Targeting the NFAT1-MDM2-MDMX Network Inhibits the Proliferation and Invasion of Prostate Cancer Cells, Independent of p53 and Androgen

Targeting the MYCN-MDM2 pathways for cancer therapy: Are they druggable?

Targeting oncogenes and their interactive partners is an effective approach to developing novel targeted therapies for cancer and other chronic diseases. We and others have long suggested the MDM2 oncogene being an excellent target for cancer therapy, based on its p53-dependent and -independent oncogenic activities in a variety of cancers. The MYC family proteins are transcription factors that also regulate diverse biological functions. Dysregulation of MYC, such as amplification of MYCN, is associated with tumorigenesis, especially for neuroblastoma. Although the general survival rate of neuroblastoma patients has significantly improved over the past few decades, high-risk neuroblastoma still presents a poor prognosis. Therefore, innovative and more potent therapeutic strategies are needed to eradicate these aggressive neoplasms. This review focuses on the oncogenic properties of MYCN and its molecular regulation and summarizes the major therapeutic strategies being developed based on preclinical findings. We also highlight the potential benefits of targeting both the MYCN and MDM2 oncogenes, providing preclinical evidence of the efficacy and safety of this approach. In conclusion, the development of effective small molecules that inhibit both MYCN and MDM2 represents a promising new strategy for the treatment of neuroblastoma and other cancers.

Cellular, Structural Basis, and Recent Progress for Targeting Murine Double Minute X (MDMX) in Tumors

Murine double minute X (MDMX) is an oncoprotein that mainly has a negative regulatory effect on the tumor suppressor p53 to induce tumorigenesis. As MDMX is highly expressed in various types of tumor cells, targeting and inhibiting MDMX are becoming a promising strategy for treating cancers. However, the high degree of structural homology between MDMX and its homologous protein murine double minute 2 (MDM2) is a great challenge for the development of MDMX-targeted therapies. This review introduces the structure, distribution, and regulation of the MDMX, summarizes the structural features and structure-activity relationships (SARs) of MDMX ligands, and focuses on the differences between MDMX and MDM2 in these aspects. Our purpose of this work is to propose potential strategies to achieve the specific targeting of MDMX.

MDMX in Cancer: A Partner of p53 and a p53-Independent Effector

The p53 tumor suppressor protein plays an important role in physiological and pathological processes. MDM2 and its homolog MDMX are the most important negative regulators of p53. Many studies have shown that MDMX promotes the growth of cancer cells by influencing the regulation of the downstream target gene of tumor suppressor p53. Studies have found that inhibiting the MDMX-p53 interaction can effectively restore the tumor suppressor activity of p53. MDMX has growth-promoting activities without p53 or in the presence of mutant p53. Therefore, it is extremely important to study the function of MDMX in tumorigenesis, progression and prognosis. This article mainly reviews the current research progress and mechanism on MDMX function, summarizes known MDMX inhibitors and provides new ideas for the development of more specific and effective MDMX inhibitors for cancer treatment.

NFAT signaling dysregulation in cancer: Emerging roles in cancer stem cells

The nuclear factor of activated T cells (NFAT) was first identified as a transcriptional regulator of activated T cells. The NFAT family is involved in the development of tumors. Furthermore, recent evidence reveals that NFAT proteins regulate the development of inflammatory and immune responses. New discoveries have also been made about the mechanisms by which NFAT regulates cancer progression through cancer stem cells (CSC). Here, we discuss the role of the NFAT family in the immune system and various cancer types.

Structural studies of antitumor compounds that target the RING domain of MDM2

Mouse double minute 2 homolog (MDM2) is an E3 ubiquitin-protein ligase that is involved in the transfer of ubiquitin to p53 and other protein substrates. The expression of MDM2 is elevated in cancer cells and inhibitors of MDM2 showed potent anticancer activities. Many inhibitors target the p53 binding domain of MDM2. However, inhibitors such as Inulanolide A and MA242 are found to bind the RING domain of MDM2 to block ubiquitin transfer. In this report, crystal structures of MDM2 RING domain in complex with Inulanolide A and MA242 were solved. These inhibitors primarily bind in a hydrophobic site centered at the sidechain of Tyr489 at the C-terminus of MDM2 RING domain. The C-terminus of MDM2 RING domain, especially residue Tyr489, is required for ubiquitin discharge induced by MDM2. The binding of these inhibitors at Tyr489 may interrupt interactions between the MDM2 RING domain and the E2-Ubiquitin complex to inhibit ubiquitin transfer, regardless of what the substrate is. Our results suggest a new mechanism of inhibition of MDM2 E3 activity for a broad spectrum of substrates.

