Bruton tyrosine kinase degradation as a therapeutic strategy for cancer

Bruton Tyrosine Kinase Degraders: Current Concepts

Bruton tyrosine kinase (BTK) is a key enzyme involved in B-cell development and signaling, making it a crucial target in the treatment of B-cell malignancies, such as chronic lymphocytic leukemia and non-Hodgkin lymphoma. While BTK inhibitors (BTKi), such as ibrutinib, have been effective, resistance-both intrinsic and acquired-poses a significant challenge, often associated with BTK mutations like C481S. To address this, novel BTK degraders have been developed, leveraging proteolysis-targeting chimeras to selectively degrade both wild-type and mutant BTK forms. This approach offers a promising strategy to overcome BTKi resistance. Agents such as NRX-0492, BGB-16673, NX-5948, NX-2127, HZ-Q1060, ABBV-101, and AC676 have shown significant BTK degradation in preclinical and early clinical trials. NRX-0492 demonstrated over 90% BTK degradation with sustained pharmacodynamic effects, whereas BGB-16673 achieved clinical responses in 67% of patients with relapsed/refractory B-cell malignancies. Similarly, NX-5948 and NX-2127 showed potent BTK degradation, with NX-2127, in addition, targeting immunomodulatory proteins, resulting in partial and stable responses in chronic lymphocytic leukemia and non-Hodgkin lymphoma patients. HZ-Q1060, a preclinical candidate, displayed rapid and sustained BTK degradation in vivo. Early-phase trials of ABBV-101 and AC676 are also showing promising results. These BTK degraders have demonstrated favorable safety profiles, with manageable adverse events, and offer a novel therapeutic avenue for patients with BTKi-resistant malignancies. As clinical trials progress, these degraders hold the potential to significantly enhance treatment outcomes, offering a new frontier in personalized cancer therapy.

POD24-Based prognostic signature enables personalized risk stratification in mantle cell lymphoma

Mantle cell lymphoma (MCL) exhibits significant biological and clinical heterogeneity, necessitating a refined prognostic model. According to the drawbacks of existing models which do not truly define the complexity of the disease, we used the clinical and molecular data from nine medical centers of China to validate the predictive utility of progression of disease within 24 months (POD24), and also established a novel prognostic risk model to predict the survival outcome of MCL patients. POD24 occurred in 37.7% of evaluable patients, with the median over survival being 21 months (vs. 122 months for those without POD24, P < 0.0001). The POD24-based risk model had the highest sensitivity to predict survival with the most satisfying AUC value for risk score (AUC = 0.869). In conclusion, we confirm the obviously predictive performance of POD24 and established a novel risk model combined POD24 and clinical factors. Our new prognostic model might be helpful in effectively classify MCL patients with high-risk groups in terms of survival rate, which may help in selecting high-risk MCL patients for more intensive treatment at time of relapse.

Chronic Lymphocytic Leukemia: 2025 Update on the Epidemiology, Pathogenesis, Diagnosis, and Therapy

DISEASE OVERVIEW

Chronic lymphocytic leukemia (CLL) is the most frequent type of leukemia. It typically occurs in older patients and has a highly variable clinical course. Leukemic transformation is initiated by specific genomic alterations that interfere with the regulation of proliferation and apoptosis in clonal B-cells.

DIAGNOSIS

The diagnosis is established by blood counts, blood smears, and immunophenotyping of circulating B-lymphocytes, which identify a clonal B-cell population carrying the CD5 antigen as well as typical B-cell markers.

PROGNOSIS AND STAGING

Two clinical staging systems, Rai and Binet, provide prognostic information by using the results of physical examination and blood counts. Various biological and genetic markers provide additional prognostic information. Deletions of the short arm of chromosome 17 (del(17p)) and/or mutations of the TP53 gene predict a shorter time to progression with most targeted therapies. The CLL international prognostic index (CLL-IPI) integrates genetic, biological, and clinical variables to identify distinct risk groups of patients with CLL. The CLL-IPI retains its significance in the era of targeted agents, but the overall prognosis of CLL patients with high-risk stages has improved.

THERAPY

Only patients with active or symptomatic disease or with advanced Binet or Rai stages require therapy. When treatment is indicated, several therapeutic options exist: combinations of the BCL2 inhibitor venetoclax with obinutuzumab, or venetoclax with ibrutinib, or monotherapy with one of the inhibitors of Bruton tyrosine kinase (BTK). At relapse, the initial treatment may be repeated if the treatment-free interval exceeds 3 years. If the leukemia relapses earlier, therapy should be changed using an alternative regimen.

FUTURE CHALLENGES

Combinations of targeted agents now provide efficient therapies with a fixed duration that generate deep and durable remissions. These fixed-duration therapies have gained territory in the management of CLL, as they are cost-effective, avoid the emergence of resistance, and offer treatment free time to the patient. The cure rate of these novel combination regimens is unknown. Moreover, the optimal sequencing of targeted therapies remains to be determined. A medical challenge is to treat patients who are double-refractory to both BTK and BCL2 inhibitors. These patients need to be treated within experimental protocols using novel drugs.

Unraveling MCL biology to understand resistance and identify vulnerabilities

ABSTRACT

Mantle cell lymphoma (MCL) is a rare (5%-7%), aggressive B-cell non-Hodgkin lymphoma with well-defined hallmarks (eg, cyclin D1, SOX11), and its expansion is highly dependent on the tumor microenvironment (TME). Parallel drastic progress in the understanding of lymphomagenesis and improved treatments led to a paradigm shift in this B-cell malignancy with now prolonged disease-free survival after intensive chemotherapy and anti-CD20-based maintenance. However, this toxic strategy is not applicable in frail or older patients, and a small but significant part of the cases present a refractory disease representing unmet medical needs. Importantly, the field has recently seen the rapid emergence of targeted and immune-based strategies with effective combinations relying on biological rationales to overcome malignant plasticity and intratumor heterogeneity. In this review, we expose how unraveling the biology of MCL allows to better understand the therapeutic resistances and to identify neo-vulnerabilities in tumors, which are essential to offer efficient novel strategies for high-risk patients. We first highlight the tumor intrinsic resistance mechanisms and associated Achilles heels within various pathways, such as NF-κB, mitochondrial apoptosis, DNA repair, and epigenetic regulators. We then place the tumor in its complex ecosystem to decipher the dialog with the multiple TME components and show how the resulting protumoral signals could be disrupted with innovative therapeutic strategies. Finally, we discuss how these progresses could be integrated into a personalized approach in MCL.

