A therapeutic patent overview of MDM2/X-targeted therapies (2014–2018)

Regio- and Stereoselective Intermolecular 1,2-Difunctionalization of Terminal Alkynes: An Approach to Access (Z)-β-Amidovinylsulfones

We have developed the first I2/base-catalyzed regio- and stereoselective intermolecular β-amidosulfonylation of terminal alkynes using sodium sulfinates and quinoxalinone derivatives. The present methodology is compatible with a broad spectrum of various heterocyclic amides, terminal alkynes, and sodium sulfinates. It provides rapid access to valuable (Z)-β-amidovinyl sulfones at mild conditions. Moreover, the synthetic application of this methodology was demonstrated by the late-stage functionalization of numerous bioactive molecules.

MDM2 Inhibition in the Treatment of Glioblastoma: From Concept to Clinical Investigation

Inhibition of the interaction between MDM2 and p53 has emerged as a promising strategy for combating cancer, including the treatment of glioblastoma (GBM). Numerous MDM2 inhibitors have been developed and are currently undergoing rigorous testing for their potential in GBM therapy. Encouraging results from studies conducted in cell culture and animal models suggest that MDM2 inhibitors could effectively treat a specific subset of GBM patients with wild-type TP53 or functional p53. Combination therapy with clinically established treatment modalities such as radiation and chemotherapy offers the potential to achieve a more profound therapeutic response. Furthermore, an increasing array of other molecularly targeted therapies are being explored in combination with MDM2 inhibitors to increase the effects of individual treatments. While some MDM2 inhibitors have progressed to early phase clinical trials in GBM, their efficacy, alone and in combination, is yet to be confirmed. In this article, we present an overview of MDM2 inhibitors currently under preclinical and clinical investigation, with a specific focus on the drugs being assessed in ongoing clinical trials for GBM patients.

Targeting Biomolecular Condensation and Protein Aggregation against Cancer

Biomolecular condensates, membrane-less entities arising from liquid-liquid phase separation, hold dichotomous roles in health and disease. Alongside their physiological functions, these condensates can transition to a solid phase, producing amyloid-like structures implicated in degenerative diseases and cancer. This review thoroughly examines the dual nature of biomolecular condensates, spotlighting their role in cancer, particularly concerning the p53 tumor suppressor. Given that over half of the malignant tumors possess mutations in the TP53 gene, this topic carries profound implications for future cancer treatment strategies. Notably, p53 not only misfolds but also forms biomolecular condensates and aggregates analogous to other protein-based amyloids, thus significantly influencing cancer progression through loss-of-function, negative dominance, and gain-of-function pathways. The exact molecular mechanisms underpinning the gain-of-function in mutant p53 remain elusive. However, cofactors like nucleic acids and glycosaminoglycans are known to be critical players in this intersection between diseases. Importantly, we reveal that molecules capable of inhibiting mutant p53 aggregation can curtail tumor proliferation and migration. Hence, targeting phase transitions to solid-like amorphous and amyloid-like states of mutant p53 offers a promising direction for innovative cancer diagnostics and therapeutics.

Verbenalin attenuates hepatic damage and mitochondrial dysfunction in alcohol-associated steatohepatitis by regulating MDMX/PPARα-mediated ferroptosis

ETHNOPHARMACOLOGICAL RELEVANCE

Verbenalin is a major compound in Verbena officinalis L. Verbena officinalis L was first recorded in the 'Supplementary Records of Famous Physicians.' Verbenalin (VE) is its active constituent and has been found to have many biological effects, including anti-obesity, anti-inflammatory, and antioxidant activities, removing jaundice, and treating malaria. It could treat lump accumulation, dysmenorrhea, throat obstruction, edema, jaundice, and malaria. Palmitic acid (PA), oleic acid (OA), ethanol, and acetaminophen liver injuries have been proven to benefit from verbenalin.

AIM OF THE STUDY

To study the effects of verbenalin on the prevention of alcoholic steatohepatitis (ASH) through the regulation of oxidative stress and mitochondrial dysfunction by regulating MDMX (Murine double minute X)/PPARα (Peroxisome proliferator-activated receptor alpha)-mediated ferroptosis.

