The p53-MDM2/MDMX axis - A chemotype perspective

Photoinduced radical cascade domino Heck coupling of N-aryl acrylamide with vinyl arenes enabled by palladium catalysis

Here, a redox-neutral palladium-catalyzed photo-induced radical cascade domino Heck reaction of N-aryl acrylamide with vinyl arenes is described. A diverse range of bioactive oxindoles, featuring an all-carbon quaternary center, were synthesized. The reaction is proposed to proceed via an open-shell intermediate and occurs under mild reaction conditions, exhibiting excellent functional group tolerance. Importantly, the synthesized products can be readily transformed into biologically active molecules, including (±)-physostigmine and (±)-physovenine.

Optimized spirooxindole-pyrazole hybrids targeting the p53-MDM2 interplay induce apoptosis and synergize with doxorubicin in A549 cells

Recently, cancer research protocols have introduced clinical-stage spirooxindole-based MDM2 inhibitors. However, several studies reported tumor resistance to the treatment. This directed efforts to invest in designing various combinatorial libraries of spirooxindoles. Herein, we introduce new series of spirooxindoles via hybridization of the chemically stable core spiro[3H-indole-3,2'-pyrrolidin]-2(1H)-one and the pyrazole motif inspired by lead pyrazole-based p53 activators, the MDM2 inhibitor BI-0252 and promising molecules previously reported by our group. Single crystal X-ray diffraction analysis confirmed the chemical identity of a representative derivative. Fifteen derivatives were screened for cytotoxic activities via MTT assay against a panel of four cancer cell lines expressing wild-type p53 (A2780, A549, HepG2) and mutant p53 (MDA-MB-453). The hits were 8h against A2780 (IC₅₀ = 10.3 µM) and HepG2 (IC₅₀ = 18.6 µM), 8m against A549 (IC₅₀ = 17.7 µM), and 8k against MDA-MB-453 (IC₅₀ = 21.4 µM). Further MTT experiments showed that 8h and 8j potentiated doxorubicin activity and reduced its IC₅₀ by at least 25% in combinations. Western blot analysis demonstrated that 8k and 8m downmodulated MDM2 in A549 cells. Their possible binding mode with MDM2 were simulated by docking analysis.

The role of ETFS amino acids on the stability and inhibition of p53-MDM2 complex of anticancer p53-derivatives peptides: Density functional theory and molecular docking studies

Cancer is one of the leading causes of mortality in the world. Despite the existence of diverse antineoplastic treatments, these do not possess the expected efficacy in many cases. Knowledge of the molecular mechanisms involved in tumor processes allows the identification of a greater number of therapeutic targets employed in the study of new anticancer drugs. In the last decades, peptide-based therapy design using computational chemistry has gained importance in the field of oncology therapeutics. This work aims to evaluate the electronic structure, physicochemical properties, stability, and inhibition of ETFS amino acids and peptides derived from the p53-MDM2 binding domain with action in cancer cells; by means of chemical descriptors at the DFT-BHandHLYP level in an aqueous solution, and its intermolecular interactions through molecular docking studies. The results show that The ETFS fragment plays a critical role in the intermolecular interactions. Thus, the amino acids E17, T18 and S20 increase intermolecular interactions through hydrogen bonds and enhance structural stability. F19, W23 and V25 enhance the formation of the alpha-helix. The hydrogen bonds formed by the backbone atoms for PNC-27, PNC-27-B and PNC-28 stabilize the α-helices more than hydrogen bonds formed by the side chains atoms. Also, molecular docking indicated that the PNC27B-MDM2, PNC28B-MDM2, PNC27-MDM2 and PNC28A-MDM2 complexes show the best binding energy. Therefore, DFT and molecular docking studies showed that the proposed peptides: PNC-28B, PNC-27B and PNC-28A could inhibit the binding of MDM2 to the p53 protein, decreasing the translocation and degradation of p53 native protein.

Inclusion of Nitrofurantoin into the Realm of Cancer Chemotherapy via Biology-Oriented Synthesis and Drug Repurposing

Structural modifications of the antibacterial drug nitrofurantoin were envisioned, employing drug repurposing and biology-oriented drug synthesis, to serve as possible anticancer agents. Eleven compounds showed superior safety in non-cancerous human cells. Their antitumor efficacy was assessed on colorectal, breast, cervical, and liver cancer cells. Three compounds induced oxidative DNA damage in cancer cells with subsequent cellular apoptosis. They also upregulated the expression of Bax while downregulated that of Bcl-2 along with activating caspase 3/7. The DNA damage induced by these compounds, demonstrated by pATM nuclear shuttling, was comparable in both MCF7 and MDA-MB-231 (p53 mutant) cell lines. Mechanistic studies confirmed the dependence of these compounds on p53-mediated pathways as they suppressed the p53-MDM2 interaction. Indeed, exposure of radiosensitive prostatic cancer cells to low non-cytotoxic concentrations of compound 1 enhanced the cytotoxic response to radiation indicating a possible synergistic effect. In vivo antitumor activity was verified in an MCF7-xenograft animal model.

