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The study of protein–protein interactions is of great interest. Several early studies focused on the murine double minute 2 (Mdm2)–tumor suppressor protein p53 interactions. However, the effect of plasma treatment on Mdm2 and p53 is still absent from the literature. This study investigated the structural changes in Mdm2, p53, and the Mdm2–p53 complex before and after possible plasma oxidation through molecular dynamic (MD) simulations. MD calculation revealed that the oxidized Mdm2 bounded or unbounded showed high flexibility that might increase the availability of tumor suppressor protein p53 in plasma-treated cells. This study provides insight into Mdm2 and p53 for a better understanding of plasma oncology.

Background Some ribosomal proteins (RPs) might regulate the MDM2–p53 loop by binding to RPL5 or RPL11. This study aimed to explore whether ribosomal protein S27a (RPS27a) interacted with the ribosomal protein L11 (RPL11) to regulate p53 in lung adenocarcinoma (LUAD) cells. Methods RPL11-interacting proteins were identified using a proteomics approach. Co-immunoprecipitation (co-IP), docking analysis, GST-fusion and in vitro ubiquitination assay were used to analyze the interaction of RPS27a and RPL11. Cell cycle, apoptosis, cell invasion, cell viability and colony-formation assay were analyzed by knocking down RPS27a. The RPS27a mRNA expression in LUAD was analyzed based on the TCGA dataset and the RPS27a expression was detected by immunohistochemistry in LUAD samples. At last, the RPS27a and p53 expression were analyzed by immunohistochemistry in xenograft tumors by blocking RPS27a. Results The ablation of RPS27a inhibits murine double minute 2 (MDM2)-mediated p53 ubiquitination, induced G1/S cell cycle arrest and apoptosis, and inhibited the proliferation of LUAD cells. Also, it induced p53-dependent cell cycle arrest and RPL11-dependent p53 activation. The protein–protein docking results revealed that RPS27a and RPL11 formed a stable complex structure. The GST-fusion protein–protein association assay demonstrated that RPS27a bound to RPL11. The overexpressed RPS27a in LUAD was found to be correlated with a poorer prognosis based on the TCGA dataset. RPS27a expression was high in patients with LUAD. Blocking RPS27a increased p53, thus, suppressing cell proliferation and A549 xenograft growth in nude mice. Conclusions This study was novel in reporting that RPs bound to RPL11 to regulate the MDM2-p53 feedback loop, revealing that RPS27a plays an important function in LUAD growth. Hence, RPS27a might provide a diagnostic marker or therapeutic target for patients with LUAD.

Glioblastomas, aggressive tumors that arise from malignant transformation of astrocytes, account for 60% brain cancer cases. Current treatments including radiation and chemotherapy accompanied by surgeries result in an average survival increment of 15 months. New therapeutics based on molecular pathology and pathways demonstrate great scope. p53, a tumor-suppressor protein is downregulated by MDM2. In malignant conditions, MDM2 levels increase immensely due to genetic mutations, causing excessive p53 downregulation, thereby enhancing malignancy to extremities. Inhibition of MDM-2 to p53 interaction by potent inhibitors can be a potent therapy but the use of synthetic inhibitors poses many side effects. Natural dietary flavonoids like epicatechin possess high antioxidant and anti-carcinogenic properties. Molecular docking and MD simulation approaches were used to reveal the effectiveness of epicatechin in this regard, a high negative binding energy of -9.619 kcal/mol with Ki value of 82.34 nM and 6 hydrogen bonds with the leading residues responsible for MDM2 p53 interaction were noticed. MD simulation of 100 ns revealed that epicatechin continues to interact with the vital residues of MDM2 and p53 and occupies the hydrophobic p53-binding cleft in MDM2. Significant structural modifications in MDM2-p53 complex due to epicatechin interactions were observed. The increase in RMSD and Rg values of MDM2-p53 complex in presence of epicatechin provides evidence for the destabilization of complex. The extreme increase in RMSF values of p53 in turn indicates towards its reduced interaction with MDM2. Hence, epicatechin can promisingly treat adverse glioblastoma pathologies by inhibiting MDM2-p53 interactions, therefore exhaustive research is urgently demanded.

