Radiosensitization of lung cancer by nutlin, an inhibitor of murine double minute 2

Harnessing p53 for targeted cancer therapy: new advances and future directions

The transcription factor p53 is the most frequently impaired tumor suppressor in human cancers. In response to various stress stimuli, p53 activates transcription of genes that mediate its tumor-suppressive functions. Distinctive characteristics of p53 outlined here enable a well-defined program of genes involved in cell cycle arrest, apoptosis, senescence, differentiation, metabolism, autophagy, DNA repair, anti-viral response, and anti-metastatic functions, as well as facilitating autoregulation within the p53 network. This versatile, anti-cancer network governed chiefly by a single protein represents an immense opportunity for targeted cancer treatment, since about half of human tumors retain unmutated p53. During the last two decades, numerous compounds have been developed to block the interaction of p53 with the main negative regulator MDM2. However, small molecule inhibitors of MDM2 only induce a therapeutically desirable apoptotic response in a limited number of cancer types. Moreover, clinical trials of the MDM2 inhibitors as monotherapies have not met expectations and have revealed hematological toxicity as a characteristic adverse effect across this drug class. Currently, combination treatments are the leading strategy for enhancing efficacy and reducing adverse effects of MDM2 inhibitors. This review summarizes efforts to identify and test therapeutics that work synergistically with MDM2 inhibitors. Two main types of drugs have emerged among compounds used in the following combination treatments: first, modulators of the p53-regulated transcriptome (including chromatin modifiers), translatome, and proteome, and second, drugs targeting the downstream pathways such as apoptosis, cell cycle arrest, DNA repair, metabolic stress response, immune response, ferroptosis, and growth factor signaling. Here, we review the current literature in this field, while also highlighting overarching principles that could guide target selection in future combination treatments.

MDM2: current research status and prospects of tumor treatment

Mousedouble minute 2 (MDM2) is one of the molecules activated by p53 and plays an important role in the regulation of p53. MDM2 is generally believed to function as a negative regulator of p53 by facilitating its ubiquitination and subsequent degradation. Consequently, blocked p53 activity often fails in damaged cells to undergo cell cycle arrest or apoptosis. Given that around 50% of human cancers involve the inactivation of p53 through genetic mutations, and directly targeting p53 through drug development has limited feasibility, targeting molecular regulation related to p53 has great potential and has become a research hotspot. For example, developing drugs that target the interaction between p53 and MDM2. Such drugs aim to reactivate p53 by targeting either MDM2 binding or p53 phosphorylation. Researchers have identified various compounds that can serve as inhibitors, either by directly binding to MDM2 or by modifying p53 through phosphorylation. Furthermore, a significant correlation exists between the expression of MDM2 in tumors and the effectiveness of immunotherapy, predominantly in the context of immune checkpoint inhibition. This review presents a comprehensive overview of the molecular characteristics of MDM2 and the current state of research on MDM2-targeting inhibitors. It includes a review of the impact of MDM2 targeting on the efficacy of immunotherapy, providing guidance and direction for the development of drugs targeting the p53-MDM2 interaction and optimization of immunotherapy.

Therapeutics Targeting p53-MDM2 Interaction to Induce Cancer Cell Death

Named as the guardian of the genome, p53 is a tumor suppressor that regulates cell function, often through many different mechanisms such as DNA repair, apoptosis, cell cycle arrest, senescence, metabolism, and autophagy. One of the genes that p53 activates is MDM2, which forms a negative feedback loop since MDM2 induces the degradation of p53. When p53 activity is inhibited, damaged cells do not undergo cell cycle arrest or apoptosis. As 50% of human cancers inactivate p53 by mutation, current research focuses on reactivating p53 by developing drugs that target the p53-MDM2 interaction, which includes the binding of MDM2 and phosphorylation of p53. The objective of this article is to provide a short list and description of p53-MDM2 antagonists that may be excellent candidates for inducing cancer cell death. Relevant articles were searched for and identified using online databases such as PubMed and ScienceDirect. Increasing p53 levels, by targeting the p53-MDM2 interaction, can help p53 play its role as a tumor suppressor and induce cancer cell death. Researchers have identified different compounds that can act as inhibitors, either by directly binding to MDM2 or by modifying p53 with phosphorylation. The results associated with the drugs demonstrate the importance of targeting such interactions to inhibit cancer cell growth, which indicates that the use of the compounds may improve cancer therapeutics.

MDM2/X Inhibitors as Radiosensitizers for Glioblastoma Targeted Therapy

Inhibition of the MDM2/X-p53 interaction is recognized as a potential anti-cancer strategy, including the treatment of glioblastoma (GB). In response to cellular stressors, such as DNA damage, the tumor suppression protein p53 is activated and responds by mediating cellular damage through DNA repair, cell cycle arrest and apoptosis. Hence, p53 activation plays a central role in cell survival and the effectiveness of cancer therapies. Alterations and reduced activity of p53 occur in 25-30% of primary GB tumors, but this number increases drastically to 60-70% in secondary GB. As a result, reactivating p53 is suggested as a treatment strategy, either by using targeted molecules to convert the mutant p53 back to its wild type form or by using MDM2 and MDMX (also known as MDM4) inhibitors. MDM2 down regulates p53 activity via ubiquitin-dependent degradation and is amplified or overexpressed in 14% of GB cases. Thus, suppression of MDM2 offers an opportunity for urgently needed new therapeutic interventions for GB. Numerous small molecule MDM2 inhibitors are currently undergoing clinical evaluation, either as monotherapy or in combination with chemotherapy and/or other targeted agents. In addition, considering the major role of both p53 and MDM2 in the downstream signaling response to radiation-induced DNA damage, the combination of MDM2 inhibitors with radiation may offer a valuable therapeutic radiosensitizing approach for GB therapy. This review covers the role of MDM2/X in cancer and more specifically in GB, followed by the rationale for the potential radiosensitizing effect of MDM2 inhibition. Finally, the current status of MDM2/X inhibition and p53 activation for the treatment of GB is given.