Synthesis and Biological Evaluation of Novel Dispiro-Indolinones with Anticancer Activity

Novel variously substituted thiohydantoin-based dispiro-indolinones were prepared using a regio- and diastereoselective synthetic route from 5-arylidene-2-thiohydantoins, isatines, and sarcosine. The obtained molecules were subsequently evaluated in vitro against the cancer cell lines LNCaP, PC3, HCT^wt, and HCT^(-/-). Several compounds demonstrated a relatively high cytotoxic activity vs. LNCaP cells (IC₅₀ = 1.2-3.5 µM) and a reasonable selectivity index (SI = 3-10). Confocal microscopy revealed that the conjugate of propargyl-substituted dispiro-indolinone with the fluorescent dye Sulfo-Cy5-azide was mainly localized in the cytoplasm of HEK293 cells. P388-inoculated mice and HCT116-xenograft BALB/c nude mice were used to evaluate the anticancer activity of compound 29 in vivo. Particularly, the TGRI value for the P388 model was 93% at the final control timepoint. No mortality was registered among the population up to day 31 of the study. In the HCT116 xenograft model, the compound (170 mg/kg, i.p., o.d., 10 days) provided a T/C ratio close to 60% on day 8 after the treatment was completed. The therapeutic index-estimated as LD₅₀/ED₅₀-for compound 29 in mice was ≥2.5. Molecular docking studies were carried out to predict the possible binding modes of the examined molecules towards MDM2 as the feasible biological target. However, such a mechanism was not confirmed by Western blot data and, apparently, the synthesized compounds have a different mechanism of cytotoxic action.

Understanding the interaction of 14-3-3 proteins with hDMX and hDM2: a structural and biophysical study

p53 plays a critical role in regulating diverse biological processes: DNA repair, cell cycle arrest, apoptosis and senescence. The p53 pathway has therefore served as the focus of multiple drug-discovery efforts. p53 is negatively regulated by hDMX and hDM2; prior studies have identified 14-3-3 proteins as hDMX and hDM2 client proteins. 14-3-3 proteins are adaptor proteins that modulate localization, degradation and interactions of their targets in response to phosphorylation. Thus, 14-3-3 proteins may indirectly modulate the interaction between hDMX or hDM2 and p53 and represent potential targets for modulation of the p53 pathway. In this manuscript, we report on the biophysical and structural characterization of peptide/protein interactions that are representative of the interaction between 14-3-3 and hDMX or hDM2. The data establish that proximal phosphosites spaced ~20-25 residues apart in both hDMX and hDM2 co-operate to facilitate high-affinity 14-3-3 binding and provide structural insight that can be utilized in future stabilizer/inhibitor discovery efforts.

Molecular hybridization design and synthesis of novel spirooxindole-based MDM2 inhibitors endowed with BCL2 signaling attenuation; a step towards the next generation p53 activators

Despite the achieved progress in developing efficient MDM2-p53 protein-protein interaction inhibitors (MDM2 inhibitors), the acquired resistance of tumor cells to such p53 activators posed an argument about the druggability of the pathway. Combination studies disclosed that concomitant inhibition of MDM2 and BCL2 functions can sensitize the tumor cells and synergistically induce apoptosis. Herein, we employed a rapid combinatorial approach to generate a novel series of hybrid spirooxindole-based MDM2 inhibitors (5a-s) endowed with BCL2 signaling attenuation. The adducts were designed to mimic the thematic features of the chemically stable potent spiro[3H-indole-3,2'-pyrrolidin]-2(1H)-ones MDM2 inhibitors while installing a pyrrole ring on the core via a carbonyl spacer inspired by the natural product marinopyrrole A that efficiently inhibits BCL2 family functions by various mechanisms. NCI 60 cell-line panel screening revealed their promising broad-spectrum antiproliferative activities. The NCI-selected derivatives were screened for cytotoxic activities against normal fibroblasts, MDA-MB 231, HepG-2, and Caco-2 cells via MTT assay, subjected to mechanistic apoptosis studies for assessment of p53, BCL2, p21, and caspase 3/7 status, then evaluated for potential MDM2 inhibition utilizing MST assay. The most balanced potent and safe derivatives; 5i and 5q were more active than 5-fluorouracil, exhibited low μmrange MDM2 binding (KD=1.32and 1.72 μm, respectively), induced apoptosis-dependent anticancer activities up to 50%, activated p53 by 47-63%, downregulated the BCL2 gene to 59.8%, and reduced its protein level (13.75%) in the treated cancer cells. Further downstream p53 signaling studies revealed > 2 folds p21 upregulation and > 3 folds caspase 3/7 activation. Docking simulations displayed that the active MDM2 inhibitors resided well into the p53 binding sites of MDM2, and shared key interactions with the co-crystalized inhibitor posed by the indolinone scaffold (5i, 5p, and 5q), the halogen substituents (5r), or the installed spiro ring (5s). Finally, in silico ADMET profiling predicted acceptable drug-like properties with full accordance to Lipinski's, Veber's, and Muegge's bioavailability parameters for 5i and a single violation for 5q.

