Natural products targeting the p53-MDM2 pathway and mutant p53: Recent advances and implications in cancer medicine

Blockade of IGF/IGF-1R signaling axis with soluble IGF-1R mutants suppresses the cell proliferation and tumor growth of human osteosarcoma

Primary bone tumor, also known as osteosarcoma (OS), is the most common primary malignancy of bone in children and young adults. Current treatment protocols yield a 5-year survival rate of near 70% although approximately 80% of patients have metastatic disease at the time of diagnosis. However, long-term survival rates have remained virtually unchanged for nearly four decades, largely due to our limited understanding of the disease process. One major signaling pathway that has been implicated in human OS tumorigenesis is the insulin-like growth factor (IGF)/insulin-like growth factor-1 receptor (IGF1R) signaling axis. IGF1R is a heterotetrameric α2β2 receptor, in which the α subunits comprise the ligand binding site, whereas the β subunits are transmembrane proteins containing intracellular tyrosine kinase domains. Although numerous strategies have been devised to target IGF/IGF1R axis, most of them have failed in clinical trials due to the lack of specificity and/or limited efficacy. Here, we investigated whether a more effective and specific blockade of IGF1R activity in human OS cells can be accomplished by employing dominant-negative IGF1R (dnIGF1R) mutants. We engineered the recombinant adenoviruses expressing two IGF1R mutants derived from the α (aa 1-524) and β (aa 741-936) subunits, and found that either dnIGF1Rα and/or dnIGF1Rβ effectively inhibited cell migration, colony formation, and cell cycle progression of human OS cells, which could be reversed by exogenous IGF1. Furthermore, dnIGF1Rα and/or dnIGF1Rβ inhibited OS xenograft tumor growth in vivo, with the greatest inhibition of tumor growth shown by dnIGF1Rα. Mechanistically, the dnIGF1R mutants down-regulated the expression of PI3K/AKT and RAS/RAF/MAPK, BCL2, Cyclin D1 and most EMT regulators, while up-regulating pro-apoptotic genes in human OS cells. Collectively, these findings strongly suggest that the dnIGF1R mutants, especially dnIGF1Rα, may be further developed as novel anticancer agents that target IGF signaling axis with high specificity and efficacy.

Targeting the p53-MDM2 pathway for neuroblastoma therapy: Rays of hope

Despite being the subject of extensive research and clinical trials, neuroblastoma remains a major therapeutic challenge in pediatric oncology. The p53 protein is a central safeguard that protects cells against genome instability and malignant transformation. Mutated TP53 (the gene encoding p53) is implicated in many human cancers, but the majority of neuroblastomas have wild type p53 with intact transcriptional function. In fact, the TP53 mutation rate does not exceed 1-2% in neuroblastomas. However, overexpression of the murine double minute 2 (MDM2) gene in neuroblastoma is relatively common, and leads to inhibition of p53. It is also associated with other non-canonical p53-independent functions, including drug resistance and increased translation of MYCN and VEGF mRNA. The p53-MDM2 pathway in neuroblastoma is also modulated at several different molecular levels, including via interactions with other proteins (MYCN, p14^ARF). In addition, the overexpression of MDM2 in tumors is linked to a poorer prognosis for cancer patients. Thus, restoring p53 function by inhibiting its interaction with MDM2 is a potential therapeutic strategy for neuroblastoma. A number of p53-MDM2 antagonists have been designed and studied for this purpose. This review summarizes the current understanding of p53 biology and the p53-dependent and -independent oncogenic functions of MDM2 in neuroblastoma, and also the regulation of the p53-MDM2 axis in neuroblastoma. This review also highlights the use of MDM2 as a molecular target for the disease, and describes the MDM2 inhibitors currently being investigated in preclinical and clinical studies. We also briefly explain the various strategies that have been used and future directions to take in the development of effective MDM2 inhibitors for neuroblastoma.

The E2 ubiquitin-conjugating enzyme UbcH5c: an emerging target in cancer and immune disorders

Ubiquitination is a crucial post-translational modification (PTM) of proteins and regulates their stabilities and activities, thereby modulating multiple signaling pathways. UbcH5c, a member of the UbcH5 ubiquitin-conjugating enzyme (E2) protein family, engages in the ubiquitination of dozens of proteins and regulates nuclear factor kappa-B (NF-κB), p53 tumor suppressor, and several other essential signaling pathways. UbcH5c has been reported to be abnormally expressed in human cancer and immune disorders and is involved in the initiation and progression of these diseases. In this review, we mainly focus on UbcH5c structure, activity, signaling pathways, and its relevance to cancer and immune disorders. We end by integrating all known factors relating to UbcH5c inhibition as a potential cancer therapy method, and discuss associated challenges.

