PROTAC'ing oncoproteins: targeted protein degradation for cancer therapy

Dual-payload antibody-drug conjugates: Taking a dual shot

Antibody-drug conjugates (ADCs) enable the precise delivery of cytotoxic agents by conjugating small-molecule drugs with monoclonal antibodies (mAbs). Over recent decades, ADCs have demonstrated substantial clinical efficacy. However, conventional ADCs often encounter various clinical challenges, including suboptimal efficacy, significant adverse effects, and the development of drug resistance, limiting their broader clinical application. Encouragingly, a next-generation approach-dual-payload ADCs-has emerged as a pioneering strategy to address these challenges. Dual-payload ADCs are characterized by the incorporation of two distinct therapeutic payloads on the same antibody, enhancing treatment efficacy by promoting synergistic effects and reducing the risk of drug resistance. However, the synthesis of dual-payload ADCs is complex due to the presence of multiple functional groups on antibodies. In this review, we comprehensively summarize the construction strategies for dual-payload ADCs, ranging from the design of ADC components to orthogonal chemistry. The subsequent sections explore current challenges and propose prospective strategies, highlighting recent advancements in dual-payload ADC research, thereby laying the foundation for the development of next-generation ADCs.

Next-generation cancer therapeutics: PROTACs and the role of heterocyclic warheads in targeting resistance

One of the major obstacles to sustained cancer treatment effectiveness is the development of medication resistance. Current therapies that block proteins associated with cancer progression often lose their efficacy due to acquired drug resistance, which is frequently driven by mutated or overexpressed protein targets. Proteolysis-targeting chimeras (PROTACs) offer an alternative therapeutic strategy by hijacking the cell's ubiquitin-proteasome system to degrade disease-causing proteins, presenting several potential advantages. Over the past few years, PROTACs have been developed to target various cancer-related proteins, offering new treatment options for patients with previously untreatable malignancies and serving as a foundation for next-generation therapeutics. One of the notable benefits of PROTACs is their ability to overcome certain resistance mechanisms that limit the effectiveness of conventional targeted therapies, as shown in several recent studies. Additionally, research teams are investigating how PROTACs can selectively degrade mutant proteins responsible for resistance to first-line cancer therapies. In the pursuit of novel and effective treatments, this review highlights recent advancements in the development of PROTACs aimed at overcoming cancer resistance. When it comes to drug design, heterocyclic scaffolds often serve as a foundational framework, offering opportunities for modification and optimization of novel molecules. Researchers are similarly exploring various heterocyclic derivatives as "warheads" in the design of PROTACs has been instrumental in pushing the boundaries of targeted protein degradation. As warheads, these heterocyclic compounds are responsible for recognizing and binding to the target protein, which ultimately leads to its degradation via the ubiquitin-proteasome system. This study aims to provide a comprehensive overview of cutting-edge strategies in PROTAC design, offering detailed insights into key concepts and methodologies for creating effective PROTACs. Special emphasis is placed on structure-based rational design, the development of novel warheads, and their critical in influencing biological activity.

Exploring a new chapter in traditional Chinese medicine: The potential of Calculus bovis in liver cancer treatment

In the ongoing quest for new treatments in medicine, traditional Chinese medicine offers unique insights and potential. Recently, studies on the ability of Calculus bovis to inhibit M2-type tumour-associated macrophage polarisation by modulating the Wnt/β-catenin signalling pathway to suppress liver cancer have undoubtedly revealed new benefits and hope for this field of research. The purpose of this article is to comment on this study and explore its strengths and weaknesses, thereby providing ideas for the future treatment of liver cancer.

Repurposing Tolfenamic Acid to Anchor the Uncharacterized Pocket of the PUB Domain for Proteolysis of the Atypical E3 Ligase HOIP

The E3 ligase HOIP is vital for the NF-κB pathway and is implicated in cancer and immunity. However, it remains challenging to achieve high selectivity by directly targeting the conserved catalytic RBR domain of HOIP. Herein, we identified four low-molecular-weight compounds that bind to an uncharacterized pocket of the HOIP PUB domain (HOIPPUB). The complex structure facilitated the discovery of the first single-digit micromolar ligand of HOIPPUB, tolfenamic acid, which exhibited over 30-fold selectivity due to the low sequence identity of the uncharacterized pocket of HOIPPUB. Although tolfenamic acid did not block the substrate recognition and linear ubiquitination activity of HOIP, a ligand of the uncharacterized PUB pocket of HOIP (LUPH), by chemical linking pomalidomide with tolfenamic acid, degraded HOIP, reduced NEMO ubiquitination and p65 phosphorylation, and eventually inhibited NF-κB activation and breast cancer cell proliferation. Our work proposes an alternative strategy to target the nonfunctional pocket of the PUB domain with high sequence diversity to promote HOIP degradation, rather than targeting the conserved RBR domain to block the catalytic function of HOIP.