Proposing novel MDM2 inhibitors: Combined physics-driven high-throughput virtual screening and in vitro studies

The mouse double minute 2 (MDM2) protein acts as a negative regulator of the p53 tumor suppressor. It directly binds to the N terminus of p53 and promotes p53 ubiquitination and degradation. Since the most common p53-suppressing mechanisms involve the MDM2, proposing novel inhibitors has been the focus of many in silico and also experimental studies. Thus, here we screened around 500,000 small organic molecules from Enamine database at the binding pocket of this oncogenic target. The screening was achieved systematically with starting from the high-throughput virtual screening method followed by more sophisticated docking approaches. The initial high number of screened molecules was reduced to 100 hits which then were studied extensively for their therapeutic activity and pharmacokinetic properties using binary QSAR models. The structural and dynamical profiles of the selected molecules at the binding pocket of the target were studied thoroughly by all-atom molecular dynamics simulations. The free energy of the binding of the hit molecules was estimated by the MM/GBSA method. Based on docking simulations, binary QSAR model results, and free energy calculations, 11 compounds (E1-E11) were selected for in vitro studies. HUVEC vascular endothelium, colon cancer, and breast cancer cell lines were used for testing the binding affinities of the identified hits and for further cellular effects on human cancer cell. Based on in vitro studies, six compounds (E1, E2, E5, E6, E9, and E11) in breast cancer cell lines and six compounds (E1, E2, E5, E6, E8, and E10) in colon cancer cell lines were found as active. Our results showed that these compounds inhibit proliferation and lead to apoptosis.

Structure-Based Design of Potent and Orally Active Isoindolinone Inhibitors of MDM2-p53 Protein-Protein Interaction

Inhibition of murine double minute 2 (MDM2)-p53 protein-protein interaction with small molecules has been shown to reactivate p53 and inhibit tumor growth. Here, we describe rational, structure-guided, design of novel isoindolinone-based MDM2 inhibitors. MDM2 X-ray crystallography, quantum mechanics ligand-based design, and metabolite identification all contributed toward the discovery of potent in vitro and in vivo inhibitors of the MDM2-p53 interaction with representative compounds inducing cytostasis in an SJSA-1 osteosarcoma xenograft model following once-daily oral administration.

Small-molecule MDM2/X inhibitors and PROTAC degraders for cancer therapy: advances and perspectives

Blocking the MDM2/X–P53 protein–protein interaction has been widely recognized as an attractive therapeutic strategy for the treatment of cancers. Numerous small-molecule MDM2 inhibitors have been reported since the release of the structure of the MDM2–P53 interaction in 1996, SAR405838, NVP-CGM097, MK-8242, RG7112, RG7388, DS-3032b, and AMG232 currently undergo clinical evaluation for cancer therapy. This review is intended to provide a comprehensive and updated overview of MDM2 inhibitors and proteolysis targeting chimera (PROTAC) degraders with a particular focus on how these inhibitors or degraders are identified from starting points, strategies employed, structure–activity relationship (SAR) studies, binding modes or co-crystal structures, biochemical data, mechanistic studies, and preclinical/clinical studies. Moreover, we briefly discuss the challenges of designing MDM2/X inhibitors for cancer therapy such as dual MDM2/X inhibition, acquired resistance and toxicity of P53 activation as well as future directions.

