In vitro modelling of Alzheimer's disease: degeneration and cell death induced by viral delivery of amyloid and tau.

With increasing life expectancy, Alzheimer's disease (AD) and other dementias pose an increasing and as yet unresolved health problem. A variety of cellular models of AD has helped to decipher some key aspects of amyloid and tau related degeneration. The initial approach of extracellular applications of synthetic peptides has now been replaced by the introduction of amyloid precursor protein (APP) and tau genes. In the present study adenoviral transductions were exploited for gene delivery into primary rat hippocampal and dorsal root ganglion (DRG) cultures to enable comparative and mechanistic studies at the cellular level and subsequent drug testing. Time lapse experiments revealed a different pattern of cell death: apoptotic-like for APP whereas tau positive cells joined and formed clusters. Mutated human APP or tau expression caused accelerated neuronal damage and cell death (cf. EGFP: -50% for APP at 5 days; -40% for tau at 3 days). This reduction in viability was preceded by decreased excitability, monitored via responses to depolarising KCl-challenges in Ca(2+) imaging experiments. Additionally, both transgenes reduced neurite outgrowth in DRG neurones. Treatment studies confirmed that APP induced-damage can be ameliorated by ß- and γ-secretase inhibitors (providing protection to 60-100% of control levels), clioquinol (80%) and lithium (100%); while anti-aggregation treatments were beneficial for tau-induced damage (60-90% recovery towards controls). Interestingly, caffeine was the most promising drug candidate for therapeutic intervention with high efficacy in both APP (77%) and tau-induced models (72% recovery). Overall, these cellular models offer advantages for mechanistic studies and target identification in AD and related disorders.

iASPP inhibition: increased options in targeting the p53 family for cancer therapy.

Strategies to induce p53 for cancer therapy offer appeal but many tumors harbor inactivating p53 mutations. One way to address this situation may be to activate the p53-related protein p73, which functions similarly, but unlike p53, is rarely lost or mutated in cancer. Along these lines, a recent study reports that a p53-derived peptide that targets iASPP-a common negative regulator of p53 family members--can effectively trigger tumor cell death by a p73-dependent mechanism. These findings promote further study of iASPP targeting as a therapeutic strategy to activate p73.

Targeting the p53 family for cancer therapy: 'big brother' joins the fight.

Inactivation of p53-mediated signaling plays a major role in both the genesis and therapy resistance of human cancer. Nearly all tumors contain mutations in p53 itself or have perturbations in the p53 pathway. Since there is clear evidence that many tumor cells are more likely to die in response to wild-type p53 activation or restoration than are their normal counterparts, there has been considerable interest in the development of small molecules that target p53 for therapeutic gain. These include compounds that either revert mutant p53 back to its wild-type conformation or compounds which interfere with the binding to, or the ubiquitylation of, p53 by MDM2. In both cases, however, the efficacy of the strategy depends on the presence of either mutant or wild-type p53 respectively thereby limiting their application to specific tumor settings. As a result, recent strategies have turned to the p53 family member, p73, which like p53 is a potent inducer of death, but in contrast is rarely lost or mutated in tumors. We discuss here all these different strategies and in particular focus on the discovery of an apoptotic peptide which targets not just p73, but potentially all p53 family members to cause tumor cell death.

A p53-derived apoptotic peptide derepresses p73 to cause tumor regression in vivo.

The tumor suppressor p53 is a potent inducer of tumor cell death, and strategies exist to exploit p53 for therapeutic gain. However, because about half of human cancers contain mutant p53, application of these strategies is restricted. p53 family members, in particular p73, are in many ways functional paralogs of p53, but are rarely mutated in cancer. Methods for specific activation of p73, however, remain to be elucidated. We describe here a minimal p53-derived apoptotic peptide that induced death in multiple cell types regardless of p53 status. While unable to activate gene expression directly, this peptide retained the capacity to bind iASPP - a common negative regulator of p53 family members. Concordantly, in p53-null cells, this peptide derepressed p73, causing p73-mediated gene activation and death. Moreover, systemic nanoparticle delivery of a transgene expressing this peptide caused tumor regression in vivo via p73. This study therefore heralds what we believe to be the first strategy to directly and selectively activate p73 therapeutically and may lead to the development of broadly applicable agents for the treatment of malignant disease.

Intracellular signalling and cancer: complex pathways lead to multiple targets.

Normal cells proliferate, die and differentiate as and when they should for the proper functioning of any particular tissue type. These processes are governed by a complex series of intracellular pathways that have many internal checkpoints and safety nets. These ensuring a fine, but tight, balance on overall tissue growth and distribution. A series of key aberrations, resulting in the disruption of these intracellular pathways, can lead to the development of a malignancy. The nature of these alterations is often not only tumour-specific, but also different between individuals with the same tumour type. As a result, these pathways have to be carefully dissected and functionally assessed to identify valid targets with therapeutic potential in a wide range of tumour types.

Molecular mechanisms underlying dexamethasone inhibition of iNOS expression and activity in C6 glioma cells.

The synthetic glucocorticoid dexamethasone is routinely used to stabilize patients with malignant gliomas. One putative target for glucocorticoid action is inducible nitric oxide synthase (iNOS), which is produced by the tumor cells as well as the host immune cells. In this study, we characterize the stimulatory effects of lipopolysaccharide (LPS) and the cytokine, tumor necrosis factor-alpha (TNFalpha), as well as the inhibitory effect of glucocorticoids, on iNOS gene expression and activity in C6 glioma cells cultured in vitro. LPS significantly increased iNOS mRNA expression, peaking at 6 h, while nitrite formation increased with time up to 72 h. Although TNFalpha alone induced neither iNOS mRNA expression nor nitrite formation, it significantly potentiated the effect of LPS on both. iNOS activity induced by LPS with or without TNFalpha was dose-dependently inhibited by dexamethasone, reaching a maximum of approximately 83% inhibition. This was completely reversed by the addition of RU38486, an antagonist of glucocorticoid receptors (GR). Dexamethasone inhibited iNOS mRNA expression; however, the maximum inhibition obtained was only 10%. These results suggest that as for induction of iNOS activity in C6 cells in vitro, the stimulatory effect of LPS is mainly due to an action at the transcriptional level. TNFalpha does not have intrinsic inducing activity, but has potentiating effects at the transcriptional and possibly at the posttranscriptional levels in the presence of LPS. The inhibitory effect of dexamethasone is GR-mediated and is mainly due to action at the posttranscriptional level.