Functional roles of E3 ubiquitin ligases in prostate cancer

Prostate cancer (PCa) is a malignant epithelial tumor of the prostate gland with a high male cancer incidence. Numerous studies indicate that abnormal function of ubiquitin-proteasome system (UPS) is associated with the progression and metastasis of PCa. E3 ubiquitin ligases, key components of UPS, determine the specificity of substrates, and substantial advances of E3 ubiquitin ligases have been reached recently. Herein, we introduce the structures and functions of E3 ubiquitin ligases and summarize the mechanisms of E3 ubiquitin ligases-related PCa signaling pathways. In addition, some progresses in the development of inhibitors targeting E3 ubiquitin ligases are also included.

miR-1307-5p suppresses proliferation and tumorigenesis of bladder cancer via targeting MDM4 and the Hippo signaling pathway

BACKGROUND

Emerging evidence has shown that miR-1307-5p is involved in tumorigenesis of various types of cancer. This study aims to assess the role and mechanism of miR-1307-5p in bladder cancer.

METHODS

Bioinformatics analyses were carried out with clinical datasets in the public domains. To investigate the cellular functions of miR-1307-5p, assays of cell proliferation, cell cycle and cell apoptosis were conducted in bladder cancer cell lines and xenografts. The molecular mechanisms of miR-1307-5p were studied using luciferase reporter, RT-qPCR, and western blotting analyses.

RESULTS

We found that miR-1307-5p expression was significantly decreased in bladder cancer tissues, and its lower level was associated with poor prognosis. Cellular assays indicated the tumor-suppressor roles of miR-1307-5p were linked to cell proliferation, cell cycle inhibition, and cell apoptosis promotion. Conversely, anti-miR-1307-5p facilitated cell proliferation and cell cycle and antagonized cell apoptosis. In the in vivo setting, tumor growth was suppressed by miR-1307-5p overexpression. We found by bioinformatic and luciferase reporter assays that miR-1307-5p targets the 3'-UTR of MDM4, a well-known Inhibitor of TP53-mediated transactivation, cell cycle arrest and apoptosis. Specifically, miR-1307-5p markedly reduced MDM4 proteins expression, decreased the expression of Ki-67 and PCNA, and increased the expression of cleaved-caspase 3 and caspase 9. While in parallel assays, anti-miR-1307-5p had opposite effects. In addition, we found that miR-1307-5p overexpression would suppress bladder cancer cell growth by inhibiting MDM4 and its downstream Hippo pathway.

CONCLUSION

In bladder cancer, miR-1307-5p functions as a tumor suppressor and has the potentials as biomarker and therapeutical agent.

Japonicone A and related dimeric sesquiterpene lactones: molecular targets and mechanisms of anticancer activity

OBJECTIVE AND DESIGN

Japonicone A (Jap-A) is a sesquiterpene lactone (SL) dimer isolated from the plant Inula japonica Thunb. and the leading compound in the japonicone series of SL dimers which comprises 25 members (Jap-A to Jap-Y). We have analyzed the anticancer properties of Jap-A and the associated molecular targets.

METHODS

All literature data on japonicones and related SL dimers, including inulanolide A (Inu-A) and lineariifolianoid A (Lin-A) have been analyzed. Molecular models of the compound/target interactions were constructed to support our analysis.

RESULTS

Inulae Flos (Xuan Fu Hua) is used in traditional medicine in China and Korea to treat inflammatory diseases. The plant contains diverse japonicones and structurally related SL dimers. The interactions of Jap-A with the two main proteins, the pro-inflammatory cytokine TNF-α and the ubiquitin ligase MDM2, are at the origin of the anti-inflammatory and anticancer effects. Molecular docking analyses suggest that Inu-A is better adapted than Lin-A and Jap-A to form stable complexes with both TNF-α and MDM2. Jap-A exhibits marked capacities to inhibit cancer cell proliferation and dissemination and to trigger apoptosis, both in vitro and in vivo in several tumor models in mice. Its analogue Inu-A is more potent, functioning as a dual inhibitor of the MDM2-NFAT1 pathway.

