Antisense oligonucleotides directed against p53 have antiproliferative effects unrelated to effects on p53 expression

p53-regulated lncRNAs in cancers: from proliferation and metastasis to therapy

Long non-coding RNAs (lncRNAs) have been identified as master gene regulators through various mechanisms such as transcription, translation, protein modification and RNA-protein complexes. LncRNA dysregulation is frequently associated with a variety of biological functions and human diseases including cancer. The p53 network is a key tumor-suppressive mechanism that transcriptionally activates target genes to suppress cellular proliferation in human malignancies. Recent research indicates that lncRNAs play an important role in the p53 signaling pathway. In this review, we summarize the current knowledge of lncRNAs in p53-relevant functions and provide an overview of how these altered lncRNAs contribute to tumor initiation and progression. We also discuss the association between lncRNA and up- or downstream genes of p53. These findings imply that lncRNAs can help identify cellular vulnerabilities that may prove to be promising potential biomarkers and therapeutic targets for cancer treatment.

Review : p53 in the pathogenesis, diagnosis, and treatment of cancer

Objective. The cellular functions of p53, the conse quences of the loss of p53 function, and the potential impact of p53 in oncology are reviewed within the framework of an overview of the molecular basis of cancer and cell cycle control.

Data Sources. A MEDLINE search of articles from 1976 to the present was conducted using the terms p53 protein and p53 gene. The search was restricted to the English language. Oncology and molecular biology textbooks were used as additional references.

Data Extraction. We reviewed the literature to discuss the cellular function of p53, the mechanisms of p53 inactivation, the cellular consequences of the loss of p53 function, the role of p53 loss in tumori genesis, and the potential applications of this knowl edge.

Data Synthesis. p53 mutations are found in ~ 50% of human cancers. Knowledge of p53 functions and defects provides the basis for potential applica tions in the areas of cancer epidemiology, cancer diagnosis, and determination of prognosis. An under standing of the functions and defects of p53 also presents a host of opportunities for the design of novel cancer therapies. Therapeutic approaches be ing studied include the restoration of p53 by gene therapy, the alteration of mutant p53 expression by antisense therapy, and the use of p53 mutations as a target for directing therapy to cancer cells; some of these approaches are already under phase I investiga tion. As knowledge of p53 unfolds, additional thera peutic approaches will certainly be developed. The story of p53 illustrates that the manipulation of mo lecular interactions is a new frontier in therapeutics and offers an additional role for oncology pharmacy specialists.

Determination of cellular uptake and intracellular levels of Cenersen (Aezea(®), EL625), a p53 antisense oligonucleotide in acute myeloid leukemia cells

TP53 encodes for tumor protein p53. The suppression of p53 protein results in interruption of DNA repair mechanisms in dividing malignant cells thereby increasing the DNA damage and activating p53-independent mechanisms of apoptosis. This ultimately may translate into enhanced cytotoxic effects of standard chemotherapy. Based on this rationale, Cenersen, a phosphorothioate oligonucleotide antisense to p53-mRNA was synthesized and tested in clinical trials for patients with acute myeloid leukemia (AML). An important component of Cenersen clinical development is to develop a sensitive and specific method to quantify plasma and intracellular levels of Cenersen in different biologic matrices in order to determine tissue and intracellular distribution of the parent compound and its metabolites. Ultimately, this will allow us to determine pharmacokinetic and pharmacodynamic relationship for dose-effect correlation and design effective regimen to be rapidly translate into the clinic. An ELISA-based assay was adapted for assay development and validation of Cenersen in mouse plasma and cell lysate. Cellular uptake of Cenersen was studied in MV4-11 and KASUMI-1 AML cell lines. Real-time RT-PCR was used to measure P53-mRNA expression changes in treated cells. The assay had a limit of quantification of 35pmol/L in mouse plasma. Within-day and between-day precision of <15% and accuracy nearly 100% were observed in a linear range of 10-2000pmol/L (R(2)=0.99) in AML cell lysate. The selectivity of this assay examined as cross-reactivity with its 3'N-1, 3'N-2-metabolites, was 16.8% and 0.4%, respectively, and with its mismatch and the scramble oligonucleotides was 0.06% and 0.4%, respectively. Cenersen was stable in mouse plasma up to 8h at 37°C. When exposed to 0.1-1μmol/L Cenersen, MV4-11 and KASUMI-1 cells showed intracellular concentration in the range of 9.97-45.34nmol/mg protein and 0.1-2.1nmol/mg protein, respectively. Successful downregulation of p53-mRNA expression was observed in Cenersen treated cells. This ELISA-based assay was applicable to plasma and intracellular concentration measurement of Cenersen. Assessment of achievable concentration of Cenersen in different biologic matrices will be useful to elucidate the biological and clinical activity of this promising drug and define its recommended dose in future clinical trials.