Combination Strategies to Improve Targeted Radionuclide Therapy

In recent years, targeted radionuclide therapy (TRT) has emerged as a promising strategy for cancer treatment. In contrast to conventional radiotherapy, TRT delivers ionizing radiation to tumors in a targeted manner, reducing the dose that healthy tissues are exposed to. Existing TRT strategies include the use of 177Lu-DOTATATE, 131I-metaiodobenzylguanidine, Bexxar, and Zevalin, clinically approved agents for the treatment of neuroendocrine tumors, neuroblastoma, and non-Hodgkin lymphoma, respectively. Although promising results have been obtained with these agents, clinical evidence acquired to date suggests that only a small percentage of patients achieves complete response. Consequently, there have been attempts to improve TRT outcomes through combinations with other therapeutic agents; such strategies include administering concurrent TRT and chemotherapy, and the use of TRT with known or putative radiosensitizers such as poly(adenosine diphosphate ribose) polymerase and mammalian-target-of-rapamycin inhibitors. In addition to potentially achieving greater therapeutic effects than the respective monotherapies, these strategies may lead to lower dosages or numbers of cycles required and, in turn, reduce unwanted toxicities. As of now, several clinical trials have been conducted to assess the benefits of TRT-based combination therapies, sometimes despite limited preclinical evidence being available in the public domain to support their use. Although some clinical trials have yielded promising results, others have shown no clear survival benefit from particular combination treatments. Here, we present a comprehensive review of combination strategies with TRT reported in the literature to date and evaluate their therapeutic potential.

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.

Radiation Potentiates Monocyte Infiltration into Tumors by Ninjurin1 Expression in Endothelial Cells

Radiation is a widely used treatment for cancer patients, with over half the cancer patients receiving radiation therapy during their course of treatment. Considerable evidence from both preclinical and clinical studies show that tumor recurrence gets restored following radiotherapy, due to the influx of circulating cells consisting primarily of monocytes. The attachment of monocyte to endothelial cell is the first step of the extravasation process. However, the exact molecules that direct the transmigration of monocyte from the blood vessels to the tumors remain largely unknown. The nerve injury-induced protein 1 (Ninjurin1 or Ninj1) gene, which encodes a homophilic adhesion molecule and cell surface protein, was found to be upregulated in inflammatory lesions, particularly in macrophages/monocytes, neutrophils, and endothelial cells. More recently Ninj1 was reported to be regulated following p53 activation. Considering p53 has been known to be activated by radiation, we wondered whether Ninj1 could be increased in the endothelial cells by radiation and it might contribute to the recruiting of monocytes in the tumor. Here we demonstrate that radiation-mediated up-regulation of Ninj1 in endothelial cell lines such as human umbilical vein endothelial cells (HUVECs), EA.hy926, and immortalized HUVECs. Consistent with this, we found over-expressed Ninj1 in irradiated xenograft tumors, and increased monocyte infiltration into tumors. Radiation-induced Ninj1 was transcriptionally regulated by p53, as confirmed by transfection of p53 siRNA. In addition, Ninj1 over-expression in endothelial cells accelerated monocyte adhesion. Irradiation-induced endothelial cells and monocyte interaction was inhibited by knock-down of Ninj1. Furthermore, over-expressed Ninj1 stimulated MMP-2 and MMP-9 expression in monocyte cell lines, whereas the MMP-2 and MMP-9 expression were attenuated by Ninj1 knock-down in monocytes. Taken together, we provide evidence that Ninj1 is a key molecule that generates an interaction between endothelial cells and monocytes. This result suggests that radiation-mediated Ninj1 expression in endothelial cells could be involved in the post-radiotherapy recurrence mechanism.

MDM2 Inhibition in a Subset of Sarcoma Cell Lines Increases Susceptibility to Radiation Therapy by Inducing Senescence in the Polyploid Cells

Purpose

Inhibition of p53 by amplification of MDM2 is one of the key contributors in the oncogenesis of a subset of soft tissue sarcoma (STS) known as well-/dedifferentiated liposarcoma. A small molecule MDM2 antagonist, nutlin-3, induces the p53 pathway by disrupting the interaction between MDM2 and p53. Radiation therapy is an integral component for treating liposarcoma and induces p53. Based on wild-type TP53 status in liposarcoma, it was investigated whether MDM2 inhibition with irradiation led to enhanced reactivation of p53 and subsequent p53-mediated effects in liposarcoma.

Methods and Materials

Clonogenic assays, immunoblotting, flow cytometry/fluorescence-activated cell sorting, and senescence assays were employed in liposarcoma cell lines after co-treatment with nutlin-3 and radiation.

Results

Upon treatment with nutlin-3, 2 of the well-/dedifferentiated liposarcoma (MDM2^Amp/TP53^WT) cell lines displayed radiosensitivity with sensitization enhancement ratio values of >1. In contrast, the cell line with mutant TP53 showed sensitization enhancement ratio values of ∼1. Immunoblotting revealed induced reactivation of the p53-MDM2-p21 signaling axis in response to combination therapy in all cell lines with wild-type TP53. Removal of MDM2 inhibitor (with or without radiation therapy) led to the emergence of ploidy-based heterogeneous subpopulations (4N and >4N) in TP53 wild-type cells and not in TP53 mutant cells. Immunoblotting of cell cycle markers (G1, G2/M) revealed the generation of 4N G1 cells. Sorting and long-term fate analysis of different populations (2N, 4N, and >4N) by colony assay displayed attenuated colony-forming potential and augmented senescence of the 4N and >4N cells contributing to the radiosensitization effect.