Screening, identification and functional validation of Microcystin-LR direct binding target proteins based on thermal proteomics profiling

Microcystin-LR (MC-LR) is one of the most common harmful cyanobacterial toxin and poses a serious threat to human health and ecosystems. The accepted toxic effect of MC-LR is to inhibit its enzymatic activity by covalently binding to protein phosphatase 2A (PP2A). However, numerous researches have revealed that the toxic effects of MC-LR are not solely dependent on PP2A. To date, there have been no relevant reports of MC-LR binding to other exact targets to produce toxic effects, and there is an urgent need to decipher the potential direct targets of MC-LR. Thermal proteome profiling (TPP) is a novel technique for the identification of active small molecule target proteins based on the principle that protein-ligand binding can increase the thermal stability of proteins. For this purpose, we used the TPP technique in combination with SWATH-DIA mass spectrometry to systematically assess the changes in the thermal stability of the proteins, thus searching for potential direct-acting target proteins of MC-LR. The results showed that 129 proteins, including PP2A, were potential binding targets of MC-LR. Bioinformatics analysis of 129 proteins enriched for response to dopamine, proteasome complex, and NF-kappaB binding was consistent with previous MC-LR toxicity studies. MC-LR could directly bind to target proteins such as PSMD4, PSMB9, HDAC2, and MAPK1 by CETSA-Western blot and MST assay. It was further confirmed by functional validation that MC-LR may lead to inhibition of proteasome activity through binding to PSMD4/PSMB9, suggesting that the proteasome is one of the toxic targets of MC-LR. This study reveals the existence of multiple targets of MC-LR after entering the organism, which broadens the horizon and provides a valuable reference for the study of the toxicity mechanism of MC-LR.

Recent advances in dual PROTACs degrader strategies for disease treatment

Proteolysis-targeting chimeras (PROTACs) is regarded as an emerging therapeutic strategy with unlimited potential because of its mechanism of inducing target protein degradation though harnessing ubiquitin-proteasome system (UPS). Recently, researchers are combining the advantages of PROTACs and dual-targeted drugs to explore some new types of dual PROTACs degraders. The utilization of dual PROTACs not only enhances the efficiency of selective degradation for two or more distinct proteins, but also facilitates synergistic interactions between target proteins to optimize therapeutic efficacy as well as overcome resistance. In this review, we briefly investigate the innovative strategies of dual degraders based on bivalent or trivalent "Y-type" PROTACs in recent years, outline their design principles, degradation effects, and anticancer activities. Moreover, their advantages and limitations compared with traditional PROTACs will be discussed and provide the outlook on the associated challenges. Meaningfully, the development and application of these dual-targeted PROTACs may point out new directions for replacing numerous combination regimens in the future.

Advances in designing ternary complexes: Integrating in-silico and biochemical methods for PROTAC optimisation in target protein degradation

Target protein degradation (TPD) is an emerging approach to mitigate disease-causing proteins. TPD contains several strategies, and one of the strategies that gained immersive importance in recent times is Proteolysis Targeting Chimeras (PROTACs); the PROTACs recruit small molecules to induce the poly-ubiquitination of disease-causing protein by hijacking the ubiquitin-proteasome system (UPS) by bringing the E3 ligase and protein of interest (POI) into appropriate proximity. The steps involved in designing and evaluating the PROTACs remain critical in optimising the PROTACs to degrade the POI. It is observed that using in-silico and biochemical methods to study the ternary complexes (TCs) of the POI-PROTAC-E3 ligase is essential to understanding the structural activity, cooperativity, and stability of formed TCs. A better understanding of the above-mentioned leads to an appropriate rationale for designing the PROTACs targeting the disease-causing proteins. In this review, we tried to summarise the approaches used to design the ternary complexes, i.e., in-silico and in-vitro methods, to understand the behaviour of the PROTAC-induced ternary complexes.

Role of Proteins in Oncology: Advances in Cancer Diagnosis, Prognosis, and Targeted Therapy-A Narrative Review

Modern oncology increasingly relies on the role of proteins as key components in cancer diagnosis, prognosis, and targeted therapy. This review examines advancements in protein biomarkers across several cancer types, including breast cancer, lung cancer, ovarian cancer, and hepatocellular carcinoma. These biomarkers have proven critical for early detection, treatment response monitoring, and tailoring personalized therapeutic strategies. The article highlights the utility of targeted therapies, such as tyrosine kinase inhibitors and monoclonal antibodies, in improving treatment efficacy while minimizing systemic toxicity. Despite these advancements, challenges like tumor resistance, variability in protein expression, and diagnostic heterogeneity persist, complicating universal application. The review underscores future directions, including the integration of artificial intelligence, advanced protein analysis technologies, and the development of combination therapies to overcome these barriers and refine personalized cancer treatment.

How to target membrane proteins for degradation: Bringing GPCRs into the TPD fold

We are now in the middle of a so-called "fourth wave" of drug innovation: multispecific medicines aimed at diseases and targets previously thought to be "undruggable"; by inducing proximity between two or more proteins, for example, a target and an effector that do not naturally interact, such modalities have potential far beyond the scope of conventional drugs. In particular, targeted protein degradation (TPD) strategies to destroy disease-associated proteins have emerged as an exciting pipeline in drug discovery. Most efforts are focused on intracellular proteins, whereas membrane proteins have been less thoroughly explored despite the fact that they comprise roughly a quarter of the human proteome with G-protein coupled receptors (GPCRs) notably dysregulated in many diseases. Here, we discuss the opportunities and challenges of developing degraders for membrane proteins with a focus on GPCRs. We provide an overview of different TPD platforms in the context of membrane-tethered targets, and we present recent degradation technologies highlighting their potential application to GPCRs.

