LYTACs that engage the asialoglycoprotein receptor for targeted protein degradation

Targeted protein degradation combined with PET imaging reveals the role of host PD-L1 in determining anti-PD-1 therapy efficacy

PURPOSE

Immunohistochemical staining of programmed death-ligand 1 (PD-L1) in tumor biopsies acquired through invasive procedures is routinely employed in clinical practice to identify patients who are most likely to benefit from anti-programmed cell death protein 1 (PD-1) therapy. Nevertheless, PD-L1 expression is observed in various cellular subsets within tumors and their microenvironments, including tumor cells, dendritic cells, and macrophages. The impact of PD-L1 expression across these different cell types on the responsiveness to anti-PD-1 treatment is yet to be fully understood.

METHODS

We synthesized polymer-based lysosome-targeting chimeras (LYTACs) that incorporate both PD-L1-targeting motifs and liver cell-specific asialoglycoprotein receptor (ASGPR) recognition elements. Small-animal positron emission tomography (PET) imaging of PD-L1 expression was also conducted using a PD-L1-specific radiotracer 89Zr-αPD-L1/Fab.

RESULTS

The PD-L1 LYTAC platform was capable of specifically degrading PD-L1 expressed on liver cancer cells through the lysosomal degradation pathway via ASGPR without impacting the PD-L1 expression on host cells. When coupled with whole-body PD-L1 PET imaging, our studies revealed that host cell PD-L1, rather than tumor cell PD-L1, is pivotal in the antitumor response to anti-PD-1 therapy in a mouse model of liver cancer.

CONCLUSION

The LYTAC strategy, enhanced by PET imaging, has the potential to surmount the limitations of knockout mouse models and to provide a versatile approach for the selective degradation of target proteins in vivo. This could significantly aid in the investigation of the roles and mechanisms of protein functions associated with specific cell subsets in living subjects.

Proteolysis-targeting drug delivery system (ProDDS): integrating targeted protein degradation concepts into formulation design

Targeted protein degradation (TPD) has emerged as a revolutionary paradigm in drug discovery and development, offering a promising avenue to tackle challenging therapeutic targets. Unlike traditional drug discovery approaches that focus on inhibiting protein function, TPD aims to eliminate proteins of interest (POIs) using modular chimeric structures. This is achieved through the utilization of proteolysis-targeting chimeras (PROTACs), which redirect POIs to E3 ubiquitin ligases, rendering them for degradation by the cellular ubiquitin-proteasome system (UPS). Additionally, other TPD technologies such as lysosome-targeting chimeras (LYTACs) and autophagy-based protein degraders facilitate the transportation of proteins to  endo-lysosomal or autophagy-lysosomal pathways for degradation, respectively. Despite significant growth in preclinical TPD research, many chimeras fail to progress beyond this stage in the drug development. Various factors contribute to the limited success of TPD agents, including a significant hurdle of inadequate delivery to the target site. Integrating TPD into delivery platforms could surmount the challenges of in vivo applications of TPD strategies by reshaping their pharmacokinetics and pharmacodynamic profiles. These proteolysis-targeting drug delivery systems (ProDDSs) exhibit superior delivery performance, enhanced targetability, and reduced off-tissue side effects. In this review, we will survey the latest progress in TPD-inspired drug delivery systems, highlight the importance of introducing delivery ideas or technologies to the development of protein degraders, outline design principles of protein degrader-inspired delivery systems, discuss the current challenges, and provide an outlook on future opportunities in this field.

Heat Shock Protein 90 Interactome-Mediated Proteolysis Targeting Chimera (HIM-PROTAC) Degrading Glutathione Peroxidase 4 to Trigger Ferroptosis

Targeted protein degradation (TPD) is an emerging therapeutic paradigm aimed at eliminating the disease-causing protein with aberrant expression. Herein, we report a new approach to inducing intracellular glutathione peroxidase 4 (GPX4) protein degradation to trigger ferroptosis by bridging the target protein to heat shock protein 90 (HSP90), termed HSP90 interactome-mediated proteolysis targeting chimera (HIM-PROTAC). Different series of HIM-PROTACs were synthesized and evaluated, and two of them, GDCNF-2/GDCNF-11 potently induced ferroptosis via HSP90-mediated ubiquitin-proteasomal degradation of GPX4 in HT-1080 cells with DC50 values of 0.18 and 0.08 μM, respectively. In particular, GDCNF-11 showed 15-fold more ferroptosis selectivity over GPX4 inhibitor ML162. Moreover, these two degraders effectively suppress tumor growth in the mice model with relatively low toxicity as compared to the combination therapy of GPX4 and HSP90 inhibitors. In general, this study demonstrated the feasibility of degrading GPX4 via HSP90 interactome, and thus provided a significant complement to existing TPD strategies.

Leveraging Covalency to Stabilize Ternary Complex Formation For Cell-Cell "Induced Proximity"

Recent advances in the field of translational chemical biology use diverse "proximity-inducing" synthetic modalities to elicit new modes of "event driven" pharmacology. These include mechanisms of targeted protein degradation and immune clearance of pathogenic cells. Heterobifunctional "chimeric" compounds like Proteolysis TArgeting Chimeras (PROTACs) and Antibody Recruiting Molecules (ARMs) leverage these mechanisms, respectively. Both systems function through the formation of reversible "ternary" or higher-order biomolecular complexes. Critical to function are key parameters, such as bifunctional molecule affinity for endogenous proteins, target residence time, and turnover. To probe the mechanism and enhance function, covalent chemical approaches have been developed to kinetically stabilize ternary complexes. These include electrophilic PROTACs and Covalent Immune Recruiters (CIRs), the latter designed to uniquely enforce cell-cell induced proximity. Inducing cell-cell proximity is associated with key challenges arising from a combination of steric and/or mechanical based destabilizing forces on the ternary complex. These factors can attenuate the formation of ternary complexes driven by high affinity bifunctional/proximity inducing molecules. This Account describes initial efforts in our lab to address these challenges using the CIR strategy in antibody recruitment or receptor engineered T cell model systems of cell-cell induced proximity. ARMs form ternary complexes with serum antibodies and surface protein antigens on tumor cells that subsequently engage immune cells via Fc receptors. Binding and clustering of Fc receptors trigger immune cell killing of the tumor cell. We applied the CIR strategy to convert ARMs to covalent chimeras, which "irreversibly" recruit serum antibodies to tumor cells. These covalent chimeras leverage electrophile preorganization and kinetic effective molarity to achieve fast and selective covalent engagement of the target ternary complex protein, e.g., serum antibody. Importantly, covalent engagement can proceed via diverse binding site amino acids beyond cysteine. Covalent chimeras demonstrated striking functional enhancements compared to noncovalent ARM analogs in functional immune assays. We revealed this enhancement was in fact due to the increased kinetic stability and not concentration, of ternary complexes. This finding was recapitulated using analogous CIR modalities that integrate peptidic or carbohydrate binding ligands with Sulfur(VI) Fluoride Exchange (SuFEx) electrophiles to induce cell-cell proximity. Mechanistic studies in a distinct model system that uses T cells engineered with receptors that recognize covalent chimeras or ARMs, revealed covalent receptor engagement uniquely enforces downstream activation signaling. Finally, this Account discusses potential challenges and future directions for adapting and optimizing covalent chimeric/bifunctional molecules for diverse applications in cell-cell induced proximity.

