A novel drug discovery strategy: mechanistic investigation of an enantiomeric antitumor agent targeting dual p53 and NF-κB pathways

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.

Molecular Hybridization-Inspired Optimization of Diarylbenzopyrimidines as HIV-1 Nonnucleoside Reverse Transcriptase Inhibitors with Improved Activity against K103N and E138K Mutants and Pharmacokinetic Profiles

Molecular hybridization is a powerful strategy in drug discovery. A series of novel diarylbenzopyrimidine (DABP) analogues were developed by the hybridization of FDA-approved drugs etravirine (ETR) and efavirenz (EFV) as potential HIV-1 nonnucleoside reverse transcriptase inhibitors (NNRTIs). Substituent modifications resulted in the identification of new DABPs with the combination of the strengths of the two drugs, especially compound 12d, which showed promising activity toward the EFV-resistant K103N mutant. 12d also had a favorable pharmacokinetic (PK) profile with liver microsome clearances of 14.4 μL/min/mg (human) and 33.2 μL/min/mg (rat) and an oral bioavailability of 15.5% in rat. However, its activity against the E138K mutant was still unsatisfactory; E138K is the most prevalent NNRTI resistance-associated mutant in ETR treatment. Further optimizations resulted in a highly potent compound (12z) with no substituents on the phenyl ring and a 2-methyl-6-nitro substitution pattern on the 4-cyanovinyl-2,6-disubstitued phenyl motif. The antiviral activity of this compound was much higher than those of ETR and EFV against the WT, E138K, and K103N variants (EC₅₀ = 3.4, 4.3, and 3.6 nM, respectively), and the cytotoxicity was decreased while the selectivity index (SI) was increased. In particular, this compound exhibited acceptable intrinsic liver microsome stability (human, 34.5 μL/min/mg; rat, 33.2 μL/min/mg) and maintained the good PK profile of its parent compound EFV and showed an oral bioavailability of 16.5% in rat. Molecular docking and structure-activity relationship (SAR) analysis provided further insights into the binding of the DABPs with HIV-1 reverse transcriptase and provided a deeper understanding of the key structural features responsible for their interactions.

p73 promotes glioblastoma cell invasion by directly activating POSTN (periostin) expression

Glioblastoma Multiforme is one of the most highly metastatic cancers and constitutes 70% of all gliomas. Despite aggressive treatments these tumours have an exceptionally bad prognosis, mainly due to therapy resistance and tumour recurrence. Here we show that the transcription factor p73 confers an invasive phenotype by directly activating expression of POSTN (periostin, HGNC:16953) in glioblastoma cells. Knock down of endogenous p73 reduces invasiveness and chemo-resistance, and promotes differentiation in vitro. Using chromatin immunoprecipitation and reporter assays we demonstrate that POSTN, an integrin binding protein that has recently been shown to play a major role in metastasis, is a transcriptional target of TAp73. We further show that POSTN overexpression is sufficient to rescue the invasive phenotype of glioblastoma cells after p73 knock down. Additionally, bioinformatics analysis revealed that an intact p73/POSTN axis, where POSTN and p73 expression is correlated, predicts bad prognosis in several cancer types. Taken together, our results support a novel role of TAp73 in controlling glioblastoma cell invasion by regulating the expression of the matricellular protein POSTN.

Rapid identification of dual p53-MDM2/MDMX interaction inhibitors through virtual screening and hit-based substructure search

A virtual screening method coupled with hit-based substructure search strategy was developed to identify dual inhibitors of the p53-MDM2/MDMX interactions and a series of novel scaffolds with moderate inhibitory activity were obtained.

Medicinal Chemistry Strategies to Disrupt the p53-MDM2/MDMX Interaction

The growth inhibitory activity of p53 tumor suppressor is tightly regulated by interaction with two negative regulatory proteins, murine double minute 2 (MDM2) and X (MDMX), which are overexpressed in about half of all human tumors. The elucidation of crystallographic structures of MDM2/MDMX complexes with p53 has been pivotal for the identification of several classes of inhibitors of the p53-MDM2/MDMX interaction. The present review provides in silico strategies and screening approaches used in drug discovery as well as an overview of the most relevant classes of small-molecule inhibitors of the p53-MDM2/MDMX interaction, their progress in pipeline, and highlights particularities of each class of inhibitors. Most of the progress made with high-throughput screening has led to the development of inhibitors belonging to the cis-imidazoline, piperidinone, and spiro-oxindole series. However, novel potent and selective classes of inhibitors of the p53-MDM2 interaction with promising antitumor activity are emerging. Even with the discovery of the 3D structure of complex p53-MDMX, only two small molecules were reported as selective p53-MDMX antagonists, WK298 and SJ-172550. Dual inhibition of the p53-MDM2/MDMX interaction has shown to be an alternative approach since it results in full activation of the p53-dependent pathway. The knowledge of structural requirements crucial to the development of small-molecule inhibitors of the p53-MDMs interactions has enabled the identification of novel antitumor agents with improved in vivo efficacy.