Optimized Inhibitors of MDM2 via an Attempted Protein-Templated Reductive Amination

Innovative and efficient hit-identification techniques are required to accelerate drug discovery. Protein-templated fragment ligations represent a promising strategy in early drug discovery, enabling the target to assemble and select its binders from a pool of building blocks. Development of new protein-templated reactions to access a larger structural diversity and expansion of the variety of targets to demonstrate the scope of the technique are of prime interest for medicinal chemists. Herein, we present our attempts to use a protein-templated reductive amination to target protein-protein interactions (PPIs), a challenging class of drug targets. We address a flexible pocket, which is difficult to achieve by structure-based drug design. After careful analysis we did not find one of the possible products in the kinetic target-guided synthesis (KTGS) approach, however subsequent synthesis and biochemical evaluation of each library member demonstrated that all the obtained molecules inhibit MDM2. The most potent library member (Ki =0.095 μm) identified is almost as active as Nutlin-3, a potent inhibitor of the p53-MDM2 PPI.

Design and development of high affinity dual anticancer peptide-inhibitors against p53-MDM2/X interaction

AIMS

Inhibition of P53-MDM2/X interaction is known as an effective cancer therapy strategy. In this regard, pDI peptide was introduced previously with the potential of targeting MDM2. In this research, the large-scale peptide mutation screening was used to achieve the best sequence of pDI with the highest affinity for inhibition activity against MDM2/X.

MAIN METHODS

Three mutant peptides of pDI as dual inhibitor peptides including single mutations of pDIm/4W, pDIm/11M and double mutations of pDIdm/4W11M were presented with the high affinities to inhibit both MDM2/X. The selected mutants were then evaluated comprehensively to confirm their ability as potent MDM2/X inhibitors, using a theoretical simulation approach.

KEY FINDINGS

MD simulations analyses confirmed their dual inhibition potential against both MDM2/X interactions with p53 protein. The developed pDIm and mainly pDIdm peptides showed stable conformations over the simulation time with conserved secondary structure and effective interaction with MDM2/X by physical binding such as hydrogen bonding. Besides, umbrella sampling free energy calculation indicated higher binding energy, ΔG_binding, of pDIm-MDM2/X and pDIdm-MDM2/X compared to pDI-MDM2/X.

SIGNIFICANCE

The optimized and improved mutant pDI, pDIdm, with more effective ΔG_binding values of -30 and -25 kcal/mol to MDMX and MDM2, respectively, is recommended as a promising anticancer agent and suitable candidate for experimental evaluations.

MDM2-p53 Interaction Inhibitors: The Current State-of-Art and Updated Patent Review (2010-Present)

Background:

Mouse Double Minute 2 protein (MDM2) is a cellular regulator of p53 tumor suppressor (p53). Inhibition of the interaction between MDM2 and p53 proteins is a promising anticancer therapy.

Objective:

This updated patent review is an attempt to compile the research and achievements of the various researchers working on small molecule MDM2 inhibitors from 2010 to date. We provide an outlook into the future for therapy based on MDM2 inhibition by presenting an overview of the most relevant patents which have recently appeared in the literature.

Methods:

Literature and recent patents focusing on the anticancer potential of MDM2-p53 interaction inhibitors and its applications have been analyzed. We put the main emphasis on the most perspective compounds which are or were examined in clinical trials.

Results:

Literature data indicated that MDM2 inhibitors are therapeutically effective in specific types of cancer or non-cancer diseases. A great number of patents and research work around new MDM2- p53 interaction inhibitors, possible combinations, new indications, clinical regimens in previous years prove that this targeted therapy is in the scope of interest for many business and academic research groups.

Conclusion:

Novel MDM2 inhibitors thanks to higher potency and better ADME properties have shown effectiveness in preclinical and clinical development however the final improvement of therapeutic potential for MDM2 inhibitors might depend on the useful combination therapy and exploring new cancer and non-cancer indications.

Asymmetric synthesis of spirooxindole–pyranoindole products via Friedel–Crafts alkylation/cyclization of the indole carbocyclic ring

Enantioselective Friedel–Crafts alkylation/cyclization of the indole carbocyclic ring with isatylidene malononitriles was performed using a new bifunctional catalyst.

p53-Dependent Apoptotic Effect of Puromycin via Binding of Ribosomal Protein L5 and L11 to MDM2 and its Combination Effect with RITA or Doxorubicin