A Kinetic Scout Approach Accelerates Targeted Protein Degrader Development

Bifunctional molecules such as targeted protein degraders induce proximity to promote gain-of-function pharmacology. These powerful approaches have gained broad traction across academia and the pharmaceutical industry, leading to an intensive focus on strategies that can accelerate their identification and optimization. We and others have previously used chemical proteomics to map degradable target space, and these datasets have been used to develop and train multiparameter models to extend degradability predictions across the proteome. In this study, we now turn our attention to develop generalizable chemistry strategies to accelerate the development of new bifunctional degraders. We implement lysine-targeted reversible-covalent chemistry to rationally tune the binding kinetics at the protein-of-interest across a set of 25 targets. We define an unbiased workflow consisting of global proteomics analysis, IP/MS of ternary complexes and the E-STUB assay, to mechanistically characterize the effects of ligand residence time on targeted protein degradation and formulate hypotheses about the rate-limiting step of degradation for each target. Our key finding is that target residence time is a major determinant of degrader activity, and this can be rapidly and rationally tuned through the synthesis of a minimal number of analogues to accelerate early degrader discovery and optimization.

Characterization of Amorphous Ibrutinib Thermal Stability

The choice of method for drug amorphization depends on various factors, including the physicochemical properties of the active pharmaceutical ingredients, the desired formulation, and scalability requirements. It is often important to consider a combination of methods or the use of excipients to further enhance the stability and performance of the amorphous drug. This study presents a comparison of techniques including melt quench, hot melt extrusion, solvent evaporation, ball milling, and lyophilization used for the preparation of amorphous ibrutinib. The amorphous material was thoroughly investigated using numerous techniques to examine changes in the physicochemical properties, stability, and degradation pathways of the drug product. During the examination, the temperature was discovered to be a key parameter for controlling the solubility and permeability of ibrutinib, which is influenced by the presence of the degradation product. We found that this degradation product could potentially polymerize and increase the molecular weight. The quantity, polymerization rate, and structure of the impurity can be regulated by the temperature variation during the amorphization processes. Additionally, the molecular weight of the degradation product was determined using Zimm plot analysis, which appeared for the first time in the literature for molecules of this category.

PROTACs in platelets: emerging antithrombotic strategies and future perspectives

PURPOSE OF REVIEW

Proteolysis-targeted chimeras (PROTACs) are heterobifunctional compounds that selectively target proteins for degradation and are an emerging therapeutic modality to treat diseases such as cancer and neurodegenerative disorders. This review will widen the area of application by highlighting the ability of PROTACs to remove proteins from the anucleate platelets and evaluate their antithrombotic potential.

RECENT FINDINGS

Proteomic and biochemical studies demonstrated that human platelets possess the Ubiquitin Proteasomal System as well as the E3 ligase cereblon (CRBN) and therefore may be susceptible to PROTAC-mediated protein degradation. Recent findings confirmed that CRBN ligand-based PROTACs targeting generic tyrosine kinases, Btk and/or Fak lead to efficacious and selective protein degradation in human platelets. Downregulation of Btk, a key player involved in signalling to thrombosis, but not haemostasis, resulted in impaired in-vitro thrombus formation.

SUMMARY

Platelets are susceptible to targeted protein degradation by CRBN ligand-based PROTACs and have limited ability to resynthesise proteins, ensuring long-term downregulation of target proteins. Therefore, PROTACs serve as an additional research tool to study platelet function and offer new therapeutic potential to prevent thrombosis. Future studies should focus on enhancing cell specificity to avoid on-target side effects on other blood cells.

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.

Design, Synthesis, and Activity Evaluation of BRD4 PROTAC Based on Alkenyl Oxindole-DCAF11 Pair

Proteolytic targeting chimera (PROTAC) represent an advanced strategy for targeting undruggable proteins, and the molecular warheads targeting E3 ligases play a crucial role. Recently, we explored an alkenyl oxindole warhead targeting the E3 ligase DCAF11 and sought to validate its potential. In this study, we synthesized a range of BRD4 PROTACs (8a-8o, 14a-14f, 22a-22m) with modified alkenyl oxindole warheads and developed a high-throughput screening system based on high-content imaging. We identified L134 (22a) as a potent BRD4 degrader, achieving BRD4 degradation (Dmax > 98%, DC50 = 7.36 nM) and demonstrating antitumor activity. Mechanically, BRD4 degradation by L134 was mediated through the ubiquitin-proteasome system in a DCAF11-dependent manner. Therefore, this study provides a rapid screening method for effective PROTACs and highlights the PROTAC L134 based on alkenyl oxindole-DCAF11 pair as a promising candidate for treating BRD4-driven cancers.

Targeted protein degradation: advances in drug discovery and clinical practice

Targeted protein degradation (TPD) represents a revolutionary therapeutic strategy in disease management, providing a stark contrast to traditional therapeutic approaches like small molecule inhibitors that primarily focus on inhibiting protein function. This advanced technology capitalizes on the cell's intrinsic proteolytic systems, including the proteasome and lysosomal pathways, to selectively eliminate disease-causing proteins. TPD not only enhances the efficacy of treatments but also expands the scope of protein degradation applications. Despite its considerable potential, TPD faces challenges related to the properties of the drugs and their rational design. This review thoroughly explores the mechanisms and clinical advancements of TPD, from its initial conceptualization to practical implementation, with a particular focus on proteolysis-targeting chimeras and molecular glues. In addition, the review delves into emerging technologies and methodologies aimed at addressing these challenges and enhancing therapeutic efficacy. We also discuss the significant clinical trials and highlight the promising therapeutic outcomes associated with TPD drugs, illustrating their potential to transform the treatment landscape. Furthermore, the review considers the benefits of combining TPD with other therapies to enhance overall treatment effectiveness and overcome drug resistance. The future directions of TPD applications are also explored, presenting an optimistic perspective on further innovations. By offering a comprehensive overview of the current innovations and the challenges faced, this review assesses the transformative potential of TPD in revolutionizing drug development and disease management, setting the stage for a new era in medical therapy.

Advances in Targeted Therapy: Addressing Resistance to BTK Inhibition in B-Cell Lymphoid Malignancies

B-cell lymphoid malignancies are a heterogeneous group of hematologic cancers, where Bruton's tyrosine kinase (BTK) inhibitors have received FDA approval for several subtypes. The first-in-class covalent BTK inhibitor, Ibrutinib, binds to the C481 amino acid residue to block the BTK enzyme and prevent the downstream signaling. Resistance to covalent BTK inhibitors (BTKi) can occur through mutations at the BTK binding site (C481S) but also other BTK sites and the phospholipase C gamma 2 (PLCγ2) resulting in downstream signaling. To bypass the C481S mutation, non-covalent BTKi, such as Pirtobrutinib, were developed and are active against both wild-type and the C481S mutation. In this review, we discuss the molecular and genetic mechanisms which contribute to acquisition of resistance to covalent and non-covalent BTKi. In addition, we discuss the new emerging class of BTK degraders, which utilize the evolution of proteolysis-targeting chimeras (PROTACs) to degrade the BTK protein and constitute an important avenue of overcoming resistance. The moving landscape of resistance to BTKi and the development of new therapeutic strategies highlight the ongoing advances being made towards the pursuit of a cure for B-cell lymphoid malignancies.

