB-0124 effectively induced apoptosis and cell cycle arrest in these two cell lines. Our data clarified that SKLB-0124 is a promising selective PRMT6 degrader for cancer therapy which is worthy of further evaluation.

Kinase Inhibitors and Kinase-Targeted Cancer Therapies: Recent Advances and Future Perspectives

Over 120 small-molecule kinase inhibitors (SMKIs) have been approved worldwide for treating various diseases, with nearly 70 FDA approvals specifically for cancer treatment, focusing on targets like the epidermal growth factor receptor (EGFR) family. Kinase-targeted strategies encompass monoclonal antibodies and their derivatives, such as nanobodies and peptides, along with innovative approaches like the use of kinase degraders and protein kinase interaction inhibitors, which have recently demonstrated clinical progress and potential in overcoming resistance. Nevertheless, kinase-targeted strategies encounter significant hurdles, including drug resistance, which greatly impacts the clinical benefits for cancer patients, as well as concerning toxicity when combined with immunotherapy, which restricts the full utilization of current treatment modalities. Despite these challenges, the development of kinase inhibitors remains highly promising. The extensively studied tyrosine kinase family has 70% of its targets in various stages of development, while 30% of the kinase family remains inadequately explored. Computational technologies play a vital role in accelerating the development of novel kinase inhibitors and repurposing existing drugs. Recent FDA-approved SMKIs underscore the importance of blood-brain barrier permeability for long-term patient benefits. This review provides a comprehensive summary of recent FDA-approved SMKIs based on their mechanisms of action and targets. We summarize the latest developments in potential new targets and explore emerging kinase inhibition strategies from a clinical perspective. Lastly, we outline current obstacles and future prospects in kinase inhibition.

The design, synthesis and bioactivity evaluation of novel androgen receptor degraders based on hydrophobic tagging

Prostate Cancer (PCa) easily progress to metastatic Castration-Resistant Prostate Cancer (mCRPC) that remains a significant cause of cancer-related death. Androgen receptor (AR)-dependent transcription is a major driver of prostate tumor cell proliferation. Proteolysis-targeting chimaera (PROTAC) technology based on Hydrophobic Tagging (HyT) represents an intriguing strategy to regulate the function of therapeutically androgen receptor proteins. In the present study, we have designed, synthesized, and evaluated a series of PROTAC-HyT AR degraders using AR antagonists, RU59063, which were connected with adamantane-based hydrophobic moieties by different alkyl chains. Compound D-4-6 exhibited significant AR protein degradation activity, with a degradation rate of 57 % at 5 μM and nearly 90 % at 20 μM in 24 h, and inhibited the proliferation of LNCaP cells significantly with an IC50 value of 4.77 ± 0.26 μM in a time-concentration-dependent manner. In conclusion, the present study lays the foundation for the development of a completely new class of therapeutic agents for the treatment of mCRPC, and further design and synthesis of AR-targeting degraders are currently in progress for better degradation rate.

Insight into Recent Advances in Degrading Androgen Receptor for Castration-Resistant Prostate Cancer

Induced protein degradation has emerged as an innovative drug discovery approach, complementary to the classical method of suppressing protein function. The androgen receptor signaling pathway has been identified as the primary driving force in the development and progression of lethal castration-resistant prostate cancer. Since androgen receptor degraders function differently from androgen receptor antagonists, they hold the promise to overcome the drug resistance challenges faced by current therapeutics. Proteolysis-targeting chimeras (PROTACs), monomeric degraders, hydrophobic tagging, molecular glues, and autophagic degradation have demonstrated their capability in downregulating intracellular androgen receptor concentrations. The potential of these androgen receptor degraders to treat castration-resistant prostate cancer is substantiated by the advancement of six PROTACs and two monomeric androgen receptor degraders into phase I or II clinical trials. Although the chemical structures, in vitro and in vivo data, and degradation mechanisms of androgen receptor degraders have been reviewed, it is crucial to stay updated on recent advances in this field as novel androgen receptor degraders and new strategies continue to emerge. This review thus provides insight into recent advancements in this paradigm, offering an overview of the progress made since 2020.

A novel scaffold long-acting selective estrogen receptor antagonist and degrader with superior preclinical profile against ER+ breast cancer

Breast cancer is one of the most common malignant tumors in women worldwide, with the majority of cases showing expression of estrogen receptors (ERs). Although drugs targeting ER have significantly improved survival rates in ER-positive patients, drug resistance remains an unmet clinical need. Fulvestrant, which overcomes selective estrogen receptor modulator (SERM) and AI (aromatase inhibitor) resistance, is currently the only long-acting selective estrogen receptor degrader (SERD) approved for both first and second-line settings. However, it fails to achieve satisfactory efficacy due to its poor solubility. Therefore, we designed and synthesized a series of novel scaffold (THC) derivatives, identifying their activities as ER antagonists and degraders. G-5b, the optimal compound, exhibited binding, antagonistic, degradation or anti-proliferative activities comparable to fulvestrant in ER+ wild type and mutants breast cancer cells. Notably, G-5b showed considerably improved stability and solubility. Research into the underlying mechanism indicated that G-5b engaged the proteasome pathway to degrade ER, subsequently inhibiting the ER signaling pathway and leading to the induction of apoptosis and cell cycle arrest events. Furthermore, G-5b displayed superior in vivo pharmacokinetics and pharmacodynamics properties, coupled with a favorable safety profile in the MCF-7 tamoxifen-resistant (MCF-7/TR) tumor xenograft model. Collectively, G-5b has emerged as a highly promising lead compound, offering potent antagonistic and degradation activities, positioning it as a novel long-acting SERD worthy of further refinement and optimization.

The expanding repertoire of covalent warheads for drug discovery

The reactive functionalities of drugs that engage in covalent interactions with the enzyme/receptor residue in either a reversible or an irreversible manner are called 'warheads'. Covalent warheads that were previously neglected because of safety concerns have recently gained center stage as a result of their various advantages over noncovalent drugs, including increased selectivity, increased residence time, and higher potency. With the approval of several covalent inhibitors over the past decade, research in this area has accelerated. Various strategies are being continuously developed to tune the characteristics of warheads to improve their potency and mitigate toxicity. Here, we review research progress in warhead discovery over the past 5 years to provide valuable insights for future drug discovery.