Cooperation of Nutlin-3a and a Wip1 inhibitor to induce p53 activity

Rescue of p53 functions by in vitro-transcribed mRNA impedes the growth of high-grade serous ovarian cancer

BACKGROUND

The cellular tumor protein p53 (TP53) is a tumor suppressor gene that is frequently mutated in human cancers. Among various cancer types, the very aggressive high-grade serous ovarian carcinoma (HGSOC) exhibits the highest prevalence of TP53 mutations, present in >96% of cases. Despite intensive efforts to reactivate p53, no clinical drug has been approved to rescue p53 function. In this study, our primary objective was to administer in vitro-transcribed (IVT) wild-type (WT) p53-mRNA to HGSOC cell lines, primary cells, and orthotopic mouse models, with the aim of exploring its impact on inhibiting tumor growth and dissemination, both in vitro and in vivo.

METHODS

To restore the activity of p53, WT p53 was exogenously expressed in HGSOC cell lines using a mammalian vector system. Moreover, IVT WT p53 mRNA was delivered into different HGSOC model systems (primary cells and patient-derived organoids) using liposomes and studied for proliferation, cell cycle progression, apoptosis, colony formation, and chromosomal instability. Transcriptomic alterations induced by p53 mRNA were analyzed using RNA sequencing in OVCAR-8 and primary HGSOC cells, followed by ingenuity pathway analysis. In vivo effects on tumor growth and metastasis were studied using orthotopic xenografts and metastatic intraperitoneal mouse models.

RESULTS

Reactivation of the TP53 tumor suppressor gene was explored in different HGSOC model systems using newly designed IVT mRNA-based methods. The introduction of WT p53 mRNA triggered dose-dependent apoptosis, cell cycle arrest, and potent long-lasting inhibition of HGSOC cell proliferation. Transcriptome analysis of OVCAR-8 cells upon mRNA-based p53 reactivation revealed significant alterations in gene expression related to p53 signaling, such as apoptosis, cell cycle regulation, and DNA damage. Restoring p53 function concurrently reduces chromosomal instability within the HGSOC cells, underscoring its crucial contribution in safeguarding genomic integrity by moderating the baseline occurrence of double-strand breaks arising from replication stress. Furthermore, in various mouse models, treatment with p53 mRNA reduced tumor growth and inhibited tumor cell dissemination in the peritoneal cavity in a dose-dependent manner.

CONCLUSIONS

The IVT mRNA-based reactivation of p53 holds promise as a potential therapeutic strategy for HGSOC, providing valuable insights into the molecular mechanisms underlying p53 function and its relevance in ovarian cancer treatment.

miR-16-5p enhances sensitivity to RG7388 through targeting PPM1D expression (WIP1) in Childhood Acute Lymphoblastic Leukemia

Aim: Given the encouraging results of the p53-Mdm2 inhibitor RG7388 in clinical trials and the vital function of miR-16-5p in suppressing cell proliferation, the aim of the present study was to investigate the combined impact of RG7388 and miR-16-5p overexpression on the childhood acute lymphoblastic leukemia (chALL). Methods: miRTarBase and miRDB, along with KEGG and STRING databases, were used to predict miR-16-5p target genes and explore protein-protein interaction networks, respectively. B- and T-lymphoblastic cell lines, in addition to patient primary cells, were treated with RG7388. Ectopic overexpression of miR-16-5p in Nalm6 cell line was induced through cell electroporation and transfection of microRNA mimics was confirmed by qRT-PCR. Cell viability was evaluated using the MTT assay. Western blot analyses were performed to evaluate the effects of RG7388 and miR-16-5p upregulation on the protein levels of p53 and its downstream target genes in chALL cells. Paired sample t-test was employed for statistical analyses. Results: MTT assay showed RG7388-induced cytotoxicity in wild-type p53 Nalm6 cell line and p53 functional patient primary cells. However, CCRF-CEM and p53 non-functional leukemic cells indicated drug resistance. Western blot analyses validated the bioinformatics results, confirming the downregulation of WIP1, p53 stabilization, as well as overexpression of p21^WAF1 and Mdm2 proteins in Nalm6 cells transfected with miR-16-5p. Moreover, enhanced sensitivity to RG7388 was observed in the transfected cells. Conclusion: This is the first study indicating the mechanistic importance of miR-16-5p overexpression in chALL and its inhibitory role in leukemia treatment when combined with the p53-Mdm2 antagonist, RG7388. These findings might be useful for researchers and clinicians to pave the way for better management of chALL.

PPM1D suppresses p53-dependent transactivation and cell death by inhibiting the Integrated Stress Response

The p53 transcription factor is a master regulator of cellular stress responses inhibited by repressors such as MDM2 and the phosphatase PPM1D. Activation of p53 with pharmacological inhibitors of its repressors is being tested in clinical trials for cancer therapy, but efficacy has been limited by poor induction of tumor cell death. We demonstrate that dual inhibition of MDM2 and PPM1D induces apoptosis in multiple cancer cell types via amplification of the p53 transcriptional program through the eIF2α-ATF4 pathway. PPM1D inhibition induces phosphorylation of eIF2α, ATF4 accumulation, and ATF4-dependent enhancement of p53-dependent transactivation upon MDM2 inhibition. Dual inhibition of p53 repressors depletes heme and induces HRI-dependent eIF2α phosphorylation. Pharmacological induction of eIF2α phosphorylation synergizes with MDM2 inhibition to induce cell death and halt tumor growth in mice. These results demonstrate that PPM1D inhibits both the p53 network and the integrated stress response controlled by eIF2α-ATF4, with clear therapeutic implications.

