Traditional drug discovery mainly focuses on direct regulation of protein activity. The development and application of protein activity modulators, particularly inhibitors, has been the mainstream in drug development. In recent years, PROteolysis TArgeting Chimeras (PROTAC) technology has emerged as one of the most promising approaches to remove specific disease-associated proteins by exploiting cells' own destruction machinery. In addition to PROTAC, many different targeted protein degradation (TPD) strategies including, but not limited to, molecular glue, Lysosome-Targeting Chimaera (LYTAC), and Antibody-based PROTAC (AbTAC), are emerging. These technologies have not only greatly expanded the scope of TPD, but also provided fresh insights into drug discovery. Here, we summarize recent advances of major TPD technologies, discuss their potential applications, and hope to provide a prime for both biologists and chemists who are interested in this vibrant field. 

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Targeted protein degradation: mechanisms, strategies and application

Targeted protein degradation technology has evolved a brand-new therapeutic modality from an innovative drug discovery perspective. Though the classical PROTACs has pioneered the way for protein degraders, certain inherent defects such as poor druggability, uncontrollable catalysis caused off-targets, and limited E3 ubiquitin ligases available constitute obstacles that impede further advances. Recent medicinal chemists have preferred to investigate a type of optimized degraders beyond the classical PROTACs, bypassing such disadvantages to better facilitate targeted protein degradation. In this perspective, we comprehensively spotlighted the emerging approaches and techniques applied to the targeted protein degradation, specifically the PROTACs-derived strategies and other alternatives to realize protein degradation via proteasome or lysosome. Besides, contemporary confronted opportunities as well as challenges were further analyzed, with the aim to guide future discovery of novel protein degraders. 

Emerging targeted protein degradation tools for innovative drug discovery: From classical PROTACs to the novel and beyond.

Proteolysis Targeting Chimeras (PROTACs), an emerging therapeutic entity designed to degrade target proteins by hijacking the ubiquitin-proteasome system, have the potential to revolutionize the healthcare industry. The broad applicability of this protein degradation strategy has been verified with a few E3 ligases and a variety of distinct targets through the construction of modular chimeric structures. Despite recent efforts to promote the use of PROTACs for clinical applications, most PROTACs do not make it beyond the preclinical stage of drug development. There are several reasons that prevent PROTACs from reaching the market, and the inadequate delivery to the target site is one of the most challenging hurdles. With the increasing need for accelerating the translational process, combining the concepts of PROTACs and delivery systems has been explored to enhance the in vivo performance of PROTACs. These improved delivery strategies can eliminate unfavorable physicochemical properties of PROTACs, improve their targetability, and decrease their off-target side effects. The integration of powerful PROTACs and versatile delivery systems will inaugurate a burgeoning orientation for the field of targeted protein degradation. In this review, we will survey the latest progress in improving the in vivo degradation efficacy of PROTACs through delivery strategies, outline design principles for PROTAC-based delivery systems, discuss the current challenges with PROTACs, and outlook future opportunities in this field.

Proteolysis-targeting chimera (PROTAC) delivery system: advancing protein degraders towards clinical translation.

Proteolysis targeting chimeras (PROTACs), which hijack proteins of interest (POIs) and recruit E3 ligases for target degradation via the ubiquitin-proteasome pathway, are a novel drug discovery paradigm that has been widely used as biological tools and medicinal molecules with the potential of clinical application value. To date, a wide variety of small molecule PROTACs have been developed. Importantly, VHL-based PROTACs have emerged to be a promising approach for proteins, including those non-druggable ones, such as transcriptional factors and scaffold proteins. VHL-based PRTOACs have been developed for the treatment of diseases that are difficult to be dealt with by conventional methods, such as radiotherapy, chemotherapy, and small molecule inhibitors. In this review, the recent advances of VHL-based PRTOACs were summarized, and the chances and challenges associated with this area were also highlighted. 

Yujing Zhang

Papers

Developments of CRBN-based PROTACs as potential therapeutic agents

VHL-based PROTACs as potential therapeutic agents: Recent progress and perspectives

PROTACs technology for targeting non-oncoproteins: Advances and perspectives.

Emerging Tubulin Inhibitors: A New Hope for Fungicides.