A Kinetic Scout Approach Accelerates Targeted Protein Degrader Development

Bifunctional molecules such as targeted protein degraders induce proximity to promote gain-of-function pharmacology. These powerful approaches have gained broad traction across academia and the pharmaceutical industry, leading to an intensive focus on strategies that can accelerate their identification and optimization. We and others have previously used chemical proteomics to map degradable target space, and these datasets have been used to develop and train multiparameter models to extend degradability predictions across the proteome. In this study, we now turn our attention to develop generalizable chemistry strategies to accelerate the development of new bifunctional degraders. We implement lysine-targeted reversible-covalent chemistry to rationally tune the binding kinetics at the protein-of-interest across a set of 25 targets. We define an unbiased workflow consisting of global proteomics analysis, IP/MS of ternary complexes and the E-STUB assay, to mechanistically characterize the effects of ligand residence time on targeted protein degradation and formulate hypotheses about the rate-limiting step of degradation for each target. Our key finding is that target residence time is a major determinant of degrader activity, and this can be rapidly and rationally tuned through the synthesis of a minimal number of analogues to accelerate early degrader discovery and optimization efforts.

PI3K Inhibitors in Hematology: When One Door Closes…

The PI3K signaling pathway regulates key cellular processes and is one of the most aberrantly activated pathways in cancer. The class I PI3K catalytic subunits p110γ and p110δ are highly enriched in leukocytes, providing an additional rationale for targeting these PI3Ks in hematologic malignancies. In 2014, the PI3Kδ inhibitor idelalisib was the first of four PI3K inhibitors (PI3Ki) to receive regulatory approval for relapsed B-cell malignancies. This was followed by approvals of the pan-class I inhibitor copanlisib (2017), the dual PI3Kγ/δ inhibitor duvelisib (2018), and the PI3Kδ and casein kinase 1ε inhibitor umbralisib (2021). Copanlisib and umbralisib received accelerated approvals, whereas idelalisib and duvelisib received initial accelerated approvals followed by full approvals. The accelerated approvals were based on overall response rates; however, follow-up studies showed increased risk of death and serious side effects. Furthermore, the confirmatory trial with copanlisib failed to show an improvement in progression-free survival when compared with chemoimmunotherapy. These developments led to black box warnings for idelalisib and duvelisib and withdrawal of copanlisib and umbralisib from the market by their manufacturers. Given the uncertain future of this drug class, additional manufacturers terminated ongoing phase III trials with novel PI3Kis. In this study, we review the development and current status of PI3Kis in hematology, limitations to their use, and our perspective on whether there is a future for PI3Kis in hematology.

Mechanisms of resistance to tyrosine kinase inhibitor-targeted therapy and overcoming strategies

Tyrosine kinase inhibitor (TKI)-targeted therapy has revolutionized cancer treatment by selectively blocking specific signaling pathways crucial for tumor growth, offering improved outcomes with fewer side effects compared with conventional chemotherapy. However, despite their initial effectiveness, resistance to TKIs remains a significant challenge in clinical practice. Understanding the mechanisms underlying TKI resistance is paramount for improving patient outcomes and developing more effective treatment strategies. In this review, we explored various mechanisms contributing to TKI resistance, including on-target mechanisms and off-target mechanisms, as well as changes in the tumor histology and tumor microenvironment (intrinsic mechanisms). Additionally, we summarized current therapeutic approaches aiming at circumventing TKI resistance, including the development of next-generation TKIs and combination therapies. We also discussed emerging strategies such as the use of dual-targeted antibodies and PROteolysis Targeting Chimeras. Furthermore, we explored future directions in TKI-targeted therapy, including the methods for detecting and monitoring drug resistance during treatment, identification of novel targets, exploration of dual-acting kinase inhibitors, application of nanotechnologies in targeted therapy, and so on. Overall, this review provides a comprehensive overview of the challenges and opportunities in TKI-targeted therapy, aiming to advance our understanding of resistance mechanisms and guide the development of more effective therapeutic approaches in cancer treatment.

Targeted protein degradation in hematologic malignancies: clinical progression towards novel therapeutics

Targeted therapies, such as small molecule kinase inhibitors, have made significant progress in the treatment of hematologic malignancies by directly modulating protein activity. However, issues such as drug toxicity, drug resistance due to target mutations, and the absence of key active sites limit the therapeutic efficacy of these drugs. Targeted protein degradation (TPD) presents an emergent and rapidly evolving therapeutic approach that selectively targets proteins of interest (POI) based on endogenous degradation processes. With an event-driven pharmacology of action, TPD achieves efficacy with catalytic amounts, avoiding drug-related toxicity. Furthermore, TPD has the unique mode of degrading the entire POI, such that resistance derived from mutations in the targeted protein has less impact on its degradation function. Proteolysis-targeting chimeras (PROTACs) and molecular glue degraders (MGDs) are the most maturely developed TPD techniques. In this review, we focus on both preclinical experiments and clinical trials to provide a comprehensive summary of the safety and clinical effectiveness of PROTACs and MGDs in hematologic malignancies over the past two decades. In addition, we also delineate the challenges and opportunities associated with these burgeoning degradation techniques. TPD, as an approach to the precise degradation of specific proteins, provides an important impetus for its future application in the treatment of patients with hematologic malignancies.

Lysineless HiBiT and NanoLuc Tagging Systems as Alternative Tools for Monitoring Targeted Protein Degradation

Target protein degradation (TPD) has emerged as a revolutionary approach in drug discovery, leveraging the cell's intrinsic machinery to selectively degrade disease-associated proteins. Nanoluciferase (nLuc) fusion proteins and the NanoBiT technology offer two robust and sensitive screening platforms to monitor the subtle changes in protein abundance induced by TPD molecules. Despite these advantages, concerns have arisen regarding potential degradation artifacts introduced by tagging systems due to the presence of lysine residues on them, prompting the development of alternative tools. In this study, we introduce HiBiT-RR and nLucK0, variants devoid of lysine residues, to mitigate such artifacts. Our findings demonstrate that HiBiT-RR maintains a similar sensitivity and binding affinity with the original HiBiT. Moreover, the comparison between nLucWT and nLucK0 constructs reveals variations in degradation patterns induced by certain TPD molecules, emphasizing the importance of choosing appropriate tagging systems to ensure the reliability of experimental outcomes in studying protein degradation processes.