In vitro and in vivo study of GSK2830371 and RG7388 combination in liver adenocarcinoma

Intrahepatic cholangiocarcinoma (iCCA) is an adenocarcinoma arising from the intrahepatic bile duct and accounts for the second highest incidence of primary liver cancers after hepatocellular carcinoma. The lack of effective treatment leads to a poor prognosis for advanced iCCA, so new targeted therapy is needed. The impairment of wild-type (WT) p53 tumor suppressor function by its negative regulators frequently occurs in iCCA. Therefore, restoration of WT p53 function by inhibiting its negative regulators is a therapeutic strategy being explored for cancer treatment. Combining an MDM2 inhibitor (MDM2i, RG7388) to stabilize p53 and a WIP1 inhibitor (WIP1i, GSK2830371) to increase p53 phosphorylation enhances p53 function. The combination of MDM2 and WIP1 inhibitors has been reported in several cancer types but in vivo studies are lacking. In the current study, liver adenocarcinoma cell lines, RBE and SK-Hep-1, were treated with RG7388 alone and in combination with GSK2830371. Cell proliferation, clonogenicity, protein and mRNA expressions, and cell cycle distribution were performed to investigate the effect and mechanism of growth suppression. To evaluate the antitumor efficacy of RG7388 and GSK2830371 in vivo, SK-Hep-1 xenografts in NOD-SCID mice were treated with combination therapy for two weeks. The combination of MDM2i and WIP1i significantly increased the growth inhibition, cytotoxicty, p53 protein expression, and phosphorylation (Ser15), leading to transactivation of downstream targets (p21^WAF1 and MDM2). The in vivo results demonstrated that the combination treatment can significantly inhibit tumor growth. In this study, the liver adenocarcinoma cell lines responded to combination treatment via reactivation of p53 function evidenced by increased p53 expression, phosphorylation and expression of its downstream targets. This efficacy was also demonstrated in vivo. The current research provides a novel strategy for targeting the p53 pathway in liver adenocarcinoma that warrants further investigation.

Tipping Growth Inhibition into Apoptosis by Combining Treatment with MDM2 and WIP1 Inhibitors in p53WT Uterine Leiomyosarcoma

As there is no optimal therapeutic strategy defined for women with advanced or recurrent uLMS, there is an urgent need for the discovery of novel, targeted approaches. One such area of interest is the pharmacological inhibition of the MDM2-p53 interaction with small-molecular-weight MDM2 inhibitors. Growth inhibition and cytotoxic assays were used to evaluate uLMS cell line responses to MDM2 inhibitors as single agents and in combination, qRT-PCR to assess transcriptional changes and Caspase-Glo 3/7 assay to detect apoptosis. RG7388 and HDM201 are potent, selective antagonists of the MDM2-p53 interaction that can effectively stabilise and activate p53 in a dose-dependent manner. GSK2830371, a potent and selective WIP1 phosphatase inhibitor, was shown to significantly potentiate the growth inhibitory effects of RG7388 and HDM201, and significantly increase the mRNA expression of p53 transcriptional target genes in a p53^WT cell line at a concentration that has no growth inhibitory effects as a single agent. RG7388, HDM201 and GSK2830371 failed to induce apoptosis as single agents; however, a combination treatment tipped cells into apoptosis from senescence. These data present the possibility of MDM2 and WIP1 inhibitor combinations as a potential treatment option for p53^WT uLMS patients that warrants further investigation.

Therapeutic opportunities in cancer therapy: targeting the p53-MDM2/MDMX interactions

Ubiquitination is a key enzymatic post-translational modification that influences p53 stability and function. p53 protein regulates the expression of MDM2 (mouse double-minute 2 protein) E3 ligase and MDMX (double-minute 4 protein), through proteasome-based degradation. Exploration of targeting the ubiquitination pathway offers a potentially promising strategy for precision therapy in a variety of cancers. The p53-MDM2-MDMX pathway provides multiple molecular targets for small molecule screening as potential therapies for wild-type p53. As a result of its effect on molecular carcinogenesis, a personalized therapeutic approach based on the wild-type and mutant p53 protein is desirable. We highlighted the implications of p53 mutations in cancer, p53 ubiquitination mechanistic details, targeting p53-MDM2/MDMX interactions, significant discoveries related to MDM2 inhibitor drug development, MDM2 and MDMX dual target inhibitors, and clinical trials with p53-MDM2/MDMX-targeted drugs. We also investigated potential therapeutic repurposing of selective estrogen receptor modulators (SERMs) in targeting p53-MDM2/MDMX interactions. Molecular docking studies of SERMs were performed utilizing the solved structures of the p53/MDM2/MDMX proteins. These studies identified ormeloxifene as a potential dual inhibitor of p53/MDM2/MDMX interaction, suggesting that repurposing SERMs for dual targeting of p53/MDM2 and p53/MDMX interactions is an attractive strategy for targeting wild-type p53 tumors and warrants further preclinical research.

Resistance mechanisms to inhibitors of p53-MDM2 interactions in cancer therapy: can we overcome them?

Since the discovery of the first MDM2 inhibitors, we have gained deeper insights into the cellular roles of MDM2 and p53. In this review, we focus on MDM2 inhibitors that bind to the p53-binding domain of MDM2 and aim to disrupt the binding of MDM2 to p53. We describe the basic mechanism of action of these MDM2 inhibitors, such as nutlin-3a, summarise the determinants of sensitivity to MDM2 inhibition from p53-dependent and p53-independent points of view and discuss the problems with innate and acquired resistance to MDM2 inhibition. Despite progress in MDM2 inhibitor design and ongoing clinical trials, their broad use in cancer treatment is not fulfilling expectations in heterogenous human cancers. We assess the MDM2 inhibitor types in clinical trials and provide an overview of possible sources of resistance to MDM2 inhibition, underlining the need for patient stratification based on these aspects to gain better clinical responses, including the use of combination therapies for personalised medicine.

