PROteolysis TArgeting Chimeras (PROTACs) - Past, present and future

A novel FAK-degrading PROTAC molecule exhibited both anti-tumor activities and efficient MDR reversal effects

FAK (focal adhesion kinase) is widely involved in cancer growth and drug resistance development. Thus, FAK inhibition has emerged as an effective strategy for tumor treatment both as a monotherapy or in combination with other treatments. But the current FAK inhibitors mainly concentrate on its kinase activity, overlooking the potential significance of FAK scaffold proteins. In this study we employed the PROTAC technology, and designed a novel PROTAC molecule F2 targeting FAK based on the FAK inhibitor IN10018. F2 exhibited potent inhibitory activities against 4T1, MDA-MB-231, MDA-MB-468 and MDA-MB-435 cells with IC50 values of 0.73, 1.09, 5.84 and 3.05 μM, respectively. On the other hand, F2 also remarkably reversed the multidrug resistance (MDR) in HCT8/T, A549/T and MCF-7/ADR cells. Both the effects of F2 were stronger than the FAK inhibitor IN10018. To our knowledge, F2 was the first reported FAK-targeted PROTAC molecule exhibiting reversing effects on chemotherapeutic drug resistance, and its highest reversal fold could reach 158 times. The anti-tumor and MDR-reversing effects of F2 might be based on its inhibition on AKT (protein kinase B, PKB) and ERK (extracellular signal-regulated kinase) signaling pathways, as well as its impact on EMT (epithelial-mesenchymal transition). Furthermore, we found that F2 could reduce the protein level of P-gp in HCT8/T cells, thereby contributing to reverse drug resistance from another perspective. Our results will boost confidence in future research focusing on targeting FAK and encourage further investigation of PROTAC with potent in vivo effects.

Targeted degradation of specific TEAD paralogs by small molecule degraders

The transcription factors, TEAD1-4 together with their co-activator YAP/TAZ function as key downstream effectors of the Hippo pathway. Hyperactivation of TEAD-YAP/TAZ activity is observed in many human cancers. TEAD1-4 possess distinct physiological and pathological functions, with conserved sequences and structures. Targeting specific isoforms within TEAD1-4 can serve as valuable chemical probes for investigating TEAD-related functions in both development and diseases. We report the TEAD-targeting proteolysis targeting chimera (PROTAC), HC278, which achieves effective and specific targeting of TEAD1 and TEAD3 at low nanomolar doses while weakly degrading TEAD2 and TEAD4 at higher doses. Proteomic analysis of >6000 proteins confirmed their highly selective TEAD1 and TEAD3 degradation. Consistently, HC278 can suppress the proliferation of YAP-dependent NCI-H226 mesothelioma cells. Mechanistic exploration revealed that both CRBN and proteasome systems are involved in the TEAD degradation induced by HC278. Moreover, RNA-seq and Gene Set Enrichment Analysis (GSEA) revealed that the YAP signature genes such as CTGF, CYR61, and ANKRD1 are significantly downregulated by HC278 treatment. Overall, HC278 serves as a valuable chemical tool for unraveling the intricate biological roles of TEAD1 and TEAD3 and holds the potential as a lead compound for developing targeted therapy for TEAD1/3-driven pathologies.

Translational modelling to predict human pharmacokinetics and pharmacodynamics of a Bruton's tyrosine kinase-targeted protein degrader BGB-16673

BACKGROUND AND PURPOSE

Bifunctional small molecule degraders, which link the target protein with E3 ubiquitin ligase, could lead to the efficient degradation of the target protein. BGB-16673 is a Bruton's tyrosine kinase (BTK) degrader. A translational PK/PD modelling approach was used to predict the human BTK degradation of BGB-16673 from preclinical in vitro and in vivo data.

EXPERIMENTAL APPROACH

A simplified mechanistic PK/PD model was used to establish the correlation between the in vitro and in vivo BTK degradation by BGB-16673 in a mouse model. Human and mouse species differences were compared using the parameters generated from in vitro human or mouse blood, and human or mouse serum spiked TMD-8 cells. Human PD was then predicted using the simplified mechanistic PK/PD model.

KEY RESULTS

BGB-16673 showed potent BTK degradation in mouse whole blood, human whole blood, and TMD-8 tumour cells in vitro. Furthermore, BGB-16673 showed BTK degradation in a murine TMD-8 xenograft model in vivo. The PK/PD model predicted human PD and the observed BTK degradation in clinical studies both showed robust BTK degradation in blood and tumour at clinical dose range.

CONCLUSION AND IMPLICATIONS

The presented simplified mechanistic model with reduced number of model parameters is practically easier to be applied to research projects compared with the full mechanistic model. It can be used as a tool to better understand the PK/PD behaviour for targeted protein degraders and increase the confidence when moving to the clinical stage.

Selective degradation of mutant FMS-like tyrosine kinase-3 requires BIM-dependent depletion of heat shock proteins

Internal tandem duplications in the FMS-like tyrosine kinase-3 (FLT3-ITD) are common mutations in acute myeloid leukemia (AML). Proteolysis-targeting chimeras (PROTACs) that induce proteasomal degradation of mutated FLT3 emerge as innovative pharmacological approach. Molecular mechanisms that control targeted proteolysis beyond the ubiquitin-proteasome-system are undefined and PROTACs are the only known type of FLT3 degraders. We report that the von-Hippel-Lindau ubiquitin-ligase based FLT3 PROTAC MA49 (melotinib-49) and the FLT3 hydrophobic tagging molecule MA50 (halotinib-50) reduce endoplasmic reticulum-associated, oncogenic FLT3-ITD but spare FLT3. Nanomolar doses of MA49 and MA50 induce apoptosis of human leukemic cell lines and primary AML blasts with FLT3-ITD (p < 0.05-0.0001), but not of primary hematopoietic stem cells and differentiated immune cells, FLT3 wild-type cells, retinal cells, and c-KIT-dependent cells. In vivo activity of MA49 against FLT3-ITD-positive leukemia cells is verified in a Danio rerio model. The degrader-induced loss of FLT3-ITD involves the pro-apoptotic BH3-only protein BIM and a previously unidentified degrader-induced depletion of protein-folding chaperones. The expression levels of HSP90 and HSP110 correlate with reduced AML patient survival (p < 0.1) and HSP90, HSP110, and BIM are linked to the expression of FLT3 in primary AML cells (p < 0.01). HSP90 suppresses degrader-induced FLT3-ITD elimination and thereby establishes a mechanistically defined feed-back circuit.