Targeting the tumor microenvironment for treating double-refractory chronic lymphocytic leukemia

ABSTRACT

The introduction of BTK inhibitors and BCL2 antagonists to the treatment of chronic lymphocytic leukemia (CLL) has revolutionized therapy and improved patient outcomes. These agents have replaced chemoimmunotherapy as standard of care. Despite this progress, a new group of patients is currently emerging, which has become refractory or intolerant to both classes of agents, creating an unmet medical need. Here, we propose that the targeted modulation of the tumor microenvironment provides new therapeutic options for this group of double-refractory patients. Furthermore, we outline a sequential strategy for tumor microenvironment-directed combination therapies in CLL that can be tested in clinical protocols.

Targeted Therapies in the Treatment of Mantle Cell Lymphoma

Mantle cell lymphoma (MCL) is a rare, heterogeneous B-cell non-Hodgkin's lymphoma. The standard front-line treatment utilizes chemotherapy, often followed by consolidation with an autologous hematopoietic cell transplant; however, in most patients, the lymphoma will recur and require subsequent treatments. Additionally, mantle cell lymphoma primarily affects older patients and is frequently chemotherapy-resistant, which has further fostered the necessity for new, chemotherapy-free treatment options. In the past decade, targeted therapies in mantle cell lymphoma have been practice-changing as the treatment paradigm shifts further away from relying primarily on cytotoxic agents. Here, we will review the pathophysiology of mantle cell lymphoma and discuss the emergence of targeted, chemotherapy-free treatments aimed at disrupting the abnormal biology driving its lymphomagenesis. Treatments targeting the constitutive activation of NF-kB, Bruton's Tyrosine Kinase signaling, and anti-apoptosis will be the primary focus as we discuss their clinical data and toxicities. Our review will also focus primarily on the emergence and use of targeted therapies in the relapsed/refractory setting but will also discuss the emergence of their use in front-line therapy and in combination with other agents.

Lysineless HiBiT and NanoLuc Tagging Systems as Alternative Tools Monitoring Targeted Protein Degradation

Target protein degradation (TPD) has emerged as a revolutionary approach in drug discovery, leveraging the cell's intrinsic machinery to selectively degrade disease-associated proteins. Proteolysis-Targeting Chimeras (PROTACs) exemplify this strategy, exploiting heterobifunctional molecules to induce ubiquitination and subsequent degradation of target proteins. The clinical advancement of PROTACs underscores their potential in therapeutic intervention, with numerous projects progressing through clinical stages. However, monitoring subtle changes in protein abundance induced by TPD molecules demands highly sensitive assays. Nano-luciferase (nLuc) fusion proteins, or the NanoBiT technology derived from it, offer a robust screening platform due to their high sensitivity and stability. Despite these advantages, concerns have arisen regarding potential degradation artifacts introduced by tagging systems due to the presence of lysine residues on them, prompting the development of alternative tools. In this study, we introduce HiBiT-RR and nLuc K0 , variants devoid of lysine residues, to mitigate such artifacts. Our findings demonstrate that HiBiT-RR maintains similar sensitivity and binding affinity with the original HiBiT. Moreover, the comparison between nLuc WT and nLuc K0 constructs reveals variations in degradation patterns induced by certain PROTAC molecules, emphasizing the importance of choosing appropriate tagging systems to ensure the reliability of experimental outcomes in studying protein degradation processes.

Application of covalent modality in proximity-induced drug pharmacology: Early development, current strategy, and feature directions

With a growing number of covalent drugs securing FDA approval as successful therapies across various indications, particularly in the realm of cancer treatment, the covalent modulating strategy is undergoing a resurgence. The renewed interest in covalent bioactive compounds has captured significant attention from both the academic and biopharmaceutical industry sectors. Covalent chemistry presents several advantages over traditional noncovalent proximity-induced drugs, including heightened potency, reduced molecular size, and the ability to target "undruggable" entities. Within this perspective, we have compiled a comprehensive overview of current covalent modalities applied to proximity-induced molecules, delving into their advantages and drawbacks. Our aim is to stimulate more profound insights and ideas within the scientific community, guiding future research endeavors in this dynamic field.

Discovery and Preclinical Pharmacology of NX-2127, an Orally Bioavailable Degrader of Bruton's Tyrosine Kinase with Immunomodulatory Activity for the Treatment of Patients with B Cell Malignancies

Bruton's tyrosine kinase (BTK), a member of the TEC family of kinases, is an essential effector of B-cell receptor (BCR) signaling. Chronic activation of BTK-mediated BCR signaling is a hallmark of many hematological malignancies, which makes it an attractive therapeutic target. Pharmacological inhibition of BTK enzymatic function is now a well-proven strategy for the treatment of patients with these malignancies. We report the discovery and characterization of NX-2127, a BTK degrader with concomitant immunomodulatory activity. By design, NX-2127 mediates the degradation of transcription factors IKZF1 and IKZF3 through molecular glue interactions with the cereblon E3 ubiquitin ligase complex. NX-2127 degrades common BTK resistance mutants, including BTKC481S. NX-2127 is orally bioavailable, exhibits in vivo degradation across species, and demonstrates efficacy in preclinical oncology models. NX-2127 has advanced into first-in-human clinical trials and achieves deep and sustained degradation of BTK following daily oral dosing at 100 mg.

Design, Synthesis, and In Vitro and In Vivo Evaluation of Cereblon Binding Bruton's Tyrosine Kinase (BTK) Degrader CD79b Targeted Antibody-Drug Conjugates

Antibody-drug conjugates (ADCs) are an established modality that allow for targeted delivery of a potent molecule, or payload, to a desired site of action. ADCs, wherein the payload is a targeted protein degrader, are an emerging area in the field. Herein we describe our efforts of delivering a Bruton's tyrosine kinase (BTK) bifunctional degrader 1 via a CD79b mAb (monoclonal antibody) where the degrader is linked at the ligase binding portion of the payload via a cleavable linker to the mAb. The resulting CD79b ADCs, 3 and 4, exhibit in vitro degradation and cytotoxicity comparable with that of 1, and ADC 3 can achieve more sustained in vivo degradation than intravenously administered 1 with markedly reduced systemic exposure of the payload.