Conclusions

Nutlin-3 increases the vulnerability of liposarcoma cell lines to radiation by augmented activation of p53. The cells underwent senescence. Presence and activation of p53 are required for exertion of the radiosensitizing effect by nutlin-3, but this is not the sole determinant of the effect. This study opens avenues for the clinical translation in a stratified group of patients with liposarcoma.

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.

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.

Mycoplasma hyorhinis reduces sensitivity of human lung carcinoma cells to Nutlin-3 and promotes their malignant phenotype

PURPOSE

MDM2 inhibitors are promising anticancer agents that induce cell cycle arrest and tumor cells death via p53 reactivation. We examined the influence of Mycoplasma hyorhinis infection on sensitivity of human lung carcinoma cells NCI-H292 to MDM2 inhibitor Nutlin-3. In order to unveil possible mechanisms underlying the revealed effect, we investigated gene expression changes and signal transduction networks activated in NCI-H292 cells in response to mycoplasma infection.

METHODS

Sensitivity of NCI-Н292 cells to Nutlin-3 was estimated by resazurin-based cell viability assay. Genome-wide transcriptional profiles of NCI-H292 and NCI-Н292Myc.h cell lines were determined using Illumina Human HT-12 v3 Expression BeadChip. Search for key transcription factors and key node molecules was performed using the geneXplain platform. Ability for anchorage-independent growth was tested by soft agar colony formation assay.

RESULTS

NCI-Н292Myc.h cells were shown to be 1.5- and 5.2-fold more resistant to killing by Nutlin-3 at concentrations of 15 and 30 µM than uninfected NCI-Н292 cells (P < 0.05 and P < 0.001, respectively). Transcriptome analysis revealed differential expression of multiple genes involved in cancer progression and metastasis as well as epithelial-mesenchymal transition (EMT). Moreover, we have shown experimentally that NCI-Н292Myc.h cells were more capable of growing and dividing without binding to a substrate. The most likely mechanism explaining the observed changes was found to be TLR4- and IL-1b-mediated activation of NF-κB pathway.

CONCLUSIONS

Our results provide evidence that mycoplasma infection is an important factor modulating the effect of MDM2 inhibitors on cancer cells and is able to induce EMT-related changes.

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.

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.

Nutlin-3a Nanodisks Induce p53 Stabilization and Apoptosis in a Subset of Cultured Glioblastoma Cells

Nanodisks (ND) are ternary complexes of phospholipid, one or more hydrophobic bioactive agents and an apolipoprotein scaffold. These nanoscale assemblies are organized as a disk-shaped lipid bilayer whose perimeter is stabilized by an apolipoprotein scaffold. Solubilization of hydrophobic bioactive agents is achieved by their integration into the ND lipid milieu. When the cis-imidazoline, nutlin-3a, was incubated with phosphatidylcholine and apolipoprotein A-I, it was conferred with aqueous solubility as judged by spectroscopic analysis. Nondenaturing polyacrylamide gel electrophoresis yielded evidence of a homogeneous population of ND particles ~9 nm in diameter. Gel filtration chromatography experiments revealed the association of nutlin-3a with ND is reversible. Biological activity of nutlin-3a ND was examined in three distinct glioblastoma cell lines, U87MG, SF763 and SF767. Incubation of U87MG cells with nutlin-3a ND induced concentration-dependent cell growth arrest and apoptosis. SF763 cells demonstrated modest cell growth arrest only at high concentrations of nutlin-3a ND and no apoptosis. SF767 cells were unaffected by nutlin-3a ND. Immunoblot analysis revealed nutlin-3a ND induced time-dependent stabilization of the master tumor suppressor, p53, and up regulation of the E3 ubiquitin ligase, murine double minute 2 in U87MG cells, but not the other glioma cell lines. The nanoscale size of the formulation particles, their facile assembly and nutlin-3a solubilization capability suggest ND represent a potentially useful vehicle for in vivo administration of this anti-tumor agent.

Roles of TP53 in determining therapeutic sensitivity, growth, cellular senescence, invasion and metastasis

TP53 is a critical tumor suppressor gene that regulates cell cycle progression, apoptosis, cellular senescence and many other properties critical for control of normal cellular growth and death. Due to the pleiotropic effects that TP53 has on gene expression and cellular physiology, mutations at this tumor suppressor gene result in diverse physiological effects. T53 mutations are frequently detected in numerous cancers. The expression of TP53 can be induced by various agents used to treat cancer patients such as chemotherapeutic drugs and ionizing radiation. Radiation will induce Ataxia telangiectasia mutated (ATM) and other kinases that results in the phosphorylation and activation of TP53. TP53 is also negatively regulated by other mechanisms, such as ubiquitination by ligases such as MDM2. While TP53 has been documented to control the expression of many "classical" genes (e.g., p21^Cip-1, PUMA, Bax) by transcriptional mechanisms for quite some time, more recently TP53 has been shown to regulate microRNA (miR) gene expression. Different miRs can promote oncogenesis (oncomiR) whereas others act to inhibit tumor progression (tumor suppressor miRs). Targeted therapies to stabilize TP53 have been developed by various approaches, MDM2/MDM4 inhibitors have been developed to stabilize TP53 in TP53-wild type (WT) tumors. In addition, small molecules have been isolated that will reactivate certain mutant TP53s. Both of these types of inhibitors are in clinical trials. Understanding the actions of TP53 may yield novel approaches to suppress cancer, aging and other health problems.

Preliminary evaluation of prostate-targeted radiotherapy using (131) I-MIP-1095 in combination with radiosensitising chemotherapeutic drugs

Objectives

Despite recent advances in the treatment of metastatic prostate cancer, survival rates are low and treatment options are limited to chemotherapy and hormonal therapy. ¹³¹I‐MIP‐1095 is a recently developed prostate‐specific membrane antigen (PSMA)‐targeting, small molecular weight radiopharmaceutical which has anti‐tumour activity as a single agent. Our purpose was to determine in vitro the potential benefit to be gained by combining ¹³¹I‐MIP‐1095 with cytotoxic drug treatments.

