The novel cereblon modulator CC-885 inhibits mitophagy via selective degradation of BNIP3L

Leukemia and mitophagy: a novel perspective for understanding oncogenesis and resistance

Mitophagy, the selective autophagic process that specifically degrades mitochondria, serves as a vital regulatory mechanism for eliminating damaged mitochondria and maintaining cellular balance. Emerging research underscores the central role of mitophagy in the initiation, advancement, and treatment of cancer. Mitophagy is widely acknowledged to govern mitochondrial homeostasis in hematopoietic stem cells (HSCs), influencing their metabolic dynamics. In this article, we integrate recent data to elucidate the regulatory mechanisms governing mitophagy and its intricate significance in the context of leukemia. An in-depth molecular elucidation of the processes governing mitophagy may serve as a basis for the development of pioneering approaches in targeted therapeutic interventions.

Applications of protein ubiquitylation and deubiquitylation in drug discovery

The ubiquitin (Ub)-proteasome system (UPS) is the major machinery mediating specific protein turnover in eukaryotic cells. By ubiquitylating unwanted, damaged, or harmful proteins and driving their degradation, UPS is involved in many important cellular processes. Several new UPS-based technologies, including molecular glue degraders and PROTACs (proteolysis-targeting chimeras) to promote protein degradation, and DUBTACs (deubiquitinase-targeting chimeras) to increase protein stability, have been developed. By specifically inducing the interactions between different Ub ligases and targeted proteins that are not otherwise related, molecular glue degraders and PROTACs degrade targeted proteins via the UPS; in contrast, by inducing the proximity of targeted proteins to deubiquitinases, DUBTACs are created to clear degradable poly-Ub chains to stabilize targeted proteins. In this review, we summarize the recent research progress in molecular glue degraders, PROTACs, and DUBTACs and their applications. We discuss immunomodulatory drugs, sulfonamides, cyclin-dependent kinase-targeting molecular glue degraders, and new development of PROTACs. We also introduce the principle of DUBTAC and its applications. Finally, we propose a few future directions of these three technologies related to targeted protein homeostasis.

Crbn-based molecular Glues: Breakthroughs and perspectives

CRBN is a substrate receptor for the Cullin Ring E3 ubiquitin ligase 4 (CRL4) complex. It has been observed that CRBN can be exploited by small molecules to facilitate the recruitment and ubiquitination of non-natural CRL4 substrates, resulting in the degradation of neosubstrate through the ubiquitin-proteasome system. This phenomenon, known as molecular glue-induced protein degradation, has emerged as an innovative therapeutic approach in contrast to traditional small-molecule drugs. One key advantage of molecular glues, in comparison to conventional small-molecule drugs adhering to Lipinski's Rule of Five, is their ability to operate without the necessity for specific binding pockets on target proteins. This unique characteristic empowers molecular glues to interact with conventionally intractable protein targets, such as transcription factors and scaffold proteins. The ability to induce the degradation of these previously elusive targets by hijacking the ubiquitin-proteasome system presents a promising avenue for the treatment of recalcitrant diseases. Nevertheless, the rational design of molecular glues remains a formidable challenge due to the limited understanding of their mechanisms and actions. This review offers an overview of recent advances and breakthroughs in the field of CRBN-based molecular glues, while also exploring the prospects for a systematic approach to designing these compounds.

Targeting autophagy drug discovery: Targets, indications and development trends

Autophagy plays a vital role in sustaining cellular homeostasis and its alterations have been implicated in the etiology of many diseases. Drugs development targeting autophagy began decades ago and hundreds of agents were developed, some of which are licensed for the clinical usage. However, no existing intervention specifically aimed at modulating autophagy is available. The obstacles that prevent drug developments come from the complexity of the actual impact of autophagy regulators in disease scenarios. With the development and application of new technologies, several promising categories of compounds for autophagy-based therapy have emerged in recent years. In this paper, the autophagy-targeted drugs based on their targets at various hierarchical sites of the autophagic signaling network, e.g., the upstream and downstream of the autophagosome and the autophagic components with enzyme activities are reviewed and analyzed respectively, with special attention paid to those at preclinical or clinical trials. The drugs tailored to specific autophagy alone and combination with drugs/adjuvant therapies widely used in clinical for various diseases treatments are also emphasized. The emerging drug design and development targeting selective autophagy receptors (SARs) and their related proteins, which would be expected to arrest or reverse the progression of disease in various cancers, inflammation, neurodegeneration, and metabolic disorders, are critically reviewed. And the challenges and perspective in clinically developing autophagy-targeted drugs and possible combinations with other medicine are considered in the review.