The synthesis of 1,2,3-triazoles as binders of D-dopachrome tautomerase (D-DT) for the development of dual-targeting inhibitors

Despite recent advances in the treatment of cancer, the issue of therapy resistance remains one of the most significant challenges in the field. In this context, signaling molecules, such as cytokines have emerged as promising targets for drug discovery. Examples of cytokines include macrophage migration inhibitory factor (MIF) and its closely related analogue D-dopachrome tautomerase (D-DT). In this study we aim to develop a new chemical class of D-DT binders and subsequently create a dual-targeted inhibitor that can potentially trigger D-DT degradation via the Proteolysis Targeting Chimera (PROTAC) technology. Here we describe the synthesis of a novel library of 1,2,3-triazoles targeting D-DT. The most potent derivative 19c (IC50 of 0.5 ± 0.04 μM with high selectivity toward D-DT) was attached to a cereblon (CRBN) ligand through aliphatic amides, which were synthesized by a remarkably convenient and effective solvent-free reaction. Enzyme inhibition experiments led to the discovery of the compound 10d, which exhibited moderate inhibitory potency (IC50 of 5.9 ± 0.7 μM), but unfortunately demonstrated no activity in D-DT degradation experiments. In conclusion, this study offers valuable insight into the SAR of D-DT inhibition, paving the way for the development of novel molecules as tools to study D-DT functions in tumor proliferation and, ultimately, new therapeutics for cancer treatment.

Using Förster Resonance Energy Transfer (FRET) to Understand the Ubiquitination Landscape

Förster resonance energy transfer (FRET) is a fluorescence technique that allows quantitative measurement of protein interactions, kinetics and dynamics. This review covers the use of FRET to study the structures and mechanisms of ubiquitination and related proteins. We survey FRET assays that have been developed where donor and acceptor fluorophores are placed on E1, E2 or E3 enzymes and ubiquitin (Ub) to monitor steady-state and real-time transfer of Ub through the ubiquitination cascade. Specialized FRET probes placed on Ub and Ub-like proteins have been developed to monitor Ub removal by deubiquitinating enzymes (DUBs) that result in a loss of a FRET signal upon cleavage of the FRET probes. FRET has also been used to understand conformational changes in large complexes such as multimeric E3 ligases and the proteasome, frequently using sophisticated single molecule methods. Overall, FRET is a powerful tool to help unravel the intricacies of the complex ubiquitination system.

The value of protein allostery in rational anticancer drug design: an update

INTRODUCTION

Allosteric drugs are advantageous. However, they still face hurdles, including identification of allosteric sites that will effectively alter the active site. Current strategies largely focus on identifying pockets away from the active sites into which the allosteric ligand will dock and do not account for exactly how the active site is altered. Favorable allosteric inhibitors dock into sites that are nearby the active sites and follow nature, mimicking diverse allosteric regulation strategies.

AREAS COVERED

The following article underscores the immense significance of allostery in drug design, describes current allosteric strategies, and especially offers a direction going forward. The article concludes with the authors' expert perspectives on the subject.

EXPERT OPINION

To select a productive venue in allosteric inhibitor development, we should learn from nature. Currently, useful strategies follow this route. Consider, for example, the mechanisms exploited in relieving autoinhibition and in harnessing allosteric degraders. Mimicking compensatory, or rescue mutations may also fall into such a thesis, as can molecular glues that capture features of scaffolding proteins. Capturing nature and creatively tailoring its mimicry can continue to innovate allosteric drug discovery.

Design, synthesis, and anticancer assessment of structural analogues of (E)-1-((3,4,5-trimethoxybenzylidene)amino)-4-(3,4,5-trimethoxyphenyl)imidazo[1,2-a]quinoxaline-2-carbonitrile (6b), an imidazo[1,2-a]quinoxaline-based non-covalent EGFR inhibitor

In our quest to find improved anticancer therapeutics, we expedite the lead optimization of (E)-1-((3,4,5-trimethoxybenzylidene)amino)-4-(3,4,5-trimethoxyphenyl)imidazo[1,2-a]quinoxaline-2-carbonitrile (6b), an EGFR inhibitor previously discovered in our laboratory through an in-house screening program. The lead optimization was rationally initiated considering the catalytic site of EGFR. We synthesized twenty-nine new analogues of 6b and assessed their anticancer activities. SAR studies highlighted the role of important groups in controlling anticancer activities. Among all, 5a and 5l were found to exhibit improved EGFR inhibition with anticancer asset potential. In silico studies corroborated with in vitro EGFR inhibitory results. The deeper analysis of 5a and 5l revealed that these synthetics could alter the MMP (ΔΨ m) and significantly reduce the ROS levels in lung cancer cells. This is a vital prerequisite for better plausible EGFR inhibitors devoid of cardiotoxicity. qPCR analysis further revealed that the investigational compounds 5a and 5l were able to downregulate the expression of key oncogenes, viz., KRAS, MAP2K, and EGFR. The downregulation of these genes suggests that the investigational compounds could interact and inhibit key players in the signalling cascade along with the EGFR, which may lead to the inhibition of the growth and prognosis of cancer cells via a holistic approach.

