Discovery, synthesis, and biological evaluation of orally active pyrrolidone derivatives as novel inhibitors of p53-MDM2 protein-protein interaction

Michael Acceptor Pyrrolidone Derivatives and Their Activity against Diffuse Large B-cell Lymphoma

OBJECTIVE

This study aimed to design and evaluate the efficacy of pyrrolidone derivatives as potential therapeutic agents against diffuse large B-cell lymphoma (DLBCL), a common and heterogeneous malignancy of the adult lymphohematopoietic system. Given the limitations of current therapies, there is a pressing need to develop new and effective drugs for DLBCL treatment.

METHODS

A series of pyrrolidone derivatives were synthesized, and their antitumor activities were assessed, particularly against DLBCL cell lines. Structure-activity relationship (SAR) analysis was conducted to identify key structural components essential for activity. The most promising compound, referred to as compound 7, was selected for further mechanistic studies. The expression levels of relevant mRNA and protein were detected by RT-qPCR and Western blotting, and the expression of mitochondrial membrane potential and ROS was detected using flow cytometry for further assessment of cell cycle arrest and apoptosis.

RESULTS

The compound 7 exhibited good antitumor activity among the synthesized derivatives, specifically in DLBCL cell lines. SAR analysis highlighted the critical role of α, β-unsaturated ketones in the antitumor efficacy of these compounds. Mechanistically, compound 7 was found to induce significant DNA damage, trigger an inflammatory response, cause mitochondrial dysfunction, and disrupt cell cycle progression, ultimately leading to apoptosis of DLBCL cells.

CONCLUSION

The compound 7 has good antitumor activity and can induce multiple cellular mechanisms leading to cancer cell death. These findings warrant further investigation of the compound 7 as a potential therapeutic agent for DLBCL.

Construction of Phosphorothiolated 2-Pyrrolidinones via Photoredox/Copper-Catalyzed Cascade Radical Cyclization/Phosphorothiolation

A photoredox/copper-catalyzed cascade radical cyclization/phosphorothiolation reaction of N-allylbromoacetamides and P(O)SH compounds has been established. A broad range of novel nonfluorine- or difluoro-substituted 2-pyrrolidinones bearing the C(sp3)-SP(O)(OR)2 moiety can be conveniently constructed in moderate to good yields under mild conditions. Importantly, most of the tested phosphorothiolated 2-pyrrolidinones showed potent inhibitory effects toward both AChE and BChE.

Recent advances in targeting the "undruggable" proteins: from drug discovery to clinical trials

Undruggable proteins are a class of proteins that are often characterized by large, complex structures or functions that are difficult to interfere with using conventional drug design strategies. Targeting such undruggable targets has been considered also a great opportunity for treatment of human diseases and has attracted substantial efforts in the field of medicine. Therefore, in this review, we focus on the recent development of drug discovery targeting "undruggable" proteins and their application in clinic. To make this review well organized, we discuss the design strategies targeting the undruggable proteins, including covalent regulation, allosteric inhibition, protein-protein/DNA interaction inhibition, targeted proteins regulation, nucleic acid-based approach, immunotherapy and others.

Rational Design, Synthesis, Separation, and Characterization of New Spiroxindoles Combined with Benzimidazole Scaffold as an MDM2 Inhibitor

Rational design for a new spiroxindoles, combined with a benzimidazole scaffold to identify a new murine double minute two (MDM2) inhibitor was synthesized and characterized. The desired spiroxindoles were achieved via a [3+2] cycloaddition reaction approach which afforded the cycloadducts with four asymmetric centers separated in an excellent regioselective and diastereoselective compound. The separated spiroxindoles were subjected to a set of biochemical assays including an NCI cell panel assay, MTT assay, and MDM2 binding analysis by a microscale thermophoresis assay. The anticancer reactivity for the tested compounds showed IC50 (µM) in the range between 3.797–6.879 µM, and compound 7d with IC50 = 3.797 ± 0.205 µM was the most active candidate between the series. The results showed promising results that identified that compound 7a could be inhibited the MDM2 with KD = 2.38 μm. Compound 7a developed a network of interactions with the MDM2 receptor studied in silico by molecular docking.

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.

