Restoration of wild-type p53 function in human tumors: strategies for efficient cancer therapy

Targeting multifunctional magnetic nanowires for drug delivery in cancer cell death: an emerging paradigm

Apoptosis, often known as programmed cell death is a mechanism used by numerous species to maintain tissue homeostasis. The process leading to cell death is complicated because it requires the stimulation of caspases. According to several studies, nanowires have important medical benefits, can kill cells by adhering to cancer cells, destroying them, and killing the entire cell using a triple attack that integrates vibration, heat, and drug delivery to trigger apoptosis. The sewage effluents and industrial, fertilizer and organic wastes decomposition can produce elevated levels of chemicals in the environment which may interrupt the cell cycle and activate apoptosis. The purpose of this review is to give a thorough summary of the evidence that is currently available on apoptosis. Current review discussed topics like the morphological and biochemical alterations that occur during apoptosis, as well as the various mechanisms that cause cell death, including the intrinsic (or mitochondrial), extrinsic (or death receptor), and intrinsic endoplasmic reticulum pathway. The apoptosis reduction in cancer development is mediated by (i) an imbalance between pro- and anti-apoptotic proteins, such as members of the B-cell lymphoma-2 (BCL2) family of proteins, tumour protein 53 and inhibitor of apoptosis proteins, (ii) a reduction in caspase activity, and (iii) impaired death receptor signalling. This review does an excellent task of outlining the function of nanowires in both apoptosis induction and targeted drug delivery for cancer cells. A comprehensive summary of the relevance of nanowires synthesised for the purpose of inducing apoptosis in cancer cells has been compiled collectively.

Asperolide A induces apoptosis and cell cycle arrest of human hepatoma cells with p53-Y220C mutant through p38 mediating phosphorylation of p53 (S33)

Asperolides A (AA), one of the new tetranorlabdane diterpenoids, is proved to inhibit the proliferation of lung cancer cells and bone metastasis of breast cancer cells. Herein, we report that AA induces apoptosis and cell cycle arrest of hepatoma cells. It intensely inhibits proliferation of Huh-7 cell, compared with HepG-2 and L02 cells. AA elevates the activity of mitogen-activated protein kinases (MAPKs), in which the activation of ERK and JNK improves cell survival. However, phosphorylation of p53 at S33 by p38 activation could be a principal factor in the AA-induced apoptosis and G2/M cell cycle arrest of Huh-7 cells. The S33 site of p53-Y220C mutant, as the specific activation site of p38, reactivates the wild-type function of mutant p53 protein, which leads to a higher sensitivity of Huh-7 cells to AA. These results provide new insights into the molecular mechanisms of AA as a developing mutant p53 rescue drug.

Silencing E3 Ubiqutin ligase ITCH as a potential therapy to enhance chemotherapy efficacy in p53 mutant neuroblastoma cells

P53 mutations are responsible for drug-resistance of tumour cells which impacts on the efficacy of treatment. Alternative tumour suppressor pathways need to be explored to treat p53- deficient tumours. The E3 ubiquitin ligase, ITCH, negatively regulates the tumour suppressor protein TP73, providing a therapeutic target to enhance the sensitivity of the tumour cells to the treatment. In the present study, two p53-mutant neuroblastoma cell lines were used as in vitro models. Using immunostaining, western blot and qPCR methods, we firstly identified that ITCH was expressed on p53-mutant neuroblastoma cell lines. Transfection of these cell lines with ITCH siRNA could effectively silence the ITCH expression, and result in the stabilization of TP73 protein, which mediated the apoptosis of the neuroblastoma cells upon irradiation treatment. Finally, in vivo delivery of the ITCH siRNA using nanoparticles to the neuroblastoma xenograft mouse model showed around 15–20% ITCH silencing 48 hours after transfection. Our data suggest that ITCH could be silenced both in vitro and in vivo using nanoparticles, and silencing of ITCH sensitizes the tumour cells to irradiation treatment. This strategy could be further explored to combine the chemotherapy/radiotherapy treatment to enhance the therapeutic effects on p53-deficient neuroblastoma.