Background This study aimed to investigate the aberrant expression of hsa_circ_0002874 in non-small cell lung cancer (NSCLC) and elucidate associated molecular mechanisms that influence apoptosis and induce paclitaxel (PTX) resistance. Methods Inhibitors were used to downregulate circRNA or miRNA expression. pCDNA plasmid transfection and mimics were used to upregulate circRNA or miRNA expression. Dual-luciferase reporter assays were conducted to evaluate interactions between miR1273f and MDM2. Xenograft tumor models were used to assess the effect of hsa_circ_0002874 and miR1273f on tumor growth. NSCLC tissues and matched non-cancerous tissues were also collected for correlation analysis. Results hsa_circ_0002874 acts as a sponge for miR1273f which targets MDM2/P53. The stability of the hsa_circ_0002874/miR1273f/MDM2/P53 pathway was verified by upregulating and downregulating the expression of hsa_circ_0002874 and miR1273f. hsa_circ_0002874 downregulation or miR1273f upregulation reversed the resistance of the A549/Taxol cells in xenograft models. The expression of hsa_circ_0002874 was high, and the level of MDM2 was low in NSCLC tissues. P53 was only weakly expressed in NSCLC tissues with high expression of MDM2. Conclusions hsa_circ_0002874 is strongly expressed in NSCLC tissues and maybe a potential marker for PTX resistance. hsa_circ_0002874 downregulation could regulate miR1273f/MDM2/P53 signaling pathway to reverse the PTX resistance of NSCLC and induce apoptosis in vitro and vivo.

Screening for small-molecule fragments that can lead to potent inhibitors of protein&ndash, protein interactions (PPIs) is often a laborious step as the fragments cannot dissociate the targeted PPI due to their low &mu, M&ndash, mM affinities. Here, we describe an NMR competition assay called w-AIDA-NMR (weak-antagonist induced dissociation assay-NMR), which is sensitive to weak &mu, mM ligand&ndash, protein interactions and which can be used in initial fragment screening campaigns. By introducing point mutations in the complex&rsquo, 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.

Pituitary adenomas constitute one of the most common intracranial tumors. MicroRNAs play an important role in development and progression of pituitary adenomas. In this study, we showed that miR-219a-2-3p was significantly down-regulated in pituitary adenomas cells. Overexpression of miR-219a-2-3p suppressed the proliferation and promoted apoptosis of pituitary adenomas cells. After bioinformatics analysis, we found that MDM2 was one of the downstream targets of miR-219a-2-3p. Further researches showed that miR-219a-2-3p could reduce the protein level of MDM2 by binding to the 3ʹ-UTR of MDM2 and promoted p53 expression. Then, we overexpressed both miR-219a-2-3p and MDM2 in the same group and found that it could counteract the effect of overexpressing miR-219a-2-3p alone on proliferation and apoptosis of pituitary adenoma cells. Taken together, these results suggested that miR-219a-2-3p regulated the proliferation and apoptosis by targeting MDM2/p53 in pituitary adenomas. Therefore, miR-219a-2-3p may serve as a novel marker and therapeutic target for pituitary adenomas.

In tumor cells, p53 is always inactivated due to the mutation or deletion of TP53 gene or inhibited by the overexpressed MDM2. Small-molecule induced restoring of p53 function by blocking MDM2-p53 protein-protein interactions has been highly pursued as an attractive therapeutic strategy for cancer therapy. To date, a large number of small-molecule inhibitors have been identified based on the compact and well-defined MDM2-p53 interactions, of which SAR405838, MK-8242, DS-3032b, NVP-CGM097, RG7112, HDM201, RG7388, ALRN-6924 and AMG 232 are undergoing clinical assessment at different phases for cancer therapy. This review is focused on the discovery and development of piperidinone-based MDM2-p53 inhibitors for cancer therapy, including the identification of hit compounds, hit-to-lead optimizations, binding models of ligands in the active site of MDM2, metabolic studies, and preclinical data of advanced piperidinone-based MDM2-p53 inhibitors. Additionally, acquired resistance of MDM2 inhibitors and potential toxicity toward normal tissues are briefly discussed.

MDM2 is a key oncogenic protein that serves as a negative regulator of the tumor suppressor p53. While a number of inhibitors of the MDM2-p53 interaction have progressed to clinical testing as treatments for a variety of hematologic and solid tumor cancers, the results thus far have been mixed, with perhaps the strongest responses observed in relapsed/refractory acute myeloid leukemia (AML). In an effort to improve the efficacy for this class of compounds, researchers have turned to targeted degradation of MDM2. IMiD-based MDM2 PROTAC 8, which potently reduces MDM2 protein levels through targeted degradation, exhibits enhanced efficacy in the RS4;11 xenograft model relative to a nondegrading MDM2-p53 inhibitor MI-1061.