Methods

Various cytotoxic agents were evaluated in combination with ¹³¹I‐MIP‐1095 for their capacity to delay the growth of LNCaP cells cultured as multicellular tumour spheroids. Two end‐points were used to assess treatment efficacy: (i) the time required for doubling of spheroid volume and (ii) the area under the volume–time growth curves.

Key findings

The PARP‐1 inhibitor olaparib, the topoisomerase I inhibitor topotecan, the proteasome inhibitor bortezomib, the inhibitor of the P53–MDM2 interaction nutlin‐3 and the copper‐chelated form of the oxidising agent disulfiram (DSF:Cu) all significantly enhanced the inhibition of the growth of spheroids induced by ¹³¹I‐MIP‐1095. However, the Chk1 inhibitor AZD7762 failed to potentiate the effect of ¹³¹I‐MIP‐1095.

Conclusions

These results indicate that targeted radiotherapy of prostate cancer may be optimised by combining its administration with chemotherapy.

Relative apoptotic potential and specific G1 arrest of stigmasterol and cinnamic acid isolated from the brown algae Padina gymnospora in HeLa and A549 cells

Isolation, characterisation and identification of the molecular mechanism of apoptosis by small molecules from the Padina gymnospora of south east coast of India revealed that they exhibit tumor suppression mediated by p53 activation.

Drugging the p53 pathway: understanding the route to clinical efficacy

The tumour suppressor p53 is the most frequently mutated gene in human cancer, with more than half of all human tumours carrying mutations in this particular gene. Intense efforts to develop drugs that could activate or restore the p53 pathway have now reached clinical trials. The first clinical results with inhibitors of MDM2, a negative regulator of p53, have shown efficacy but hint at on-target toxicities. Here, we describe the current state of the development of p53 pathway modulators and new pathway targets that have emerged. The challenge of targeting protein-protein interactions and a fragile mutant transcription factor has stimulated many exciting new approaches to drug discovery.

Serdemetan antagonizes the Mdm2-HIF1α axis leading to decreased levels of glycolytic enzymes

Serdemetan (JNJ-26854165), an antagonist to Mdm2, was anticipated to promote the activation of p53. While regulation of p53 by Mdm2 is important, Mdm2 also regulates numerous proteins involved in diverse cellular functions. We investigated if Serdemetan would alter the Mdm2-HIF1α axis and affect cell survival in human glioblastoma cells independently of p53. Treatment of cells with Serdemetan under hypoxia resulted in a decrease in HIF1α levels. HIF1α downstream targets, VEGF and the glycolytic enzymes (enolase, phosphoglycerate kinase1/2, and glucose transporter 1), were all decreased in response to Serdemetan. The involvement of Mdm2 in regulating gene expression of glycolytic enzymes raises the possibility of side effects associated with therapeutically targeting Mdm2.

[P53 family proteins provide new insights into lung carcinogenesis and clinical treatment]

P53作为转录因子，其转录激活功能维持了基因组的稳定性，对防止肿瘤的形成起着重要作用，是目前研究得最为广泛、深入的抑癌基因，被称为“基因卫士”。P53家族的成员p63、p73与p53在DNA结合结构域上有高度的同源性，某些p53家族亚型可以与p53-反应基因相结合起着转录激活的作用，另外一些则起着负性调节作用。肺癌是世界上患病率最高的恶性肿瘤之一，p53家族成员在肺癌中的异常表达与肺癌的发生有密切联系，并导致不良的预后及对放疗、化疗的抵抗。对p53家族成员在肺癌致病机制的深入研究可有助于为临床提供合理的化疗方案及靶向治疗策略。本文着重回顾总结p53家族成员在肺癌发生、化疗敏感性以及肺癌靶向治疗中的独特的作用。

Nutlin-3a, an MDM2 antagonist and p53 activator, helps to preserve the replicative potential of cancer cells treated with a genotoxic dose of resveratrol

Resveratrol is a natural compound that has been intensely studied due to its role in cancer prevention and potential as an anti-cancer therapy. Its effects include induction of apoptosis and senescence-like growth inhibition. Here, we report that two cancer cell lines (U-2 OS and A549) differ significantly in their molecular responses to resveratrol. Specifically, in U-2 OS cells, the activation of the p53 pathway is attenuated when compared to the activation in A549 cells. This attenuation is accompanied by a point mutation (458: CGA→TGA) in the PPM1D gene and overexpression of the encoded protein, which is a negative regulator of p53. Experimentally induced knockdown of PPM1D in U-2 OS cells resulted in slightly increased activation of the p53 pathway, most clearly visible as stronger phosphorylation of p53 Ser37. When treated with nutlin-3a, a non-genotoxic activator of p53, U-2 OS and A549 cells both responded with substantial activation of the p53 pathway. Nutlin-3a improved the clonogenic survival of both cell lines treated with resveratrol. This improvement was associated with lower activation of DNA-damage signaling (phosphorylation of ATM, CHK2, and histone H2AX) and higher accumulation of cells in the G1 phase of the cell cycle. Thus, the hyperactivation of p53 by nutlin-3a helps to preserve the replicative potential of cells exposed to resveratrol.