Among ribosomal proteins essential for protein synthesis, the functions of ribosomal protein L5 (RPL5) and RPL11 still remain unclear to date. Here, the roles of RPL5 and RPL11 were investigated in association with p53/p21 signaling in the antitumor effect of puromycin mainly in HCT116 and H1299 cancer cells. Cell proliferation assays using 3-[4,5-dimethylthiazole-2-yl]-2,5-diphenyltetrazolium bromide (MTT) assays and colony formation assays, cell cycle analysis, Reverse transcription polymerase chain reaction (RT-PCR) and Western blotting were performed in cancer cells. Puromycin exerted cytotoxic and anti-proliferative effects in p53 wild-type HCT116 more than in p53 null H1299 cells. Consistently, puromycin increased sub-G1, cleaved Poly (ADP-ribose) polymerase (PARP), activated p53, p21, and Mouse double minute 2 homolog (MDM2), and attenuated expression of c-Myc in HCT116 cells. Notably, puromycin upregulated the expression of RPL5 and RPL11 to directly bind to MDM2 in HCT116 cells. Conversely, deletion of RPL5 and RPL11 blocked the activation of p53, p21, and MDM2 in HCT116 cells. Also, puromycin enhanced the antitumor effect with reactivating p53 and inducing tumor apoptosis (RITA) or doxorubicin in HCT116 cells. These findings suggest that puromycin induces p53-dependent apoptosis via upregulation of RPL5 or RPL11 for binding with MDM2, and so can be used more effectively in p53 wild-type cancers by combination with RITA or doxorubicin.

The catalytic asymmetric synthesis of CF3-containing spiro-oxindole–pyrrolidine–pyrazolone compounds through squaramide-catalyzed 1,3-dipolar cycloaddition

Pharmaceutically important compounds were synthesized through the organocatalytic 1,3-dipolar cycloaddition reaction.

The asymmetric construction of CF3-containing spiro-thiazolone-pyrrolidine compoundsvia[3 + 2] cycloaddition

An organocatalytic method for the asymmetric construction of CF₃-containing spiro-thiazolone-pyrrolidine compounds has been developed.

Artificial Macrocycles

Artificial macrocycles recently became popular as a novel research field in drug discovery. As opposed to their natural twins, artificial macrocycles promise to have better control on synthesizability and control over their physicochemical properties resulting in druglike properties. Very few synthetic methods allow for the convergent, fast but diverse access to large macrocycles chemical space. One synthetic technology to access artificial macrocycles with potential biological activity, multicomponent reactions, is reviewed here, with a focus on our own work. We believe that synthetic chemists have to acquaint themselves more with structure and activity to leverage the design aspect of their daily work.

Computer-Aided Identification and Lead Optimization of Dual Murine Double Minute 2 and 4 Binders: Structure-Activity Relationship Studies and Pharmacological Activity

The function of p53 protein, also known as "genome guardian", might be impaired by the overexpression of its primary cellular inhibitor, the murine double minute 2 protein (MDM2). However, the recent finding that MDM2-selective inhibitors induce high levels of its homologue MDM4, prompt us to identify, through a receptor-based virtual screening on an in house database, dual MDM2/MDM4 binders. Compound 1 turned out to possess an IC₅₀ of 93.7 and of 4.6 nM on MDM2 and MDM4, respectively. A series of compounds were synthesized to optimize its activity on MDM2. As a result, compound 12 showed low nanomolar IC₅₀ for both targets. NMR studies confirmed the pocket of binding of 12 as predicted by the Glide docking software. Notably, 12 was able to cause concentration-dependent inhibition of cell proliferation, yielding an IC₅₀ value of 356 ± 21 nM in neuroblastoma SHSY5Y cells and proved even to efficiently block cancer stem cell growth.

Development of a novel immunoassay to detect interactions with the transactivation domain of p53: application to screening of new drugs

Tumor protein p53 acts as a trans-activator that negatively regulates cell division by controlling a set of genes required for cell cycle regulation, making it a tumor suppressor in different types of tumors. Because the transcriptional activity of p53 plays an important role in the occurrence and development of tumors, reactivation of p53 transcriptional activity has been sought as a novel cancer therapeutic strategy. There is great interest in developing high-throughput assays to identify inhibitors of molecules that bind the transcription-activation domain of p53, especially for wt p53-containing tumors. In the present study, taking MDM2 as an example, a novel amplified luminescent proximity homogeneous assay (AlphaLISA) was modified from a binding competition assay to detect the interactions between the transcription-activation domain of p53 and its ligands. This assay can be adapted as a high-throughput assay for screening new inhibitors. A panel of well-known p53-MDM2 binding inhibitors was used to validate this method, and demonstrated its utility, sensitivity and robustness. In summary, we have developed a novel protein-protein interaction detection immunoassay that can be used in a high-throughput format to screen new drug candidates for reactivation of p53. This assay has been successfully validated through a series of p53-MDM2 binding inhibitors.