Discovery of the cereblon-recruiting tubulin PROTACs effective in overcoming Taxol resistance in vitro and in vivo

Overexpression of β3-tubulin is a common occurrence in human tumors and is associated with resistance to microtubule-targeting agents. PROTAC strategy has demonstrated significant potential in overcoming drug resistance. Herein, we report the discovery of W13 as the first PROTAC against tubulin, which was created by connecting a CRBN ligand to the widely recognized microtubule-destabilizing agent CA-4. Notably, it retains the inhibitory activity of the parental CA-4 and further exhibits substantial degradation of α/β/β3-tubulin in both A549 and A549/Taxol cell lines. The degradation of tubulin was subsequently verified to be mediated by the ubiquitin-proteasome system. Importantly, tumor xenograft research clearly showed W13's promising antitumor activity against human lung cancer. Taken together, the discovery of W13 demonstrated the practicality and feasibility of PROTAC targeting tubulin, hence establishing a potential therapeutic approach for treating NSCLC caused by the overexpression of β3-tubulin.

Kinase-impaired BTK mutations are susceptible to clinical-stage BTK and IKZF1/3 degrader NX-2127

Increasing use of covalent and noncovalent inhibitors of Bruton's tyrosine kinase (BTK) has elucidated a series of acquired drug-resistant BTK mutations in patients with B cell malignancies. Here we identify inhibitor resistance mutations in BTK with distinct enzymatic activities, including some that impair BTK enzymatic activity while imparting novel protein-protein interactions that sustain B cell receptor (BCR) signaling. Furthermore, we describe a clinical-stage BTK and IKZF1/3 degrader, NX-2127, that can bind and proteasomally degrade each mutant BTK proteoform, resulting in potent blockade of BCR signaling. Treatment of chronic lymphocytic leukemia with NX-2127 achieves >80% degradation of BTK in patients and demonstrates proof-of-concept therapeutic benefit. These data reveal an oncogenic scaffold function of mutant BTK that confers resistance across clinically approved BTK inhibitors but is overcome by BTK degradation in patients.

Targeting phosphatases: From molecule design to clinical trials

Phosphatase is a kind of enzyme that can dephosphorylate target proteins, which can be divided into serine/threonine phosphatase and tyrosine phosphatase according to its mode of action. Current evidence showed multiple phosphatases were highly correlated with diseases including various cancers, demonstrating them as potential targets. However, currently, targeting phosphatases with small molecules faces many challenges, resulting in no drug approved. In this case, phosphatases are even regarded as "undruggable" targets for a long time. Recently, a variety of strategies have been adopted in the design of small molecule inhibitors targeting phosphatases, leading many of them to enter into the clinical trials. In this review, we classified these inhibitors into 4 types, including (1) molecular glues, (2) small molecules targeting catalytic sites, (3) allosteric inhibition, and (4) bifunctional molecules (proteolysis targeting chimeras, PROTACs). These molecules with diverse strategies prove the feasibility of phosphatases as drug targets. In addition, the combination therapy of phosphatase inhibitors with other drugs has also entered clinical trials, which suggests a broad prospect. Thus, targeting phosphatases with small molecules by different strategies is emerging as a promising way in the modulation of pathogenetic phosphorylation.

Novel treatment for mantle cell lymphoma - impact of BTK inhibitors and beyond

Mantle cell lymphoma (MCL) primarily affects older adults, accounting for 3-10% of all non-Hodgkin lymphoma (NHL) in western countries. The disease course of MCL is heterogenous; driven by clinical, cytogenetics, and molecular features that shape differences in outcomes, including proliferation index, MIPI scores, and mutational profile such as TP53 aberration. The advent of novel agents has fundamentally evolved the treatment landscape for MCL with treatment strategies that can now be more effectively tailored based on both patient- and disease-specific factors. In this review, we discuss the major classes of novel agents used for the treatment of MCL, focusing on efficacy and notable toxicities of BTK inhibitors. We further examine effective novel combination regimens and, lastly, discuss future directions for the evolution of targeted approaches for the treatment of MCL.

Waldenström Macroglobulinemia: Targeted Agents Taking Center Stage

With the worldwide approval of the oral covalent Bruton tyrosine kinase (BTK) inhibitors ibrutinib and zanubrutinib for treating patients with Waldenström macroglobulinemia (WM), targeted agents have certainly taken center stage in the therapeutic landscape of WM. This review discusses the biological and clinical data supporting current and up-and-coming targeted agents in WM. Bruton tyrosine kinase inhibitors induce fast, deep, and durable responses in patients with WM, comparable to chemoimmunotherapy; however, there is a glaring absence of comparative studies between these regimens. The high response and progression-free survival rate and the ease of administration of BTK inhibitors must be balanced against their specific adverse-event profile with unique toxicity (e.g., bleeding and cardiac arrhythmia) and the indefinite duration of the therapy. Novel targeted agents of interest include BCL2 antagonists (e.g., venetoclax and sonrotoclax) and non-covalent BTK inhibitors (e.g., pirtobrutinib and nemtabrutinib), among others. The therapeutic landscape of patients with WM will benefit from the robust participation of patients in clinical trials.

CARD11 gain of function upregulates BCL2A1 expression and promotes resistance to targeted therapies combination in B-cell lymphoma

A strategy combining targeted therapies is effective in B-cell lymphomas (BCL), such as mantle cell lymphoma (MCL), but acquired resistances remain a recurrent issue. In this study, we performed integrative longitudinal genomic and single-cell RNA-sequencing analyses of patients with MCL who were treated with targeted therapies against CD20, BCL2, and Bruton tyrosine kinase (OAsIs trial). We revealed the emergence of subclones with a selective advantage against OAsIs combination in vivo and showed that resistant cells were characterized by B-cell receptor (BCR)-independent overexpression of NF-κB1 target genes, especially owing to CARD11 mutations. Functional studies demonstrated that CARD11 gain of function not only resulted in BCR independence but also directly increased the transcription of the antiapoptotic BCL2A1, leading to resistance against venetoclax and OAsIs combination. Based on the transcriptional profile of OAsIs-resistant subclones, we designed a 16-gene resistance signature that was also predictive for patients with MCL who were treated with conventional chemotherapy, underlying a common escape mechanism. Among druggable strategies to inhibit CARD11-dependent NF-κB1 transduction, we evaluated the selective inhibition of its essential partner MALT1. We demonstrated that MALT1 protease inhibition led to a reduction in the expression of genes involved in OAsIs resistance, including BCL2A1. Consequently, MALT1 inhibition induced synergistic cell death in combination with BCL2 inhibition, irrespective of CARD11 mutational status, both in vitro and in vivo. Taken together, our study identified mechanisms of resistance to targeted therapies and provided a novel strategy to overcome resistance in aggressive BCL. The OAsIs trial was registered at www.clinicaltrials.gov #NCT02558816.

