Combination of Inhibitors of USP7 and PLK1 has a Strong Synergism against Paclitaxel Resistance

Drug resistance mechanisms and treatment strategies mediated by Ubiquitin-Specific Proteases (USPs) in cancers: new directions and therapeutic options

Drug resistance represents a significant obstacle in cancer treatment, underscoring the need for the discovery of novel therapeutic targets. Ubiquitin-specific proteases (USPs), a subclass of deubiquitinating enzymes, play a pivotal role in protein deubiquitination. As scientific research advances, USPs have been recognized as key regulators of drug resistance across a spectrum of treatment modalities, including chemotherapy, targeted therapy, immunotherapy, and radiotherapy. This comprehensive review examines the complex relationship between USPs and drug resistance mechanisms, focusing on specific treatment strategies and highlighting the influence of USPs on DNA damage repair, apoptosis, characteristics of cancer stem cells, immune evasion, and other crucial biological functions. Additionally, the review highlights the potential clinical significance of USP inhibitors as a means to counter drug resistance in cancer treatment. By inhibiting particular USP, cancer cells can become more susceptible to a variety of anti-cancer drugs. The integration of USP inhibitors with current anti-cancer therapies offers a promising strategy to circumvent drug resistance. Therefore, this review emphasizes the importance of USPs as viable therapeutic targets and offers insight into fruitful directions for future research and drug development. Targeting USPs presents an effective method to combat drug resistance across various cancer types, leading to enhanced treatment strategies and better patient outcomes.

Identification of YCH2823 as a novel USP7 inhibitor for cancer therapy

Inhibition of the human ubiquitin-specific protease 7 (USP7), the key deubiquitylating enzyme in regulating p53 protein levels, has been considered an attractive anticancer strategy. In order to enhance the cellular activity of FT671, scaffold hopping strategy was employed. This endeavor resulted in the discovery of YCH2823, a novel and potent USP7 inhibitor.YCH2823 demonstrated remarkable efficacy in inhibiting the growth of a specific subset of TP53 wild-type, -mutant, and MYCN-amplified cell lines, surpassing the potency of FT671 by approximately 5-fold. The mechanism of action of YCH2823 involves direct interaction with the catalytic domain of USP7, thereby impeding the cleavage of ubiquitinated substrates. An increase in the expression of p53 and p21, accompanied by G1 phase arrest and apoptosis, was observed upon treatment with YCH2823. Subsequently, the knockdown of p53 or p21 in CHP-212 cells exhibited a substantial reduction in sensitivity to YCH2823, as evidenced by a considerable increase in IC50 values up to 690-fold. Furthermore, YCH2823 treatment specifically enhanced the transcriptional and protein levels of BCL6 in sensitive cells. Moreover, a synergistic effect between USP7 inhibitors and mTOR inhibitors was observed, suggesting the possibility of novel therapeutic strategies for cancer treatment. In conclusion, YCH2823 exhibits potential as an anticancer agent for the treatment of both TP53 wild-type and -mutant tumors.

Eph signal inhibition potentiates the growth-inhibitory effects of PLK1 inhibition toward cancer cells

Anti-mitotic drugs are clinically used as anti-cancer treatments. Polo-like kinase 1 (PLK1) is a promising target against cancer cell division due to its importance in the whole process of mitosis, and thus PLK1-targeting agents have been developed in the last few decades. Clinical trial studies show that several PLK1 inhibitors are generally well-tolerated. However, the response rates are limited; therefore, it is needed to improve the efficacy of those drugs. Here, we show that NVP-BHG712, an erythropoietin-producing human hepatocellular (Eph) signaling inhibitor, potentiates the growth-inhibitory effects of the PLK1 inhibitors BI2536 and BI6727 in cancer cells. This combination treatment strongly suppresses cancer spheroid formation. Moreover, the combination drastically arrests cells at mitosis by continuous activation of the spindle assembly checkpoint (SAC), thereby inducing apoptosis. SAC activation caused by the combination of NVP-BHG712 and BI2536 is due to the inhibition of centrosome maturation and separation. Although the inactivation level of the PLK1 kinase is comparable between BI2536 treatment alone and combination treatment, the combination treatment strongly inactivates MAPK signaling in mitosis. Since inhibition of MAPK signaling potentiates the efficacy of BI2536 treatment, inactivation of PLK1 kinase and MAPK signaling contributes to the strong inhibition of centrosome separation. These results suggest that Eph signal inhibition potentiates the effect of PLK1 inhibition, leading to strong mitotic arrest via SAC activation and the subsequent reduction of cancer cell survival. The combination of PLK1 inhibition and Eph signal inhibition will provide a new effective strategy for targeting cancer cell division.