Targeting MDMX for Cancer Therapy: Rationale, Strategies, and Challenges

The oncogene MDMX, also known as MDM4 is a critical negative regulator of the tumor suppressor p53 and has been implicated in the initiation and progression of human cancers. Increasing evidence indicates that MDMX is often amplified and highly expressed in human cancers, promotes cancer cell growth, and inhibits apoptosis by dampening p53-mediated transcription of its target genes. Inhibiting MDMX-p53 interaction has been found to be effective for restoring the tumor suppressor activity of p53. Therefore, MDMX is becoming one of the most promising molecular targets for developing anticancer therapeutics. In the present review, we mainly focus on the current MDMX-targeting strategies and known MDMX inhibitors, as well as their mechanisms of action and in vitro and in vivo anticancer activities. We also propose other potential targeting strategies for developing more specific and effective MDMX inhibitors for cancer therapy.

Targeting IFN/STAT1 Pathway as a Promising Strategy to Overcome Radioresistance

The interferon (IFN)-mediated activation of the Janus kinase (JAK)-signal transducer and activator of transcription 1 (STAT1) signaling is crucial for cell sensitivity to ionizing radiation. Several preclinical studies have reported that the IFN/STAT1 pathway mediates radioresistance in the tumor microenvironment by shielding the immune responses and activating survival signaling pathways. This review focuses on the oncogenic function of the IFN/STAT1 pathway, emphasizing the major signaling pathway in radiation sensitization. Furthermore, it highlights the possibility of mediatory roles of the IFN/STAT1 pathway as a prognostic therapeutic target in the modulation of resistance to radiotherapy and chemotherapy. MicroRNA involved in the regulation of the IFN/STAT1 pathway is also discussed. A better understanding of radiation-induced IFN/STAT1 signaling will open new opportunities for the development of novel therapeutic strategies, as well as define new approaches to enhance radio-immunotherapy efficacy in the treatment of various types of cancers.

Creating and screening natural product libraries

Covering: up to 2020The National Cancer Institute of the United States (NCI) has initiated a Cancer Moonshot program entitled the NCI Program for Natural Product Discovery. As part of this effort, the NCI is producing a library of 1 000 000 partially purified natural product fractions which are being plated into 384-well plates and provided to the research community free of charge. As the first 326 000 of these fractions have now been made available, this review seeks to describe the general methods used to collect organisms, extract those organisms, and create a prefractionated library. Importantly, this review also details both cell-based and cell-free bioassay methods and the adaptations necessary to those methods to productively screen natural product libraries. Finally, this review briefly describes post-screen dereplication and compound purification and scale up procedures which can efficiently identify active compounds and produce sufficient quantities of natural products for further pre-clinical development.

Targeting β-Catenin Signaling by Natural Products for Cancer Prevention and Therapy

The mutations and deregulation of Wnt signaling pathway occur commonly in human cancer and cause the aberrant activation of β-catenin and β-catenin-dependent transcription, thus contributing to cancer development and progression. Therefore, β-catenin has been demonstrated as a promising target for cancer prevention and therapy. Many natural products have been characterized as inhibitors of the β-catenin signaling through down-regulating β-catenin expression, modulating its phosphorylation, promoting its ubiquitination and proteasomal degradation, inhibiting its nuclear translocation, or other molecular mechanisms. These natural product inhibitors have shown preventive and therapeutic efficacy in various cancer models in vitro and in vivo. In the present review, we comprehensively discuss the natural product β-catenin inhibitors, their in vitro and in vivo anticancer activities, and underlying molecular mechanisms. We also discuss the current β-catenin-targeting strategies and other potential strategies that may be examined for identifying new β-catenin inhibitors as cancer preventive and therapeutic drugs.

