Selective Protein of Interest Degradation through the Split-and-Mix Liposome Proteolysis Targeting Chimera Approach

PROTAC technology: From drug development to probe technology for target deconvolution

Drug development remains a critical focus within the global pharmaceutical industry. To date, more than 80 % of disease targets are considered difficult to target. The emergence of PROTAC technology has, to some extent, alleviated this challenge. Since introduction, PROTAC technology has evolved through the peptide E3 ligase ligand phase and the small molecule E3 ligase ligand phase. Currently, multiple PROTAC molecules are in the clinical research phase, showing promising potential for addressing drug resistance, disease recurrence, and intractable targets. Target deconvolution is a crucial step in the drug discovery and development process. Due to the exceptional targeting ability and specificity of PROTAC, it is widely used and promoted as an innovative technology for discovering new drug targets, leading to significant breakthroughs. The use of PROTAC probe requires only a catalytic dose and weak interaction with the target protein to achieve target degradation. Thus, it offers substantial advantages over traditional probes, particularly in identifying new targets that are low-abundance or difficult to target. This review provides a comprehensive overview of the advancements made by PROTAC technology in drug development and drug target discovery, while also systematically reviewing the workflow of PROTAC probe. With the ongoing development of PROTAC technology, PROTAC probe is poised to become a key research area in future drug target deconvolution.

Progress of proteolysis-targeting chimeras (PROTACs) delivery system in tumor treatment

Proteolysis targeting chimeras (PROTACs) can use the intrinsic protein degradation system in cells to degrade pathogenic target proteins, and are currently a revolutionary frontier of development strategy for tumor treatment with small molecules. However, the poor water solubility, low cellular permeability, and off-target side effects of most PROTACs have prevented them from passing the preclinical research stage of drug development. This requires the use of appropriate delivery systems to overcome these challenging hurdles and ensure precise delivery of PROTACs towards the tumor site. Therefore, the combination of PROTACs and multifunctional delivery systems will open up new research directions for targeted degradation of tumor proteins. In this review, we systematically reviewed the design principles and the most recent advances of various PROTACs delivery systems. Moreover, the constructive strategies for developing multifunctional PROTACs delivery systems were proposed comprehensively. This review aims to deepen the understanding of PROTACs drugs and promote the further development of PROTACs delivery system.

Modular Development of Enzyme-Activatable Proteolysis Targeting Chimeras for Selective Protein Degradation and Cancer Targeting

As an emerging therapeutic modality, proteolysis targeting chimeras (PROTACs) indiscriminately degrade proteins in both healthy and diseased cells, posing a risk of on-target off-site toxicity in normal tissues. Herein, we present the modular development of enzyme-activatable PROTACs, which utilize enzyme-recognition moieties to block protein degradation activities and can be specifically activated by elevated enzymes in cancer cells to enable cell-selective protein degradation and cancer targeting. We identified the methylene alkoxy carbamate (MAC) unit as an optimal self-immolative linker, possessing high stability and release efficiency for conjugating enzyme-recognition moieties with PROTACs. Leveraging the MAC linker, we developed a series of enzyme-activatable PROTACs, harnessing distinct enzymes for cancer-cell-selective protein degradation. Significantly, we introduced the first dual-enzyme-activatable PROTAC that requires the presence of two cancer-associated enzymes for activation, demonstrating highly selective protein degradation in cancer cells over nonmalignant cells, potent in vivo antitumor efficacy, and no off-tumor toxicity to normal tissues. The broad applicability of enzyme-activatable PROTACs was further demonstrated by caging other PROTACs via the MAC linker to target different proteins and E3 ligases. Our work underscores the substantial potential of enzyme-activatable PROTACs in overcoming the off-site toxicity associated with conventional PROTACs and offers new opportunities for targeted cancer treatment.

A photoactivatable upconverting nanodevice boosts the lysosomal escape of PROTAC degraders for enhanced combination therapy