CONCLUSION

This review shed some new light on the molecular targets and potential therapeutic benefits of these SL dimers and should help the design of novel anticancer agents derived from these compounds.

The Adipokine Component in the Molecular Regulation of Cancer Cell Survival, Proliferation and Metastasis

A hormonal imbalance may disrupt the rigorously monitored cellular microenvironment by hampering the natural homeostatic mechanisms. The most common example of such hormonal glitch could be seen in obesity where the uprise in adipokine levels is in virtue of the expanding bulk of adipose tissue. Such aberrant endocrine signaling disrupts the regulation of cellular fate, rendering the cells to live in a tumor supportive microenvironment. Previously, it was believed that the adipokines support cancer proliferation and metastasis with no direct involvement in neoplastic transformations and tumorigenesis. However, the recent studies have reported discrete mechanisms that establish the direct involvement of adipokine signaling in tumorigenesis. Moreover, the individual adipokine profile of the patients has never been considered in the prognosis and staging of the disease. Hence, the present manuscript has focused on the reported extensive mechanisms that culminate the basis of poor prognosis and diminished survival rate in obese cancer patients.

PROTAC: An Effective Targeted Protein Degradation Strategy for Cancer Therapy

Proteolysis targeting chimeric (PROTAC) technology is an effective endogenous protein degradation tool developed in recent years that can ubiquitinate the target proteins through the ubiquitin-proteasome system (UPS) to achieve an effect on tumor growth. A number of literature studies on PROTAC technology have proved an insight into the feasibility of PROTAC technology to degrade target proteins. Additionally, the first oral PROTACs (ARV-110 and ARV-471) have shown encouraging results in clinical trials for prostate and breast cancer treatment, which inspires a greater enthusiasm for PROTAC research. Here we focus on the structures and mechanisms of PROTACs and describe several classes of effective PROTAC degraders based on E3 ligases.

Hsa_circ_0080229 upregulates the expression of murine double minute-2 (MDM2) and promotes glioma tumorigenesis and invasion via the miR-1827 sponging mechanism

Background

Glioma is the most common and fatal primary cranial tumor. The epidermal growth factor receptor (EGFR) plays an important role in the occurrence and treatment of glioma, which might function through a circular ribonucleic acid (circRNA)-related mechanism. Hsa_circ_0080229 (circ_0080229) has been identified as a circRNA arising from an EGFR gene in gliomas; however, little is known about its molecular mechanism to date.

Methods

To address this question, a series of experiments were conducted to confirm the effect of circ_0080229 in gliomas and identify the downstream mechanism. A quantitative real-time polymerase chain reaction (qRT-PCR) analysis and in-situ hybridization/fluorescence in-situ hybridization (ISH/FISH) testing were performed to identify the expression of circ_0080229 in patient samples. Bioinformatic analysis was carried out to explore the possible mechanism. Next, a series of in-vitro functional assays and in-vivo assays with a xenograft subcutaneous glioma model was carried out to confirm the effect of circ_0080229. Finally, qRT-PCR analysis and a Western Blot analysis were performed to verify the related mechanism.

Results

The expression of circ_0080229 was upregulated in both glioma tissues and cell lines related to unfavorable clinicopathologic characteristics. The expression of circ_0080229 was found to be inversely correlated with miR-1827, a micro-ribonucleic acid (miRNA) targeting murine double minute-2 (MDM2). The downregulation of circ_0080229 inhibited gliomas in vivo and suppressed U87 and U251 cell lines in vitro, which the transfection of the miR-1827 inhibitor could reverse. Concerning the mechanism, a block of circ_0080229 decreased MDM2 expression, while the inhibition of miR-1827 reversed this effect. Thus, circ_0080229 appears to target the downstream miR-1827/MDM2 signaling pathway.