Discovery of a Highly Potent and Selective BRD9 PROTAC Degrader Based on E3 Binder Investigation for the Treatment of Hematological Tumors

BRD9 is a pivotal epigenetic factor involved in cancers and inflammatory diseases. Still, the limited selectivity and poor phenotypic activity of targeted agents make it an atypically undruggable target. PROTAC offers an alternative strategy for overcoming the issue. In this study, we explored diverse E3 ligase ligands for the contribution of BRD9 PROTAC degradation. Through molecular docking, binding affinity analysis, and structure-activity relationship study, we identified a highly potent PROTAC E5, with excellent BRD9 degradation (DC50 = 16 pM) and antiproliferation in MV4-11 cells (IC50 = 0.27 nM) and OCI-LY10 cells (IC50 = 1.04 nM). E5 can selectively degrade BRD9 and induce cell cycle arrest and apoptosis. Moreover, the therapeutic efficacy of E5 was confirmed in xenograft tumor models, accompanied by further RNA-seq analysis. Therefore, these results may pave the way and provide the reference for the discovery and investigation of highly effective PROTAC degraders.

Supramolecular artificial Nano-AUTACs enable tumor-specific metabolism protein degradation for synergistic immunotherapy

Autophagy-targeting chimera (AUTAC) has emerged as a powerful modality that can selectively degrade tumor-related pathogenic proteins, but its low bioavailability and nonspecific distribution significantly restrict their therapeutic efficacy. Inspired by the guanine structure of AUTAC molecules, we here report supramolecular artificial Nano-AUTACs (GM NPs) engineered by AUTAC molecule GN [an indoleamine 2,3-dioxygenase (IDO) degrader] and nucleoside analog methotrexate (MTX) through supramolecular interactions for tumor-specific protein degradation. Their nanostructures allow for precise localization and delivery into cancer cells, where the intracellular acidic environment can disrupt the supramolecular interactions to release MTX for eradicating tumor cells, modulating tumor-associated macrophages, activating dendritic cells, and inducing autophagy. Specifically, the induced autophagy facilitates the released GN for degrading immunosuppressive IDO to further enhance effector T cell activity and inhibit tumor growth and metastasis. This study offers a unique strategy for building a nanoplatform to advance the field of AUTAC in tumor immunotherapy.

p53/MDM2 signaling pathway in aging, senescence and tumorigenesis

A wealth of evidence has emerged that there is an association between aging, senescence and tumorigenesis. Senescence, a biological process by which cells cease to divide and enter a status of permanent cell cycle arrest, contributes to aging and aging-related diseases, including cancer. Aging populations have the higher incidence of cancer due to a lifetime of exposure to cancer-causing agents, reduction of repairing DNA damage, accumulated genetic mutations, and decreased immune system efficiency. Cancer patients undergoing cytotoxic therapies, such as chemotherapy and radiotherapy, accelerate aging. There is growing evidence that p53/MDM2 (murine double minute 2) axis is critically involved in regulation of aging, senescence and oncogenesis. Therefore, in this review, we describe the functions and mechanisms of p53/MDM2-mediated senescence, aging and carcinogenesis. Moreover, we highlight the small molecular inhibitors, natural compounds and PROTACs (proteolysis targeting chimeras) that target p53/MDM2 pathway to influence aging and cancer. Modification of p53/MDM2 could be a potential strategy for treatment of aging, senescence and tumorigenesis.

PROteolysis-Targeting Chimeras (PROTACs) in leukemia: overview and future perspectives

Leukemia is a heterogeneous group of life-threatening malignant disorders of the hematopoietic system. Immunotherapy, radiotherapy, stem cell transplantation, targeted therapy, and chemotherapy are among the approved leukemia treatments. Unfortunately, therapeutic resistance, side effects, relapses, and long-term sequelae occur in a significant proportion of patients and severely compromise the treatment efficacy. The development of novel approaches to improve outcomes is therefore an unmet need. Recently, novel leukemia drug discovery strategies, including targeted protein degradation, have shown potential to advance the field of personalized medicine for leukemia patients. Specifically, PROteolysis-TArgeting Chimeras (PROTACs) are revolutionary compounds that allow the selective degradation of a protein by the ubiquitin-proteasome system. Developed against a wide range of cancer targets, they show promising potential in overcoming many of the drawbacks associated with conventional therapies. Following the exponential growth of antileukemic PROTACs, this article reviews PROTAC-mediated degradation of leukemia-associated targets. Chemical structures, in vitro and in vivo activities, pharmacokinetics, pharmacodynamics, and clinical trials of PROTACs are critically discussed. Furthermore, advantages, challenges, and future perspectives of PROTACs in leukemia are covered, in order to understand the potential that these novel compounds may have as future drugs for leukemia treatment.

