Deubiquitinating enzymes, or DUBs, comprise a family of proteases that regulate ubiquitination dynamics. Since their discovery, genetic and functional studies have nominated DUBs as a promising class ...for drug discovery across diverse therapeutic areas. Consequent probe and drug discovery efforts over the past 15 years have resulted in over 50 reported inhibitors and advances in DUB structural studies, assay formats, and chemical biology tools. Accumulating knowledge from these studies has enabled several important recent breakthroughs. In this review, we highlight recent successes in solving DUB-ligand co-structures and the development of rigorously characterized potent and selective inhibitors. We posit that these advances in pharmacological targeting of DUBs establish the enzyme family as targetable and provide a framework for other DUBs programs. Accordingly, we envision increasingly rapid progress in the development of potent and selective inhibitors for a wide range of DUBs and advancement of DUB-targeting drugs to the clinic.
Cells are subjected to oxidative stress during the initiation and progression of tumors, and this imposes selective pressure for cancer cells to adapt mechanisms to tolerate these conditions. Here, ...we examined the dependency of cancer cells on glutathione (GSH), the most abundant cellular antioxidant. While cancer cell lines displayed a broad range of sensitivities to inhibition of GSH synthesis, the majority were resistant to GSH depletion. To identify cellular pathways required for this resistance, we carried out genetic and pharmacologic screens. Both approaches revealed that inhibition of deubiquitinating enzymes (DUBs) sensitizes cancer cells to GSH depletion. Inhibition of GSH synthesis, in combination with DUB inhibition, led to an accumulation of polyubiquitinated proteins, induction of proteotoxic stress, and cell death. These results indicate that depletion of GSH renders cancer cells dependent on DUB activity to maintain protein homeostasis and cell viability and reveal a potentially exploitable vulnerability for cancer therapy.
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•Most cancer cell lines are largely insensitive to GSH depletion•Deubiquitinases (DUBs) protect cancer cells upon inhibition of GSH synthesis•Inhibition of DUBs and GSH synthesis causes ER and proteotoxic stress and cell death•Combined targeting of DUBs and GSH blocks tumor growth
Tumor initiation and progression lead to highly oxidative stress conditions. Harris et al. show that upon glutathione depletion, cancer cells rely on deubiquitinating enzymes to maintain protein homeostasis and cell viability. Combined inhibition of deubiquitinases and glutathione synthesis leads to proteotoxic and ER stress and cell death.
Effective bone resorption by osteoclasts is critical for balanced bone remodeling. We have previously reported that mice harboring a substitution mutation of tyrosine 737 to phenylalanine in the ...adapter protein Cbl (CblY737F, YF) have increased bone volume partly due to decreased osteoclast-mediated bone resorption. The CblY737F mutation abrogates interaction between Cbl and the p85 subunit of PI3K. Here, we studied the mechanism for defective resorptive function of YF mutant osteoclasts. The YF osteoclasts had intact actin cytoskeletons and sealing zones. Expression and localization of proteins needed for acidification of the resorptive lacunae were also comparable between the WT and YF osteoclasts. In contrast, secretion of Cathepsin K, a major protease needed to degrade collagen, was diminished in the conditioned media derived from YF osteoclasts. The targeting of Cathepsin K into LAMP2-positive vesicles was also compromised due to decreased number of LAMP2-positive vesicles in YF osteoclasts. Further, we found that in contrast to WT, conditioned media derived from YF osteoclasts promoted increased numbers of alkaline phosphatase positive colonies, and increased expression of osteogenic markers in WT calvarial cultures. Cumulatively, our results suggest that the Cbl-PI3K interaction regulates Cathepsin K secretion required for proper bone resorption, and secretion of factors which promote osteogenesis.
•Cbl-PI3K interaction regulates Cathepsin K secretion, but secretion of Cathepsin D is normal.•Absence of Cbl-PI3K interaction reduces numbers of LAMP2 positive secretory lysosomes.•Dysfunctional osteoclasts derived from YF mutant mice secrete factor that promote osteogenesis.