We present the first application of hydrophobic tagging to a non-covalent inhibitor of protein–protein interactions. Nutlin-3a-HT, created by fusing the hydrophobic tag HyT13 to the MDM2–p53 interaction inhibitor Nutlin-3a, prevented cellular accumulation of MDM2 upon p53 reactivation, and had a stronger effect on cell viability and the induction of apoptosis than Nutlin-3a.

11542 Background: APG-115 is a potent, small-molecule MDM2 inhibitor and immune modulator with promising antitumor activities in various tumors, especially those wild-type TP53 with MDM2 amplification ( TP53wt+MDM2 amp). To better delineate safety, optimal dosage, and potential target population, we report updated results. Methods: Patients with advanced liposarcoma and other solid tumors received APG-115 (100-200 mg) orally every other day for 21 days of a 28-day cycle. The primary endpoints were safety and tolerability. Efficacy (assessed by RECIST v1.1), pharmacokinetics (PK) and pharmacodynamics (PD) have also been analyzed. Results: Enrollment of this Phase I study (CTR20170975) was completed. As of January 7, 2020, 21 patients (14 liposarcomas, 2 synovial sarcomas, 2 adenoid cystic carcinomas, 1 chondrosarcoma, 1 osteosarcoma, 1 rhabdomyosarcoma) were treated in 3 dose levels of APG-115: 100 mg (n = 11), 150 mg (n = 8) and 200 mg (n = 2). The median number of cycles of APG-115 was 2 (0; 6). Two DLTs were observed at 200 mg, thrombocytopenia and febrile neutropenia. The most common treatment-emergent adverse events (TEAEs) (≥20%) included leukopenia, thrombocytopenia, neutropenia, anemia, increased blood creatinine, hypercholesterolemia, hypertriglyceridemia, hypoalbuminemia, vomiting, and nausea. The incidence of TEAEs was much lower at 100 mg. Serious AEs occurred in 5 patients (23.8%) which were assessed as possibly drug related by investigators. In 20 efficacy-evaluable patients, there was 1 patient with a partial response, 12 patients with stable disease, and 7 patients with progressive disease, yielding a disease control rate (CR, PR, SD) of 61.9%. Among the 13 patients (9 liposarcomas) who benefited, 11 had TP53wt and 7 had TP53wt+MDM2 amp, including one liposarcoma patient (150 mg) who had a PR, she was kept-up over 10 months, even though the treatment was discontinued for over 5 months, indicating the host immune modulatory effects of APG-115. Another patient with liposarcoma (100 mg, TP53wt+MDM2 amp) had 28.5% tumor shrinkage at cycle 4 and remained on treatment. PK results showed an approximately dose-proportional increase in exposure on Day 1. PK-PD analyses showed the serum macrophage inhibitory cytokine-1 (MIC-1) increased with increased APG-115 exposure. Conclusions: The phase I data have demonstrated that APG-115 monotherapy was well tolerated, with minimal toxicity at 100mg (RP2D), and conferred encouraging anti-tumor activities in patients with liposarcomas. Clinical trial information: CTR20170975 .

Functions of tumor suppressor p53 and its negative regulator mouse double minute 2 homolog (Mdm2) in ovarian granulosa cells remain to be elucidated, and the current study aims at clarifying this issue. Mice with Mdm2 deficiency in ovarian granulosa cells [ Mdm2-loxP/ progesterone receptor ( Pgr)-Cre mice] were infertile as a result of impairment of oocyte maturation, ovulation, and fertilization, and those with Mdm2/p53 double deletion in granulosa cells ( Mdm2-loxP/ p53-loxP/ Pgr-Cre mice) showed normal fertility, suggesting that p53 induction in the ovarian granulosa cells is detrimental to ovarian function by disturbing oocyte quality. Another model of Mdm2 deletion in ovarian granulosa cells ( Mdm2-loxP/ anti-Mullerian hormone type 2 receptor-Cre mice) also showed subfertility as a result of the failure of ovulation and fertilization, indicating critical roles of ovarian Mdm2 in ovulation and fertilization. Mdm2-p53 pathway in cumulus granulosa cells transcriptionally controlled an orphan nuclear receptor steroidogenic factor 1 (SF1), a key regulator of ovarian function. Importantly, MDM2 and SF1 levels in human cumulus granulosa cells were positively associated with the outcome of oocyte maturation and fertilization in patients undergoing infertility treatment. These findings suggest that the Mdm2-p53-SF1 axis in ovarian cumulus granulosa cells directs ovarian function by affecting their neighboring oocyte quality.-Haraguchi, H., Hirota, Y., Saito-Fujita, T., Tanaka, T., Shimizu-Hirota, R., Harada, M., Akaeda, S., Hiraoka, T., Matsuo, M., Matsumoto, L., Hirata, T., Koga, K., Wada-Hiraike, O., Fujii, T., Osuga, Y. Mdm2-p53-SF1 pathway in ovarian granulosa cells directs ovulation and fertilization by conditioning oocyte quality.

