Nutlin-3, an Antagonist of MDM2, Enhances the Radiosensitivity of Esophageal Squamous Cancer with Wild-Type p53

p52-ZER6: a determinant of tumor cell sensitivity to MDM2-p53 binding inhibitors

Targeting MDM2-p53 interaction has emerged as a promising antitumor therapeutic strategy. Several MDM2-p53 inhibitors have advanced into clinical trials, but results are not favorable. The lack of appropriate biomarkers for selecting patients has been assumed as the critical reason for this failure. We previously identified ZER6 isoform p52-ZER6 as an oncogene upregulated in tumor tissues. In this study we investigated whether p52-ZER6 acted as a blocker of MDM2-p53 binding inhibitors, and whether p52-ZER6 could be used as a biomarker of MDM2-p53 binding inhibitors. In p53 wild-type colorectal carcinoma HCT116, hepatocarcinoma HepG2 and breast cancer MCF-7 cells, overexpression of p52-ZER6 enhanced MDM2-p53 binding and promoted p53 ubiquitination/proteasomal degradation. Furthermore, overexpression of p52-ZER6 in the tumor cells dose-dependently reduced their sensitivity to both nutlin and non-nutlin class MDM2-p53 binding inhibitors. We showed that p52-ZER6 restored tumor cell viability, which was suppressed by nutlin-3, through restoring their proliferation potential while suppressing their apoptotic rate, suggesting that MDM2-p53 binding inhibitors might not be effective for patients with high p52-ZER6 levels. We found that nutlin-3 treatment or p52-ZER6 knockdown alone promoted the accumulation of p53 protein in the tumor cells, and their combinatorial treatment significantly increased the accumulation of p53 protein. In HCT116 cell xenograft nude mouse model, administration of shp52-ZER6 combined with an MDM2-p53 binding inhibitor nutlin-3 exerted synergistic antitumor response. In conclusion, this study reveals that p52-ZER6 might be a potential biomarker for determining patients appropriate for MDM2-p53 binding inhibition-based antitumor therapy, and demonstrates the potential of combinatorial therapy using MDM2-p53 binding inhibitors and p52-ZER6 inhibition.

Nutlin-3 acts as a DNA methyltransferase inhibitor to sensitize esophageal cancer to chemoradiation

Esophageal squamous cell carcinoma (ESCC) is highly resistant to chemoradiation therapy. We aimed to examine whether Nutlin-3, a molecule that suppresses murine double min 2 (MDM2)-mediated p53 and Retinoblastoma (RB) protein degradation leading to downregulation of DNA methyltransferases (DNMTs), can be a novel therapeutic agent for ESCC. We used wild-type and chemoradiation-resistant ESCC cell lines in this study. The expression of DNMTs, p53 and RB, and methylation level of tumor suppressor genes (TSG) were analyzed upon Nutlin-3 treatment. The antitumor efficacy of Nutlin-3 was investigated in ESCC cell lines and xenograft tumor model. TSG protein expression was checked in the excised tumor tissue. Nutlin-3 induced upregulation of p53 and RB and downregulation of DNMTs proteins in the chemoradiation-resistant and aggressive ESCC cells. The methylation level of TSGs was decreased by Nutlin-3. Nutlin-3 inhibits clonogenic growth of ESCC cells and exerts a synergistic cytotoxic-effect when combined with chemotherapeutic agent cisplatin. Moreover, xenograft tumor growth in SCID mice was suppressed by Nutlin-3. The protein expression level of DNMTs was downregulated, and that of TSGs was upregulated by Nutlin-3 treatment in the excised tumor tissue. In conclusion, Nutlin-3 is a potential therapeutic agent that can potentiate the treatment efficacy of chemoradiation-resistant ESCC.

A strategy for the treatment of gastrointestinal cancer: Targeting tumor senescent cells

Gastrointestinal (GI) cancer includes a variety of cancers with high incidence that seriously threaten the lives of people worldwide. Although treatment strategies continue to improve, patient benefits are still very limited, and the ongoing search for new treatment strategies remains a priority. Cell senescence is closely related to the occurrence and development of tumors. For GI cancer, cell senescence may not only promote cancer but also bring new opportunities for treatment. Combined with relevant studies, we review the dual role of cell senescence in GI cancer, including the mechanism of inducing cell senescence, biomarkers of senescent cells, and potential of targeted senescence therapy for GI cancer.

