New insights into p53 regulation and gene therapy for cancer

Genetic aberrations of the K-ras proto-oncogene in bladder cancer in relation to pesticide exposure

In Egypt, bladder cancer is one of the most popular cancers, accounting for 31% of all cancer cases. It ranks first in males about 16.2% of male cancer. The incidence in rural areas among males is near 32 per 100,000. The exact etiology of bladder cancer is still unknown; K-ras gene is known as a critical DNA target for chemical carcinogens such as pesticide. Some occupational hazard exposure is thought to be directly genotoxic, while others might enhance the mutagenicity and carcinogenicity of directly acting genotoxic agents. Analysis of the relationship between pesticide exposure and mutation in the K-ras gene in human bladder cancer. One hundred patients were diagnosed with bladder cancer and two hundred controls attended the outpatient clinic; after taking consent and filling a questionnaire for age, sex, occupation and pesticide exposure, surgically resected specimens were collected and the samples were used to determine the k-ras mutation. Blood samples were taken to analyze the level of acetylcholinesterase enzyme and level of P₅₃. The present study indicated that pesticide exposure may play a great role in malignant transformation of the bladder cells through mutation in the K-ras gene; there was a significant correlation between the acetylcholinesterase enzyme level and k-ras mutation (p < 0.001). The results revealed that the level of P₅₃ was significantly high in comparison with the control group (p < 0.001). These findings give an alarm to decrease the amount of pesticides used in our area; also, p₅₃ may be used as an indicator to bladder cancer.

Synergism between RIZ1 gene therapy and paclitaxel in SiHa cervical cancer cells

RIZ1 is a tumor suppressor gene. The purpose of the present study was to investigate the inhibitory effect of RIZ1 gene therapy on the growth of SiHa cervical cancer cells and its synergism with paclitaxel. The expression levels of RIZ1 were examined by real-time PCR and western blotting before and after transfection of RIZ1. The effects of paclitaxel or pcDNA3.1(+)-RIZ1 alone or in combination, on the proliferation of SiHa cells were evaluated by MTT method. The inhibitory effect on the proliferation of SiHa cells was more significant in the pcDNA3.1(+)-RIZ1 combined with paclitaxel group than in the pcDNA3.1(+)-RIZ1 or paclitaxel groups (P<0.05). The expression level of RIZ1 in SiHa cells increased after treatment with paclitaxel, which indicated a synergism between them. RIZ1 gene therapy combined with paclitaxel showed stronger cell inhibition than paclitaxel alone, which indicated a synergism between them.

Epigenetic therapies as a promising strategy for overcoming chemoresistance in epithelial ovarian cancer

Over the past decades, prognosis of advanced stage epithelial ovarian cancer remains very poor, despite the development of new chemotherapeutic drugs, as well as molecular targeted agents. Late presentation and frequent chemoresistance account for the poor prognosis. Emerging studies have shown that many genetic changes, especially p53 mutation, are associated with the chemoresistance. However, recent failure of the clinical trials using p53 gene-therapy makes researchers discuss the possible reasons for the failure. Epigenetic changes are considered one of the substantial reasons. Successful restoration of the aberrant epigenetic changes may be a promising strategy for overcoming chemoresistance in epithelial ovarian cancer. Herein, we will summarize the rationale for epigenetic therapy of cancer and current status of epigenetic studies in relation to chemoresistance in epithelial ovarian cancer.

Protein kinase G type Ialpha activity in human ovarian cancer cells significantly contributes to enhanced Src activation and DNA synthesis/cell proliferation