The study of cellular mechanisms of cancer growth and survival has revealed a complex web of signalling pathways that produce the ‘hallmarks of cancer’. A number of critical cellular signalling nodes have been characterised from which many new drug targets have been proposed. A number of these nodes are regulated by protein–protein interactions, and so present attractive, if challenging, targets for drug discovery. Drug discovery efforts towards three PPI families have resulted in clinically investigated drugs: i.e. Bcl-2 family inhibitors, MDM2-p53 inhibitors and IAP inhibitors. The discovery and optimisation of these drug classes are detailed in this chapter.

Design of small-molecule inhibitors (MDM2 inhibitors) to block the MDM2–p53 protein–protein interaction has been pursued as a new cancer therapeutic strategy. In recent years, potent, selective, and efficacious MDM2 inhibitors have been successfully obtained and seven such compounds have been advanced into early phase clinical trials for the treatment of human cancers. Here, we review the design, synthesis, properties, preclinical, and clinical studies of these clinical-stage MDM2 inhibitors.

We previously reported the discovery of AMG 232, a highly potent and selective piperidinone inhibitor of the MDM2-p53 interaction. Our continued search for potent and diverse analogues led to the discovery of novel morpholinone MDM2 inhibitors. This change to a morpholinone core has a significant impact on both potency and metabolic stability compared to the piperidinone series. Within this morpholinone series, AM-8735 emerged as an inhibitor with remarkable biochemical potency (HTRF IC50 = 0.4 nM) and cellular potency (SJSA-1 EdU IC50 = 25 nM), as well as pharmacokinetic properties. Compound 4 also shows excellent antitumor activity in the SJSA-1 osteosarcoma xenograft model with an ED50 of 41 mg/kg. Lead optimization toward the discovery of this inhibitor as well as key differences between the morpholinone and the piperidinone series will be described herein.

3124 Background: APG-115 is a novel and orally active small-molecule MDM2 inhibitor. APG-115 alone or in combination with chemotherapeutic, targeted or IO agents have shown potent antitumor activities in multiple human xenograft tumor models and human cancer patient derived xenograft (PDX) models. Methods: The patients with advanced solid tumors were enrolled in this study in China (CTR20170975). The study objectives were to assess safety, pharmacokinetics (PK), pharmacodynamics (PD) and antitumor activity of APG-115. The patients received APG-115 (ranging 100–200 mg) orally QOD for first 21 days of a 28-day-cycle, until disease progression. Antitumor response assessment was performed every 8 weeks per RECIST v1.1. Archived tumor tissues were collected for analyses of MDM2 and TP53 before treatment. Results: As cut-off on Jan 4 2019, total 13 patients (9 soft tissue sarcomas (STSs), 2 adenoid cystic carcinomas (ACCs) and 2 osteosarcomas) were treated in 3 cohorts of APG-115 (100mg, 150mg, 200mg). The median number of prior systemic anticancer therapies was 2 (range 0-4). Two DLTs were observed in one patient at 200mg including thrombocytopenia and febrile neutropenia. The most common TEAEs (≥50% of pts) included: anemia, thrombocytopenia, vomiting, hypercholesterolaemia, and leukopenia. SAEs occurred in 7 patients (54%), four of which were treatment related. The most common Grade 3 or 4 TRAEs were anemia (38.5%), thrombocytopenia (38.5%), leukopenia (30.8%), and neutropenia (23.1%). One partial response was observed in a liposarcoma patient with MDM2-amplification and TP53-wild type at the 150mg cohort, 5 patients (3 STSs, 2 ACCs) had SD as the best overall response. PK analyses indicated an approximately dose proportional increase in Cmax and AUC0-t following a single or multiple oral administration across dose levels. Preliminary PD data showed that serum MIC-1 increase was exposure dependent within the dose range tested. Conclusions: Preliminary data suggested that APG-115 had promising anti-tumor activity in treatment of patients with MDM2-amplification and TP53-WT liposarcoma. Safety profile and PD effect were consistent with other MDM2 inhibitors. Dosing regimen optimization are ongoing. Clinical trial information: CTR20170975.