The identification of the ATR inhibitor VE-822 as a therapeutic strategy for enhancing cisplatin chemosensitivity in esophageal squamous cell carcinoma

Inducing DNA damage is known to be one of the mechanisms of cytotoxic chemotherapy agents for cancer such as cisplatin. The endogenous DNA damage response confers chemoresistance to these agents by repairing DNA damage. The initiation and transduction of the DNA damage response (DDR) signaling pathway, which is dependent on the activation of ATM (ataxia-telangiectasia mutated) and ATR (ataxia telangiectasia and Rad3-related), is essential for DNA damage repair, the maintenance of genomic stability and cell survival. Therefore, ATM or ATR inhibition is considered as a promising strategy for sensitizing cancer cells to chemotherapy. This study is aimed to explore the effect of ATR inhibitor on sensitizing ESCC (esophageal squamous cell carcinoma) cells to cisplatin, and whether ATM deficiency could impact the sensitization. We found that 21.5% of ESCC cases had ATM deficiency and that patients with ATR activation after neoadjuvant chemotherapy had worse chemotherapy response and poorer overall survival than that without ATR activation (32 mons vs. >140mons). Then, it was shown that VE-822 inhibited ATR-CHK1 pathway activation, leading to the accumulation of cisplatin-modified DNA. And it inhibited cell proliferation, induced cell cycle arrest in G1 phase and enhanced cell apoptosis. Moreover, VE-822 significantly sensitized ESCC cells to cisplatin, and these two drugs had synergistic effects, especially in ATM-deficient cells, in vitro and in vivo. Our results suggest that ATR inhibition combining with cisplatin is a new strategy for managing patients with ESCC, especially those with ATM-deficiency. However, this is an idea that requires further validation.

Full-length p53 tetramer bound to DNA and its quaternary dynamics

P53 is a major tumor suppressor that is mutated and inactivated in ~50% of all human cancers. Thus, reactivation of mutant p53 using small molecules has been a long sought-after anticancer therapeutic strategy. Full structural characterization of the full-length oligomeric p53 is challenging because of its complex architecture and multiple highly flexible regions. To explore p53 structural dynamics, here we developed a series of atomistic integrative models with available crystal structures of the full-length p53 (fl-p53) tetramer bound to three different DNA sequences: a p21 response element, a puma response element and a nonspecific DNA sequence. Explicitly solvated, all-atom molecular dynamics simulations of the three complexes (totaling nearly 1 μs of aggregate simulation time) yield final structures consistent with electron microscopy maps and, for the first time, show the direct interactions of the p53 C-terminal with DNA. Through a collective principal component analysis, we identify sequence-dependent differential quaternary binding modes of the p53 tetramer interfacing with DNA. Additionally, L1 loop dynamics of fl-p53 in the presence of DNA is revealed, and druggable pockets of p53 are identified via solvent mapping to aid future drug discovery studies.

Clinical utility of recombinant adenoviral human p53 gene therapy: current perspectives

Gene therapy has promised to be a highly effective antitumor treatment by introducing a tumor suppressor gene or the abrogation of an oncogene. Among the potential therapeutic transgenes, the tumor suppressor gene p53 serves as an attractive target. Restoration of wild-type p53 function in tumors can be achieved by introduction of an intact complementary deoxyribonucleic acid copy of the p53 gene using a suitable viral vector, in most cases an adenoviral vector (Adp53). Preclinical in vitro and in vivo studies have shown that Adp53 triggers a dramatic tumor regression response in various cancers. These viruses are engineered to lack certain early proteins and are thus replication defective, including Gendicine, SCH-58500, and Advexin. Several types of tumor-specific p53-expressing conditionally replicating adenovirus vectors (known as replication-competent CRAdp53 vectors) have been developed, such as ONYX 015, AdDelta24-p53, SG600-p53, OBP-702, and H101. Various clinical trials have been conducted to investigate the safety and efficiency of these adenoviral vectors. In this review we will talk about the biological mechanisms, clinical utility, and therapeutic potentials of the replication-deficient Adp53-based and replication-competent CRAdp53-based gene therapy.