MATERIAL AND METHODS

C57BL/6 mice treated with alcohol followed by the Gao-Binge protocol were administered verbenalin by gavage simultaneously. The mitochondrial mass and morphology were visualized using TEM. AML-12 cells were stimulated with ethanol to mimic ASH in vitro. Western blotting, co-immunoprecipitation, and kit determination were simultaneously performed. The target protein of verbenalin was identified by molecular docking, and cellular thermal shift assay (CETSA) further confirmed its interactions.

RESULTS

Verbenalin alleviates oxidative stress and ferroptosis in alcohol-associated steatohepatitis. To elucidate the molecular mechanism by which verbenalin inhibits abnormal mitochondrial dysfunction, molecular docking was performed, and MDMX was identified as the target protein of verbenalin. CETSA assays revealed a specific interaction between MDMX and verbenalin. Co-immunoprecipitation demonstrated that PPARα played a critical role in promoting the ability of MDMX to affect ferroptosis. Verbenalin regulates MDMX/PPARα-mediated ferroptosis in AML-12 cells.

CONCLUSION

Verbenalin regulates ferroptosis and highlights the therapeutic potential of verbenalin and ferroptosis inhibition in reducing alcoholic steatohepatitis.

A MDM2 inhibitor MX69 inhibits adipocytes adipogenesis and differentiation

Adipose tissue, a key regulator of systemic energy homeostasis, can synthesize and store triglycerides to meet long-term energy demands. In response to nutrient overload, adipose tissue expands by hypertrophy or hyperplasia. As an oncogene, MDM2 has exerted diverse biological activities including human development, tissue regeneration, and inflammation, in addition to major oncogenic activities. Recently, some studies indicated that MDM2 plays an important role in adipose tissue function. However, the role of MX69, a MDM2 inhibitor, in adipose tissue function has not been fully elucidated. Here, we administered MX69 intraperitoneally to high-fat diet-induced obesity (DIO) wild type C57BL/6 mice and found that MX69 could promote the body weight and white adipose tissue weight of DIO mice. Moreover, MX69 had no effects on glucose tolerance and insulin sensitivity in DIO mice. And MX69 treatment decreased the size of adipocytes and fat deposition in adipose tissue and inhibited 3T3-L1 preadipocytes differentiation. Mechanistically, MX69 inhibited the protein levels of MDM2 and the mRNA levels of genes related to adipogenesis and differentiation. In summary, our results indicated that MDM2 has a crucial and complex role in regulating adipose tissue function.

A Noval Established Cuproptosis-Associated LncRNA Signature for Prognosis Prediction in Primary Hepatic Carcinoma

The copper ion content in the body maintains homeostasis, and when dysregulated, it can produce cytotoxicity and induce cell death through a variety of pathways. Cuproptosis refers to copper ions combining directly with acylated molecules, leading to the accumulation of oligomerization of lipoylated protein and subsequent downregulation of iron-sulfur cluster proteins; this induces proteotoxic stress and cell death. This study on the relationship between cuproptosis-related lncRNAs (CRLns) and the prognosis of primary hepatic carcinoma (PHC) has important clinical guiding significance for the diagnosis and treatment of PHC. Prognosis-related CRLRs were identified via rank-sum tests, correlational analyses, and univariate Cox regression, and a CRLR risk-scoring model (CRLRSM) was constructed using LASSO Cox regression. Patients were divided into high-risk and low-risk groups based on the median CRLRSM scores. Variance analysis for cuproptosis-related genes, gene set enrichment analysis, and correlational analysis for risk and immunity were performed using boxplots. Quantitative polymerase chain reactions were used to verify the CRLR levels in PHC cell lines. The study results showed that patients in the CRLRSM high-risk group had worse survival rates than those in the low-risk group. The PHC stage and risk score were independent prognostic factors for hepatocellular carcinoma. There were 7 CRLRs (MIR210HG, AC099850.3, AL031985.3, AC012073.1, MKLN1-AS, KDM4A-AS1, and PLBD1-AS1) associated with PHC prognosis, primarily through cellular metabolism, growth, proliferation, apoptosis, and immunity. In conclusion, the overexpression of 7 CRLRs in patients with PHC indicates a poor prognosis.

