Discovery of intracellular self-assembly protein degraders driven by tumor-specific activatable bioorthogonal reaction

Signature of click chemistry in advanced techniques for cancer therapeutics

Click chemistry has made a revolution in the field of chemical biology owing to its high efficiency, specificity, and mild reaction conditions. The copper(i)-catalyzed azide-alkyne cycloaddition (CuAAC) and strain-promoted [3 + 2] azide-alkyne cycloaddition (SPAAC) stand out as the most popular click reactions that construct a stable triazole ring by reacting an azide with an alkyne. These two reactions represent an ideal choice for biological applications due to its specificity, reliability, and biocompatibility. As a powerful modular synthetic approach for creating new molecular entities, it has seen increasing use in anticancer drug discovery. The present "state of the art" focuses mainly on the signature of click chemistry (CuAAC and SPAAC) in advanced techniques for cancer therapeutics, which includes cancer immunotherapy, antibody-drug conjugates, development of proteolysis-targeting chimeras, targeted dual-agent combination therapy for cancer, exosome modification for cancer therapy, and photodynamic therapy (PDT).

In Vivo Self-Assembly of PROTACs by Bioorthogonal Chemistry for Precision Cancer Therapy

Proteolysis targeting chimeras (PROTACs) hold immense promise for targeted protein degradation; however, challenges such as off-target effects, poor drug-likeness properties, and the "hook effect" remain. This study introduces Nano-Click-formed PROTACs (Nano-CLIPTACs) for precise tumor protein degradation in vivo. Traditional PROTACs with high molecular weight were first divided into two smaller druglike precursors capable of self-assembling to form functional PROTACs through a bioorthogonal reaction. Then, optimal CLIPTACs precursors (W4 and Z2) were encapsulated individually into cyclic RGDfC-peptide-modified liposomes to prepare Nano-CLIPTACs, enabling tumor-targeted delivery and subsequent in situ self-assembly to form PROTACs WZ42 within tumor cells. The degradation abilities of Nano-CLIPTACs in vitro and in vivo were further verified using a key oncology target, anaplastic lymphoma kinase (ALK), validating the safety, efficacy and "anti-hook effect" of this strategy. Overall, Nano-CLIPTACs represent a critical step towards the clinical translation of PROTACs technology for precise targeted anti-cancer therapies.

Utilizing Alkyne-Nitrone Cycloaddition for the Convenient Multi-Component Assembly of Protein Degraders and Biological Probes

Proteolysis-targeting chimeras (PROTACs) have become a popular therapeutic strategy, and the development of multi-functional PROTACs has added complexity to their synthetic process. Although click reactions have been widely applied to prepare highly functionalized biomolecules, most of them are limited to two-component reactions, restricting the creation of more complex structures. Here, we developed a convenient multi-component assembly strategy via strain-promoted alkyne-nitrone cycloaddition (SPANC), which can be extended to a 3-component reaction when combined with nitrone formation. Using the 2-component assembly, we demonstrated the targeted protein degradation with both preassembled and in-cell assembled PROTACs. This strategy was also applied to facilitate the screening of E3 ligases in PROTACs and the preparation of various biological probes. Moreover, the 3-component assembly, via sequential nitrone formation and SPANC, enabled the synthesis of trifunctional 3-component PROTACs. The N-substituent, serving as an additional functional moiety, was designed as a photocage for sterically controlling PROTAC activity. The 3-component assembly can be further modified to provide additional control or enhance the cell-targeting ability of PROTACs. In short, our multi-component SPANC assembly strategy offers a modular and versatile synthetic platform for creating multi-functional PROTACs and biological probes.

Conditional PROTAC: Recent Strategies for Modulating Targeted Protein Degradation

Proteolysis-targeting chimeras (PROTACs) have emerged as a promising technology for inducing targeted protein degradation by leveraging the intrinsic ubiquitin-proteasome system (UPS). While the potential druggability of PROTACs toward undruggable proteins has accelerated their rapid development and the wide-range of applications across diverse disease contexts, off-tissue effects and side-effects of PROTACs have recently received attentions to improve their efficacy. To address these issues, spatial or temporal target protein degradation by PROTACs has been spotlighted. In this review, we explore chemical strategies for modulating protein degradation in a cell type-specific (spatio-) and time-specific (temporal-) manner, thereby offering insights for expanding PROTAC applications to overcome the current limitations of target protein degradation strategy.

