Proteolysis Targeting Chimera Degraders Research Articles

Discovery of KW0113 as a First and Effective PROTAC Degrader of DNMT1 Protein.

DNA methyltransferase 1 (DNMT1) is an attractive therapeutic target for acute myelocytic leukemia (AML) and other malignancies. It has been reported that the genetic depletion of DNMT1 inhibited AML cell proliferation through reversing DNA methylation abnormalities. However, no DNMT1-targeted PROTAC degraders have been reported yet. Herein, a series of proteolysis-targeting chimera (PROTAC) degrader of DNMT1 based on dicyanopyridine scaffold and VHL E3 ubiquitin ligase ligand was developed. Among them, KW0113 (DC50=643/899 nM in MV4-11/MOLM-13 cells) exhibited optimal DNMT1 degradation. KW0113 induced DNMT1-selective degradation in a dose- and time-dependent manner through VHL engagement. Moreover, KW0113 inhibited AML cell growth by reversing promoter DNA hypermethylation and tumor-suppressor genes silencing. In conclusion, these findings proved the capability of PROTAC strategy for inducing DNMT1 degradation, demonstrated the therapeutic potential of DNMT1-targeted PROTACs. This work also provided a convenient chemical knockdown tool for DNMT1-related studies.

Development of PROTAC Degrader Drugs for Cancer

The development of novel drug modalities is necessary to overcome the current critical issues in the treatment of cancer, namely toxicity, insufficient efficacy, and the development of resistance. Unlike classical small molecule inhibitors that only block a single function or interaction of a protein involved in oncogenic signaling, proteolysis-targeting chimeras (PROTACs) degrade the entire protein, thus offering a potential paradigm shift. PROTACs are bivalent small molecules that recruit a target protein in proximity to an E3 ligase, promoting the transfer of ubiquitin, which marks the protein for proteasomal degradation. Because of their unique properties, PROTACs offer an attractive alternative as targeted therapeutics. The first PROTAC entered the clinic 5 years ago, and since then more than 30 have followed. In this review, we discuss the current compounds being investigated in the clinic, the key aspects of their design, and their potential for treating cancer.

Design of Murine Double Minute 2 Proteolysis Targeting Chimera Degraders with a Built-In Tumor-Targeting Ability.

Proteolysis targeting chimeras (PROTACs) are heterobifunctional molecules to induce the proteasomal degradation of target proteins. Currently, there are no tumor-targeting PROTACs for modulating oncogenic murine double minute 2 (MDM2). AS1411 is a tumor-targeting aptamer that specifically recognizes nucleolin (NCL) overexpressed on the surface of tumor cells. We recently repurposed AS1411 as an MDM2 recruiter since it could form an NCL-bridged ternary complex with MDM2. In this study, we design a PROTAC molecule AS1411-VH032 via conjugating AS1411 with a recruiter of von Hippel-Lindau (VHL) ligase VH032. AS1411-VH032 facilitates tumor-selective degradation of MDM2, leading to tumor shrinkage with no detectable toxicity. Besides being a molecular target, MDM2 also serves as an E3 ligase harnessed by PROTACs. Thus, we developed an AS1411-based homo-PROTAC homoAS1411, which induces tumor-specific suicide degradation of MDM2 and prevents tumor progression without causing side effects. Both AS1411-VH032 and homoAS1411 are promising MDM2 degraders with built-in tumor-targeting ability, which balances the antitumor efficacy with a favorable safety profile.

Discovery of ZLC491 as a Potent, Selective, and Orally Bioavailable CDK12/13 PROTAC Degrader.