PROteolysis TArgeting Chimeras have received increasing attention due to their capability to induce potent degradation of various disease-related proteins. However, the effective and controlled cytosolic delivery of current small-molecule PROTACs remains a challenge, primarily due to their intrinsic shortcomings, including unfavorable solubility, poor cell permeability, and limited spatiotemporal precision. Here, we develop a near-infrared light-controlled PROTAC delivery device (abbreviated as USDPR) that allows the efficient photoactivation of PROTAC function to achieve enhanced protein degradation. The nanodevice is constructed by encapsulating the commercial BRD4-targeting PROTACs (dBET6) in the hollow cavity of mesoporous silica-coated upconversion nanoparticles, followed by coating a Rose Bengal (RB) photosensitizer conjugated poly-L-lysine (PLL-RB). This composition enables NIR light-activatable generation of cytotoxic reactive oxygen species due to the energy transfer from the UCNPs to PLL-RB, which boosts the endo/lysosomal escape and subsequent cytosolic release of dBET6. We demonstrate that USDPR is capable of effectively degrading BRD4 in a NIR light-controlled manner. This in combination with NIR light-triggered photodynamic therapy enables an enhanced antitumor effect both in vitro and in vivo. This work thus presents a versatile strategy for controlled release of PROTACs and codelivery with photosensitizers using an NIR-responsive nanodevice, providing important insight into the design of effective PROTAC-based combination therapy.

A Novel Lysosome Targeting Chimera for Targeted Protein Degradation via Split-and-Mix Strategy

Targeted protein degradation is becoming more and more important in the field of drug development. Compared with proteasomal-based degraders, lysosomal-based degraders have a broader target spectrum of targets, which have been demonstrated to have great potential, especially in degrading undruggable proteins. Recently, we developed a programmable and facile screening PROTAC development platform based on peptide self-assembly termed split-and-mix PROTAC (SM-PROTAC). In this study, we applied this technology for the development of lysosome-based degraders, named a split-and-mix chaperone-mediated autophagy-based degrader (SM-CMAD). We successfully demonstrated SM-CMAD as a universal platform by degrading several targets, including ERα, AR, MEK1/2, and BCR-ABL. Different from other lysosomal-based degraders, SM-CMAD was capable of facile screening with programmable ligand ratios. We believe that our work will promote the development of other multifunctional molecules and clinical translation for lysosomal-based degraders.

Nano-PROTACs: state of the art and perspectives

PROteolysis TArgeting Chimeras (PROTACs), as a recently identified technique in the field of new drug development, provide new concepts for disease treatment and are expected to revolutionize drug discovery. With high specificity and flexibility, PROTACs serve as an innovative research tool to target and degrade disease-relevant proteins that are not currently pharmaceutically vulnerable to eliminating their functions by hijacking the ubiquitin-proteasome system. To date, PROTACs still face the challenges of low solubility, poor permeability, off-target effects, and metabolic instability. The combination of nanotechnology and PROTACs has been explored to enhance the in vivo performance of PROTACs regarding overcoming these challenging hurdles. In this review, we summarize the latest advancements in the building-block design of PROTAC prodrug nanoparticles and provide an overview of existing/potential delivery systems and loading approaches for PROTAC drugs. Furthermore, we discuss the current status and prospects of the split-and-mix approach for PROTAC drug optimization. Additionally, the advantages and translational potentials of carrier-free nano-PROTACs and their combinational therapeutic effects are highlighted. This review aims to foster a deeper understanding of this rapidly evolving field and facilitate the progress of nano-PROTACs that will continue to push the boundaries of achieving selectivity and controlled release of PROTAC drugs.

Development of a Double-Stapled Peptide Stabilizing Both α-Helix and β-Sheet Structures for Degrading Transcription Factor AR-V7

Peptide drugs offer distinct advantages in therapeutics; however, their limited stability and membrane penetration abilities hinder their widespread application. One strategy to overcome these challenges is the hydrocarbon peptide stapling technique, which addresses issues such as poor conformational stability, weak proteolytic resistance, and limited membrane permeability. Nonetheless, while peptide stapling has successfully stabilized α-helical peptides, it has shown limited applicability for most β-sheet peptide motifs. In this study, we present the design of a novel double-stapled peptide capable of simultaneously stabilizing both α-helix and β-sheet structures. Our designed double-stapled peptide, named DSARTC, specifically targets the androgen receptor (AR) DNA binding domain and MDM2 as E3 ligase. Serving as a peptide-based PROTAC (proteolysis-targeting chimera), DSARTC exhibits the ability to degrade both the full-length AR and AR-V7. Molecular dynamics simulations and circular dichroism analysis validate the successful constraint of both secondary structures, demonstrating that DSARTC is a "first-in-class" heterogeneous-conformational double-stapled peptide drug candidate. Compared to its linear counterpart, DSARTC displays enhanced stability and an improved cell penetration ability. In an enzalutamide-resistant prostate cancer animal model, DSARTC effectively inhibits tumor growth and reduces the levels of both AR and AR-V7 proteins. These results highlight the potential of DSARTC as a more potent and specific peptide PROTAC for AR-V7. Furthermore, our findings provide a promising strategy for expanding the design of staple peptide-based PROTAC drugs, targeting a wide range of "undruggable" transcription factors.