Development and Characterization of Selective FAK Inhibitors and PROTACs with In Vivo Activity

Focal adhesion kinase (FAK) is an attractive drug target due to its overexpression in cancer. FAK functions as a non-receptor tyrosine kinase and scaffolding protein, coordinating several downstream signaling effectors and cellular processes. While drug discovery efforts have largely focused on targeting FAK kinase activity, FAK inhibitors have failed to show efficacy as single agents in clinical trials. Here, using structure-guided design, we report the development of a selective FAK inhibitor (BSJ-04-175) and degrader (BSJ-04-146) to evaluate the consequences and advantages of abolishing all FAK activity in cancer models. BSJ-04-146 achieves rapid and potent FAK degradation with high proteome-wide specificity in cancer cells and induces durable degradation in mice. Compared to kinase inhibition, targeted degradation of FAK exhibits pronounced improved activity on downstream signaling and cancer cell viability and migration. Together, BSJ-04-175 and BSJ-04-146 are valuable chemical tools to dissect the specific consequences of targeting FAK through small-molecule inhibition or degradation.

SOHO State of the Art Updates and Next Questions: Updates on BTK Inhibitors for the Treatment of Chronic Lymphocytic Leukemia

Over the last decade, targeted inhibition of Bruton's tyrosine kinase (BTK) has led to a paradigm shift in the way chronic lymphocytic leukemia (CLL) is managed. BTK inhibitors (BTKi) are broadly classified as covalent BTKI and noncovalent BTKi (cBTKi and ncBTK) Ibrutinib, as the first approved cBTKi, vastly improved outcomes for patients with CLL over prior chemoimmunotherapy regimens. However, long-term use is limited by both intolerance and resistance. The second generation of more selective BTKi were developed to improve tolerability. While these agents have led to an improved safety profile in comparison to Ibrutinib (both acalabrutinib and zanubrutinib), and improved efficacy (zanubrutinib), intolerance occasionally occurs, and resistance remains a challenge. The third generation of BTKi, which noncovalently or reversibly inhibits BTK, has shown promising results in early phase trials and are being evaluated in the phase 3 setting. These drugs could be an effective treatment option in patients with either resistance and intolerance to cBTKi. The most recent development in therapeutic agents targeting BTK is the development of BTK degraders. By removing BTK, as opposed to inhibiting it, these drugs could remain efficacious irrespective of BTK resistance mutations, however clinical data are limited at this time. This review summarizes the evolution and ongoing development of newer BTKi and BTK degraders in the management of CLL, with a focus of future directions in this field, including how emerging clinical data could inform therapeutic sequencing in CLL management.

How many kinases are druggable? A review of our current understanding

There are over 500 human kinases ranging from very well-studied to almost completely ignored. Kinases are tractable and implicated in many diseases, making them ideal targets for medicinal chemistry campaigns, but is it possible to discover a drug for each individual kinase? For every human kinase, we gathered data on their citation count, availability of chemical probes, approved and investigational drugs, PDB structures, and biochemical and cellular assays. Analysis of these factors highlights which kinase groups have a wealth of information available, and which groups still have room for progress. The data suggest a disproportionate focus on the more well characterized kinases while much of the kinome remains comparatively understudied. It is noteworthy that tool compounds for understudied kinases have already been developed, and there is still untapped potential for further development in this chemical space. Finally, this review discusses many of the different strategies employed to generate selectivity between kinases. Given the large volume of information available and the progress made over the past 20 years when it comes to drugging kinases, we believe it is possible to develop a tool compound for every human kinase. We hope this review will prove to be both a useful resource as well as inspire the discovery of a tool for every kinase.

Beyond Bruton's tyrosine kinase inhibitors in mantle cell lymphoma: bispecific antibodies, antibody-drug conjugates, CAR T-cells, and novel agents

Mantle cell lymphoma is a B cell non-Hodgkin lymphoma (NHL), representing 2-6% of all NHLs and characterized by overexpression of cyclin D1. The last decade has seen the development of many novel treatment approaches in MCL, most notably the class of Bruton's tyrosine kinase inhibitors (BTKi). BTKi has shown excellent outcomes for patients with relapsed or refractory MCL and is now being studied in the first-line setting. However, patients eventually progress on BTKi due to the development of resistance. Additionally, there is an alteration in the tumor microenvironment in these patients with varying biological and therapeutic implications. Hence, it is necessary to explore novel therapeutic strategies that can be effective in those who progressed on BTKi or potentially circumvent resistance. In this review, we provide a brief overview of BTKi, then discuss the various mechanisms of BTK resistance including the role of genetic alteration, cancer stem cells, tumor microenvironment, and adaptive reprogramming bypassing the effect of BTK inhibition, and then provide a comprehensive review of current and emerging therapeutic options beyond BTKi including novel agents, CAR T cells, bispecific antibodies, and antibody-drug conjugates.

Lenalidomide derivatives and proteolysis-targeting chimeras for controlling neosubstrate degradation

Lenalidomide, an immunomodulatory drug (IMiD), is commonly used as a first-line therapy in many haematological cancers, such as multiple myeloma (MM) and 5q myelodysplastic syndromes (5q MDS), and it functions as a molecular glue for the protein degradation of neosubstrates by CRL4CRBN. Proteolysis-targeting chimeras (PROTACs) using IMiDs with a target protein binder also induce the degradation of target proteins. The targeted protein degradation (TPD) of neosubstrates is crucial for IMiD therapy. However, current IMiDs and IMiD-based PROTACs also break down neosubstrates involved in embryonic development and disease progression. Here, we show that 6-position modifications of lenalidomide are essential for controlling neosubstrate selectivity; 6-fluoro lenalidomide induced the selective degradation of IKZF1, IKZF3, and CK1α, which are involved in anti-haematological cancer activity, and showed stronger anti-proliferative effects on MM and 5q MDS cell lines than lenalidomide. PROTACs using these lenalidomide derivatives for BET proteins induce the selective degradation of BET proteins with the same neosubstrate selectivity. PROTACs also exert anti-proliferative effects in all examined cell lines. Thus, 6-position-modified lenalidomide is a key molecule for selective TPD using thalidomide derivatives and PROTACs.