Selective degradation of cyclin-dependent kinases 12 and 13 (CDK12/13) emerges as a new potential therapeutic approach for triple-negative breast cancer (TNBC) and other human cancers. While several proteolysis-targeting chimera (PROTAC) degraders of CDK12/13 were reported, none are orally bioavailable. Here, we report the discovery of ZLC491 as a potent, selective, and orally bioavailable CDK12/13 PROTAC degrader. The compound effectively degraded CDK12 and CDK13 with DC50 values of 32 and 28 nM, respectively, in TNBC MDA-MB-231 cells. Global proteomic assessment and mechanistic studies revealed that ZLC491 selectively induced CDK12/13 degradation in a cereblon- and proteasome-dependent manner. Furthermore, the molecule efficiently suppressed transcription and expression of long genes, predominantly a subset of genes associated with DNA damage response, and significantly inhibited proliferation of multiple TNBC cell lines. Importantly, ZLC491 achieved an oral bioavailability of 46.8% in rats and demonstrated potent in vivo degradative effects on CDK12/13 in an MDA-MB-231 xenografted mouse model.

Sorafenib and SIAIS361034, a novel PROTAC degrader of BCL-xL, display synergistic antitumor effects on hepatocellular carcinoma with minimal hepatotoxicity

The overexpression of BCL-xL is closely associated with poor prognosis in hepatocellular carcinoma (HCC). While the strategy of combination of BCL-xL and MCL-1 for treating solid tumors has been reported, it presents significant hepatotoxicity. SIAIS361034, a novel proteolysis targeting chimera (PROTAC) agent, selectively induces the ubiquitination and subsequent proteasomal degradation of BCL-xL through the CRBN-E3 ubiquitin ligase. When combined with sorafenib, SIAIS361034 showed a potent synergistic effect in inhibiting hepatocellular carcinoma development both in vitro and in vivo. Since SIAIS361034 exhibits a high degree of selectivity for degrading BCL-xL in hepatocellular carcinoma, the hepatotoxicity typically associated with the combined inhibition of BCL-xL and MCL-1 is significantly reduced, thereby greatly enhancing safety. Mechanistically, BCL-xL and MCL-1 sequester the BH3-only protein BIM on mitochondria at baseline. Treatment with SIAIS361034 and sorafenib destabilizes BIM/BCL-xL and BIM/MCL1 association, resulting in the liberation of more BIM proteins to trigger apoptosis. Additionally, we discovered a novel compensatory regulation mechanism in hepatocellular carcinoma cells. BIM can rapidly respond to changes in the balance between BCL-xL and MCL-1 through their co-transcription factor MEF2C to maintain apoptosis resistance. In summary, the combination therapy of SIAIS361034 and sorafenib represents an effective and safe approach for inhibiting hepatocellular carcinoma progression. The novel balancing mechanism may also provide insights for combination and precision therapies in the treatment of hepatocellular carcinoma.

Discovery of Covalent MLKL PROTAC Degraders via Optimization of a Theophylline Derivative Ligand for Treating Necroptosis.

Mixed lineage kinase domain-like pseudokinase (MLKL) initiates necroptosis and could serve as a therapeutic target related to a series of human diseases. Proteolysis-targeting chimeras (PROTACs) are useful tools for degrading pathological proteins and blocking disease processes. Using computer-aided modeling and molecular dynamics simulations, we developed a series of covalent MLKL PROTACs by linking and optimizing a theophylline derivative that covalently targets MLKL. Via structure-activity relationship studies, MP-11 was identified as a potent MLKL PROTAC degrader. Furthermore, MP-11 showed lower toxicity than the original MLKL ligand, exhibiting nanomolar-scale antinecroptotic activity on human cell lines. Xenograft model studies showed that MP-11 effectively degraded MLKL in vivo. Importantly, our study demonstrates that the covalent binding strategy is an effective approach for designing MLKL-targeting PROTACs, serving as a model for developing PROTACs to treat future necroptosis-related human diseases.