Progress in antisense technology

Antisense technology exploits oligonucleotide analogs to bind to target RNAs via Watson-Crick hybridization. Once bound, the antisense agent either disables or induces the degradation of the target RNA. Antisense agents can also alter splicing. During the past decade, much has been learned about the basic mechanisms of antisense, the medicinal chemistry, and the pharmacologic, pharmacokinetic, and toxicologic properties of antisense molecules. Antisense technology has proven valuable in gene functionalization and target validation. With one drug marketed, Vitravenetm, and approximately 20 antisense drugs in clinical development, it appears that antisense drugs may prove important in the treatment of a wide range of diseases.

Terminally modified oligodeoxynucleotides directed against p53 in an orthotopic xenograft model: a novel adjuvant treatment strategy for pancreatic ductal carcinoma

OBJECTIVES

Investigation of a terminally modified oligodeoxynucleotide (ODN) directed against p53 mRNA (p53-3' polyethylene glycol-5' tocopherol ODN as a novel drug for pancreatic ductal carcinoma therapy in vitro and in vivo.

METHODS

The impact of lipophilic modifications at the 5' end of p53-directed ODNs on cellular uptake was analyzed in vitro using proliferation assays, fluorescence-activated cell sorting analysis, and confocal laser scanning microscopy. The in vivo effects of p53-PT-ODN on the growth of orthotopically xenografted human pancreatic ductal carcinoma cells (PancTuI) were studied in SCID beige mice. Distribution was examined in vitro and in vivo using Cy3-labeled ODNs.

RESULTS

Terminally modified p53-PT-ODN showed excellent cellular uptake without using transfection reagents. Microscopically detectable levels of p53-PT-ODN were reached in vivo within 3 hours after intraperitoneal injection, even in extraperitoneal organs. At this time, Cy3-labeled p53-PT-ODN was found in solid tumor formations. We observed a significant inhibition of tumor growth (50%) in vivo at low doses of p53-PT-ODN, whereas at high doses, 2 of 9 animals had no detectable tumors at necropsy. When p53-PT-ODN was injected on the day of tumor cell inoculation, the growth inhibition of solid tumors was significantly stronger compared with that with delayed treatment.

CONCLUSIONS

p53-Directed modified ODNs might be of therapeutic value in pancreatic ductal carcinoma, particularly as adjuvant therapy after pancreatic tumor resection.

Strategies for reversing drug resistance

Drug resistance, intrinsic or acquired, is a problem for all chemotherapeutic agents. In this review, we examine numerous strategies that have been tested or proposed to reverse drug resistance. Included among these strategies are approaches targeting the apoptosis pathway. Although the process of apoptosis is complex, it provides several potential sites for therapeutic intervention. A variety of targets and approaches are being pursued, including the suppression of proteins inhibiting apoptosis using antisense oligonucleotides (ASOs), and small molecules targeted at proteins that modulate apoptosis. An alternate strategy is based on numerous studies that have documented methylation of critical regions in the genome in human cancers. Consequently, efforts have been directed at re-expressing genes, including genes that affect drug sensitivity, using 5-azacytidine and 2'-deoxy-5-azacytidine (DAC, decitabine) as demethylating agents. While this strategy may be effective as a single modality, success will most likely be achieved if it is used to modulate gene expression in combination with other modalities such as chemotherapy. At a more basic level, attempts have been made to modulate glutathione (GSH) levels. Owing to its reactivity and high intracellular concentrations, GSH has been implicated in resistance to several chemotherapeutic agents. Several approaches designed to deplete intracellular GSH levels have been pursued including the use of buthionine-(S,R)-sulfoxime (BSO), a potent and specific inhibitor of gamma-glutamyl cysteine synthetase (gamma-GCS), the rate-limiting step in the synthesis of GSH, a hammerhead ribozyme against gamma-GCS mRNA to downregulate specifically its levels and targeting cJun expression to reduce GSH levels. Alternate strategies have targeted p53. The frequent occurrence of p53 mutations in human cancer has led to the development of numerous approaches to restore wild-type (wt) p53. The goals of these interventions are to either revert the malignant phenotype or enhance drug sensitivity. The approach most extensively investigated has utilized one of several viral vectors. An alternate approach, the use of small molecules to restore wt function to mutant p53, remains an option. Finally, the conceptually simplest mechanism of resistance is one that reduces intracellular drug accumulation. Such reduction can be effected by a variety of drug efflux pumps, of which the most widely studied is P-glycoprotein (Pgp). The first strategy utilized to inhibit Pgp function relied on the identification of non-chemotherapeutic agents as competitors. Other approaches have included the use of hammerhead ribozymes against the MDR-1 gene and MDR-1-targeted ASOs. Although modulation of drug resistance has not yet been proven to be an effective clinical tool, we have learned an enormous amount about drug resistance. Should we succeed, these pioneering basic and clinical studies will have paved the road for future developments.