Previously, we showed that basal activity of nitric oxide (NO)/cyclic GMP (cGMP)/protein kinase G (PKG) signaling pathway protects against spontaneous apoptosis and confers resistance to cisplatin-induced apoptosis in human ovarian cancer cells. The present study determines whether basal PKG kinase activity regulates Src family kinase (SFK) activity and proliferation in these cells. PKG-Ialpha was identified as predominant isoform in both OV2008 (cisplatin-sensitive, wild-type p53) and A2780cp (cisplatin-resistant, mutated p53) ovarian cancer cells. In both cell lines, ODQ (inhibitor of endogenous NO-induced cGMP biosynthesis), DT-2 (highly specific inhibitor of PKG-Ialpha kinase activity), and PKG-Ialpha knockdown (using small interfering RNA) caused concentration-dependent inhibition of DNA synthesis (assessed by bromodeoxyuridine incorporation), indicating an important role of basal cGMP/PKG-Ialpha kinase activity in promoting cell proliferation. DNA synthesis in OV2008 cells was dependent on SFK activity, determined using highly selective SFK inhibitor, 4-(4'-phenoxyanilino)-6,7-dimethoxyquinazoline (SKI-1). Studies using DT-2 and PKG-Ialpha small interfering RNA revealed that SFK activity was dependent on PKG-Ialpha kinase activity. Furthermore, SFK activity contributed to endogenous tyrosine phosphorylation of PKG-Ialpha in OV2008 and A2780cp cells. In vitro coincubation of recombinant human c-Src and PKG-Ialpha resulted in c-Src-mediated tyrosine phosphorylation of PKG-Ialpha and enhanced c-Src autophosphorylation/activation, suggesting that human c-Src directly tyrosine phosphorylates PKG-Ialpha and the c-Src/PKG-Ialpha interaction enhances Src kinase activity. Epidermal growth factor-induced stimulation of SFK activity in OV2008 cells increased PKG-Ialpha kinase activity (indicated by Ser(239) phosphorylation of the PKG substrate vasodilator-stimulated phosphoprotein), which was blocked by both SKI-1 and SU6656. The data suggest an important role of Src/PKG-Ialpha interaction in promoting DNA synthesis/cell proliferation in human ovarian cancer cells. The NO/cGMP/PKG-Ialpha signaling pathway may provide a novel therapeutic target for disrupting ovarian cancer cell proliferation.

Soluble isoforms but not the transmembrane form of coxsackie-adenovirus receptor are of clinical relevance in epithelial ovarian cancer

The coxsackie-adenovirus receptor (hCAR) has been extensively studied in context of adenoviral-based gene therapy for cancer. However, there is strong evidence that besides its decisive role in coxsackie and adenovirus cell-entry, hCAR is a component of epithelial tight junctions and involved in cell-cell adhesions in normal and cancer cells. Furthermore, this adhesion molecule behaves like a cell surface receptor endowed with tumor suppressive properties via signal transduction. Moreover, 3 truncated soluble isoforms of hCAR were recently identified. We investigated the quantitative expression of all known CAR isoforms in a training set of 140 ovarian cancer samples and 21 controls by RT-PCR. The expression levels of the various isoforms were compared with clinicopathologic parameters and their prognostic significance was assessed. Expression levels of all CAR isoforms were elevated in ovarian carcinomas as compared with those of non-malignant controls. mRNA-expression correlated with protein levels. Moreover, expression of the soluble isoforms CAR 3/7 and CAR 4/7 but not that of hCAR was significantly increased in advanced ovarian cancer as revealed by a highly significant correlation with FIGO stage and residual disease > 2 cm in diameter after debulking surgery. High expression of CAR 3/7 and 4/7 was shown to be of independent prognostic relevance for progression-free (CAR 4/7) and overall survival (CAR 3/7 and CAR 4/7). In conclusion, soluble CAR isoforms 3/7 and 4/7 may play a pivotal role in ovarian cancer biology, possibly by counteracting migration- and growth-inhibitory properties of the membranous hCAR and thus favoring cancer cell dissemination throughout the peritoneal cavity.

p53—A Natural Cancer Killer: Structural Insights and Therapeutic Concepts

Every single day, the DNA of each cell in the human body is mutated thousands of times, even in absence of oncogenes or extreme radiation. Many of these mutations could lead to cancer and, finally, death. To fight this, multicellular organisms have evolved an efficient control system with the tumor-suppressor protein p53 as the central element. An intact p53 network ensures that DNA damage is detected early on. The importance of p53 for preventing cancer is highlighted by the fact that p53 is inactivated in more than 50 % of all human tumors. Thus, for good reason, p53 is one of the most intensively studied proteins. Despite the great effort that has been made to characterize this protein, the complex function and the structural properties of p53 are still only partially known. This review highlights basic concepts and recent progress in understanding the structure and regulation of p53, focusing on emerging new mechanistic and therapeutic concepts.