Novel PROTAC probes targeting KDM3 degradation to eliminate colorectal cancer stem cells through inhibition of Wnt/β-catenin signaling

It has been demonstrated that the KDM3 family of histone demethylases (KDM3A and KDM3B) epigenetically control the functional properties of colorectal cancer stem cells (CSCs) through Wnt/β-catenin signaling. Meanwhile, a broad-spectrum histone demethylase inhibitor, IOX1, suppresses Wnt-induced colorectal tumorigenesis predominantly through inhibiting the enzymatic activity of KDM3. In this work, several cereblon (CRBN)-recruiting PROTACs with various linker lengths were designed and synthesized using IOX1 as a warhead to target KDM3 proteins for degradation. Two of the synthesized PROTACs demonstrated favorable degradation profile and selectivity towards KDM3A and KDM3B. Compound 4 demonstrated favorable in vitro metabolic profile in liver enzymes as well as no hERG-associated cardiotoxicity. Compound 4 also showed dramatic ability in suppressing oncogenic Wnt signaling to eliminate colorectal CSCs and inhibit tumor growth, with around 10- to 35-fold increased potency over IOX1. In summary, this study suggests that PROTACs provide a unique molecular tool for the development of novel small molecules from the IOX1 skeleton for selective degradation of KDM3 to eliminate colorectal CSCs via suppressing oncogenic Wnt signaling.

Discovery of novel 20S proteasome subunit β5 PROTAC degraders as potential therapeutics for pharyngeal carcinoma and Bortezomib-resistant multiple myeloma

Resistance to proteasome inhibitors like Bortezomib is a major challenge in the treatment of multiple myeloma (MM). Proteolysis targeting chimeras (PROTACs), an emerging therapeutic approach that induces selective degradation of target proteins, offer a promising solution to overcome drug resistance. In this study, we designed and synthesized novel small-molecule PROTACs that induce 20S proteasome subunit β5 degradation as a strategy to overcome Bortezomib resistance. These 20S proteasome subunit β5 PROTACs demonstrated considerable binding affinity to 20S proteasome subunit β5 and cereblon (CRBN), effectively induced 20S proteasome subunit β5 degradation, and exhibited potent antiproliferative activity against a panel of cancer cell lines. Notably, PROTACs 12f and 14 displayed robust antitumor effects against both the pharyngeal carcinoma cell line FaDu and the Bortezomib-resistant MM cell line KM3/BTZ in vitro and in vivo with excellent safety profiles. Taken together, our findings highlight the potential of PROTACs 12f and 14 as novel 20S proteasome subunit β5-degrading agents for the treatment of pharyngeal carcinoma and overcoming Bortezomib resistance in MM.

Discovery of a potent and selective JAK1-targeting PROTAC degrader with anti-tumor activities

Aberrant activation of the JAK-STAT pathway is evident in various human diseases including cancers. Proteolysis targeting chimeras (PROTACs) provide an attractive strategy for developing novel JAK-targeting drugs. Herein, a series of CRBN-directed JAK-targeting PROTACs were designed and synthesized utilizing a JAK1/JAK2 dual inhibitor-momelotinib as the warhead. The most promising compound 10c exhibited both good enzymatic potency and cellular antiproliferative effects. Western blot analysis revealed that compound 10c effectively and selectively degraded JAK1 in a proteasome-dependent manner (DC50 = 214 nM). Moreover, PROTAC 10c significantly suppressed JAK1 and its key downstream signaling. Together, compound 10c may serve as a novel lead compound for antitumor drug discovery.

Versatile Split-and-Mix Liposome PROTAC Platform for Efficient Degradation of Target Protein In Vivo

PROTAC (Proteolysis TArgeting Chimeras) is a promising therapeutic approach for targeted protein degradation that recruits an E3 ubiquitin ligase to a specific protein of interest (POI), leading to its degradation by the proteasome. Recently, we developed a novel split-and-mix PROTAC system based on liposome self-assembly (LipoSM-PROTAC) which could achieve target protein degradation at comparable concentrations comparable to small molecules. In this study, we expanded protein targets based on the LipoSM-PROTAC platform and further examined its therapeutic effects in vivo. Notably, this platform could efficiently degrade the protein level of MEK1/2 in A375 cells or Alk in NCI-H2228 cells and display obvious tumor inhibition (60-70% inhibition rate) with negligible toxicity. This study further proved the LipoSM-PROTAC's application potentials.

Distinct Amino Acid-Based PROTACs Target Oncogenic Kinases for Degradation in Non-Small Cell Lung Cancer (NSCLC)

Proteolysis-targeting chimeras (PROTACs) selectively eliminate detrimental proteins by exploiting the ubiquitin-proteasome system (UPS), representing a promising therapeutic strategy against various diseases. Effective adaptations of degradation signal sequences and E3 ligases for PROTACs remain limited. Here, we employed three amino acids─Gly, Pro, and Lys─as the ligand to recruit the corresponding E3 ligases: CRL2ZYG11B/ZER1, GID4, and UBRs, to degrade EML4-ALK and mutant EGFR, two oncogenic drivers in NSCLC. We found that the extent of EML4-ALK and EGFR reduction can be easily fine-tuned by using different degradation signals. These amino acid-based PROTACs, termed AATacs, hindered proliferation and induced cell cycle arrest and apoptosis of NSCLC cells in vitro. Compared to other PROTACs, AATacs are small, interchangeable but with different degradation efficiency. Our study further expands the repertoire of E3 ligases and their ligands for PROTAC application, improving the versatility and utility of targeted protein degradation for therapeutic purposes.

Discovery of PRMT3 Degrader for the Treatment of Acute Leukemia

Protein arginine methyltransferase 3 (PRMT3) plays an important role in gene regulation and a variety of cellular functions, thus, being a long sought-after therapeutic target for human cancers. Although a few PRMT3 inhibitors are developed to prevent the catalytic activity of PRMT3, there is little success in removing the cellular levels of PRMT3-deposited ω-NG,NG-asymmetric dimethylarginine (ADMA) with small molecules. Moreover, the non-enzymatic functions of PRMT3 remain required to be clarified. Here, the development of a first-in-class MDM2-based PRMT3-targeted Proteolysis Targeting Chimeras (PROTACs) 11 that selectively reduced both PRMT3 protein and ADMA is reported. Importantly, 11 inhibited acute leukemia cell growth and is more effective than PRMT3 inhibitor SGC707. Mechanism study shows that 11 induced global gene expression changes, including the activation of intrinsic apoptosis and endoplasmic reticulum stress signaling pathways, and the downregulation of E2F, MYC, oxidative phosphorylation pathways. Significantly, the combination of 11 and glycolysis inhibitor 2-DG has a notable synergistic antiproliferative effect by further reducing ATP production and inducing intrinsic apoptosis, thus further highlighting the potential therapeutic value of targeted PRMT3 degradation. These data clearly demonstrated that degrader 11 is a powerful chemical tool for investigating PRMT3 protein functions.

Discovery of a NCOA4 Degrader for Labile Iron-Dependent Ferroptosis Inhibition

Ferroptosis, a distinctive form of programmed cell death, has been implicated in numerous pathological conditions, and its inhibition is considered a promising therapeutic strategy. Currently, there is a scarcity of efficient antagonists for directly regulating intracellular ferrous iron. Ferritinophagy, an essential process for supplying intracellular labile iron, relies on nuclear receptor coactivator 4 (NCOA4), a selective autophagy receptor for the ferritin iron storage complex, thus playing a pivotal role in ferritinophagy. In this study, we reported a novel von Hippel-Lindau-based NCOA4 degrader, V3, as a potent ferroptosis inhibitor with an intracellular ferrous iron inhibition mechanism. V3 significantly reduced NCOA4 levels and downregulated intracellular ferrous iron (Fe2+) levels, thereby effectively suppressing ferroptosis induced by multiple pathways within cells and alleviating liver damage. This research presents a chemical knockdown tool targeting NCOA4 for further exploration into intracellular ferrous iron in ferroptosis, offering a promising therapeutic avenue for ferroptosis-related acute liver injury.