Bivalent binding of p14ARF to MDM2 RING and acidic domains inhibits E3 ligase function

ARF tumor suppressor protein is a key regulator of the MDM2-p53 signaling axis. ARF interferes with MDM2-mediated ubiquitination and degradation of p53 by sequestering MDM2 in the nucleolus and preventing MDM2-p53 interaction and nuclear export of p53. Moreover, ARF also directly inhibits MDM2 ubiquitin ligase (E3) activity, but the mechanism remains elusive. Here, we apply nuclear magnetic resonance and biochemical analyses to uncover the mechanism of ARF-mediated inhibition of MDM2 E3 activity. We show that MDM2 acidic and zinc finger domains (AD-ZnF) form a weak intramolecular interaction with the RING domain, where the binding site overlaps with the E2∼ubiquitin binding surface and thereby partially reduces MDM2 E3 activity. Binding of human N-terminal 32 residues of p14ARF to the acidic domain of MDM2 strengthens the AD-ZnF-RING domain interaction. Furthermore, the N-terminal RxFxV motifs of p14ARF participate directly in the MDM2 RING domain interaction. This bivalent binding mode of p14ARF to MDM2 acidic and RING domains restricts E2∼ubiquitin recruitment and massively hinders MDM2 E3 activity. These findings elucidate the mechanism by which ARF inhibits MDM2 E3 activity.

Application of In Silico Filtering and Isothermal Titration Calorimetry for the Discovery of Small Molecule Inhibitors of MDM2

The initial discovery phase of protein modulators, which consists of filtering molecular libraries and in vitro direct binding validation, is central in drug discovery. Thus, virtual screening of large molecular libraries, together with the evaluation of binding affinity by isothermal calorimetry, generates an efficient experimental setup. Herein, we applied virtual screening for discovering small molecule inhibitors of MDM2, a major negative regulator of the tumor suppressor p53, and thus a promising therapeutic target. A library of 20 million small molecules was screened against an averaged model derived from multiple structural conformations of MDM2 based on published structures. Selected molecules originating from the computational filtering were tested in vitro for their direct binding to MDM2 via isothermal titration calorimetry. Three new molecules, representing distinct chemical scaffolds, showed binding to MDM2. These were further evaluated by exploring structure-similar chemical analogues. Two scaffolds were further evaluated by de novo synthesis of molecules derived from the initial molecules that bound MDM2, one with a central oxoazetidine acetamide and one with benzene sulfonamide. Several molecules derived from these scaffolds increased wild-type p53 activity in MCF7 cancer cells. These set a basis for further chemical optimization and the development of new chemical entities as anticancer drugs.

FAK PROTAC Inhibits Ovarian Tumor Growth and Metastasis by Disrupting Kinase Dependent and Independent Pathways

Focal adhesion kinase (FAK) is highly expressed in a variety of human cancers and is a target for cancer therapy. Since FAK kinase inhibitors only block the kinase activity of FAK, they are not highly effective in clinical trials. FAK also functions as a scaffold protein in a kinase-independent pathway. To effectively target FAK, it is required to block both FAK kinase-dependent and FAK-independent pathways. Thus, we tested a new generation drug FAK PROTAC for ovarian cancer therapy, which blocks both kinase and scaffold activity. We tested the efficacy of FAK PROTAC and its parent kinase inhibitor (VS-6063) in ovarian cancer cell lines in vitro by performing cell functional assays including cell proliferation, migration, invasion. We also tested in vivo activity in orthotopic ovarian cancer mouse models. In addition, we assessed whether FAK PROTAC disrupts kinase-dependent and kinase-independent pathways. We demonstrated that FAK PROTAC is highly effective as compared to its parent FAK kinase inhibitor VS-6063 in inhibiting cell proliferation, survival, migration, and invasion. FAK PROTAC not only inhibits the FAK kinase activity but also FAK scaffold function by disrupting the interaction between FAK and its interaction protein ASAP1. We further showed that FAK PROTAC effectively inhibits ovarian tumor growth and metastasis. Taken together, FAK PROTAC inhibits both FAK kinase activity and its scaffold protein activity by disrupting the interaction between FAK and ASAP1 and is highly effective in inhibiting ovarian tumor growth and metastasis.

Novel MDM2 Inhibitor XR-2 Exerts Potent Anti-Tumor Efficacy and Overcomes Enzalutamide Resistance in Prostate Cancer

Background: The inactivation of tumor-suppressor p53 plays an important role in second generation anti-androgens (SGAs) drug resistance and neuroendocrine differentiation in castration-resistant prostate cancer (CRPC). The reactivation of p53 by blocking the MDM2–p53 interaction represents an attractive therapeutic remedy in cancers with wild-type or functional p53. Whether MDM2-p53 inhibitor could overcome SGAs drug resistance in CRPC is still needed further research. Here, we investigated the anti-tumor efficacy and mechanisms of a novel MDM2-p53 inhibitor XR-2 in CRPC.