TPS3166 Background: Inactivation of tumor protein 53 (TP53) is a central mechanism of tumors to promote survival and proliferation. The murine double minute 2 ( MDM2) oncogene is the primary cellular negative regulator of TP53. Small molecule inhibitors of the MDM2-p53 interaction are currently being evaluated in clinical trials as new anti-cancer drugs, and clinical data published to date support the rationale to target MDM2-amplified tumors. BI 907828 is a potent MDM2-p53 antagonist that has shown efficacy in mouse models of human cancer. Methods: NCT03449381 is a Phase 1a/1b, open-label, multicenter, dose-escalation trial of BI 907828 in patients aged ≥18 years with advanced/metastatic solid tumors. Primary objectives of the Phase 1a (dose-escalation) part are to determine: the maximum tolerated dose (MTD) of BI 907828 based on dose-limiting toxicities (DLTs) during the first treatment cycle; the recommended dose for expansion (RDE); safety and tolerability. Patients in Arm A will receive one dose of BI 907828 every 21 days, and patients in Arm B one dose on Days 1 and 8, every 28 days. Secondary objectives include pharmacokinetics (PK), pharmacodynamics (PD) [GDF-15 induction in plasma], and preliminary anti-tumor activity. Primary endpoints are the number of patients with DLTs during the first treatment cycle, and the MTD. Phase 1a will include ≈50 evaluable patients with locally advanced or metastatic solid tumors with either a known TP53 wild type (wt) status or unknown TP53 status, regardless of MDM2 amplification status at the time of study entry. The main objectives of Phase 1b (expansion cohorts) are to assess efficacy, safety, and PK profiles at the RDE, and to determine the recommended dose for Phase 2. The primary endpoint is objective response, where best response is determined according to RECIST v1.1, or RANO criteria for patients with glioblastoma. Phase 1b will include up to 150 evaluable patients with TP53 wt tumors, assigned to four different cohorts, including non-squamous NSCLC, soft tissue sarcoma, glioblastoma, urothelial carcinoma, and solid tumors with brain metastases. As of 8th February 2019, 11 patients have been enrolled. Clinical trial information: NCT03449381.

The interaction between murine double minute (MDM2) and p53 is a major target in anticancer drug design. Several potent compound series, including the nutlins and spirooxindoles, have previously been established as high-affinity antagonists of MDM2. In this paper, we describe the interaction of isoindolinone inhibitors with MDM2, as characterized by nuclear magnetic resonance spectroscopy. Isoindolinone inhibitors bind specifically to the MDM2 p53 binding site and exploit all sub-pockets used by p53, nutlins and spirooxindoles. Furthermore, isoindolinones bind with low micromolar to high nanomolar affinities, with the best compound approaching the potency of nutlin-3.

In response to cellular stress, the p53 tumor suppressor is activated to modulate cell cycle progression, DNA repair, and cell death. The activity of p53 is tightly regulated by MDM2, an E3 ubiquitin ligase that targets p53 for proteasomal degradation. Inhibition of the MDM2-p53 interaction in tumors carrying wild-type p53 can therefore reactivate p53 and elicit an anti-cancer effect. Small molecule inhibitors of the MDM2-p53 interaction remains a promising strategy for cancer therapy and a number of these compounds are in clinical development. An isoindolinone series, identified by the Northern Institute for Cancer Research (NICR), has been used as a starting point for the development of potent MDM2-p53 inhibitors. Structure based drug design was applied during lead optimisation to gain potency whilst also focusing on stabilizing the main metabolically labile position and reducing lipophilicity. This approach led to potent compounds with EC50 Citation Format: Lynsey Fazal, Maria Ahn, Luke Bevan, Ildiko Buck, Juan Castro, Gianni Chessari, Ben Cons, Keisha Hearn, Steven Howard, Chris Johnson, Judith Reeks, Emiliano Tamanini, Neil Thompson, Hugh Walton, Pamela Williams, Ruth H. Bawn, Tim J. Blackburn, Celine Cano, Sarah J. Cully, Bernard Golding, Roger Griffin, Karen Haggerty, Ian Hardcastle, Herbie Newell, Martin Noble, Huw Thomas, Elaine Willmore, Yan Zhao, Steve Wedge. Development of a potent class of small molecule inhibitors of the MDM2-p53 protein-protein interaction [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 1652.