Combinational adenovirus-mediated gene therapy and dendritic cell vaccine in combating well-established tumors

Recent developments in tumor immunology and biotechnology have made cancer gene therapy and immunotherapy feasible. The current efforts for cancer gene therapy mainly focus on using immunogenes, chemogenes and tumor suppressor genes. Central to all these therapies is the development of efficient vectors for gene therapy. By far, adenovirus (AdV)-mediated gene therapy is one of the most promising approaches, as has confirmed by studies relating to animal tumor models and clinical trials. Dendritic cells (DCs) are highly efficient, specialized antigen-presenting cells, and DC-based tumor vaccines are regarded as having much potential in cancer immunotherapy. Vaccination with DCs pulsed with tumor peptides, lysates, or RNA, or loaded with apoptotic/necrotic tumor cells, or engineered to express certain cytokines or chemokines could induce significant antitumor cytotoxic T lymphocyte (CTL) responses and antitumor immunity. Although both AdV-mediated gene therapy and DC vaccine can both stimulate antitumor immune responses, their therapeutic efficiency has been limited to generation of prophylactic antitumor immunity against re-challenge with the parental tumor cells or to growth inhibition of small tumors. However, this approach has been unsuccessful in combating well-established tumors in animal models. Therefore, a major strategic goal of current cancer immunotherapy has become the development of novel therapeutic strategies that can combat well-established tumors, thus resembling real clinical practice since a good proportion of cancer patients generally present with significant disease. In this paper, we review the recent progress in AdV-mediated cancer gene therapy and DC-based cancer vaccines, and discuss combined immunotherapy including gene therapy and DC vaccines. We underscore the fact that combined therapy may have some advantages in combating well-established tumors vis-a-vis either modality administered as a monotherapy.

Cleavage of p53-vimentin complex enhances tumor necrosis factor-related apoptosis-inducing ligand-mediated apoptosis of rheumatoid arthritis synovial fibroblasts

Rheumatoid arthritis synovial fibroblasts (RASFs) contribute to arthritic cartilage degradation. Although RASFs are normally resistant to apoptosis, Apo2L/tumor necrosis factor-related apoptosis-inducing ligand (TRAIL)-based gene therapy has been successfully used in a mouse model of arthritis. We investigated this further by treating human RASFs with nontoxic doses of the proteasome inhibitor lactacystin. Treatment induced cytosolic accumulation of p53 and enhanced the susceptibility of RASFs to apoptosis mediated by TRAIL-R2 (DR5) but not Fas. A specific role for p53 in TRAIL-R2-mediated apoptosis was indicated by the ability of p53 siRNA to significantly reduce RASF apoptosis and by the reduced apoptosis of RASFs bearing p53 mutations on treatment with anti-DR5 antibody or anti-DR5 antibody plus lactacystin. p53 immunoprecipitation followed by mass spectrometry identified a vimentin-p53 complex, an interaction that was confirmed by reciprocal vimentin-p53 immunoprecipitation and by co-immunofluorescence. Interestingly, human caspase-4 cleaved human vimentin, and blockade of caspase-4 with a chemical inhibitor or with specific siRNA significantly inhibited TRAIL-R2-mediated apoptosis of RASFs. Furthermore, blockade of caspase-4 was paralleled by persistence of a cytosolic pattern of p53 and absence of p53 translocation to the nucleus. Taken together, our findings suggest a unique role for caspase-4 in cleaving vimentin and releasing cytosolic p53 for nuclear translocation, events that may regulate the sensitivity of RASFs to receptor-mediated apoptosis.