Molecular biology of pancreatic cancer: potential clinical implications

The development of cancer involves the accumulation of genetic changes. Over the past decade there has a been spectacular advance in the knowledge of the genetic basis of cancer, mainly as a result of the rapid progression of molecular technology. Pancreatic cancer is one of the most lethal cancers. Conventional therapeutic approaches have not had much impact on the course of this aggressive neoplasm. Knowledge of the molecular biology of pancreatic cancer has grown rapidly. Genetic alterations in pancreatic cancer include oncogene mutations (most commonly K-ras mutations), and tumour suppressor gene alterations (mainly p53, p16, DCC, etc.). These advances have potential implications for the management of this deadly disease. Identification of a hereditary genetic predisposition to pancreatic cancer has led to the formation of pancreatic cancer registries around the world, with voluntary screening of patients and siblings for the hereditary genetic defect. Asymptomatic population screening remains unrealistic, but the recognition of subpopulations at increased risk from pancreatic cancer, along with novel and sensitive detection techniques, means that targeted population screening is a step closer. Intensive research is performed in specialist laboratories to improve the diagnostic approach in patients with pancreatic cancer. The use of such molecular diagnostic methods is likely to expand. Molecular biology may also have a great impact on the treatment of pancreatic cancer, and many therapeutic approaches are being evaluated in clinical trials, including gene replacement therapy, genetic prodrug activation therapy, antisense immunology and peptide technology. The 'molecular age' has the promise of delivering still better results. This review summarises recent data relating to the molecular biology of pancreatic cancer, with emphasis on features that may be of clinical significance for diagnosis and/or therapy.

The mononucleotide-dependent, nonantisense mechanism of action of phosphodiester and phosphorothioate oligonucleotides depends upon the activity of an ecto-5'-nucleotidase

Many reports indicate different nonantisense yet sequence-specific effects of antisense phosphorothioate oligonucleotides. Products of enzymatic degradation of the oligonucleotides can also influence cell proliferation. The cytotoxic effects of deoxyribonucleoside-5'-phosphates (dNMPs) and their 5'-phosphorothioate analogs, deoxyribonucleoside-5'-monophosphorothioates (dNMPSs) on 4 human cell types (HeLa, HL-60, K-562, and endothelial cells) were examined, and the effects were correlated with the catabolism of these compounds. The results indicate that differences in cytotoxicity of dNMPs or dNMPSs in these cells depend upon different activity of an ecto-5'-nucleotidase. It has also been found that dNMPSs stimulate proliferation of human umbilical vein endothelial cells and HL-60 cells in a concentration-dependent manner. This stimulation might be caused by the binding of deoxynucleoside-5'-phosphorothioates to as-yet unidentified nucleotide receptor(s) at the cell surface. (Blood. 2001;98:995-1002)

Constitutive expression of functional GABA(B) receptors in mIL-tsA58 cells requires both GABA(B(1)) and GABA(B(2)) genes

Studies of gamma-aminobutyric acid (GABA)(B) receptor function in heterologous cell systems have suggested that expression of two distinct seven transmembrane G-protein coupled receptor subunits is necessary for receptor activation and signal transduction. Some results suggest that both receptor proteins must be inserted into the plasma membrane to create heterodimers; however, it is possible that subunit monomers or homodimers are functional in cells which constitutively express GABA(B) receptors. A new pituitary intermediate lobe melanotrope cell clone (mIL tsA58) has been isolated which constitutively expresses GABA(B), D(2) and corticotrophin releasing factor receptors. Here, we report on characterization of the GABA(B) receptors. Solution hybridization-nuclease protection assays reveal the presence of GABA(B(1)) and GABA(B(2)) transcripts. Western blots show GABA(B(1a)) and one of two GABA(B(2)) proteins. Addition of the GABA(B) agonist baclofen to cultured mIL-tsA58 (mIL) cells inhibits high voltage activated Ca(2+) channels, as measured by agonist-induced inhibition of the K(+)-depolarization-stimulated increase in Ca(2+) influx. CGP55845, a GABA(B) antagonist, blocks the response to baclofen. Knockdown of either GABA(B(1)) or GABA(B(2)) subunits with selective antisense oligodeoxynucleotides reduced GABA(B) protein levels and completely abolished the GABA(B) receptor response in the mIL cells. Taken together, these results indicate that functionally active GABA(B) receptors in mIL cells require the constitutive expression of both GABA(B) genes. This is a physiologic validation of results from recombinant overexpression in naive cells and shows that the mIL cell line is a useful model for studying GABA(B) receptor expression, regulation and function.