Discovery of a potent PROTAC degrader for RNA demethylase FTO as antileukemic therapy

The fat mass and obesity-associated protein (FTO) is an RNA demethylase required for catalytic demethylation of N6-methyladenosine (m6A); it is highly expressed and functions as an oncogene in acute myeloid leukemia (AML). Currently, the overarching objective of targeting FTO is to precisely inhibit the catalytic activity. Meanwhile, whether FTO degradation also exerts antileukemic effects remains unknown. Herein, we designed the first FTO-targeting proteolysis targeting chimera (PROTAC) degrader QP73 using our FTO inhibitor Dac85—which potently inhibits FTO demethylation in AML cell lines—as a warhead. Notably, QP73 significantly induced FTO degradation in a time-, dose-, and ubiquitin–proteasome system-dependent manner and had superior antiproliferative activities to the FTO inhibitor Dac85 in various AML cell lines. Moreover, QP73 treatment significantly increased m6A modification on mRNA, promoted myeloid differentiation, and induced apoptosis of AML cells. Quantitative proteomics analysis showed that QP73 induced complete FTO degradation, upregulating RARA and ASB2 abundance and downregulating CEBPA, MYC, PFKP, and LDHB levels in AML cells. Lastly, QP73 exhibited antileukemic activity by increasing m6A modification and decreasing FTO levels in xenograft AML tumors. This proof-of-concept study shows that FTO-targeting PROTAC degraders can regulate the FTO signaling pathway and have potential antileukemia applications.

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

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

A RIPK1-specific PROTAC degrader achieves potent antitumor activity by enhancing immunogenic cell death

Receptor-interacting serine/threonine-protein kinase 1 (RIPK1) functions as a critical stress sentinel that coordinates cell survival, inflammation, and immunogenic cell death (ICD). Although the catalytic function of RIPK1 is required to trigger cell death, its non-catalytic scaffold function mediates strong pro-survival signaling. Accordingly, cancer cells can hijack RIPK1 to block necroptosis and evade immune detection. We generated a small-molecule proteolysis-targeting chimera (PROTAC) that selectively degraded human and murine RIPK1. PROTAC-mediated depletion of RIPK1 deregulated TNFR1 and TLR3/4 signaling hubs, accentuating the output of NF-κB, MAPK, and IFN signaling. Additionally, RIPK1 degradation simultaneously promoted RIPK3 activation and necroptosis induction. We further demonstrated that RIPK1 degradation enhanced the immunostimulatory effects of radio- and immunotherapy by sensitizing cancer cells to treatment-induced TNF and interferons. This promoted ICD, antitumor immunity, and durable treatment responses. Consequently, targeting RIPK1 by PROTACs emerges as a promising approach to overcome radio- or immunotherapy resistance and enhance anticancer therapies.

Discovery of First-in-Class PROTAC Degraders of SARS-CoV-2 Main Protease.

We have witnessed three coronavirus (CoV) outbreaks in the past two decades, including the COVID-19 pandemic caused by SARS-CoV-2. Main protease (MPro), a highly conserved protease among various CoVs, is essential for viral replication and pathogenesis, making it a prime target for antiviral drug development. Here, we leverage proteolysis targeting chimera (PROTAC) technology to develop a new class of small-molecule antivirals that induce the degradation of SARS-CoV-2 MPro. Among them, MPD2 was demonstrated to effectively reduce MPro protein levels in 293T cells, relying on a time-dependent, CRBN-mediated, and proteasome-driven mechanism. Furthermore, MPD2 exhibited remarkable efficacy in diminishing MPro protein levels in SARS-CoV-2-infected A549-ACE2 cells. MPD2 also displayed potent antiviral activity against various SARS-CoV-2 strains and exhibited enhanced potency against nirmatrelvir-resistant viruses. Overall, this proof-of-concept study highlights the potential of targeted protein degradation of MPro as an innovative approach for developing antivirals that could fight against drug-resistant viral variants.

Discovery of the First-in-Class G9a/GLP PROTAC Degrader.