Regulation of post-translational modification of PD-L1 and associated opportunities for novel small-molecule therapeutics

PD-L1 is overexpressed on the surface of tumor cells and binds to PD-1, resulting in tumor immune escape. Therapeutic strategies to target the PD-1/PD-L1 pathway involve blocking the binding. Immune checkpoint inhibitors have limited efficacy against tumors because PD-L1 is also present in the cytoplasm. PD-L1 of post-translational modifications (PTMs) have uncovered numerous mechanisms contributing to carcinogenesis and have identified potential therapeutic targets. Therefore, small molecule inhibitors can block crucial carcinogenic signaling pathways, making them a potential therapeutic option. To better develop small molecule inhibitors, we have summarized the PTMs of PD-L1. This review discusses the regulatory mechanisms of small molecule inhibitors in carcinogenesis and explore their potential applications, proposing a novel approach for tumor immunotherapy based on PD-L1 PTM.

CDK9 targeting PROTAC L055 inhibits ERα-positive breast cancer

Breast cancer is one of the most prevalent malignancies affecting women worldwide, underscoring the urgent need for more effective and specific treatments. Proteolysis-targeting chimeras (PROTACs) have emerged as a promising strategy to develop new lead compounds by selectively targeting oncoproteins for degradation. In this study, we designed, synthesized and evaluated a CRBN-based PROTAC, L055, which targets CDK9. Our findings demonstrate that L055 effectively inhibits the proliferation, induces cell cycle arrest, and decreases the survival of ERα-positive breast cancer cells in vitro. L055 specifically binds to CDK9, facilitating its degradation via the CRBN-dependent proteasomal pathway. Additionally, L055 suppressed the growth of organoids and tumors derived from T47D and MCF7 cells in nude mice. Thus, L055 represents a potential novel therapeutic agent for ERα-positive breast cancer and potentially other malignancies.

Discovery of Potent and Selective G9a Degraders for the Treatment of Pancreatic Cancer

G9a, which was initially identified as a histone H3 Lys9 (H3K9) methyltransferase, is potentially an attractive therapeutic target for human cancers. Despite its importance, there is no available selective G9a chemical probe because its homologous protein GLP shares approximately 80% of its sequence with G9a. The development of G9a chemical probes with high selectivity for G9a over GLP is a big challenge but is extremely valuable for understanding G9a-related biology. Herein, we developed a first-in-class selective G9a degrader G9D-4, which induced a dose- and time-dependent G9a degradation without degradation of GLP. G9D-4 exhibited effective antiproliferative activities in a panel of pancreatic cancer cell lines and was able to sensitize KRASG12D mutant pancreatic cancer cells to KRASG12D inhibitor MRTX1133. These data clearly demonstrated the practicality and importance of a selective G9a degrader as a preliminary chemical probe suitable for understanding G9a-related biology and a promising strategy for the treatment of pancreatic cancer.

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.

Quantitative Measurement of Rate of Targeted Protein Degradation

Targeted protein degradation (TPD) is a therapeutic approach that leverages the cell's natural machinery to degrade targets instead of inhibiting them. This is accomplished by using mono- or bifunctional small molecules designed to induce the proximity of target proteins and E3 ubiquitin ligases, leading to ubiquitination and subsequent proteasome-dependent degradation of the target. One of the most significant attributes of the TPD approach is its proposed catalytic mechanism of action, which permits substoichiometric exposure to achieve the desired pharmacological effects. However, apart from one in vitro study, studies supporting the catalytic mechanism of degraders are largely inferred based on potency. A more comprehensive understanding of the degrader catalytic mechanism of action can help aspects of compound development. To address this knowledge gap, we developed a workflow for the quantitative measurement of the catalytic rate of degraders in cells. Comparing a selective and promiscuous BTK degrader, we demonstrate that both compounds function as efficient catalysts of BTK degradation, with the promiscuous degrader exhibiting faster rates due to its ability to induce more favorable ternary complexes. By leveraging computational modeling, we show that the catalytic rate is highly dynamic as the target is depleted from cells. Further investigation of the promiscuous kinase degrader revealed that the catalytic rate is a better predictor of optimal degrader activity toward a specific target compared to degradation magnitude alone. In summary, we present a versatile method for mapping the catalytic activity of any degrader for TPD in cells.

Discovery of a Highly Potent, Selective and Efficacious USP7 Degrader for the Treatment of Acute Lymphoblastic Leukemia

USP7 is an attractive therapeutic target for cancers, especially for acute lymphoblastic leukemia (ALL) with wild-type p53. Herein, we report the discovery of XM-U-14 as a highly potent, selective and efficacious USP7 proteolysis-targeting chimera degrader. XM-U-14 achieves DC50 values of 0.74 nM and Dmax of 93% in inducing USP7 degradation in RS4;11 cell lines, and also significantly inhibits ALL cell growth. XM-U-14 even at 5 mg/kg dosed daily effectively inhibits RS4;11 tumor growth with 64.7% tumor regressions and causes no signs of toxicity in mice. XM-U-14 is a promising USP7 degrader for further optimization for ALL treatment.

Ultrasound-Activated PROTAC Prodrugs Overcome Immunosuppression to Actuate Efficient Deep-Tissue Sono-Immunotherapy in Orthotopic Pancreatic Tumor Mouse Models

The degradation of oncoproteins mediated by proteolysis-targeting chimera (PROTAC) has emerged as a potent strategy in cancer therapy. However, the clinical application of PROTACs is hampered by challenges such as poor water solubility and off-target adverse effects. Herein, we present an ultrasound (US)-activatable PROTAC prodrug termed NPCe6+PRO for actuating efficient sono-immunotherapy in a spatiotemporally controllable manner. Specifically, US irradiation, which exhibits deep-tissue penetration capability, results in Ce6-mediated generation of ROS, facilitating sonodynamic therapy (SDT) and inducing immunogenic cell death (ICD). Simultaneously, the generated ROS cleaves the thioketal (TK) linker through a ROS-responsive mechanism, realizing the on-demand activation of the PROTAC prodrug in deep tissues. This prodrug activation results in the degradation of the target protein BRD4, while simultaneously reversing the upregulation of PD-L1 expression associated with the SDT process. In the orthotopic mouse model of pancreatic tumors, NPCe6+PRO effectively suppressed tumor growth in conjunction with US stimulation.

IMHB-Mediated Chameleonicity in Drug Design: A Focus on Structurally Related PROTACs

Molecular chameleonicity may enable compounds to compensate for the unfavorable ADME properties typically associated with complex molecules, such as PROTACs. Here we present a few in silico strategies to implement chameleonicity considerations in drug design. Initially, we identified six structurally related CRBN-based PROTACs targeting BET proteins and experimentally verified whether chameleonicity is needed to obtain an acceptable physicochemical profile. Then, we utilized experimental data to validate our novel computational strategies based on tools crafted to encompass a spectrum of complexities and innovative features. After confirming that the formation of IMHBs is the primary driving factor behind chameleonicity, we initially utilized conformational sampling data to define cChameCS, an IMHB-mediated, simple, and rapid chameleonicity predictor index suitable for early drug discovery. Subsequently, we identified dynamic IMHB patterns relevant to chameleonicity through molecular dynamics simulations. Finally, we proposed a workflow for designing structurally related chameleonic PROTACs of potential application in the lead optimization process.