Methods: To investigate the functions and mechanisms of XR-2 in prostate cancer, in vitro and in vivo biofunctional assays were performed. Western blot and qRT-PCR assay were performed to detect the protein and mRNA expression levels of indicated genes. CCK8, colony formation, flow cytometry and senescence assays were performed for cell function identifications. RNA-sequencing and bioinformatics analysis were mainly used to identify the influence of XR-2 on prostate cancer cells transcriptome. Subcutaneous 22Rv1 derived xenografts mice model was used to investigate the in vivo anti-tumor activity of XR-2. In addition, the broad-spectrum anti-tumor activities in vivo of XR-2 were evaluated by different xenografts mice models.

Results: XR-2 could directly bind to MDM2, potently reactivate the p53 pathway and thus induce cell cycle arrest and apoptosis in wild-type p53 CRPC cell lines. XR-2 also suppresses the AR pathway as p53 regulates AR transcription inhibition and MDM2 participates in AR degradation. As a result, XR-2 efficiently inhibited CRPC cell viability, showed a synergistic effect with enzalutamide and overcame enzalutamide resistance both in vitro and in vivo. Moreover, results illustrated that XR-2 possesses broad-spectrum anti-tumor activities in vivo with favourable safety.

Conclusion: MDM2-p53 inhibitor (XR-2) possesses potently prostate cancer progresses inhibition activity both in vitro and in vivo. XR-2 shows a synergistic effect with enzalutamide and overcomes enzalutamide resistance.

[Metabolic pathways controlled by E3 ligases: an opportunity for therapeutic targeting]

Since its discovery, the Ubiquitin Proteasome System (UPS) has been recognized for its major role in controlling most of the cell's metabolic pathways. In addition to its essential role in the degradation of proteins, it is also involved in the addressing, signaling or repair of DNA, which makes it a key player in cellular homeostasis. Although other control systems exist in the cell, the UPS is often referred to as the conductor. In view of its importance, any dysregulation of the UPS leads to more or less severe disorders for the cell and therefore the body, which accounts for UPS implication in many pathologies (cancer, Alzheimer's disease, Huntington's disease, etc.). UPS is made up of more than 1000 different proteins, the combinations of which allow the fine targeting of virtually all proteins in the body. UPS uses an enzymatic cascade (E1, 2 members; E2 > 35; E3 > 800) which allows the transfer of ubiquitin, a small protein of 8.5 kDa onto the protein to be targeted either for its degradation or to modify its activity. This ubiquitinylation signal is reversible and many deubiquitinylases (DUB, ∼ 80 isoforms) also have an important role. E3 enzymes are the most numerous and their function is to recognize the target protein, which makes them important players in the specific action of UPS. The very nature of E3 and the complexity of their interactions with different partners offer a very broad field of investigation and therefore significant potential for the development of therapeutic approaches. Without being exhaustive, this review illustrates the different strategies that have already been implemented to fight against different pathologies (excluding bacterial or viral infections).

Recent Progress and Clinical Development of Inhibitors that Block MDM4/p53 Protein-Protein Interactions

MDM4 is a homologue of MDM2, serving cooperatively as the negative regulator of tumor suppressor p53. Under the shadow of MDM2 inhibitors, limited efforts had been put into the discovery of MDM4 modulators. Recent studies of the experimental drug ALRN-6924, a dual MDM4 and MDM2 inhibitor, suggest that concurrent inhibition of MDM4 and MDM2 might be beneficial over only MDM2 inhibition. In view of the present research progress, we summarized published inhibitors of MDM4/p53 interactions including both peptide-based compounds and small molecules. Cocrystal structures of ligand/MDM4 complexes have been examined, and their structural features were compiled and compared in order to show the molecular basis required for high MDM4 binding affinities. Representative examples of small-molecule MDM4 inhibitors were discussed, followed by clinical results of ALRN-6924, together, providing a consolidated reference for further development of MDM4 inhibitors, either dual or selective.