Small Molecule Drugs Targeting Viral Polymerases

Small molecules that specifically target viral polymerases-crucial enzymes governing viral genome transcription and replication-play a pivotal role in combating viral infections. Presently, approved polymerase inhibitors cover nine human viruses, spanning both DNA and RNA viruses. This review provides a comprehensive analysis of these licensed drugs, encompassing nucleoside/nucleotide inhibitors (NIs), non-nucleoside inhibitors (NNIs), and mutagenic agents. For each compound, we describe the specific targeted virus and related polymerase enzyme, the mechanism of action, and the relevant bioactivity data. This wealth of information serves as a valuable resource for researchers actively engaged in antiviral drug discovery efforts, offering a complete overview of established strategies as well as insights for shaping the development of next-generation antiviral therapeutics.

PROTAC EZH2 degrader-1 overcomes the resistance of podophyllotoxin derivatives in refractory small cell lung cancer with leptomeningeal metastasis

BACKGROUND

Leptomeningeal metastasis (LM) of small cell lung cancer (SCLC) is a highly detrimental occurrence associated with severe neurological disorders, lacking effective treatment currently. Proteolysis-targeting chimeric molecules (PROTACs) may provide new therapeutic avenues for treatment of podophyllotoxin derivatives-resistant SCLC with LM, warranting further exploration.

METHODS

The SCLC cell line H128 expressing luciferase were mutated by MNNG to generate H128-Mut cell line. After subcutaneous inoculation of H128-Mut into nude mice, H128-LM and H128-BPM (brain parenchymal metastasis) cell lines were primarily cultured from LM and BPM tissues individually, and employed to in vitro drug testing. The SCLC-LM mouse model was established by inoculating H128-LM into nude mice via carotid artery and subjected to in vivo drug testing. RNA-seq and immunoblotting were conducted to uncover the molecular targets for LM.

RESULTS

The SCLC-LM mouse model was successfully established, confirmed by in vivo live imaging and histological examination. The upregulated genes included EZH2, SLC44A4, VEGFA, etc. in both BPM and LM cells, while SLC44A4 was particularly upregulated in LM cells. When combined with PROTAC EZH2 degrader-1, the drug sensitivity of cisplatin, etoposide (VP16), and teniposide (VM26) for H128-LM was significantly increased in vitro. The in vivo drug trials with SCLC-LM mouse model demonstrated that PROTAC EZH2 degrader-1 plus VM26 or cisplatin/ VP16 inhibited H128-LM tumour significantly compared to VM26 or cisplatin/ VP16 alone (P < 0.01).

CONCLUSION

The SCLC-LM model effectively simulates the pathophysiological process of SCLC metastasis to the leptomeninges. PROTAC EZH2 degrader-1 overcomes chemoresistance in SCLC, suggesting its potential therapeutic value for SCLC LM.

PTMs of PD-1/PD-L1 and PROTACs application for improving cancer immunotherapy

Immunotherapy has been developed, which harnesses and enhances the innate powers of the immune system to fight disease, particularly cancer. PD-1 (programmed death-1) and PD-L1 (programmed death ligand-1) are key components in the regulation of the immune system, particularly in the context of cancer immunotherapy. PD-1 and PD-L1 are regulated by PTMs, including phosphorylation, ubiquitination, deubiquitination, acetylation, palmitoylation and glycosylation. PROTACs (Proteolysis Targeting Chimeras) are a type of new drug design technology. They are specifically engineered molecules that target specific proteins within a cell for degradation. PROTACs have been designed and demonstrated their inhibitory activity against the PD-1/PD-L1 pathway, and showed their ability to degrade PD-1/PD-L1 proteins. In this review, we describe how PROTACs target PD-1 and PD-L1 proteins to improve the efficacy of immunotherapy. PROTACs could be a novel strategy to combine with radiotherapy, chemotherapy and immunotherapy for cancer patients.

Exploring the next generation of antibody-drug conjugates

Antibody-drug conjugates (ADCs) are a promising cancer treatment modality that enables the selective delivery of highly cytotoxic payloads to tumours. However, realizing the full potential of this platform necessitates innovative molecular designs to tackle several clinical challenges such as drug resistance, tumour heterogeneity and treatment-related adverse effects. Several emerging ADC formats exist, including bispecific ADCs, conditionally active ADCs (also known as probody-drug conjugates), immune-stimulating ADCs, protein-degrader ADCs and dual-drug ADCs, and each offers unique capabilities for tackling these various challenges. For example, probody-drug conjugates can enhance tumour specificity, whereas bispecific ADCs and dual-drug ADCs can address resistance and heterogeneity with enhanced activity. The incorporation of immune-stimulating and protein-degrader ADCs, which have distinct mechanisms of action, into existing treatment strategies could enable multimodal cancer treatment. Despite the promising outlook, the importance of patient stratification and biomarker identification cannot be overstated for these emerging ADCs, as these factors are crucial to identify patients who are most likely to derive benefit. As we continue to deepen our understanding of tumour biology and refine ADC design, we will edge closer to developing truly effective and safe ADCs for patients with treatment-refractory cancers. In this Review, we highlight advances in each ADC component (the monoclonal antibody, payload, linker and conjugation chemistry) and provide more-detailed discussions on selected examples of emerging novel ADCs of each format, enabled by engineering of one or more of these components.