Deubiquitinating enzymes (DUBs), ~100 of which are found in human cells, are proteases that remove ubiquitin conjugates from proteins, thereby regulating protein turnover. They are involved in a wide ...range of cellular activities and are emerging therapeutic targets for cancer and other diseases. Drugs targeting USP1 and USP30 are in clinical development for cancer and kidney disease respectively. However, the majority of substrates and pathways regulated by DUBs remain unknown, impeding efforts to prioritize specific enzymes for research and drug development. To assemble a knowledgebase of DUB activities, co-dependent genes, and substrates, we combined targeted experiments using CRISPR libraries and inhibitors with systematic mining of functional genomic databases. Analysis of the Dependency Map, Connectivity Map, Cancer Cell Line Encyclopedia, and multiple protein-protein interaction databases yielded specific hypotheses about DUB function, a subset of which were confirmed in follow-on experiments. The data in this paper are browsable online in a newly developed
DUB Portal
and promise to improve understanding of DUBs as a family as well as the activities of incompletely characterized DUBs (e.g. USPL1 and USP32) and those already targeted with investigational cancer therapeutics (e.g. USP14, UCHL5, and USP7).
Lateral compression type-1 pelvic fractures are a common fragility fracture in older adults. Patients who do not mobilise due to ongoing pain are at greater risk of immobility-related complications. ...Standard treatment in the United Kingdom is provision of pain relief and early mobilisation, unlike fragility hip fractures, which are usually treated surgically based on evidence that early surgery is associated with better outcomes. Currently there is no evidence on whether patients with lateral compression type-1 fragility fractures would have a better recovery with surgery than non-surgical management.
To assess the clinical and cost effectiveness of surgical fixation with internal fixation device compared to non-surgical management of lateral compression type-1 fragility fractures in older adults.
Pragmatic, randomised controlled superiority trial, with 12-month internal pilot; target sample size was 600 participants. Participants were randomised between surgical and non-surgical management (1 : 1 allocation ratio). An economic evaluation was planned.
UK Major Trauma Centres.
Patients aged 60 years or older with a lateral compression type-1 pelvic fracture, arising from a low-energy fall and unable to mobilise independently to a distance of 3 m and back due to pelvic pain 72 hours after injury.
Internal fixation device surgical fixation and non-surgical management. Participants, surgeons and outcome assessors were not blinded to treatment allocation.
Primary outcome - average patient health-related quality of life, over 6 months, assessed by the EuroQol-5 Dimensions, five-level version utility score. Secondary outcomes (over the 6 months following injury) - self-rated health, physical function, mental health, pain, delirium, displacement of pelvis, mortality, complications and adverse events, and resource use data for the economic evaluation.
The trial closed early, at the end of the internal pilot, due to low recruitment. The internal pilot was undertaken in two separate phases because of a pause in recruitment due to the coronavirus disease 2019 pandemic. The planned statistical and health economic analyses were not conducted. Outcome data were summarised descriptively. Eleven sites opened for recruitment for a combined total of 92 months. Three-hundred and sixteen patients were assessed for eligibility, of whom 43 were eligible (13.6%). The main reason for ineligibility was that the patient was able to mobilise independently to 3 m and back (
= 161). Of the 43 eligible participants, 36 (83.7%) were approached for consent, of whom 11 (30.6%) provided consent. The most common reason for eligible patients not consenting to take part was that they were unwilling to be randomised to a treatment (
= 10). There were 11 participants, 5 randomised to surgical management with internal fixation device and 6 to non-surgical management. The average age of participants was 83.0 years (interquartile range 76.0, 89.0) and the EuroQol-5 Dimensions, five-level version utility score at 6 months post randomisation (
= 8) was 0.32 (standard deviation 0.37). A limitation of the trial was that study objectives were not addressed due to poor recruitment.
It was not feasible to recruit to this trial in the current context. Further research to understand the treatment and recovery pathways of this group of patients, along with their outcomes, would be needed prior to undertaking a future trial.
Exploration of equipoise across different healthcare professional groups. Investigate longer-term patient outcomes.
This trial is registered as ISRCTN16478561.