Role of Sex in the Therapeutic Targeting of p53 Circuitry

Sex profoundly affects cancer incidence and susceptibility to therapy, with sex hormones highly contributing to this disparity. Various studies and omics data suggest a relationship between sex and the oncosuppressor p53 circuitry, including its regulators MDM2 and MDM4. Association of this network with genetic variation underlies sex-related altered cancer risk, age of onset, and cancer sensitivity to therapy. Moreover, sex-related factors, mainly estrogenic hormones, can affect the levels and/or function of the p53 network both in hormone-dependent and independent cancer. Despite this evidence, preclinical and clinical studies aimed to evaluate p53 targeted therapy rarely consider sex and related factors. This review summarizes the studies reporting the relationship between sex and the p53 circuitry, including its associated regulators, MDM2 and MDM4, with particular emphasis on estrogenic hormones. Moreover, we reviewed the evaluation of sex/hormone in preclinical studies and clinical trials employing p53-target therapies, and discuss how patients’ sex and hormonal status could impact these therapeutic approaches.

MDM2/X Inhibitors as Radiosensitizers for Glioblastoma Targeted Therapy

Inhibition of the MDM2/X-p53 interaction is recognized as a potential anti-cancer strategy, including the treatment of glioblastoma (GB). In response to cellular stressors, such as DNA damage, the tumor suppression protein p53 is activated and responds by mediating cellular damage through DNA repair, cell cycle arrest and apoptosis. Hence, p53 activation plays a central role in cell survival and the effectiveness of cancer therapies. Alterations and reduced activity of p53 occur in 25-30% of primary GB tumors, but this number increases drastically to 60-70% in secondary GB. As a result, reactivating p53 is suggested as a treatment strategy, either by using targeted molecules to convert the mutant p53 back to its wild type form or by using MDM2 and MDMX (also known as MDM4) inhibitors. MDM2 down regulates p53 activity via ubiquitin-dependent degradation and is amplified or overexpressed in 14% of GB cases. Thus, suppression of MDM2 offers an opportunity for urgently needed new therapeutic interventions for GB. Numerous small molecule MDM2 inhibitors are currently undergoing clinical evaluation, either as monotherapy or in combination with chemotherapy and/or other targeted agents. In addition, considering the major role of both p53 and MDM2 in the downstream signaling response to radiation-induced DNA damage, the combination of MDM2 inhibitors with radiation may offer a valuable therapeutic radiosensitizing approach for GB therapy. This review covers the role of MDM2/X in cancer and more specifically in GB, followed by the rationale for the potential radiosensitizing effect of MDM2 inhibition. Finally, the current status of MDM2/X inhibition and p53 activation for the treatment of GB is given.

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.

First in class dual MDM2/MDMX inhibitor ALRN-6924 enhances antitumor efficacy of chemotherapy in TP53 wild-type hormone receptor-positive breast cancer models

BACKGROUND

MDM2/MDMX proteins are frequently elevated in hormone receptor-positive (ER+) breast cancer. We sought to determine the antitumor efficacy of the combination of ALRN-6924, a dual inhibitor of MDM2/MDMX, with chemotherapy in ER+ breast cancer models.

METHODS

Three hundred two cell lines representing multiple tumor types were screened to confirm the role of TP53 status in ALRN-6924 efficacy. ER+ breast cancer cell lines (MCF-7 and ZR-75-1) were used to investigate the antitumor efficacy of ALRN-6924 combination. In vitro cell proliferation, cell cycle, and apoptosis assays were performed. Xenograft tumor volumes were measured, and reverse-phase protein array (RPPA), immunohistochemistry (IHC), and TUNEL assay of tumor tissues were performed to evaluate the in vivo pharmacodynamic effects of ALRN-6924 with paclitaxel.

RESULTS

ALRN-6924 was active in wild-type TP53 (WT-TP53) cancer cell lines, but not mutant TP53. On ER+ breast cancer cell lines, it was synergistic in vitro and had enhanced in vivo antitumor activity with both paclitaxel and eribulin. Flow cytometry revealed signs of mitotic crisis in all treatment groups; however, S phase was only decreased in MCF-7 single agent and combinatorial ALRN-6924 arms. RPPA and IHC demonstrated an increase in p21 expression in both combinatorial and single agent ALRN-6924 in vivo treatment groups. Apoptotic assays revealed a significantly enhanced in vivo apoptotic rate in ALRN-6924 combined with paclitaxel treatment arm compared to either single agent.