Inhibition of telomerase by 2'-O-(2-methoxyethyl) RNA oligomers: effect of length, phosphorothioate substitution and time inside cells

2'-O-(2-methoxyethyl) (2'-MOE) RNA possesses favorable pharmocokinetic properties that make it a promising option for the design of oligonucleotide drugs. Telomerase is a ribonucleoprotein that is up-regulated in many types of cancer, but its potential as a target for chemotherapy awaits the development of potent and selective inhibitors. Here we report inhibition of human telomerase by 2'-MOE RNA oligomers that are complementary to the RNA template region. Fully complementary oligomers inhibited telomerase in a cell extract with IC(50) values of 5-10 nM at 37 degrees C. IC(50) values for mismatch-containing oligomers varied with length and phosphorothioate substitution. After introduction into DU 145 prostate cancer cells inhibition of telomerase activity persisted for up to 7 days, equivalent to six population doublings. Inside cells discrimination between complementary and mismatch-containing oligomers increased over time. Our results reveal two oligomers as especially promising candidates for initiation of in vivo preclinical trials and emphasize that conclusions regarding oligonucleotide efficacy and specificity in cell extracts do not necessarily offer accurate predictions of activity inside cells.

Molecular technology and pancreatic cancer

BACKGROUND

Pancreatic cancer is the fifth leading cause of cancer death in the Western world. Despite improvement in operative mortality rates, little impact has been made on overall 5-year survival. This review discusses the molecular changes peculiar to pancreatic cancer and how the use of molecular technology might affect detection, screening, diagnosis and treatment of the disease.

METHODS

A literature review was performed using the National Library of Medicine's Pubmed database; this was combined with ongoing work within the Queen Elizabeth Hospital, Birmingham.

RESULTS

Over the past 20 years great strides have been made in our understanding of the molecular basis of disease. Advances in molecular biology are now reshaping how diseases are screened for, diagnosed, investigated and treated. In recent years collaboration between clinicians and basic scientists has revealed a unique pattern of genetic and molecular events in pancreatic cancer. This review discusses how these advances may impact on patients with this disease.

CONCLUSION

The past decade has seen some improvement in outlook for patients with pancreatic cancer, but the 'molecular age' promises to deliver even better results.

Molecular biology of pancreatic cancer; oncogenes, tumour suppressor genes, growth factors, and their receptors from a clinical perspective

Pancreatic cancer represents the fourth leading cause of cancer death in men and the fifth in women. Prognosis remains dismal, mainly because the diagnosis is made late in the clinical course of the disease. The need to improve the diagnosis, detection, and treatment of pancreatic cancer is great. It is in this type of cancer, in which the mortality is so great and the clinical detection so difficult that the recent advances of molecular biology may have a significant impact. Genetic alterations can be detected at different levels. These alterations include oncogene mutations (most commonly, K-ras mutations, which occur in 75% to more than 95% of pancreatic cancer tissues), tumour suppressor genes alterations (mainly, p53, p16, DCC, etc.), overexpression of growth factors (such as EGF, TGF alpha, TGF beta 1-3, aFGF, bTGF, etc.) and their receptors (i.e., EGF receptor, TGF beta receptor I-III, etc.). Insights into the molecular genetics of pancreatic carcinogenesis are beginning to form a genetic model for pancreatic cancer and its precursors. These improvements in our understanding of the molecular biology of pancreatic cancer are not simply of research interest, but may have clinical implications, such as risk assessment, early diagnosis, treatment, and prognosis evaluation.

Antiproliferative activity of G-rich oligonucleotides correlates with protein binding

Oligonucleotides have been extensively studied as antisense or antigene agents that can potentially modulate the expression of specific genes. These strategies rely on sequence-specific hybridization of the oligonucleotide to mRNA or genomic DNA. Recently, it has become clear that oligonucleotides often have biological activities that cannot be attributed to their sequence-specific interactions with nucleic acids. Here we describe a series of guanosine-rich phosphodiester oligodeoxynucleotides that strongly inhibit proliferation in a number of human tumor cell lines. The presence of G-quartets in the active oligonucleotides is demonstrated using an UV melting technique. We show that G-rich oligonucleotides bind to a specific cellular protein and that the biological activity of the oligonucleotides correlates with binding to this protein. The G-rich oligonucleotide-binding protein was detected in both nuclear and cytoplasmic extracts and in proteins derived from the plasma membrane of cells. We present strong evidence that this protein is nucleolin, a multifunctional phosphoprotein whose levels are related to the rate of cell proliferation. Our results indicate that binding of G-rich oligonucleotides to nucleolin may be responsible for their non-sequence-specific effects. Furthermore, these oligonucleotides represent a new class of potentially therapeutic agents with a novel mechanism of action.