Conclusions

Our results showed that the silencing of circ_0080229 upregulates the expression of miR-1827, which in turn resulted in the suppression of MDM2, and the mediation of the downstream P53 signaling pathway. Circ_0080229 exerted an effect in mediating tumor progression through the MDM2 signaling pathway by sponging miR-1827. Its importance as a potential prognostic biomarker in gliomas has thus been established.

The role of miRNAs in MDMX-p53 interplay

MicroRNAs (miRNAs) are endogenous noncoding RNAs of 19-24 nucleotides in length and are tightly related to tumorigenesis and progression. Recent studies have demonstrated that the tumor suppressor p53 and its negative controller MDMX are regulated by miRNAs in different ways. Some miRNAs directly target p53 and regulate its expression and function, whereas some miRNAs target MDMX and regulate p53's activity indirectly. The overexpression of several miRNAs can restore the activity of p53 by negatively regulating MDMX in cancer cells. Therefore, a better understanding of the miRNAs-MDMX-p53 network will put forward potential research directions for developing anticancer therapeutics. In the present review, we mainly focus on the regulatory effects of miRNAs on the MDMX-p53 interplay as well as the role of the miRNAs-MDMX-p53 network in human cancer.

Cytotoxic Fractions from Hechtia glomerata Extracts and p-Coumaric Acid as MAPK Inhibitors

Preliminary bioassay-guided fractionation was performed to identify cytotoxic compounds from Hechtia glomerata, a plant that is used in Mexican ethnomedicine. Organic and aqueous extracts were prepared from H. glomerata’s leaves and evaluated against two cancer cell lines. The CHCl₃/MeOH (1:1) active extract was fractionated, and the resulting fractions were assayed against prostate adenocarcinoma PC3 and breast adenocarcinoma MCF7 cell lines. Active fraction 4 was further analyzed by high-performance liquid chromatography–quadrupole time-of-flight–mass spectrometry analysis to identify its active constituents. Among the compounds that were responsible for the cytotoxic effects of this fraction were flavonoids, phenolic acids, and aromatic compounds, of which p-coumaric acid (p-CA) and its derivatives were abundant. To understand the mechanisms that underlie p-CA cytotoxicity, a microarray assay was performed on PC3 cells that were treated or not with this compound. The results showed that mitogen-activated protein kinases (MAPKs) that regulate many cancer-related pathways were targeted by p-CA, which could be related to the reported effects of reactive oxygen species (ROS). A molecular docking study of p-CA showed that this phenolic acid targeted these protein active sites (MAPK8 and Serine/Threonine protein kinase 3) at the same binding site as their inhibitors. Thus, we hypothesize that p-CA produces ROS, directly affects the MAPK signaling pathway, and consequently causes apoptosis, among other effects. Additionally, p-CA could be used as a platform for the design of new MAPK inhibitors and re-sensitizing agents for resistant cancers.

Antimicrobial Peptide Reverses ABCB1-Mediated Chemotherapeutic Drug Resistance

Multidrug resistance (MDR) of tumor cells to chemotherapeutic agents is the main reason for the failure of cancer chemotherapy. Overexpression of ABCB1 transporter that actively pumps various drugs out of the cells has been considered a major contributing factor for MDR. Over the past decade, many antimicrobial peptides with antitumor activity have been identified or synthesized, and some antitumor peptides have entered the clinical practice. In this study, we report that peptide HX-12C has the effect of reversing ABCB1-mediated chemotherapy resistance. In ABCB1-overexpressing cells, nontoxic dose of peptide HX-12C inhibited drug resistance and increased the effective intracellular concentration of paclitaxel and other ABCB1 substrate drugs. The mechanism study showed that peptide HX-12C stimulated ABCB1 ATPase activity without changing the expression level and localization patterns of ABCB1. Molecular docking predicted the binding modes between peptide HX-12C and ABCB1. Overall, we found that peptide HX-12C reverses ABCB1-mediated MDR through interacting with ABCB1 and blocking its function without affecting the transporter's expression and cellular localization. Our findings suggest that this antimicrobial peptide may be used as a novel prospective cancer therapeutic strategy in combination with conventional anticancer agents.