A global bibliometric and visualized analysis of the links between the autophagy and acute myeloid leukemia

Background and objectives: Autophagy is a cellular process where damaged organelles or unwanted proteins are packaged into a double-membrane structure and transported to lysosomes for degradation. Autophagy plays a regulatory role in various hematologic malignancies, including acute myeloid leukemia (AML). However, there are few bibliometric studies on the role of autophagy in AML. The purpose of this study is to clarify the role of autophagy in acute myeloid leukemia through bibliometric analysis. Methods: The literature on autophagy and AML research from 2003 to 2023 was searched in Web of Science Core Collection, and bibliometric tools such as VOSviewer 1.6.18, Cite Space (6.1.R3), RStudio (R package bibliometrix), and Scimago Graphica were used to understand the current status and hotspots of autophagy and AML research. The study conducted an analysis of various dimensions including the quantity of publications, countries, institutions, journals, authors, co-references, keywords, and to predict future development trends in this field by drawing relevant visualization maps. Results: A total of 343 articles were obtained, published in 169 journals, written by 2,323 authors from 295 institutions in 43 countries. The journals with the most publications were Blood and Oncotarget. China had the most publications, and Chongqing Medical University and Sun Yat-sen University had the most publications. The author with the highest number of publications was Tschan, Mario P. The main types of research included clinical research, in vitro experiments, in vivo experiments, public database information, and reviews, and the forms of therapeutic effects mainly focused on genetic regulation, traditional Chinese medicine combination, autophagy inhibitors, and drug targets. The research hotspots of autophagy and AML in the past 17 years have focused on genetic regulation, autophagy inhibition, and targeted drugs. Chemotherapy resistance and mitochondrial autophagy will be the forefront of research. Conclusion: The gradual increase in the literature on autophagy and AML research and the decline after 2022 could be a result of authors focusing more on the type of research and the quality of the literature. The current research hotspots are mainly genetic regulation, autophagy inhibition, and autophagy-related targeted drugs. In future, autophagy will remain the focus of the AML field, with research trends likely to focus more on AML chemotherapy resistance and mitochondrial autophagy.

From Thalidomide to Rational Molecular Glue Design for Targeted Protein Degradation

Thalidomide and its derivatives are powerful cancer therapeutics that are among the best-understood molecular glue degraders (MGDs). These drugs selectively reprogram the E3 ubiquitin ligase cereblon (CRBN) to commit target proteins for degradation by the ubiquitin-proteasome system. MGDs create novel recognition interfaces on the surface of the E3 ligase that engage in induced protein-protein interactions with neosubstrates. Molecular insight into their mechanism of action opens exciting opportunities to engage a plethora of targets through a specific recognition motif, the G-loop. Our analysis shows that current CRBN-based MGDs can in principle recognize over 2,500 proteins in the human proteome that contain a G-loop. We review recent advances in tuning the specificity between CRBN and its MGD-induced neosubstrates and deduce a set of simple rules that govern these interactions. We conclude that rational MGD design efforts will enable selective degradation of many more proteins, expanding this therapeutic modality to more disease areas.

A proteomic landscape of pharmacologic perturbations for functional relevance

Pharmacological perturbation studies based on protein-level signatures are fundamental for drug discovery. In the present study, we used a mass spectrometry (MS)-based proteomic platform to profile the whole proteome of the breast cancer MCF7 cell line under stress induced by 78 bioactive compounds. The integrated analysis of perturbed signal abundance revealed the connectivity between phenotypic behaviors and molecular features in cancer cells. Our data showed functional relevance in exploring the novel pharmacological activity of phenolic xanthohumol, as well as the noncanonical targets of clinically approved tamoxifen, lovastatin, and their derivatives. Furthermore, the rational design of synergistic inhibition using a combination of histone methyltransferase and topoisomerase was identified based on their complementary drug fingerprints. This study provides rich resources for the proteomic landscape of drug responses for precision therapeutic medicine.