Designed endocytosis-inducing proteins degrade targets and amplify signals

Endocytosis and lysosomal trafficking of cell surface receptors can be triggered by endogenous ligands. Therapeutic approaches such as lysosome-targeting chimaeras1,2 (LYTACs) and cytokine receptor-targeting chimeras3 (KineTACs) have used this to target specific proteins for degradation by fusing modified native ligands to target binding proteins. Although powerful, these approaches can be limited by competition with native ligands and requirements for chemical modification that limit genetic encodability and can complicate manufacturing, and, more generally, there may be no native ligands that stimulate endocytosis through a given receptor. Here we describe computational design approaches for endocytosis-triggering binding proteins (EndoTags) that overcome these challenges. We present EndoTags for insulin-like growth factor 2 receptor (IGF2R) and asialoglycoprotein receptor (ASGPR), sortilin and transferrin receptors, and show that fusing these tags to soluble or transmembrane target protein binders leads to lysosomal trafficking and target degradation. As these receptors have different tissue distributions, the different EndoTags could enable targeting of degradation to different tissues. EndoTag fusion to a PD-L1 antibody considerably increases efficacy in a mouse tumour model compared to antibody alone. The modularity and genetic encodability of EndoTags enables AND gate control for higher-specificity targeted degradation, and the localized secretion of degraders from engineered cells. By promoting endocytosis, EndoTag fusion increases signalling through an engineered ligand-receptor system by nearly 100-fold. EndoTags have considerable therapeutic potential as targeted degradation inducers, signalling activators for endocytosis-dependent pathways, and cellular uptake inducers for targeted antibody-drug and antibody-RNA conjugates.

Transferrin receptor targeting chimeras for membrane protein degradation

Cancer cells require high levels of iron for rapid proliferation, leading to significant upregulation of cell-surface transferrin receptor 1 (TfR1), which mediates iron uptake by binding to the iron-carrying protein transferrin1-3. Leveraging this phenomenon and the fast endocytosis rate of TfR1 (refs. 4,5), we developed transferrin receptor targeting chimeras (TransTACs), a heterobispecific antibody modality for membrane protein degradation. TransTACs are engineered to drive rapid co-internalization of a target protein of interest and TfR1 from the cell surface, and to enable target protein entry into the lysosomal degradation pathway. We show that TransTACs can efficiently degrade a diverse range of single-pass, multi-pass, native or synthetic membrane proteins, including epidermal growth factor receptor, programmed cell death 1 ligand 1, cluster of differentiation 20 and chimeric antigen receptor. In example applications, TransTACs enabled the reversible control of human primary chimeric antigen receptor T cells and the targeting of drug-resistant epidermal growth factor receptor-driven lung cancer with the exon 19 deletion/T790M/C797S mutations in a mouse xenograft model. TransTACs represent a promising new family of bifunctional antibodies for precise manipulation of membrane proteins and targeted cancer therapy.

Powering up targeted protein degradation through active and passive tumour-targeting strategies: Current and future scopes

Targeted protein degradation (TPD) has emerged as a prominent and vital strategy for therapeutic intervention of cancers and other diseases. One such approach involves the exploration of proteolysis targeting chimeras (PROTACs) for the selective elimination of disease-causing proteins through the innate ubiquitin-proteasome pathway. Due to the unprecedented achievements of various PROTAC molecules in clinical trials, researchers have moved towards other physiological protein degradation approaches for the targeted degradation of abnormal proteins, including lysosome-targeting chimeras (LYTACs), autophagy-targeting chimeras (AUTACs), autophagosome-tethering compounds (ATTECs), molecular glue degraders, and other derivatives for their precise mode of action. Despite numerous advantages, these molecules face challenges in solubility, permeability, bioavailability, and potential off-target or on-target off-tissue effects. Thus, an urgent need arises to direct the action of these degrader molecules specifically against cancer cells, leaving the proteins of non-cancerous cells intact. Recent advancements in TPD have led to innovative delivery methods that ensure the degraders are delivered in a cell- or tissue-specific manner to achieve cell/tissue-selective degradation of target proteins. Such receptor-specific active delivery or nano-based passive delivery of the PROTACs could be achieved by conjugating them with targeting ligands (antibodies, aptamers, peptides, or small molecule ligands) or nano-based carriers. These techniques help to achieve precise delivery of PROTAC payloads to the target sites. Notably, the successful entry of a Degrader Antibody Conjugate (DAC), ORM-5029, into a phase 1 clinical trial underscores the therapeutic potential of these conjugates, including LYTAC-antibody conjugates (LACs) and aptamer-based targeted protein degraders. Further, using bispecific antibody-based degraders (AbTACs) and delivering the PROTAC pre-fused with E3 ligases provides a solution for cell type-specific protein degradation. Here, we highlighted the current advancements and challenges associated with developing new tumour-specific protein degrader approaches and summarized their potential as single agents or combination therapeutics for cancer.

Molecular glue-mediated targeted protein degradation: A novel strategy in small-molecule drug development

Small-molecule drugs are effective and thus most widely used. However, their applications are limited by their reliance on active high-affinity binding sites, restricting their target options. A breakthrough approach involves molecular glues, a novel class of small-molecule compounds capable of inducing protein-protein interactions (PPIs). This opens avenues to target conventionally undruggable proteins, overcoming limitations seen in conventional small-molecule drugs. Molecular glues play a key role in targeted protein degradation (TPD) techniques, including ubiquitin-proteasome system-based approaches such as proteolysis targeting chimeras (PROTACs) and molecular glue degraders and recently emergent lysosome system-based techniques like molecular degraders of extracellular proteins through the asialoglycoprotein receptors (MoDE-As) and macroautophagy degradation targeting chimeras (MADTACs). These techniques enable an innovative targeted degradation strategy for prolonged inhibition of pathology-associated proteins. This review provides an overview of them, emphasizing the clinical potential of molecular glues and guiding the development of molecular-glue-mediated TPD techniques.

New therapies on the horizon: Targeted protein degradation in neuroscience

This minireview explores the burgeoning field of targeted protein degradation (TPD) and its promising applications in neuroscience and clinical development. TPD offers innovative strategies for modulating protein levels, presenting a paradigm shift in small-molecule drug discovery and therapeutic interventions. Importantly, small-molecule protein degraders specifically target and remove pathogenic proteins from central nervous system cells without the drug delivery challenges of genomic and antibody-based modalities. Here, we review recent advancements in TPD technologies, highlight proteolysis targeting chimera (PROTAC) protein degrader molecules with proximity-induced degradation event-driven and iterative pharmacology, provide applications in neuroscience research, and discuss the high potential for translation of TPD into clinical settings.