Role of p53 in Regulating Radiation Responses

p53 is known as the guardian of the genome and plays various roles in DNA damage and cancer suppression. The p53 gene was found to express multiple p53 splice variants (isoforms) in a physiological, tissue-dependent manner. The various genes that up- and down-regulated p53 are involved in cell viability, senescence, inflammation, and carcinogenesis. Moreover, p53 affects the radioadaptive response. Given that several studies have already been published on p53, this review presents its role in the response to gamma irradiation by interacting with MDM2, NF-κB, and miRNA, as well as in the inflammation processes, senescence, carcinogenesis, and radiation adaptive responses. Finally, the potential of p53 as a biomarker is discussed.

Downregulation of Long Noncoding RNA CRYBG3 Enhances Radiosensitivity in Non-Small Cell Lung Cancer Depending on p53 Status

Non-small cell lung cancer (NSCLC) is the most common type of lung cancer with high recurrence and metastasis rates, and more than half of the patients diagnosed with NSCLC receive local radiotherapy. However, the intrinsic radio-resistance of cancer cells is a major barrier to effective radiotherapy for NSCLC. CRYBG3 is a long noncoding RNA (lncRNA) that was originally identified to be upregulated in NSCLC and enhanced metastasis of NSCLC cells by interacting with eEF1A1 to promote murine double minute 2 (MDM2) expression. The aims of this study were to reveal the contribution of CRYBG3 to the radioresistance of NSCLC and determine whether that is associated with MDM2-p53 pathway. Therefore, CRYBG3 was stably downregulated in A549 (wild-type p53) and H1299 (deficient p53) cells by infecting short hairpin RNA (shRNA) lentiviral particles. The results showed that downregulation of CRYBG3 increased DNA damage, enhanced apoptosis and pro-apoptotic protein expression in A549 or p53-overexpressed H1299 cells but not in H1299 or p53-silenced A549 cells after X-ray irradiation. However, the contribution of CRYBG3 to radioresistance was abolished by eEF1A1 or MDM2 knockdown in A549 cells. Thus, we concluded that downregulation of CRYBG3 enhanced radiosensitivity by reducing MDM2 expression then leading to decreased MDM2-mediated degradation of p53 in wild-type p53 expressing NSCLC cells. These findings suggested that CRYBG3 can be a potential target for therapeutic intervention of certain lung cancer subtypes.

A Radioresponse-Related lncRNA Biomarker Signature for Risk Classification and Prognosis Prediction in Non-Small-Cell Lung Cancer

Purpose

Radiotherapy resistance is now recognized as the major obstacle to the effective therapeutic management of non-small-cell lung cancer (NSCLC). As a single biomarker has limited effect in stratifying NSCLC patients, this research aimed to identify long non-coding RNAs (lncRNAs) correlated with radiotherapy response to ameliorate forecast of NSCLC prognosis.

Methods

In a cohort of NSCLC patients with radiotherapy history (n = 96) from TCGA, genetic data of lncRNA expression profiling were performed. To identify radioresponse-related lncRNA sets which dysregulated significantly between radiosensitive (RS) and radioresistant (RR) groups, differential expression analysis was carried out. Cox relative regression was implemented to set up a radioresponse-related risk model. Moreover, we adopted survival analysis to measure the predictive potentiality of the prognosis model.

Results

Four radioresponse-related lncRNAs (CASC19, LINC01977, LINC02471, and MAGI2-AS3) were screened to create a prognostic signature. Then, we described a lncRNA signature-based regulatory network and explored the correlation of the immune microenvironment and the signature. Additionally, in vitro assays uncovered inhibition of LINC01977 weakened radioresistance of NSCLC cells.

Conclusion

We provided a novel radioresponse-related lncRNAs signature with excellent clinical potency for an effective prognostic forecast of patients.

miR-498 inhibits autophagy and M2-like polarization of tumor-associated macrophages in esophageal cancer via MDM2/ATF3

Structured abstract Aim: To elucidate the effect of miRNA (miR)-498 on autophagy and M2-like macrophage polarization in esophageal cancer. Methods: Autophagy was evaluated in esophageal cancer. Macrophage markers specific for M1- or M2-like phenotype were determined. The binding relationships between miR-498 and MDM2, MDM2 and ATF3 were analyzed. Results: miR-498 was downregulated in esophageal cancer and was associated with disease-free and overall patient survival. Enhanced miR-498 reduced LC3I conversion to LC3II and increased p62 accumulation in KYSE-150 cells, and increased macrophage polarization to M2-like phenotype in KYSE-150 and TAM co-culture. miR-498 inhibited MDM2-mediated ATF3 degradation, thus suppressing autophagy and M2-like polarization of macrophages in esophageal cancer. Conclusion: miR-498 may inhibit autophagy and M2-like polarization of macrophages to suppress esophageal cancer via MDM2/ATF3.