Small molecule BMH-compounds that inhibit RNA polymerase I and cause nucleolar stress

Activation of the p53 pathway has been considered a therapeutic strategy to target cancers. We have previously identified several p53-activating small molecules in a cell-based screen. Two of the compounds activated p53 by causing DNA damage, but this modality was absent in the other four. We recently showed that one of these, BMH-21, inhibits RNA polymerase I (Pol I) transcription, causes the degradation of Pol I catalytic subunit RPA194, and has potent anticancer activity. We show here that three remaining compounds in this screen, BMH-9, BMH-22, and BMH-23, cause reorganization of nucleolar marker proteins consistent with segregation of the nucleolus, a hallmark of Pol I transcription stress. Further, the compounds destabilize RPA194 in a proteasome-dependent manner and inhibit nascent rRNA synthesis and expression of the 45S rRNA precursor. BMH-9- and BMH-22-mediated nucleolar stress was detected in ex vivo-cultured human prostate tissues indicating good tissue bioactivity. Testing of closely related analogues showed that their activities were chemically constrained. Viability screen for BMH-9, BMH-22, and BMH-23 in the NCI60 cancer cell lines showed potent anticancer activity across many tumor types. Finally, we show that the Pol I transcription stress by BMH-9, BMH-22, and BMH-23 is independent of p53 function. These results highlight the dominant impact of Pol I transcription stress on p53 pathway activation and bring forward chemically novel lead molecules for Pol I inhibition, and, potentially, cancer targeting.

SIRT1 inhibition restores apoptotic sensitivity in p53-mutated human keratinocytes

Mutations to the p53 gene are common in UV-exposed keratinocytes and contribute to apoptotic resistance in skin cancer. P53-dependent activity is modulated, in part, by a complex, self-limiting feedback loop imposed by miR-34a-mediated regulation of the lysine deacetylase, SIRT1. Expression of numerous microRNAs is dysregulated in squamous and basal cell carcinomas; however the contribution of specific microRNAs to the pathogenesis of skin cancer remains untested. Through use of RNAi, miRNA target site blocking oligonucleotides and small molecule inhibitors, this study explored the influence of p53 mutational status, SIRT1 activity and miR-34a levels on apoptotic sensitivity in primary (NHEK) and p53-mutated (HaCaT) keratinocyte cell lines. SIRT1 and p53 are overexpressed in p53-mutated keratinocytes, whilst miR-34a levels are 90% less in HaCaT cells. HaCaTs have impaired responses to p53/SIRT1/miR-34a axis manipulation which enhanced survival during exposure to the chemotherapeutic agent, camptothecin. Inhibition of SIRT1 activity in this cell line increased p53 acetylation and doubled camptothecin-induced cell death. Our results demonstrate that p53 mutations increase apoptotic resistance in keratinocytes by interfering with miR-34a-mediated regulation of SIRT1 expression. Thus, SIRT1 inhibitors may have a therapeutic potential for overcoming apoptotic resistance during skin cancer treatment.

Supramolecular self-assembly forming a multifunctional synergistic system for targeted co-delivery of gene and drug

For developing a multifunctional bioreducible targeted and synergistic co-delivery system for anticancer drug paclitaxel (PTX) and p53 gene for potential cancer therapy, supramolecular self-assembled inclusion complex was prepared from PTX and star-shaped cationic polymer containing γ-cyclodextrin (γ-CD) and multiple oligoethylenimine (OEI) arms with folic acid (FA) conjugated via a disulfide linker. The inclusion complex, termed as γ-CD-OEI-SS-FA/PTX, was formed between PTX and the hydrophobic cavity of γ-CD core of the star polymer. The γ-CD-OEI-SS-FA/PTX complex further formed polyplexes with pDNA to give positively charged nanoparticles, becoming multifunctional supramolecular self-assembled co-delivery system for PTX and pDNA targeting to cancer cells that overexpress folate receptors (FRs). The results showed that the FA-targeted function induced higher gene transfection efficiency in the FR-positive KB cells. The redox-sensitive disulfide linker in the self-assembly system led to the detachment of the FA groups from the carrier after the FR-mediated endocytosis, which resulted in the release of the bound FRs followed by the recycling of the FRs from the cytosol onto the cell membrane surface, facilitating continuous FR-mediated endocytosis to achieve enhanced gene transfection. In addition, the complexed PTX was co-delivered to the cells with pDNA, which further enhanced the gene transfection even at low N/P ratios in the FR-positive KB cells. Further, the efficient delivery of wild-type p53 gene resulted in large cell population at sub G1 and G2/M phases, inducing significant cell apoptosis. Therefore, the multifunctional γ-CD-OEI-SS-FA/PTX self-assembly system with the synergistic effects of redox-sensitive FA-targeted and PTX-enhanced p53 gene delivery may be promising for cancer therapeutic application.