Scaffold hopping via ANCHOR.QUERY: β-lactams as potent p53-MDM2 antagonists†

Using the pharmacophore-based virtual screening platform ANCHOR.QUERY, we morphed our recently described Ugi-4CR scaffold towards a β-lactam scaffold with potent p53-MDM2 antagonizing activities. 2D-HSQC and FP measurements confirm potent MDM2 binding. Molecular modeling studies are used to understand the observed SAR in the β-lactam series.

Discovery of Novel Spiro[3H-indole-3,2'-pyrrolidin]-2(1H)-one Compounds as Chemically Stable and Orally Active Inhibitors of the MDM2-p53 Interaction

Scaffold modification based on Wang's pioneering MDM2-p53 inhibitors led to novel, chemically stable spiro-oxindole compounds bearing a spiro[3H-indole-3,2'-pyrrolidin]-2(1H)-one scaffold that are not prone to epimerization as observed for the initial spiro[3H-indole-3,3'-pyrrolidin]-2(1H)-one scaffold. Further structure-based optimization inspired by natural product architectures led to a complex fused ring system ideally suited to bind to the MDM2 protein and to interrupt its protein-protein interaction (PPI) with TP53. The compounds are highly selective and show in vivo efficacy in a SJSA-1 xenograft model even when given as a single dose as demonstrated for 4-[(3S,3'S,3'aS,5'R,6'aS)-6-chloro-3'-(3-chloro-2-fluorophenyl)-1'-(cyclopropylmethyl)-2-oxo-1,2,3',3'a,4',5',6',6'a-octahydro-1'H-spiro[indole-3,2'-pyrrolo[3,2-b]pyrrole]-5'-yl]benzoic acid (BI-0252).

How To Design a Successful p53-MDM2/X Interaction Inhibitor: A Thorough Overview Based on Crystal Structures

A recent therapeutic strategy in oncology is based on blocking the protein-protein interaction between the murine double minute (MDM) homologues MDM2/X and the tumor-suppressor protein p53. Inhibiting the binding between wild-type (WT) p53 and its negative regulators MDM2 and/or MDMX has become an important target in oncology to restore the antitumor activity of p53, the so-called guardian of our genome. Interestingly, based on the multiple disclosed compound classes and structural analysis of small-molecule-MDM2 adducts, the p53-MDM2 complex is perhaps the best studied and most targeted protein-protein interaction. Several classes of small molecules have been identified as potent, selective, and efficient inhibitors of the p53-MDM2/X interaction, and many co-crystal structures with the protein are available. Herein we review the properties as well as preclinical and clinical studies of these small molecules and peptides, categorized by scaffold type. A particular emphasis is made on crystallographic structures and the observed binding modes of these compounds, including conserved water molecules present.

Probing Protein Surfaces: QSAR Analysis with Helix Mimetics

α-Helix-mediated protein-protein interactions (PPIs) are important targets for small-molecule inhibition; however, generic approaches to inhibitor design are in their infancy and would benefit from QSAR analyses to rationalise the noncovalent basis of molecular recognition by designed ligands. Using a helix mimetic based on an oligoamide scaffold, we have exploited the power of a modular synthesis to access compounds that can readily be used to understand the noncovalent determinants of hDM2 recognition by this series of cell-active p53/hDM2 inhibitors.

Small-molecule MDM2-p53 inhibitors: recent advances

Potent and selective small-molecule inhibitors of the p53-MDM2 interaction intended for the treatment of p53 wild-type tumors have been designed and optimized in a number of chemical series. This review details recent disclosures of compounds in advanced optimization and features key series that have given rise to clinical trial candidates. The structure-activity relationships for inhibitor classes are discussed with reference to x-ray structures, and common structural features are identified.

Spirooxadiazoline oxindoles with promising in vitro antitumor activities

This paper reports the synthesis and biological evaluation of thirty one spirooxadiazoline oxindoles as potential anticancer agents.

Searching for Dual Inhibitors of the MDM2-p53 and MDMX-p53 Protein-Protein Interaction by a Scaffold-Hopping Approach

Two libraries of substituted benzimidazoles were designed using a 'scaffold-hopping' approach based on reported MDM2-p53 inhibitors. Substituents were chosen following library enumeration and docking into an MDM2 X-ray structure. Benzimidazole libraries were prepared using an efficient solution-phase approach and screened for inhibition of the MDM2-p53 and MDMX-p53 protein-protein interactions. Key examples showed inhibitory activity against both targets.

Multivalent helix mimetics for PPI-inhibition

A multivalent helix mimetic is developed that inhibits the p53/hDM2 and induces dimerization/aggregation of its target – hDM2.