The potential for gene therapy in pancreatic cancer

Pancreatic cancer is highly aggressive and is a leading cause of cancer death in the Western world. Currently, there is no effective treatment for this disease; resection is only available to a small fraction of patients and has a marginal effect on overall survival rates. Chemotherapy and radiation also have very limited effects on patient survival. There is clearly a need for new approaches to treatment of such an aggressive disease. Gene therapy is of potential use in the treatment of cancer, and all currently available strategies are discussed with relevance to pancreatic cancer. A key to such strategy is specific delivery and selective gene expression in target cells. Current approaches include replacement of tumor suppressor genes, the use of antisense (AS) oligonucleotides, gene-directed enzyme prodrug therapy (GDEPT), and immunotherapy. The scene is now set for the next phase of development in clinical trials.

Phase I clinical/pharmacokinetic and pharmacodynamic trial of the c-raf-1 antisense oligonucleotide ISIS 5132 (CGP 69846A)

PURPOSE

Raf-1 is a protein kinase that plays a broad role in oncogenic signaling and acts as a downstream effector of Ras in the mitogen-activated protein kinase pathway. The present study was designed to determine the maximum-tolerated dose (MTD), toxicity profile, pharmacokinetics, and antitumor activity of the c-raf-1 antisense oligodeoxynucleotide ISIS 5132 (CGP 69846A; ISIS Pharmaceuticals Inc, Carlsbad, CA). The effect of ISIS 5132 on c-raf-1 gene expression in peripheral-blood mononuclear cells (PBMCs) of treated patients was studied using a reverse transcriptase polymerase chain reaction assay.

PATIENTS AND METHODS

Patients with refractory malignancies received ISIS 5132 as a 2-hour intravenous infusion three times weekly for 3 consecutive weeks. Pharmacokinetic sampling was performed during the first cycle in all patients; PBMCs for c-raf-1 mRNA analysis were collected at baseline and on days 3, 5, 8, and 15 of cycle 1 and on day 1 of each cycle thereafter.

RESULTS

Thirty-one patients received ISIS 5132 at one of nine dose levels ranging from 0.5 mg/kg to 6.0 mg/kg. Clinical toxicities included fever and fatigue, but these were not dose limiting. A clinically defined MTD was not reached. The harmonic mean half-life of ISIS 5132 was 59.8 minutes (range, 35.5 to 107.3 minutes). The area under the concentration-time curve increased linearly with dose, and mean plasma clearance was 1.86 mL/kg/min (range, 1.21 to 2.41 mL/kg/min). Two patients experienced prolonged stable disease lasting more than 7 months, which was associated with persistent reduction in c-raf-1 expression in PBMCs. Significant decreases in c-raf-1 expression were identified at time points after the baseline value (P <.05) at doses >/= 2.5 mg/kg.

CONCLUSION

ISIS 5132 is well tolerated at doses up to 6.0 mg/kg when administered as a thrice weekly 2-hour infusion for 3 consecutive weeks. The pharmacokinetic behavior of the drug is reproducible, and suppression of target gene expression is observed in circulating PBMCs.

p53-oriented cancer therapies: current progress

Nearly twenty years after the initial discovery of p53, we are now in an ideal position to exploit our vast knowledge of p53 biology in the creation of novel cancer therapies. Disruption of p53 function through mutation, or other means, occurs very frequently in human cancer. Loss of p53 function has been linked with unfavourable prognosis in a large number of tumour types, as indicated by more aggressive tumours, early metastasis and decreased survival rates. Many different avenues of research have converged upon p53 to highlight this protein as being one of the foremost cellular responders to stress, in particular to DNA damage. Huge advances have been made in understanding the complex role p53 plays in the regulation of apoptosis and cell cycle arrest. This review is not meant to be a comprehensive description of p53 biology, but rather serves to highlight current progress in the development of p53-oriented cancer therapies. These may be categorised into three basic strategies: gene replacement therapy using wild-type p53, restoration of p53 function by other means and, finally, targeting of the p53 dysfunction itself. Rapid progress is expected to be made regarding the identification of conventional pharmaceutical agents which either work in a p53-independent manner or act preferentially in p53 defective cells. Gene replacement therapy with wild-type p53 also holds considerable potential for obtaining clinically relevant results quickly. The other forms of cancer therapies based around p53 are much further behind in the developmental process, but may prove to more efficacious in the long run, especially in terms of specificity. As with many other fields, the innovation of successful p53-oriented cancer therapies is only limited by our understanding of p53 biology and the creative use of such knowledge.