A platform for the rapid synthesis of molecular glues (Rapid-Glue) under miniaturized conditions for direct biological screening

Molecular glues, functioning via inducing degradation of the target protein while having similar molecular weight as traditional small molecule drugs, are emerging as a promising modality for the development of therapeutic agents. However, the development of molecular glues is limited by the lack of general principles and systematic methods. Not surprisingly, most molecular glues have been identified serendipitously or through phenotypic screening of large libraries. However, the preparation of large and diverse molecular glue libraries is not an easy task and requires extensive resources. We previously developed platforms for rapid synthesis of proteolysis targeting chimeras (PROTACs) that can be used directly for biological screening with minimal resources. Herein, we report a platform of rapid synthesis of molecular glues (Rapid-Glue) via a micromolar scale coupling reaction between hydrazide motif on the E3 ligase ligands and commercially available aldehydes with diverse structures. A pilot library of 1520 compounds is generated under miniaturized conditions in a high throughput manner without any further manipulation including purification after the synthesis. Through this platform, we identified two highly selective GSPT1 molecular glues through direct screening in cell-based assays. Three additional analogues were prepared from readily available starting materials by replacing the hydrolytic labile acylhydrazone linker with a more stable amide linker based on the two hits. All three analogues showed significant GSPT1 degradation activity and two of them possess comparable activity to the corresponding hit. The feasibility of our strategy is thus verified. Further studies by increasing the diversity and size of the library followed by appropriate assays will likely yield distinct molecular glues targeting novel neo-substrates.

Emerging approaches to CDK inhibitor development, a structural perspective

Aberrant activity of the cyclin-dependent kinase family is frequently noted in a number of diseases identifying them as potential targets for drug development. However, current CDK inhibitors lack specificity owing to the high sequence and structural conservation of the ATP binding cleft across family members, highlighting the necessity of finding novel modes of CDK inhibition. The wealth of structural information regarding CDK assemblies and inhibitor complexes derived from X-ray crystallographic studies has been recently complemented through the use of cryo-electron microscopy. These recent advances have provided insights into the functional roles and regulatory mechanisms of CDKs and their interaction partners. This review explores the conformational malleability of the CDK subunit, the importance of SLiM recognition sites in CDK complexes, the progress made in chemically induced CDK degradation and how these studies can contribute to CDK inhibitor design. Additionally, fragment-based drug discovery can be utilised to identify small molecules that bind to allosteric sites on the CDK surface employing interactions which mimic those of native protein-protein interactions. These recent structural advances in CDK inhibitor mechanisms and in chemical probes which do not occupy the orthosteric ATP binding site can provide important insights for targeted CDK therapies.

Targeting cereblon in hematologic malignancies

The protein cereblon (CRBN) is a substrate receptor of the cullin 4-really interesting new gene (RING) E3 ubiquitin ligase complex CRL4^CRBN. Targeting CRBN mediates selective protein ubiquitination and subsequent degradation via the proteasome. This review describes novel thalidomide analogs, immunomodulatory drugs, also known as CRBN E3 ubiquitin ligase modulators or molecular glues (avadomide, iberdomide, CC-885, CC-90009, BTX-1188, CC-92480, CC-99282, CFT7455, and CC-91633), and CRBN-based proteolysis targeting chimeras (PROTACs) with increased efficacy and potent activity for application in hematologic malignancies. Both types of CRBN-binding drugs, molecular glues, and PROTACs stimulate the interaction between CRBN and its neosubstrates, recruiting target disease-promoting proteins and the E3 ubiquitin ligase CRL4^CRBN. Proteins that are traditionally difficult to target (transcription factors and oncoproteins) can be polyubiquitinated and degraded in this way. The competition of CRBN neosubstrates with endogenous CRBN-interacting proteins and the pharmacology and rational combination therapies of and mechanisms of resistance to CRL4^CRBN modulators or CRBN-based PROTACs are described.

Targeting CRL4 suppresses chemoresistant ovarian cancer growth by inducing mitophagy

Chemoresistance has long been the bottleneck of ovarian cancer (OC) prognosis. It has been shown that mitochondria play a crucial role in cell response to chemotherapy and that dysregulated mitochondrial dynamics is intricately linked with diseases like OC, but the underlying mechanisms remain equivocal. Here, we demonstrate a new mechanism where CRL4^CUL4A/DDB1 manipulates OC cell chemoresistance by regulating mitochondrial dynamics and mitophagy. CRL4^CUL4A/DDB1 depletion enhanced mitochondrial fission by upregulating AMPKα^Thr172 and MFF^{Ser172/Ser146} phosphorylation, which in turn recruited DRP1 to mitochondria. CRL4^CUL4A/DDB1 loss stimulated mitophagy through the Parkin-PINK1 pathway to degrade the dysfunctional and fragmented mitochondria. Importantly, CRL4^CUL4A/DDB1 loss inhibited OC cell proliferation, whereas inhibiting autophagy partially reversed this disruption. Our findings provide novel insight into the multifaceted function of the CRL4 E3 ubiquitin ligase complex in regulating mitochondrial fission, mitophagy, and OC chemoresistance. Disruption of CRL4^CUL4A/DDB1 and mitophagy may be a promising therapeutic strategy to overcome chemoresistance in OC.