Precision treatment in advanced hepatocellular carcinoma

The past decade has witnessed significant advances in the systemic treatment of advanced hepatocellular carcinoma (HCC). Nevertheless, the newly developed treatment strategies have not achieved universal success and HCC patients frequently exhibit therapeutic resistance to these therapies. Precision treatment represents a paradigm shift in cancer treatment in recent years. This approach utilizes the unique molecular characteristics of individual patient to personalize treatment modalities, aiming to maximize therapeutic efficacy while minimizing side effects. Although precision treatment has shown significant success in multiple cancer types, its application in HCC remains in its infancy. In this review, we discuss key aspects of precision treatment in HCC, including therapeutic biomarkers, molecular classifications, and the heterogeneity of the tumor microenvironment. We also propose future directions, ranging from revolutionizing current treatment methodologies to personalizing therapy through functional assays, which will accelerate the next phase of advancements in this area.

Molecular glues targeting GSPT1 in cancers: A potent therapy

G1 to S phase transition 1 (GSPT1) is a key translation termination factor that significantly overexpressed in various cancer tissues and cells. Molecular glue is a kind of small molecule, which can bind to an E3 ligase such as cereblon (CRBN) and subsequently recruit neosubstrate proteins for ubiquitination-proteasomal degradation. This emerging therapeutic approach shows great potential in treating cancers and other diseases. This review aims to introduce current understanding of antitumor mechanism of molecular glues targeting GSPT1, summarize pharmacology profiles of existing molecular glues, and outline development strategies of novel molecular glues. The insights provided in this review will be valuable for future studies.

Proteolysis Targeting Chimeras (PROTACs) based on celastrol induce multiple protein degradation for triple-negative breast cancer treatment

The pursuit of single drugs targeting multiple targets has become a prominent trend in modern cancer therapeutics. Natural products, known for their multi-targeting capabilities, accessibility, and cost-effectiveness, hold great potential for the development of multi-target drugs. However, their therapeutic efficacy is often hindered by complex structural modifications and limited anti-tumor activity. In this study, we present a novel approach using celastrol (CST)-based Proteolysis Targeting Chimeras (PROTACs) for breast cancer therapy. Through rational design, we have successfully developed compound 6a, a potent multiple protein degrader capable of selectively degrading GRP94 and CDK1/4 in tumor cells via the endogenous ubiquitin-proteasome system. Furthermore, compound 6a has demonstrated remarkable inhibitory effects on cell proliferation and migration, and induction of apoptosis in 4T1 cells through cell cycle arrest and activation of the Bcl-2/Bax/cleaved Caspase-3 apoptotic pathway. In vivo administration of compound 6a has effectively suppressed tumor growth with an acceptable safety profile. Our findings suggest that the CST-based PROTACs described herein can be readily extended to other natural products, offering a potential avenue for the development of natural product-based PROTACs for cancer treatment.

Correlation between Membrane Permeability and the Intracellular Degradation Activity of Proteolysis-Targeting Chimeras

Proteolysis-targeting chimeras (PROTACs) have attracted attention as an innovative drug modality that induces the selective degradation of target proteins. This technology shows higher activity than conventional inhibitors and holds great potential in the field of drug discovery. Optimization of the linker is essential for PROTACs to achieve sufficient activity, particularly with regard to cell membrane permeability. However, the correlation between membrane permeability and the activity of PROTACs has not been fully explored. To address this, we established a new molecular design approach to remove the linker and optimize PROTAC structure. These PROTAC compound groups were used to analyze the correlation between membrane permeability and activity using LC-tandem mass spectrometry (LC-MS/MS). Results revealed that the degradation activity of PROTACs fluctuates with increasing membrane permeability and changes in response to linker optimization, while sufficient proteolytic activity can be retained. These findings demonstrate the importance of considering the balance between membrane permeability and activity in PROTAC design and provide a new strategy for developing more effective PROTACs.

Recent advancements in targeted protein knockdown technologies-emerging paradigms for targeted therapy

A generalized therapeutic strategy for various disease conditions, including cancer, is to deplete or inactivate harmful protein targets. Various forms of protein or gene silencing molecules, e.g., small molecule inhibitors, RNA interference (RNAi), and microRNAs (miRNAs) have been used against druggable targets. Over the past few years, targeted protein degradation (TPD) approaches have been developed for direct degradation of candidate proteins. Among the TPD approaches, proteolysis targeting chimeras (PROTACs) have emerged as one of the most promising approaches for the selective elimination of proteins via the ubiquitin-proteasome system. Other than PROTACs, TPD methods with potential therapeutic use include intrabody-mediated protein knockdown and tripartite motif-21 (TRIM-21) mediated TRIM-Away. In this review, protein knockdown approaches, their modes of action, and their advantages over conventional gene knockdown approaches are summarized. In cancers, disease-associated protein functions are often executed by specific post-translational modifications (PTMs). The role of TRIM-Away is highlighted in the direct knockdown of PTM forms of target proteins. Moreover, the application challenges and the prospective clinical use of TPD approaches in various diseases are also discussed.