Synthesis, structure prediction, pharmacokinetic properties, molecular docking and antitumor activities of some novel thiazinone derivatives

Convenient synthesis of [1,3]thiazin-4-ones by the unprecedented cyclization of acetylene diesters with 3-alkyl-2,6-diarylpiperidin-4-one thiosemicarbazone derivatives and their antitumor evaluation.

Small-molecule inhibitors of the MDM2-p53 protein-protein interaction (MDM2 Inhibitors) in clinical trials for cancer treatment

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.

A small-molecule modulator of the tumor-suppressor miR34a inhibits the growth of hepatocellular carcinoma

Small molecules that restore the expression of growth-inhibitory microRNAs (miRNA) downregulated in tumors may have potential as anticancer agents. miR34a functions as a tumor suppressor and is downregulated or silenced commonly in a variety of human cancers, including hepatocellular carcinoma (HCC). In this study, we used an HCC cell-based miR34a luciferase reporter system to screen for miR34a modulators that could exert anticancer activity. One compound identified as a lead candidate, termed Rubone, was identified through its ability to specifically upregulate miR34a in HCC cells. Rubone activated miR34a expression in HCC cells with wild-type or mutated p53 but not in cells with p53 deletions. Notably, Rubone lacked growth-inhibitory effects on nontumorigenic human hepatocytes. In a mouse xenograft model of HCC, Rubone dramatically inhibited tumor growth, exhibiting stronger anti-HCC activity than sorafenib both in vitro and in vivo. Mechanistic investigations showed that Rubone decreased expression of cyclin D1, Bcl-2, and other miR34a target genes and that it enhanced the occupancy of p53 on the miR34a promoter. Taken together, our results offer a preclinical proof of concept for Rubone as a lead candidate for further investigation as a new class of HCC therapeutic based on restoration of miR34a tumor-suppressor function.

Fragment-based library generation for the discovery of a peptidomimetic p53-Mdm4 inhibitor

On the basis of our recently resolved first cocrystal structure of Mdm4 in complex with a small molecule inhibitor (PDB ID 3LBJ ), we devised an approach for the generation of potential Mdm4 selective ligands. We performed the Ugi four-component reaction (Ugi-4CR) in 96-well plates with an indole fragment, which is specially designed to mimic Trp23, a key amino acid for the interaction between p53 and Mdm4. Generally the reaction yielded mostly precipitates collected by 96-well filter plates. The best hit compound was found to be active and selective for Mdm4 (Ki=5 μM, 10-fold stronger than Mdm2). This initial hit may serve as the starting point for designing selective p53-Mdm4 inhibitor with higher affinity.

The fluorescent two-hybrid assay to screen for protein-protein interaction inhibitors in live cells: targeting the interaction of p53 with Mdm2 and Mdm4

Protein-protein interactions (PPIs) are attractive but challenging targets for drug discovery. To overcome numerous limitations of the currently available cell-based PPI assays, we have recently established a fully reversible microscopy-assisted fluorescent two-hybrid (F2H) assay. The F2H assay offers a fast and straightforward readout: an interaction-dependent co-localization of two distinguishable fluorescent signals at a defined spot in the nucleus of mammalian cells. We developed two reversible F2H assays for the interactions between the tumor suppressor p53 and its negative regulators, Mdm2 and Mdm4. We then performed a pilot F2H screen with a subset of compounds, including small molecules (such as Nutlin-3) and stapled peptides. We identified five cell-penetrating compounds as potent p53-Mdm2 inhibitors. However, none exhibited intracellular activity on p53-Mdm4. Live cell data generated by the F2H assays enable the characterization of stapled peptides based on their ability to penetrate cells and disrupt p53-Mdm2 interaction as well as p53-Mdm4 interaction. Here, we show that the F2H assays enable side-by-side analysis of substances' dual Mdm2-Mdm4 activity. In addition, they are suitable for testing various types of compounds (e.g., small molecules and peptidic inhibitors) and concurrently provide initial data on cellular toxicity. Furthermore, F2H assays readily allow real-time visualization of PPI dynamics in living cells.