Programming DNA Nanoassemblies into Polyvalent Lysosomal Degraders for Potent Degradation of Pathogenic Membrane Proteins

Lysosome-targeting chimera (LYTAC) shows great promise for protein-based therapeutics by targeted degradation of disease-associated membrane or extracellular proteins, yet its efficiency is constrained by the limited binding affinity between LYTAC reagents and designated proteins. Here, we established a programmable and multivalent LYTAC system by tandem assembly of DNA into a high-affinity protein degrader, a heterodimer aptamer nanostructure targeting both pathogenic membrane protein and lysosome-targeting receptor (insulin-like growth factor 2 receptor, IGF2R) with adjustable spatial distribution or organization pattern. The DNA-based multivalent LYTACs showed enhanced efficacy in removing immune-checkpoint protein programmable death-ligand 1 (PD-L1) and vascular endothelial growth factor receptor 2 (VEGFR2) in tumor cell membrane that respectively motivated a significant increase in T cell activity and a potent effect on cancer cell growth inhibition. With high programmability and versatility, this multivalent LYTAC system holds considerable promise for realizing protein therapeutics with enhanced activity.

Development of Integrin-Facilitated Bispecific Aptamer Chimeras for Membrane Protein Degradation

The emergence of lysosome-targeting chimeras (LYTACs), which represents a promising strategy for membrane protein degradation based on lysosomal pathways, has attracted much attention in disease intervention and treatment. However, the expression level of commonly used lysosome-targeting receptors (LTRs) varies in different cell lines, thus limiting the broad applications of LYTACs. To overcome this difficulty, we herein report the development of integrin α3β1 (ITGA3B1)-facilitated bispecific aptamer chimeras (ITGBACs) as a platform for the degradation of membrane proteins. ITGBACs consist of two aptamers, one targeting ITGA3B1 and another binding to the membrane-associated protein of interest (POI), effectively transporting the POI into lysosomes for degradation. Our findings demonstrate that ITGBACs effectively eliminate pathological membrane proteins, such as CD71 and PTK7, inducing significant cell-cycle arrest and apoptosis and markedly inhibiting tumor growth in tumor-bearing mice models. Therefore, this work provides a novel and versatile membrane protein degradation platform, offering a promising targeted therapy based on tumor-specific LTRs.

Targeted protein degradation: current molecular targets, localization, and strategies

Targeted protein degradation (TPD) has revolutionized drug discovery by selectively eliminating specific proteins within and outside the cellular context. Over the past two decades, TPD has expanded its focus beyond well-established targets, exploring diverse proteins beyond cancer-related ones. This evolution extends the potential of TPD to various diseases. Notably, TPD can target proteins at demanding locations, such as the extracellular matrix (ECM) and cellular membranes, presenting both opportunities and challenges for future research. In this review, we comprehensively examine the exciting opportunities in the burgeoning field of TPD, highlighting different targets, their cellular environment, and innovative strategies for modern drug discovery.

Liver-targeting chimeras as a potential modality for the treatment of liver diseases

Liver diseases pose significant challenges to global public health. In the realm of drug discovery and development, overcoming 'on-target off-tissue' effects remains a substantial barrier for various diseases. In this study, we have pioneered a Liver-Targeting Chimera (LIVTAC) approach using a proteolysis-targeting chimera (PROTAC) molecule coupled to the liver-specific asialoglycoprotein receptor (ASGPR) through an innovative linker attachment strategy for the precise induction of target protein degradation within the liver. As a proof-of-concept study, we designed XZ1606, a mammalian bromodomain and extra-terminal domain (BET)-targeting LIVTAC agent, which not only demonstrated enduring tumor suppression (over 2 months) in combination with sorafenib but also an improved safety profile, notably ameliorating the incidence of thrombocytopenia, a common and severe on-target dose-limiting toxic effect associated with conventional BET inhibitors. These encouraging results highlight the potential of LIVTAC as a versatile platform for addressing a broad spectrum of liver diseases.

Targeted protein degradation: from mechanisms to clinic

Targeted protein degradation refers to the use of small molecules to induce the selective degradation of proteins. In its most common form, this degradation is achieved through ligand-mediated neo-interactions between ubiquitin E3 ligases - the principal waste disposal machines of a cell - and the protein targets of interest, resulting in ubiquitylation and subsequent proteasomal degradation. Notable advances have been made in biological and mechanistic understanding of serendipitously discovered degraders. This improved understanding and novel chemistry has not only provided clinical proof of concept for targeted protein degradation but has also led to rapid growth of the field, with dozens of investigational drugs in active clinical trials. Two distinct classes of protein degradation therapeutics are being widely explored: bifunctional PROTACs and molecular glue degraders, both of which have their unique advantages and challenges. Here, we review the current landscape of targeted protein degradation approaches and how they have parallels in biological processes. We also outline the ongoing clinical exploration of novel degraders and provide some perspectives on the directions the field might take.

Transforming the Discovery of Targeted Protein Degraders: The Translational Power of Predictive PK/PD Modeling

Targeted protein degraders (TPDs), an emerging therapeutic modality, are attracting considerable interest with the promise to address disease-related proteins that are not druggable with conventional small molecule inhibitors. Despite their novel mechanism of action, the PK/PD relationship of degraders is still approached with a mindset deeply rooted in inhibitor drugs. Here, we establish how predictive mechanistic modeling specifically tailored to TPDs can significantly enhance the value of the available information during lead generation and optimization. By integrating the results from in vitro assays with routinely collected PK data, modeling accurately predicts degradation in vivo. These predictions transform the prioritization of compounds for in vivo studies as well as the selection of optimal dose schedules and most informative measurement time points with the least number of animals. Moreover, the comprehensive modeling framework (1) identifies the PK/PD driver of targeted protein degradation and subsequent downstream pharmacodynamic effects, and (2) uncovers the fundamental difference between degrader and inhibitor PK/PD relationships. The practical utility of our predictive modeling is demonstrated with relevant use cases. This framework will allow researchers to transition from current, mostly serendipity-based approaches to more sound model-informed decision making. Going forward, the presented predictive PK/PD modeling framework lays out a rational path to incorporate inter-species differences in the pharmacology and thus promises to help with getting the dose right in clinical trials.

Subcellular targeting strategies for protein and peptide delivery

Cytosolic delivery of proteins and peptides provides opportunities for effective disease treatment, as they can specifically modulate intracellular processes. However, most of protein-based therapeutics only have extracellular targets and are cell-membrane impermeable due to relatively large size and hydrophilicity. The use of organelle-targeting strategy offers great potential to overcome extracellular and cell membrane barriers, and enables localization of protein and peptide therapeutics in the organelles. Although progresses have been made in the recent years, organelle-targeted protein and peptide delivery is still challenging and under exploration. We reviewed recent advances in subcellular targeted delivery of proteins/peptides with a focus on targeting mechanisms and strategies, and highlight recent examples of active and passive organelle-specific protein and peptide delivery systems. This emerging platform could open a new avenue to develop more effective protein and peptide therapeutics.

Engineering artificial non-coding RNAs for targeted protein degradation

Targeted protein degradation has become a notable drug development strategy, but its application has been limited by the dependence on protein-based chimeras with restricted genetic manipulation capabilities. The use of long non-coding RNAs (lncRNAs) has emerged as a viable alternative, offering interactions with cellular proteins to modulate pathways and enhance degradation capabilities. Here we introduce a strategy employing artificial lncRNAs (alncRNAs) for precise targeted protein degradation. By integrating RNA aptamers and sequences from the lncRNA HOTAIR, our alncRNAs specifically target and facilitate the ubiquitination and degradation of oncogenic transcription factors and tumor-related proteins, such as c-MYC, NF-κB, ETS-1, KRAS and EGFR. These alncRNAs show potential in reducing malignant phenotypes in cells, both in vitro and in vivo, offering advantages in efficiency, adaptability and versatility. This research enhances knowledge of lncRNA-driven protein degradation and presents an effective method for targeted therapies.