WIP1 Inhibition by GSK2830371 Potentiates HDM201 through Enhanced p53 Phosphorylation and Activation in Liver Adenocarcinoma Cells

Simple Summary

Patients with advanced intrahepatic cholangiocarcinoma (iCCA) have a very poor prognosis, and no targeted therapy is approved for advanced iCCA. A therapeutic strategy for wild-type p53 cancers is the reactivation of p53 by inhibition of its the negative regulators, MDM2, and WIP1. In the present study, we used HDM201 (an MDM2-p53 binding antagonist) to increase p53 stabilization and upregulate the expression of downstream targets (p21 and MDM2) in RBE and SK-Hep-1 liver adenocarcinoma cell lines. The survival rate and clonogenicity decreased after HDM201 treatment in a dose-dependent manner. Combined treatment with HDM201 and GSK2830371 (WIP1 inhibitor) increased p53 phosphorylation, leading to sustained p53 activation. This combination treatment resulted in G2/M phase arrest and promoted cytotoxicity compared with MDM2 inhibitor monotherapy. Furthermore, increased expression of p53 signaling pathway target genes were identified following combination treatment with HDM201 and GSK2830371, suggesting potential roles for this combination strategy in iCCA therapy.

Abstract

Background: Intrahepatic cholangiocarcinoma (iCCA) is an adenocarcinoma arising from the intrahepatic bile duct. It is the second most common primary liver cancer and has a poor prognosis. Activation of p53 by targeting its negative regulators, MDM2 and WIP1, is a potential therapy for wild-type p53 cancers, but few reports for iCCA or liver adenocarcinoma exist. Methods: Both RBE and SK-Hep-1 liver adenocarcinoma cell lines were treated with the HDM201 (Siremadlin) MDM2-p53 binding antagonist alone or in combination with the GSK2830371 WIP1 phosphatase inhibitor. Cell proliferation, clonogenicity, protein and mRNA expression, cell cycle distribution, and RNA sequencing were performed to investigate the effect and mechanism of this combination. Results: GSK2830371 alone demonstrated minimal activity on proliferation and colony formation, but potentiated growth inhibition (two-fold decrease in GI₅₀) and cytotoxicity (four-fold decrease in IC₅₀) by HDM201 on RBE and SK-Hep-1 cells. HDM201 increased p53 protein expression, leading to transactivation of downstream targets (p21 and MDM2). Combination with GSK2830371 increased p53 phosphorylation, resulting in an increase in both p53 accumulation and p53-dependent trans-activation. G2/M arrest was observed by flow cytometry after this treatment combination. RNA sequencing identified 21 significantly up-regulated genes and five downregulated genes following p53 reactivation by HDM201 in combination with GSK2830371 at 6 h and 24 h time points compared with untreated controls. These genes were predominantly known transcriptional targets regulated by the p53 signaling pathway, indicating enhanced p53 activation as the predominant effect of this combination. Conclusion: The current study demonstrated that GSK2830371 enhanced the p53-dependent antiproliferative and cytotoxic effect of HDM201 on RBE and SK-Hep-1 cells, providing a novel strategy for potentiating the efficacy of targeting the p53 pathway in iCCA.

Analysis framework and experimental design for evaluating synergy-driving gene expression

The mechanisms by which genetic risk variants interact with each other, as well as environmental factors, to contribute to complex genetic disorders remain unclear. We describe in detail our recently published approach to resolve distinct additive and synergistic transcriptomic effects after combinatorial manipulation of genetic variants and/or chemical perturbagens. Although first developed for CRISPR-based perturbation studies of isogenic human induced pluripotent stem cell-derived neurons, our methodology can be broadly applied to any RNA sequencing dataset, provided that raw read counts are available. Whereas other differential expression analyses reveal the effect of individual perturbations, here we specifically query interactions between two or more perturbagens, resolving the extent of non-additive (synergistic) interactions between perturbations. We discuss the careful experimental design required to resolve synergistic effects and considerations of statistical power and how to quantify observed synergy between experiments. Additionally, we speculate on potential future applications and explore the obvious limitations of this approach. Overall, by interrogating the effect of independent factors, alone and in combination, our analytic framework and experimental design facilitate the discovery of convergence and synergy downstream of gene and/or treatment perturbations hypothesized to contribute to complex diseases. We think that this protocol can be successfully applied by any scientist with bioinformatic skills and basic proficiency in the R programming language. Our computational pipeline ( https://github.com/nadschro/synergy-analysis ) is straightforward, does not require supercomputing support and can be conducted in a single day upon completion of RNA sequencing experiments.

Tumor-Associated Antigen xCT and Mutant-p53 as Molecular Targets for New Combinatorial Antitumor Strategies

The cystine/glutamate antiporter xCT is a tumor-associated antigen that has been newly identified in many cancer types. By participating in glutathione biosynthesis, xCT protects cancer cells from oxidative stress conditions and ferroptosis, and contributes to metabolic reprogramming, thus promoting tumor progression and chemoresistance. Moreover, xCT is overexpressed in cancer stem cells. These features render xCT a promising target for cancer therapy, as has been widely reported in the literature and in our work on its immunotargeting. Interestingly, studies on the TP53 gene have revealed that both wild-type and mutant p53 induce the post-transcriptional down modulation of xCT, contributing to ferroptosis. Moreover, APR-246, a small molecule drug that can restore wild-type p53 function in cancer cells, has been described as an indirect modulator of xCT expression in tumors with mutant p53 accumulation, and is thus a promising drug to use in combination with xCT inhibition. This review summarizes the current knowledge of xCT and its regulation by p53, with a focus on the crosstalk of these two molecules in ferroptosis, and also considers some possible combinatorial strategies that can make use of APR-246 treatment in combination with anti-xCT immunotargeting.