Aberrantly expressed lysine methyltransferases G9a and GLP, which catalyze mono- and dimethylation of histone H3 lysine 9 (H3K9), have been implicated in numerous cancers. Recent studies have uncovered both catalytic and noncatalytic oncogenic functions of G9a/GLP. As such, G9a/GLP catalytic inhibitors have displayed limited anticancer activity. Here, we report the discovery of the first-in-class G9a/GLP proteolysis targeting chimera (PROTAC) degrader 10 (MS8709), as a potential anticancer therapeutic. 10 induces G9a/GLP degradation in a concentration-, time-, and ubiquitin-proteasome system (UPS)-dependent manner. Futhermore, 10 does not alter the mRNA expression of G9a/GLP and is selective for G9a/GLP over other methyltransferases. Moreover, 10 displays superior cell growth inhibition to the parent G9a/GLP inhibitor UNC0642 in prostate, leukemia, and lung cancer cells and has suitable mouse pharmacokinetic properties for in vivo efficacy studies. Overall, 10 is a valuable chemical biology tool to further investigate the functions of G9a/GLP and a potential therapeutic for treating G9a/GLP-dependent cancers.

Targeting BRD4 with PROTAC degrader ameliorates LPS-induced acute lung injury by inhibiting M1 alveolar macrophage polarization

ObjectivesAcute lung injury (ALI) is a highly inflammatory condition with the involvement of M1 alveolar macrophages (AMs) polarization, eventually leading to the development of non-cardiogenic edema in alveolar and interstitial regions, accompanied by persistent hypoxemia. Given the significant mortality rate associated with ALI, it is imperative to investigate the underlying mechanisms of this condition so as to identify potential therapeutic targets. The therapeutic effects of the inhibition of bromodomain containing protein 4 (BRD4), an epigenetic reader, has been proven with high efficacy in ameliorating various inflammatory diseases through mediating immune cell activation. However, little is known about the therapeutic potential of BRD4 degradation in acute lung injury. MethodsThis study aimed to assess the protective efficacy of ARV-825, a novel BRD4-targeted proteolysis targeting chimera (PROTAC), against ALI through histopathological examination in lung tissues and biochemical analysis in bronchoalveolar lavage fluid (BALF). Additionally, the underlying mechanism by which BRD4 regulated M1 AMs was elucidated by using CUT & Tag assay. ResultsIn this study, we found the upregulation of BRD4 in a lipopolysaccharide (LPS)-induced ALI model. Furthermore, we observed that intraperitoneal administration of ARV-825, significantly alleviated LPS-induced pulmonary pathological changes and inflammatory responses. These effects were accompanied by the suppression of M1 AMs. In addition, our findings revealed that the administration of ARV-825 effectively suppressed M1 AMs by inhibiting the expression of IRF7, a crucial transcriptional factor involved in M1 macrophages. ConclusionOur study suggested that targeting BRD4 using ARV-825 is a potential therapeutic approach for ALI.

Abstract LB179: Identification of the highly potent and orally available ER-targeting PROTAC degrader HP568 for the treatment of breast cancer

Abstract Breast cancer remains an unmet medical need. It has become the most occurring and deadliest cancer for women globally. Estrogen receptor (ER) is expressed in 75% of breast cancers and has the key role in tumorigenesis and progression of ER+ breast cancers. Endocrine treatments that target ER are the mainstay therapies for the ER+ breast cancers, yet drug resistance unavoidably develops due to mutations in the ER gene. The ER-targeting proteolysis targeting chimera (PROTAC) degrader is an emerging new modality that interrupts the ER signaling through degradation of ER and offers unprecedented potential for solving the endocrine resistance. We have discovered HP568, an ER-targeting PROTAC that is highly potent against both the wild-type ER and ER mutants. HP568 has a favorable ADME profile that is superior to known competitor ER-targeting PROTAC. In the head-to-head comparison efficacy studies, HP568 has demonstrated the dose-dependent and superior efficacy that is well consistent with the drug exposure profile and PD biomarkers. HP568 also shows a synergetic effect in combination with a CDK4/6 inhibitor. HP568 is clean in the secondary pharmacology profiling, and well tolerated in animal tox studies. HP568 is under the preclinical development and has the potential to be the best-in-class ER-targeting degrader. HP568 structure will not be disclosed. Citation Format: Wu Du, Zhilin Tu, Dekun Qin, Haibo Li, Jingyi Duan, Shijuan Liu, Meng Zhang, Zhenyan Nie, Zhihui Yuan, Jing Li, Xinghai Li. Identification of the highly potent and orally available ER-targeting PROTAC degrader HP568 for the treatment of breast cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 2 (Late-Breaking, Clinical Trial, and Invited Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(7_Suppl):Abstract nr LB179.