A Brief Review: Advancement in the Synthesis of Amine through the Leuckart Reaction

This review presents a summary of reactions that take place during the “Leuckart-type reaction”. The significance of, as well as recent advancements in, the synthesis of amines through simple and inexpensive methods using readily available raw materials is discussed. This review includes all catalytic and noncatalytic reactions that involve the Leuckart method. Recent studies have shown that at least a quarter of C–N bond-forming reactions in the pharmaceutical industry are occur with the support of reductive amination. Recently, experimental conditions have achieved excellent yields. The “Leuckart-type reaction” is technically associated with Eschweiler–Clarke methylation. Compounds are grouped in accordance with the precept of action. This includes drugs affecting the central nervous system, cardiovascular system and gastrointestinal tract; anticancer drugs, antibiotics, antiviral and antifungal drugs; drugs affecting anxiety; convulsant, biotic, and HIV drugs; and antidiabetic drugs. Therefore, this review supports the development of the Leuckart-type preparation of nitrogenous compounds, as well as their advancement in other areas of human development.

Homobivalent, Trivalent, and Covalent PROTACs: Emerging Strategies for Protein Degradation

Proteolysis-targeting chimeras (PROTACs) is a fast-growing technology providing many strengths over inhibition of protein activity directly and is attracting increasing interest in new drug discovery and development. However, efficiently identifying potent and drug-like degraders is still challenging in the development of PROTACs. Complementary to traditional PROTACs, several emerging types of PROTACs, such as homobivalent PROTACs based on two E3 ligases (e.g., CRBN, VHL, MDM2, TRIM24), chemical- or biological-based trivalent/multitargeted PROTACs, and covalent PROTACs, are rising for targeted protein degradation. These new types of PROTACs have several advantages over the traditional PROTACs including high selectivity, low toxicity, better therapeutic effects, and so on. In this perspective, we will summarize the latest development of representative PROTACs focusing on research mainly in past 10 years and discuss their advantages and disadvantages. Moreover, the outlook and perspectives on the associated challenges and future directions will be provided.

Synthesis and Biological Evaluation of Novel Synthetic Indolone Derivatives as Anti-Tumor Agents Targeting p53-MDM2 and p53-MDMX

A series of novel indolone derivatives were synthesized and evaluated for their binding affinities toward MDM2 and MDMX. Some compounds showed potent MDM2 and moderate MDMX activities. Among them, compound A13 exhibited the most potent affinity toward MDM2 and MDMX, with a K_i of 0.031 and 7.24 μM, respectively. A13 was also the most potent agent against HCT116, MCF7, and A549, with IC₅₀ values of 6.17, 11.21, and 12.49 μM, respectively. Western blot analysis confirmed that A13 upregulated the expression of MDM2, MDMX, and p53 by Western blot analysis. These results indicate that A13 is a potent dual p53-MDM2 and p53-MDMX inhibitor and deserves further investigation.

Exploring the Synthetic Potential of γ-Lactam Derivatives Obtained from a Multicomponent Reaction. Applications as Antiproliferative Agents

A study on the reactivity of 3-amino α,β-unsaturated γ-lactam derivatives obtained from a multicomponent reaction is presented. Key features of the substrates are the presence of an endocyclic α,β-unsaturated amide moiety and an enamine functionality. Following different synthetic protocols, the functionalization at three different positions of the lactam core is achieved. In the presence of a soft base, under thermodynamic conditions, the functionalization at C-4 takes place where the substrates behave as enamines, while the use of a strong base, under kinetic conditions, leads to the formation of C-5-functionalized γ-lactams, in the presence of ethyl glyoxalate, through a highly diastereoselective vinylogous aldol reaction. Moreover, the nucleophilic addition of organometallic species allows the functionalization at C-3, through the imine tautomer, affording γ-lactams bearing tetrasubstituted stereocenters, where the substrates act as imine electrophiles. Taking into account the advantage of the presence of a chiral stereocenter in C-5 substituted γ-lactams, further diastereoselective transformations are also explored, leading to novel bicyclic substrates holding a fused γ and δ-lactam skeleton. Remarkably, an example of a highly stereoselective formal [3+3] cycloaddition reaction of chiral γ-lactam substrates is reported for the synthesis of 1,4-dihidropyridines, where a non-covalent attractive interaction of a carbonyl group with an electron-deficient arene seems to drive the stereoselectivity of the reaction to the exclusive formation of the cis isomer. In order to unambiguously determine the substitution pattern resulting from the diverse reactions, an extensive characterization of the substrates is detailed through 2D NMR and/or X-ray experiments. Likewise, applications of the substrates as antiproliferative agents against lung and ovarian cancer cells are also described.