Zanubrutinib Ameliorates Cardiac Fibrosis and Inflammation Induced by Chronic Sympathetic Activation

(1) Background: Heart failure (HF) is the final stage of multiple cardiac diseases, which have now become a severe public health problem worldwide. β-Adrenergic receptor (β-AR) overactivation is a major pathological factor associated with multiple cardiac diseases and mediates cardiac fibrosis and inflammation. Previous research has demonstrated that Bruton's tyrosine kinase (BTK) mediated cardiac fibrosis by TGF-β related signal pathways, indicating that BTK was a potential drug target for cardiac fibrosis. Zanubrutinib, a second-generation BTK inhibitor, has shown anti-fibrosis effects in previous research. However, it is unclear whether Zanubrutinib can alleviate cardiac fibrosis induced by β-AR overactivation; (2) Methods: In vivo: Male C57BL/6J mice were treated with or without the β-AR agonist isoproterenol (ISO) to establish a cardiac fibrosis animal model; (3) Results: In vivo: Results showed that the BTK inhibitor Zanubrutinib (ZB) had a great effect on cardiac fibrosis and inflammation induced by β-AR. In vitro: Results showed that ZB alleviated β-AR-induced cardiac fibroblast activation and macrophage pro-inflammatory cytokine production. Further mechanism studies demonstrated that ZB inhibited β-AR-induced cardiac fibrosis and inflammation by the BTK, STAT3, NF-κB, and PI3K/Akt signal pathways both in vivo and in vitro; (4) Conclusions: our research provides evidence that ZB ameliorates β-AR-induced cardiac fibrosis and inflammation.

Novel Agents in Waldenström Macroglobulinemia

Owing to the indolent nature of Waldenström macroglobulinemia, most patients experience a prolonged life expectancy, although many lines of therapy will likely be required to maintain disease control. Despite the currently available therapies, most patients will develop intolerance or resistance to multiple treatments. Therefore, new therapeutic options are being developed with a focus on targeted agents, such as novel Bruton tyrosine kinase (BTK) inhibitors and BTK degraders, as well as C-X-C chemokine receptor type 4, mucosa-associated lymphoid tissue translocation protein 1, and interleukin-1 receptor-associated kinase 4.

Advances in protein kinase drug discovery through targeting gatekeeper mutations

INTRODUCTION

Acquired resistance caused by gatekeeper mutations has become a major challenge for approved kinase inhibitors used in the clinic. Consequently, the development of new-generation inhibitors or degraders to overcome clinical resistance has become an important research focus for the field.

AREAS COVERED

This review summarizes the common gatekeeper mutations in druggable kinases and the constantly evolving inhibitors or degraders designed to overcome single or double mutations of gatekeeper residues. Furthermore, the authors provide their perspectives on the medicinal chemistry strategies for addressing clinical resistance with gatekeeper mutations.

EXPERT OPINION

The authors suggest optimizing kinase inhibitors to interact effectively with gatekeeper residues, altering the binding mode or binding pocket to avoid steric clashes, improving binding affinity with the target, utilizing protein degraders, and developing combination therapy. These approaches have the potential to be effective in overcoming resistance due to gatekeeper residues.

Discovery of Novel Bruton's Tyrosine Kinase PROTACs with Enhanced Selectivity and Cellular Efficacy

Bruton's tyrosine kinase (BTK) is a target for treating B-cell malignancies and autoimmune diseases, and several BTK inhibitors are already approved for use in humans. Heterobivalent BTK protein degraders are also in development, based on the premise that proteolysis targeting chimeras (PROTACs) may provide additional therapeutic benefits. However, most BTK PROTACs are based on the BTK inhibitor ibrutinib raising concerns about their selectivity profiles, given the known off-target effects of ibrutinib. Here, we disclose the discovery and in vitro characterization of BTK PROTACs based on the selective BTK inhibitor GDC-0853 and the cereblon recruitment ligand pomalidomide. PTD10 is a highly potent BTK degrader (DC50 0.5 nM) that inhibited cell growth and induced apoptosis at lower concentrations than the two parent molecules, as well as three previously reported BTK PROTACs, and had improved selectivity compared to ibrutinib-based BTK PROTACs.

Modeling the Tumor Microenvironment and Cancer Immunotherapy in Next-Generation Humanized Mice

Cancer immunotherapy has brought significant clinical benefits to numerous patients with malignant disease. However, only a fraction of patients experiences complete and durable responses to currently available immunotherapies. This highlights the need for more effective immunotherapies, combination treatments and predictive biomarkers. The molecular properties of a tumor, intratumor heterogeneity and the tumor immune microenvironment decisively shape tumor evolution, metastasis and therapy resistance and are therefore key targets for precision cancer medicine. Humanized mice that support the engraftment of patient-derived tumors and recapitulate the human tumor immune microenvironment of patients represent a promising preclinical model to address fundamental questions in precision immuno-oncology and cancer immunotherapy. In this review, we provide an overview of next-generation humanized mouse models suitable for the establishment and study of patient-derived tumors. Furthermore, we discuss the opportunities and challenges of modeling the tumor immune microenvironment and testing a variety of immunotherapeutic approaches using human immune system mouse models.

ITK degradation to block T cell receptor signaling and overcome therapeutic resistance in T cell lymphomas

Interleukin (IL)-2-inducible T cell kinase (ITK) is essential for T cell receptor (TCR) signaling and plays an integral role in T cell proliferation and differentiation. Unlike the ITK homolog BTK, no inhibitors of ITK are currently US Food and Drug Administration (FDA) approved. In addition, recent studies have identified mutations within BTK that confer resistance to both covalent and non-covalent inhibitors. Here, as an alternative strategy, we report the development of BSJ-05-037, a potent and selective heterobifunctional degrader of ITK. BSJ-05-037 displayed enhanced anti-proliferative effects relative to its parent inhibitor BMS-509744, blocked the activation of NF-kB/GATA-3 signaling, and increased the sensitivity of T cell lymphoma cells to cytotoxic chemotherapy both in vitro and in vivo. In summary, targeted degradation of ITK is a novel approach to modulate TCR signal strength that could have broad application for the investigation and treatment of T cell-mediated diseases.

PROTAC'ing oncoproteins: targeted protein degradation for cancer therapy

Molecularly targeted cancer therapies substantially improve patient outcomes, although the durability of their effectiveness can be limited. Resistance to these therapies is often related to adaptive changes in the target oncoprotein which reduce binding affinity. The arsenal of targeted cancer therapies, moreover, lacks coverage of several notorious oncoproteins with challenging features for inhibitor development. Degraders are a relatively new therapeutic modality which deplete the target protein by hijacking the cellular protein destruction machinery. Degraders offer several advantages for cancer therapy including resiliency to acquired mutations in the target protein, enhanced selectivity, lower dosing requirements, and the potential to abrogate oncogenic transcription factors and scaffolding proteins. Herein, we review the development of proteolysis targeting chimeras (PROTACs) for selected cancer therapy targets and their reported biological activities. The medicinal chemistry of PROTAC design has been a challenging area of active research, but the recent advances in the field will usher in an era of rational degrader design.