Adenovirus-mediated IKKβKA expression sensitizes prostate carcinoma cells to TRAIL-induced apoptosis

Despite the fact that tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) can selectively induce apoptosis in cancer cells, TRAIL resistance in cancer cells has challenged the use of TRAIL as a therapeutic agent. First, prostate carcinoma cell lines (DU145, LNCaP and PC3) were screened for sensitivity to adenovirus delivery of TRAIL (Ad5hTRAIL). As amplified Ikappa B kinase (IKK) activity is responsible for the constitutive nuclear factor-kappaB (NF-kappaB) activation leading to uncontrolled cell growth and metastasis, a dual vector approach using both an adenovirus vector (Ad) expressing the dominant-negative mutant of IKKbeta (AdIKKbetaKA) and Ad5hTRAIL was employed to determine if prostate cancer cells were sensitized to TRAIL in the setting of IKK inhibition. Inhibition of the NF-kappaB pathway through IKK blockade sensitized all three prostate cancer cell lines to TRAIL, regardless of NF-kappaB activation or decoy receptor gene expression. Moreover, a novel quantitative real-time RT-PCR assay and conventional flow cytometry analysis indicated that TRAIL-resistant DU145 and LNCaP cells, but not TRAIL-sensitive PC3 cells, expressed substantial amounts of TRAIL Decoy Receptor 4. In conclusion, TRAIL decoy receptor expression appeared to be the chief determinant of TRAIL resistance encountered in prostate carcinoma cell lines.

Surface TRAIL decoy receptor-4 expression is correlated with TRAIL resistance in MCF7 breast cancer cells

Background

Tumor Necrosis Factor (TNF)-Related Apoptosis-Inducing Ligand (TRAIL) selectively induces apoptosis in cancer cells but not in normal cells. Despite this promising feature, TRAIL resistance observed in cancer cells seriously challenged the use of TRAIL as a death ligand in gene therapy. The current dispute concerns whether or not TRAIL receptor expression pattern is the primary determinant of TRAIL sensitivity in cancer cells. This study investigates TRAIL receptor expression pattern and its connection to TRAIL resistance in breast cancer cells. In addition, a DcR2 siRNA approach and a complementary gene therapy modality involving IKK inhibition (AdIKKβKA) were also tested to verify if these approaches could sensitize MCF7 breast cancer cells to adenovirus delivery of TRAIL (Ad5hTRAIL).

Methods

TRAIL sensitivity assays were conducted using Molecular Probe's Live/Dead Cellular Viability/Cytotoxicity Kit following the infection of breast cancer cells with Ad5hTRAIL. The molecular mechanism of TRAIL induced cell death under the setting of IKK inhibition was revealed by Annexin V binding. Novel quantitative Real Time RT-PCR and flow cytometry analysis were performed to disclose TRAIL receptor composition in breast cancer cells.

Results

MCF7 but not MDA-MB-231 breast cancer cells displayed strong resistance to adenovirus delivery of TRAIL. Only the combinatorial use of Ad5hTRAIL and AdIKKβKA infection sensitized MCF7 breast cancer cells to TRAIL induced cell death. Moreover, novel quantitative Real Time RT-PCR assays suggested that while the level of TRAIL Decoy Receptor-4 (TRAIL-R4) expression was the highest in MCF7 cells, it was the lowest TRAIL receptor expressed in MDA-MB-231 cells. In addition, conventional flow cytometry analysis demonstrated that TRAIL resistant MCF7 cells exhibited substantial levels of TRAIL-R4 expression but not TRAIL decoy receptor-3 (TRAIL-R3) on surface. On the contrary, TRAIL sensitive MDA-MB-231 cells displayed very low levels of surface TRAIL-R4 expression. Furthermore, a DcR2 siRNA approach lowered TRAIL-R4 expression on surface and this sensitized MCF7 cells to TRAIL.

Conclusion

The expression of TRAIL-R4 decoy receptor appeared to be well correlated with TRAIL resistance encountered in breast cancer cells. Both adenovirus mediated IKKβKA expression and a DcR2 siRNA approach sensitized MCF7 breast cancer cells to TRAIL.