Integrated virtual screening and molecular dynamics simulation revealed promising drug candidates of p53-MDM2 interaction

In the vast majority of malignancies, the p53 tumor suppressor pathway is compromised. In some cancer cells, high levels of MDM2 polyubiquitinate p53 and mark it for destruction, thereby leading to a corresponding downregulation of the protein. MDM2 interacts with p53 via its hydrophobic pocket, and chemical entities that block the dimerization of the protein-protein complex can restore p53 activity. Thus far, only a few chemical compounds have been reported as potent arsenals against p53-MDM2. The Protein Data Bank has crystallogaphic structures of MDM2 in complex with certain compounds. Herein, we have exploited one of the complexes in the identification of new p53-MDM2 antagonists using a hierarchical virtual screening technique. The initial stage was to compile a targeted library of structurally appropriate compounds related to a known effective inhibitor, Nutlin 2, from the PubChem database. The identified 57 compounds were subjected to virtual screening using molecular docking to discover inhibitors with high binding affinity for MDM2. Consequently, five compounds with higher binding affinity than the standard emerged as the most promising therapeutic candidates. When compared to Nutlin 2, four of the drug candidates (CID_140017825, CID_69844501, CID_22721108, and CID_22720965) demonstrated satisfactory pharmacokinetic and pharmacodynamic profiles. Finally, MD simulation of the dynamic behavior of lead-protein complexes reveals the stability of the complexes after a 100,000 ps simulation period. In particular, when compared to the other three leads, overall computational modeling found CID_140017825 to be the best pharmacological candidate. Following thorough experimental trials, it may emerge as a promising chemical entity for cancer therapy.

Multicomponent Synthesis of Unsaturated γ-Lactam Derivatives. Applications as Antiproliferative Agents through the Bioisosterism Approach: Carbonyl vs. Phosphoryl Group

We report efficient synthetic methodologies for the preparation of 3-amino and 3-hydroxy 3-pyrrolin-2-ones (unsaturated γ-lactams) through a multicomponent reaction of amines, aldehydes and acetylene or pyruvate derivatives. The densely substituted γ-lactam substrates show in vitro cytotoxicity, inhibiting the growth of the carcinoma human tumor cell lines RKO (human colon epithelial carcinoma), SKOV3 (human ovarian carcinoma) and A549 (carcinomic human alveolar basal epithelial cell). In view of the possibilities for the diversity of the substituents that offer a multicomponent, synthetic methodology, an extensive structure–activity profile is presented. In addition, the bioisosteric replacement of the flat ester group by a tetrahedral phosphonate or phosphine oxide moiety in γ-lactam substrates leads to increased growth inhibition activity. Cell morphology analysis and flow cytometry assays indicate that the main pathway by which our compounds induce cytotoxicity is based on the activation of the intracellular apoptotic mechanism.

Jellynolide A, pokepola esters, and sponalisolides from the aquaculture sponge Spongia officinalis L

Jellynolide A, an unreported bicyclic diterpenoid with an unprecedented penta-substituted carbon skeleton which implied an irregular biogenic pathway, together with four pairs of rare phosphate triesters, (±)-pokepola ester B-E, one undescribed related racemic furanoterpenoid, (±)-sponalisolide C, one undescribed furanoterpenoid, (-)-sponalisolide D, and two known (±)-sponalisolide B and dendrolasin carboxylic acid were isolated from the aquaculture Spongia officinalis L. Their structures were elucidated by comprehensive spectroscopic analysis, quantum chemical calculation of NMR parameters, and electronic circular dichroism (ECD). The plausible biosynthetic pathway of jellynolide A was proposed. (±)-Pokepola ester C exhibited significant inhibition against Wnt, HIF1 signaling pathways. (+)-Pokepola ester B and (-)-pokepola ester D showed moderate cytotoxicity activities.

It’s Getting Complicated—A Fresh Look at p53-MDM2-ARF Triangle in Tumorigenesis and Cancer Therapy

Anti-tumorigenic mechanisms mediated by the tumor suppressor p53, upon oncogenic stresses, are our bodies’ greatest weapons to battle against cancer onset and development. Consequently, factors that possess significant p53-regulating activities have been subjects of serious interest from the cancer research community. Among them, MDM2 and ARF are considered the most influential p53 regulators due to their abilities to inhibit and activate p53 functions, respectively. MDM2 inhibits p53 by promoting ubiquitination and proteasome-mediated degradation of p53, while ARF activates p53 by physically interacting with MDM2 to block its access to p53. This conventional understanding of p53-MDM2-ARF functional triangle have guided the direction of p53 research, as well as the development of p53-based therapeutic strategies for the last 30 years. Our increasing knowledge of this triangle during this time, especially through identification of p53-independent functions of MDM2 and ARF, have uncovered many under-appreciated molecular mechanisms connecting these three proteins. Through recognizing both antagonizing and synergizing relationships among them, our consideration for harnessing these relationships to develop effective cancer therapies needs an update accordingly. In this review, we will re-visit the conventional wisdom regarding p53-MDM2-ARF tumor-regulating mechanisms, highlight impactful studies contributing to the modern look of their relationships, and summarize ongoing efforts to target this pathway for effective cancer treatments. A refreshed appreciation of p53-MDM2-ARF network can bring innovative approaches to develop new generations of genetically-informed and clinically-effective cancer therapies.