Phosphatase magnesium-dependent 1 δ (PPM1D), serine/threonine protein phosphatase and novel pharmacological target in cancer

Aberrations in DNA damage response genes are recognized mediators of tumorigenesis and resistance to chemo- and radiotherapy. While protein phosphatase magnesium-dependent 1 δ (PPM1D), located on the long arm of chromosome 17 at 17q22-23, is a key regulator of cellular responses to DNA damage, amplification, overexpression, or mutation of this gene is important in a wide range of pathologic processes. In this review, we describe the physiologic function of PPM1D, as well as its role in diverse processes, including fertility, development, stemness, immunity, tumorigenesis, and treatment responsiveness. We highlight both the advances and limitations of current approaches to targeting malignant processes mediated by pathogenic alterations in PPM1D with the goal of providing rationale for continued research and development of clinically viable treatment approaches for PPM1D-associated diseases.

Protein phosphatase, Mg2+/Mn2+-dependent 1D (PPM1D) mutations in haematological cancer

Until recently, the protein phosphatase, Mg²⁺/Mn²⁺-dependent 1D (PPM1D) gene had not been examined in haematological cancer, but several studies have now explored the functional role of this gene and its aberrations. It is often mutated in the context of clonal haemopoiesis (including in patients with lymphoma, myeloproliferative neoplasms and myelodysplastic syndrome) and mutations have been associated with exposure to cytotoxic and radiation therapy, development of therapy-related neoplasms and inferior survival. The vast majority of PPM1D mutations found in haematopoietic cells are of the nonsense or frameshift type and located within terminal exon 6. These genetic defects are rarely found in the blood of healthy individuals. PPM1D encodes the PPM1D phosphatase [also named wild-type p53-induced phosphatase 1 (WIP1)], which negatively regulates signalling molecules within the DNA damage response pathway, including tumour suppressor p53. Clonal expansion of PPM1D mutant haematopoietic cells can potentially be prevented with inhibitors; however, human trials are awaited. In the present review, we provide a review of the literature regarding PPM1D and its role in haematological cancer.

The biological function and the regulatory roles of wild-type p53-induced phosphatase 1 in immune system

Wild-type p53-induced phosphatase 1 (WIP1) belongs to the protein phosphatase 2C (PP2C) family and is a mammalian serine/threonine specific protein phosphatase to dephosphorylate numerous signaling molecules. Mammalian WIP1 regulates a wide array of targeting molecules and plays key regulatory roles in many cell processes such as DNA damage and repair, cell proliferation, differentiation, apoptosis, and senescence. WIP1 promotes the formation and development of tumors as an oncogene and a negative regulator of p53. It is also involved in the regulation of aging, neurological diseases and immune diseases. Recent studies demonstrated the critical roles of WIP1 in the differentiation and function of immune cells including T cells, neutrophils and macrophages. In the present manuscript, we briefly summarized the expression patterns, biological function and the target molecules and signal pathways of WIP1 and mainly discussed the latest advances on the regulatory effects of WIP1 in the immune system. WIP1 may be a potential target molecule to treat cancers and immune diseases such as allergic asthma.

Design, Synthesis, and Biological Evaluation of Aromatic Amide-Substituted Benzimidazole-Derived Chalcones. The Effect of Upregulating TP53 Protein Expression

A series of benzimidazole-derived chalcones containing aromatic amide substituent were designed and synthesized. All of the chalcone compounds were tested for their in vitro antitumor activity against human cancer cell lines (HCT116, HepG2, A549, and CRL-5908). The antiproliferative activity of compounds 3, 6, 9, 14, 15, 16 against HCT116 cells was significantly better than that that of 5-Fluorouracil (IC50: 94.63 µM). The antitumor activity of these compounds showed obvious differences between the wild type HCT116 and mutant HCT116 (TP53^−/−) cells. A preliminary mechanistic study suggested that these compounds act by upregulating the expression of TP53 protein in tumor cells without inhibiting the MDM2-TP53 interaction.

The role of PPM1D in cancer and advances in studies of its inhibitors

A greater understanding of factors causing cancer initiation, progression and evolution is of paramount importance. Among them, the serine/threonine phosphatase PPM1D, also referred to as wild-type p53-induced phosphatase 1 (Wip1) or protein phosphatase 2C delta (PP2Cδ), is emerging as an important oncoprotein due to its negative regulation on a number of crucial cancer suppressor pathways. Initially identified as a p53-regulated gene, PPM1D has been afterwards found amplified and more recently mutated in many human cancers such as breast cancer. The latest progress in this field further reveals that selective inhibition of PPM1D to delay tumor onset or reduce tumor burden represents a promising anti-cancer strategy. Here, we review the advances in the studies of the PPM1D activity and its relevance to various cancers, and recent progress in development of PPM1D inhibitors and discuss their potential application in cancer therapy. Consecutive research on PPM1D and its relationship with cancer is essential, as it ultimately contributes to the etiology and treatment of cancer.