Radiosensitization of wildtype p53 cancer cells by the MDM2-inhibitor PXN727 is associated with altered heat shock protein 70 (Hsp70) levels

The oncoprotein MDM2 (murine double minute 2) is often overexpressed in human tumors and thereby attenuates the function of the tumor suppressor p53. In this study, we investigated the effects of the novel MDM2-inhibitor PXN727 on p53 activation, cell proliferation, cell cycle distribution and radiosensitivity. Since the localization of heat shock protein 70 (Hsp70) exerts different effects on radioresistance of tumor cells, we investigated the impact of PXN727 on intracellular, membrane, and secreted Hsp70 levels. We could show that PXN727 exerts its effects on wildtype p53 (HCT116 p53⁺/⁺, A549) but not p53 depleted (HCT116 p53⁻/⁻) or mutated (FaDu) tumor cells. PXN727 activates p53, induces the expression of p21, reduces the proportion of cells in the radioresistant S-phase and induces senescence. Radiosensitivity was significantly increased by PXN727 in HCT116 p53⁺/⁺ tumor cells. Furthermore, PXN727 causes a downregulation of Hsp70 membrane expression and an upregulated secretion of Hsp70 in wildtype p53 tumor cells. Our data suggest that re-activation of p53 by MDM2-inhibition modulates Hsp70 membrane expression and secretion which might contribute to the radiosensitizing effect of the MDM2-inhibitor PXN727.

MDM2 inhibitor Nutlin-3a suppresses proliferation and promotes apoptosis in osteosarcoma cells

Restoring p53 activity by inhibiting the interaction between p53 and the mouse double minutes clone 2 (MDM2) offers an attractive approach to cancer therapy. Nutlin-3a is a small-molecule inhibitor that inhibits MDM2 binding to p53 and subsequent p53-dependent DNA damage signaling. In this study, we determined the efficacy of Nutlin-3a in inducing p53-mediated cell death in osteosarcoma (OS) cell lines both in vivo and in vitro. Targeted disruption of the p53-MDM2 interaction by Nutlin-3a stabilizes p53 and selectively activates the p53 pathway only in OS cells with wild-type p53, resulting in a pronounced anti-proliferative and cytotoxic effect due to G1 cell cycle arrest and apoptosis both in vitro and in vivo. p53 dependence of these alternative outcomes of Nutlin-3a treatment was shown by the abrogation of these effects when p53 was knocked-down by small interfering RNA. These data suggest that the disruption of p53-MDM2 interaction by Nutlin-3a might be beneficial for OS patients with MDM2 amplification and wt p53 status.

Pirh2 RING-finger E3 ubiquitin ligase: its role in tumorigenesis and cancer therapy

The ubiquitin-dependent proteasome system plays a critical role in many cellular processes and pathogenesis of various human diseases, including cancer. Although there are a large number of E3 ubiquitin ligases, the majority are RING-finger type E3s. Pirh2, a target of p53 transcription factor, contains a highly conserved C(3)H(2)C(3) type RING domain. Importantly, Pirh2 was found to regulate a group of key factors dedicated to the DNA damage response, such as p53, p73, PolH, and c-Myc. Interestingly, Pirh2 was upregulated or downregulated in different types of cancers. These suggest that Pirh2 is implicated in either promoting or suppressing tumor progression in a tissue-dependent manner. This review will focus on the major findings in these studies and discuss the potential to explore Pirh2 as a cancer therapeutic target.

The p53 circuit board

The p53 tumor suppressor is embedded in a large gene network controlling diverse cellular and organismal phenotypes. Multiple signaling pathways converge onto p53 activation, mostly by relieving the inhibitory effects of its repressors, MDM2 and MDM4. In turn, signals originating from increased p53 activity diverge into distinct effector pathways to deliver a specific cellular response to the activating stimuli. Much attention has been devoted to dissecting how the various input pathways trigger p53 activation and how the activity of the p53 protein itself can be modulated by a plethora of co-factors and post-translational modifications. In this review we will focus instead on the multiple configurations of the effector pathways. We will discuss how p53-generated signals are transmitted, amplified, resisted and eventually integrated by downstream gene circuits operating at the transcriptional, post-transcriptional and post-translational levels. We will also discuss how context-dependent variations in these gene circuits define the cellular response to p53 activation and how they may impact the clinical efficacy of p53-based targeted therapies.

A small-molecule p53 activator induces apoptosis through inhibiting MDMX expression in breast cancer cells

The tumor suppressor p53 is often inactivated in breast cancer cells because the overexpression of its repressors (e.g., MDM2 and MDMX). Restoration of p53 activity by small molecules through counteracting p53 repressors can lead to in vivo tumor regression and is therefore considered a promising strategy for treatments of cancer. Recent efforts in high-throughput drug screening and rational drug design have identified several structurally diverse small-molecule p53 activators, including a pseudourea derivative XI-011 (NSC146109). This small molecule strongly activates p53 while selectively inhibiting growth of transformed cells without inducing genotoxicity, indicating its potential as a drug lead for p53-targeted therapy. However, the mechanism(s) by which XI-011 activates p53 and the effects of XI-011 on growth of breast cancer cells are currently unknown. Here, we report that XI-011 promoted breast cancer cells to undergo apoptosis through activating p53 and inducing expression of proapoptotic genes. Importantly, we found that activation of p53 by this small molecule was achieved through a novel mechanism, that is, inhibition of MDMX expression. XI-011 repressed the MDMX promoter, resulting in down-regulation of MDMX messenger RNA level in MCF-7 cells. In line with these results, XI-011 decreased the viability of breast cancer cells expressing low levels of MDMX in a less-efficient manner. Interestingly, XI-011 acted additively with the MDM2 antagonist Nutlin-3a to inhibit growth of breast cancer cells. We conclude that XI-011 belongs to a novel class of small-molecule p53 activators that target MDMX and could be of value in treating breast cancer.