A computer-aided drug design approach to discover tumour suppressor p53 protein activators for colorectal cancer therapy

Colorectal cancer (CRC) is the third most detected cancer and the second foremost cause of cancer deaths in the world. Intervention targeting p53 provides potential therapeutic strategies, but thus far no p53-based therapy has been successfully translated into clinical cancer treatment. Here we developed a Quantitative Structure-Activity Relationships (QSAR) classification models using empirical molecular descriptors and fingerprints to predict the activity against the p53 protein, using the potency value with the active or inactive label, were developed. These models were built using in total 10,505 molecules that were extracted from the ChEMBL, ZINC and Reaxys® databases, and recent literature. Three machine learning (ML) techniques e.g., Random Forest, Support Vector Machine, Convolutional Neural Network were explored to build models for p53 inhibitor prediction. The performances of the models were successfully evaluated by internal and external validation. Moreover, based on the best in silico p53 model, a virtual screening campaign was carried out using 1443 FDA-approved drugs that were extracted from the ZINC database. A list of virtual screening hits was assented on base of some limits established in this approach, such as: (1) probability of being active against p53; (2) applicability domain; (3) prediction of the affinity between the p53, and ligands, through molecular docking. The most promising according to the limits established above was dihydroergocristine. This compound revealed cytotoxic activity against a p53-expressing CRC cell line with an IC₅₀ of 56.8 µM. This study demonstrated that the computer-aided drug design approach can be used to identify previously unknown molecules for targeting p53 protein with anti-cancer activity and thus pave the way for the study of a therapeutic solution for CRC.

Amination of 5-Spiro-Substituted 3-Hydroxy-1,5-dihydro-2H-pyrrol-2-ones

The 3-hydroxy-1,5-dihydro-2H-pyrrol-2-one motif is a valuable scaffold in drug discovery. The replacement of the 3-oxy fragment in 3-hydroxy-1,5-dihydro-2H-pyrrol-2-ones-based compounds with a 3-amino one (3-amino analogs of 3-hydroxy-1,5-dihydro-2H-pyrrol-2-ones, 3-amino-1,5-dihydro-2H-pyrrol-2-ones) can play a crucial role in their biological effect. Thus, approaches to 3-amino-1,5-dihydro-2H-pyrrol-2-ones are of significant interest. We developed an approach to 5-spiro-substituted 3-amino-1,5-dihydro-2H-pyrrol-2-ones that could not be obtained using previously reported approaches (reactions of 3-hydroxy-1,5-dihydro-2H-pyrrol-2-ones with amines). The developed approach is based on the thermal decomposition of 1,3-disubstituted urea derivatives of 5-spiro-substituted 3-hydroxy-1,5-dihydro-2H-pyrrol-2-ones, which were prepared via their reaction with carbodiimides.

Design, synthesis and biological evaluation of novel pyrrolidone-based derivatives as potent p53-MDM2 inhibitors

Inhibition of the interactions of the tumor suppressor protein p53 with its negative regulators MDM2 in vitro and in vivo, representing a valuable therapeutic strategy for cancer treatment. The natural product chalcone exhibited moderate inhibitory activity against MDM2, thus based on the binding mode between chalcone and MDM2, a hit unsaturated pyrrolidone scaffold was obtained through virtual screening. Several unsaturated pyrrolidone derivatives were synthesized and biological evaluated. As a result, because the three critical hydrophobic pockets of MDM2 were occupied by the substituted-phenyl linked at the pyrrolidone fragment, compound 4 h demonstrated good binding affinity with the MDM2. Additionally, compound 4 h also showed excellent antitumor activity and selectivity, and no cytotoxicity against normal cells in vitro. The further antitumor mechanism studies were indicated that compound 4 h could successfully induce the activation of p53 and corresponding downstream p21 proteins, thus successfully causing HCT116 cell cycle arrest in the G1/M phase and apoptosis. Thus, the novel unsaturated pyrrolidone p53-MDM2 inhibitors could be developed as novel antitumor agents.