p53 as an intervention target for cancer and aging

p53 is well known for suppressing tumors but could also affect other aging processes not associated with tumor suppression. As a transcription factor, p53 responds to a variety of stresses to either induce apoptosis (cell death) or cell cycle arrest (cell preservation) to suppress tumor development. Yet, the effect p53 has on the non-cancer aspects of aging is complicated and not well understood. On one side, p53 could induce cellular senescence or apoptosis to suppress cancer but as an unintended consequence enhance the aging process especially if these responses diminish stem and progenitor cell populations. But on the flip side, p53 could reduce growth and growth-related stress to enable cell survival and ultimately delay the aging process. A better understanding of diverse functions of p53 is essential to elucidate its influences on the aging process and the possibility of targeting p53 or p53 transcriptional targets to treat cancer and ameliorate general aging.

Identification of potential synthetic lethal genes to p53 using a computational biology approach

BACKGROUND

Identification of genes that are synthetic lethal to p53 is an important strategy for anticancer therapy as p53 mutations have been reported to occur in more than half of all human cancer cases. Although genome-wide RNAi screening is an effective approach to finding synthetic lethal genes, it is costly and labor-intensive.

METHODS

To illustrate this approach, we identified potentially druggable genes synthetically lethal for p53 using three microarray datasets for gene expression profiles of the NCI-60 cancer cell lines, one next-generation sequencing (RNA-Seq) dataset from the Cancer Genome Atlas (TCGA) project, and one gene expression data from the Cancer Cell Line Encyclopedia (CCLE) project. We selected the genes which encoded kinases and had significantly higher expression in the tumors with functional p53 mutations (somatic mutations) than in the tumors without functional p53 mutations as the candidates of druggable synthetic lethal genes for p53. We identified important regulatory networks and functional categories pertinent to these genes, and performed an extensive survey of literature to find experimental evidence that support the synthetic lethality relationships between the genes identified and p53. We also examined the drug sensitivity difference between NCI-60 cell lines with functional p53 mutations and NCI-60 cell lines without functional p53 mutations for the compounds that target the kinases encoded by the genes identified.

RESULTS

Our results indicated that some of the candidate genes we identified had been experimentally verified to be synthetic lethal for p53 and promising targets for anticancer therapy while some other genes were putative targets for development of cancer therapeutic agents.

CONCLUSIONS

Our study indicated that pre-screening of potential synthetic lethal genes using gene expression profiles is a promising approach for improving the efficiency of synthetic lethal RNAi screening.

p53-stabilizing agent CP-31398 prevents growth and invasion of urothelial cancer of the bladder in transgenic UPII-SV40T mice

The high prevalence of bladder cancer and its recurrence make it an important target for chemoprevention. About half of invasive urothelial tumors have mutations in p53. We determined the chemopreventive efficacy of a p53-stabilizing agent, CP-31398, in a transgenic UPII-SV40T mouse model of bladder transitional cell carcinoma (TCC) that strongly resembles human TCC. After genotyping, six-week-old UPII-SV40T mice (n = 30/group) were fed control (AIN-76A) or experimental diets containing 150 or 300 ppm of CP-31398 for 34 weeks. Progression of bladder cancer growth was monitored by magnetic resonance imaging. At 40 weeks of age, all mice were killed; urinary bladders were collected to determine weights, tumor incidence, and histopathology. There was a significant increase in bladder weights of transgenic versus wild-type mice (male: 140.2 mg vs 27.3 mg, P < .0001; female: 34.2 mg vs 14.8 mg, P < .0001). A significant decrease in the bladder tumor weights (by 68.6-80.2%, P < .0001 in males and by 36.9-55.3%, P < .0001 in females) was observed in CP-31398-treated mice. Invasive papillary TCC incidence was 100% in transgenic mice fed control diet. Both male and female mice exposed to CP-31398 showed inhibition of invasive TCC. CP-31398 (300 ppm) completely blocked invasion in female mice. Molecular analysis of the bladder tumors showed an increase in apoptosis markers (p53, p21, Bax, and Annexin V) with a decrease in vascular endothelial growth factor in transgenic mice fed CP-31398. These results suggest that p53-modulating agents can serve as potential chemopreventive agents for bladder TCC.