PLK1 regulating chemoradiotherapy sensitivity of esophageal squamous cell carcinoma through pentose phosphate pathway/ferroptosis

BACKGROUND

Esophageal squamous cell carcinoma (ESCC) is the most common pathological type of esophageal cancer in China, accounting for more than 90 %. Most patients were diagnosed with advanced-stage ESCC, for whom new adjuvant therapy is recommended. Therefore, it is urgent to explore new therapeutic targets for ESCC. Ferroptosis, a newly discovered iron-dependent programmed cell death, has been shown to play an important role in carcinogenesis by many studies. This study explored the effect of Polo like kinase 1 (PLK1) on chemoradiotherapy sensitivity of ESCC through ferroptosis METHODS: In this study, we knocked out the expression of PLK1 (PLK1-KO) in ESCC cell lines (KYSE150 and ECA109) with CRISPR/CAS9. The effects of PLK1-knock out on G6PD, the rate-limiting enzyme of pentose phosphate pathway (PPP), and downstream NADPH and GSH were explored. The lipid peroxidation was observed by flow cytometry, and the changes in mitochondria were observed by transmission electron microscopy. Next, through the CCK-8 assay and clone formation assay, the sensitivity to cobalt 60 rays, paclitaxel, and cisplatin were assessed after PLK1-knock out, and the nude mouse tumorigenesis experiment further verified it. The regulation of transcription factor YY1 on PLK1 was evaluated by dual luciferase reporter assay. The expression and correlation of PLK1 and YY1, and their impact on prognosis were analyzed in more than 300 ESCC cases from the GEO database and our center. Finally, the above results were further proved by single-cell sequencing.

RESULTS

After PLK1 knockout, the expression of G6PD dimer and the level of NADPH and GSH in KYSE150 and ECA109 cells significantly decreased. Accordingly, lipid peroxidation increased, mitochondria became smaller, membrane density increased, and ferroptosis was more likely to occur. However, with the stimulation of exogenous GSH (10 mM), there was no significant difference in lipid peroxidation and ferroptosis between the PLK1-KO group and the control group. After ionizing radiation, the PLK1-KO group had higher lipid peroxidation ratio, more cell death, and was more sensitive to radiation, while exogenous GSH (10 mM) could eliminate this difference. Similar results could also be observed when receiving paclitaxel combined with cisplatin and chemoradiotherapy. The expression of PLK1, G6PD dimer, and the level of NADPH and GSH in KYSE150, ECA109, and 293 T cells stably transfected with YY1-shRNAs significantly decreased, and the cells were more sensitive to radiotherapy and chemotherapy. ESCC patients from the GEO database and our center, YY1 and PLK1 expression were significantly positively-correlated, and the survival of patients with high expression of PLK1 was significantly shorter. Further analysis of single-cell sequencing specimens of ESCC in our center confirmed the above results.

CONCLUSION

In ESCC, down-regulation of PLK1 can inhibit PPP, and reduce the level of NADPH and GSH, thereby promoting ferroptosis and improving their sensitivity to radiotherapy and chemotherapy. Transcription factor YY1 has a positive regulatory effect on PLK1, and their expressions were positively correlated. PLK1 may be a target for predicting and enhancing the chemoradiotherapy sensitivity of ESCC.

A small HDM2 antagonist peptide and a USP7 inhibitor synergistically inhibit the p53-HDM2-USP7 circuit

HDM2, an E3 ubiquitin ligase, is a crucial regulator of many proliferation-related pathways. It is also one of the primary regulators of p53. USP7, a deubiquitinase, also plays a key role in the regulation of both p53 and HDM2, thus forming a small regulatory network with them. This network has emerged as an important drug target. Development of a synergistic combination targeting both proteins is desirable and important for regulating this module. We have developed a small helically constrained peptide that potently inhibited p53-HDM2 interaction and exerted anti-proliferative effects on p53+/+ cells. A combination of this peptide-when attached to cell entry and nuclear localization tags-and a USP7 inhibitor showed synergistic anti-proliferative effects against cells harboring wild-type alleles of p53. Synergistic inhibition of two important drug targets may lead to novel therapeutic strategies.