Serum anti-p53 autoantibodies in angiosarcoma

There is no biomarker for detecting the status of angiosarcoma patients. Studies have reported that serum anti-p53 antibody (Ab) levels are often high in patients with various types of malignant tumors, suggesting the potential use of this Ab as a biomarker for various tumors, including angiosarcoma. The aim of this study was to assess the usefulness of serum anti-p53 Ab as a potent angiosarcoma biomarker. Nineteen angiosarcoma patients were included. All patients had histologically been diagnosed with cutaneous angiosarcoma. We compared p53 protein expression and serum p53 Ab levels between angiosarcoma in the scalp patients (n = 19) and normal controls (n = 30). We evaluated Ab levels before and after therapy. Increased p53 expression was detected in angiosarcoma skin tissues compared with that observed in normal skin tissues. We evaluated serum from angiosarcoma patients and controls for the presence of the anti-p53 Ab. Serum anti-p53 Ab levels were significantly higher in angiosarcoma patients than in controls．Serum anti-p53 Ab levels of patients who showed disease progression after therapy increased in correlation with the medical condition. The Ab levels of three patients, who showed partial response after therapy, decreased in correlation with the medical condition. The Ab levels of the other three patients were low at all time points. Anti-p53 Ab levels were significantly higher in angiosarcoma patients than in the controls. We demonstrated that serum anti-p53 Ab levels would reflect the clinical course of angiosarcoma patients, suggesting that serum anti-p53 Ab can be a potent diagnostic and prognostic biomarker of angiosarcoma.

Targeting USP7-Mediated Deubiquitination of MDM2/MDMX-p53 Pathway for Cancer Therapy: Are We There Yet?

The p53 tumor suppressor protein and its major negative regulators MDM2 and MDMX oncoproteins form the MDM2/MDMX-p53 circuitry, which plays critical roles in regulating cancer cell growth, proliferation, cell cycle progression, apoptosis, senescence, angiogenesis, and immune response. Recent studies have shown that the stabilities of p53, MDM2, and MDMX are tightly controlled by the ubiquitin-proteasome system. Ubiquitin specific protease 7 (USP7), one of the most studied deubiquitinating enzymes plays a crucial role in protecting MDM2 and MDMX from ubiquitination-mediated proteasomal degradation. USP7 is overexpressed in human cancers and contributes to cancer initiation and progression. USP7 inhibition promotes the degradation of MDM2 and MDMX, activates the p53 signaling, and causes cell cycle arrest and apoptosis, making USP7 a potential target for cancer therapy. Several small-molecule inhibitors of USP7 have been developed and shown promising efficacy in preclinical settings. In the present review, we focus on recent advances in the understanding of the USP7-MDM2/MDMX-p53 network in human cancers as well as the discovery and development of USP7 inhibitors for cancer therapy.

A Novel BCL-2 Inhibitor APG-2575 Exerts Synthetic Lethality With BTK or MDM2-p53 Inhibitor in Diffuse Large B-Cell Lymphoma

Despite therapeutic advances, the effective treatment for relapsed or refractory diffuse large B-cell lymphoma (DLBCL) remains a major clinical challenge. Evasion of apoptosis through upregulating antiapoptotic B-cell lymphoma-2 (BCL-2) family members and p53 inactivation, and abnormal activation of B-cell receptor signaling pathway are two important pathogenic factors for DLBCL. In this study, our aim is to explore a rational combination of BCL-2 inhibitor plus Bruton’s tyrosine kinase (BTK) blockade or p53 activation for treating DLBCL with the above characteristics. We demonstrated that a novel BCL-2 selective inhibitor APG-2575 effectively suppressed DLBCL with BCL-2 high expression via activating the mitochondrial apoptosis pathway. BTK inhibitor ibrutinib combined with BCL-2 inhibitors showed synergistic antitumor effect in DLBCL with mean expression of BCL-2 and myeloid cell leukemia-1 (MCL-1) through upregulating the expression level of BIM and modulating MCL-1 and p-Akt expression. For p53 wild-type DLBCL with high expression of BCL-2, APG-2575 showed strong synergic effect with mouse double minute 2 (MDM2)–p53 inhibitor APG-115 that can achieve potent antitumor effect and markedly prolong survival in animal models. Collectively, our data provide an effective and precise therapeutic strategy through rational combination of BCL-2 and BTK or MDM2–p53 inhibitors for DLBCL, which deserves further clinical investigation.

