New p53-based anti-cancer therapeutic strategies

Induction of efficient apoptosis and cell-cycle arrest in tumor cells by adenovirus-mediated p53 A4 mutant

p53 is an effective tumor suppressor and is inactivated in numerous cancer cells. In the present study, p53 mutant A4, which carries mutations in C-terminus of the protein and is resistant to murine double minute 2-mediated degradation, was exploited to introduce p53 function in tumor cells. The effect of p53 A4 mutant with recombinant adenovirus vector (Ad-p53 A4) was examined. Ad-p53 A4 infection at a low multiplicity of infection showed significant accumulation of p53 protein and strongly induced a killing effect on osteosarcoma cell line MG-63 that is less sensitive to transduction of wild-type p53. DNA fragmentation assay and caspase assay showed that the cell death induced by Ad-p53 A4 was more rapid and higher than that by Ad-p53 wild-type infection. It is also showed Ad-p53 A4 induces cell-cycle arrest in G1 phase. Moreover, a similar effect was observed in some human cancer cell lines (HeLa, HepG2, KATO III and Saos-2) in various status of endogenous p53 expression. These results suggest that Ad-p53 A4 has the ability to strongly suppress tumor cells and is a promising, novel tool for cancer gene therapy.

Role of apoptosis in intracranial aneurysm rupture

OBJECT

Mechanisms involved in the rupture of intracranial aneurysms remain unclear, and the literature on apoptosis in these lesions is extremely limited. The hypothesis that apoptosis may reduce aneurysm wall resistance, thus contributing to its rupture, warrants investigation. The authors in this study focused on the comparative evaluation of apoptosis in ruptured and unruptured intracranial aneurysms. Peripheral arteries in patients harboring the aneurysms and in a group of controls were also analyzed.

METHODS

Between September 1999 and February 2002, specimens from 27 intracranial aneurysms were studied. In 13 of these patients apoptosis was also evaluated in specimens of the middle meningeal artery (MMA) and the superficial temporal artery (STA). The terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick-end labeling technique was used to study apoptosis via optical microscopy; electron microscopy evaluation was performed as well. Apoptotic cell levels were related to patient age and sex, aneurysm volume and shape, and surgical timing. Significant differences in apoptosis were observed when comparing ruptured and unruptured aneurysms. High levels of apoptosis were found in 88% of ruptured aneurysms and in only 10% of unruptured lesions (p < 0.001). Elevated apoptosis levels were also detected in all MMA and STA specimens obtained in patients harboring ruptured aneurysms, whereas absent or very low apoptosis levels were observed in MMA and STA specimens from patients with unruptured aneurysms. A significant correlation between aneurysm shape and apoptosis was found.

CONCLUSIONS

In this series, aneurysm rupture appeared to be more related to elevated apoptosis levels than to the volume of the aneurysm sac. Data in this study could open the field to investigations clarifying the causes of aneurysm enlargement and rupture.

Apoptosis in lung fibrosis and repair

Cell death by apoptosis has fundamental significance in both normal lung homeostasis and a variety of pathologic processes, and for this reason apoptosis in the lung is a rapidly growing area of investigation. Evidence from human lung biopsy specimens and from animal models of lung fibrosis points to important roles for apoptosis in both the pathogenesis and resolution of fibrotic lesions. As more evidence accumulates, the more apparent becomes the paucity of information on the regulation of this mode of cell death in the many different cell types of the lung parenchyma. This discussion will review the current state of knowledge regarding the roles of apoptosis in lung fibrosis and will focus on its role in pathogenesis.

Tp53 gene therapy: a key to modulating resistance to anticancer therapies?

Abnormalities in the p53 tumor suppressor have been identified in over 60% of human cancers. The status of p53 within tumor cells has been proposed to be one of the major determinants of the response to anticancer therapies. In this review we examine the relationship between functional p53 and sensitivity, or resistance, to chemotherapy and radiotherapy. We also discuss the potential of current gene-therapy approaches to restore functional p53 to tumors as a means of modulating the effects of radiation and chemotherapy.

Apoptosis in lung pathophysiology

As recently as 1993, fewer than 10 manuscripts had been published on the topic of apoptosis specifically in the lung. Although that number is increasing, far fewer papers appear each year on apoptosis in the lung than in the other major organs. Therefore, our knowledge of this important aspect of lung cell physiology is relatively rudimentary. Recent literature is beginning to define important roles for apoptosis in normal lung cell turnover, lung development, and the pathogenesis of diseases such as interstitial pulmonary fibrosis, acute respiratory distress syndrome, and chronic obstructive pulmonary disease. Although the involvement of lung cell apoptosis in each of these examples seems clear, the many factors comprising the normal and abnormal regulation of cell death remain to be elucidated and are likely to be different in each situation. The definition of those factors will be an exciting and challenging field of research for many years to come. In that context, the goal of this symposium was to discuss, from a physiological perspective, some of the most recent and exciting advances in the definition of signaling mechanisms involved in the regulation of apoptosis specifically in lung cell populations.