A Multicomponent Protocol for the Synthesis of Highly Functionalized γ-Lactam Derivatives and Their Applications as Antiproliferative Agents

An efficient synthetic methodology for the preparation of 3-amino 1,5-dihydro-2H-pyrrol-2-ones through a multicomponent reaction of amines, aldehydes, and pyruvate derivatives is reported. In addition, the densely substituted lactam substrates show in vitro cytotoxicity, inhibiting the growth of carcinoma human tumor cell lines HEK293 (human embryonic kidney), MCF7 (human breast adenocarcinoma), HTB81 (human prostate carcinoma), HeLa (human epithelioid cervix carcinoma), RKO (human colon epithelial carcinoma), SKOV3 (human ovarian carcinoma), and A549 (carcinomic human alveolar basal epithelial cell). Given the possibilities in the diversity of the substituents that offer the multicomponent synthetic methodology, an extensive structure-activity profile is presented. In addition, both enantiomers of phosphonate-derived γ-lactam have been synthesized and isolated and a study of the cytotoxic activity of the racemic substrate vs. its two enantiomers is also presented. Cell morphology analysis and flow cytometry assays indicate that the main pathway by which our compounds induce cytotoxicity is based on the activation of the intracellular apoptotic mechanism.

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.

Photocatalytic Cyclization/Defluorination Domino Sequence to Access 3-Fluoro-1,5-dihydro-2H-pyrrol-2-one Scaffold

We herein report an unprecedented photoinduced cyclization/defluorination domino process of N-allylbromodifluoroacetamide with cyclic secondary amines. Consequently, a wide array of valuable 3-fluoro-1,5-dihydro-2H-pyrrol-2-ones were facilely prepared from readily available starting materials under mild conditions. Preliminary mechanistic investigations suggest that a radical chain propagation and amine-promoted defluorination pathway are presumably involved in this transformation.

Homo-PROTAC mediated suicide of MDM2 to treat non-small cell lung cancer

The dose-related adverse effects of MDM2‒P53 inhibitors have caused significant concern in the development of clinical safe anticancer agents. Herein we report an unprecedented homo-PROTAC strategy for more effective disruption of MDM2‒P53 interaction. The design concept is inspired by the capacity of sub-stoichiometric catalytic PROTACs enabling to degrade an unwanted protein and the dual functions of MDM2 as an E3 ubiquitin ligase and a binding protein with tumor suppressor P53. The new homo-PROTACs are designed to induce self-degradation of MDM2. The results of the investigation have shown that PROTAC 11a efficiently dimerizes MDM2 with highly competitive binding activity and induces proteasome-dependent self-degradation of MDM2 in A549 non-small cell lung cancer cells. Furthermore, markedly, enantiomer 11a-1 exhibits potent in vivo antitumor activity in A549 xenograft nude mouse model, which is the first example of homo-PROTAC with in vivo therapeutic potency. This study demonstrates the potential of the homo-PROTAC as an alternative chemical tool for tumorigenic MDM2 knockdown, which could be developed into a safe therapy for cancer treatment.

Photocatalytic intramolecular radical cyclization involved synergistic SET and HAT: synthesis of 3,3-difluoro-γ-lactams

A mild and metal-free protocol for visible-light induced intramolecular radical cyclization of N-allyl(propargyl)-2-bromo-2,2-difluoro-N-arylacetamide has been developed.

Discovery of dihydropyrrolidones as novel inhibitors against influenza A virus

More effective prophylactic and therapeutic strategies to combat influenza viruses are urgently required worldwide because the conventional anti-influenza drugs are facing drug resistance. Here, dihydropyrrolidones (DHPs), the products of an efficient multi-components reaction, were found to possess good activities against influenza A virus (IAV). Primary structure-activity relationship indicated that the activities of DHPs were greatly influenced by substituents and four of them had IC₅₀ values lower than 10 μM (DHPs 5-2, 8, 14 and 19: IC₅₀ = 3.11-9.23 μM). The activities against multiple IAV strains and mechanism of DHPs were further investigated by using 5-2 (IC₅₀ = 3.11 μM). It was found that 5-2 possessed antiviral effects against all the investigated subtypes of IAVs with the IC₅₀ values from 3.11 to 7.13 μM. Moreover, 5-2 showed very low cytotoxicity with CC₅₀ > 400 μM. Results of mechanism study indicated that 5-2 could efficiently inhibit replication of IAV, up-regulate the expression of key antiviral cytokines IFN-β and antiviral protein MxA, and suppress the production of the NDAPH oxidase NOX1 in MDCK cells. These results indicated that 5-2 could be used as a potential inhibitor against wide subtypes of IAVs.