Targeting EGFR with molecular degraders as a promising strategy to overcome resistance to EGFR inhibitors

Abnormal activation of EGFR is often associated with various malignant tumors, making it an important target for antitumor therapy. However, traditional targeted inhibitors have several limitations, such as drug resistance and side effects. Many studies have focused on the development of EGFR degraders to overcome this resistance and enhance the therapeutic effect on tumors. Proteolysis targeting chimeras (PROTAC) and Lysosome-based degradation techniques have made significant progress in degrading EGFR. This review provides a summary of the structural and function of EGFR, the resistance, particularly the research progress and activity of EGFR degraders via the proteasome and lysosome. Furthermore, this review aims to provide insights for the development of the novel EGFR degraders.

A plug-and-play monofunctional platform for targeted degradation of extracellular proteins and vesicles

Existing strategies use bifunctional chimaeras to mediate extracellular protein degradation. However, these strategies rely on specific lysosome-trafficking receptors to facilitate lysosomal delivery, which may raise resistance concerns due to intrinsic cell-to-cell variation in receptor expression and mutations or downregulation of the receptors. Another challenge is establishing a universal platform applicable in multiple scenarios. Here, we develop MONOTAB (MOdified NanOparticle with TArgeting Binders), a plug-and-play monofunctional degradation platform that can drag extracellular targets into lysosomes for degradation. MONOTAB harnesses the inherent lysosome-targeting ability of certain nanoparticles to obviate specific receptor dependency and the hook effect. To achieve high modularity and programmable target specificity, we utilize the streptavidin-biotin interaction to immobilize antibodies or other targeting molecules on nanoparticles, through an antibody mounting approach or by direct binding. Our study reveals that MONOTAB can induce efficient degradation of diverse therapeutic targets, including membrane proteins, secreted proteins, and even extracellular vesicles.

Targeted Protein Degradation (TPD) for Immunotherapy: Understanding Proteolysis Targeting Chimera-Driven Ubiquitin-Proteasome Interactions

Targeted protein degradation or TPD, is rapidly emerging as a treatment that utilizes small molecules to degrade proteins that cause diseases. TPD allows for the selective removal of disease-causing proteins, including proteasome-mediated degradation, lysosome-mediated degradation, and autophagy-mediated degradation. This approach has shown great promise in preclinical studies and is now being translated to treat numerous diseases, including neurodegenerative diseases, infectious diseases, and cancer. This review discusses the latest advances in TPD and its potential as a new chemical modality for immunotherapy, with a special focus on the innovative applications and cutting-edge research of PROTACs (Proteolysis TArgeting Chimeras) and their efficient translation from scientific discovery to technological achievements. Our review also addresses the significant obstacles and potential prospects in this domain, while also offering insights into the future of TPD for immunotherapeutic applications.

Targeted degradation of VEGF with bispecific aptamer-based LYTACs ameliorates pathological retinal angiogenesis

Rationale: Neovascular ocular diseases (NODs) represent the leading cause of visual impairment globally. Despite significant advances in anti-angiogenic therapies targeting vascular endothelial growth factor (VEGF), persistent challenges remain prevalent. As a proof-of-concept study, we herein demonstrate the effectiveness of targeted degradation of VEGF with bispecific aptamer-based lysosome-targeting chimeras (referred to as VED-LYTACs). Methods: VED-LYTACs were constructed with three distinct modules: a mannose-6-phosphate receptor (M6PR)-binding motif containing an M6PR aptamer, a VEGF-binding module with an aptamer targeting VEGF, and a linker essential for bridging and stabilizing the two-aptamer structure. The degradation efficiency of VED-LYTACs via the autophagy-lysosome system was examined using an enzyme-linked immunosorbent assay (ELISA) and immunofluorescence staining. Subsequently, the anti-angiogenic effects of VED-LYTACs were evaluated using in vitro wound healing assay, tube formation assay, three-dimensional sprouting assay, and ex vivo aortic ring sprouting assay. Finally, the potential therapeutic effects of VED-LYTACs on pathological retinal neovascularization and vascular leakage were tested by employing mouse models of NODs. Results: The engineered VED-LYTACs promote the interaction between M6PR and VEGF, consequently facilitating the translocation and degradation of VEGF through the lysosome. Our data show that treatment with VED-LYTACs significantly suppresses VEGF-induced angiogenic activities both in vitro and ex vivo. In addition, intravitreal injection of VED-LYTACs remarkably ameliorates abnormal vascular proliferation and leakage in mouse models of NODs. Conclusion: Our findings present a novel strategy for targeting VEGF degradation with an aptamer-based LYTAC system, effectively ameliorating pathological retinal angiogenesis. These results suggest that VED-LYTACs have potential as therapeutic agents for managing NODs.

Therapeutic potential of cis-targeting bispecific antibodies

The growing clinical success of bispecific antibodies (bsAbs) has led to rapid interest in leveraging dual targeting in order to generate novel modes of therapeutic action beyond mono-targeting approaches. While bsAbs that bind targets on two different cells (trans-targeting) are showing promise in the clinic, the co-targeting of two proteins on the same cell surface through cis-targeting bsAbs (cis-bsAbs) is an emerging strategy to elicit new functionalities. This includes the ability to induce proximity, enhance binding to a target, increase target/cell selectivity, and/or co-modulate function on the cell surface with the goal of altering, reversing, or eradicating abnormal cellular activity that contributes to disease. In this review, we focus on the impact of cis-bsAbs in the clinic, their emerging applications, and untangle the intricacies of improving bsAb discovery and development.

Tau in neurodegenerative diseases: molecular mechanisms, biomarkers, and therapeutic strategies

The deposition of abnormal tau protein is characteristic of Alzheimer's disease (AD) and a class of neurodegenerative diseases called tauopathies. Physiologically, tau maintains an intrinsically disordered structure and plays diverse roles in neurons. Pathologically, tau undergoes abnormal post-translational modifications and forms oligomers or fibrous aggregates in tauopathies. In this review, we briefly introduce several tauopathies and discuss the mechanisms mediating tau aggregation and propagation. We also describe the toxicity of tau pathology. Finally, we explore the early diagnostic biomarkers and treatments targeting tau. Although some encouraging results have been achieved in animal experiments and preclinical studies, there is still no cure for tauopathies. More in-depth basic and clinical research on the pathogenesis of tauopathies is necessary.

Targeted degradation of membrane and extracellular proteins with LYTACs

Targeted protein degradation technology has gained substantial momentum over the past two decades as a revolutionary strategy for eliminating pathogenic proteins that are otherwise refractory to treatment. Among the various approaches developed to harness the body's innate protein homeostasis mechanisms for this purpose, lysosome targeting chimeras (LYTACs) that exploit the lysosomal degradation pathway by coupling the target proteins with lysosome-trafficking receptors represent the latest innovation. These chimeras are uniquely tailored to degrade proteins that are membrane-bound and extracellular, encompassing approximately 40% of all proteome. Several novel LYTAC formulas have been developed recently, providing valuable insights for the design and development of therapeutic degraders. This review delineates the recent progresses of LYTAC technology, its practical applications, and the factors that dictate target degradation efficiency. The potential and emerging trends of this technology are discussed as well. LYTAC technology offers a promising avenue for targeted protein degradation, potentially revolutionizing the therapeutic landscape for numerous diseases.