Proteomic characterization of post-translational modifications in drug discovery

Protein post-translational modifications (PTMs), which are usually enzymatically catalyzed, are major regulators of protein activity and involved in almost all celluar processes. Dysregulation of PTMs is associated with various types of diseases. Therefore, PTM regulatory enzymes represent as an attractive and important class of targets in drug research and development. Inhibitors against kinases, methyltransferases, deacetyltransferases, ubiquitin ligases have achieved remarkable success in clinical application. Mass spectrometry-based proteomics technologies serve as a powerful approach for system-wide characterization of PTMs, which facilitates the identification of drug targets, elucidation of the mechanisms of action of drugs, and discovery of biomakers in personalized therapy. In this review, we summarize recent advances of proteomics-based studies on PTM targeting drugs and discuss how proteomics strategies facilicate drug target identification, mechanism elucidation, and new therapy development in precision medicine.

PPAR agonists attenuate lenalidomide's anti-myeloma activity in vitro and in vivo

Many patients with multiple myeloma (MM) have comorbidities and are treated with PPAR agonists. Immunomodulatory agents (IMiDs) are the cornerstones for MM therapy. Currently, little is known about how co-administration of PPAR agonists impacts lenalidomide treatment in patients with MM. Here, we determined the effects of PPAR agonists on anti-myeloma activities of lenalidomide in vitro and in a myeloma xenograft mouse model. Genetic overexpression and CRISPR/cas9 knockout experiments were performed to determine the role of CRBN in the PPAR-mediated pathway. A retrospective cohort study was performed to determine the correlation of PPAR expression with the outcomes of patients with MM. PPAR agonists down-regulated CRBN expression and reduced the anti-myeloma efficacy of lenalidomide in vitro and in vivo. Co-treatment with PPAR antagonists increased CRBN expression and improved sensitivity to lenalidomide. PPAR expression was higher in bone marrow cells of patients with newly diagnosed MM than in normal control bone marrow samples. High PPAR expression was correlated with poor clinical outcomes. Our study provides the first evidence that PPARs transcriptionally regulate CRBN and that drug-drug interactions between PPAR agonists and IMiDs may impact myeloma treatment outcomes.

CRL4CRBN E3 Ligase Complex as a Therapeutic Target in Multiple Myeloma

Simple Summary

Immunomodulatory drugs (IMiDs) are effective in the treatment of multiple myeloma (MM) and other hematological malignancies. Cereblon (CRBN), a target of IMiDs, forms the CRL4 E3 ubiquitin ligase complex (CRL4^CRBN) with DDB1, CUL4A and RBX1. The insight into the molecular mechanism of IMiDs action has advanced dramatically since the identification of cereblon (CRBN) as their direct target. Targeting CRBN by IMiDs modifies CRL4^CRBN substrate specificity towards non-physiological protein targets which are subsequently ubiquitinated and degraded by the proteasome. To date, IMiDs are the only known group of protein degraders used in clinical practice. This review provides the current state of knowledge about thalidomide and its derivatives’ mechanisms of action, and highlights the future perspectives for targeted protein degraders.

Abstract

Multiple myeloma (MM) is the second most common hematological malignancy with a recurrent clinical course. The introduction of immunomodulatory drugs (IMiDs) was one of the milestones in MM therapy leading to a significant improvement in patients’ prognosis. Currently, IMiDs are the backbone of MM therapy in newly diagnosed and relapsed/refractory settings. It is now known that IMiDs exert their anti-myeloma activity mainly by binding cereblon (CRBN), the substrate receptor protein of the CRL4 E3 ubiquitin ligase (CRL4^CRBN) complex. By binding CRBN, IMiDs alter its substrate specificity, leading to ubiquitination and proteasomal degradation of proteins essential for MM cell survival. Following the success of IMiDs, it is not surprising that the possibility of using the CRL4^CRBN complex’s activity to treat MM is being further explored. In this review, we summarize the current state of knowledge about novel players in the MM therapeutic landscape, namely the CRBN E3 ligase modulators (CELMoDs), the next generation of IMiDs with broader biological activity. In addition, we discuss a new strategy of tailored proteolysis called proteolysis targeting chimeras (PROTACs) using the CRL4^CRBN to degrade typically undruggable proteins, which may have relevance for the treatment of MM and other malignancies in the future.