Ubiquitin-specific protease 7 (USP7): an emerging drug target for cancer treatment

INTRODUCTION

Ubiquitin-specific protease 7 (USP7) also known as herpesvirus-associated ubiquitin-specific protease (HAUSP) is a well-characterized cysteine protease that belongs to the largest subfamily of deubiquitinating enzymes (DUBs). It is involved in multiple signaling pathways, some of them dysregulated in malignant tumors. USP7 inhibition can lead to cell growth arrest and apoptosis through inhibition of tumor promoters and stabilization of tumor suppressors, making it a promising druggable target for cancer therapy.

AREAS COVERED

This review covers the structure of USP7, its function in multiple signaling pathways and relevance in cancer, as well as recent advances and future perspectives in the development of USP7 inhibitors for cancer therapy.

EXPERT OPINION

Literature reports display the multiple antitumor activities of USP7 inhibitors, both in vitro and in vivo. Nonetheless, none have entered clinical trials so far, highlighting the need to delve into a deeper understanding of USP7 binding sites and the development of more accurate compound screening methods. Despite these challenges, further development of USP7 inhibitors is promising as a valuable new approach for cancer treatment, including the ability to address chemoresistance.

Molecular Target and Action Mechanism of Anti-Cancer Agents

Precision oncology, also known as personalized medicine, is an evolving approach to cancer treatment that aims to tailor therapies to individual patients based on their unique molecular profile, including genetic alterations and other biomarkers [...].

USP7 - a crucial regulator of cancer hallmarks

Over the course of three decades of study, the deubiquitinase Herpesvirus associated Ubiquitin-Specific Protease/Ubiquitin-Specific Protease 7 (HAUSP/USP7) has gradually come to be recognized as a crucially important molecule in cellular physiology. The fact that USP7 is overexpressed in a number of cancers, including breast, prostate, colorectal, and lung cancers, supports the idea that USP7 is also an important regulator of tumorigenesis. In this review, we discuss USP7's function in relation to the cancer hallmarks described by Hanahan and Weinberg. This post-translational modifier can support increased proliferation, block unfavorable growth signals, stop cell death, and support an unstable cellular genome by manipulating key players in the pertinent signalling circuit. It is interesting to note that USP7 also aids in the stabilization of molecules that support angiogenesis and metastasis. Targeting USP7 has now emerged as a crucial component of USP7 research because pharmacological inhibition of USP7 supports p53-mediated cell cycle arrest and apoptosis. Efficacious USP7 inhibition is currently being investigated in both synthetic and natural compounds, but issues with selectivity and a lack of co-crystal structure have hindered USP7 inhibition from being tested in clinical settings. Moreover, the development of new, more effective USP7 inhibitors and their encouraging implications by numerous groups give us a glimmer of hope for USP7-targeting medications as effective substitutes for hazardous cancer chemotherapeutics.

Ubiquitin specific peptidases and prostate cancer

Protein ubiquitination is an important post-translational modification mechanism, which regulates protein stability and activity. The ubiquitination of proteins can be reversed by deubiquitinating enzymes (DUBs). Ubiquitin-specific proteases (USPs), the largest DUB subfamily, can regulate cellular functions by removing ubiquitin(s) from the target proteins. Prostate cancer (PCa) is the second leading type of cancer and the most common cause of cancer-related deaths in men worldwide. Numerous studies have demonstrated that the development of PCa is highly correlated with USPs. The expression of USPs is either high or low in PCa cells, thereby regulating the downstream signaling pathways and causing the development or suppression of PCa. This review summarized the functional roles of USPs in the development PCa and explored their potential applications as therapeutic targets for PCa.

Chromatin Separation Regulators Predict the Prognosis and Immune Microenvironment Estimation in Lung Adenocarcinoma

Background: Abnormal chromosome segregation is identified to be a common hallmark of cancer. However, the specific predictive value of it in lung adenocarcinoma (LUAD) is unclear.

Method: The RNA sequencing and the clinical data of LUAD were acquired from The Cancer Genome Atlas (TACG) database, and the prognosis-related genes were identified. The Kyoto Encyclopedia of Genes and Genomes (KEGG) and Gene Ontology (GO) were carried out for functional enrichment analysis of the prognosis genes. The independent prognosis signature was determined to construct the nomogram Cox model. Unsupervised clustering analysis was performed to identify the distinguishing clusters in LUAD-samples based on the expression of chromosome segregation regulators (CSRs). The differentially expressed genes (DEGs) and the enriched biological processes and pathways between different clusters were identified. The immune environment estimation, including immune cell infiltration, HLA family genes, immune checkpoint genes, and tumor immune dysfunction and exclusion (TIDE), was assessed between the clusters. The potential small-molecular chemotherapeutics for the individual treatments were predicted via the connectivity map (CMap) database.