Quantitative analysis of residual folding and DNA binding in mutant p53 core domain: definition of mutant states for rescue in cancer therapy

The tumour suppressor p53 is mutated in half of all human cancers, most frequently with missense substitutions in its core domain. We present a new assessment of the mutation database based on quantitative folding and DNA-binding studies of the isolated core domain. Our data identify five distinct mutant classes that correlate with four well-defined regions of the core domain structure. On extrapolation to 37 degrees C the wild-type protein has a stability of 3.0 kcal/mol. This also emerges as an oncogenic threshold: all beta-sandwich mutants destabilized by this amount (50% denatured) are expected to promote cancer. Other weakly destabilizing mutations are restricted to loop 3 in the DNA-binding region. Drugs that stabilize mutant p53 folding have the potential to reactivate apoptotic signalling pathways in tumour cells either by transactivation-dependent or independent pathways. Using an affinity ligand as a proof of principle we have recovered the thermodynamic stability of the hotspot G245S. With reference states for the five mutant classes as a guide, future therapeutic strategies may similarly stabilize partially structured or binding states of mutant p53 that restore limited p53 pathways to tumour suppression.

Recent developments in the virus therapy of cancer

Cancer is one of the leading causes of death in the United States. Although there has been significant progress in the areas of cancer etiology, diagnostic techniques, and cancer prevention, adequate therapeutic approaches for many cancers have lagged behind. One promising line of investigation is the virus therapy of cancer. This approach entails the use of viruses, such as retroviruses, adenovirus, and vaccinia virus, to modify tumor cells so that they become more susceptible to being killed by the host immune response, chemotherapeutic agents, or programmed cell death. This review discusses recent advances in the virus therapy of cancer from both basic science and clinical perspectives. Given the potential of viruses to kill tumor cells directly or transduce desired gene products to allow a vigorous host antitumor immune response, the virus therapy of cancer holds great promise in the treatment of cancer.

Gene Therapy for Lung Cancer

Gene therapy is emerging as a promising modality for the treatment of lung cancer. Diverse strategies employing gene therapy for lung cancer have been investigated in vitro and in animal models, and a number of these approaches have met with promising results. Several phase I and II clinical trials have been undertaken, and early results suggest that it may be safe to administer gene therapy to lung cancer patients. It remains to be determined whether this modality will be efficacious as primary or adjunctive therapy in the setting of lung cancer.

Options for modulation of drug resistance in ovarian cancer

The objective of this paper is to present an update of mechanisms responsible for drug resistance in ovarian cancer and the possible therapeutic options to modulate this resistance using literature review with emphasis on data acquired in studies comprising ovarian tumor samples. The classic concepts on resistance in ovarian cancer, namely platinum and multidrug resistance, are briefly discussed, followed by a description of more recent insights concerning the role of apoptosis in the development of chemoresistance. A wide variety of mechanisms may be responsible for drug resistance in ovarian cancer. However, a growing body of evidence indicates that defects in the intra- and extracellular apoptotic pathways are an important cause of resistance to cytotoxic agents which opens several new treatment strategies.

Discovering novel chemotherapeutic drugs for the third millennium

There is enormous potential for the discovery of innovative cancer drugs with improved efficacy and selectivity for the third millennium. In this review we show how novel mechanism-based agents are being discovered by focusing on the molecular targets and pathways that are causally involved in cancer formation, maintenance and progression. We also show how new technologies, from genomics through high through-put bioscience, combinatorial chemistry, rational drug design and molecular pharmacodynamic and imaging techniques, are accelerating the pace of cancer drug discovery. The process of contemporary small molecule drug discovery is described and progress and current issues are reviewed. New and potential targets and pathways for therapeutic intervention are illustrated. The first examples of a new generation of molecular therapeutics are now entering hypothesis-testing clinical trials and showing activity. The early years of the new millennium will see a range of exciting new agents moving from bench to bedside and beginning to impact on the management and cure of cancer.

Predicting the future: a critical appraisal of cancer prognosis studies

Many studies have attempted to define useful prognostic and predictive factors in cancer but few have achieved acceptance in clinical practice because of methodological weaknesses. These include failure to test clearly formulated hypotheses, inadequate sample size, inappropriate multiple significance testing, arbitrary definition of patient groups, inadequately reproducible assays, and failure to verify prognostic factors with data independent of the data which suggested the original hypothesis. This unsatisfactory situation will persist until critical attention is routinely paid to study design and prospective validation of supposed prognostic and predictive factors, without which classical approaches will be suboptimally exploited and the flood of data from new molecular technologies will not be used effectively. We propose that prognostic factors should be evaluated in three phases: I, assay definition; II, retrospective testing; III, prospective testing, ideally as a designed part of clinical trials.