Mechanisms underlying linear ubiquitination and implications in tumorigenesis and drug discovery

Linear ubiquitination is a distinct type of ubiquitination that involves attaching a head-to-tail polyubiquitin chain to a substrate protein. Early studies found that linear ubiquitin chains are essential for the TNFα- and IL-1-mediated NF-κB signaling pathways. However, recent studies have discovered at least sixteen linear ubiquitination substrates, which exhibit a broader activity than expected and mediate many other signaling pathways beyond NF-κB signaling. Dysregulation of linear ubiquitination in these pathways has been linked to many types of cancers, such as lymphoma, liver cancer, and breast cancer. Since the discovery of linear ubiquitin, extensive effort has been made to delineate the molecular mechanisms of how dysregulation of linear ubiquitination causes tumorigenesis and cancer development. In this review, we highlight newly discovered linear ubiquitination-mediated signaling pathways, recent advances in the role of linear ubiquitin in different types of cancers, and the development of linear ubiquitin inhibitors. Video Abstract.

Revolutionizing Drug Targeting Strategies: Integrating Artificial Intelligence and Structure-Based Methods in PROTAC Development

PROteolysis TArgeting Chimera (PROTAC) is an emerging technology in chemical biology and drug discovery. This technique facilitates the complete removal of the target proteins that are "undruggable" or challenging to target through chemical molecules via the Ubiquitin-Proteasome System (UPS). PROTACs have been widely explored and outperformed not only in cancer but also in other diseases. During the past few decades, several academic institutes and pharma companies have poured more efforts into PROTAC-related technologies, setting the stage for several major degrader trial readouts in clinical phases. Despite their promising results, the formation of robust ternary orientation, off-target activity, poor permeability, and binding affinity are some of the limitations that hinder their development. Recent advancements in computational technologies have facilitated progress in the development of PROTACs. Researchers have been able to utilize these technologies to explore a wider range of E3 ligases and optimize linkers, thereby gaining a better understanding of the effectiveness and safety of PROTACs in clinical settings. In this review, we briefly explore the computational strategies reported to date for the formation of PROTAC components and discuss the key challenges and opportunities for further research in this area.

PROTAC-Based Protein Degradation as a Promising Strategy for Targeted Therapy in Sarcomas

Sarcomas are heterogeneous bone and soft tissue cancers representing the second most common tumor type in children and adolescents. Histology and genetic profiling discovered more than 100 subtypes, which are characterized by peculiar molecular vulnerabilities. However, limited therapeutic options exist beyond standard therapy and clinical benefits from targeted therapies were observed only in a minority of patients with sarcomas. The rarity of these tumors, paucity of actionable mutations, and limitations in the chemical composition of current targeted therapies hindered the use of these approaches in sarcomas. Targeted protein degradation (TPD) is an innovative pharmacological modality to directly alter protein abundance with promising clinical potential in cancer, even for undruggable proteins. TPD is based on the use of small molecules called degraders or proteolysis-targeting chimeras (PROTACs), which trigger ubiquitin-dependent degradation of protein of interest. In this review, we will discuss major features of PROTAC and PROTAC-derived genetic systems for target validation and cancer treatment and focus on the potential of these approaches to overcome major issues connected to targeted therapies in sarcomas, including drug resistance, target specificity, and undruggable targets. A deeper understanding of these strategies might provide new fuel to drive molecular and personalized medicine to sarcomas.

Navigating the ERK1/2 MAPK Cascade

The RAS-ERK pathway is a fundamental signaling cascade crucial for many biological processes including proliferation, cell cycle control, growth, and survival; common across all cell types. Notably, ERK1/2 are implicated in specific processes in a context-dependent manner as in stem cells and pancreatic β-cells. Alterations in the different components of this cascade result in dysregulation of the effector kinases ERK1/2 which communicate with hundreds of substrates. Aberrant activation of the pathway contributes to a range of disorders, including cancer. This review provides an overview of the structure, activation, regulation, and mutational frequency of the different tiers of the cascade; with a particular focus on ERK1/2. We highlight the importance of scaffold proteins that contribute to kinase localization and coordinate interaction dynamics of the kinases with substrates, activators, and inhibitors. Additionally, we explore innovative therapeutic approaches emphasizing promising avenues in this field.

Proactive and reactive roles of TGF-β in cancer

Cancer cells adapt to varying stress conditions to survive through plasticity. Stem cells exhibit a high degree of plasticity, allowing them to generate more stem cells or differentiate them into specialized cell types to contribute to tissue development, growth, and repair. Cancer cells can also exhibit plasticity and acquire properties that enhance their survival. TGF-β is an unrivaled growth factor exploited by cancer cells to gain plasticity. TGF-β-mediated signaling enables carcinoma cells to alter their epithelial and mesenchymal properties through epithelial-mesenchymal plasticity (EMP). However, TGF-β is a multifunctional cytokine; thus, the signaling by TGF-β can be detrimental or beneficial to cancer cells depending on the cellular context. Those cells that overcome the anti-tumor effect of TGF-β can induce epithelial-mesenchymal transition (EMT) to gain EMP benefits. EMP allows cancer cells to alter their cell properties and the tumor immune microenvironment (TIME), facilitating their survival. Due to the significant roles of TGF-β and EMP in carcinoma progression, it is essential to understand how TGF-β enables EMP and how cancer cells exploit this plasticity. This understanding will guide the development of effective TGF-β-targeting therapies that eliminate cancer cell plasticity.