This award was funded by the National Institute for Health and Care Research (NIHR) Health Technology Assessment programme (NIHR award ref: 16/167/57) and is published in full in
; Vol. 28, No. 15. See the NIHR Funding and Awards website for further award information.
Oncogenic forms of the kinase FLT3 are important therapeutic targets in acute myeloid leukemia (AML); however, clinical responses to small-molecule kinase inhibitors are short-lived as a result of ...the rapid emergence of resistance due to point mutations or compensatory increases in FLT3 expression. We sought to develop a complementary pharmacological approach whereby proteasome-mediated FLT3 degradation could be promoted by inhibitors of the deubiquitinating enzymes (DUBs) responsible for cleaving ubiquitin from FLT3. Because the relevant DUBs for FLT3 are not known, we assembled a focused library of most reported small-molecule DUB inhibitors and carried out a cellular phenotypic screen to identify compounds that could induce the degradation of oncogenic FLT3. Subsequent target deconvolution efforts allowed us to identify USP10 as the critical DUB required to stabilize FLT3. Targeting of USP10 showed efficacy in preclinical models of mutant-FLT3 AML, including cell lines, primary patient specimens and mouse models of oncogenic-FLT3-driven leukemia.
Ubiquitin specific peptidase 7 (USP7) is a deubiquitinating enzyme (DUB) that removes ubiquitin tags from specific protein substrates in order to alter their degradation rate and sub-cellular ...localization. USP7 has been proposed as a therapeutic target in several cancers because it has many reported substrates with a role in cancer progression, including FOXO4, MDM2, N-Myc, and PTEN. The multi-substrate nature of USP7, combined with the modest potency and selectivity of early generation USP7 inhibitors, has presented a challenge in defining predictors of response to USP7 and potential patient populations that would benefit most from USP7-targeted drugs. Here, we describe the structure-guided development of XL177A, which irreversibly inhibits USP7 with sub-nM potency and selectivity across the human proteome. Evaluation of the cellular effects of XL177A reveals that selective USP7 inhibition suppresses cancer cell growth predominantly through a p53-dependent mechanism: XL177A specifically upregulates p53 transcriptional targets transcriptome-wide, hotspot mutations in TP53 but not any other genes predict response to XL177A across a panel of ~500 cancer cell lines, and TP53 knockout rescues XL177A-mediated growth suppression of TP53 wild-type (WT) cells. Together, these findings suggest TP53 mutational status as a biomarker for response to USP7 inhibition. We find that Ewing sarcoma and malignant rhabdoid tumor (MRT), two pediatric cancers that are sensitive to other p53-dependent cytotoxic drugs, also display increased sensitivity to XL177A.
Insufficient and delayed fracture healing remain significant public health problems with limited therapeutic options. Phosphoinositide 3-kinase (PI3K) signaling, a major pathway involved in ...regulation of fracture healing, promotes proliferation, migration, and differentiation of osteoprogenitors. We have recently reported that knock-in mice with a global increase in PI3K signaling (gCblYF) show enhanced femoral fracture healing characterized by an extraordinary periosteal response to injury. Interestingly, of all growth factor receptors involved in fracture healing, PI3K directly binds only to PDGFR. Given these findings, we hypothesized a PDGFR-PI3K interaction is necessary for mediating robust periosteal cell activation following fracture. In this study, we isolated primary periosteal cells from gCblYF mice to analyze cross-talk between the PDGFRβ and PI3K signaling pathways. We found PDGFRβ signaling contributes to robust Akt phosphorylation in periosteal cells in comparison with other growth factor signaling pathways. Additionally, we performed femoral fractures on gCblYF mice with a conditional removal of PDGFRβ in mesenchymal progenitors using inducible alpha smooth muscle actin (αSMA) CreERT2 mice. Our studies showed that depletion of PDGFRβ signaling within these progenitors in the early phase of fracture healing significantly abrogates PI3K-mediated periosteal activation and proliferation three days after fracture. Combined, these results suggest that PDGFRβ signaling through PI3K is necessary for robust periosteal activation in the earliest phases of fracture healing.
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