Abstract LB178: HP518, an oral AR-targeting PROTAC for the treatment of AR positive triple negative breast cancer with a novel mechanism of action

Abstract Triple negative breast cancer (TNBC) accounts for 15-20% of all breast carcinomas and has poor prognosis. Chemotherapy is the mainstay treatment for TNBC patients, yet with limited clinical benefit. Androgen receptor (AR) is expressed in approximately 50% of TNBC tumors and thus the anti-androgen therapy could be a promising solution for the treatment of AR+ TNBC. Nevertheless, AR inhibitors including enzalutamide and bicalutamide or the androgen biosynthesis inhibitor abiraterone have failed to demonstrate satisfying anti-tumor activity in clinical trials. We have discovered HP518, an AR-targeting PROTAC (proteolysis targeting chimera) that induces potent degradation of both the wild-type AR and AR mutants. HP518 is currently under the clinical development for the treatment of mCRPC. Here we report the preclinical data on HP518 for the treatment of AR+ TNBC. HP518 robustly degrades AR in multiple TNBC cell lines with a half-maximal degradation concentration (DC50) < 1 nM. HP518 strongly inhibits AR+ TNBC cell growth, whereas the AR inhibitor enzalutamide does not show significant anti-proliferative effect on these cells in the presence or absence of androgen. Consistent with the in vitro results, HP518 significantly and dose-dependently inhibits tumor growth in MDA-MB-453 cell line derived tumor xenograft (CDX) and patient-derived xenograft (PDX) mouse models. PI3KCA activating mutations are frequently expressed in AR+ TNBC. HP518 in combination with alpelisib, a PI3Kα inhibitor shows a synergistic anti-tumor activity. Mechanistically, HP518, but not AR inhibitor enzalutamide downregulates the mRNA expression levels of a set of DNA replication-related genes in AR+ TNBC cells, indicating a novel and ligand-independent role for AR in regulating growth of AR+ TNBC cells. Therefore, HP518, an AR-targeting PROTAC degrader holds great potential to fulfill the unmet clinical needs for the AR+ TNBC therapy. Selected pre-clinical data will be presented. HP518 structure will not be disclosed. Citation Format: Jing Li, Hongwei Yuan, Kefan Chen, Yongxu Huo, Guoqing Liu, Wu Du, Xinghai Li. HP518, an oral AR-targeting PROTAC for the treatment of AR positive triple negative breast cancer with a novel mechanism of action [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 2 (Late-Breaking, Clinical Trial, and Invited Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(7_Suppl):Abstract nr LB178.

Development of an orally bioavailable mSWI/SNF ATPase degrader and acquired mechanisms of resistance in prostate cancer