WIP1 Promotes Homologous Recombination and Modulates Sensitivity to PARP Inhibitors

Genotoxic stress triggers a combined action of DNA repair and cell cycle checkpoint pathways. Protein phosphatase 2C delta (referred to as WIP1) is involved in timely inactivation of DNA damage response by suppressing function of p53 and other targets at chromatin. Here we show that WIP1 promotes DNA repair through homologous recombination. Loss or inhibition of WIP1 delayed disappearance of the ionizing radiation-induced 53BP1 foci in S/G2 cells and promoted cell death. We identify breast cancer associated protein 1 (BRCA1) as interactor and substrate of WIP1 and demonstrate that WIP1 activity is needed for correct dynamics of BRCA1 recruitment to chromatin flanking the DNA lesion. In addition, WIP1 dephosphorylates 53BP1 at Threonine 543 that was previously implicated in mediating interaction with RIF1. Finally, we report that inhibition of WIP1 allowed accumulation of DNA damage in S/G2 cells and increased sensitivity of cancer cells to a poly-(ADP-ribose) polymerase inhibitor olaparib. We propose that inhibition of WIP1 may increase sensitivity of BRCA1-proficient cancer cells to olaparib.

Helping the Released Guardian: Drug Combinations for Supporting the Anticancer Activity of HDM2 (MDM2) Antagonists

The protein p53, known as the "Guardian of the Genome", plays an important role in maintaining DNA integrity, providing protection against cancer-promoting mutations. Dysfunction of p53 is observed in almost every cancer, with 50% of cases bearing loss-of-function mutations/deletions in the TP53 gene. In the remaining 50% of cases the overexpression of HDM2 (mouse double minute 2, human homolog) protein, which is a natural inhibitor of p53, is the most common way of keeping p53 inactive. Disruption of HDM2-p53 interaction with the use of HDM2 antagonists leads to the release of p53 and expression of its target genes, engaged in the induction of cell cycle arrest, DNA repair, senescence, and apoptosis. The induction of apoptosis, however, is restricted to only a handful of p53wt cells, and, generally, cancer cells treated with HDM2 antagonists are not efficiently eliminated. For this reason, HDM2 antagonists were tested in combinations with multiple other therapeutics in a search for synergy that would enhance the cancer eradication. This manuscript aims at reviewing the recent progress in developing strategies of combined cancer treatment with the use of HDM2 antagonists.

Wip1 cooperates with KPNA2 to modulate the cell proliferation and migration of colorectal cancer via a p53-dependent manner

Due to the increasing incidence and mortality, the early diagnosis, specific targeted therapies, and prognosis for colorectal cancer (CRC) attract more and more attention. Wild-type p53-induced phosphatase 1 (Wip1) and karyopherin α2 (KPNA2) have been regarded as oncogenes in many cancers, including CRC. Wip1 dephosphorylates p53 to inactivate it. TP53 activator and Wip1 inhibitor downregulate KPNA2 expression. Therefore, we speculate that Wip1 may co-operate with KPNA2 to modulate CRC progression in a p53-dependent manner. Here, Wip1 and KPNA2 messenger RNA expression and protein levels are significantly increased in CRC tissues and cell lines and are positively correlated with each other. Wip1 silence increases p53 phosphorylation while decreases KPNA2 protein. Wip1 knockdown remarkably suppresses CRC cell proliferation and migration while KPNA2 overexpression exerts an opposing effect. KPNA2 overexpression could partially rescue Wip1 silence-inhibited CRC cell proliferation and migration. Finally, Wip1 interacts with KPNA2 to modulate the activation of AKT/GSK-3β signaling and metastasis-related factors. In summary, Wip1 could co-operate with KPNA2 to modulate CRC cell proliferation and migration, possibly via a p53-dependent manner, through downstream AKT/GSK-3β pathway. We provided a novel mechanism of Wip1 interacting with KPNA2, therefore modulating CRC cell proliferation and migration.

The past, present and future of potential small-molecule drugs targeting p53-MDM2/MDMX for cancer therapy

The p53 gene, a well-known tumor suppressor gene, plays a crucial role in cell cycle regulation, DNA repair, cell differentiation, and apoptosis. MDM2 exerts p53-dependent activity mainly by binding to p53 protein to form MDM2-p53 negative feedback loop. In addition, MDM2 is involved in a number of pathways that regulate cell proliferation and apoptosis, playing a p53-independent role. The p53 binding domain of MDMX bind to p53 transcriptional activation domain, inhibiting the transcriptional activity of p53 on its downstream genes, but does not mediate the degradation of p53. The anti-tumor effect is exerted by inhibiting the interaction between the MDM2/MDMX protein and the p53 protein by a small-molecule or by restoring the activity of the p53 protein. This review describes in the structural features, biological functions and mechanisms of p53-MDM2/MDMX, and summarizes small-molecule targeting p53-MDM2/MDMX.

Inhibition of invasive pancreatic cancer: restoring cell apoptosis by activating mitochondrial p53