Therapeutic potential of p53 reactivation in cervical cancer

Cervical cancer (CC) is one of most common malignancies affecting women worldwide. To date, surgical resection is the only effective radical remedy for CC at its early stages, while the prognosis of metastatic or recurrent CC is very poor. Dysfunction of the tumor suppressor p53 due to aberrant expression, post-translational modification, mutations, SNPs, and LOH as well as sequestration by viral antigens and MDM2/HDM2-mediated degradation is closely associated with the therapeutic insensitivity and relapse of many malignancies, including CC. Accumulating studies have demonstrated that restoration of p53 activity can induce cell cycle arrest and apoptosis, eliminate radio- and chemotherapy resistance, and inhibit tumor growth in CC cells. Therefore, activation of wild-type p53 as well as restoration of p53 function seems appealing as a therapeutic strategy. In this review, we focus on the potential roles of p53 reactivation in CC treatment and their underlying molecular mechanisms towards the development of novel therapies.

Multifaceted behavior of PEST sequence enriched nuclear proteins in cancer biology and role in gene therapy

The amino acid sequence enriched with proline (P), glutamic acid (E), serine (S), and threonine (T) (PEST) is a signal-transducing agent providing unique features to its substrate nuclear proteins (PEST-NPs). The PEST motif is responsible for particular posttranslational modifications (PTMs). These PTMs impart distinct properties to PEST-NPs that are responsible for their activation/inhibition, intracellular localization, and stability/degradation. PEST-NPs participate in cancer metabolism, immunity, and protein transcription as oncogenes or as tumor suppressors. Gene-based therapeutics are getting the attention of researchers because of their cell specificity. PEST-NPs are good targets to explore as cancer therapeutics. Insights into PTMs of PEST-NPs demonstrate that these proteins not only interact with each other but also recruit other proteins to/from their active site to promote/inhibit tumors. Thus, the role of PEST-NPs in cancer biology is multivariate. It is hard to obtain therapeutic objectives with single gene therapy. An especially designed combination gene therapy might be a promising strategy in cancer treatment. This review highlights the multifaceted behavior of PEST-NPs in cancer biology. We have summarized a number of studies to address the influence of structure and PEST-mediated PTMs on activation, localization, stability, and protein-protein interactions of PEST-NPs. We also recommend researchers to adopt a pragmatic approach in gene-based cancer therapy.

Model-based optimization of combination protocols for irradiation-insensitive cancers

Alternations in the p53 regulatory network may render cancer cells resistant to the radiation-induced apoptosis. In this theoretical study we search for the best protocols combining targeted therapy with radiation to treat cancers with wild-type p53, but having downregulated expression of PTEN or overexpression of Wip1 resulting in resistance to radiation monotherapy. Instead of using the maximum tolerated dose paradigm, we exploit stochastic computational model of the p53 regulatory network to calculate apoptotic fractions for both normal and cancer cells. We consider combination protocols, with irradiations repeated every 12, 18, 24, or 36 h to find that timing between Mdm2 inhibitor delivery and irradiation significantly influences the apoptotic cell fractions. We assume that uptake of the inhibitor is higher by cancer than by normal cells and that cancer cells receive higher irradiation doses from intersecting beams. These two assumptions were found necessary for the existence of protocols inducing massive apoptosis in cancer cells without killing large fraction of normal cells neighboring tumor. The best found protocols have irradiations repeated every 24 or 36 h with two inhibitor doses per irradiation cycle, and allow to induce apoptosis in more than 95% of cancer cells, killing less than 10% of normal cells.

Blockade of MDM2 with inactive Cas9 prevents epithelial to mesenchymal transition in retinal pigment epithelial cells