A review on the treatment of multiple myeloma with small molecular agents in the past five years

Multiple myeloma is currently incurable, and the incidence rate is increasing year by year worldwide. Although in recent years the combined treatment plan based on proteasome inhibitors and immunomodulatory drugs has greatly improved the treatment effect of multiple myeloma, most patients still relapse and become resistant to current treatments. To solve this problem, scientists are committed to developing drugs with higher specificity, such as iberdomide, which is highly specific to ikaros and aiolos. This review aims to focus on the small molecular agents that are being researched/clinically used for the treatment of multiple myeloma, including the target mechanism, structure-activity relationship and application prospects of small molecular agents.

A novel Cereblon E3 ligase modulator with antitumor activity in gastrointestinal cancer

Targeted protein degradation offers new opportunities to inactivate cancer drivers and has successfully entered the clinic. Ways to induce selective protein degradation include proteolysis targeting chimera (PROTAC) technology and immunomodulatory (IMiDs) / next-generation Cereblon (CRBN) E3 ligase modulating drugs (CELMoDs). Here, we aimed to develop a MYC PROTAC based on the MYC-MAX dimerization inhibitor 10058-F4 derivative 28RH and Thalidomide, called MDEG-541. We show that a subgroup of gastrointestinal cancer cell lines and primary patient-derived organoids are MDEG-541 sensitive. Although MYC expression was regulated in a CRBN-, proteasome- and ubiquitin-dependent manner, we provide evidence that MDEG-541 induced the degradation of CRBN neosubstrates, including G1 to S phase transition 1/2 (GSPT1/2) and the Polo-like kinase 1 (PLK1). In sum, we have established a CRBN-dependent degrader of relevant cancer targets with activity in gastrointestinal cancers.

Cereblon: promise and challenges for combating human diseases

Cereblon (CRBN) is a substrate recognition protein in the E3-ligase ubiquitin complex. The binding target of CRBN varies according to tissues and cells, and the protein regulates various biological functions by regulating tissue-specific targets. As new endogenous targets of CRBN have been identified over the past decade, the physiological and pathological functions of CRBN and its potential as a therapeutic target in various diseases have greatly expanded. For this purpose, in this review article, we introduce the basic principle of the ubiquitin-proteasome system, the regulation of physiological/pathological functions related to the endogenous substrate of CRBN, and the discovery of immunomodulatory imide drug-mediated neo-substrates of CRBN. In addition, the development of CRBN-based proteolysis-targeting chimeras, which has been actively researched recently, and strategies for developing therapeutic agents using them are introduced. These recent updates on CRBN will be useful in the establishment of strategies for disease treatment and utilization of CRBNs in biomedical engineering and clinical medicine.

Expression and Clinical Significance of BCL2 Interacting Protein 3 Like in Multiple Myeloma

Multiple myeloma (MM) is one of the main blood disorders threatening human health today. This study aimed to examine the expression of BCL-2/adenovirus E1B 19 kDa-interacting protein 3-like (BNIP3L) in patients with MM and explore its mechanisms in silico. Bone marrow samples (n = 36 from patients with MM and n = 12 from healthy donors) were used to conduct BNIP3L expression analysis using immunohistochemistry. Microarray or RNA sequencing data from the Sequence Read Archive, Gene Expression Omnibus, and ArrayExpress databases were used to appraise BNIP3L expression and its prognostic role in patients with MM. The co-expressed genes of BNIP3L were identified for enrichment and protein-protein interaction (PPI) analyses to determine the associated signaling pathways. Immunohistochemistry indicated that BNIP3L expression in bone marrow of patients with MM was significantly lower than that in bone marrow of healthy donors. BNIP3L mRNA expression was also significantly lower in patients with MM than in healthy donors. The overall standard mean difference (SMD) for downregulation of BNIP3L was −0.62 [−1.17, −0.06], and the area under the curve was 0.81 [0.78, 0.85] based on a total of 694 MM cases. The overall survival analysis demonstrated that BNIP3L levels could act as an independent protective indicator of MM patient survival (HR = 0.79). Moreover, 261 co-expressed genes of BNIP3L were confirmed and found to be mainly involved in the adipocytokine signaling pathway. We preliminarily proved that downregulation of BNIP3L may play an important role in the occurrence and development of MM, and the promoting cancer capacity may be related to the pathway of adipocytokine signaling pathway.