Glycoengineering in antigen-specific immunotherapies

Advances in immunotherapy have revolutionized modern medical care paradigms. However, many patients respond poorly to the current FDA-approved treatment regimens that primarily target protein-based antigens or checkpoints. Current progress in developing therapeutic strategies that target disease-associated glycans has pinpointed a new class of glycoimmune checkpoints that function orthogonally to the established protein-immune checkpoints. Glycoengineering using chemical, enzymatic, and genetic methods is also increasingly recognized for its massive potential to improve biopharmaceuticals, such as tailoring therapies with antigen-targeting agents. Here, we review the recent development and applications of glycoengineering of antibodies and cells to suit therapeutic applications. We highlight living-cell glycoengineering strategies on cancer and immune cells for better therapeutic efficacy against specific antigens by leveraging the pre-existing immune machinery or instructing de novo creation of targeting agents. We also discuss glycoengineering strategies for studying basic immuno-oncology. Collectively, glycoengineering has a significant contribution to the design of antigen-specific immunotherapies.

[Protein induced proximity and targeted degradations by new degraders: concepts, developments, challenges for clinical applications]

The review is focused on recent drug discovery advances based on targeted protein degradation strategies. This new area of research has exploded leading to the development of potential drugs useful in a large variety of human diseases. They first target disease relevant proteins difficult to counteract with other classical strategies and extend now to aggregates, organelles, nucleic acids or lipidic droplets. These degraders engaged either the ubiquitin-proteasome system for PROTACs and molecular glues (first generation), or the lysosomal system via endosome-lysosome degradation (LYTACs) and autophagy-lysosome degradation (ATTEC, AUTAC, AUTOTAC) (following generations of degraders). PROTACs have expanded from the orthodox heterobifunctional ones to new derivatives such as homo-PROTACs, pro-PROTACs, CLIPTACs, HaloPROTACs, PHOTOTACs, Bac-PROTACs, AbTACs, ARN-PROTACs. The small molecular-weight molecular glues induce the formation of new ternary complexes which implicate the targeted protein and an ubiquitin ligase E3 allowing the protein ubiquinitation followed by its proteasomal degradation. Lysosomal degraders (LYTAC, ATTEC, AUTAC, AUTOTAC) specifically recognize extracellular and membrane proteins or dysfunctional organelles and transport them into lysosomes where they are degraded. They overcome the limitations observed with proteasomal degradations induced by PROTAC and molecular glues and demonstrate their potential to treat human diseases, especially neurodegenerative ones. Pharmaceutical companies are engaged at the world level to develop these new potential drugs targeting cancers, immuno-inflammatory and neurodegenerative diseases as well as a variety of other ones. Efficiency and risks for these novel therapeutic strategies are discussed.

Ubiquitin recruiting chimera: more than just a PROTAC

Ubiquitinylation of protein substrates results in various but distinct biological consequences, among which ubiquitin-mediated degradation is most well studied for its therapeutic application. Accordingly, artificially targeted ubiquitin-dependent degradation of various proteins has evolved into the therapeutically relevant PROTAC technology. This tethered ubiquitinylation of various targets coupled with a broad assortment of modifying E3 ubiquitin ligases has been made possible by rational design of bi-specific chimeric molecules that bring these proteins in proximity. However, forced ubiquitinylation inflicted by the binary warheads of a chimeric PROTAC molecule should not necessarily result in protein degradation but can be used to modulate other cellular functions. In this respect it should be noted that the ubiquitinylation of a diverse set of proteins is known to control their transport, transcriptional activity, and protein-protein interactions. This review provides examples of potential PROTAC usage based on non-degradable ubiquitinylation.

Functionalized extracellular nanovesicles as advanced CRISPR delivery systems

The clustered regularly interspaced short palindromic repeat (CRISPR) system, an emerging tool for genome editing, has garnered significant public interest for its potential in treating genetic diseases. Despite the rapid advancements in CRISPR technology, the progress in developing effective delivery strategies lags, impeding its clinical application. Extracellular nanovesicles (EVs), either in their endogenous forms or with engineered modifications, have emerged as a promising solution for CRISPR delivery. These EVs offer several advantages, including high biocompatibility, biological permeability, negligible immunogenicity, and straightforward production. Herein, we first summarize various types of functional EVs for CRISPR delivery, such as unmodified, modified, engineered virus-like particles (VLPs), and exosome-liposome hybrid vesicles, and examine their distinct intracellular pathways. Then, we outline the cutting-edge techniques for functionalizing extracellular vesicles, involving producer cell engineering, vesicle engineering, and virus-like particle engineering, emphasizing the diverse CRISPR delivery capabilities of these nanovesicles. Lastly, we address the current challenges and propose rational design strategies for their clinical translation, offering future perspectives on the development of functionalized EVs.

Phase Separation Enhanced PROTAC for Highly Efficient Protein Degradation

Biomacromolecular condensates formed via phase separation establish compartments for the enrichment of specific compositions, which is also used as a biological tool to enhance molecule condensation, thereby increasing the efficiency of biological processes. Proteolysis-targeting chimeras (PROTACs) have been developed as powerful tools for targeted protein degradation in cells, offering a promising approach for therapies for different diseases. Herein, we introduce an intrinsically disordered region in the PROTAC (denoted PSETAC), which led to the formation of droplets of target proteins in the cells and increased degradation efficiency compared with PROTAC without phase separation. Further, using a nucleus targeting intrinsically disordered domain, the PSETAC was able to target and degrade nuclear-located proteins. Finally, we demonstrated intracellular delivery of PSETAC using lipid nanoparticle-encapsulated mRNA (mRNA-LNP) for the degradation of the endogenous target protein. This study established the PSETAC mRNA-LNP method as a potentially translatable, safe therapeutic strategy for the development of clinical applications based on PROTAC.

Lysosome Targeting Chimaeras for Glut1-Facilitated Targeted Protein Degradation

Targeted protein degradation technology holds great potential in biomedicine, particularly in treating tumors and other protein-related diseases. Research on intracellular protein degradation using molecular glues and PROTAC technology is leading, while research on the degradation of membrane proteins and extracellular proteins through the lysosomal pathway is still in the preclinical stage. The scarcity of useful targets is an immense limitation to technological advancement, making it essential to explore novel, potentially effective approaches for targeted lysosomal degradation. Here, we employed the glucose transporter Glut1 as an innovative lysosome-targeting receptor and devised the Glut1-Facilitated Lysosomal Degradation (GFLD) strategy. We synthesized potential Glut1 ligands via reversible addition-fragmentation chain transfer (RAFT) polymerization and acquired antibody-glycooligomer conjugates through bioorthogonal reactions as lysosome-targeting protein degradation molecules, utilized in the management of PD-L1 high-expressing triple-negative breast cancer. The glucose transporter Glut1 as a lysosome-targeting receptor exhibits potential for the advancement of a broader array of medications in the future.