Results: A total of 2,416 genes were determined as the prognosis-related genes in LUAD. Chromosome segregation is found to be the main bioprocess enriched by the prognostic genes. A total of 48 CSRs were found to be differentially expressed in LUAD samples and were correlated with the poor outcome in LUAD. Nine CSRs were identified as the independent prognostic signatures to construct the nomogram Cox model. The LUAD-samples were divided into two distinct clusters according to the expression of the 48 CSRs. Cell cycle and chromosome segregation regulated genes were enriched in cluster 1, while metabolism regulated genes were enriched in cluster 2. Patients in cluster 2 had a higher score of immune, stroma, and HLA family components, while those in cluster 1 had higher scores of TIDES and immune checkpoint genes. According to the hub genes highly expressed in cluster 1, 74 small-molecular chemotherapeutics were predicted to be effective for the patients at high risk.

Conclusion: Our results indicate that the CSRs were correlated with the poor prognosis and the possible immunotherapy resistance in LUAD.

Present and Future Perspective on PLK1 Inhibition in Cancer Treatment

Polo-like kinase 1 (PLK1) is the principle member of the well conserved serine/threonine kinase family. PLK1 has a key role in the progression of mitosis and recent evidence suggest its important involvement in regulating the G2/M checkpoint, in DNA damage and replication stress response, and in cell death pathways. PLK1 expression is tightly spatially and temporally regulated to ensure its nuclear activation at the late S-phase, until the peak of expression at the G2/M-phase. Recently, new roles of PLK1 have been reported in literature on its implication in the regulation of inflammation and immunological responses. All these biological processes are altered in tumors and, considering that PLK1 is often found overexpressed in several tumor types, its targeting has emerged as a promising anti-cancer therapeutic strategy. In this review, we will summarize the evidence suggesting the role of PLK1 in response to DNA damage, including DNA repair, cell cycle progression, epithelial to mesenchymal transition, cell death pathways and cancer-related immunity. An update of PLK1 inhibitors currently investigated in preclinical and clinical studies, in monotherapy and in combination with existing chemotherapeutic drugs and targeted therapies will be discussed.

PLK1 inhibition-based combination therapies for cancer management

Polo-like kinase I (PLK1), a cell cycle regulating kinase, has been shown to have oncogenic function in several cancers. Although PLK1 inhibitors, such as BI2536, BI6727 (volasertib) and NMS-1286937 (onvansertib) are generally well-tolerated with a favorable pharmacokinetic profile, clinical successes are limited due to partial responses in cancer patients, especially those in advanced stages. Recently, combination therapies targeting multiple pathways are being tested for cancer management. In this review, we first discuss structure and function of PLK1, role of PLK1 in cancers, PLK1 specific inhibitors, and advantages of using combination therapy versus monotherapy followed by a critical account on PLK1-based combination therapies in cancer treatments, especially highlighting recent advancements and challenges. PLK1 inhibitors in combination with chemotherapy drugs and targeted small molecules have shown superior effects against cancer both in vitro and in vivo. PLK1-based combination therapies have shown increased apoptosis, disrupted cell cycle, and potential to overcome resistance in cancer cells/tissues over monotherapies. Further, with successes in preclinical experiments, researchers are validating such approaches in clinical trials. Although PLK1-based combination therapies have achieved initial success in clinical studies, there are examples where they have failed to improve patient survival. Therefore, further research is needed to identify and validate novel biologically informed co-targets for PLK1-based combinatorial therapies. Employing a network-based analysis, we identified potential PLK1 co-targets that could be examined further. In addition, understanding the mechanisms of synergism between PLK1 inhibitors and other agents may lead to a better approach on which agents to pair with PLK1 inhibition for optimum cancer treatment.