Computational identification of a transiently open L1/S3 pocket for reactivation of mutant p53

The tumour suppressor p53 is the most frequently mutated gene in human cancer. Reactivation of mutant p53 by small molecules is an exciting potential cancer therapy. Although several compounds restore wild-type function to mutant p53, their binding sites and mechanisms of action are elusive. Here computational methods identify a transiently open binding pocket between loop L1 and sheet S3 of the p53 core domain. Mutation of residue Cys124, located at the centre of the pocket, abolishes p53 reactivation of mutant R175H by PRIMA-1, a known reactivation compound. Ensemble-based virtual screening against this newly revealed pocket selects stictic acid as a potential p53 reactivation compound. In human osteosarcoma cells, stictic acid exhibits dose-dependent reactivation of p21 expression for mutant R175H more strongly than does PRIMA-1. These results indicate the L1/S3 pocket as a target for pharmaceutical reactivation of p53 mutants.

About 40% of human cancers carry missense mutations in the tumour suppressor protein p53. Here the authors identify a transiently open pocket in the protein, and by targeting a small molecule to it, partially restore mutant p53 tumour suppressor activity.

Pharmacokinetics and tissue and tumor exposure of CP-31398, a p53-stabilizing agent, in rats

PURPOSE

CP-31398 (N0-[2-[(E)-2-(4-methoxyphenyl)ethenyl] quinazolin-4-yl]-N,N-dimethylpropane-1,3-diamine hydrochloride) is one of the new class of agents that can stabilize the DNA-binding domain of p53 and thereby maintain the activity of p53 as a tumor suppressor and transcription factor. Through its activity as a p53 stabilizer, CP-31398 demonstrates significant cancer preventive and therapeutic activity in several in vivo animal models. The objective of the current study was to describe the pharmacokinetic profile and tissue distribution of this novel agent following intravenous or oral (gavage and dietary) administration.

METHODS

CP-31398 was administered to male CD and F344 rats as a single intravenous bolus dose or by daily oral gavage dosing. Male F344 rats also received drug as an ad libitum dietary supplement. Plasma, liver, skin, colon, and colon tumor samples were collected after oral dosing. Concentrations of CP-31398 in plasma and tissue samples were analyzed using LC–MS/MS, and the resultant data were subjected to a non-compartmental pharmacokinetic analysis.

RESULTS

Bioavailability (12–32%), elimination half-life (14–20 h), clearance (4.2–4.8 l/h/kg), and volume of distribution (70–82 l/kg) were determined. Tissue levels of CP-31398 after oral (gavage or diet) administration were several orders of magnitude higher than were corresponding plasma concentrations; CP-31398 levels were especially high in colon and liver. Levels of CP-31398 in tissues were higher after gavage dosing than after dietary administration.

CONCLUSIONS

CP-31398 is bioavailable and has a relatively long elimination half-life, which supports the achievement of plasma steady-state levels with a once daily dosing regimen. CP-31398 exhibits a dramatically high volume of distribution, which is consistent with its tissue concentrations being much higher than corresponding plasma levels. It is accumulated in colon tumor tissues, albeit at lower concentrations than found in liver, skin, and colon.

Interference with p53 functions in human viral infections, a target for novel antiviral strategies?