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.

RNF126, 168 and CUL1: The Potential Utilization of Multi-Functional E3 Ubiquitin Ligases in Genome Maintenance for Cancer Therapy

Ubiquitination is a post-translational modification (PTM) that is involved in proteolysis, protein-protein interaction, and signal transduction. Accumulation of mutations and genomic instability are characteristic of cancer cells, and dysfunction of the ubiquitin pathway can contribute to abnormal cell physiology. Because mutations can be critical for cells, DNA damage repair, cell cycle regulation, and apoptosis are pathways that are in close communication to maintain genomic integrity. Uncontrolled cell proliferation due to abnormal processes is a hallmark of cancer, and mutations, changes in expression levels, and other alterations of ubiquitination factors are often involved. Here, three E3 ubiquitin ligases will be reviewed in detail. RNF126, RNF168 and CUL1 are involved in DNA damage response (DDR), DNA double-strand break (DSB) repair, cell cycle regulation, and ultimately, cancer cell proliferation control. Their involvement in multiple cellular pathways makes them an attractive candidate for cancer-targeting therapy. Functional studies of these E3 ligases have increased over the years, and their significance in cancer is well reported. There are continuous efforts to develop drugs targeting the ubiquitin pathway for anticancer therapy, which opens up the possibility for these E3 ligases to be evaluated for their potential as a target protein for anticancer therapy.

Discovery of HyT-Based Degraders of CDK9-Cyclin T1 Complex

Direct modulation of the non-kinase functions of cyclin and CDK-cyclin complexes poses challenges. We utilize hydrophobic tag (HyT) based small-molecule degraders induced degradation of cyclin T1 and its corresponding kinase partner CDK9. LL-CDK9-12 demonstrated the most potent and selective degradation ability, with DC50 values of 0.362 μM against CDK9 and 0.680 μM against cyclin T1. In prostate cancer cells, LL-CDK9-12 showed enhanced anti-proliferative activity than its parental molecule SNS032 and LL-K9-3, the previous reported CDK9-cyclin T1 degrader. Moreover, LL-CDK9-12 suppressed the downstream signaling of CDK9 and AR efficiently. Altogether, LL-CDK9-12 was an effective dual degrader of CDK9-cyclin T1 and helped study the unknown function of CDK9-cyclin T1. These results suggest that HyT-based degraders could be used as a strategy to induce the degradation of protein complexes, providing insights for the design of protein complexes' degraders.

Update on Autophagy Inhibitors in Cancer: Opening up to a Therapeutic Combination with Immune Checkpoint Inhibitors

Autophagy is a highly conserved and natural degradation process that helps maintain cell homeostasis through the elimination of old, worn, and defective cellular components, ensuring proper cell energy intake. The degradative pathway constitutes a protective barrier against diverse human diseases including cancer. Autophagy basal level has been reported to be completely dysregulated during the entire oncogenic process. Autophagy influences not only cancer initiation, development, and maintenance but also regulates cancer response to therapy. Currently, autophagy inhibitor candidates mainly target the early autophagy process without any successful preclinical/clinical development. Lessons learned from autophagy pharmaceutical manipulation as a curative option progressively help to improve drug design and to encounter new targets of interest. Combinatorial strategies with autophagy modulators are supported by abundant evidence, especially dealing with immune checkpoint inhibitors, for which encouraging preclinical results have been recently published. GNS561, a PPT1 inhibitor, is a promising autophagy modulator as it has started a phase 2 clinical trial in liver cancer indication, combined with atezolizumab and bevacizumab, an assessment without precedent in the field. This approach paves a new road, leading to the resurgence of anticancer autophagy inhibitors as an attractive therapeutic target in cancer.

BRD4 Protein as a Target for Lung Cancer and Hematological Cancer Therapy: A Review

The BET protein family plays a crucial role in regulating the epigenetic landscape of the genome. Their role in regulating tumor-related gene expression and its impact on the survival of tumor cells is widely acknowledged. Among the BET family constituents, BRD4 is a significant protein. It is a bromodomain-containing protein located at the outer terminal that recognizes histones that have undergone acetylation. It is present in the promoter or enhancer region of the target gene and is responsible for initiating and sustaining the expression of genes associated with tumorigenesis. BRD4 expression is significantly elevated in various tumor types. Research has indicated that BRD4 plays a significant role in regulating various transcription factors and chromatin modification, as well as in repairing DNA damage and preserving telomere function, ultimately contributing to the survival of cancerous cells. The protein BRD4 has a significant impact on antitumor therapy, particularly in the management of lung cancer and hematological malignancies, and the promising potential of BRD4 inhibitors in the realm of cancer prevention and treatment is a topic of great interest. Therefore, BRD4 is considered a promising candidate for prophylaxis and therapy of neoplastic diseases. However, further research is required to fully comprehend the significance and indispensability of BRD4 in cancer and its potential as a therapeutic target.