Application of machine learning models for property prediction to targeted protein degraders

Machine learning (ML) systems can model quantitative structure-property relationships (QSPR) using existing experimental data and make property predictions for new molecules. With the advent of modalities such as targeted protein degraders (TPD), the applicability of QSPR models is questioned and ML usage in TPD-centric projects remains limited. Herein, ML models are developed and evaluated for TPDs' property predictions, including passive permeability, metabolic clearance, cytochrome P450 inhibition, plasma protein binding, and lipophilicity. Interestingly, performance on TPDs is comparable to that of other modalities. Predictions for glues and heterobifunctionals often yield lower and higher errors, respectively. For permeability, CYP3A4 inhibition, and human and rat microsomal clearance, misclassification errors into high and low risk categories are lower than 4% for glues and 15% for heterobifunctionals. For all modalities, misclassification errors range from 0.8% to 8.1%. Investigated transfer learning strategies improve predictions for heterobifunctionals. This is the first comprehensive evaluation of ML for the prediction of absorption, distribution, metabolism, and excretion (ADME) and physicochemical properties of TPD molecules, including heterobifunctional and molecular glue sub-modalities. Taken together, our investigations show that ML-based QSPR models are applicable to TPDs and support ML usage for TPDs' design, to potentially accelerate drug discovery.

Phase Separation Enhanced PROTAC for Highly Efficient Protein Degradation

Biomacromolecular condensates formed via phase separation establish compartments for the enrichment of specific compositions, which is also used as a biological tool to enhance molecule condensation, thereby increasing the efficiency of biological processes. Proteolysis-targeting chimeras (PROTACs) have been developed as powerful tools for targeted protein degradation in cells, offering a promising approach for therapies for different diseases. Herein, we introduce an intrinsically disordered region in the PROTAC (denoted PSETAC), which led to the formation of droplets of target proteins in the cells and increased degradation efficiency compared with PROTAC without phase separation. Further, using a nucleus targeting intrinsically disordered domain, the PSETAC was able to target and degrade nuclear-located proteins. Finally, we demonstrated intracellular delivery of PSETAC using lipid nanoparticle-encapsulated mRNA (mRNA-LNP) for the degradation of the endogenous target protein. This study established the PSETAC mRNA-LNP method as a potentially translatable, safe therapeutic strategy for the development of clinical applications based on PROTAC.

NAMPT-targeting PROTAC and nicotinic acid co-administration elicit safe and robust anti-tumor efficacy in NAPRT-deficient pan-cancers

Nicotinamide phosphoribosyltransferase (NAMPT) catalyzes the biosynthesis of nicotinamide adenine dinucleotide (NAD+), making it a potential target for cancer therapy. Two challenges hinder its translation in the clinic: targeting the extracellular form of NAMPT (eNAMPT) remains insufficient, and side effects are observed in normal tissues. We previously utilized proteolysis-targeting chimera (PROTAC) to develop two compounds capable of simultaneously degrading iNAMPT and eNAMPT. Unfortunately, the pharmacokinetic properties were inadequate, and toxicities similar to those associated with traditional inhibitors arose. We have developed a next-generation PROTAC molecule 632005 to address these challenges, demonstrating exceptional target selectivity and bioavailability, improved in vivo exposure, extended half-life, and reduced clearance rate. When combined with nicotinic acid, 632005 exhibits safety and robust efficacy in treating NAPRT-deficient pan-cancers, including xenograft models with hematologic malignancy and prostate cancer and patient-derived xenograft (PDX) models with liver cancer. Our findings provide clinical references for patient selection and treatment strategies involving NAMPT-targeting PROTACs.

The AID2 system offers a potent tool for rapid, reversible, or sustained degradation of essential proteins in live mice

Studying essential genes required for dynamic processes in live mice is challenging as genetic perturbations are irreversible and limited by slow protein depletion kinetics. The first-generation auxin-inducible-degron (AID) system is a powerful tool for analyzing inducible protein loss in cultured cells. However, auxin administration is toxic to mice, preventing its long-term use in animals. Here, we use an optimized second-generation AID system to achieve the conditional and reversible loss of the essential centrosomal protein CEP192 in live mice. We show that the auxin derivative 5-Ph-IAA is well tolerated over two weeks and drives near-complete CEP192-mAID degradation in less than one hour in vivo. Prolonged CEP192 loss led to cell division failure and cell death in proliferative tissues. Thus, the second-generation AID system is well suited for rapid and/or sustained protein depletion in live mice, offering a valuable new tool for interrogating protein function in vivo.

Design, Synthesis, and Evaluation of BCL-2 Targeting PROTACs

BCL-2, a member of the BCL-2 protein family, is an antiapoptotic factor that regulates the intrinsic pathway of apoptosis. Due to its aberrant activity, it is frequently implicated in haematopoietic cancers and represents an attractive target for the development of therapeutics that antagonize its activity. A selective BCL-2 inhibitor, venetoclax, was approved for treating chronic lymphocytic leukaemia, acute myeloid leukemia, and other haematologic malignancies, validating BCL-2 as an anticancer target. Since then, alternative therapeutic approaches to modulate the activity of BCL-2 have been explored, such as antibody-drug conjugates and proteolysis-targeting chimeras. Despite numerous research groups focusing on developing degraders of BCL-2 family member proteins, selective BCL-2 PROTACs remain elusive, as disclosed compounds only show dual BCL-xL/BCL-2 degradation. Herein, we report our efforts to develop BCL-2 degraders by incorporating two BCL-2 binding moieties into chimeric compounds that aim to hijack one of three E3 ligases: CRBN, VHL, and IAPs. Even though our project did not result in obtaining a potent and selective BCL-2 PROTAC, our research will aid in understanding the narrow chemical space of BCL-2 degraders.

Single-domain antibody-based protein degrader for synucleinopathies

Synucleinopathies are a group of neurodegenerative diseases characterized by the accumulation of α-synuclein (α-syn) in the brain, leading to motor and neuropsychiatric symptoms. Currently, there are no known cures for synucleinopathies, and treatments mainly focus on symptom management. In this study, we developed a single-domain antibody (sdAb)-based protein degrader with features designed to enhance proteasomal degradation of α-syn. This sdAb derivative targets both α-syn and Cereblon (CRBN), a substrate-receptor for the E3-ubiquitin ligase CRL4CRBN, and thereby induces α-syn ubiquitination and proteasomal degradation. Our results indicate that this therapeutic candidate enhances proteasomal degradation of α-syn, in addition to the endogenous lysosomal degradation machinery. By promoting proteasomal degradation of α-syn, we improved clearance of α-syn in primary culture and mouse models of synucleinopathy. These findings indicate that our sdAb-based protein degrader is a promising therapeutic candidate for synucleinopathies. Considering that only a small percentage of antibodies enter the brain, more potent sdAbs with greater brain entry than whole antibodies could enhance clinical benefits of antibody-based therapies.