Discovery of novel penetrating peptides able to target human leukemia and lymphoma for enhanced PROTAC delivery

Proteolysis targeting chimeras (PROTAC) are bifunctional chimeric molecules capable of directly degrading binding proteins through the ubiquitin-proteasome pathway. PROTACs have demonstrated significant potential in overcoming drug resistance and targeting previously untreatable targets. However, several limitations still need to be addressed, including their high molecular weight resulting in poor membrane permeability and bioavailability. In this study, we proposed that cancer-targeted penetrating peptides could enhance the cell permeability of PROTACs. We developed 26 novel targeted penetrating peptides for leukemia and lymphoma cells, among which C9C-f(3Bta) and Cyclo-C9C-R exhibited superior membrane permeability, targetability, and stability. By combining C9C-f(3Bta) and Cyclo-C9C-R with IMA-PROTAC, we effectively enhanced the anti-proliferative activity of IMA-PROTAC, facilitated degradation of Bcr-Abl protein in K562 cells, and reduced downstream STAT5 phosphorylation. Furthermore, the combined application promoted cell apoptosis while blocking G1 phase progression. HPLC-MRM-MS revealed that the combination of C9C-f(3Bta) or Cyclo-C9C-R with IMA-PROTAC significantly enhanced intracellular IMA-PROTAC content. In summary, our proof-of-concept study validated the hypothesis that combining PROTACs with targeted penetrating peptides can improve protein degradation efficiency as well as anti-proliferative capabilities.

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.

Recent advances and future directions on small molecule VEGFR inhibitors in oncological conditions

"A journey of mixed emotions" is a quote that best describes the progress chart of vascular endothelial growth factor receptor (VEGFR) inhibitors as cancer therapeutics in the last decade. Exhilarated with the Food and Drug Administration (FDA) approvals of numerous VEGFR inhibitors coupled with the annoyance of encountering the complications associated with their use, drug discovery enthusiasts are on their toes with an unswerving determination to enhance the rate of translation of VEGFR inhibitors from preclinical to clinical stage. The recently crafted armory of VEGFR inhibitors is a testament to their growing dominance over other antiangiogenic therapies for cancer treatment. This review perspicuously underscores the earnest attempts of the researchers to extract the antiproliferative potential of VEGFR inhibitors through the design of mechanistically diverse structural assemblages. Moreover, this review encompasses sections on structural/molecular properties and physiological functions of VEGFR, FDA-approved VEGFR inhibitors, and hurdles restricting the activity range/clinical applicability of VEGFR targeting antitumor agents. In addition, tactics to overcome the limitations of VEGFR inhibitors are discussed. A clear-cut viewpoint transmitted through this compilation can provide practical directions to push the cart of VEGFR inhibitors to advanced-stage clinical investigations in diverse malignancies.

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.

Click chemistry in the development of PROTACs

Proteolysis-targeting chimeras or PROTACs are hetero-bifunctional molecules designed to mediate the disposal of a target protein via recruitment of the ubiquitination-proteasome degradation machinery. Because of the chimeric nature of such molecules, their synthesis requires a key step of "assembling" whether in the lab or in situ. Furthermore, targeted PROTACs often are hetero-trifunctional and require a second "assembling" step. Click chemistry has the unique advantages of tethering two or more molecular entities of choice under near physiological conditions and therefore has been applied to the development of PROTACs in various ways. This review provides a succinct summary of this field with a critical analysis of various factors that need to be considered for optimal results. Specifically, we examine issues including applications of click chemistry in in situ assembly for improved delivery, conjugation with a targeting group for selectivity, rapid synthesis for linker optimization, and lysosomal degradation of extracellular and membrane-associated proteins. We also examine reaction kinetics issues whenever possible or warranted.

Current advances and development strategies of orally bioavailable PROTACs

Proteolysis-targeting chimeras (PROTACs) have been an area of intensive research with the potential to extend drug space not target to traditional molecules. In the last half decade, we have witnessed several PROTACs initiated phase I/II/III clinical trials, which inspired us a lot. However, the structure of PROTACs beyond "rule of 5" resulted in developing PROTACs with acceptable oral pharmacokinetic (PK) properties remain one of the biggest bottleneck tasks. Many reports have demonstrated that it is possible to access orally bioavailable PROTACs through rational ligand and linker modifications. In this review, we systematically reviewed and highlighted the most recent advances in orally bioavailable PROTACs development, especially focused on the medicinal chemistry campaign of discovery process and in vivo oral PK properties. Moreover, the constructive strategies for developing oral PROTACs were proposed comprehensively. Collectively, we believe that the strategies summarized here may provide references for further development of oral PROTACs.

Click Chemistry and Targeted Degradation: A Winning Combination for Medicinal Chemists?

Click chemistry is universally recognized as a powerful strategy for the fast and precise assembly of diverse building blocks. Targeted Protein Degradation (TPD) is a new therapeutic modality based on heterobifunctional small-molecule degraders that provides new opportunities to medicinal chemists dealing with undruggable targets and incurable diseases. Here, we highlight how very recently the TPD field and that of click chemistry have merged, opening up the possibility for fine-tuning the properties of a degrader, chemically assembled through a "click" synthesis. By reviewing concrete examples, we want to provide the reader with the insight that the application of click and bioorthogonal chemistry in the TDP field may be a winning combination.