Epithelial to mesenchymal transition (EMT) plays an important role in the pathogenesis of proliferative vitreoretinopathy (PVR). We aimed to demonstrate the role of mouse double minute 2 (MDM2) in transforming growth factor-beta 2 (TGF-β2)-induced EMT in human retinal pigment epithelial cells (RPEs). Immunofluorescence was used to assess MDM2 expression in epiretinal membranes (ERMs) from patients with PVR. A single guide (sg)RNA targeting the second promoter of MDM2 was cloned into a mutant lentiviral Clustered Regularly Interspaced Short Palindromic Repeats (lentiCRISPR) v2 (D10A and H840A) vector for expressing nuclease dead Cas9 (dCas9)/MDM2-sgRNA in RPEs. In addition, MDM2-sgRNA was also cloned into a pLV-sgRNA-dCas9-Kruppel associated box (KRAB) vector for expressing dCas9 fused with a transcriptional repressor KRAB/MDM2-sgRNA. TGF-β2-induced expression of MDM2 and EMT biomarkers were assessed by quantitative polymerase chain reaction (q-PCR), western blot, or immunofluorescence. Wound-healing and proliferation assays were used to evaluate the role of MDM2 in TGF-β2-induced responses in RPEs. As a result, we found that MDM2 was expressed obviously in ERMs, and that TGF-β2-induced expression of MDM2 and EMT biomarkers Fibronectin, N-cadherin and Vimentin in RPEs. Importantly, we discovered that the dCas9/MDM2-sgRNA blocked TGF-β2-induced expression of MDM2 and the EMT biomarkers without affecting their basal expression, whereas the dCas9-KRAB/MDM2-sgRNA suppressed basal MDM2 expression in RPEs. These cells could not be maintained continuously because their viability was greatly reduced. Next, we found that Nutlin-3, a small molecule blocking the interaction of MDM2 with p53, inhibited TGF-β2-induced expression of Fibronectin and N-cadherin but not Vimentin in RPEs, indicating that MDM2 functions in both p53-dependent and -independent pathways. Finally, our experimental data demonstrated that dCas9/MDM2-sgRNA suppressed TGF-β2-dependent cell proliferation and migration without disturbing the unstimulated basal activity. In conclusion, the CRISPR/dCas9 capability for blocking TGF-β2-induced expression of MDM2 and EMT biomarkers can be exploited for a therapeutic approach to PVR.

Resistance of human primary mesenchymal stem cells to cytotoxic effects of nutlin-3 in vitro

BACKGROUND

The small-molecule nutlin-3 was found to be an effective therapeutic compound and p53 activator, and acts as a murine double minute 2 antagonist, although these findings need to be clinically confirmed. The essential components of the bone marrow include mesenchymal stem cells (MSCs), which play a key role in protecting, regenerating, and proliferating hematopoietic stem cells (HSCs). This feature is vital for HSC after exposure to myelotoxic anticancer agents; nevertheless, the effects of nutlin-3 on MSCs remain to be disclosed. The present research study was conducted to examine the antiproliferative and proapoptotic effectiveness of nutlin-3 in bone marrow MSCs (BMSCs).

MATERIALS AND METHODS

Human-derived BMSCs were cultured for different durations, that is, 24, 48, and 72 hours, and treated using various concentrations of nutlin-3, including 5, 10, 25, 50, and 100 μΜ. To investigate the effect of nutlin-3 on the apoptosis, cell vitality and proliferation in BMSCs, the terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL), thiazolyl blue tetrazolium bromide, propidium iodide (PI) and annexin V assay, as well as real-time polymerase chain reaction, were used.

RESULTS

BMSCs viability significantly decreased (P < .05) in the cells treated at concentrations of 50 and 100 μM for 24 hours and concentrations of 25, 50, and 100 μM for 48 hours and at all concentrations for 72 hours. The apoptosis of BMSCs (TUNEL positive) was significantly more visible at concentrations of 25 and 50 μM compared with that in the controls (P < .05), while this increased through dose-dependent processes. Annexin V/PI staining revealed negligible dose-dependent increases in all the apoptotic cells after 72 hours of incubation, and this apoptosis elevation was significant at 25 and 50 μM (P < .05).

CONCLUSION

Resistance to nutlin-3 was observed in human bone marrow-derived MSCs; nevertheless, further clinical data are required to be obtained with long-duration exposure to confirm the present findings.

Dual-channel surface plasmon resonance monitoring of intracellular levels of the p53-MDM2 complex and caspase-3 induced by MDM2 antagonist Nutlin-3