Targeting MDMX for Cancer Therapy: Rationale, Strategies, and Challenges

The oncogene MDMX, also known as MDM4 is a critical negative regulator of the tumor suppressor p53 and has been implicated in the initiation and progression of human cancers. Increasing evidence indicates that MDMX is often amplified and highly expressed in human cancers, promotes cancer cell growth, and inhibits apoptosis by dampening p53-mediated transcription of its target genes. Inhibiting MDMX-p53 interaction has been found to be effective for restoring the tumor suppressor activity of p53. Therefore, MDMX is becoming one of the most promising molecular targets for developing anticancer therapeutics. In the present review, we mainly focus on the current MDMX-targeting strategies and known MDMX inhibitors, as well as their mechanisms of action and in vitro and in vivo anticancer activities. We also propose other potential targeting strategies for developing more specific and effective MDMX inhibitors for cancer therapy.

Identifying Drug Targets in Pancreatic Ductal Adenocarcinoma Through Machine Learning, Analyzing Biomolecular Networks, and Structural Modeling

Pancreatic ductal adenocarcinoma (PDAC) is one of the leading causes of cancer-related death and has an extremely poor prognosis. Thus, identifying new disease-associated genes and targets for PDAC diagnosis and therapy is urgently needed. This requires investigations into the underlying molecular mechanisms of PDAC at both the systems and molecular levels. Herein, we developed a computational method of predicting cancer genes and anticancer drug targets that combined three independent expression microarray datasets of PDAC patients and protein-protein interaction data. First, Support Vector Machine–Recursive Feature Elimination was applied to the gene expression data to rank the differentially expressed genes (DEGs) between PDAC patients and controls. Then, protein-protein interaction networks were constructed based on the DEGs, and a new score comprising gene expression and network topological information was proposed to identify cancer genes. Finally, these genes were validated by “druggability” prediction, survival and common network analysis, and functional enrichment analysis. Furthermore, two integrins were screened to investigate their structures and dynamics as potential drug targets for PDAC. Collectively, 17 disease genes and some stroma-related pathways including extracellular matrix-receptor interactions were predicted to be potential drug targets and important pathways for treating PDAC. The protein-drug interactions and hinge sites predication of ITGAV and ITGA2 suggest potential drug binding residues in the Thigh domain. These findings provide new possibilities for targeted therapeutic interventions in PDAC, which may have further applications in other cancer types.

Terphenyllin Suppresses Orthotopic Pancreatic Tumor Growth and Prevents Metastasis in Mice

Pancreatic cancer (PC) is an aggressive and fatal disease with high incidences of metastasis and recurrence. However, there are no effective treatment options for the majority of PC patients, especially for those with locally advanced tumors and metastatic diseases. Therefore, it is urgently needed to develop safe and effective anti-PC therapeutic agents. We have recently identified a novel marine-derived natural product terphenyllin with potent anti-PC activity. The present study was designed to investigate the efficacy and mechanisms of action of terphenyllin in several human PC cell lines and an orthotopic PC mouse model. The results showed that terphenyllin significantly inhibited the viability of all PC cell lines with minimal effects on a normal human pancreatic cell line (HPNE). We next demonstrated the effects of terphenyllin on colony formation, apoptosis, migration, and invasion in both Panc1 and HPAC cell lines in a concentration-dependent manner. Terphenyllin also suppressed the tumor growth and metastasis in the Panc1 orthotopic mouse model. We further showed the profound effects of terphenyllin on the expression of apoptosis-associated proteins, including Bax, Bad, Puma, BimL, Bcl-2, phos-Bcl-2 (Ser70), Bcl-xL, caspase 7, and PARP, which contributed to its anti-PC activity. In summary, terphenyllin suppressed the PC cell growth and metastasis in vitro and in vivo and may be developed as an anti-PC therapeutic agent in the future.

Targeting USP7-Mediated Deubiquitination of MDM2/MDMX-p53 Pathway for Cancer Therapy: Are We There Yet?