Viral infections cause a major stress in host cells. The cellular responses to stress are mediated by p53, which by deregulation of cell cycle and apoptosis, may also be part of the host cell reaction to fight infections. Therefore, during evolutionary viral adaptation to host organisms, viruses have developed strategies to manipulate host cell p53 dependent pathways to facilitate their viral life cycles. Thus, interference with p53 function is an important component in viral pathogenesis. Many viruses have proteins that directly affect p53, whereas others alter the regulation of p53 in an indirect manner, mediated by Hdm2 or Akt, or induction of interferon. Rescue of p53 activity is becoming an area of therapeutic development in oncology. It might be feasible that manipulation of p53 mediated responses can become a therapeutic option to limit viral replication or dissemination. In this report, the mechanisms by which viral proteins manipulate p53 responses are reviewed, and it is proposed that a pharmacological rescue of p53 functions might help to control viral infections.

[Recent advances in mutant p53 and novel personalized strategies for cancer therapy]

Protein p53 is the most intensively studied tumor suppressor protein. Recent studies keep revealing its new function in metabolism and reproduction. At the same time, it is also found that varieties of p53 mutant gained new function in promoting tumorigenesis. These studies provide the basis for understanding the personalized gain of function of p53 mu-tants and help us searching for the new strategies for reactivation of wild-type p53 and correction of the function of p53 mutants. The personalized treatment targeting different p53 mutants will be the focus for cancer treatment. Here, we re-viewed the discovered gain of function of some p53 mutants and the molecular strategies for reactivating wild type p53 function: by use of small molecules or polypeptides to reactivate the wild type function of p53 mutants in tumor cells; by exogenous expression of wild type p53 carried by recombinant adenovirus in tumor cells; and by inhibition the interaction between p53 and mdm2 to stabilize wild type p53 proteins. Further study of variety of p53 point mutations farcilitates de-signing more effectively personalized strategies in the cancer therapy.

Combination of vorinostat and flavopiridol is selectively cytotoxic to multidrug-resistant neuroblastoma cell lines with mutant TP53

As p53 loss of function (LOF) confers high-level drug resistance in neuroblastoma, p53-independent therapies might have superior activity in recurrent neuroblastoma. We tested the activity of vorinostat, a histone deacetylase inhibitor, and flavopiridol, a pan-Cdk inhibitor, in a panel of multidrug-resistant neuroblastoma cell lines that included lines with wild-type (wt) and transcriptionally active TP53 (n = 3), mutated (mt), and LOF TP53 (n = 4) or p14(ARF) deletion (n = 1). The combination of vorinostat and flavopiridol was synergistic and significantly more cytotoxic (P < 0.001) in cell lines with p53-LOF and in the clones stably transfected with dominant-negative p53 plasmids. Cell cycle analysis by flow cytometry showed prominent cell-cycle arrest in G(2)/M (37%) for a cell line with wt TP53 (SK-N-RA) at 16 to 20 hours, while cells with mt TP53 (CHLA-90) slipped into sub-G(1) at 6 to 24 hours (25%-40% specific cell death). The morphological hallmarks of mitotic cell death, including defective spindle formation and abnormal cytokinesis, were detected by confocal microscopy after the treatment with vorinostat + flavopiridol combination in CHLA-90. The combination caused reduction in the expression of G(2)/M proteins (cyclin B1, Mad2, MPM2) in 2 cell lines with mt TP53 but not in those with wt TP53. Plk1 expression was reduced in all treated lines. Small interfering RNA knockdown of Mad2 and cyclin B1 or Plk1 synergistically reduced the clonogenicity of CHLA-90 cells. The combination of HDAC inhibitor and flavopiridol may be a unique approach to treating neuroblastomas with p53 LOF, one that evokes induction of mitotic failure.

Anti-tumor effect of adenoviral vector-mediated p53 gene transfer on the growth of canine osteosarcoma xenografts in nude mice

We evaluated the anti-tumor effect of adenoviral vector-mediated p53 gene therapy on the growth of canine osteosarcoma xenografts formed in nude mice. Nude mice were subcutaneously transplanted with cells of 2 P53 mutant canine osteosarcoma cell lines, POS and CHOS. The osteosarcoma xenografts were injected with either an adenoviral vector that expresses canine wild-type P53 (AxCA-cp53) or LacZ (AxCA-LacZ). Tumor growth was significantly inhibited in the xenografts injected with AxCA-cp53 in comparison to those injected with AxCA-LacZ or PBS during the observation period of 27 days. An increase of the amount of p21(WAF1/CDKN1A) mRNA, and the number of apoptotic cells was shown in the tumors injected with AxCA-cp53 in comparison to those injected with AxCA-LacZ or PBS. The present study revealed that the adenoviral vector-mediated p53 gene transfer had an anti-tumor effect in canine osteosarcoma xenografts formed in nude mice.