The application of targeted protein degradation technologies to G protein-coupled receptors

The ubiquitin-proteasome system is one of the major pathways for the degradation of cellular proteins. In recent years, methods have been developed to exploit the ubiquitin-proteasome system to artificially degrade target proteins. Targeted protein degraders are extremely useful as biological tools for discovery research. They have also been developed as novel therapeutics with several targeted protein degraders currently in clinical trials. However, almost all targeted protein degrader technologies have been developed for cytosolic proteins. The G protein-coupled receptor (GPCR) superfamily is one of the most important classes of drug targets, yet only limited examples of GPCR degradation exist. Here, we review these examples and provide a perspective on the different strategies that have been used to apply targeted protein degradation to GPCRs. We also discuss whether alternative approaches that have been used to degrade other integral membrane proteins could be applied to the degradation of GPCRs. LINKED ARTICLES: This article is part of a themed issue Therapeutic Targeting of G Protein-Coupled Receptors: hot topics from the Australasian Society of Clinical and Experimental Pharmacologists and Toxicologists 2021 Virtual Annual Scientific Meeting. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v181.14/issuetoc.

Design principles and therapeutic applications of novel synthetic WNT signaling agonists

Wingless-related integration site or Wingless and Int-1 or Wingless-Int (WNT) signaling is crucial for embryonic development, and adult tissue homeostasis and regeneration, through its essential roles in cell fate, patterning, and stem cell regulation. The biophysical characteristics of WNT ligands have hindered efforts to interrogate ligand activity in vivo and prevented their development as therapeutics. Recent breakthroughs have enabled the generation of synthetic WNT signaling molecules that possess characteristics of natural ligands and potently activate the pathway, while also providing distinct advantages for therapeutic development and manufacturing. This review provides a detailed discussion of the protein engineering of these molecular platforms for WNT signaling agonism. We discuss the importance of WNT signaling in several organs and share insights from the initial application of these new classes of molecules in vitro and in vivo. These molecules offer a unique opportunity to enhance our understanding of how WNT signaling agonism promotes tissue repair, enabling targeted development of tailored therapeutics.

Anti-tumor immunotherapy using engineered bacterial outer membrane vesicles fused to lysosome-targeting chimeras mediated by transferrin receptor

The lysosome-targeting chimera (LYTAC) approach has shown promise for the targeted degradation of secreted and membrane proteins via lysosomes. However, there have been challenges in design, development, and targeting. Here, we have designed a genetically engineered transferrin receptor (TfR)-mediated lysosome-targeting chimera (TfR-LYTAC) that is efficiently internalized via TfR-mediate endocytosis and targets PD-L1 for lysosomal degradation in cultured cells but not in vivo due to short half-life and poor tumor targeting. A delivery platform was developed by fusing TfR-LYTAC to the surface of bacterial outer membrane vesicles (OMVs). The engineered OMV-LYTAC combines PD-1/PD-L1 pathway inhibition with LYTAC and immune activation by bacterial OMVs. OMV-LYTAC significantly reduced tumor growth in vivo. We have provided a modular and simple genetic strategy for lysosomal degradation as well as a delivery platform for in vivo tumor targeting. The study paves the way for the targeting and degradation of extracellular proteins using the TfR-LYTAC system.

Targeting the undruggables-the power of protein degraders

Undruggable targets typically refer to a class of therapeutic targets that are difficult to target through conventional methods or have not yet been targeted, but are of great clinical significance. According to statistics, over 80% of disease-related pathogenic proteins cannot be targeted by current conventional treatment methods. In recent years, with the advancement of basic research and new technologies, the development of various new technologies and mechanisms has brought new perspectives to overcome challenging drug targets. Among them, targeted protein degradation technology is a breakthrough drug development strategy for challenging drug targets. This technology can specifically identify target proteins and directly degrade pathogenic target proteins by utilizing the inherent protein degradation pathways within cells. This new form of drug development includes various types such as proteolysis targeting chimera (PROTAC), molecular glue, lysosome-targeting Chimaera (LYTAC), autophagosome-tethering compound (ATTEC), autophagy-targeting chimera (AUTAC), autophagy-targeting chimera (AUTOTAC), degrader-antibody conjugate (DAC). This article systematically summarizes the application of targeted protein degradation technology in the development of degraders for challenging drug targets. Finally, the article looks forward to the future development direction and application prospects of targeted protein degradation technology.

Bifunctional Molecules That Induce Both Targeted Degradation and Transcytosis of Extracellular Proteins in Brain Cells

Targeted protein degradation (TPD) has emerged as an effective therapeutic strategy for a wide range of diseases; however, the blood-brain barrier (BBB) limits access of degraders into the central nervous system (CNS). Here, we present a new class of bifunctional small molecules, called TransMoDEs (Transcytosis-inducing molecular degraders of extracellular proteins), capable of both (1) removal of target protein via lysosomal proteolysis and (2) transcytosis of protein targets across brain endothelial cells. TransMoDEs are derived from Angiopep-2, a peptide motif previously employed as a covalent tag to facilitate receptor-mediated transcytosis across the BBB. We demonstrate that TransMoDEs containing either a biotin or chloroalkane ligand can trigger endocytosis of streptavidin or HaloTag protein, respectively. Interestingly, although low-density lipoprotein receptor-related protein 1 (LRP1) has been reported as the primary receptor for Angiopep-2, TransMoDE-mediated target uptake does not rely exclusively on this pathway. Furthermore, TransMoDE-mediated endocytosis of streptavidin in a bEnd.3 BBB model occurs in a clathrin-mediated mechanism and results in both lysosomal localization and transcytosis of the target protein. This study demonstrates that TransMoDEs can recruit, transcytose, and degrade proteins of interest in cells relevant to the CNS, supporting their further development for the removal of pathogenic neuroproteins.

Targeted protein degradation systems to enhance Wnt signaling

Molecules that facilitate targeted protein degradation (TPD) offer great promise as novel therapeutics. The human hepatic lectin asialoglycoprotein receptor (ASGR) is selectively expressed on hepatocytes. We have previously engineered an anti-ASGR1 antibody-mutant RSPO2 (RSPO2RA) fusion protein (called SWEETS) to drive tissue-specific degradation of ZNRF3/RNF43 E3 ubiquitin ligases, which achieved hepatocyte-specific enhanced Wnt signaling, proliferation, and restored liver function in mouse models, and an antibody-RSPO2RA fusion molecule is currently in human clinical trials. In the current study, we identified two new ASGR1- and ASGR1/2-specific antibodies, 8M24 and 8G8. High-resolution crystal structures of ASGR1:8M24 and ASGR2:8G8 complexes revealed that these antibodies bind to distinct epitopes on opposing sides of ASGR, away from the substrate-binding site. Both antibodies enhanced Wnt activity when assembled as SWEETS molecules with RSPO2RA through specific effects sequestering E3 ligases. In addition, 8M24-RSPO2RA and 8G8-RSPO2RA efficiently downregulate ASGR1 through TPD mechanisms. These results demonstrate the possibility of combining different therapeutic effects and degradation mechanisms in a single molecule.