The p53 tumor suppressor protein and its major negative regulators MDM2 and MDMX oncoproteins form the MDM2/MDMX-p53 circuitry, which plays critical roles in regulating cancer cell growth, proliferation, cell cycle progression, apoptosis, senescence, angiogenesis, and immune response. Recent studies have shown that the stabilities of p53, MDM2, and MDMX are tightly controlled by the ubiquitin-proteasome system. Ubiquitin specific protease 7 (USP7), one of the most studied deubiquitinating enzymes plays a crucial role in protecting MDM2 and MDMX from ubiquitination-mediated proteasomal degradation. USP7 is overexpressed in human cancers and contributes to cancer initiation and progression. USP7 inhibition promotes the degradation of MDM2 and MDMX, activates the p53 signaling, and causes cell cycle arrest and apoptosis, making USP7 a potential target for cancer therapy. Several small-molecule inhibitors of USP7 have been developed and shown promising efficacy in preclinical settings. In the present review, we focus on recent advances in the understanding of the USP7-MDM2/MDMX-p53 network in human cancers as well as the discovery and development of USP7 inhibitors for cancer therapy.

Recombinant Dual-target MDM2/MDMX Inhibitor Reverses Doxorubicin Resistance through Activation of the TAB1/TAK1/p38 MAPK Pathway in Wild-type p53 Multidrug-resistant Breast Cancer Cells

Chemotherapy resistance represents a major obstacle for the treatment of patients with breast cancer (BC) and greatly restricts the therapeutic effect of the first-line chemotherapeutic agent doxorubicin (DOX). The present study aimed to investigate the feasibility of the recombinant dual-target murine double minute 2 (MDM2) and murine double minute X (MDMX) inhibitor in reversing the DOX resistance of BC. Both DOX-resistant human breast carcinoma cell lines exhibited a multidrug resistance (MDR) phenotype. The ability of the dual-target MDM2/MDMX inhibitor in reversing doxorubicin resistance was subsequently verified, (9.15 and 13.92 - fold reversal indexes) respectively. We observed that the MDM2/MDMX inhibitor in combination with DOX could suppress proliferation, promote cell cycle arrest and induce apoptosis. In addition, it was capable of reducing rhodamine123 efflux in DOX-resistance BC cell lines and further played a key role in BC nude mice model. The groups that were treated with the combination of the drugs had decreased P-glycoprotein/multidrug resistance-associated protein/cdc 2/Bcl-2 expression and increased CyclinB1/Bax expression. These effects were caused due to activation of the transforming growth factor β-activated kinase 1 (TAK1)-binding protein 1 (TAB1)/TAK1/p38 mitogen-activated protein kinase (MAPK) signaling pathway, as shown by small interfering RNA (siRNA) silencing and immumohistochemical staining of BC tissue sections. Furthermore, high MDM2/MDMX expression was positively associated with weak TAB1 expression in BC patients. Therefore, the recombinant dual-target MDM2/MDMX inhibitor could reverse doxorubicin resistance via the activation of the TAB1/TAK1/p38 MAPK pathway in wild-type p53 multidrug-resistant BC.

Naturally occurring [4 + 2] type terpenoid dimers: sources, bioactivities and total syntheses

This review article highlights recent progress on their sources, bioactivities, biosynthetic hypotheses and total chemical syntheses of naturally occurring [4 + 2] type terpenoid dimers.

Natural disesquiterpenoids: an update

This review highlights the progress on the isolation, bioactivity, biogenesis and total synthesis of dimeric sesquiterpenoids since 2010.

Targeting MDM2 for novel molecular therapy: Beyond oncology

The murine double minute 2 (MDM2) oncogene exerts major oncogenic activities in human cancers; it is not only the best-documented negative regulator of the p53 tumor suppressor, but also exerts p53-independent activities. There is an increasing interest in developing MDM2-based targeted therapies. Several classes of MDM2 inhibitors have been evaluated in preclinical models, with a few entering clinical trials, mainly for cancer therapy. However, noncarcinogenic roles for MDM2 have also been identified, demonstrating that MDM2 is involved in many chronic diseases and conditions such as inflammation and autoimmune diseases, dementia and neurodegenerative diseases, heart failure and cardiovascular diseases, nephropathy, diabetes, obesity, and sterility. MDM2 inhibitors have been shown to have promising therapeutic efficacy for treating inflammation and other nonmalignant diseases in preclinical evaluations. Therefore, targeting MDM2 may represent a promising approach for treating and preventing these nonmalignant diseases. In addition, a better understanding of how MDM2 works in nonmalignant diseases may provide new biomarkers for their diagnosis, prognostic prediction, and monitoring of therapeutic outcome. In this review article, we pay special attention to the recent findings related to the roles of MDM2 in the pathogenesis of several nonmalignant diseases, the therapeutic potential of its downregulation or inhibition, and its use as a biomarker.