A primary failsafe program against unrestrained proliferation and oncogenesis is provided by the p53 tumor suppressor protein, inactivation of which is considered as a hallmark of cancer. Intriguingly, mutations of the TP53 gene are rarely encountered in neuroblastoma tumors, suggesting that alternative p53-inactivating lesions account for escape from p53 control in this childhood malignancy. Several recent studies have shed light on the mechanisms by which neuroblastoma cells circumvent the p53-driven antitumor barrier. We review here these mechanisms for evasion of p53-mediated growth control and conclude that deregulation of the p14(ARF)-MDM2-p53 axis seems to be the principal mode of p53 inactivation in neuroblastoma, opening new perspectives for targeted therapeutic intervention.

The p53 protein, a tumor suppressor, is inactivated in many human cancers through mutations or by its interaction with an oncoprotein, MDM2. Blocking the MDM2-p53 protein-protein interaction has the effect of activating wild-type p53 and has been pursued as a novel anticancer strategy. Small-molecule inhibitors of the MDM2-p53 interaction have been discovered through various approaches, and a number of them have progressed into clinical trials for cancer treatment. Here, we describe the methods and techniques used in the discovery of small-molecule inhibitors of the MDM2-p53 interaction.

OBJECTIVE To explore whether MDM2 transfection can alter the MDM2-p53 autoregulatory feedback loop so as to change the sensitivity of ovarian cancer cell lines to cisplatin.

Abnormalities in the TP53 gene and overexpression of MDM2, a transcriptional target and negative regulator of p53, are commonly observed in cancers. The MDM2–p53 feedback loop plays an important role in tumor progression and thus, increased understanding of the pathway has the potential to improve clinical outcomes for cancer patients. Hepatocellular carcinoma (HCC) has emerged as one of the most commonly diagnosed forms of human cancer; yet, the current treatment for HCC is less effective than those used against other cancers. We review the current studies of the MDM2–p53 pathway in cancer with a focus on HCC and specifically discuss the impact of p53 mutations along with other alterations of the MDM2–p53 feedback loop in HCC. We also discuss the potential diagnostic and prognostic applications of p53 and MDM2 in malignant tumors as well as therapeutic avenues that are being developed to target the MDM2–p53 pathway. Cancer Res; 74(24); 7161–7. ©2014 AACR.

The general model of epitope-type MDM2 inhibitor was developed based on the structural information on the complexes between MDM2 and various low molecular weight ligands found in the PDB database. Application of this model to our in-house library has led us to a new scaffold capable of interrupting protein-protein interactions. A synthetic library based on this and related scaffolds resulted in new classes of compounds that possess biochemical and cellular activity and good pharmacokinetic properties. We assume that such general approach to PPI inhibitors design may be useful for the development of inhibitors of various PPI types, including Bcl/XL.

Cancer drug discovery activities in the postgenomic era have sought to identify small molecules able to modulate molecular targets identified as being intimately linked to the “hallmark” characteristics of cancer. The tractability of protein–protein interactions as molecular targets for small-molecule drugs has been examined, raising the possibility that small molecules, able to bind with sufficient affinity to hotspot clusters, would be able to antagonize a given protein–protein interaction. The therapeutic hypothesis for MDM2–p53 inhibition proposes that a potent inhibitor of the protein–protein interaction will liberate p53 from the repressive control of MDM2, and subsequently activate p53-mediated cell death in the tumor. A number of small-molecule MDM2–p53 inhibitors have been discovered and clinical trials are ongoing to establish their efficacy.

The oncoprotein MDM2 (murine double minute 2) negatively regulates the activity and stability of tumor suppressor p53. Inactivation of the MDM2–p53 interaction by potent inhibitors offers new possibilities for anticancer therapy. Molecular dynamics (MD) simulations were performed on three inhibitors–MDM2 complexes to investigate the stability and structural transitions. Simulations show that the backbone of MDM2 maintains stable during the whole time. However, slightly structural changes of inhibitors and MDM2 are observed. Furthermore, the molecular mechanics generalized Born surface area (MM-GBSA) approach was introduced to analyze the interactions between inhibitors and MDM2. The results show that binding of inhibitor pDIQ to MDM2 is significantly stronger than that of pMI and pDI to MDM2. The side chains of residues have more contribution than backbone of residues in energy decomposition. The structure–affinity analyses show that L54, I61, M62, Y67, Q72, H73 and V93 produce important interaction energy with inhibitors. The residue W/Y22′ is also very important to the interaction between the inhibitors and MDM2. The three-dimensional structures at different times indicate that the mobility of Y100 influences on the binding of inhibitors to MDM2, and its change has important role in conformations of inhibitors and MDM2.