Mammalian switch/sucrose nonfermentable (mSWI/SNF) ATPase degraders have been shown to be effective in enhancer-driven cancers by functioning to impede oncogenic transcription factor chromatin accessibility. Here, we developed AU-24118, an orally bioavailable proteolysis-targeting chimera (PROTAC) degrader of mSWI/SNF ATPases (SMARCA2 and SMARCA4) and PBRM1. AU-24118 demonstrated tumor regression in a model of castration-resistant prostate cancer (CRPC) which was further enhanced with combination enzalutamide treatment, a standard of care androgen receptor (AR) antagonist used in CRPC patients. Importantly, AU-24118 exhibited favorable pharmacokinetic profiles in preclinical analyses in mice and rats, and further toxicity testing in mice showed a favorable safety profile. As acquired resistance is common with targeted cancer therapeutics, experiments were designed to explore potential mechanisms of resistance that may arise with long-term mSWI/SNF ATPase PROTAC treatment. Prostate cancer cell lines exposed to long-term treatment with high doses of a mSWI/SNF ATPase degrader developed SMARCA4 bromodomain mutations and ABCB1 (ATP binding cassette subfamily B member 1) overexpression as acquired mechanisms of resistance. Intriguingly, while SMARCA4 mutations provided specific resistance to mSWI/SNF degraders, ABCB1 overexpression provided broader resistance to other potent PROTAC degraders targeting bromodomain-containing protein 4 and AR. The ABCB1 inhibitor, zosuquidar, reversed resistance to all three PROTAC degraders tested. Combined, these findings position mSWI/SNF degraders for clinical translation for patients with enhancer-driven cancers and define strategies to overcome resistance mechanisms that may arise.

Abstract 2898: Development of the lipid kinase PIKfyve PROTAC degrader against neuroendocrine prostate cancer

Abstract Therapies targeting the androgen receptor (AR) as the main driver of prostate cancer (PCa) can lead to various mechanisms of resistance and promote progression to castration-resistant PCa (CRPC), which has a median survival of only 13-23 months. Amongst recurrent CRPC, 17%-30% of patients develop neuroendocrine prostate cancer (NEPC), which is a PCa subtype characterized by a unique histology. NEPC exhibits a loss of AR signaling during neuroendocrine transdifferentiation which results in resistance to AR-targeted therapies and gain of cell characteristics resembling poorly differentiated neuroendocrine tumors. Despite advances in the understanding of NEPC development, treatment options remain limited, with platinum-based chemotherapy as the first-line treatment for both de novo and treatment-induced NEPC. However, response to first-line chemotherapy in NEPC is short, with a median survival of only seven months. The poor prognosis of NEPC is attributed in part to late diagnosis and a lack of effective therapeutic agents. Our previous work demonstrated that NEPC and AR-negative PCa exhibit higher dependency on the lipid kinase PIKfyve than AR-positive CRPC. Thus, development of PIKfyve inhibitory therapies targeting the emergent vulnerabilities of NEPC or AR-negative forms of PCa is a promising approach. Using a proteolysis targeting chimera (PROTAC) technology, we designed a class of PIKfyve specific degrader. The in vitro degradation efficiency were determined by immunoblotting, and DC50s (degradation concentration at 50%) were calculated for top candidates. Pharmacokinetic and pharmacodynamic were evaluated for in vivo study. In summary, we have developed a class of PIKfyve specific degrader using the E3 ligase von Hippel-Lindau (VHL) as a ligand via a diverse set of linkers. Mechanistic studies revealed that it induced PIKfyve degradation in a VHL- and proteasome-dependent manner. Citation Format: Yuanyuan Qiao, Chungen Li, Yang Zheng, Xia Jiang, Sarah Nicole Yee, Caleb Cheng, Yi Bao, Yuping Zhang, Yuzhuo Wang, Zhen Wang, Ke Ding, Arul Chinnaiyan. Development of the lipid kinase PIKfyve PROTAC degrader against neuroendocrine prostate cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 2898.

Uncovering PROTAC Sensitivity and Efficacy by Multidimensional Proteome Profiling: A Case for STAT3.