CONCLUSION

The significant synergy observed with ALRN-6924 in combination with chemotherapeutic agents supports further evaluation in patients with hormone receptor-positive breast cancer.

Pharmacological Activation of p53 during Human Monocyte to Macrophage Differentiation Attenuates Their Pro-Inflammatory Activation by TLR4, TLR7 and TLR8 Agonists

Simple Summary

Pharmacological activation of tumor suppressor p53 is a promising therapeutic strategy for a range of hematologic and solid cancers. Whether p53 activation augments or suppresses anti-tumor innate immunity is less understood. Here we show that treatment of differentiating human macrophages with a p53 activator idasanutlin suppresses their inflammatory responses to activators of toll-like receptors (TLR) -4 and -7/8. This is accompanied by reduced expression of TLR7, TLR8, as well as TLR4 co-receptor CD14. These data help evaluating the possibilities of combining p53-targeting and immunostimulatory anti-cancer therapies.

Abstract

The transcription factor p53 has well-recognized roles in regulating cell cycle, DNA damage repair, cell death, and metabolism. It is an important tumor suppressor and pharmacological activation of p53 by interrupting its interaction with the ubiquitin E3 ligase mouse double minute 2 homolog (MDM2) is actively explored for anti-tumor therapies. In immune cells, p53 modulates inflammatory responses, but the impact of p53 on macrophages remains incompletely understood. In this study, we used the MDM2 antagonist idasanutlin (RG7388) to investigate the responses of primary human macrophages to pharmacological p53 activation. Idasanutlin induced a robust p53-dependent transcriptional signature in macrophages, including several pro-apoptotic genes. However, idasanutlin did not generally sensitize macrophages to apoptosis, except for an enhanced response to a Fas-stimulating antibody. In fully differentiated macrophages, idasanutlin did not affect pro-inflammatory gene expression induced by toll-like receptor 4 (TLR4), TLR3, and TLR7/8 agonists, but inhibited interleukin-4-induced macrophage polarization. However, when present during monocyte to macrophage differentiation, idasanutlin attenuated inflammatory responses towards activation of TLR4 and TLR7/8 by low doses of lipopolysaccharide or resiquimod (R848). This was accompanied by a reduced expression of CD14, TLR7, and TLR8 in macrophages differentiated in the presence of idasanutlin. Our data suggest anti-inflammatory effects of pharmacological p53 activation in differentiating human macrophages.

Mouse double minute 2 amplification in oesophageal squamous cell carcinoma is associated with better outcome

AIMS

This study aimed to determine the frequency of mouse double minute 2 (MDM2) amplification in oesophageal squamous cell carcinomas (ESCC) and to clarify its prognostic significance.

METHODS AND RESULTS

We investigated MDM2 amplification on tissue microarrays using fluorescence in-situ hybridisation and analysed its correlations with clinicopathological features and outcomes in 515 Chinese ESCC patients. MDM2 amplifications were found in 37 of 515 ESCC patients (7.2%). They were significantly negatively correlated with tumour size (P = 0.045), disease progression (P = 0.002) and death (P = 0.003). Univariate analysis showed that the following clinicopathological factors were associated with disease-free survival (DFS) and overall survival (OS): differentiation (P = 0.025 for DFS and P = 0.061 for OS), vessel invasion (P = 0.001 and P = 0.002), nerve invasion (P = 0.009 and P = 0.001), clinical stage (P < 0.001 and P < 0.001) and MDM2 amplification (P = 0.012 and P = 0.014). Multivariate Cox regression analysis showed that MDM2 amplification was an independent prognostic factor for improved outcomes (P = 0.023 for DFS, P = 0.027 for OS) and the clinical stage was an independent prognostic factor for poor outcomes (P < 0.001). When survival analyses were conducted at different clinical stages, MDM2 amplification was associated with longer DFS and OS in stages I-II ESCC (P = 0.003 for DFS and P = 0.003 for OS), but there was no significant survival difference in stages III-IVa ESCC.

CONCLUSIONS

MDM2 amplification was significantly correlated with an improved patient outcome, especially in stage I and II disease, and was verified as an independent prognostic factor in our patients. Therefore, MDM2 amplification may be a potential biomarker for risk stratification of the lower stages of ESCC.

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.