NRX-0492 degrades wild-type and C481 mutant BTK and demonstrates in vivo activity in CLL patient-derived xenografts

Bruton tyrosine kinase (BTK) is essential for B-cell receptor (BCR) signaling, a driver of chronic lymphocytic leukemia (CLL). Covalent inhibitors bind C481 in the active site of BTK and have become a preferred CLL therapy. Disease progression on covalent BTK inhibitors is commonly associated with C481 mutations. Here, we investigated a targeted protein degrader, NRX-0492, that links a noncovalent BTK-binding domain to cereblon, an adaptor protein of the E3 ubiquitin ligase complex. NRX-0492 selectively catalyzes ubiquitylation and proteasomal degradation of BTK. In primary CLL cells, NRX-0492 induced rapid and sustained degradation of both wild-type and C481 mutant BTK at half maximal degradation concentration (DC50) of ≤0.2 nM and DC90 of ≤0.5 nM, respectively. Sustained degrader activity was maintained for at least 24 hours after washout and was equally observed in high-risk (deletion 17p) and standard-risk (deletion 13q only) CLL subtypes. In in vitro testing against treatment-naïve CLL samples, NRX-0492 was as effective as ibrutinib at inhibiting BCR-mediated signaling, transcriptional programs, and chemokine secretion. In patient-derived xenografts, orally administered NRX-0492 induced BTK degradation and inhibited activation and proliferation of CLL cells in blood and spleen and remained efficacious against primary C481S mutant CLL cells collected from a patient progressing on ibrutinib. Oral bioavailability, >90% degradation of BTK at subnanomolar concentrations, and sustained pharmacodynamic effects after drug clearance make this class of targeted protein degraders uniquely suitable for clinical translation, in particular as a strategy to overcome BTK inhibitor resistance. Clinical studies testing this approach have been initiated (NCT04830137, NCT05131022).

The In-Cell Western immunofluorescence assay to monitor PROTAC mediated protein degradation

The In-Cell Western plate-based immunofluorescence assay is a useful methodology for monitoring protein levels and provides a facile moderate through-put method for PROTAC and degrader optimization. The method is compared to other reported assays used for PROTAC development. The advantages of this method are the greater through-put compared to Western blots due to its plate-based method and the ease to transfer between cells lines. Adherent cell lines are preferred, although suspension cells can be used following recommended modifications and precautions to the protocol. This method requires a high-quality antibody that recognizes the protein epitope in its cellular context, and in general provides data similar to Western blots with higher assay through-put.

Targeted protein degradation as an antiviral approach

Targeted protein degradation (TPD) has emerged as a new modality in drug discovery. In this approach, small molecules are used to drive degradation of the target protein of interest. Whereas most direct-acting antivirals (DAAs) inhibit or derange the activity of their viral protein targets and have occupancy-driven pharmacology, small molecules with a TPD-based mechanism have event-driven pharmacology exerted through their ability to induce target degradation. These contrasting mechanisms can result in significant differences in drug efficacy and pharmacodynamics that may be useful in the development of new classes of antivirals. While now being widely pursued in cancer biology and autoimmune disease, TPD has not yet been widely applied as an antiviral strategy. Here, we briefly review TPD pharmacology along with the current status of tools available for developing small molecules that achieve antiviral activity through a TPD mechanism. We also highlight aspects of TPD that may be especially useful in the development of antivirals and that we hope will motivate pursuit of TPD-based antivirals by the antivirals research community.

Progress of small molecules for targeted protein degradation: PROTACs and other technologies

Recent years have witnessed the rapid development of targeted protein degradation (TPD), especially proteolysis targeting chimeras. These degraders have manifested many advantages over small molecule inhibitors. To date, a huge number of degraders have been excavated against over 70 disease-related targets. In particular, degraders against estrogen receptor and androgen receptor have crowded into phase II clinical trial. TPD technologies largely expand the scope of druggable targets, and provide powerful tools for addressing intractable problems that can not be tackled by traditional small molecule inhibitors. In this review, we mainly focus on the structures and biological activities of small molecule degraders as well as the elucidation of mechanisms of emerging TPD technologies. We also propose the challenges that exist in the TPD field at present.

PROTACs: Walking through hematological malignancies

Proteolysis targeting chimeras (PROTACs) are heterobifunctional small molecules that uses the proteasome ubiquitin system to target proteins of interest and promote their degradation with remarkable selectivity. Importantly, unlike conventional small molecule inhibitors, PROTACs have proven highly effective in targeting undruggable proteins and those bearing mutations. Because of these considerations, PROTACs have increasingly become an emerging technology for the development of novel targeted anticancer therapeutics. Interestingly, many PROTACs have demonstrated a great potency and specificity in degrading several oncogenic drivers. Many of these, following extensive preclinical evaluation, have reached advanced stages of clinical testing in various cancers including hematologic malignancies. In this review, we provide a comprehensive summary of the recent advances in the development of PROTACs as therapeutic strategies in diverse hematological malignancies. A particular attention has been given to clinically relevant PROTACs and those targeting oncogenic mutants that drive resistance to therapies. We also discus limitations, and various considerations to optimize the design for effective PROTACs.

PROTAC: targeted drug strategy. Principles and limitations

The PROTAC (PROteolysis TArgeting Chimera) technology is a method of targeting intracellular proteins previously considered undruggable. This technology utilizes the ubiquitin-proteasome system in cells to specifically degrade target proteins, thereby offering significant advantages over conventional small-molecule inhibitors of the enzymatic function. Preclinical and preliminary clinical trials of PROTAC-based compounds (degraders) are presented. The review considers the general principles of the design of degraders. Advances and challenges of the PROTAC technology are discussed.

Targeting micro-environmental pathways by PROTACs as a therapeutic strategy

Tumor microenvironment (TME) composes of multiple cell types and non-cellular components, which supports the proliferation, metastasis and immune surveillance evasion of tumor cells, as well as accounts for the resistance to therapies. Therefore, therapeutic strategies using small molecule inhibitors (SMIs) and antibodies to block potential targets in TME are practical for cancer treatment. Targeted protein degradation using PROteolysis-TArgeting Chimera (PROTAC) technic has several advantages over traditional SMIs and antibodies, including overcoming drug resistance. Thus many PROTACs are currently under development for cancer treatment. In this review, we summarize the recent progress of PROTAC development that target TME pathways and propose the potential direction of future PROTAC technique to advance as novel cancer treatment options.