p53: An Attractive Therapeutic Target for Cancer

Cancer is a leading cause of death worldwide. It initiates when cell cycle regulatory genes lose their function either by environmental and/or by internal factors. Tumor suppressor protein p53, known as "Guardian of genome", plays a central role in maintaining genomic stability of the cell. Mutation of TP53 is documented in more than 50% of human cancers, usually by overexpression of negative regulator protein MDM2. Hence, reactivation of p53 by blocking the protein-protein interaction between the murine double minute 2 (MDM2) and the tumor suppressor protein p53 has become the most promising therapeutic strategy in oncology. Several classes of small molecules have been identified as potent, selective and efficient p53-MDM2 inhibitors. Herein, we review the druggability of p53-MDM2 inhibitors and their optimization approaches as well as clinical candidates categorized by scaffold type.

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.

Recent Synthetic Approaches towards Small Molecule Reactivators of p53

The tumor suppressor protein p53 is often called "the genome guardian" and controls the cell cycle and the integrity of DNA, as well as other important cellular functions. Its main function is to trigger the process of apoptosis in tumor cells, and approximately 50% of all cancers are related to the inactivation of the p53 protein through mutations in the TP53 gene. Due to the association of mutant p53 with cancer therapy resistance, different forms of restoration of p53 have been subject of intense research in recent years. In this sense, this review focus on the main currently adopted approaches for activation and reactivation of p53 tumor suppressor function, focusing on the synthetic approaches that are involved in the development and preparation of such small molecules.

Discovery of Nonpeptide, Environmentally Sensitive Fluorescent Probes for Imaging p53-MDM2 Interactions in Living Cell Lines and Tissue Slice

Based on structural optimization work, probes 9-11 with practical activity and selectivity in tissue as well as living cell lines are well designed and synthesized. All the probes showed potent inhibitory and acceptable cell toxicity compared with the commercially available p53-MDM2 inhibitor Nutlin-3, and can increase the protein expression level of p53 and MDM2 in the A549 cell line; in particular, probes 10 and 11 can increase the protein expression level of p53 better than Nutlin-3. Moreover, their application in imaging and detecting wild-type p53-MDM2 protein-protein interactions have been well demonstrated in at the cell and tissue levels. Overall, these environmentally sensitive fluorescent turn-on probes are affordable and rapid for imaging, which is expected for applications in target drug screening as well as in pathologic diagnosis.

Regulator of G-protein signaling (RGS) proteins as drug targets: Progress and future potentials

G protein-coupled receptors (GPCRs) play critical roles in regulating processes such as cellular homeostasis, responses to stimuli, and cell signaling. Accordingly, GPCRs have long served as extraordinarily successful drug targets. It is therefore not surprising that the discovery in the mid-1990s of a family of proteins that regulate processes downstream of GPCRs generated great excitement in the field. This finding enhanced the understanding of these critical signaling pathways and provided potentially new targets for pharmacological intervention. These regulators of G-protein signaling (RGS) proteins were viewed by many as nodes downstream of GPCRs that could be targeted with small molecules to tune signaling processes. In this review, we provide a brief overview of the discovery of RGS proteins and of the gradual and continuing discovery of their roles in disease states, focusing particularly on cancer and neurological disorders. We also discuss high-throughput screening efforts that have led to the discovery first of peptide-based and then of small-molecule inhibitors targeting a subset of the RGS proteins. We explore the unique mechanisms of RGS inhibition these chemical tools have revealed and highlight the most up-to-date studies using these tools in animal experiments. Finally, we discuss the future opportunities in the field, as there are clearly more avenues left to be explored and potentials to be realized.

Direct Transformation of N-Protected α,β-Unsaturated γ-Amino Amides into γ-Lactams through a Base-Mediated Molecular Rearrangement

Here, we are reporting a single-step transformation of N-protected α,β-unsaturated γ-amino amides into 5,5-disubstituted γ-lactams through a base-mediated new molecular rearrangement. In contrast to the known N- to C(O) cyclization of saturated γ-amino acids into corresponding γ-lactams, the new rearrangement involves the cyclization between N-terminal C^γ- to C-terminal amide N. The cyclization process was initiated by the migration of double bond from α,β → β,γ position. The enamine-imine tautomerization of the new β,γ-double bond and subsequent 5-exo-trig cyclization of terminal amide leads to the formation of N-protected 5,5-disubstituted γ-lactam. The structures of various γ-lactams obtained from the rearrangement were studied in single crystals. Overall, the results reported here demonstrate the facile and single-step transformation of N-protected α,β-unsaturated γ-amino amides into γ-lactams and provided an excellent opportunity to construct small-molecule peptidomimetics.