MDM2 inhibition: an important step forward in cancer therapy

Targeting the interaction between tumor suppressor p53 and the E3 ligase MDM2 represents an attractive treatment approach for cancers with wild-type or functional TP53. Indeed, several small molecules have been developed and evaluated in various malignancies. We provide an overview of MDM2 inhibitors under preclinical and clinical investigation, with a focus on molecules with ongoing clinical trials, as indicated by ClinicalTrials.gov . Because preclinical and clinical exploration of combination strategies is underway, data supporting these combinations are also described. We identified the following molecules for inclusion in this review: RG7112 (RO5045337), idasanutlin (RG7388), AMG-232 (KRT-232), APG-115, BI-907828, CGM097, siremadlin (HDM201), and milademetan (DS-3032b). Information about each MDM2 inhibitor was collected from major congress records and PubMed using the following search terms: each molecule name, "MDM2"and "HDM2." Only congress records were limited by date (January 1, 2012-March 6, 2020). Special attention was given to available data in hematologic malignancies; however, available safety data in any indication are reported. Overall, targeting MDM2 is a promising treatment strategy, as evidenced by the increasing number of MDM2 inhibitors entering the clinic. Additional clinical investigation is needed to further elucidate the role of MDM2 inhibitors in the treatment of human cancers.

Competition NMR for Detection of Hit/Lead Inhibitors of Protein-Protein Interactions

Screening for small-molecule fragments that can lead to potent inhibitors of protein–protein interactions (PPIs) is often a laborious step as the fragments cannot dissociate the targeted PPI due to their low μM–mM affinities. Here, we describe an NMR competition assay called w-AIDA-NMR (weak-antagonist induced dissociation assay-NMR), which is sensitive to weak μM–mM ligand–protein interactions and which can be used in initial fragment screening campaigns. By introducing point mutations in the complex’s protein that is not targeted by the inhibitor, we lower the effective affinity of the complex, allowing for short fragments to dissociate the complex. We illustrate the method with the compounds that block the Mdm2/X-p53 and PD-1/PD-L1 oncogenic interactions. Targeting the PD-/PD-L1 PPI has profoundly advanced the treatment of different types of cancers.

Hitting on the move: Targeting intrinsically disordered protein states of the MDM2-p53 interaction

Intrinsically disordered proteins are an emerging class of proteins without a folded structure and currently disorder-based drug targeting remains a challenge. p53 is the principal regulator of cell division and growth whereas MDM2 consists its main negative regulator. The MDM2-p53 recognition is a dynamic and multistage process that amongst other, employs the dissociation of a transient α-helical N-terminal ''lid'' segment of MDM2 from the proximity of the p53-complementary interface. Several small molecule inhibitors have been reported to inhibit the formation of the p53-MDM2 complex with the vast majority mimicking the p53 residues Phe19, Trp23 and Leu26. Recently, we have described the transit from the 3-point to 4-point pharmacophore model stabilizing this intrinsically disordered N-terminus by increasing the binding affinity by a factor of 3. Therefore, we performed a thorough SAR analysis, including chiral separation of key compound which was evaluated by FP and 2D NMR. Finally, p53-specific anti-cancer activity towards p53-wild-type cancer cells was observed for several representative compounds.

Helping the Released Guardian: Drug Combinations for Supporting the Anticancer Activity of HDM2 (MDM2) Antagonists

The protein p53, known as the “Guardian of the Genome”, plays an important role in maintaining DNA integrity, providing protection against cancer-promoting mutations. Dysfunction of p53 is observed in almost every cancer, with 50% of cases bearing loss-of-function mutations/deletions in the TP53 gene. In the remaining 50% of cases the overexpression of HDM2 (mouse double minute 2, human homolog) protein, which is a natural inhibitor of p53, is the most common way of keeping p53 inactive. Disruption of HDM2-p53 interaction with the use of HDM2 antagonists leads to the release of p53 and expression of its target genes, engaged in the induction of cell cycle arrest, DNA repair, senescence, and apoptosis. The induction of apoptosis, however, is restricted to only a handful of p53^wt cells, and, generally, cancer cells treated with HDM2 antagonists are not efficiently eliminated. For this reason, HDM2 antagonists were tested in combinations with multiple other therapeutics in a search for synergy that would enhance the cancer eradication. This manuscript aims at reviewing the recent progress in developing strategies of combined cancer treatment with the use of HDM2 antagonists.