Contemplations on MDMX (MDM4) driving triple negative breast cancer circulating tumor cells and metastasis

MDMX (MDM4) is emerging as an important breast cancer (BC) biomarker, and oncoprotein, that can be targeted in combination with its well-known family member MDM2. While MDM2 has previously been implicated in driving BC metastasis, information about the role of MDMX in driving circulating tumor cells (CTCs) and BC metastasis is lacking. BCs often have alterations of MDM2, MDMX, and mutant p53 (mtp53). Therefore, the role of MDM2 and MDMX in the context of mtp53 in BCs requires further clarification. Our group has recently reported that triple negative breast cancer (TNBC) metastasis is dependent on both MDM2 and MDMX, and depleting MDM2 results in increased MDMX, but depleting MDMX does not cause an increase in MDM2. In the context of human TNBC expressing mtp53 in an orthotopic mouse model the down-regulation of MDMX virtually cleared CTCs from the blood. Contemplations, using the available literature, suggest that disrupting the stability and/or function of MDMX protein (and its downstream targets), in the context of mtp53 expressing BCs, might be beneficial for patient survival. It remains to be determined if blocking mtp53-MDMX pathways can inhibit early stage TNBC and eliminate CTCs that have the potential to form metastatic lesions.

The long and the short of it: the MDM4 tail so far

The mouse double minute 4 (MDM4) is emerging from the shadow of its more famous relative MDM2 and is starting to steal the limelight, largely due to its therapeutic possibilities. MDM4 is a vital regulator of the tumor suppressor p53. It restricts p53 transcriptional activity and also, at least in development, facilitates MDM2's E3 ligase activity toward p53. These functions of MDM4 are critical for normal cell function and a proper response to stress. Their importance for proper cell maintenance and proliferation identifies them as a risk for deregulation associated with the uncontrolled growth of cancer. MDM4 tails are vital for its function, where its N-terminus transactivation domain engages p53 and its C-terminus RING domain binds to MDM2. In this review, we highlight recently identified cellular functions of MDM4 and survey emerging therapies directed to correcting its dysregulation in disease.

Evaluation of the anticancer and anti-metastasis effects of novel synthetic sodium channel blockers in prostate cancer cells in vitro and in vivo

BACKGROUND

Voltage-gated sodium channels (VGSCs) are involved in several cellular processes related to cancer cell growth and metastasis, including adhesion, proliferation, apoptosis, migration, and invasion. We here in investigated the effects of S0154 and S0161, two novel synthetic sodium channel blockers (SCBs), on human prostate cancer cells (PC3, DU145, and LnCaP) and a prostate cancer xenograft model.

METHODS

The MTT assay was used to assess the anticancer effects of SCBs in PC3, DU145, and LnCaP cells. Sodium indicator and glucose uptake assays were used to determine the effects of S0154 and S0161 in PC3 cells. The impact of these SCBs on the proliferation, cell cycle, apoptosis, migration, and invasion of PC3 cells were determined using a CFDA-SE cell proliferation assay, cell cycle assay, annexin V-FITC apoptosis assay, transwell cell invasion assay, and wound-healing assay, respectively. The protein expression levels of Nav1.6, Nav1.7, CDK1, cyclin B1, MMP2, MMP9 in PC3 cells were analysis by Western blotting. The in vivo anticancer activity was evaluated using a PC3 xenograft model in nude mice.