Signal transduction pathways as novel therapy targets in lung cancer

Cytotoxic therapy for lung-cancer patients has only moderately improved during the last decades. Simultaneously, efforts of intensive research to increase our understanding of the molecular basis of lung cancer have been undertaken. The cancer cell has been characterised by several genetic changes that lead to altered cellular functions. In addition, multiple factors of the cancer-cell environment further affect the tumour cell via various receptors and subsequent signaling pathways. The increased knowledge of cellular signaling offers the opportunity to develop novel substances that target specific pathway molecules. In the current review, some of the most essential receptors and signaling pathways involved in lung cancer will be described. In conjunction, examples of novel target-specific agents that have already found their way into clinical trials will be discussed.

Effects of Electrogenetherapy with p53wt Combined with Cisplatin on Survival of Human Tumor Cell Lines with Different p53 Status

The aim of our study was to evaluate electrogenetherapy with p53wt alone or combined with cisplatin on two colorectal (HT-29 and LoVo) and two prostatic (PC-3 and Du145) carcinoma cell lines with different p53 status. In addition, the feasibility of electrogenetherapy with p53wt was tested also in vivo on PC-3 prostatic cancer xenografts. Electrogenetherapy with p53wt was dependent on the p53 status of the cell lines used. Electrogenetherapy was the most effective on the PC-3 (p53 null) and Du145 (p53mt) cells, and to the much lesser extent in LoVo cells (p53wt). The exception was the HT-29 cell line with overexpressed mutated p53, where electrogenetherapy with p53wt was the least effective. Sensitivity of the cell lines to cisplatin was independent of the p53 status. Furthermore, the presence of exogenous p53 due to electrogenetherapy did not enhance cisplatin cytotoxicity, since the combination of these therapies resulted in additive cytotoxic effect. The effectiveness of electrogenetherapy with p53wt was also demonstrated in vivo by successful treatment of subcutaneous PC-3 tumors in mice. In conclusion, our study shows that electrogenetherapy with p53wt is feasible, and resulted in comparable cytotoxic and antitumor effectiveness to viral-mediated p53wt gene therapy. This therapy was effective and dependent on the p53 status of the tumor cell lines. Combination of electrogenetherapy and cisplatin resulted in additional cell kill by cisplatin, and was not dependent on the p53 status.

Etoposide upregulates Bax-enhancing tumour necrosis factor-related apoptosis inducing ligand-mediated apoptosis in the human hepatocellular carcinoma cell line QGY-7703

Tumour necrosis factor-related apoptosis-inducing ligand (TRAIL) has attracted much attention because of its ability to kill tumour cells. In this study, we demonstrated that treatment of QGY-7703 cells with the combination of TRAIL and etoposide resulted in synergistic cytotoxic effects. In dissecting the mechanism underlying this synergistic effect, we found that treatment with etoposide alone resulted in the upregulation of Bax, while the level of truncated Bid (tBid) was unchanged. In contrast, while treatment with TRAIL alone significantly increased the level of tBid, the expression of Bax remained unaffected. The enhanced apoptosis was accompanied by an increased release of cytochrome c and second mitochondria-derived activator of caspase/direct IAP binding protein with low pI (DIABLO) from mitochondria, leading to the activation of cellular caspase-8, -9, -3 and -7, as well as poly ADP-ribose polymerase. This enhanced release of cytochrome c and second mitochondria-derived activator of caspase/DIABLO was inhibited by the general caspase inhibitor N-benzyloxycarbonyl-Val-Ala-Asp-fluoromethylketone. The RT-PCR and Western blotting results demonstrated that the levels of both mRNA and protein for death receptor-4, death receptor-5 and decoy receptor-2 remained unchanged in response to etoposide, indicating that the synergistic effect of TRAIL and etoposide is not a result of increasing the expression for TRAIL receptors, but rather is associated with amplification of the mitochondrial signal pathway.

Why did p53 gene therapy fail in ovarian cancer?