Ubiquitin-Specific Peptidase 7: A Novel Deubiquitinase That Regulates Protein Homeostasis and Cancers

Ubiquitin-Specific Peptidase 7 (USP7), or herpes virus-associated protease (HAUSP), is the largest family of the deubiquitinating enzymes (DUBs). Recent studies have shown that USP7 plays a vital role in regulating various physiological and pathological processes. Dysregulation of these processes mediated by USP7 may contribute to many diseases, such as cancers. Moreover, USP7 with aberrant expression levels and abnormal activity are found in cancers. Therefore, given the association between USP7 and cancers, targeting USP7 could be considered as an attractive and potential therapeutic approach in cancer treatment. This review describes the functions of USP7 and the regulatory mechanisms of its expression and activity, aiming to emphasize the necessity of research on USP7, and provide a better understanding of USP7-related biological processes and cancer.

Dual Targeting of EGFR with PLK1 Exerts Therapeutic Synergism in Taxane-Resistant Lung Adenocarcinoma by Suppressing ABC Transporters

Simple Summary

Our previous studies led us to hypothesize that downregulation of PLK1 expression or its activity can overcome the hurdles of taxane resistance by downregulating ABC transporters. Targeting PLK1 with shRNA or non-functional mutants downregulated ABCB1, ABCC9, and ABCG2 in paclitaxel-resistant lung adenocarcinoma (LUAD^TXR), similar to the downregulation effects from treatment with PLK1 inhibitors. Since EGFR is highly expressed in LUAD^TXR cells, gefitinib was combined with PLK1 inhibitors. Under these conditions, LUAD^TXR cells tend to undergo apoptosis more effectively than parental cells, showing a synergistic effect on downregulation of ABC transporters through c-Myc or AP-1. Clinical data provide evidence for the relationship between survival rates and expressions of PLK1 and EGFR in LUAD patients. Taken together, our data suggest that a combination of gefitinib and PLK1 inhibitors exerts strong synergism in LUAD^TXR, providing a benefit to overcome the limitations associated with taxanes.

Abstract

To overcome the limitations of chemoresistance, combination therapies using druggable targets have been investigated. Our previous studies led us to hypothesize that the downregulation of PLK1 expression or activity can be one strategy to overcome the hurdles of taxane resistance by the downregulation of ABC transporters. To explore this, various versions of PLK1 including a constitutively active version, kinase-dead form, and polo-box domain mutant were expressed in paclitaxel-resistant lung adenocarcinoma (LUAD^TXR). Targeting PLK1 using shRNA or non-functional mutants downregulated ABCB1, ABCC9, and ABCG2 in LUAD^TXR cells, which was similar to the downregulation effects from treatment with PLK1 inhibitors. The high expression of EGFR in LUAD led us to administer gefitinib, showing a markedly reduced EGFR level in LUAD^TXR cells. When gefitinib and PLK1 inhibitors were combined, LUAD^TXR cells tended to undergo apoptosis more effectively than parental cells, showing a synergistic effect on the downregulation of ABC transporters through c-Myc and AP-1. Clinical data provide evidence for the relevance between survival rates and expressions of PLK1 and EGFR in LUAD patients. Based on these results, we suggest that a combination of gefitinib and PLK1 inhibitors exerts strong synergism in LUAD^TXR, which helps to overcome the limitations associated with taxanes.

Targeting Ubiquitin-Specific Protease 7 (USP7) in Cancer: A New Insight to Overcome Drug Resistance

Chemoresistance is one of the leading causes for the failure of tumor treatment. Hence, it is necessary to study further and understand the potential mechanisms of tumor resistance to design and develop novel anti-tumor drugs. Post-translational modifications are critical for proteins’ function under physiological and pathological conditions, among which ubiquitination is the most common one. The protein degradation process mediated by the ubiquitin-proteasome system is the most well-known function of ubiquitination modification. However, ubiquitination also participates in the regulation of many other biological processes, such as protein trafficking and protein-protein interaction. A group of proteins named deubiquitinases can hydrolyze the isopeptide bond and disassemble the ubiquitin-protein conjugates, thus preventing substrate proteins form degradation or other outcomes. Ubiquitin-specific protease 7 (USP7) is one of the most extensively studied deubiquitinases. USP7 exhibits a high expression signature in various malignant tumors, and increased USP7 expression often indicates the poor tumor prognosis, suggesting that USP7 is a marker of tumor prognosis and a potential drug target for anti-tumor therapy. In this review, we first discussed the structure and function of USP7. Further, we summarized the underlying mechanisms by which tumor cells develop resistance to anti-tumor therapies, provided theoretical support for targeting USP7 to overcome drug resistance, and some inspiration for the design and development of USP7 inhibitors.