Targeting p53 for Novel Anticancer Therapy

Carcinogenesis is a multistage process, involving oncogene activation and tumor suppressor gene inactivation as well as complex interactions between tumor and host tissues, leading ultimately to an aggressive metastatic phenotype. Among many genetic lesions, mutational inactivation of p53 tumor suppressor, the "guardian of the genome," is the most frequent event found in 50% of human cancers. p53 plays a critical role in tumor suppression mainly by inducing growth arrest, apoptosis, and senescence, as well as by blocking angiogenesis. In addition, p53 generally confers the cancer cell sensitivity to chemoradiation. Thus, p53 becomes the most appealing target for mechanism-driven anticancer drug discovery. This review will focus on the approaches currently undertaken to target p53 and its regulators with an overall goal either to activate p53 in cancer cells for killing or to inactivate p53 temporarily in normal cells for chemoradiation protection. The compounds that activate wild type (wt) p53 would have an application for the treatment of wt p53-containing human cancer. Likewise, the compounds that change p53 conformation from mutant to wt p53 (p53 reactivation) or that kill the cancer cells with mutant p53 using a synthetic lethal mechanism can be used to selectively treat human cancer harboring a mutant p53. The inhibitors of wt p53 can be used on a temporary basis to reduce the normal cell toxicity derived from p53 activation. Thus, successful development of these three classes of p53 modulators, to be used alone or in combination with chemoradiation, will revolutionize current anticancer therapies and benefit cancer patients.

MDM2 antagonist Nutlin-3a potentiates antitumour activity of cytotoxic drugs in sarcoma cell lines

Background

Frequent failure and severe side effects of current sarcoma therapy warrants new therapeutic approaches. The small-molecule MDM2 antagonist Nutlin-3a activates the p53 pathway and efficiently induces apoptosis in tumours with amplified MDM2 gene and overexpression of MDM2 protein. However, the majority of human sarcomas have normal level of MDM2 and the therapeutic potential of MDM2 antagonists in this group is still unclear. We have investigated if Nutlin-3a could be employed to augment the response to traditional therapy and/or reduce the genotoxic burden of chemotherapy.

Methods

A panel of sarcoma cell lines with different TP53 and MDM2 status were treated with Nutlin-3a combined with Doxorubicin, Methotrexate or Cisplatin, and their combination index determined.

Results

Clear synergism was observed when Doxorubicin and Nutlin-3a were combined in cell lines with wild-type TP53 and amplified MDM2, or with Methotrexate in both MDM2 normal and amplified sarcoma cell lines, allowing for up to tenfold reduction of cytotoxic drug dose. Interestingly, Nutlin-3a seemed to potentiate the effect of classical drugs as Doxorubicin and Cisplatin in cell lines with mutated TP53, but inhibited the effect of Methotrexate.

Conclusion

The use of Nutlin in combination with classical sarcoma chemotherapy shows promising preclinical potential, but since clear biomarkers are still lacking, clinical trials should be followed up with detailed tumour profiling.

Pharmacologic activation of p53 by small-molecule MDM2 antagonists

Restoring p53 activity by inhibiting the interaction between p53 and MDM2 represents an attractive approach for cancer therapy. To this end, a number of small-molecule p53-MDM2 binding inhibitors have been developed during the past several years. Nutlin-3 is a potent and selective small-molecule MDM2 antagonist that has shown considerable promise in pre-clinical studies. This review will highlight recent advances in the development of small-molecule MDM2 antagonists as potential cancer therapeutics, with special emphasis on Nutlin-3.

A small-molecule inhibitor of MDMX activates p53 and induces apoptosis

The p53 inactivation caused by aberrant expression of its major regulators (e.g., MDM2 and MDMX) contributes to the genesis of a large number of human cancers. Recent studies have shown that restoration of p53 activity by counteracting p53 repressors is a promising anticancer strategy. Although agents (e.g., nutlin-3a) that disrupt MDM2-p53 interaction can inhibit tumor growth, they are less effective in cancer cells that express high levels of MDMX. MDMX binds to p53 and can repress the tumor suppressor function of p53 through inhibiting its trans-activation activity and/or destabilizing the protein. Here we report the identification of a benzofuroxan derivative [7-(4-methylpiperazin-1-yl)-4-nitro-1-oxido-2,1,3-benzoxadiazol-1-ium, NSC207895] that could inhibit MDMX expression in cancer cells through a reporter-based drug screening. Treatments of MCF-7 cells with this small-molecule MDMX inhibitor activated p53, resulting in elevated expression of proapoptotic genes (e.g., PUMA, BAX, and PIG3). Importantly, this novel small-molecule p53 activator caused MCF-7 cells to undergo apoptosis and acted additively with nutlin-3a to activate p53 and decrease the viability of cancer cells. These results thus show that small molecules targeting MDMX expression would be of therapeutic benefits.

Translating p53 into the clinic

Mutations in the TP53 gene are a feature of 50% of all reported cancer cases. In the other 50% of cases, the TP53 gene itself is not mutated but the p53 pathway is often partially inactivated. Cancer therapies that target specific mutant genes are proving to be highly active and trials assessing agents that exploit the p53 system are ongoing. Many trials are aimed at stratifying patients on the basis of TP53 status. In another approach, TP53 is delivered as a gene therapy; this is the only currently approved p53-based treatment. The p53 protein is overexpressed in many cancers and p53-based vaccines are undergoing trials. Processed cell-surface p53 is being exploited as a target for protein-drug conjugates, and small-molecule drugs that inhibit the activity of MDM2, the E3 ligase that regulates p53 levels, have been developed by several companies. The first MDM2 inhibitors are being trialed in both hematologic and solid malignancies. Finally, the first agent found to restore the active function of mutant TP53 has just entered the clinic. Here we discuss the basis of these trials and the future of p53-based therapy.

Nutlin-3, the small-molecule inhibitor of MDM2, promotes senescence and radiosensitises laryngeal carcinoma cells harbouring wild-type p53

BACKGROUND

Primary radiotherapy (RT) is a mainstay of treatment for laryngeal squamous cell carcinoma (LSCC). Although the cure rates for early (T1) vocal cord tumours are high, RT proves ineffective in up to a third of T3 carcinomas. Moreover, RT is associated with debilitating early- and late-treatment-related toxicity, thus finding means to de-escalate therapy, while retaining/augmenting therapeutic effectiveness, is highly desirable. p53 is a key mediator of radiation responses; we therefore investigated whether Nutlin-3, a small-molecule inhibitor of MDM2 (mouse double minute 2; an essential negative regulator of p53), might radiosensitise LSCC cells.