Emerging paradigms and recent progress in targeting ErbB in cancers

The epidermal growth factor receptor (EGFR) family is a class of transmembrane proteins, highly regarded as anticancer targets due to their pivotal role in various malignancies. Standard cancer treatments targeting the ErbB receptors include tyrosine kinase inhibitors (TKIs) and monoclonal antibodies (mAbs). Despite their substantial survival benefits, the achievement of curative outcomes is hindered by acquired resistance. Recent advancements in anti-ErbB approaches, such as inhibitory peptides, nanobodies, targeted-protein degradation strategies, and bispecific antibodies (BsAbs), aim to overcome such resistance. More recently, emerging insights into the cell surface interactome of the ErbB family open new avenues for modulating ErbB signaling by targeting specific domains of ErbB partners. Here, we review recent progress in ErbB targeting and elucidate emerging paradigms that underscore the significance of EGF domain-containing proteins (EDCPs) as new ErbB-targeting pathways.

Expanding the horizons of targeted protein degradation: A non-small molecule perspective

Targeted protein degradation (TPD) represented by proteolysis targeting chimeras (PROTACs) marks a significant stride in drug discovery. A plethora of innovative technologies inspired by PROTAC have not only revolutionized the landscape of TPD but have the potential to unlock functionalities beyond degradation. Non-small-molecule-based approaches play an irreplaceable role in this field. A wide variety of agents spanning a broad chemical spectrum, including peptides, nucleic acids, antibodies, and even vaccines, which not only prove instrumental in overcoming the constraints of conventional small molecule entities but also provided rapidly renewing paradigms. Herein we summarize the burgeoning non-small molecule technological platforms inspired by PROTACs, including three major trajectories, to provide insights for the design strategies based on novel paradigms.

Biomimetic Nano-Degrader Based CD47-SIRPα Immune Checkpoint Inhibition Promotes Macrophage Efferocytosis for Cardiac Repair

CD47-SIRPα axis is an immunotherapeutic target in tumor therapy. However, current monoclonal antibody targeting CD47-SIRPα axis is associated with on-target off-tumor and antigen sink effects, which significantly limit its potential clinical application. Herein, a biomimetic nano-degrader is developed to inhibit CD47-SIRPα axis in a site-specific manner through SIRPα degradation, and its efficacy in acute myocardial infarction (AMI) is evaluated. The nano-degrader is constructed by hybridizing liposome with red blood cell (RBC) membrane (RLP), which mimics the CD47 density of senescent RBCs and possesses a natural high-affinity binding capability to SIRPα on macrophages without signaling capacity. RLP would bind with SIRPα and induce its lysosomal degradation through receptor-mediated endocytosis. To enhance its tissue specificity, Ly6G antibody conjugation (aRLP) is applied, enabling its attachment to neutrophils and accumulation within inflammatory sites. In the myocardial infarction model, aRLP accumulated in the infarcted myocardium blocks CD47-SIRPα axis and subsequently promoted the efferocytosis of apoptotic cardiomyocytes by macrophage, improved heart repair. This nano-degrader efficiently degraded SIRPα in lysosomes, providing a new strategy for immunotherapy with great clinical transformation potential.

Multivalent Aptamer-Based Lysosome-Targeting Chimeras (LYTACs) Platform for Mono- or Dual-Targeted Proteins Degradation on Cell Surface

Selective protein degradation platforms have opened novel avenues in therapeutic development and biological inquiry. Antibody-based lysosome-targeting chimeras (LYTACs) have emerged as a promising technology that extends the scope of targeted protein degradation to extracellular targets. Aptamers offer an advantageous alternative owing to their potential for modification and manipulation toward a multivalent state. In this study, a chemically engineered platform of multivalent aptamer-based LYTACs (AptLYTACs) is established for the targeted degradation of either single or dual protein targets. Leveraging the biotin-streptavidin system as a molecular scaffold, this investigation reveals that trivalently mono-targeted AptLYTACs demonstrate optimum efficiency in degrading membrane proteins. The development of this multivalent AptLYTACs platform provides a principle of concept for mono-/dual-targets degradation, expanding the possibilities of targeted protein degradation.

Engineering small-molecule and protein drugs for targeting bone tumors

Bone cancer is common and severe. Both primary (e.g., osteosarcoma, Ewing sarcoma) and secondary (e.g., metastatic) bone cancers lead to significant health problems and death. Currently, treatments such as chemotherapy, hormone therapy, and radiation therapy are used to treat bone cancer, but they often only shrink or slow tumor growth and do not eliminate cancer completely. The bone microenvironment contributes unique signals that influence cancer growth, immunogenicity, and metastasis. Traditional cancer therapies have limited effectiveness due to off-target effects and poor distribution on bones. As a result, therapies with improved specificity and efficacy for treating bone tumors are highly needed. One of the most promising strategies involves the targeted delivery of pharmaceutical agents to the site of bone cancer by introduction of bone-targeting moieties, such as bisphosphonates or oligopeptides. These moieties have high affinities to the bone hydroxyapatite matrix, a structure found exclusively in skeletal tissue, and can enhance the targeting ability and efficacy of anticancer drugs when combating bone tumors. This review focuses on the engineering of small molecules and proteins with bone-targeting moieties for the treatment of bone tumors.

Restraining the power of Proteolysis Targeting Chimeras in the cage: A necessary and important refinement for therapeutic safety

Proteolysis Targeting Chimeras (PROTACs) represent a significant advancement in therapeutic drug development by leveraging the ubiquitin-proteasome system to enable targeted protein degradation, particularly impacting oncology. This review delves into the various types of PROTACs, such as peptide-based, nucleic acid-based, and small molecule PROTACs, each addressing distinct challenges in protein degradation. It also discusses innovative strategies like bridged PROTACs and conditional switch-activated PROTACs, offering precise targeting of previously "undruggable" proteins. The potential of PROTACs extends beyond oncology, with ongoing research and technological advancements needed to maximize their therapeutic potential. Future progress in this field relies on interdisciplinary collaboration and the integration of advanced computational tools to open new treatment avenues across various diseases.

CD44: a cancer stem cell marker and therapeutic target in leukemia treatment

CD44 is a ubiquitous leukocyte adhesion molecule involved in cell-cell interaction, cell adhesion, migration, homing and differentiation. CD44 can mediate the interaction between leukemic stem cells and the surrounding extracellular matrix, thereby inducing a cascade of signaling pathways to regulate their various behaviors. In this review, we focus on the impact of CD44s/CD44v as biomarkers in leukemia development and discuss the current research and prospects for CD44-related interventions in clinical application.

Reducing PD-L1 Expression by Degraders and Downregulators as a Novel Strategy to Target the PD-1/PD-L1 Pathway

Targeting the programmed cell death protein-1 (PD-1)/programmed cell death-ligand 1 (PD-L1) pathway has evolved into one of the most promising strategies for tumor immunotherapy. Thus far, multiple monoclonal antibody drugs have been approved for treating a variety of tumors, while the development of small-molecule PD-1/PD-L1 inhibitors has lagged far behind, with only a few small-molecule inhibitors entering clinical trials. In addition to antibody drugs and small-molecule inhibitors, reducing the expression levels of PD-L1 has attracted extensive research interest as another promising strategy to target the PD-1/PD-L1 pathway. Herein, we analyze the structures and mechanisms of molecules that reduce PD-L1 expression and classify them as degraders and downregulators according to whether they directly bind to PD-L1. Moreover, we discuss the potential prospects for developing PD-L1-targeting drugs based on these molecules. It is hoped that this perspective will provide profound insights into the discovery of potent antitumor immunity drugs.