Medicinal chemistry strategies to discover P-glycoprotein inhibitors: An update

The presence of multidrug resistance (MDR) in malignant tumors is one of the primary causes of treatment failure in cancer chemotherapy. The overexpression of the ATP binding cassette (ABC) transporter, P-glycoprotein (P-gp), which significantly increases the efflux of certain anticancer drugs from tumor cells, produces MDR. Therefore, inhibition of P-gp may represent a viable therapeutic strategy to overcome cancer MDR. Over the past 4 decades, many compounds with P-gp inhibitory efficacy (referred to as first- and second-generation P-gp inhibitors) have been identified or synthesized. However, these compounds were not successful in clinical trials due to a lack of efficacy and/or untoward toxicity. Subsequently, third- and fourth-generation P-gp inhibitors were developed but dedicated clinical trials did not indicate a significant therapeutic effect. In recent years, an extraordinary array of highly potent, selective, and low-toxicity P-gp inhibitors have been reported. Herein, we provide a comprehensive review of the synthetic and natural products that have specific inhibitory activity on P-gp drug efflux as well as promising chemosensitizing efficacy in MDR cancer cells. The present review focuses primarily on the structural features, design strategies, and structure-activity relationships (SAR) of these compounds.

A balancing act: using small molecules for therapeutic intervention of the p53 pathway in cancer

Small molecules targeting various aspects of the p53 protein pathway have shown significant promise in the treatment of a number of cancer types.

Targeting MDM2 for novel molecular therapy: Beyond oncology

The murine double minute 2 (MDM2) oncogene exerts major oncogenic activities in human cancers; it is not only the best-documented negative regulator of the p53 tumor suppressor, but also exerts p53-independent activities. There is an increasing interest in developing MDM2-based targeted therapies. Several classes of MDM2 inhibitors have been evaluated in preclinical models, with a few entering clinical trials, mainly for cancer therapy. However, noncarcinogenic roles for MDM2 have also been identified, demonstrating that MDM2 is involved in many chronic diseases and conditions such as inflammation and autoimmune diseases, dementia and neurodegenerative diseases, heart failure and cardiovascular diseases, nephropathy, diabetes, obesity, and sterility. MDM2 inhibitors have been shown to have promising therapeutic efficacy for treating inflammation and other nonmalignant diseases in preclinical evaluations. Therefore, targeting MDM2 may represent a promising approach for treating and preventing these nonmalignant diseases. In addition, a better understanding of how MDM2 works in nonmalignant diseases may provide new biomarkers for their diagnosis, prognostic prediction, and monitoring of therapeutic outcome. In this review article, we pay special attention to the recent findings related to the roles of MDM2 in the pathogenesis of several nonmalignant diseases, the therapeutic potential of its downregulation or inhibition, and its use as a biomarker.

Alantolactone enhances gemcitabine sensitivity of lung cancer cells through the reactive oxygen species-mediated endoplasmic reticulum stress and Akt/GSK3β pathway

Lung cancer is one of the leading causes of cancer‑associated mortality in China and globally. Gemcitabine (GEM), as a first‑line therapeutic drug, has been used to treat lung cancer, but GEM resistance poses a major limitation on the efficacy of GEM chemotherapy. Alantolactone (ALT), a sesquiterpene lactone compound isolated from Inula helenium, has been identified to exert anticancer activity in various types of cancer, including breast, pancreatic, lung squamous and colorectal cancer. However, the underlying mechanisms of the anticancer activity of ALT in lung cancer remain to be fully elucidated. The present study aimed to determine whether ALT enhances the anticancer efficacy of GEM in lung cancer cells and investigated the underlying mechanisms. The cell viability was assessed with a Cell Counting Kit‑8 assay. The cell cycle, apoptosis and the level of reactive oxygen species (ROS) were assessed by flow cytometry, and the expression of cell cycle‑associated and apoptosis‑associated proteins were determined by western blot analysis. The results demonstrated that ALT inhibited cell growth and induced S‑phase arrest and cell apoptosis in A549 and NCI‑H520 cells. Furthermore, ALT increased the level of ROS, inhibited the Akt/glycogen synthase kinase (GSK)3β pathway and induced endoplasmic reticulum (ER) stress in A549 and NCI‑H520 cells. Additionally, ALT treatment sensitized lung cancer cells to GEM. Analysis of the molecular mechanisms further revealed that ALT enhanced the anticancer effects of GEM via ROS‑mediated activation of the Akt/GSK3β and ER stress pathways. In conclusion, combined treatment with ALT and GEM may have potential as a clinical strategy for lung cancer treatment.