Discovery of γ-lactam derivatives containing 1,3-benzodioxole unit as potential anti-phytopathogenic fungus agents

A series of γ-lactam analogs containing 1,3-benzodioxole moiety were designed, and these derivatives were synthesized from the lead compound of lactam via a structural diversity-oriented synthesis, their structures were confirmed by ¹HNMR,¹³CNMR, ESI-MS spectrum. Their antifungal activities were evaluated against four serious and typically crop-threatening agricultural fungi, including Rhizoctonia solani, Alternaria tenuis Nees, Gloeosporium theae-sinensis, and Fusarium graminearum. Some of these derivatives exhibited activity against Alternaria tenuis Nees higher than that of commercial fungicides carbendazim, such as compounds 7a, 7b, and 7i, compared with the blank control, some of these derivatives showed good antifungal activities against Gloeosporium theae-sinensis and Fusarium graminearum. The systematic study provides evidences for further structural modification and application of lactam analogues as antifungal agents for agriculture.

2,4,5-Tris(alkoxyaryl)imidazoline derivatives as potent scaffold for novel p53-MDM2 interaction inhibitors: Design, synthesis, and biological evaluation

Imidazoline-based small molecule inhibitors of p53-MDM2 interaction intended for the treatment of p53 wild-type tumors are the promising structures for design of anticancer drugs. Based on fragment approach we have investigated a key role of substituents in cis-imidazoline core for biological activity of nutlin family compounds. Although the necessity of the substituents in the phenyl rings of cis-imidazoline has been shown, there are no studies in which the replacements of a halogen by other substituents have been investigated. A series of simple cis-imidazoline derivatives containing halogen, hydroxy and alkoxy-substituents were synthesized. The biological activity of the compounds was studied using assays of cytotoxicity (MTT) and p53 level. It was found that the hydroxyl-derivatives were not cytotoxic whereas the alkoxy analogues were the same or more active as halogen-substituted compounds in cell viability test. The synthesized alkoxy derivatives induced an increase of p53 level and did not promote necrotic cell death in the concentration up to 40 µM.

A Brønsted Acid-Catalyzed Multicomponent Reaction for the Synthesis of Highly Functionalized γ-Lactam Derivatives

Brønsted acids catalyze a multicomponent reaction of benzaldehyde with amines and diethyl acetylenedicarboxylate to afford highly functionalized γ-lactam derivatives. The reaction consists of a Mannich reaction of an enamine to an imine, both generated in situ, promoted by a phosphoric acid catalyst and a subsequent intramolecular cyclization. The hydrolysis of the cyclic enamine substrate can provide enol derivatives and, moreover, a second attack of the amine on the carboxylate can afford amide derivatives. An optimization of the reaction conditions is presented in order to obtain selectively cyclic enamines that can afford the enol species after selective hydrolysis.

Design and synthesis of new substituted spirooxindoles as potential inhibitors of the MDM2-p53 interaction

The designed compounds, 4a-p, were synthesized using a simple and smooth method with an asymmetric 1,3-dipolar reaction as the key step. The chemical structures for all synthesized compounds were elucidated and confirmed by spectral analysis. The molecular complexity and the absolute stereochemistry of 4b and 4e designed analogs were determined by X-ray crystallographic analysis. The anticancer activities of the synthesized compounds were tested against colon (HCT-116), prostate (PC-3), and hepatocellular (HepG-2) cancer cell lines. Molecular modeling revealed that the compound 4d binds through hydrophobic-hydrophobic interactions with the essential amino acids (LEU: 57, GLY: 58, ILE: 61, and HIS: 96) in the p53-binding cleft, as a standard p53-MDM2 inhibitor (6SJ). The mechanism underlying the anticancer activity of compound 4d was further evaluated, and the study showed that compound 4d inhibited colony formation, cell migration, arrested cancer cell growth at G2/M, and induced apoptosis through intrinsic and extrinsic pathways. Transactivation of p53 was confirmed by flow cytometry, where compound 4d increased the level of activated p53 and induced mRNA levels of cell cycle inhibitor, p21.