Discovery of as an Autophagy-Tethering Compound for the Degradation of Discoidin Domain Receptor 1

Discoidin domain receptor 1 (DDR1) is a potential target for cancer drug discovery. Although several DDR1 kinase inhibitors have been developed, recent studies have revealed the critical roles of the noncatalytic functions of DDR1 in tumor progression, metastasis, and immune exclusion. Degradation of DDR1 presents an opportunity to block its noncatalytic functions. Here, we report the discovery of the DDR1 degrader LLC355 by employing autophagosome-tethering compound technology. Compound LLC355 efficiently degraded DDR1 protein with a DC50 value of 150.8 nM in non-small cell lung cancer NCI-H23 cells. Mechanistic studies revealed compound LLC355 to induce DDR1 degradation via lysosome-mediated autophagy. Importantly, compound LLC355 potently suppressed cancer cell tumorigenicity, migration, and invasion and significantly outperformed the corresponding inhibitor 1. These results underline the therapeutic advantage of targeting the noncatalytic function of DDR1 over inhibition of its kinase activity.

Targeted Degradation of CDK9 Potently Disrupts the MYC Transcriptional Network

Cyclin-dependent kinase 9 (CDK9) coordinates signaling events that regulate RNA polymerase II (Pol II) pause-release states. It is an important co-factor for transcription factors, such as MYC, that drive aberrant cell proliferation when their expression is deregulated. CDK9 modulation offers an approach for attenuating dysregulation in such transcriptional programs. As a result, numerous drug development campaigns to inhibit CDK9 kinase activity have been pursued. More recently, targeted degradation has emerged as an attractive approach. However, comprehensive evaluation of degradation versus inhibition is still critically needed to assess the biological contexts in which degradation might offer superior therapeutic benefits. We validated that CDK9 inhibition triggers a compensatory mechanism that dampens its effect on MYC expression and found that this feedback mechanism was absent when the kinase is degraded. Importantly, CDK9 degradation is more effective than its inhibition for disrupting MYC transcriptional regulatory circuitry likely through the abrogation of both enzymatic and scaffolding functions of CDK9.

Highlights

- KI-CDK9d-32 is a highly potent and selective CDK9 degrader. - KI-CDK9d-32 leads to rapid downregulation of MYC protein and mRNA transcripts levels. - KI-CDK9d-32 represses canonical MYC pathways and leads to a destabilization of nucleolar homeostasis. - Multidrug resistance ABCB1 gene emerged as the strongest resistance marker for the CDK9 PROTAC degrader.

Tailoring Biomaterials Ameliorate Inflammatory Bone Loss

Inflammatory diseases, such as rheumatoid arthritis, periodontitis, chronic obstructive pulmonary disease, and celiac disease, disrupt the delicate balance between bone resorption and formation, leading to inflammatory bone loss. Conventional approaches to tackle this issue encompass pharmaceutical interventions and surgical procedures. Nevertheless, pharmaceutical interventions exhibit limited efficacy, while surgical treatments impose trauma and significant financial burden upon patients. Biomaterials show outstanding spatiotemporal controllability, possess a remarkable specific surface area, and demonstrate exceptional reactivity. In the present era, the advancement of emerging biomaterials has bestowed upon more efficacious solutions for combatting the detrimental consequences of inflammatory bone loss. In this review, the advances of biomaterials for ameliorating inflammatory bone loss are listed. Additionally, the advantages and disadvantages of various biomaterials-mediated strategies are summarized. Finally, the challenges and perspectives of biomaterials are analyzed. This review aims to provide new possibilities for developing more advanced biomaterials toward inflammatory bone loss.

Role of STAT3 in cancer cell epithelial‑mesenchymal transition (Review)

Since its discovery, the role of the transcription factor, signal transducer and activator of transcription 3 (STAT3), in both normal physiology and the pathology of numerous diseases, including cancer, has been extensively studied. STAT3 is aberrantly activated in different types of cancer, fulfilling a critical role in cancer progression. The biological process, epithelial‑mesenchymal transition (EMT), is indispensable for embryonic morphogenesis. During the development of cancer, EMT is hijacked to confer motility, tumor cell stemness, drug resistance and adaptation to changes in the microenvironment. The aim of the present review was to outline recent advances in knowledge of the role of STAT3 in EMT, which may contribute to the understanding of the function of STAT3 in EMT in various types of cancer. Delineating the underlying mechanisms associated with the STAT3‑EMT signaling axis may generate novel diagnostic and therapeutic options for cancer treatment.

A PROTAC Augmenter for Photo-Driven Pyroptosis in Breast Cancer

Proteolysis targeting chimera (PROTAC) has recently emerged as a promising strategy for inducing post-translational knockdown of target proteins in disease treatment. The degradation of bromodomain-containing protein 4 (BRD4), an essential nuclear protein for gene transcription, induced by PROTAC is proposed as an epigenetic approach to treat breast cancer. However, the poor membrane permeability and indiscriminate distribution of PROTAC in vivo results in low bioavailability, limiting its development and application. Herein, a nano "targeting chimera" (abbreviated as L@NBMZ) consisting of BRD4-PROTAC combined with a photosensitizer, to serve as the first augmenter for photo-driven pyroptosis in breast cancer, is developed. With excellent BRD4 degradation ability, high biosafety, and biocompatibility, L@NBMZ blocks gene transcription by degrading BRD4 through proteasomes in vivo, and surprisingly, induces the cleavage of caspase-3. This type of caspase-3 cleavage is synergistically amplified by light irradiation in the presence of photosensitizers, leading to efficient photo-driven pyroptosis. Both in vitro and in vivo outcomes demonstrate the remarkable anti-cancer efficacy of this augmenter, which significantly inhibits the lung metastasis of breast cancer in vivo. Thus, the photo-PROTAC "targeting chimera" augmenter construction strategy may pave a new way for expanding PROTAC applications within anti-cancer paradigms.

Generation of tau dephosphorylation-targeting chimeras for the treatment of Alzheimer's disease and related tauopathies

Abnormal hyperphosphorylation and accumulation of tau protein play a pivotal role in neurodegeneration in Alzheimer's disease (AD) and many other tauopathies. Selective elimination of hyperphosphorylated tau is promising for the therapy of these diseases. We have conceptualized a strategy, named dephosphorylation-targeting chimeras (DEPTACs), for specifically hijacking phosphatases to tau to debilitate its hyperphosphorylation. Here, we conducted the step-by-step optimization of each constituent motif to generate DEPTACs with reasonable effectiveness in facilitating the dephosphorylation and subsequent clearance of pathological tau. Specifically, for one of the selected chimeras, D16, we demonstrated its significant efficiency in rescuing the neurodegeneration caused by neurotoxic K18-tau seeds in vitro. Moreover, intravenous administration of D16 also alleviated tau pathologies in the brain and improved memory deficits in AD mice. These results suggested DEPTACs as targeted modulators of tau phosphorylation, which hold therapeutic potential for AD and other tauopathies.