METHODS

We performed clonogenic assays to measure radiosensitivity in a panel of LSCC cell lines (for which we determined p53 mutational status) in the presence and absence of Nutlin-3.

RESULTS

LSCC cells harbouring wild-type p53 were significantly radiosensitised by Nutlin-3 (P<0.0001; log-rank scale), and displayed increased cell cycle arrest and significantly increased senescence (P<0.001) in the absence of increased apoptosis; thus, our data suggest that senescence may mediate this increased radiosensitivity.

CONCLUSION

This is the first study showing Nutlin-3 as an effective radiosensitiser in LSCC cells that retain wild-type p53. The clinical application of Nutlin-3 might improve local recurrence rates or allow treatment de-escalation in these patients.

Biomarkers in radiation oncology

The discovery of biomarkers in patients receiving radiation therapy for cancer is occurring at an exceptional pace. There are a number of ways to conduct biomarker investigations, although the majority of clinically relevant biomarker studies have used immunohistochemistry (IHC) on tissue specimens. Using IHC, expression of several pre-radiation biomarkers, such as VEGF, EGFR, YKL-40, murine double minute 2 and Rad51, has been associated with a poor outcome. Because tumor tissue may be difficult to obtain and IHC studies can be difficult to reproduce and standardize, investigators have attempted to find similar results when studying biomarkers of nontumor biospecimens, such as serum and urine. This has led to the discovery of a number of soluble biomarkers predictive of outcome (e.g., YKL-40, VEGF and matrix metallopeptidase-2). As we transition from the use of biopsy-based markers to surrogate soluble biomarkers in the hope of bringing these biomarkers into clinical use, we must ensure methods of standardization in sample collection, processing, storage and analysis to allow widespread reproducibility and accuracy of results.

Role of Mdm4 in drug sensitivity of breast cancer cells

The p53 tumor suppressor protein is frequently mutated in human tumors. It is thought that the p53 pathway is indirectly impaired in the remaining tumors, for example by overexpression of its important regulators Mdm2 and Mdm4, making them attractive targets for the development of anti-cancer agents. Recent studies have suggested that Mdm4 levels determine the sensitivity of tumor cells for anti-cancer therapy. To investigate this possibility, we studied the drug sensitivity of several breast cancer cell lines containing wild-type p53, but expressing different Mdm4 levels. We show that endogenous Mdm4 levels can affect the sensitivity of breast cancer cells to anti-cancer agents, but in a cell line-dependent manner and depending on an intact apoptotic response. Furthermore, treatment with the non-genotoxic agent Nutlin-3 sensitizes cells for doxorubicin, showing that activation of p53 by targeting its regulators is an efficient strategy to decrease cell viability of breast cancer cells. These results confirm a function of Mdm4 in determining the efficacy of chemotherapeutic agents to induce apoptosis of cancer cells in a p53-dependent manner, although additional undetermined factors also influence the drug response. Targeting Mdm4 to sensitize tumor cells for chemotherapeutic drugs might be a strategy to effectively treat tumors harboring wild-type p53.

Suppression of hypoxia-inducible factor 2alpha restores p53 activity via Hdm2 and reverses chemoresistance of renal carcinoma cells

p53 mutations are rarely detected in clear cell renal cell carcinoma (CCRCC), but, paradoxically, these tumors remain highly resistant to chemotherapy and death receptor-induced death. Here, we show that the accumulation of hypoxia-inducible factor 2alpha (HIF2alpha), a critical oncogenic event in CCRCC following the loss of von Hippel-Lindau (VHL) tumor suppressor protein, leads to Hdm2-mediated suppression of p53. Primary CCRCC specimens exhibiting strong hypoxic signatures show increased levels of activated nuclear phospho-Hdm2(Ser(166)), which is concomitant with low p53 expression. The abrogation of Hdm2-p53 interaction using the small-molecule Hdm2 inhibitor nutlin-3 or the downregulation of HIF2alpha via HIF2alpha-specific short hairpin RNA or wild-type VHL reconstitution restores p53 function and reverses the resistance of CCRCC cells to Fas-mediated and chemotherapy-induced cell death. These findings unveil a mechanistic link between HIF2alpha and p53 and provide a rationale for combining Hdm2 antagonists with chemotherapy for the treatment of CCRCC.

Antitumor activity of the selective MDM2 antagonist nutlin-3 against chemoresistant neuroblastoma with wild-type p53

BACKGROUND

Restoring p53 function by antagonizing its interaction with the negative regulator MDM2 is an appealing nongenotoxic approach to treating tumors with wild-type p53. Mutational inactivation of p53 is rare in neuroblastoma tumors at diagnosis and occurs in only a subset of multidrug-resistant neuroblastomas.

METHODS

The antiproliferative and cytotoxic effect of nutlin-3, a small-molecule MDM2 antagonist, was examined in chemosensitive (UKF-NB-3) and matched chemoresistant neuroblastoma cells with wild-type p53 (UKF-NB-3(r)DOX20) or with mutant p53 (UKF-NB-3(r)VCR10). Activation of the p53 pathway was assessed by expression analysis of p53 target genes, flow cytometric cell cycle analysis, and apoptosis assays. Mice with established chemoresistant tumor xenografts were treated orally with nutlin-3 or vehicle control (n = 5-10 mice per group) and were used to evaluate effects on tumor growth, p53 pathway activity, and metastatic tumor burden. All statistical tests were two-sided.