Pancreatic ductal adenocarcinoma (PDAC), constitutes >90% of pancreatic cancers (PC) and is one of the most aggressive human tumors. Standard chemotherapies for PDAC (e.g., gemcitabine, FOLFIRINOX, etc.) has proven to be largely ineffective. Herein, we report a novel molecule (i.e., compound 1) that potently inhibits proliferation and induces apoptosis of PDAC cells. As we observed in other cancer types (i.e., colorectal, breast cancer), the effect of 1 against PDAC cells is also related to microtubule destabilization and DNA damage checkpoint activation. However, in PDAC cells, the inhibitory effect of 1 was mainly controlled by mitochondrial p53-dependent apoptosis. Compound 1 worked with cells of different p53 mutant status and affected p53 activation/phosphorylation not simply by stabilizing p53 protein but through antagonizing anti-apoptotic effects of Bcl-xL and restoring p53 to activate mitochondrial-apoptotic pathways (i.e., cytochrome c release, caspase activation and PARP cleavage). Compound 1 was more efficient than a typical PDAC combination therapy (i.e., gemcitabine with paclitaxel) and showed synergism in inhibiting PDAC cell proliferation with gemcitabine (or gemcitabine with paclitaxel). This synergism varied between different types of PDAC cells and was partially controlled by the phosphorylation of p53 on Serine15 (phospho-Ser15-p53). In vivo studies in an orthotopic syngeneic murine model showed that 1 (20 mg/kg/day, 28 days, i.p.) inhibited tumor growth by 65% compared to vehicle-treated mice. No apparent acute or chronic toxicity was observed. Thus, compound 1 utilizes a distinct mechanism of action to inhibit PC growth in vitro and in vivo and is a novel anti-PDAC compound.

Etoposide-resistance in a neuroblastoma model cell line is associated with 13q14.3 mono-allelic deletion and miRNA-15a/16-1 down-regulation

Drug resistance is the major obstacle in successfully treating high-risk neuroblastoma. The aim of this study was to investigate the basis of etoposide-resistance in neuroblastoma. To this end, a MYCN-amplified neuroblastoma cell line (HTLA-230) was treated with increasing etoposide concentrations and an etoposide-resistant cell line (HTLA-ER) was obtained. HTLA-ER cells, following etoposide exposure, evaded apoptosis by altering Bax/Bcl2 ratio. While both cell populations shared a homozygous TP53 mutation encoding a partially-functioning protein, a mono-allelic deletion of 13q14.3 locus, where the P53 inducible miRNAs 15a/16-1 are located, and the consequent miRNA down-regulation were detected only in HTLA-ER cells. This event correlated with BMI-1 oncoprotein up-regulation which caused a decrease in p16 tumor suppressor content and a metabolic adaptation of HTLA-ER cells. These results, taken collectively, highlight the role of miRNAs 15a/16-1 as markers of chemoresistance.

CDK4 inhibition diminishes p53 activation by MDM2 antagonists

The genes encoding MDM2 and CDK4 are frequently co-amplified in sarcomas, and inhibitors to both targets are approved or clinically tested for therapy. However, we show that inhibitors of MDM2 and CDK4 antagonize each other in their cytotoxicity towards sarcoma cells. CDK4 inhibition attenuates the induction of p53-responsive genes upon MDM2 inhibition. Moreover, the p53 response was also attenuated when co-depleting MDM2 and CDK4 with siRNA, compared to MDM2 single knockdown. The complexes of p53 and MDM2, as well as CDK4 and Cyclin D1, physically associated with each other, suggesting direct regulation of p53 by CDK4. Interestingly, CDK4 inhibition did not reduce p53 binding or histone acetylation at promoters, but rather attenuated the subsequent recruitment of RNA Polymerase II. Taken together, our results suggest that caution must be used when considering combined CDK4 and MDM2 inhibition for patient treatment. Moreover, they uncover a hitherto unknown role for CDK4 and Cyclin D1 in sustaining p53 activity.

Genome-scale CRISPR-Cas9 screen identifies druggable dependencies in TP53 wild-type Ewing sarcoma

Stolte et al. use genome-scale CRISPR-Cas9 screening technology to identify druggable targets for TP53 wild-type Ewing sarcoma and discover reactivation of p53 through inhibition of MDM2, MDM4, Wip1, or USP7 as therapeutic strategies for the disease.

Ewing sarcoma is a pediatric cancer driven by EWS-ETS transcription factor fusion oncoproteins in an otherwise stable genomic background. The majority of tumors express wild-type TP53, and thus, therapies targeting the p53 pathway would benefit most patients. To discover targets specific for TP53 wild-type Ewing sarcoma, we used a genome-scale CRISPR-Cas9 screening approach and identified and validated MDM2, MDM4, USP7, and PPM1D as druggable dependencies. The stapled peptide inhibitor of MDM2 and MDM4, ATSP-7041, showed anti-tumor efficacy in vitro and in multiple mouse models. The USP7 inhibitor, P5091, and the Wip1/PPM1D inhibitor, GSK2830371, decreased the viability of Ewing sarcoma cells. The combination of ATSP-7041 with P5091, GSK2830371, and chemotherapeutic agents showed synergistic action on the p53 pathway. The effects of the inhibitors, including the specific USP7 inhibitor XL-188, were rescued by concurrent TP53 knockout, highlighting the essentiality of intact p53 for the observed cytotoxic activities.

An evaluation in vitro of the efficacy of nutlin-3 and topotecan in combination with 177Lu-DOTATATE for the treatment of neuroblastoma

Targeted radiotherapy of metastatic neuroblastoma using the somatostatin receptor (SSTR)-targeted octreotide analogue DOTATATE radiolabelled with lutetium-177 (¹⁷⁷Lu-DOTATATE) is a promising strategy. This study evaluates whether its effectiveness may be enhanced by combination with radiosensitising drugs. The growth rate of multicellular tumour spheroids, derived from the neuroblastoma cell lines SK-N-BE(2c), CHLA-15 and CHLA-20, was evaluated following treatment with ¹⁷⁷Lu-DOTATATE, nutlin-3 and topotecan alone or in combination. Immunoblotting, immunostaining and flow cytometric analyses were used to determine activation of p53 signalling and cell death. Exposure to ¹⁷⁷Lu-DOTATATE resulted in a significant growth delay in CHLA-15 and CHLA-20 spheroids, but not in SK-N-BE(2c) spheroids. Nutlin-3 enhanced the spheroid growth delay induced by topotecan in CHLA-15 and CHLA-20 spheroids, but not in SK-N-BE(2c) spheroids. Importantly, the combination of nutlin-3 with topotecan enhanced the spheroid growth delay induced by X-irradiation or by exposure to ¹⁷⁷Lu-DOTATATE. The efficacy of the combination treatments was p53-dependent. These results indicate that targeted radiotherapy of high risk neuroblastoma with ¹⁷⁷Lu-DOTATATE may be improved by combination with the radiosensitising drugs nutlin-3 and topotecan.