MDM2 can mediate the degradation of tumor suppressor p53 through an autoregulatory feedback loop, in which MDM2 abolishes wild-type p53 function and accelerates malignant transformation. However, the incorporation of MDM2 antagonist Nutlin-3 could reactivate the transcriptional activity of p53, up-regulate caspase-3, and induce apoptosis. In this work, the simultaneous and label-free monitoring of p53-MDM2 complex and caspase-3 levels in cancer cells before and after Nutlin-3 treatment was conducted using dual-channel surface plasmon resonance (SPR). The p53-MDM2 complex was captured in one fluidic channel covered with consensus double-stranded (ds)-DNA, while the other channel was pre-immobilized with caspase-3-specific biotinylated DEVD-containing peptides. To amplify the SPR signals, the attachment of streptavidin (SA)-conjugated anti-MDM2 antibody in both channels was achieved. The signal diversity before and after Nutlin-3 treatment is indicative of the difference in the levels of the intracellular p53-MDM2 complex and caspase-3. The limit of detection for p53-MDM2 and caspase-3 down to 4.54 pM and 0.03 ng mL^-1, respectively, was attained. Upon treatment with Nutlin-3, MCF-7 cancer cells with wild-type p53 showed decreased expression of the p53-MDM2 complex and an increased caspase-3 level, while MDA-MB-231 cancer cells with mutant p53 exhibited an elevated caspase-3 level and unchanged p53-MDM2 complex expression. The apoptosis of MCF-7 and MDA-MB-231 cancer cells upon Nutlin-3 treatment follows a p53-dependent and a p53-independent pathway, respectively. The proposed method is sensitive, selective and label-free, holding great promise for assaying intracellular p53-MDM2 complex and caspase-3 levels and differentiating Nutlin-3-mediated p53-dependent or p53-independent apoptotic pathways.

Inhibition of MDM2 via Nutlin-3A: A Potential Therapeutic Approach for Pleural Mesotheliomas with MDM2-Induced Inactivation of Wild-Type P53

Previously, our group demonstrated that nuclear expression of E3 ubiquitin ligase (MDM2) in malignant pleural mesothelioma (MPM) is significantly associated with decreased overall survival. A possible explanation may be that overexpression of MDM2 leads to a proteasomal degradation of TP53 that eventually results in a loss of TP53-induced apoptosis and senescence. It is well known from other tumor entities that restoration of TP53 activity, e.g., by MDM2 inhibition, results in an instant TP53-induced stress and/or DNA damage response of cancer cells. Nutlin-3A (a cis-imidazoline analogue) has been described as a potent and selective MDM2 inhibitor preventing MDM2-TP53-interaction by specific binding to the hydrophobic TP53-binding pocket of MDM2. In the present study, the effects of MDM2 inhibition in MPM via Nutlin-3A and standard platinum based chemotherapeutic agents were comparatively tested in three MPM cell lines (NCI-H2052, MSTO-211H, and NCI-H2452) showing different expression profiles of TP53, MDM2, and its physiological inhibitor of MDM2—P14/ARF. Our in vitro experiments on MPM cell lines revealed that Nutlin-3A in combination with cisplatin resulted in up to 9.75 times higher induction of senescence (p=0.0050) and up to 5 times higher apoptosis rate (p=0.0067) compared to the commonly applied cisplatin and pemetrexed regimens. Thus Nutlin-3A, a potent inhibitor of MDM2, is associated with a significant induction of senescence and apoptosis in MPM cell lines, making Nutlin-3A a promising substance for a targeted therapy in the subgroup of MPM showing MDM2 overexpression.

MDM2-p53 Interactions in Human Hepatocellular Carcinoma: What Is the Role of Nutlins and New Therapeutic Options?

Human hepatocellular carcinoma (HCC) is the fifth most common cancer and is associated with poor prognosis worldwide. The molecular mechanisms underlying the pathogenesis of HCC have been an area of continuing interest, and recent studies using next generation sequencing (NGS) have revealed much regarding previously unsettled issues. Molecular studies using HCC samples have been mainly targeted with the aim to identify the fundamental mechanisms contributing to HCC and identify more effective treatments. In response to cellular stresses (e.g., DNA damage or oncogenes), activated p53 elicits appropriate responses that aim at DNA repair, genetic stability, cell cycle arrest, and the deletion of DNA-damaged cells. On the other hand, the murine double minute 2 (MDM2) oncogene protein is an important cellular antagonist of p53. MDM2 negatively regulates p53 activity through the induction of p53 protein degradation. However, current research has shown that the mechanisms underlying MDM2-p53 interactions are more complex than previously thought. Microarray data have added new insight into the transcription changes in HCC. Recently, Nutlin-3 has shown potency against p53-MDM2 binding and the enhancement of p53 stabilization as well as an increment of p53 cellular accumulation with potential therapeutic effects. This review outlines the molecular mechanisms involved in the p53-MDM2 pathways, the biological factors influencing these pathways, and their roles in the pathogenesis of HCC. It also discusses the action of Nutlin-3 treatment in inducing growth arrest in HCC and elaborates on future directions in research in this area. More research on the biology of p53-MDM2 interactions may offer a better understanding of these mechanisms and discover new biomarkers, sensitive prognostic indicators as well as new therapeutic interventions in HCC.