APR-246 exhibits anti-leukemic activity and synergism with conventional chemotherapeutic drugs in acute myeloid leukemia cells

BACKGROUND

APR-246 belongs to a new generation of the compounds that restore normal p53 function in cells with mutated or wild type p53. The purpose of this study was to examine the effects of APR-246 alone and in combination with other drugs in acute myeloid leukemia (AML) cells.

METHODS

Primary leukemic cells from patients with AML and AML cell lines were studied with respect to cytotoxic and apoptotic effects and mechanism of action of APR-246, alone and in combination with Ara-C, daunorubicin and fludarabine.

RESULTS

APR-246 showed dose-dependent cytotoxic and apoptotic effects in AML cell lines as well as in primary AML patient cells. Cells from patients with TP53 mutation and complex karyotype were more resistant to conventional drugs while these factors did not significantly affect the sensitivity to APR-246. APR-246 increased active caspase-3, upregulated p53 protein levels, and increased the bax/bcl-2 ratio independently of TP53 mutational status in patient cells sensitive to APR-246. AML cells with high p14(ARF) expression were significantly more sensitive to APR-246. APR-246 induced significant synergistic effects in combination with conventional chemotherapeutic agents. Pre-incubation with APR-246 induced more synergistic effects compared to other schedules. In patient cells, pronounced synergism was found when combining APR-246 with danuorubicin.

CONCLUSION

We conclude that APR-246 is effective in AML cells irrespectively of TP53 mutational status and that it has promising properties for combination studies in AML.

Pro-oncogenic and anti-oncogenic pathways: opportunities and challenges of cancer therapy

Carcinogenesis is the uncontrolled growth of cells gaining the potential to invade and disrupt vital tissue functions. This malignant process includes the occurrence of 'unwanted' gene mutations that induce the transformation of normal cells, for example, by overactivation of pro-oncogenic pathways and inactivation of tumor-suppressive or anti-oncogenic pathways. It is now recognized that the number of major signaling pathways that control oncogenesis is not unlimited; therefore, suppressing these pathways can conceivably lead to a cancer cure. However, the clinical application of cancer intervention has not matched up to scientific expectations. Increasing numbers of studies have revealed that many oncogenic-signaling elements show double faces, in which they can promote or suppress cancer pathogenesis depending on tissue type, cancer stage, gene dosage and their interaction with other players in carcinogenesis. This complexity of oncogenic signaling poses challenges to traditional cancer therapy and calls for considerable caution when designing an anticancer drug strategy. We propose future oncology interventions with the concept of integrative cancer therapy.

Radiation-induced cell death mechanisms

The main goal when treating malignancies with radiation therapy is to deprive tumor cells of their reproductive potential. One approach to achieve this is by inducing tumor cell apoptosis. Accumulating evidences suggest that induction of apoptosis alone is insufficient to account for the therapeutic effect of radiotherapy. It has become obvious in the last few years that inhibition of the proliferative capacity of malignant cells following irradiation, especially with solid tumors, can occur via alternative cell death modalities or permanent cell cycle arrests, i.e., senescence. In this review, apoptosis and mitotic catastrophe, the two major cell deaths induced by radiation, are described and dissected in terms of activating mechanisms. Furthermore, treatment-induced senescence and its relevance for the outcome of radiotherapy of cancer will be discussed. The importance of p53 for the induction and execution of these different types of cell deaths is highlighted. The efficiency of radiotherapy and radioimmunotherapy has much to gain by understanding the cell death mechanisms that are induced in tumor cells following irradiation. Strategies to use specific inhibitors that will manipulate key molecules in these pathways in combination with radiation might potentiate therapy and enhance tumor cell kill.