Targeting negative regulation of p53 by MDM2 and WIP1 as a therapeutic strategy in cutaneous melanoma

BACKGROUND

Cutaneous melanoma is the most serious skin malignancy and new therapeutic strategies are needed for advanced melanoma. TP53 mutations are rare in cutaneous melanoma and hence activation of wild-type p53 is a potential therapeutic strategy in cutaneous melanoma. Here, we investigated the WIP1 inhibitor, GSK2830371, and MDM2-p53 binding antagonists (nutlin-3, RG7388 and HDM201) alone and in combination treatment in cutaneous melanoma cell lines and explored the mechanistic basis of these responses in relation to the genotype and induced gene expression profile of the cells.

METHODS

A panel of three p53WT (A375, WM35 and C8161) and three p53MUT (WM164, WM35-R and CHL-1) melanoma cell lines were used. The effects of MDM2 and WIP1 inhibition were evaluated by growth inhibition and clonogenic assays, immunoblotting, qRT-PCR gene expression profiling and flow cytometry.

RESULTS

GSK2830371, at doses (⩽10 μM) that alone had no growth-inhibitory or cytotoxic effects on the cells, nevertheless significantly potentiated the growth-inhibitory and clonogenic cell killing effects of MDM2 inhibitors in p53WT but not p53MUT melanoma cells, indicating the potentiation worked in a p53-dependent manner. The siRNA-mediated knockdown of p53 provided further evidence to support the p53 dependence. GSK2830371 increased p53 stabilisation through Ser15 phosphorylation and consequent Lys382 acetylation, and decreased ubiquitination and proteasome-dependent degradation when it was combined with MDM2 inhibitors. These changes were at least partly ATM mediated, shown by reversal with the ATM inhibitor (KU55933). GSK2830371 enhanced the induction of p53 transcriptional target genes, cell cycle arrest and apoptosis.

CONCLUSIONS

GSK2830371, a WIP1 inhibitor, at doses with no growth-inhibitory activity alone, potentiated the growth-inhibitory and cytotoxic activity of MDM2 inhibitors by increasing phosphorylation, acetylation and stabilisation of p53 in cutaneous melanoma cells in a functional p53-dependent manner.

The role of p53 in cancer drug resistance and targeted chemotherapy

Cancer has long been a grievous disease complicated by innumerable players aggravating its cure. Many clinical studies demonstrated the prognostic relevance of the tumor suppressor protein p53 for many human tumor types. Overexpression of mutated p53 with reduced or abolished function is often connected to resistance to standard medications, including cisplatin, alkylating agents (temozolomide), anthracyclines, (doxorubicin), antimetabolites (gemcitabine), antiestrogenes (tamoxifen) and EGFR-inhibitors (cetuximab). Such mutations in the TP53 gene are often accompanied by changes in the conformation of the p53 protein. Small molecules that restore the wild-type conformation of p53 and, consequently, rebuild its proper function have been identified. These promising agents include PRIMA-1, MIRA-1, and several derivatives of the thiosemicarbazone family. In addition to mutations in p53 itself, p53 activity may be also be impaired due to alterations in p53s regulating proteins such as MDM2. MDM2 functions as primary cellular p53 inhibitor and deregulation of the MDM2/p53-balance has serious consequences. MDM2 alterations often result in its overexpression and therefore promote inhibition of p53 activity. To deal with this problem, a judicious approach is to employ MDM2 inhibitors. Several promising MDM2 inhibitors have been described such as nutlins, benzodiazepinediones or spiro-oxindoles as well as novel compound classes such as xanthone derivatives and trisubstituted aminothiophenes. Furthermore, even naturally derived inhibitor compounds such as a-mangostin, gambogic acid and siladenoserinols have been discovered. In this review, we discuss in detail such small molecules that play a pertinent role in affecting the p53-MDM2 signaling axis and analyze their potential as cancer chemotherapeutics.

Network dynamics-based cancer panel stratification for systemic prediction of anticancer drug response

Cancer is a complex disease involving multiple genomic alterations that disrupt the dynamic response of signaling networks. The heterogeneous nature of cancer, which results in highly variable drug response, is a major obstacle to developing effective cancer therapy. Previous studies of cancer therapeutic response mostly focus on static analysis of genome-wide alterations, thus they are unable to unravel the dynamic, network-specific origin of variation. Here we present a network dynamics-based approach to integrate cancer genomics with dynamics of biological network for drug response prediction and design of drug combination. We select the p53 network as an example and analyze its cancer-specific state transition dynamics under distinct anticancer drug treatments by attractor landscape analysis. Our results not only enable stratification of cancer into distinct drug response groups, but also reveal network-specific drug targets that maximize p53 network-mediated cell death, providing a basis to design combinatorial therapeutic strategies for distinct cancer genomic subtypes.

Genomic alterations underlie the variability of drug responses between cancers, but our mechanistic understanding is limited. Here the authors use the p53 network to study how rewiring of signalling networks by genomic alterations impact their dynamic response to pharmacological perturbation.