The p53 tumor suppressor protein is a transcriptional factor that plays a key role in regulation of several cellular processes, including the cell cycle, apoptosis, DNA repair, and angiogenesis. The murine double minute 2 (MDM2) protein is the primary cellular inhibitor of p53, functioning through direct interaction with p53. Design of non-peptide, small-molecule inhibitors that block the MDM2-p53 interaction has been sought as an attractive strategy to activate p53 for the treatment of cancer and other human diseases. In recent years, major advances have been made in the design of small-molecule inhibitors of the MDM2-p53 interaction in recent years, and several compounds have moved into advanced preclinical development or clinical trials. In this chapter, we will highlight these advances in the design and development of MDM2 inhibitors, and discuss lessons learned from these efforts.

Mdm2 has been thought to regulate the tumor suppressor p53 in two ways: by masking p53's access to transcriptional machinery, and by ubiquitinating p53, targeting it for proteasomal degradation. This dogma was recently challenged by data generated from knockin mice in which Mdm2's RING E3 ubiquitin ligase activity was abrogated by a single point mutation. The RING mutant Mdm2 is fully capable of binding with p53, yet cannot suppress p53 activity, suggesting that Mdm2 cannot block p53 by binding alone, without ubiquitination. Data from the RING knockin mice also revealed that endogenous Mdm2 does not, as previously thought, regulate its own stability by self-ubiquitination. In this review, we will discuss these findings and their relevance to the field, including potential reasons for the discrepancies between previous data and that generated by our knockin mice, as well as the feasibility of targeting Mdm2's E3 ubiquitin ligase activity in cancer. We will also discuss additional research questions that may be addressed using our mouse model.

In a recent issue of Molecular Cell, Taira et al. (2007) and Rinaldo et al. (2007) provide insight into the involvement of the DYRK2 kinase and a surprising role of MDM2 in regulation of DNA damage-induced apoptosis via p53 phosphorylation.

Prostate cancer: On the right path—Stat3 signalling controls the ARF–Mdm2–p53 tumour-suppressor pathway

Mdm2 is a cellular antagonist of p53 that keeps a balanced cellular level of p53. The two proteins are linked by a negative regulatory feedback loop and physically bind to each other via a putative helix formed by residues 18-26 of p53 transactivation domain (TAD) and its binding pocket located within the N-terminal 100-residue domain of mdm2 (Kussie, P. H., Gorina, S., Marechal, V., Elenbaas, B., Moreau, J., Levine, A. J., and Pavletich, N. P. (1996) Science 274, 948-953). In a previous report we demonstrated that p53 TAD in the mdm2-freee state is mostly unstructured but contains two nascent turns in addition to a "preformed" helix that is the same as the putative helix mediating p53-mdm2 binding. Here, using heteronuclear multidimensional NMR methods, we show that the two nascent turn motifs in p53 TAD, turn I (residues 40-45) and turn II (residues 49-54), are also capable of binding to mdm2. In particular, the turn II motif has a higher mdm2 binding affinity ( approximately 20 mum) than the turn I and targets the same site in mdm2 as the helix. Upon mdm2 binding this motif becomes a well defined full helix turn whose hydrophobic face formed by the side chains of Ile-50, Trp-53, and Phe-54 inserts deeply into the helix binding pocket. Our results suggest that p53-mdm2 binding is subtler than previously thought and involves global contacts such as multiple "non-contiguous" minimally structured motifs instead of being localized to one small helix mini-domain in p53 TAD.

Inhibition of E3 ligase-substrate binding is the most direct approach for blocking protein ubiquitylation and degradation. However, protein-protein interactions have proven to be difficult targets for discovery of small molecules that bind at the interface and modulate protein activity in a selective manner. Recently, we developed the first potent and selective small-molecule inhibitors of the binding between MDM2 E3 ligase and its substrate p53 (Vassilev et al., 2004). This process was aided significantly by the acquisition and use of structural information. We describe herein how such information was obtained and used at various stages in the program. These applications included assessment of MDM2 as a target, evaluation of hits from high-throughput screening and the selection of lead molecules, and analysis of binding strategies used by the inhibitors as a basis for guiding studies of similar systems. These tools are likely to be useful in any attempt to find and develop druglike compounds that modulate the function of a protein-protein interaction.