RESULTS

Nutlin-3 induced a similar activation of the p53 pathway in UKF-NB-3 and UKF-NB-3(r)DOX20 cells, as evidenced by increased expression of p53 target genes, G1 cell cycle arrest, and induction of apoptosis. No such response was observed in UKF-NB-3(r)VCR10 cells with mutant p53. Oral administration of nutlin-3 to UKF-NB-3(r)DOX20 xenograft-bearing mice led to inhibition of primary tumor growth (mean tumor volume after 3 weeks of treatment, nutlin-3- vs vehicle-treated mice: 772 vs 1661 mm3, difference = 890 mm3, 95% confidence interval = 469 to 1311 mm3, P < .001), p53 pathway activation, and reduction in the extent of metastatic disease. The growth of UKF-NB-3(r)VCR10 xenografts was unaffected by nutlin-3.

CONCLUSIONS

Nutlin-3 activates the p53 pathway and suppresses tumor growth in this model system of chemoresistant neuroblastoma, provided that wild-type p53 is present.

Recent advances in validating MDM2 as a cancer target

The MDM2 oncogene is overexpressed in various human cancers. Its expression correlates with the phenotypes of high-grade, late-stage, and more resistant tumors. The auto-regulatory loop between MDM2 and the tumor suppressor p53 has long been considered the epitome of a rational target for cancer therapy. As such, many novel agents have been generated to interfere with the interaction of the two proteins, which results in the activation of p53. Among these agents are several small molecule inhibitors synthesized based upon the crystal structures of the MDM2-p53 complex. With use of high-throughput screening, several specific and effective agents for inhibition of the protein-protein interaction were discovered. Recent investigations, however, have demonstrated that many proteins regulate the MDM2-p53 interaction, and that MDM2 may have p53-independent oncogenic functions. In order for novel MDM2 inhibitors to be translated to the clinic, it is necessary to obtain a better understanding of the regulation of MDM2 and of the MDM2-p53 interaction. In particular, the implications of various interactions between certain regulator(s) and MDM2/p53 under different circumstances need to be elucidated to determine which pathway(s) represent the best targets for therapy. Targeting both MDM2 itself and regulators of MDM2 and the MDM2-p53 interaction, or use of MDM2 inhibitors in combination with conventional treatments, may improve prospects for tumor eradication.

Radiosensitising agents for the radiotherapy of cancer: novel molecularly targeted approaches

BACKGROUND

The efficacy of radiotherapy (RT) for cancer treatment is limited by normal tissue toxicity and by the intrinsic or acquired radioresistance of many tumours. Therefore, continuing efforts are conducted to identify radiosensitising agents that preferentially sensitise tumour cells to the cytotoxic action of RT. Recent progresses in molecular oncology have uncovered an array of novel targets, which may be exploited for RT enhancement.

OBJECTIVE

To survey the patent literature of the past 4 years pertaining to the development of molecularly targeted agents as potential tumour radiosensitisers.

METHODS

Patents were searched with a set of relevant keywords using several search engines. A Medline search on the same topics was performed in parallel.

RESULTS/CONCLUSION

A total of 48 patents/applications were selected. These concerned agents target molecular components of pathways involved in DNA damage repair, cell growth and survival signalling, apoptosis modulation and tumour angiogenesis. Current trials of some of these agents may reveal their value as clinical radiosensitisers.

Nutlin-3 enhances tumor necrosis factor-related apoptosis-inducing ligand (TRAIL)-induced apoptosis through up-regulation of death receptor 5 (DR5) in human sarcoma HOS cells and human colon cancer HCT116 cells

MDM2 is a critical negative regulator of the p53 tumor suppressor protein. Recently, nutlins, small-molecule antagonists of MDM2, have been developed to inhibit the p53-MDM2 interaction and activate p53 signaling. The expressions of DR4 and DR5, Tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL) receptors, are regulated by p53. In this study, the combined effects of nutlin-3 and TRAIL on apoptosis were investigated in HOS and HCT116 cells, which express wild-type p53. Nutlin-3 and TRAIL synergistically enhanced apoptosis owing to their intrinsic and extrinsic pathway signals, respectively. The increase in the Bid expression level and the decrease in the expression levels of anti-apoptotic proteins, c-FLIP and XIAP, were involved in this apoptosis enhancement. Furthermore, nutlin-3 activated the DR5 promoter and increased the expression levels of DR5 at mRNA and protein levels. These results indicate that the combination, treated with nutlin-3 and TRAIL, is useful for apoptosis induction in malignant cells expressing wild-type p53.

Implications of endoplasmic reticulum stress, the unfolded protein response and apoptosis for molecular cancer therapy. Part I: targeting p53, Mdm2, GADD153/CHOP, GRP78/BiP and heat shock proteins

BACKGROUND

In eukaryotes, endoplasmic reticulum stress (ERS) and the unfolded protein response (UPR) are coordinately regulated to maintain steady-state levels and activities of various cellular proteins to ensure cell survival.

OBJECTIVE

This review (Part I of II) focuses on specific ERS and UPR signalling regulators, their expression in the cancer phenotype and apoptosis, and proposes how their implication in these processes can be rationalised into proteasome inhibition, apoptosis induction and the development of more efficacious targeted molecular cancer therapies.

METHOD

In this review, we contextualise many ERS and UPR client proteins that are deregulated or mutated in cancers and show links between ERS and the UPR, their implication in oncogenic transformation, tumour progression and escape from immune surveillance, apoptosis inhibition, angiogenesis, metastasis, acquired drug resistance and poor cancer prognosis.

CONCLUSION

Evasion of programmed cell death or apoptosis is a hallmark of cancer that enables tumour cells to proliferate uncontrollably. Successful eradication of cancer cells through targeting ERS- and UPR-associated proteins to induce apoptosis is currently being pursued as a central tenet of anticancer drug discovery.