Targeting p53-MDM2-MDMX loop for cancer therapy

The tumor suppressor p53 plays a central role in anti-tumorigenesis and cancer therapy. It has been described as "the guardian of the genome", because it is essential for conserving genomic stability by preventing mutation, and its mutation and inactivation are highly related to all human cancers. Two important p53 regulators, MDM2 and MDMX, inactivate p53 by directly inhibiting its transcriptional activity and mediating its ubiquitination in a feedback fashion, as their genes are also the transcriptional targets of p53. On account of the importance of the p53-MDM2-MDMX loop in the initiation and development of wild type p53-containing tumors, intensive studies over the past decade have been aiming to identify small molecules or peptides that could specifically target individual protein molecules of this pathway for developing better anti-cancer therapeutics. In this chapter, we review the approaches for screening and discovering efficient and selective MDM2 inhibitors with emphasis on the most advanced synthetic small molecules that interfere with the p53-MDM2 interaction and are currently on Phase I clinical trials. Other therapeutically useful strategies targeting this loop, which potentially improve the prospects of cancer therapy and prevention, will also be discussed briefly.

Benzimidazole-2-one: a novel anchoring principle for antagonizing p53-Mdm2

Herein we propose the benzimidazole-2-one substructure as a suitable tryptophan mimic and thus a reasonable starting point for the design of p53 Mdm2 antagonists. We devise a short multicomponent reaction route to hitherto unknown 2-(2-oxo-2,3-dihydro-1H-benzo[d]imidazol-1-yl)acetamides by reacting mono N-carbamate protected phenylenediamine in a Ugi-3CR followed by base induced cyclisation. Our preliminary synthesis and screening results are presented here. The finding of the benzimidazolone moiety as a tryptophan replacement in mdm2 is significant as it offers access to novel scaffolds with potentially higher selectivity and potency and improved biological activities. Observing low μM affinities to mdm2 by NMR and fluorescence polarization we conclude that the 2-(2-oxo-2,3-dihydro-1H-benzo[d]imidazol-1-yl)acetamide scaffold might be a good starting point to further optimize the affinities to Mdm2.

P53 mdm2 inhibitors

The protein-protein interaction (PPI) between p53 and its negative regulator MDM2 comprises one of the most important and intensely studied PPI's involved in preventing the initiation of cancer. The interaction between p53 and MDM2 is conformation-based and is tightly regulated on multiple levels. Due to the Angstrom level structural insight there is a reasonable understanding of the structural requirements needed for a molecule to bind to MDM2 and successfully inhibit the p53/MDM2 interaction. The current review summarizes the binding characteristics of the different disclosed small molecules for inhibition of MDM2 with a co-crystal structure. Synthetic access to these compounds as well as their derivatives are described in detail.

Mdm2 and MdmX inhibitors for the treatment of cancer: a patent review (2011-present)

INTRODUCTION

One of the hallmarks of cancer cells is the inactivation of the p53 pathway either due to mutations in the p53 gene or over-expression of negative regulators, Mdm2 and/or MdmX. Pharmacological disruption of the Mdm2/X-p53 interaction to restore p53 activity is an attractive concept, aiming at a targeted and non-toxic cancer treatment.

AREAS COVERED

The introduction covers the biological role of p53 pathway and its regulation by Mdm2 and MdmX in normal and cancer cells and the current repertoire and development status of inhibitors of the Mdm2/X-p53 interaction for the treatment of cancer. The main part of the article covers patents and patent applications describing small molecule inhibitors of the Mdm2/X-p53 interaction published from 2011 until 2012.

EXPERT OPINION

The area of small molecule Mdm2/X-p53 interaction inhibitor development is progressing fast. Several Phase I clinical studies and preclinical programs are now in progress, however, the clinical proof concept has yet to be demonstrated. Multiple available compounds inhibit Mdm2-p53 interaction with nanomolar affinities, but MdmX is still missing such potent binders. Since research points to a complementary mode of Mdm2 and MdmX action, the future compound classes will possibly want to include dual actions versus Mdm2 and MdmX.

Mechanisms of small-molecule binding to intrinsically disordered proteins

IDPs (intrinsically disordered proteins) play crucial roles in many important cellular processes such as signalling or transcription and are attractive therapeutic targets for several diseases. The considerable structural flexibility of IDPs poses a challenge for rational drug discovery approaches. Consequently, structure-based drug design efforts to date have mostly focused on inhibiting interactions of IDPs with other proteins whose structure can be solved by conventional biophysical methods. Yet, in recent years, several examples of small molecules that bind to monomeric IDPs in their disordered states have been reported, suggesting that this approach may offer new opportunities for therapeutic interventions. Further developments of this strategy will greatly benefit from an improved understanding of molecular recognition mechanisms between small molecules and IDPs. The present article summarizes findings from experimental and computational studies of the mechanisms of interaction between small molecules and three IDPs in their disordered states: c-Myc, Aβ (amyloid β-peptide) and α-synuclein.