Single-Domain Antibody-Based Protein Degrader for Synucleinopathies

Synucleinopathies are a group of neurodegenerative diseases characterized by the accumulation of α-synuclein (α-syn) in the brain, leading to motor and neuropsychiatric symptoms. Currently, there are no known cures for synucleinopathies, and treatments mainly focus on symptom management. In this study, we developed a single-domain antibody (sdAb)-based protein degrader with features designed to enhance proteasomal degradation of α-syn. This sdAb derivative targets both α-syn and Cereblon (CRBN), a substrate-receptor for the E3-ubiquitin ligase CRL4CRBN, and thereby induces α-syn ubiquitination and proteasomal degradation. Our results indicate that this therapeutic candidate enhances proteasomal degradation of α-syn, in addition to the endogenous lysosomal degradation machinery. By promoting proteasomal degradation of α-syn, we improved clearance of α-syn in primary culture and mouse models of synucleinopathy. These findings indicate that our sdAb-based protein degrader is a promising therapeutic candidate for synucleinopathies. Considering that only a small percentage of antibodies enter the brain, more potent sdAbs with greater brain entry than whole antibodies could enhance clinical benefits of antibody-based therapies.

Liposomal STAT3-Degrading PROTAC Prodrugs Promote Anti-Hepatocellular Carcinoma Immunity via Chemically Reprogramming Cancer Stem Cells

Cancer stem cells (CSCs) with hyperactivated signal transducer and activator of transcription 3 (STAT3) are a major driver of hepatocellular carcinoma (HCC). Herein, we report a nanointegrative proteolysis-targeting chimera (PROTAC)-based STAT3 degradation strategy that enables efficient chemical reprogramming of HCC-associated CSCs, which potently inhibits CSC growth while evoking anti-HCC immune responses. The PROTAC prodrug was synthesized by conjugating the STAT3 binding domain (inS3) with a thioketal-caged E3 ligase ligand (VL-TK) via an oligo(ethylene glycol) linker (OEG) with tuned length and flexibility and encapsulating it in cRGD-modified cationic liposomes for CSC-targeted delivery while facilitating their lysosomal escape. The PROTAC prodrugs were activated by the upregulated ROS levels in CSCs and efficiently degraded STAT3 for chemical reprogramming, which would not only impair their stemness features but also remodel the immunosuppressive TME into an immunosupportive state to boost anti-HCC immunity. This strategy provides an approach for improving HCC treatment in clinics.

Targeting Moonlighting Enzymes in Cancer

Moonlighting enzymes are multifunctional proteins that perform multiple functions beyond their primary role as catalytic enzymes. Extensive research and clinical practice have demonstrated their pivotal roles in the development and progression of cancer, making them promising targets for drug development. This article delves into multiple notable moonlighting enzymes, including GSK-3, GAPDH, and ENO1, and with a particular emphasis on an enigmatic phosphatase, PTP4A3. We scrutinize their distinct roles in cancer and the mechanisms that dictate their ability to switch roles. Lastly, we discuss the potential of an innovative approach to develop drugs targeting these moonlighting enzymes: target protein degradation. This strategy holds promise for effectively tackling moonlighting enzymes in the context of cancer therapy.

New approaches for challenging therapeutic targets

Despite successes with new drug approvals over the past two decades through conventional drug development approaches, many human diseases remain intractable to current therapeutic interventions. Possible barriers may be that the complexity of the target, and disease biology, are impervious to such conventional drug development approaches. The US National Institutes of Health hosted a workshop with the goal of identifying challenges and opportunities with alternative modalities for developing treatments across diseases associated with historically undruggable targets. This report highlights key issues discussed during the workshop that, if addressed, could expand the pool of therapeutic approaches for treating various diseases.

Orphan GPR52 as an emerging neurotherapeutic target

GPR52 is a highly conserved, brain-enriched, Gs/olf-coupled orphan G protein-coupled receptor (GPCR) that controls various cyclic AMP (cAMP)-dependent physiological and pathological processes. Stimulation of GPR52 activity might be beneficial for the treatment of schizophrenia, psychiatric disorders and other human neurological diseases, whereas inhibition of its activity might provide a potential therapeutic approach for Huntington's disease. Excitingly, HTL0048149 (HTL'149), an orally available GPR52 agonist, has been advanced into phase I human clinical trials for the treatment of schizophrenia. In this concise review, we summarize the current understanding of GPR52 receptor distribution as well as its structure and functions, highlighting the recent advances in drug discovery efforts towards small-molecule GPR52 ligands. The opportunities and challenges presented by targeting GPR52 for novel therapeutics are also briefly discussed.

EGFR degraders in non-small-cell lung cancer: Breakthrough and unresolved issue

The epidermal growth factor receptor (EGFR) has been well validated as a therapeutic target for anticancer drug discovery. Osimertinib has become the first globally accessible third-generation EGFR inhibitor, representing one of the most advanced developments in non-small-cell lung cancer (NSCLC) therapy. However, a tertiary Cys797 to Ser797 (C797S) point mutation has hampered osimertinib treatment in patients with advanced EGFR-mutated NSCLC. Several classes of fourth-generation EGFR inhibitors were consequently discovered with the aim of overcoming the EGFRC797S mutation-mediated resistance. However, no clinical efficacy data of the fourth-generation EGFR inhibitors were reported to date, and EGFRC797S mutation-mediated resistance remains an "unmet clinical need." Proteolysis-targeting chimeric molecules (PROTACs) obtained from EGFR-TKIs have been developed to target drug resistance EGFR in NSCLC. Some PROTACs are from nature products. These degraders compared with EGFR inhibitors showed better efficiency in their cellular potency, inhibition, and toxicity profiles. In this review, we first introduce the structural properties of EGFR, the resistance, and mutations of EGFR, and then mainly focus on the recent advances of EGFR-targeting degraders along with its advantages and outstanding challenges.

Expansion of targeted degradation by Gilteritinib-Warheaded PROTACs to ALK fusion proteins

Proteolysis targeting chimeras (PROTACs) induce the ubiquitination and subsequent proteasomal degradation of targeted proteins. Numerous PROTACs have emerged as promising drug candidates for various disease-related proteins. This study investigates PROTACs targeted to degrade anaplastic lymphoma kinase (ALK) fusion proteins, which are implicated in diseases such as anaplastic large cell lymphoma and non-small cell lung cancer. We recently reported the development of a gilteritinib-warheaded PROTAC to target and degrade the Fms-like tyrosine kinase 3 (FLT3) protein. Gilteritinib is a tyrosine kinase inhibitor that targets FLT3, and recent studies have revealed that it also functions as an ALK inhibitor. We conducted a structure-activity relationship (SAR) study and expanded the range of target proteins for gilteritinib-warheaded PROTACs to include echinoderm microtubule-associated protein-like 4 (EML4)-ALK and nucleophosmin (NPM)-ALK, in addition to FLT3. Our SAR study utilized three types of ligands for E3 ligase- inhibitor of apoptosis protein (IAP), cereblon (CRBN), and von Hippel-Lindau (VHL)- in the PROTAC designs and we observed varied efficacy in the degradation of target proteins. The CRBN-based PROTAC effectively reduced the protein expression of FLT3, EML4-ALK, and NPM-ALK. The IAP-based PROTAC reduced expression of both FLT3 and EML4-ALK proteins but not that of NPM-ALK, while the VHL-based PROTAC was ineffective against all target proteins. Several ALK-targeted PROTACs have already been developed using CRBN or VHL as E3 ligase, but this is the first report of an IAP-based ALK degrader. The length of the linker structure utilized in PROTAC also had a significant effect on their efficacy and activity. PROTACs formed with shorter linkers demonstrated an enhanced degradation activity to target proteins compared with those formed with longer linkers. These findings provide valuable insight for the development of effective PROTACs to target and degrade ALK fusion proteins.