Proteolysis-targeting chimera (PROTAC) is a powerful technology that can effectively trigger the degradation of target proteins. The intricate interplay among various factors leads to a heterogeneous drug response, bringing about significant challenges in comprehending drug mechanisms. Our study applied data-independent acquisition-based mass spectrometry to multidimensional proteome profiling of PROTAC (DIA-MPP) to uncover the efficacy and sensitivity of the PROTAC compound. We profiled the signal transducer and activator of transcription 3 (STAT3) PROTAC degrader in six leukemia and lymphoma cell lines under multiple conditions, demonstrating the pharmacodynamic properties and downstream biological responses. Through comparison between sensitive and insensitive cell lines, we revealed that STAT1 can be regarded as a biomarker for STAT3 PROTAC degrader, which was validated in cells, patient-derived organoids, and mouse models. These results set an example for a comprehensive description of the multidimensional PROTAC pharmacodynamic response and PROTAC drug sensitivity biomarker exploration.

Discovery of LHF418 as a new potent SOS1 PROTAC degrader

Son of sevenless homolog 1 (SOS1) plays a pivotal role as a molecular switch in the conversion of GDP-bound inactive KRAS to its active GTP-bound form, making SOS1 a promising therapeutic target for KRAS-driven cancers. While the most advanced SOS1 inhibitor has processed to phase I clinical trial, the exploration of novel SOS1 targeting strategies with distinct modes of action remains required. By employing proteolysis targeting chimera (PROTAC) technology, we obtained a series of new SOS1 degraders. The representative compound LHF418 potently induced SOS1 degradation with a DC50 value of 209.4 nM and a Dmax value of over 80 %. Mechanistic studies have illuminated that compound LHF418 induced the formation of ternary complex involving SOS1-PROTAC-cereblon (CRBN) and triggered SOS1 protein degradation in a CRBN- and proteasome-dependent manner. In addition, compound LHF418 effectively inhibited KRAS-RAF-ERK signalling, leading to the suppression of colony formation in KRAS-driven cancer cells. Overall, compound LHF418 represents a new lead compound in the developing novel and potent therapy for the treatment of KRAS-driven cancers.

Discovery of Novel Potent and Fast BTK PROTACs for the Treatment of Osteoclasts-Related Inflammatory Diseases.

Bruton's tyrosine kinase (BTK) is an attractive target in inflammatory and autoimmune diseases. However, the effectiveness of BTK inhibitors is limited by side effects and drug resistance. In this study, we report the development of novel BTK proteolysis targeting chimeras (PROTACs) with different classes of BTK-targeting ligands (e.g., spebrutinib) other than ibrutinib. Compound 23 was identified as a potent and fast BTK PROTAC degrader, exhibiting outstanding degradation potency and efficiency in Mino cells (DC50,4h = 1.29 ± 0.3 nM, t1/2,20nM = 0.59 ± 0.20 h). Furthermore, compound 23 forms a stable ternary complex, as confirmed by the HTRF assay. Notably, 23 down-regulated the BTK-PLCγ2-Ca2+-NFATc1 signaling pathway activated by RANKL, thus inhibiting osteoclastogenesis and attenuating alveolar bone resorption in a mouse periodontitis model. These findings suggest that compound 23 is a potent and promising candidate for osteoclast-related inflammatory diseases, expanding the potential of BTK PROTACs.

Co-opting the E3 ligase KLHDC2 for targeted protein degradation by small molecules.

Targeted protein degradation (TPD) by PROTAC (proteolysis-targeting chimera) and molecular glue small molecules is an emerging therapeutic strategy. To expand the roster of E3 ligases that can be utilized for TPD, we describe the discovery and biochemical characterization of small-molecule ligands targeting the E3 ligase KLHDC2. Furthermore, we functionalize these KLHDC2-targeting ligands into KLHDC2-based BET-family and AR PROTAC degraders and demonstrate KLHDC2-dependent target-protein degradation. Additionally, we offer insight into the assembly of the KLHDC2 E3 ligase complex. Using biochemical binding studies, X-ray crystallography and cryo-EM, we show that the KLHDC2 E3 ligase assembles into a dynamic tetramer held together via its own C terminus, and that this assembly can be modulated by substrate and ligand engagement.