Compared with many normal tissues, cancer cells are highly sensitized to apoptotic signals, and survive only because they have acquired lesions - such as loss of p53 - that prevent or impede cell death. We are now beginning to understand the complex mechanisms that regulate whether or not a cell dies in response to p53 - insights that will ultimately contribute to the development of therapeutic strategies to repair the apoptotic p53 response in cancers.

The p53 tumor suppressor is controlled by MDM2, which binds p53 and negatively regulates its transcriptional activity and stability. Many tumors overproduce MDM2 to impair p53 function. Therefore, restoration of p53 activity by inhibiting the p53-MDM2 binding represents an attractive novel approach to cancer therapy. We previously reported the discovery AM-8553, a potent and selective piperidinone inhibitor of the MDM2-p53 interaction (Rew et al. J. Med. Chem. 2012, 55, 4936). We report here continued research on the N-alkyl substituent of this series, focused in particular on a previously underutilized interaction in a shallow cleft on the MDM2 surface that led to the discovery of variety of sulfonamides and sulfones which gave rise to substantial improvements in biochemical and cellular potency. Further work led to discovery of AMG 232, which is currently being evaluated in human clinical trials for the treatment of cancer. AMG 232 is an extremely potent MDM2 inhibitor (SPR KD = 0.045 nM, SJSA-1 EdU IC50 = 9.1 nM), with remarkable pharmacokinetic properties. The compound interacts specifically with the p53-binding pocket of MDM2 and releases the p53 protein from negative control. Treatment of cancer cells expressing wild-type p53 with AMG 232, stabilizes p53 and activates the p53 pathway, leading to cell cycle arrest and apoptosis. The compound showed excellent efficacy in a number of mouse tumor xenograft models and was well tolerated in preclinical toxicology studies at therapeutically relevant dosages. Citation Format: Zhihong Li. Discovery of AMG 232, an inhibitor of the MDM2-p53 interaction: From lead to a clinical candidate. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 1645. doi:10.1158/1538-7445.AM2014-1645

Avoiding the inhibitory effects of p53 on cell growth is important for tumor progression. In this issue of Cancer Cell, Picchiorri et al. describe epigenetic silencing of MDM2-targeting microRNAs in multiple myeloma (MM), which generally appears to have intact p53 function. This provides the rationale for microRNA-targeted therapy for MM.

The murine double minutes 2 (MDM2) oncoprotein inhibits p53-mediated tumor suppression. MDM2 has been shown to be overexpressed in sarcomas and more recently was implicated in the pathogenesis of carcinomas. The purpose of this study was to determine the expression pattern of MDM2 in adenomas and colorectal adenocarcinomas and decide whether there is a correlation between MDM2 and p53 protein status. Paraffin-embedded tissues from 52 colorectal cancer (CRC) specimens and their adjacent normal tissue (N-CRC) were studied. In addition, 56 sporadic adenomas were investigated for the immunohistochemical expression of MDM2 and p53 proteins. Immunoreactivity of p53 indicating p53 gene mutation (p53 +) was significantly higher in CRC (44%) compared to adenomas (23.2%) (P

Screening identified 2-(3-((4,6-dioxo-2-thioxotetrahydropyrimidin-5(2H)-ylidene)methyl)-2,5-dimethyl-1H-pyrrol-1-yl)-4,5,6,7-tetrahydrobenzo[b]thiophene-3-carbonitrile as an MDM2–p53 inhibitor (IC50 = 12.3 μM). MDM2–p53 and MDMX–p53 activity was seen for 5-((1-(4-chlorophenyl)-2,5-diphenyl-1H-pyrrol-3-yl)methylene)-2-thioxodihydropyrimidine-4,6(1H,5H)-dione (MDM2 IC50 = 0.11 μM; MDMX IC50 = 4.2 μM) and 5-((1-(4-nitrophenyl)-2,5-diphenyl-1H-pyrrol-3-yl)methylene)pyrimidine-2,4,6(1H,3H,5H)-trione (MDM2 IC50 = 0.15 μM; MDMX IC50 = 4.2 μM), and cellular activity consistent with p53 activation in MDM2 amplified cells. Further SAR studies demonstrated the requirement for the triarylpyrrole moiety for MDMX–p53 activity but not for MDM2–p53 inhibition.

The author would like to thank Maureen Murphy, Stuart Lutzker, and Deborah Freedman for critical input and advice. The author regrets the lack of citations for many important observations mentioned in the text, but their omission is made necessary by restrictions in the preparation of review manuscripts. The author thanks T. Barney for her help with the manuscript.