MDM2 inhibitor RG7388 potently inhibits tumors by activating p53 pathway in nasopharyngeal carcinoma

Nasopharyngeal carcinoma (NPC) is a high-risk head and neck cancer with poor clinical outcomes and insufficient treatments. The mouse double minute 2 homolog (MDM2) is the main molecular target in the clinical treatment of cancer. Indeed, MDM2 negatively regulates p53 through ubiquitin-dependent degradation. Thus, inhibition of MDM2-p53 interaction is a potential strategy for treating NPC. The latest generation MDM2 inhibitor, RG7388, shows increased potency and improved bioavailability compared to previous treatments. In this study, we investigated the efficacy and specificity of this inhibitor in NPC cell lines, and tumor-bearing mice were used to examine the therapeutic efficacy and effects of RG7388 treatment. The results showed that RG7388 potently decreased cell proliferation and activated p53-dependent pathway, resulting in cell cycle arrest and apoptosis. RG7388 significantly inhibited tumors in tumor-bearing mice. Activation of the p53 pathway-inhibited cell proliferation, as observed by detecting Ki67-positive cells. Additionally, the activity of apoptotic caspase family proteins was induced in the cleaved caspase-3-positive cells in vivo. Our results demonstrate that the MDM2 small-molecule inhibitor RG7388 is effective for NPC tumors, supporting further clinical investigation as a potential therapy for NPC.

ROS -mediated p53 activation by juglone enhances apoptosis and autophagy in vivo and in vitro

Juglone (JG) exhibits a broad-spectrum of cytotoxicity against some cancer cells. However, its molecular mechanisms have not been investigated well. Here, the present results showed that JG significantly inhibited tumor growth in vivo. CCK-8 assays, flow cytometric analysis, western blotting and immunohistochemistry revealed that JG effectively inhibited cell proliferation and induced apoptosis through extrinsic pathways. We also observed that JG treatment induced autophagy flux via activiting the AMPK-mTOR signaling pathway. In addition, we found that JG enhanced p53 activation by increasing down-regulation of ubiquitin-mediated degradation. Inhibition of p53 by siRNA attenuated JG-induced cell death and autophagy. Moreover, JG enhanced the generation of hydrogen peroxide (H₂O₂) and superoxide anion radical (O₂^{• -}). Further experiments proved that H₂O₂ was a major factor since the H₂O₂ scavenger catalase (CAT) reduced both autophagy and cell death to a greater extent than the O₂^{• -} scavenger SOD. Overall, our results illustrated that JG caused apoptosis and autophagy via activating the ROS-mediated p53 pathway in human liver cancer cells in vitro and in vivo, which provided basic scientific evidence that JG serves as a potential anti-cancer agent.

Dual Effects of Chinese Herbal Medicines on Angiogenesis in Cancer and Ischemic Stroke Treatments: Role of HIF-1 Network

Hypoxia-inducible factor-1 (HIF-1)–induced angiogenesis has been involved in numerous pathological conditions, and it may be harmful or beneficial depending on the types of diseases. Exploration on angiogenesis has sparked hopes in providing novel therapeutic approaches on multiple diseases with high mortality rates, such as cancer and ischemic stroke. The HIF-1 pathway is considered to be a major regulator of angiogenesis. HIF-1 seems to be involved in the vascular formation process by synergistic correlations with other proangiogenic factors in cancer and cerebrovascular disease. The regulation of HIF-1–dependent angiogenesis is related to the modulation of HIF-1 bioactivity by regulating HIF-1α transcription or protein translation, HIF-1α DNA binding, HIF-1α and HIF-1α dimerization, and HIF-1 degradation. Traditional Chinese herbal medicines have a long history of clinical use in both cancer and stroke treatments in Asia. Growing evidence has demonstrated potential proangiogenic benefits of Chinese herbal medicines in ischemic stroke, whereas tumor angiogenesis could be inhibited by the active components in Chinese herbal medicines. The objective of this review is to provide comprehensive insight on the effects of Chinese herbal medicines on angiogenesis by regulating HIF-1 pathways in both cancer and ischemic stroke.

Discussion on action mechanism of traditional Chinese medicine on chronic atrophic gastritis from the perspective of gene regulation

At present, research on tumor genes related to chronic atrophic gastritis (CAG), a form of precancerous lesion of gastric cancer, has become a hot topic. In this paper, we discuss the mechanism of action of traditional Chinese medicine treatment on CAG from the aspects of protooncogenes, tumor suppressor genes, and apoptosis-related genes, with an aim to provide new ideas for clinical treatment and prevention of CAG.

Anticancer activity and mechanism of total saponins from the residual seed cake of Camellia oleifera Abel. in hepatoma-22 tumor-bearing mice

Total saponins from the residual seed cake of Camellia oleifera Abel. exhibited beneficial properties on anticancer activity in hepatoma-22 tumor-bearing mice and represents a promising species for food applications.