Design, synthesis, and biological evaluation of pyrido[2,3-d]pyrimidin-7(8H)-one derivatives as potent USP1 inhibitors

Conformational restriction enables discovering a series of chroman derivatives as potent and selective NaV1.8 inhibitors with improved pharmacokinetic properties

Voltage-gated sodium channel 1.8 (NaV1.8) is a promising analgesic target due to its unique biophysical characteristics and specific role in nociceptive sensation. VX-150 initially completed proof-of-concept studies in clinical trials, but with high dosages and frequent administration. Herein, based on VX-150, we report the design, synthesis and structure-activity relationship (SAR) study aiming to identify novel, potent and selective NaV1.8 inhibitors with improved pharmacokinetic properties. Conformational restriction strategy and subsequent optimization led to the identification of the chroman derivative (R)-40 as the most promising hNaV1.8 inhibitor showing an IC50 value of 5.9 ± 1.0 nM and good selectivity over other tested NaV channels and hERG channel. More importantly, (R)-40 showed good in vitro metabolic stability in liver microsomes across multiple species and excellent in vivo PK profiles in rats and dogs. Notably, (R)-40 exerted dose-dependent analgesic activities in both rat models with postoperative and inflammatory pain, and a wide safety margin in neurotoxicity evaluation. Overall, these results confirmed conformational restriction as an effective strategy to improve PK profile, and our detailed study provided a valuable foundation for developing novel NaV1.8 inhibitors.

Harnessing the Deubiquitinase USP1 for Targeted Protein Stabilization

Deubiquitinase-targeting chimera (DUBTAC) has emerged as a promising technology for targeted protein stabilization (TPS) by harnessing deubiquitinases (DUBs) to remove polyubiquitin chains from target proteins. Despite the presence of over 100 human DUBs, only OTUB1 and USP7 have been utilized in the development of DUBTAC. Hence, there is an urgent need to harness additional DUBs to expand the DUBTAC arsenal. In this work, we demonstrate for the first time that the USP1 deubiquitinase, which is overexpressed in several human cancers, can be leveraged for TPS. We report the development of novel USP1-recruiting DUBTACs by utilizing a noncovalent small-molecule inhibitor of USP1. First, we generated a USP1-based CFTR DUBTAC, MS5310, which effectively stabilized CFTR and is more potent than previously reported CFTR DUBTACs. Next, we developed first-in-class USP1-recruiting UTX DUBTACs, including MS7131, from a small-molecule inhibitor of UTX and JMJD3. Notably, MS7131 effectively stabilized the tumor suppressor UTX in a concentration- and time-dependent manner, while sparing the oncoprotein JMJD3, despite it retaining potent inhibition of JMJD3. Furthermore, UTX stabilization induced by MS7131 was dependent on the engagement of both USP1 and UTX. Consequently, MS7131, but not the parent USP1 inhibitor or UTX inhibitor, effectively reduced histone H3 lysine 27 trimethylation and significantly suppressed the proliferation and clonogenicity of cancer cells. Overall, this study highlights that USP1 can be harnessed for DUBTAC development. Moreover, we developed a valuable chemical tool, MS7131, for the investigation of UTX's distinct functions. This advancement paves the way for leveraging DUBTACs in the treatment of related diseases.

Recent advances in small molecule inhibitors of deubiquitinating enzymes

Proteins play a pivotal role in maintaining cellular homeostasis. Their degradation primarily orchestrated through the ubiquitin-proteasome system (UPS) and cellular autophagy. Dysfunction of the UPS is associated with various human diseases, including cancer, autoimmune disorders, and neurodegenerative conditions. Consequently, the UPS has emerged as a promising therapeutic target. Deubiquitinases (DUBs) have garnered significant attention as potential targets for therapeutic intervention due to their role in modulating protein stability and function. This review focuses on recent advancements of DUBs, particularly their relevance in the UPS and their potential as drug targets. Notably, inhibitors targeting specific DUBs, such as USP1, USP7, USP14, and USP30 have shown promise in preclinical and clinical studies for cancer therapy. Additionally, DUB inhibitors have been involved in novel therapeutic approaches lately, including as targets for proteolysis-targeting chimeras (PROTACs) or as tools in deubiquitinase-targeting chimeras (DUBTACs).

Discovery and Optimization of a Series of Novel Morpholine-Containing USP1 Inhibitors

Ubiquitin-specific protease 1 (USP1), a well-known member of the deubiquitinating enzymes, serves as a key regulator in DNA damage repair (DDR) processes. Herein, we utilized ring-opening and cyclization strategies based on KSQ-4279 to design a novel series of USP1 inhibitors featuring a morpholine scaffold. Notably, compound 38-P2 exhibited a more potent enzymatic and cellular inhibition activity compared to KSQ-4279. Mechanistically, 38-P2 was characterized as a selective, reversible, and noncompetitive USP1 inhibitor. 38-P2 efficiently activated the DDR pathway, induced cell cycle arrest and cell apoptosis, and inhibited cell survival. Importantly, it enhanced the sensitivity of olaparib-resistant cells to olaparib and showed a synergetic effect with andrographolide in BRCA-proficient cancer cells. Furthermore, 38-P2 had favorable pharmacokinetic profiles and good safety properties in vitro and in vivo. In the MDA-MB-436 xenograft model, 38-P2 displayed significant, dose-dependent antitumor efficacy. Overall, these findings indicate that 38-P2 is a promising lead compound for further drug development.