Antisense oligonucleotides to gastrin inhibit growth of human pancreatic cancer

Human pancreatic cancer is stimulated by the autocrine production of gastrin. In this study, the effects of administration of antisense oligonucleotides to gastrin on growth of pancreatic cancer were evaluated in vitro and in vivo. Log phase BxPC-3 human pancreatic cancer cells in culture were exposed to increasing concentrations (0.5-10 microM) of a synthetic 20-mer antisense phosphorothioate oligonucleotide to gastrin for 48 h and growth was assessed by the cellular proliferation assay. Growth was inhibited up to 88% by anti-gastrin oligonucleotides in a dose-related fashion compared to cells treated with diluent or a randomized sequence with the same composition as the anti-gastrin oligonucleotide. In vivo nude mice bearing BxPC-3 xenografts were treated daily for 14 days with a 0.1-ml intratumoral injection of either anti-gastrin (5 microM), the scrambled sequence control phosphorothioate oligonucleotide (5 microM), or buffer. Tumors from the anti-gastrin-treated mice were significantly smaller in volume and weight and had less gastrin detected by radioimmunoassay than either controls. These results support the role of gastrin as a stimulatory peptide for growth of human pancreatic cancer. Antisense oligonucleotide to gastrin may have a role in the future treatment of patients with pancreatic cancer.

Inactivation of p53 in normal human cells increases G2/M arrest and sensitivity to DNA-damaging agents

p53 mutations are found in about 70% of human cancers. In order to evaluate the role of these mutations in response to chemotherapeutic agents, it is important to distinguish between p53 response to DNA-damaging agents in normal and in tumour cells. Here, using normal human fibroblasts (NHFs), we show that cisplatin and UV radiation induce G2/M arrest which is temporally linked to p53-protein induction. To study the contribution of p53 to this G2/M arrest, we inhibited p53 induction in NHFs using p53 anti-sense oligonucleotides. Following exposure of NHFs to UV radiation, the inhibition of p53-protein induction leads to a greater accumulation of cells in the G2/M phase, but also to a decreased fraction of cells in the G1 phase. We propose that p53 does not induce G2/M arrest directly, and that the extent of this arrest may depend on the fraction of cells that do not stop at the G1 phase following exposure to DNA-damaging agents. Furthermore, inhibition of p53-protein induction leads to increased sensitivity of NHFs to UV radiation. These results suggest that inhibition of p53 protein enhances sensitivity to DNA-damaging agents in normal human cells.

A novel strategy for inhibiting growth of human pancreatic cancer cells by blocking cyclin-dependent kinase activity

Pancreatic cancers frequently carry mutations in the K-ras, p53, and p16 genes, which regulate cell proliferation. Transition from G1 to S phase of the cell cycle requires activation of cyclin-dependent kinase 2 (Cdk2) which is inhibited by olomoucine and roscovitine. The purpose of this study was to determine whether olomoucine and roscovitine can block Cdk2 kinase activity and inhibit proliferation of four human pancreatic cancer cell lines with various genetic alterations. Human pancreatic carcinoma cell lines BxPC-3, PANC-1 Capan-2, and CAV were treated with olomoucine or roscovitine. Cdk2 kinase activity was determined using histone H1 as the substrate. Cell cycle distribution was analyzed by DNA flow cytometry. Cell numbers were quantitated by Coulter counter. Olomoucine and roscovitine blocked Cdk2 activity in all four pancreatic cancer cell lines. Both compounds also inhibited cell proliferation in a dose-dependent fashion. Roscovitine was at least threefold more potent than olomoucine for both Cdk2 activity and cell proliferation. We have shown that Cdk inhibitors, olomoucine and roscovitine, block proliferation of human pancreatic cancer cells regardless of their mutations in K-ras p53, or p16 genes. These compounds represent a novel therapeutic strategy with potential therapeutic benefits for pancreatic cancers.

Clinical significance of serum p53 antigen in patients with pancreatic carcinomas

BACKGROUND

Alterations in the p53 gene are often found in pancreatic cancer, and accumulation of the p53 protein has been noted in tumour cells.

AIMS

To investigate whether serum p53 protein concentrations could be used as markers for p53 gene mutations in neoplasms of the pancreas.

METHODS

Serum p53 protein concentrations were determined by an enzyme linked immunosorbent assay (ELISA) in 104 cases of pancreatic adenocarcinoma, and 61 matched formalin fixed tissue sections were also stained by an anti-p53 DO-7 monoclonal antibody.

