Extracellular protein degradation via the lysosome

Targeted protein degradation in drug development: Recent advances and future challenges

Targeted protein degradation (TPD) has emerged as a promising therapeutic approach with potential advantages over traditional occupancy-based inhibitors in terms of dosing, side effects and targeting "undruggable" proteins. Targeted degraders can theoretically bind any nook or cranny of targeted proteins to drive degradation. This offers convenience versus the small-molecule inhibitors that must function in a well-defined pocket. The degradation process depends mainly on two cell self-destruction mechanisms, namely the ubiquitin-proteasome system and the lysosomal degradation pathway. Various TPD strategies (e.g., proteolytic-targeting chimeras, molecular glues, lysosome-targeting chimeras, and autophagy-targeting chimeras) have been developed. These approaches hold great potential for targeting dysregulated proteins, potentially offering therapeutic benefits. In this article, we systematically review the mechanisms of various TPD strategies, potential applications to drug discovery, and recent advances. We also discuss the benefits and challenges associated with these TPD strategies, aiming to provide insight into the targeting of dysregulated proteins and facilitate their clinical applications.

Fluorescent Turn-On Probes for Visualizing GPx4 Levels in Live Cells and Predicting Drug Sensitivity

Glutathione peroxidase 4 (GPx4) is the membrane peroxidase in mammals that is essential for protecting cells against oxidative damage and critical for ferroptosis. However, no live cell probe is currently available to specifically label GPx4. Herein, we report both inhibitory and noninhibitory fluorescent turn-on probes for specific labeling of GPx4 in live cells. With these probes, the GPx4 expression levels and degradation kinetics in live cells could be visualized, and their real-time responses to the cellular selenium availability were revealed. These probes could also potentially serve as staining reagents to predict the sensitivity of GPx4-related ferroptosis drugs. In view of these features, these GPx4-selective probes will offer opportunities for a deeper understanding of GPx4 function in natural habitats and hold great promise for biomedical applications.

Protein and Energy Supplements for the Elderly

The proportion of elderly individuals is rising globally, and data have shown that as high as 8% of the elderly community suffer from malnutrition. Protein energy malnutrition has shown to elevate morbidity and mortality risk in the elderly; therefore, protein and energy supplement are needed for the elderly populations to create healthy conditions. This chapter describes about general structure of protein, protein turnover, amino acid metabolism including metabolism in the elderly, protein change in aging, supplementation of amino acid as well as vitamin and mineral for the elderly. The discussion in this section aims to provide a general description of protein, amino acids, changes in amino acid metabolism in the elderly, and the benefits of supplementing amino acids as well as vitamins and minerals for the elderly.

Progress and Challenges in Targeted Protein Degradation for Neurodegenerative Disease Therapy

Neurodegenerative diseases (NDs) are currently incurable diseases that cause progressive degeneration of nerve cells. Many of the disease-causing proteins of NDs are "undruggable" for traditional small-molecule inhibitors (SMIs). None of the compounds that attenuated the amyloid-β (Aβ) accumulation process have entered clinical practice, and many phase III clinical trials of SMIs for Alzheimer's disease (AD) have failed. In recent years, emerging targeted protein degradation (TPD) technologies such as proteolysis-targeting chimeras (PROTACs), lysosome-targeting chimaeras (LYTACs), and autophagy-targeting chimeras (AUTACs) with TPD-assistive technologies such as click-formed proteolysis-targeting chimeras (CLIPTACs) and deubiquitinase-targeting chimera (DUBTAC) have developed rapidly. In vitro and in vivo experiments have also confirmed that TPD technology can target the degradation of ND pathogenic proteins, bringing hope for the treatment of NDs. Herein, we review the latest TPD technologies, introduce their targets and technical characteristics, and discuss the emerging TPD technologies with potential in ND research, with the hope of providing a new perspective for the development of TPD technology in the NDs field.

Targeting Protein Degradation Pathways in Tumors: Focusing on their Role in Hematological Malignancies

Cells must maintain their proteome homeostasis by balancing protein synthesis and degradation. This is facilitated by evolutionarily-conserved processes, including the unfolded protein response and the proteasome-based system of protein clearance, autophagy, and chaperone-mediated autophagy. In some hematological malignancies, including acute myeloid leukemia, misfolding or aggregation of the wild-type p53 tumor-suppressor renders cells unable to undergo apoptosis, even with an intact p53 DNA sequence. Moreover, blocking the proteasome pathway triggers lymphoma cell apoptosis. Extensive studies have led to the development of proteasome inhibitors, which have advanced into drugs (such as bortezomib) used in the treatment of certain hematological tumors, including multiple myeloma. New therapeutic options have been studied making use of the so-called proteolysis-targeting chimeras (PROTACs), that bind desired proteins with a linker that connects them to an E3 ubiquitin ligase, resulting in proteasomal-targeted degradation. This review examines the mechanisms of protein degradation in the cells of the hematopoietic system, explains the role of dysfunctional protein degradation in the pathogenesis of hematological malignancies, and discusses the current and future advances of therapies targeting these pathways, based on an extensive search of the articles and conference proceedings from 2005 to April 2022.

Molecular glues: enhanced protein-protein interactions and cell proteome editing

The druggable genome is limited by structural features that can be targeted by small molecules in disease-relevant proteins. While orthosteric and allosteric protein modulators have been well studied, they are limited to antagonistic/agonistic functions. This approach to protein modulation leaves many disease-relevant proteins as undruggable targets. Recently, protein-protein interaction modulation has emerged as a promising therapeutic field for previously undruggable protein targets. Molecular glues and heterobifunctional degraders such as PROTACs can facilitate protein interactions and bring the proteasome into proximity to induce targeted protein degradation. In this review, we discuss the function and rational design of molecular glues, heterobifunctional degraders, and hydrophobic tag degraders. We also review historic and novel molecular glues and targets and discuss the challenges and opportunities in this new therapeutic field.

Protein degradation technology: a strategic paradigm shift in drug discovery

Targeting pathogenic proteins with small-molecule inhibitors (SMIs) has become a widely used strategy for treating malignant tumors. However, most intracellular proteins have been proven to be undruggable due to a lack of active sites, leading to a significant challenge in the design and development of SMIs. In recent years, the proteolysis-targeting chimeric technology and related emerging degradation technologies have provided additional approaches for targeting these undruggable proteins. These degradation technologies show a tendency of superiority over SMIs, including the rapid and continuous target consumption as well as the stronger pharmacological effects, being a hot topic in current research. This review mainly focuses on summarizing the development of protein degradation technologies in recent years. Their advantages, potential applications, and limitations are also discussed. We hope this review would shed light on the design, discovery, and clinical application of drugs associated with these degradation technologies.