RESULTS

S0154 and S0161 both showed anticancer and anti-metastatic effects against prostate cancer cells and significantly inhibited cell viability, with IC₅₀ values in the range of 10.51-26.60 μmol/L (S0154) and 5.07-11.92 μmol/L (S0161). Both compounds also increased the intracellular level of sodium, inhibited the protein expression of two α subunits of VGSCs (Nav1.6 and Nav1.7), and caused G2/M phase cell cycle arrest, with no or minor effects on cell apoptosis. Concentrations of 5 and 10 μmol/L of S0154 and S0161 significantly decreased the glucose uptake of PC3 cells. The compounds also inhibited the proliferation of PC3 cells and decreased their invasion in transwell assays. Furthermore, S0161 exerted antitumor activity in an in vivo PC3 xenograft model in nude mice, inhibiting the growth of the tumors by about 51% compared to the control group.

CONCLUSIONS

These results suggest that S0154 and S0161 have anticancer and anti-metastasis effects in prostate cancer cells both in vitro and in vivo, supporting their further development as potential therapeutic agents for prostate cancer.

Dual-target MDM2/MDMX inhibitor increases the sensitization of doxorubicin and inhibits migration and invasion abilities of triple-negative breast cancer cells through activation of TAB1/TAK1/p38 MAPK pathway

Triple-negative breast cancer (TNBC) has a poor prognosis mainly due to insensitivity or resistance to standard anthracycline- and taxane-based chemotherapy, urgently calling for new adjuvants to reverse drug resistance. Dual-target murine double minute 2 (MDM2) and murine double minute X (MDMX) inhibitor has been proved to play a critical part against cancer, particularly focusing on the tremendous potential to enhance the efficacy of doxorubicin (DOX), however little was reported in TNBC. In the present study, we investigated the synergistic antitumor effect of the MDM2/MDMX inhibitor with DOX using three TNBC cell lines, two in situ transplantation tumor models and 214 clinical samples. We observed that the MDM2/MDMX inhibitor combined with DOX could not only inhibit cell vitality and migration and invasion abilities, but also highly inhibit tumor growth in TNBC nude mice. Besides, co-treatment of MDM2/MDMX inhibitor and DOX suppressed epithelial to mesenchymal transition (EMT) through increasing the TAK1-binding protein 1 (TAB1), transforming growth factor β-activated kinase 1 (TAK1) and p38 mitogen-activated protein kinase (MAPK) expression. Small interfering RNA-mediated TAB1 knockdown induced the EMT, desensitized cells to DOX and enhanced the migration and invasion abilities. High MDM2/MDMX expression was positively associated with weak TAB1 expression in 214 TNBC tumor tissues confirmed by immumohistochemical staining and MDM2/MDMX/TAB1 expression was significantly related to TNBC patient survival. These findings indicate that dual-target MDM2/MDMX inhibitor could increase the sensitization of doxorubicin and inhibit migration and invasion abilities in TNBC cells through p38 MAPK pathway activation caused EMT suppression and hence could be useful in TNBC treatments in future.

Natural products targeting the p53-MDM2 pathway and mutant p53: Recent advances and implications in cancer medicine

The p53 tumor suppressor plays a major role in controlling the initiation and development of cancer by regulating cell cycle arrest, apoptosis, senescence, and DNA repair. The MDM2 oncogene is a major negative regulator of p53 that inhibits the activity of p53 and reduces its protein stability. MDM2, p53, and the p53-MDM2 pathway represent well-documented targets for preventing and/or treating cancer. Natural products, especially those from medicinal and food plants, are a rich source for the discovery and development of novel therapeutic and preventive agents against human cancers. Many natural product-derived MDM2 inhibitors have shown potent efficacy against various human cancers. In contrast to synthetic small-molecule MDM2 inhibitors, the majority of which have been designed to inhibit MDM2-p53 binding and activate p53, many natural product inhibitors directly decrease MDM2 expression and/or MDM2 stability, exerting their anticancer activity in both p53-dependent and p53-independent manners. More recently, several natural products have been reported to target mutant p53 in cancer. Therefore, identification of natural products targeting MDM2, mutant p53, and the p53-MDM2 pathway can provide a promising strategy for the development of novel cancer chemopreventive and chemotherapeutic agents. In this review, we focus our discussion on the recent advances in the discovery and development of anticancer natural products that target the p53-MDM2 pathway, emphasizing several emerging issues, such as the efficacy, mechanism of action, and specificity of these natural products.