An inhibitor of the Keap1-Nrf2 protein-protein interaction protects NCM460 colonic cells and alleviates experimental colitis

Ulcerative colitis (UC) is a chronic relapsing-remitting form of inflammatory bowel disease (IBD) that increases the risk of colorectal cancer, the third most common malignancy in humans. Oxidative stress is a risk factor for the development of UC. The Keap1-Nrf2-ARE pathway is one of the most important defensive mechanisms against oxidative and/or electrophilic stresses. In this study, we identified CPUY192018 as a potent small-molecule inhibitor of the Keap1-Nrf2 PPI, investigated the cyto-protective effects of CPUY192018 on the NCM460 colonic cells and evaluated whether treatment with the inhibitor of the Keap1-Nrf2 PPI exerts protection on an established experimental model of UC induced by dextran sodium sulfate (DSS). Our study clearly demonstrated that CPUY192018 had a cytoprotective effect against DSS in both NCM460 cells and mouse colon via the activation of Nrf2 signaling. These results suggested that activation of Nrf2 by directly inhibiting the Keap1-Nrf2 PPI may be beneficial as a treatment for UC.

Chemical Variations on the p53 Reactivation Theme

Among the tumor suppressor genes, p53 is one of the most studied. It is widely regarded as the "guardian of the genome", playing a major role in carcinogenesis. In fact, direct inactivation of the TP53 gene occurs in more than 50% of malignancies, and in tumors that retain wild-type p53 status, its function is usually inactivated by overexpression of negative regulators (e.g., MDM2 and MDMX). Hence, restoring p53 function in cancer cells represents a valuable anticancer approach. In this review, we will present an updated overview of the most relevant small molecules developed to restore p53 function in cancer cells through inhibition of the p53-MDMs interaction, or direct targeting of wild-type p53 or mutated p53. In addition, optimization approaches used for the development of small molecules that have entered clinical trials will be presented.

A Novel Class of Small Molecule Compounds that Inhibit Hepatitis C Virus Infection by Targeting the Prohibitin-CRaf Pathway

Identification of novel drug targets and affordable therapeutic agents remains a high priority in the fight against chronic hepatitis C virus (HCV) infection. Here, we report that the cellular proteins prohibitin 1 (PHB1) and 2 (PHB2) are pan-genotypic HCV entry factors functioning at a post-binding step. While predominantly found in mitochondria, PHBs localize to the plasma membrane of hepatocytes through their transmembrane domains and interact with both EGFR and CRaf. Targeting PHB by rocaglamide (Roc-A), a natural product that binds PHB1 and 2, reduced cell surface PHB1 and 2, disrupted PHB-CRaf interaction, and inhibited HCV entry at low nanomolar concentrations. A structure-activity analysis of 32 synthetic Roc-A analogs indicated that the chiral, racemic version of aglaroxin C, a natural product biosynthetically related to Roc-A, displayed improved potency and therapeutic index against HCV infection. This study reveals a new class of HCV entry inhibitors that target the PHB1/2-CRaf pathway.

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Cellular proteins prohibitins 1 and 2 are essential HCV entry factors that function at a post-binding step.

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The natural compound Roc-A potently blocks HCV infection by disrupting prohibitins-CRaf interaction

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The Roc-A derivative, aglaroxin C, displays improved potency and therapeutic index towards HCV infection

Current FDA-approved HCV drugs all target viral proteins. We now demonstrate that a group of small molecules, the rocaglates, potently block HCV entry at low nanomolar concentrations. Roc-A inhibits HCV entry by disrupting the important interaction between two pan-genomic HCV entry factors, PHB1 and 2, and the signaling molecule CRaf. Overall, Roc-A and related rocaglates represent a new class of compounds that hold significant therapeutic promise in treating HCV infection.

State-of-the-art strategies for targeting protein-protein interactions by small-molecule inhibitors

Targeting protein-protein interactions (PPIs) has emerged as a viable approach in modern drug discovery. However, the identification of small molecules enabling us to effectively interrupt their interactions presents significant challenges. In the recent past, significant advances have been made in the development of new biological and chemical strategies to facilitate the discovery process of small-molecule PPI inhibitors. This review aims to highlight the state-of-the-art technologies and the achievements made recently in this field. The "hot spots" of PPIs have been proved to be critical for small molecules to bind. Three strategies including screening, designing, and synthetic approaches have been explored for discovering PPI inhibitors by targeting the "hot spots". Although the classic high throughput screening approach can be used, fragment screening, fragment-based drug design and newly improved virtual screening are demonstrated to be more effective in the discovery of PPI inhibitors. In addition to screening approaches, design strategies including anchor-based and small molecule mimetics of secondary structures involved in PPIs have become powerful tools as well. Finally, constructing new chemically spaced libraries with high diversity and complexity is becoming an important area of interest for PPI inhibitors. The successful cases from the recent five year studies are used to illustrate how these approaches are implemented to uncover and optimize small molecule PPI inhibitors and notably some of them have become promising therapeutics.