Clinical Significance of the Wild Type p53-Induced Phosphatase 1 Expression in Invasive Breast Cancer

BACKGROUND

Wild type p53-induced phosphatase 1 (Wip1), encoded by the protein phosphatase magnesium dependent 1 delta (PPM1D), inhibits p53. PPM1D amplification has been reported in breast cancer. Breast cancer can sometimes develop without a tumor protein 53 (TP53) mutation. In these cases, the p53 pathway might be disrupted by alternative mechanisms, and Wip1 is reported to be a key molecule involved.

MATERIALS AND METHODS

Primary invasive ductal carcinoma specimens were obtained from 201 cases, for which archival tissue samples for immunohistochemistry were available. We evaluated Wip1 and p21 protein expression (201 cases), Wip1 mRNA expression (63 cases), PPM1D DNA copy number (71 cases) and TP53 status (36 cases) using available samples among the 201 cases, and analyzed their relationships with clinicopathological factors and prognosis.

RESULTS

The nuclear expression of Wip1 protein was positive in 21 cases (10.4%). The PPM1D DNA copy number was significantly correlated with Wip1 protein expression. All cases with PPM1D amplification by single-nucleotide polymorphism comparative genomic hybridization array showed positive nuclear Wip1 expression. Wip1 protein expression was positively correlated with p21 expression. The tumors with positive Wip1 and negative p21 expression showed the poorest prognosis among all tumor types.

CONCLUSION

The protein expression of Wip1 might be regulated by PPM1D amplification, independent of TP53 status. Positive Wip1 and negative p21 expression was associated with the poorest prognosis and suggests the loss of p53 function.

WIP1 phosphatase as pharmacological target in cancer therapy

DNA damage response (DDR) pathway protects cells from genome instability and prevents cancer development. Tumor suppressor p53 is a key molecule that interconnects DDR, cell cycle checkpoints, and cell fate decisions in the presence of genotoxic stress. Inactivating mutations in TP53 and other genes implicated in DDR potentiate cancer development and also influence the sensitivity of cancer cells to treatment. Protein phosphatase 2C delta (referred to as WIP1) is a negative regulator of DDR and has been proposed as potential pharmaceutical target. Until recently, exploitation of WIP1 inhibition for suppression of cancer cell growth was compromised by the lack of selective small-molecule inhibitors effective at cellular and organismal levels. Here, we review recent advances in development of WIP1 inhibitors and discuss their potential use in cancer treatment.

Wip1: A candidate phosphatase for cancer diagnosis and treatment

The critical regulatory mechanisms in numerous cellular pathways including cell survival and DNA damage response mostly depend on phosphorylation and dephosphorylation of proteins. The serine/threonine phosphatase wild-type p53-induced phosphatase 1 (Wip1) is a growth-promoting phosphatase and its numerous downstream targets are important tumor suppressors. Here, we review the Wip1 activity and its relevance to cancer as an oncoprotein. Consecutive investigations about Wip1 and its relation to cancer is critical, as these studies ultimately contribute to the etiology of cancer. A number of innovative studies have recently investigated the importance of Wip1 as a new candidate for cancer diagnosis and prognosis. Accordingly, we discuss the present challenges of using Wip1 as a target for cancer treatment.

Negative auto-regulators trap p53 in their web

The transcriptional factor p53 activates the expression of a myriad of target genes involving a complicated signalling network, resulting in various cellular outcomes, such as growth arrest, senescence, apoptosis, and metabolic changes, and leading to consequent suppression of tumour growth and progression. Because of the profoundly adverse effect of p53 on growth and proliferation of cancer cells, several feedback mechanisms have been employed by the cells to constrain p53 activity. Two major antagonists MDM2 and MDMX (the long forms) are transcriptionally induced by p53, but in return block p53 activity, forming a negative feedback circuit and rendering chemoresistance of several cancer cells. However, they are not alone, as cancer cells also employ other proteins encoded by p53 target genes to inhibit p53 activity at transcriptional, translational, and posttranslational levels. This essay is thus composed to review a recent progress in understanding the mechanisms for how cancer cells hijack the p53 autoregulation by these proteins for their growth advantage and to discuss the clinical implications of these autoregulatory loops.

Wip1 inhibitor GSK2830371 inhibits neuroblastoma growth by inducing Chk2/p53-mediated apoptosis

Neuroblastoma (NB) is the most common extracranial tumor in children. Unlike in most adult tumors, tumor suppressor protein 53 (p53) mutations occur with a relatively low frequency in NB and the downstream function of p53 is intact in NB cell lines. Wip1 is a negative regulator of p53 and hindrance of Wip1 activity by novel inhibitor GSK2830371 is a potential strategy to activate p53’s tumor suppressing function in NB. Yet, the in vivo efficacy and the possible mechanisms of GSK2830371 in NB have not yet been elucidated. Here we report that novel Wip1 inhibitor GSK2830371 induced Chk2/p53-mediated apoptosis in NB cells in a p53-dependent manner. In addition, GSK2830371 suppressed the colony-formation potential of p53 wild-type NB cell lines. Furthermore, GSK2830371 enhanced doxorubicin- (Dox) and etoposide- (VP-16) induced cytotoxicity in a subset of NB cell lines, including the chemoresistant LA-N-6 cell line. More importantly, GSK2830371 significantly inhibited tumor growth in an orthotopic xenograft NB mouse model by inducing Chk2/p53-mediated apoptosis in vivo. Taken together, this study suggests that GSK2830371 induces Chk2/p53-mediated apoptosis both in vitro and in vivo in a p53 dependent manner.