RESULTS

The mean serum concentration of p53 protein in the adenocarcinoma patients was 0.27 (SEM 0.02) ng/ml, and was significantly higher than in 35 healthy blood donors (0.15 (0.02) ng/ml, SD = 0.11) or in 15 cases of chronic pancreatitis (0.15 (0.02) ng/ml). Adopting an arbitrary cut off value for the serum p53 protein concentration of 0.37 ng/ml, which corresponded to a value 2 SD above the mean value from the healthy blood donors, positive serum p53 protein concentrations were found in 23 out of 104 (22.1%) patients with adenocarcinomas examined, 16 out of 47 (34.0%) patients with carcinomas with distant metastases, but only seven of 57 patients (12.3%) with carcinomas without metastases (p < 0.05). In 11 patients with pancreatic adenocarcinomas, the mean serum p53 protein concentration after tumour resection was 0.21 (0.05) ng/ml, and had decreased compared with the preoperative concentrations (0.25 (0.05) ng/ml) (P < 0.05). There were no significant associations between the serum concentrations of p53 protein and serum concentrations of markers such as CA19-9 or CEA; however, serum concentrations of p53 protein demonstrated a potential role as an additional tumour marker. Immunohistochemical studies disclosed that the p53 protein was expressed in 28 out of 61 pancreatic adenocarcinomas (45.9%). Serum p53 protein concentrations in the positively immunostained cases were significantly higher than in the negatively immunostained cases (0.35 (0.05) ng/ml v 0.15 (0.01) ng/ml; p < 0.005). Furthermore, positive immunostaining for p53 protein was found in eight out of 10 (80%) serum positive p53 protein cases with adenocarcinomas.

CONCLUSION

An increase in serum p53 protein concentrations appears during the progression of pancreatic adenocarcinoma and correlates with the accumulation of p53 protein as a result of a mutation of the p53 gene. An analysis of p53 antigen concentrations can detect p53 gene alterations, which could be useful for the selection of treatment regimens.

Inhibition of anchorage-independent growth of ras-transformed cells on polyHEMA surface by antisense oligodeoxynucleotides directed against K-ras

We examined the effect of antisense oligodeoxynucleotides (AS ODNs) directed against v-Ki-ras on the anchorage-independent growth of v-Ki-ras-transformed rat fibroblasts using plates coated with an antiadhesive polymer, poly(2-hydroxyethyl methacrylate) (polyHEMA). Among AS ODNs tested, 17mer AS ODN centered around codon 12 of v-Ki-ras inhibited the v-Ki-Ras expression and v-Ki-Ras-induced anchorage-independent growth, while its sense sequence did not affect it. Using polyHEMA plates, the direct addition of AS ODNs to the cells growing anchorage-independently and various treatment schedules of AS ODNs are now available to identify the most desirable conditions for AS ODNs treatment.

Distinct functions of Gq and G11 proteins in coupling alpha1-adrenoreceptors to Ca2+ release and Ca2+ entry in rat portal vein myocytes

In this study, we identified the subunit composition of Gq and G11 proteins coupling alpha1-adrenoreceptors to increase in cytoplasmic Ca2+ concentration ([Ca2+]i) in rat portal vein myocytes maintained in short-term primary culture. We used intranuclear antisense oligonucleotide injection to inhibit selectively the expression of subunits of G protein. Increases in [Ca2+]i were measured in response to activation of alpha1-adrenoreceptors, angiotensin AT1 receptors, and caffeine. Antisense oligonucleotides directed against the mRNAs coding for alphaq, alpha11, beta1, beta3, gamma2, and gamma3 subunits selectively inhibited the increase in [Ca2+]i activated by alpha1-adrenoreceptors. A corresponding reduction of the expression of these G protein subunits was immunochemically confirmed. In experiments performed in Ca2+-free solution only cells injected with anti-alphaq antisense oligonucleotides displayed a reduction of the alpha1-adrenoreceptor-induced Ca2+ release. In contrast, in Ca2+-containing solution, injection of anti-alpha11 antisense oligonucleotides suppressed the alpha1-adrenoreceptor-induced stimulation of the store-operated Ca2+ influx. Agents that specifically bound Gbetagamma subunits (anti-betacom antibody and overexpression of a beta-adrenergic receptor kinase carboxyl-terminal fragment) had no effect on the alpha1-adrenoreceptor-induced signal transduction. Taken together, these results suggest that alpha1-adrenoreceptors utilize two different Galpha subunits to increase [Ca2+]i. Galphaq may activate phosphatidylinositol 4,5-bisphosphate hydrolysis and induce release of Ca2+ from intracellular stores. Galpha11 may enhance the Ca2+-activated Ca2+ influx that replenishes intracellular Ca2+ stores.