Key regulators of sensitivity to immunomodulatory drugs in cancer treatment

Immunomodulatory drugs (IMiDs) include thalidomide, lenalidomide, and pomalidomide, which have shown significant efficacy in the treatment of multiple myeloma (MM), myelodysplastic syndrome (MDS) with deletion of chromosome 5q (del(5q)) and other hematological malignancies. IMiDs hijack the CRL4^CRBN ubiquitin ligase to target cellular proteins for ubiquitination and degradation, which is responsible for their clinical activity in MM and MDS with del(5q). However, intrinsic and acquired resistance frequently limit the efficacy of IMiDs. Recently, many efforts have been made to explore key regulators of IMiD sensitivity, resulting in great advances in the understanding of the regulatory networks related to this class of drugs. In this review, we describe the mechanism of IMiDs in cancer treatment and summarize the key regulators of IMiD sensitivity. Furthermore, we introduce genome-wide CRISPR-Cas9 screenings, through which the regulatory networks of IMiD sensitivity could be identified.

Cereblon modulator CC-885 induces CRBN-dependent ubiquitination and degradation of CDK4 in multiple myeloma

Molecular glue degraders that hijack cellular E3 ubiquitin ligases to target disease-driven proteins for proteosome-dependent degradation are emerging as a promising treatment. Immunomodulatory drugs are classical molecular glue that bind to cereblon (CRBN) to repurpose the function of the CRL4(CRBN) E3 ubiquitin ligase and developed to treat various hematological malignancies. Recently, a novel cereblon modulator CC-885 was developed to elicit broad antitumor activity. Although the degradation of GSPT1 is essential for the broad in vitro antitumor activity of CC-885, it is unclear whether other neosubstrates also contribute to the pharmacological effects of CC-885, especially in multiple myeloma (MM). Here, we show that CC-885 treatment caused growth retardant of MM cells via impairment of cell cycle progression and cell death both in vitro and in vivo. Mechanically, CC-885 selectively induced the ubiquitination and degradation of CDK4 in MM cells in a CRBN-dependent manner. CC-885-mediated CDK4 destruction decreased the phosphorylation of the tumor suppressor retinoblastoma (RB) and prevented the expression of E2F downstream genes. Importantly, genetic ablation or pharmacological inhibition of CDK4 enhances CC-885-induced cytotoxicity in MM cells, suggesting CDK4 destruction contributed to the cytotoxicity of CC-885 in MM cells.

Neddylation regulation of mitochondrial structure and functions

Mitochondria are the powerhouse of a cell. The structure and function of mitochondria are precisely regulated by multiple signaling pathways. Neddylation, a post-translational modification, plays a crucial role in various cellular processes including cellular metabolism via modulating the activity, function and subcellular localization of its substrates. Recently, accumulated data demonstrated that neddylation is involved in regulation of morphology, trafficking and function of mitochondria. Mechanistic elucidation of how mitochondria is modulated by neddylation would further our understanding of mitochondrial regulation to a new level. In this review, we first briefly introduce mitochondria, then neddylation cascade, and known protein substrates subjected to neddylation modification. Next, we summarize current available data of how neddylation enzymes, its substrates (including cullins/Cullin-RING E3 ligases and non-cullins) and its inhibitor MLN4924 regulate the structure and function of mitochondria. Finally, we propose the future perspectives on this emerging and exciting field of mitochondrial research.

Selective Degradation of GSPT1 by Cereblon Modulators Identified via a Focused Combinatorial Library

Cereblon (CRBN) is an E3 ligase adapter protein that can be reprogrammed by imide-class compounds such as thalidomide, lenalidomide, and pomalidomide to induce the degradation of neo-substrate proteins. In order to identify additional small molecule CRBN modulators, we implemented a focused combinatorial library approach where we fused an imide-based CRBN-binding pharmacophore to a heterocyclic scaffold, which could be further elaborated. We screened the library for CRBN-dependent antiproliferative activity in the multiple myeloma cell line MM1.S and identified five hit compounds. Quantitative chemical proteomics of hit compounds revealed that they induced selective degradation of GSPT1, a translation termination factor that is currently being explored as a therapeutic target for the treatment of acute myeloid leukemia. Molecular docking studies with CRBN and GSPT1 followed by analogue synthesis identified a possible hydrogen bond interaction with the central pyrimidine ring as a molecular determinant of hit compounds' selectivity. This study demonstrates that a focused combinatorial library design, phenotypic screening, and chemical proteomics can provide a suitable workflow to efficiently identify novel CRBN modulators.