Targeted Degradation of Cell-Surface Proteins via Chaperone-Mediated Autophagy by Using Peptide-Conjugated Antibodies

Cell-surface proteins are important drug targets but historically have posed big challenges for the complete elimination of their functions. Herein, we report antibody-peptide conjugates (Ab-CMAs) in which a peptide targeting chaperone-mediated autophagy (CMA) was conjugated with commercially available monoclonal antibodies for specific cell-surface protein degradation by taking advantage of lysosomal degradation pathways. Unique features of Ab-CMAs, including cell-surface receptor- and E3 ligase-independent degradation, feasibility towards different cell-surface proteins (e.g., epidermal growth factor receptor (EGFR), programmed cell death ligand 1 (PD-L1), human epidermal growth factor receptor 2 (HER2)) by a simple change of the antibody, and successful tumor inhibition in vivo, make them attractive protein degraders for biomedical research and therapeutic applications. As the first example employing CMA to degrade proteins from the outside in, our findings may also shed new light on CMA, a degradation pathway typically targeting cytosolic proteins.

Cell Membrane as A Promising Therapeutic Target: From Materials Design to Biomedical Applications

The cell membrane is a crucial component of cells, protecting their integrity and stability while facilitating signal transduction and information exchange. Therefore, disrupting its structure or impairing its functions can potentially cause irreversible cell damage. Presently, the tumor cell membrane is recognized as a promising therapeutic target for various treatment methods. Given the extensive research focused on cell membranes, it is both necessary and timely to discuss these developments, from materials design to specific biomedical applications. This review covers treatments based on functional materials targeting the cell membrane, ranging from well-known membrane-anchoring photodynamic therapy to recent lysosome-targeting chimaeras for protein degradation. The diverse therapeutic mechanisms are introduced in the following sections: membrane-anchoring phototherapy, self-assembly on the membrane, in situ biosynthesis on the membrane, and degradation of cell membrane proteins by chimeras. In each section, we outline the conceptual design or general structure derived from numerous studies, emphasizing representative examples to understand advancements and draw inspiration. Finally, we discuss some challenges and future directions in membrane-targeted therapy from our perspective. This review aims to engage multidisciplinary readers and encourage researchers in related fields to advance the fundamental theories and practical applications of membrane-targeting therapeutic agents.

Targeting EGFR degradation by autophagosome degraders

Several generations of epidermal growth factor receptor (EGFR) tyrosine kinase inhibitors have been developed for the treatment of non-small cell lung cancer (NSCLC) in clinic. However, emerging drug resistance mediated by new EGFR mutations or activations by pass, leads to malignant progression of NSCLC. Proteolysis targeting chimeras (PROTACs) have been utilized to overcome the drug resistance acquired by mutant EGFR, newly potent and selective degraders are still need to be developed for clinical applications. Herein, we developed autophagosome-tethering compounds (ATTECs) in which EGFR can be anchored to microtubule-associated protein-1 light chain-3B (LC3B) on the autophagosome with the assistance of the LC3 ligand GW5074. A series of EGFR-ATTECs have been designed and synthesized. Biological evaluations showed that these compounds could degrade EGFR and exhibited moderate inhibitory effects on certain NSCLC cell lines. The ATTEC 12c potently induced the degradation of EGFR with a DC50 value of 0.98 μM and a Dmax value of 81% in HCC827 cells. Mechanistic exploration revealed that the lysosomal pathway was mainly involved in this degradation. Compound 12c also exhibited promising inhibitory activity, as well as degradation efficiency in vivo. Our study highlights that EGFR-ATTECs could be developed as a new expandable EGFR degradation tool and also reveals a novel potential therapeutic strategy to prevent drug resistance acquired EGFR mutations.

USP7-Based Deubiquitinase-Targeting Chimeras Stabilize AMPK

Deubiquitinase-targeting chimeras (DUBTACs) have been recently developed to stabilize proteins of interest, which is in contrast to targeted protein degradation (TPD) approaches that degrade disease-causing proteins. However, to date, only the OTUB1 deubiquitinase has been utilized to develop DUBTACs via an OTUB1 covalent ligand, which could unexpectedly compromise the endogenous function of OTUB1 owing to its covalent nature. Here, we show for the first time that deubiquitinase USP7 can be harnessed for DUBTAC development. Based on a noncovalent ligand of USP7, we developed USP7-based DUBTACs that stabilized the ΔF508-CFTR mutant protein as effectively as the previously reported OTUB1-based DUBTAC. Importantly, using two different noncovalent ligands of USP7, we developed the first AMPK DUBTACs that appear to selectively stabilize different isoforms of AMPKβ, leading to elevated AMPK signaling. Overall, these results highlight that, in addition to OTUB1, USP7 can be leveraged to develop DUBTACs, thus significantly expanding the limited toolbox for targeted protein stabilization and the development of novel AMPK DUBTACs as potential therapeutics.

Targeted protein degradation directly engaging lysosomes or proteasomes

Targeted protein degradation (TPD) has been established as a viable alternative to attenuate the function of a specific protein of interest in both biological and clinical contexts. The unique TPD mode-of-action has allowed previously undruggable proteins to become feasible targets, expanding the landscape of "druggable" properties and "privileged" target proteins. As TPD continues to evolve, a range of innovative strategies, which do not depend on recruiting E3 ubiquitin ligases as in proteolysis-targeting chimeras (PROTACs), have emerged. Here, we present an overview of direct lysosome- and proteasome-engaging modalities and discuss their perspectives, advantages, and limitations. We outline the chemical composition, biochemical activity, and pharmaceutical characteristics of each degrader. These alternative TPD approaches not only complement the first generation of PROTACs for intracellular protein degradation but also offer unique strategies for targeting pathologic proteins located on the cell membrane and in the extracellular space.

Drugging Protein Tyrosine Phosphatases through Targeted Protein Degradation

Protein tyrosine phosphatases (PTPs) are an important class of enzymes that regulate protein tyrosine phosphorylation levels of a large variety of proteins in cells. Anomalies in protein tyrosine phosphorylation have been associated with the development of numerous human diseases, leading to a heightened interest in PTPs as promising targets for drug development. However, therapeutic targeting of PTPs has faced skepticism about their druggability. Besides the conventional small molecule inhibitors, proteolysis-targeting chimera (PROTAC) technology offers an alternative approach to target PTPs. PROTAC molecules utilize the ubiquitin-proteasome system to degrade specific proteins and have unique advantages compared with inhibitors: 1) PROTACs are highly efficient and can work at much lower concentrations than that expected based on their biophysical binding affinity; 2) PROTACs may achieve higher selectivity for the targeted protein than that dictated by their binding affinity alone; and 3) PROTACs may engage any region of the target protein in addition to the functional site. This review focuses on the latest advancement in the development of targeted PTP degraders and deliberates on the obstacles and prospective paths of harnessing this technology for therapeutic targeting of the PTPs.