Continuous evolution of compact protein degradation tags regulated by selective molecular glues

Conditional protein degradation tags (degrons) are usually >100 amino acids long or are triggered by small molecules with substantial off-target effects, thwarting their use as specific modulators of endogenous protein levels. We developed a phage-assisted continuous evolution platform for molecular glue complexes (MG-PACE) and evolved a 36-amino acid zinc finger (ZF) degron (SD40) that binds the ubiquitin ligase substrate receptor cereblon in complex with PT-179, an orthogonal thalidomide derivative. Endogenous proteins tagged in-frame with SD40 using prime editing are degraded by otherwise inert PT-179. Cryo-electron microscopy structures of SD40 in complex with ligand-bound cereblon revealed mechanistic insights into the molecular basis of SD40's activity and specificity. Our efforts establish a system for continuous evolution of molecular glue complexes and provide ZF tags that overcome shortcomings associated with existing degrons.

Mapping the substrate landscape of protein phosphatase 2A catalytic subunit PPP2CA

Protein phosphatase 2A (PP2A) is an essential Ser/Thr phosphatase. The PP2A holoenzyme complex comprises a scaffolding (A), regulatory (B), and catalytic (C) subunit, with PPP2CA being the principal catalytic subunit. The full scope of PP2A substrates in cells remains to be defined. To address this, we employed dTAG proteolysis-targeting chimeras to efficiently and selectively degrade dTAG-PPP2CA in homozygous knock-in HEK293 cells. Unbiased global phospho-proteomics identified 2,204 proteins with significantly increased phosphorylation upon dTAG-PPP2CA degradation, implicating them as potential PPP2CA substrates. A vast majority of these are novel. Bioinformatic analyses revealed involvement of the potential PPP2CA substrates in spliceosome function, cell cycle, RNA transport, and ubiquitin-mediated proteolysis. We identify a pSP/pTP motif as a predominant target for PPP2CA and confirm some of our phospho-proteomic data with immunoblotting. We provide an in-depth atlas of potential PPP2CA substrates and establish targeted degradation as a robust tool to unveil phosphatase substrates in cells.

Degradation of Polo-like Kinase 1 by the Novel Poly-Arginine N-Degron Pathway PROTAC Regulates Tumor Growth in Nonsmall Cell Lung Cancer

Polo-like kinase 1 (PLK1), which is crucial in cell cycle regulation, is considered a promising anticancer drug target. Herein, we present the N-degron pathway-based proteolysis targeting chimera (PROTAC) for PLK1 degradation, targeting the Polo-box domain (PBD). We identified DD-2 as the most potent PROTAC that selectively induces PLK1 degradation in cancer cells, including HeLa and nonsmall cell lung cancer (NSCLC), through the N-degron pathway. DD-2 exhibited significant in vitro anticancer effects, inducing G2/M arrest and apoptosis in HeLa and NSCLC cell lines. DD-2 showed significant tumor growth inhibition in a xenograft mouse model using HeLa and NSCLC cell lines, highlighting its potential in cancer treatment. Furthermore, the combination of DD-2 with tyrosine kinase inhibitor (TKI), osimertinib, effectively suppressed tumor growth in double-mutated H1975 cell lines, emphasizing DD-2's potential in combination cancer therapies. Collectively, this study demonstrates the potential of the N-degron pathway, especially using DD-2, for targeted cancer therapies.

PROTAC-biomacromolecule conjugates for precise protein degradation in cancer therapy: A review

Proteolysis targeting chimera (PROTAC) technology is a promising new mode of targeted protein degradation with significant transformative implications for the clinical treatment of different diseases. Nevertheless, while this technology offers numerous advantages, on-target off-tumour toxicity in healthy cells remains a major challenge for clinical application in cancer therapy. Strategies are presently being explored to optimize degradation activity with cellular selectivity to minimize undesirable side effects. PROTAC-antibody conjugates and PROTAC-aptamer conjugates are unique innovations that combine PROTACs and biomacromolecules. These novel PROTAC-biomacromolecule conjugates (PBCs) can enhance the targetability of PROTACs and reduce their off-target side-effects. The combination of potent PROTACs and highly safe biomacromolecules will pioneer an emerging trend in targeted protein degradation. In our review, we have summarized recent advances in PBCs, discussed current challenges, and outlooked opportunities for future research in the field.

Progress in RAS-targeted therapeutic strategies: From small molecule inhibitors to proteolysis targeting chimeras

As a widely considerable target in chemical biology and pharmacological research, rat sarcoma (RAS) gene mutations play a critical driving factor in several fatal cancers. Despite the great progress of RAS subtype-specific inhibitors, rapid acquired drug resistance could limit their further clinical applications. Proteolysis targeting chimera (PROTAC) has emerged as a powerful tool to handle "undruggable" targets and exhibited significant therapeutic benefit for the combat of drug resistance. Owing to unique molecular mechanism and binding kinetics, PROTAC is expected to become a feasible strategy to break the bottleneck of classical RAS inhibitors. This review aims to discuss the current advances of RAS inhibitors and especially focus on PROTAC strategy targeting RAS mutations and their downstream effectors for relevant cancer treatment.

Harmony of Protein Tags and Chimeric Molecules Empowers Targeted Protein Ubiquitination and Beyond

Post-translational modifications (PTMs) are crucial mechanisms that underlie the intricacies of biological systems and disease mechanisms. This review focuses on the latest advancements in the design of heterobifunctional small molecules that hijack PTM machineries for target-specific modifications in living systems. A key innovation in this field is the development of proteolysis-targeting chimeras (PROTACs), which promote the ubiquitination of target proteins for proteasomal degradation. The past decade has seen several adaptations of the PROTAC concept to facilitate targeted (de)phosphorylation and acetylation. Protein fusion tags have been particularly vital in these proof-of-concept studies, aiding in the investigation of the functional roles of post-translationally modified proteins linked to diseases. This overview delves into protein-tagging strategies that enable the targeted modulation of ubiquitination, phosphorylation, and acetylation, emphasizing the synergies and challenges of integrating heterobifunctional molecules with protein tags in PTM research. Despite significant progress, many PTMs remain to be explored, and protein tag-assisted PTM-inducing chimeras will continue to play an important role in understanding the fundamental roles of protein PTMs and in exploring the therapeutic potential of manipulating protein modifications, particularly for targets not yet addressed by existing drugs.