Ubiquitin-Specific Protease Inhibitors for Cancer Therapy: Recent Advances and Future Prospects

Cancer management has traditionally depended on chemotherapy as the mainstay of treatment; however, recent advancements in targeted therapies and immunotherapies have offered new options. Ubiquitin-specific proteases (USPs) have emerged as promising therapeutic targets in cancer treatment due to their crucial roles in regulating protein homeostasis and various essential cellular processes. This review covers the following: (1) the structural and functional characteristics of USPs, highlighting their involvement in key cancer-related pathways, and (2) the discovery, chemical structures, mechanisms of action, and potential clinical implications of USP inhibitors in cancer therapy. Particular attention is given to the role of USP inhibitors in enhancing cancer immunotherapy, e.g., modulation of the tumor microenvironment, effect on regulatory T cell function, and influence on immune checkpoint pathways. Furthermore, this review summarizes the current progress and challenges of clinical trials involving USP inhibitors as cancer therapy. We also discuss the complexities of achieving target selectivity, the ongoing efforts to develop more specific and potent USP inhibitors, and the potential of USP inhibitors to overcome drug resistance and synergize with existing cancer treatments. We finally provide a perspective on future directions in targeting USPs, including the potential for personalized medicine based on specific gene mutations, underscoring their significant potential for enhancing cancer treatment. By elucidating their mechanisms of action, clinical progress, and potential future applications, we hope that this review could serve as a useful resource for both basic scientists and clinicians in the field of cancer therapeutics.

The other side of the coin: protein deubiquitination by Ubiquitin-Specific Protease 1 in cancer progression and therapy

Reversible protein ubiquitination is a crucial factor in cellular homeostasis, with Ubiquitin-Specific Protease 1 (USP1) serving as a key deubiquitinase involved in DNA damage response (DDR) and repair mechanisms in cancer. While ubiquitin ligases have been extensively studied, research on the reverse process of ubiquitination, particularly the mechanisms involving USP1, remains relatively limited. USP1 is overexpressed in various cancers, influencing tumor initiation and progression by regulating multiple associated proteins. Inhibiting USP1 effectively suppresses tumor proliferation and migration and may help overcome resistance to cisplatin and PARP inhibitors. As a potential synthetic lethal target, USP1 demonstrates significant research potential. This review highlights the biological mechanisms of USP1 in cancer progression, the signaling pathways it regulates, and the latest advancements in USP1 inhibitors, while also analyzing the opportunities and challenges of targeting USP1. By adopting the perspective of "the other side of the coin," this review aims to underscore the crucial yet often overlooked role of the deubiquitinase USP1, contrasting it with the extensively studied ubiquitin ligases, and emphasizing its therapeutic potential in cancer treatment.

Deubiquitinases as novel therapeutic targets for diseases

Deubiquitinating enzymes (DUBs) regulate substrate ubiquitination by removing ubiquitin or cleaving within ubiquitin chains, thereby maintaining cellular homeostasis. Approximately 100 DUBs in humans counteract E3 ubiquitin ligases, finely balancing ubiquitination and deubiquitination processes to maintain cellular proteostasis and respond to various stimuli and stresses. Given their role in modulating ubiquitination levels of various substrates, DUBs are increasingly linked to human health and disease. Here, we review the DUB family, highlighting their distinctive structural characteristics and chain-type specificities. We show that DUB family members regulate key signaling pathways, such as NF-κB, PI3K/Akt/mTOR, and MAPK, and play crucial roles in tumorigenesis and other diseases (neurodegenerative disorders, cardiovascular diseases, inflammatory disorders, and developmental diseases), making them promising therapeutic targets Our review also discusses the challenges in developing DUB inhibitors and underscores the critical role of the DUBs in cellular signaling and cancer. This comprehensive analysis enhances our understanding of the complex biological functions of the DUBs and underscores their therapeutic potential.

Structural and Biochemical Insights into the Mechanism of Action of the Clinical USP1 Inhibitor, KSQ-4279

DNA damage triggers cell signaling cascades that mediate repair. This signaling is frequently dysregulated in cancers. The proteins that mediate this signaling are potential targets for therapeutic intervention. Ubiquitin-specific protease 1 (USP1) is one such target, with small-molecule inhibitors already in clinical trials. Here, we use biochemical assays and cryo-electron microscopy (cryo-EM) to study the clinical USP1 inhibitor, KSQ-4279 (RO7623066), and compare this to the well-established tool compound, ML323. We find that KSQ-4279 binds to the same cryptic site of USP1 as ML323 but disrupts the protein structure in subtly different ways. Inhibitor binding drives a substantial increase in thermal stability of USP1, which may be mediated through the inhibitors filling a hydrophobic tunnel-like pocket in USP1. Our results contribute to the understanding of the mechanism of action of USP1 inhibitors at the molecular level.