Antisense strategy: biological utility and prospects in the treatment of hematological malignancies

The use of antisense oligonucleotides for the specific control of cellular genes expression has undergone rapid developments recently. Besides the antisense approach, which usually targets translation initiation or splicing sites, it is also possible to interfere specifically with transcription process through triple helix formation (anti-gene strategy) or through the titration of regulatory proteins (sense and aptamer approaches). Progresses in oligonucleotides chemistry have led to the synthesis of analogs with improved pharmacological properties, while their generation from recombinant vectors in situ has improved oligos deliver to their nuclear or cytoplasmic targets. Hematological malignancies provide an ideal paradigm for the development of antisense therapeutic strategies. Many disease-specific molecular lesions have been identified which provide suitable targets for systemic in vivo administration of oligonucleotides as well as for ex vivo bone marrow purging manipulation. However, oligonucleotides have also been shown to bind to unexpected cellular targets and to induce various unpredictable biological responses as well. In addition, the multi-stage nature of carcinogenesis may indicate that even if successful inhibition of a single gene by oligomer is achieved, it may still be insufficient to induce a major impact on a malignant clone. Thus, much more basic information about both the disease and antisense technology is still required before antisense strategy gains the status of an acceptable therapeutical approach.

Elucidation of gene function using C-5 propyne antisense oligonucleotides

Identification of human disease-causing genes continues to be an intense area of research. While cloning of genes may lead to diagnostic tests, development of a cure requires an understanding of the gene's function in both normal and diseased cells. Thus, there exists a need for a reproducible and simple method to elucidate gene function. We evaluate C-5 propyne pyrimidine modified phosphorothioate antisense oligonucleotides (ONs) targeted against two human cell cycle proteins that are aberrantly expressed in breast cancer: p34cdc2 kinase and cyclin B1. Dose-dependent, sequence-specific, and gene-specific inhibition of both proteins was achieved at nanomolar concentrations of ONs in normal and breast cancer cells. Precise binding of the antisense ONs to their target RNA was absolutely required for antisense activity. Four or six base-mismatched ONs eliminated antisense activity confirming the sequence specificity of the antisense ONs. Antisense inhibition of p34cdc2 kinase resulted in a significant accumulation of cells in the Gap2/mitosis phase of the cell cycle in normal cells, but caused little effect on cell cycle progression in breast cancer cells. These data demonstrate the potency, specificity, and utility of C-5 propyne modified antisense ONs as biological tools and illustrate the redundancy of cell cycle protein function that can occur in cancer cells.

Bias in nucleotide composition of antisense oligonucleotides

In this study we investigated if specific sequence motifs occur with a higher frequency in antisense oligonucleotides than can be expected on the basis of the mRNA composition to get an impression of the importance of these motifs for antisense effects. Computer analysis of 206 antisense oligonucleotides extracted from the literature and from sequence databases, all targeted against human mRNA, was performed. We compared the sequence composition of these oligonucleotides with the average of 100 equally large and randomly selected sequences from sequence databases and of their target mRNA. We found that the frequency of sequence motifs containing GG, CCC, CC, GAC, and CG is significantly higher and TT and that TCC is significantly lower in antisense oligonucleotide sequences than in the randomly selected mRNA sequences. We conclude that there is a bias in the nucleotide composition of antisense oligonucleotides. Some of these biased sequence motifs have been reported to induce nonantisense effects mediated by protein binding. Further analysis of the biologic function of these motifs is necessary to investigate if they should be avoided or incorporated into future designs of therapeutic effective oligonucleotides.

Uptake characteristics of oligonucleotides in the isolated rat liver perfusion system

The objective of this study was to examine the hepatic disposition characteristics of 20-mer model phosphodiester oligonucleotide (PO) and its partially phosphorothioated (PS3) and fully phosphorothioated (PS) derivatives in the single-pass isolated rat liver perfusion system. [32P]-labeled oligonucleotides were momentarily introduced into this system through the portal vein as a bolus input mode, and the venous outflow patterns were evaluated using statistical moment analysis. The apparent volumes of distribution of these oligonucleotides were greater than those of reference substances for vascular space (erythrocytes) and extracellular space (human serum albumin), indicating a significant interaction between oligonucleotides and the liver. Significant hepatic uptake of oligonucleotides was also observed. About 20%, 36%, and 52% of the injected dose (3 micrograms/rat) was taken up by the liver during a single passage after bolus injection of PO, PS3, and PS, respectively. In the case of PS injection, slow efflux from the liver was observed in the latter phase of perfusion. This suggests that the hepatic uptake process of these oligonucleotides greatly depended on their types. The results of collagenase perfusion experiments suggest that PS3 oligonucleotides were taken up by both liver parenchymal and nonparenchymal cells. The amount of total recovery in the liver decreased substantially by coadministration of polyinosinic acid, dextran sulfate, polycytidic acid and 4-acetamido-4'-isothiocyano-stilbene-2,2'-disulfonic acid. This suggests that PS3 was taken up by the liver as an anionic molecule in a nonspecific manner.