Enantioselective synthesis of pyrano[2,3-c]pyrrole via an organocatalytic [4 + 2] cyclization reaction of dioxopyrrolidines and azlactones

The present work provides a simple and efficient access to chiral pyrano[2,3-c]pyrrole via an asymmetric [4 + 2] cyclization reaction catalyzed by a cinchona-squaramide catalyst.

Oxidative cross-dehydrogenative [2 + 3] annulation of α-amino ketones with α-keto esters: concise synthesis of clausenamide analogues

A one-pot oxidative cross-dehydrogenative [2 + 3] annulation of α-amino ketones with α-keto esters at room temperature is reported.

Synthesis of new thiazolo-pyrrolidine-(spirooxindole) tethered to 3-acylindole as anticancer agents

Anticancer therapeutics with profiles of high potency, low toxicity, and low resistance is of considerable interest. A new series of functionalized spirooxindole linked with 3-acylindole scaffold is reported, starting from chalcones derived from 3-acetyl indole with isatin, and l-4-thiazolidinecarboxylic acid. The reactions proceeded regioselectivity, stereoselectivity, without side products in high yield (71-89%). The new spirooxindole hybrids have been evaluated in vitro for their antiproliferative effects against colon cancer (HCT-116), hepatocellular carcinoma (HepG2) and prostate cancer (PC-3). The selectivity of their activity was evaluated. Some of the synthesized compounds showed considerable anticancer activities. Compound 4k proved to retain a high cytotoxic activity and selectivity against colon cancer cells HCT-116 (IC₅₀ = 7 ± 0.27 µM, SI: 3.7), and HepG2 (IC₅₀ = 5.5 ± 0.2 µM, SI: 4.7) in comparison to (IC₅₀ = 12.6 ± 0.5, SI: 0.4 and 5.5 ± 0.3 µM, SI: 0.9, respectively). Compound 4k was less active (IC₅₀ = 6 ± 0.3 µM, SI: 4.3) than cisplatin (IC₅₀ = 5 ± 0.56 µM, SI: 1.0) but showed greater selectivity towards prostate cancer cells PC-3 in comparison to cisplatin. The details of the binding mode of the active compounds were clarified by molecular docking. Ligand Efficiency (LE) and Ligand Lipophilic Efficiency (LLE) were evaluated and revealed that compound 4k had acceptable value.

Small Molecules Simultaneously Inhibiting p53-Murine Double Minute 2 (MDM2) Interaction and Histone Deacetylases (HDACs): Discovery of Novel Multitargeting Antitumor Agents

p53-Murine double minute 2 (MDM2) interaction and histone deacetylases (HDACs) are important targets in antitumor drug development. Inspired by the synergistic effects between MDM2 and HDACs, the first MDM2/HDACs dual inhibitors were identified, which showed excellent activities against both targets. In particular, compound 14d was proven to be a potent and orally active MDM2/HDAC dual inhibitor, whose antitumor mechanisms were validated in cancer cells. Compound 14d showed excellent in vivo antitumor potency in the A549 xenograft model, providing a promising lead compound for the development of novel antitumor agents. Also, this proof-of-concept study offers a novel and efficient strategy for multitargeting antitumor drug discovery.

Selective Synthesis of 3-Substituted Pyrrolidinones by Enol-Passerini and Anomalous Enol-Passerini Condensations

Enols are used for the first time in a condensation with aldehydes and isocyanides to selectively give three- or pseudo-four-component adducts, depending on the reaction conditions. These new transformations have proven to be a convenient alternative for the synthesis of biologically relevant pyrrolidinones containing peptidic or pseudo-peptidic groups on carbon 3. More importantly, this work attests to the utility of heterocyclic enols containing conjugated electron-withdrawing groups as useful reagents in isocyanide-based multicomponent reactions.

Highly enantioselective synthesis of fused bicyclic dihydropyranones via low-loading N-heterocyclic carbene organocatalysis

Highly diastereo and enantioselective [4+2] cycloadditions have been achieved between pyrrolidone-derived cyclic enones and α-haloaldehydes under mild conditions. Relying on extremely reactive in-situ generated chiral N-heterocyclic carbenes, this stereoselective annulation proceeds efficiently even on the gram scale with the catalyst loading as low as 0.025 mol% (250 ppm). A variety of cis-substituted bicyclic dihydropyranones can be produced in up to 96% yield with up to >99% ee. In addition, simple, inexpensive linear aldehydes such as n-propanal can be used directly in asymmetric cycloadditions via oxidative N-heterocyclic carbene organocatalysis with low catalyst loading. This method may provide an economical and practical approach for the asymmetric synthesis of medicinally relevant molecules.