Promising preclinical and clinical data led to the initiation of an international randomised phase II/III trial of p53 gene-therapy trial for first-line treatment of patients with ovarian cancer. In that trial, replication-deficient adenoviral vectors carrying wild-type p53 were given intraperitoneally in combination with standard chemotherapy to patients with ovarian cancers harbouring p53 mutations. The study was closed after the first interim analysis because an adequate therapeutic benefit was not shown. In this review, we discuss the possible reasons for failure of p53 gene therapy, which include the multiple genetic changes in cancer and epigenetic dysregulations leading to aberrant silencing of genes. These complex interactions lead us to conclude that repair of single genes might not be a suitable strategy for the treatment of cancer. Moreover, dominant negative cross talk between ectopic wild-type p53 and recently identified dominant p53 mutants and splice variants of p63 and p73--which are frequently overexpressed in ovarian cancers--could seriously compromise the effectiveness of p53 gene therapy. Other substantial problems in targeting tumour cells with adenoviral vectors are the heterogeneity or lack of expression of coxsackie-adenovirus receptors and integrin co-receptors in ovarian tumours and the presence of adenovirus-neutralising antibodies in ovarian cancer-related ascites.

Restoring apoptosis as a strategy for cancer gene therapy: focus on p53 and mda-7

Understanding the molecular and genetic determinants of cancer will provide unique opportunities for developing rational and effective therapies. Malignant cells are frequently resistant to chemotherapy and radiation induced programmed cell death (apoptosis). This resistance can occur by mutations in the tumor suppressor gene p53. Strategies designed to replace this defective tumor suppressor protein, as well as forced expression of a novel cancer specific apoptosis inducing gene, melanoma differentiation associated gene-7 (mda-7), offer promise for restoring apoptosis in tumor cells. Conditional-replicating viruses that selectively induce cytolysis in tumor cells provides an additional means of targeting cancer cells for destruction. Although these approaches represent works in progress, future refinements will in all likelihood result in the next generation of cancer therapies.

Determination of molecules regulating gene delivery using adenoviral vectors in ovarian carcinomas

Gene therapeutic approaches currently favor adenoviral vectors over alternatively available vector systems. Ovarian cancer represents an attractive model for an intraperitoneal adenovirus-based gene therapy, which is now under intensive clinical investigation. Adenovirus-mediated gene transfer depends on adequate virus uptake and thus on the presence of sufficient amounts of high-affinity coxsackie-adenovirus receptor (CAR) and alphavbeta3- and alphavbeta5 integrins on target cells. This fact has been ignored in most ongoing clinical trials. This investigation, therefore, determined expression of CAR by immunohistochemistry in 37 ovarian carcinomas and compared it with that of alphavbeta3 and alphavbeta5 integrins. In all samples, except one undifferentiated carcinoma, CAR was immunohistochemically demonstrable. Grade 1 tumors exhibited stronger CAR immunostaining as compared with higher-grade cancers (P < 0.03). Integrins alphavbeta3 and alphavbeta5 were detectable in 62% and 65% of carcinomas, respectively, and staining for both classes correlated positively (P < 0.005). Cancers classified as undifferentiated completely lacked alphavbeta3 expression. Furthermore, in undifferentiated and grade 3 carcinomas the three molecules studied exhibited marked distributional heterogeneity with regard to focal positivity and negativity within the same tumor. Either the absence of CAR, alphavbeta3 and alphavbeta5 or the pronounced heterogeneity in their expression might seriously compromise the efficiency of adenovirus-based gene therapy in ovarian cancer.

Activation and activities of the p53 tumour suppressor protein

The p53 tumour suppressor protein inhibits malignant progression by mediating cell cycle arrest, apoptosis or repair following cellular stress. One of the major regulators of p53 function is the MDM2 protein, and multiple forms of cellular stress activate p53 by inhibiting the MDM2-mediated degradation of p53. Mutations in p53, or disruption of the pathways that allow activation of p53, seem to be a general feature of all cancers. Here we review recent advances in our understanding of the pathways that regulate p53 and the pathways that are induced by p53, as well as their implications for cancer therapy.