Proteolysis-targeting chimeras in biotherapeutics: Current trends and future applications

Recent advances in PROTAC-based antiviral and antibacterial therapeutics

By harnessing the ubiquitin proteasome system, proteolysis targeting chimeras (PROTACs) have emerged as a highly promising strategy in drug design for degrading pathogenic proteins. The extensive benefits of PROTAC technology have facilitated its swift and extensive adoption, resulting in numerous PROTACs advancing to clinical trials, and most of them was used for cancers, neurodegenerative diseases, and immune disorders in clinical trials. A number of antiviral PROTACs and antibacterial PROTACs have been developed, exhibiting encouraging bioactivities against various pathogenic viruses and bacterial. Herein, this review summarizes recent advances in PROTAC technology for antiviral and antibacterial drugs, we also provided an overview of the current state of PROTAC clinical trials and detailed the crystal structures of PROTAC in complex with its target protein. Hopefully, this review will contribute to the development of novel antiviral and antibacterial drugs through the utilization of PROTAC technology.

Preparation and Characterization of Ternary Complexes to Improve the Solubility and Dissolution Performance of a Proteolysis-Targeting Chimera Drug

Background/Objectives: Proteolysis-targeting chimeras (PROTACs) have shown significant potential in the treatment of intractable diseases. However, their clinical applications are limited by poor water solubility and permeability. In this study, the cyclodextrin inclusion method was employed for the first time to prepare the PROTAC-CD complex with the aim of improving the dissolution of a PROTAC drug (LC001). Methods: Initially, sulfobutyl ether-β-cyclodextrin (SBE-β-CD) was selected to improve the solubility of LC001. The polymer TPGS was screened based on the phase solubility method to enhance the efficiency of complexation and solubilization capacity, and its ratio with SBE-β-CD was optimized. The ternary complex was prepared by lyophilization with an SBE-β-CD/TPGS molar ratio of 1:0.03. Differential scanning calorimetry, powder X-ray diffraction, and scanning electron microscopy results confirmed the formation of an amorphous complex. Fourier-transform infrared and molecular docking simulations indicated the formation of hydrogen bond interactions between components. Results: The results showed that the ternary complexes significantly improved the dissolution rate and release amount of LC001 in PBS (pH 6.8) and were unaffected by changes in gastric pH compared to the binary complexes and physical mixtures. The lack of crystal structure in the lyophilized particles and the formation of nano aggregates in solution may be the reasons for the improved dissolution of the ternary complex. Conclusions: In conclusion, the addition of TPGS to the LC001-SBE-β-CD binary system has a synergistic effect on improving the solubility and dissolution of LC001. This ternary complex is a promising formulation for enhancing the dissolution of LC001.

PROTAC unleashed: Unveiling the synthetic approaches and potential therapeutic applications

Proteolysis-Targeting Chimeras (PROTACs) are a novel class of bifunctional small molecules that alter protein levels by targeted degradation. This innovative approach uses the ubiquitin-proteasome system to selectively eradicate disease-associated proteins, providing a novel therapeutic strategy for a wide spectrum of diseases. This review delineates detailed synthetic approaches involved in PROTAC building blocks, including the ligand and protein binding parts, linker attached structural components of PROTACs and the actual PROTAC molecules. Furthermore, the recent advancements in PROTAC-mediated degradation of specific oncogenic and other disease-associated proteins, such as those involved in neurodegenerative, antiviral, and autoimmune diseases, were also discussed. Additionally, we described the current landscape of PROTAC clinical trials and highlighted key studies that underscore the translational potential of this emerging therapeutic modality. These findings demonstrate the versatility of PROTACs in modulating the levels of key proteins involved in various severe diseases.

Discovery of FLT3-targeting PROTACs with potent antiproliferative activity against acute myeloid leukemia cells harboring FLT3 mutations

Acute myeloid leukemia (AML) patients harboring Fms-like tyrosine kinase 3 (FLT3) mutations often suffer from poor prognosis and relapse. Targeted protein degradation utilizing proteolysis targeting chimeras (PROTACs) is considered as a novel therapeutic strategy in drug discovery and may be a promising modality to target FLT3 mutations for the development of potent anti-AML drugs. Herein, a kind of FLT3-targeting PROTACs was rationally developed based on a FLT3 inhibitor previously reported by us. The representative compound 35 showed potent and selective antiproliferative activities against AML cells harboring FLT3 mutations. Western blot assay demonstrated that compound 35 effectively induced the degradation of FLT3-ITD and decreased the phosphorylation levels of FLT3-ITD, AKT, STAT5 and ERK in MV4-11 cells in a dose-dependent manner. Flow cytometry analysis illustrated that compound 35 strongly induced apoptosis and cell cycle arrest in MV4-11 cells in a dose-dependent manner. Moreover, compound 35 displayed favorable metabolic stability in in-vitro liver microsomes studies. Comparative molecular dynamic (MD) simulation studies further elucidated the underlying mechanism of compound 35 to stabilize the dynamic ensemble of the FLT3-compound 35-cereblon (CRBN) ternary complex. Taken together, compound 35 could serve as a lead molecule for developing FLT3 degraders against AML.

Targeted degrader technologies as prospective SARS-CoV-2 therapies

COVID-19 remains a severe public health threat despite the WHO declaring an end to the public health emergency in May 2023. Continual development of SARS-CoV-2 variants with resistance to vaccine-induced or natural immunity necessitates constant vigilance as well as new vaccines and therapeutics. Targeted protein degradation (TPD) remains relatively untapped in antiviral drug discovery and holds the promise of attenuating viral resistance development. From a unique structural design perspective, this review covers antiviral degrader merits and challenges by highlighting key coronavirus protein targets and their co-crystal structures, specifically illustrating how TPD strategies can refine existing SARS-CoV-2 3CL protease inhibitors to potentially produce superior protease-degrading agents.

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.