Insight into Recent Advances in Degrading Androgen Receptor for Castration-Resistant Prostate Cancer

Induced protein degradation has emerged as an innovative drug discovery approach, complementary to the classical method of suppressing protein function. The androgen receptor signaling pathway has been identified as the primary driving force in the development and progression of lethal castration-resistant prostate cancer. Since androgen receptor degraders function differently from androgen receptor antagonists, they hold the promise to overcome the drug resistance challenges faced by current therapeutics. Proteolysis-targeting chimeras (PROTACs), monomeric degraders, hydrophobic tagging, molecular glues, and autophagic degradation have demonstrated their capability in downregulating intracellular androgen receptor concentrations. The potential of these androgen receptor degraders to treat castration-resistant prostate cancer is substantiated by the advancement of six PROTACs and two monomeric androgen receptor degraders into phase I or II clinical trials. Although the chemical structures, in vitro and in vivo data, and degradation mechanisms of androgen receptor degraders have been reviewed, it is crucial to stay updated on recent advances in this field as novel androgen receptor degraders and new strategies continue to emerge. This review thus provides insight into recent advancements in this paradigm, offering an overview of the progress made since 2020.

BacPROTACs targeting Clp protease: a promising strategy for anti-mycobacterial drug discovery

Tuberculosis (TB) has claimed more lives over the course of two millennia than any other infectious disease worldwide. In 2021, the World Health Organization (WHO) estimated that 10.6 million people were diagnosed with TB, resulting in the deaths of 1.4 million HIV-negative individuals. The emergence of multidrug-resistant TB (MDR-TB), defined as resistance to at least rifampicin (RIF) and isoniazid (INH), and extensively drug-resistant TB (XDR-TB), poses the primary challenge to overcome in the coming years. We have recently conducted an extensive analysis of investments and research endeavours in the field, with the overarching objective of achieving the established milestone of TB eradication by the year 2030. Over the past several years, there has been notable progress in advancing a multitude of promising compounds, each possessing distinct mechanisms of action, into clinical phases of development. However, it is worth noting that strains of mycobacteria resistant to current antitubercular drugs have already emerged for some of these compounds The exploration of the innovative Proteolytic Target Chimeras (PROTACs) protein degradation approach has emerged as a viable avenue for the discovery of novel antimicrobials. While the ubiquitin system is exclusive to eukaryotic cells, certain bacteria use a similar degradation system that relies on the recognition of phosphorylated arginine residues (pArg) by the ClpC:ClpP (ClpCP) protease, thereby leading to protein degradation. In this opinion article, we have described and analized the advances in the use of PROTACs that leverage bacterial proteolytic machinery (BacPROTACs) to design new antitubercular agents. Scope Statement. The development of novel pharmaceuticals for tuberculosis treatment is deemed urgently necessary due to the emergence of resistant strains. In this context, the introduction of new technologies capable of alleviating the disease and attaining the objectives outlined by the World Health Organization is imperative. Among the innovative strategies, the degradation of proteins that are crucial for the survival of the bacillus holds promise for generating new medications, particularly those that are effective at treating latent (non-replicating) Mycobacterium tuberculosis. Within this perspective, we present the advancements and obstacles encountered in the exploration of new BacPROTAC compounds, with the intention of encouraging research and illuminating challenges associated with the implementation of BacPROTACs to address to the global tuberculosis crisis.

Aberrant MET Receptor Tyrosine Kinase Signaling in Glioblastoma: Targeted Therapy and Future Directions

Brain tumors represent a heterogeneous group of neoplasms characterized by a high degree of aggressiveness and a poor prognosis. Despite recent therapeutic advances, the treatment of brain tumors, including glioblastoma (GBM), an aggressive primary brain tumor associated with poor prognosis and resistance to therapy, remains a significant challenge. Receptor tyrosine kinases (RTKs) are critical during development and in adulthood. Dysregulation of RTKs through activating mutations and gene amplification contributes to many human cancers and provides attractive therapeutic targets for treatment. Under physiological conditions, the Met RTK, the hepatocyte growth factor/scatter factor (HGF/SF) receptor, promotes fundamental signaling cascades that modulate epithelial-to-mesenchymal transition (EMT) involved in tissue repair and embryogenesis. In cancer, increased Met activity promotes tumor growth and metastasis by providing signals for proliferation, survival, and migration/invasion. Recent clinical genomic studies have unveiled multiple mechanisms by which MET is genetically altered in GBM, including focal amplification, chromosomal rearrangements generating gene fusions, and a splicing variant mutation (exon 14 skipping, METex14del). Notably, MET overexpression contributes to chemotherapy resistance in GBM by promoting the survival of cancer stem-like cells. This is linked to distinctive Met-induced pathways, such as the upregulation of DNA repair mechanisms, which can protect tumor cells from the cytotoxic effects of chemotherapy. The development of MET-targeted therapies represents a major step forward in the treatment of brain tumours. Preclinical studies have shown that MET-targeted therapies (monoclonal antibodies or small molecule inhibitors) can suppress growth and invasion, enhancing the efficacy of conventional therapies. Early-phase clinical trials have demonstrated promising results with MET-targeted therapies in improving overall survival for patients with recurrent GBM. However, challenges remain, including the need for patient stratification, the optimization of treatment regimens, and the identification of mechanisms of resistance. This review aims to highlight the current understanding of mechanisms underlying MET dysregulation in GBM. In addition, it will focus on the ongoing preclinical and clinical assessment of therapies targeting MET dysregulation in GBM.

ASDs of PROTACs: Spray-dried solid dispersions as enabling formulations

Proteolysis targeting chimeras (PROTACs) are a promising class of pharmaceutical agents with a unique mode of action. PROTACs enable the targeting of a broad variety of structures including transcription factors and other "undruggable" targets. The poor solubility and slow dissolution of PROTACs currently limit the extensive use of their potential. Up to date, only very limited drug delivery options have been examined to address this challenge. Therefore, we explored the potential of amorphous solid dispersions (ASDs) by spray drying a model PROTAC with different polymers. The resulting formulations were assessed in terms of purity, solid state, dissolution performance, and stability. A strong increase in supersaturation compared to the physical mixture was provided, although in both systems the PROTAC molecule itself was already in the amorphous state. Evaluation of the reasons for the superiority of the ASD formulations revealed that the major factor was the homogeneous, molecular distribution of the active pharmaceutical ingredient (API) in the polymer matrix, as well as improved wettability of the formulation containing Soluplus compared to the physical mixture. The manufactured formulations were stable over a minimum of 8 weeks when protected from light and humidity.

Bifunctional Peptide Nanofibrils for Targeted Protein Degradation

Proteolysis targeting chimera (PROTAC) is a state-of-the-art technology for ablating undruggable targets. A PROTAC degrader achieves targeted protein degradation (TPD) through the simultaneous binding of a protein of interest (POI) and an E3 ligase to form a ternary complex. A nanofibril-based PROTAC strategy to form a polynary (E3)m  : PROTAC : (POI)n complex has not been reported in the TPD field up to this point. A recent innovation shows that a POI ligand and E3 ligase ligand don't have to be within a fused degrader molecule. Instead, they can be recruited to cellular proximity by a self-assembly-driving peptide and click chemistry. The resulting nanofibrils can recruit multiple POI and E3 ligase molecules to form a polynary complex as a degradation center. The so-called Nano-PROTAC provides a novel approach for TPD in cancer therapy.