Current strategies to target p53 in cancer

Tumor suppressor p53 is a transcription factor that guards the genome stability and normal cell growth. Stresses like DNA damage, oncogenic assault will turn on p53 function which leads to cell cycle arrest for DNA repair, senescence for permanent growth arrest or apoptosis for programmed cell death. At the late stage of cancer progression, p53 is hijacked in all forms of tumors either trapped in the negative regulator such as MDM2/viral proteins or directly mutated/deleted. Re-introduction of a functional p53 alone has been proven to induce tumor regression robustly. Also, an active p53 pathway is essential for effective chemo- or radio-therapy. The emerging cyclotherapy in which p53 acts as a chemoprotectant of normal tissues further expands the utility of p53 activators. Functionally, it is unquestionable that drugging p53 will render tumor-specific intervention. One direct method is to deliver the functional wild-type (wt) p53 to tumors via gene therapy. The small molecule strategies consist of activation of p53 family member such as p73, manipulating p53 posttranslational modulators to increase wt p53 protein levels, protein-protein interaction inhibitors to free wt p53 from MDM2 or viral protein, and restoring p53 function to mutant p53 by direct modulation of its conformation. Although most of the current pre-clinical leads are in microM range and need further optimization, the success in proving that small molecules can reactivate p53 marks the beginning of the clinical development of p53-based cancer therapy.

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.

PRIMA-1MET induces nucleolar translocation of Epstein-Barr virus-encoded EBNA-5 protein

The low molecular weight compound, PRIMA-1^MET restores the transcriptional transactivation function of certain p53 mutants in tumor cells. We have previously shown that PRIMA-1^MET induces nucleolar translocation of p53, PML, CBP and Hsp70. The Epstein-Barr virus encoded, latency associated antigen EBNA-5 (also known as EBNA-LP) is required for the efficient transformation of human B lymphocytes by EBV. EBNA-5 associates with p53-hMDM2-p14ARF complexes. EBNA-5 is a nuclear protein that translocates to the nucleolus upon heat shock or inhibition of proteasomes along with p53, hMDM2, Hsp70, PML and proteasome subunits. Here we show that PRIMA-1^MET induces the nucleolar translocation of EBNA-5 in EBV transformed B lymphoblasts and in transfected tumor cells. The PRIMA-1^MET induced translocation of EBNA-5 is not dependent on the presence of mutant p53. It also occurs in p53 null cells or in cells that express wild type p53. Both the native and the EGFP or DSRed conjugated EBNA-5 respond to PRIMA-1^MET treatment in the same way. Image analysis of DSRed-EBNA-5 expressing cells, using confocal fluorescence time-lapse microscopy showed that the nucleolar translocation requires several hours to complete. FRAP (fluorescence recovery after photobleaching) and FLIP (fluorescence loss in photobleaching) measurements on live cells showed that the nucleolar translocation was accompanied by the formation of EBNA-5 aggregates. The process is reversible since the aggregates are dissolved upon removal of PRIMA-1^MET. Our results suggest that mutant p53 is not the sole target of PRIMA-1^MET. We propose that PRIMA-1^MET may reversibly inhibit cellular chaperons that prevent the aggregation of misfolded proteins, and that EBNA-5 may serve as a surrogate drug target for elucidating the precise molecular action of PRIMA-1^MET.

Restoration of p53 to limit tumor growth

PURPOSE OF REVIEW

p53 mutation occurs in over half of all human tumors. Among the remaining tumors, although they may process a wild-type p53, the pathways of p53-induced cell-cycle arrest and apoptosis are deficient. Therefore, p53 serves as a unique molecular target for cancer therapy. This review focuses on the current progress regarding restoration of p53 function in human tumors for molecularly targeted therapy.

RECENT FINDINGS

Targeting p53 for cancer therapy has been intensively pursued. CP-31398 was the first small molecule identified with the ability to restore the wild-type conformation to mutant p53. Subsequently, PRIMA-1 and ellipticine were found to be able to induce mutant p53-dependent cell death. Nutlin was developed to rescue wild-type p53 from degradation mediated by MDM2. More recently, p53 family members can be activated and therefore serve as substitutes of p53 in tumor cells and induce cell death.

SUMMARY

Loss of p53 function is a characteristic of almost all human tumors. Recent advances demonstrate that reconstitution of p53 function is possible and practical as a promising antitumor strategy.