Current Pharmaceutical Design - Volume 17, Issue 3, 2011

Apoptosis is implicated in numerous pathological processes that include cancer, autoimmune disorders and neurodegenerative diseases. Recent advances in the knowledge of the molecular mechanisms underlying apoptosis is providing a number of potential therapeutic targets and allowing the development of effective drugs that are able to interfere with this type of programmed cell death. This issue of Current Pharmaceutical Design provides an extensive overview of the latest findings concerning the molecular mechanisms of apoptosis and drugs that are able to interfere with these mechanisms. This issue, in particular, comprises the following 9 contributions: Pezzino et al. discuss how the identification, prioritization and validation of preclinical therapeutics can be achieved through genomic analysis of critical pathways and networks in neuronal apoptosis and survival. They highlight the importance of the system biology approach in the process of drug discovery. They discuss how apoptosis and survival, depend on the activity of an integrated network of genes and their encoded proteins [1]. Seaborn et al. discuss the anti-apoptotic effects of Pituitary adenylate cylase-activating polypeptide (PACAP) and its derivative, together with their potential use in the treatment of post-traumatic lesions, neurodegenerative diseases, cardiac ischemia, and retinopathy [2]. Cavallucci and D'Amelio review evidence linking apoptosis to brain diseases and discuss how knowledge of these mechanisms are leading to novel therapeutics. They focus on neurodegeneration, the pathogenetic role of apoptosis in brain diseases, and on recent progress of apoptosis-based therapies [3]. Sureda et al. discuss potential pathways involved in the pathogenesis of neurodegenerative diseases, highlighting current pharmacological drug targets in neuronal apoptosis prevention and examine drugs that may have a neuroprotective effect [4]. Silva et al. discuss the use of a yeast model system to reveal novel drug targets against apoptosis. The use of this cell model is contributing to understand the function of Bcl-2 family of proteins and identify novel therapeutic opportunities [5]. Wasierska-Gadek and Maurer review the impact of inhibiting individual cellular CDKs on apoptosis. They discuss in detail the molecular mechanisms by which CDK inhibitors are able to bypass chemoresistance in tumor cells and trigger apoptosis. Pharmacological utility of CDK inhibitors is considered not only in the treatment against cancer, but also in neurodegenerative and cardiovascular diseases [6]. Grimm et al. review recent development of drugs, which interfere with apoptosis and are currently used or tested for treatment of breast cancer. These novel agents include those targeting the extrinsic pathway such as Fas, tumor necrosis factor-alpha and tumor necrosis factor related apoptosis-inducing ligand, as well as drugs targeting the intrinsic Bcl-2 family pathway, or drugs inhibiting repair enzymes such as Poly (ADP-ribose) polymerase (PARP) inhibitors [7]. Johnson et al. consider the possibility that the endoplasmic reticulum stress response (ERSR) could be a possible target to develop chemotherapeutic agents to induce toxicity in glioma cells, and describe how the ERSR pathway mediates apoptosis and how it can be a target for small molecules to cause cell death [8]. Li et al. discuss the molecular mediators of cellular apoptosis, the respective mechanisms by which these mediators are dysregulated in cellular oncogenesis, the history and development of both nucleic-acid and amino-acid based drugs, and techniques to achieve intracellular delivery of these biologics. Finally, recent applications where pro-apoptotic functionality has been achieved through delivery of intracellularacting biomacromolecular drugs are described [9].

The advent of “systems biology” has highlighted that any function of a biological system is rarely attributable to a single molecule or a single process. Hence, complex processes, such as apoptosis and survival, depend on the activity of an integrated network of genes and their encoded proteins, which almost never work alone but interact with each other in highly structured and incredibly complex ways. With the completion of genome sequencing in humans and model organisms, and the advent of DNA microarray technology, the transcriptional cascades and gene networks regulating neuronal apoptosis and survival are being elucidated providing new potential pharmacological targets. The emerging challenge is the effective selection of the myriad of targets to identify those with the most therapeutic utility. The present review will illustrate how the identification, prioritization and validation of preclinical therapeutics can be achieved through genomic analysis of critical pathways and networks in neuronal apoptosis and survival.

Apoptosis is a regulated process leading to cell death, which is implicated both in normal development and in various pathologies including heart failure, stroke and neurodegenerative diseases. Caspase-3, a key enzyme of the apoptotic pathway, is considered as a major target for the treatment of abnormal cell death. Many factors that inhibit cell death have been identified, but the mechanisms involved are not always fully understood. Pituitary adenylate cylase-activating polypeptide (PACAP) has been shown to exert neuroprotective activities during development. PACAP also inhibits apoptosis in cardiomyopathy, decreases glutamate-induced retinal injury, reduces neuronal loss in case of stroke, and prevents ethanol neurotoxicity. Most of the antiapoptotic effects of PACAP are mediated through the PAC1 receptor. This receptor activates a transduction cascade of second messengers to stimulate Bcl-2 expression which inhibits cytochrome c release and blocks in turn caspase activation. PACAP also acts through the PI3K/Akt pathway and inhibits the expression of proapoptotic factors such as c-Jun or Bax. The remarkable effect of PACAP on the apoptotic cascade suggests that innovative PACAP derivatives could potentially be useful for treatment of post-traumatic lesions, chronic neurodegenerative diseases, cardiac ischemia and/or retinopathy.

Neurodegenerative diseases that include amyotrophic lateral sclerosis, Huntington's disease, Alzheimer's disease, Parkinson's disease, stroke, brain trauma and spinal cord injury, are associated with the inappropriate activation of a neuronal cell-suicide program called apoptosis. Given that central nervous system tissue has very limited regenerative capacity it is of extreme importance to limit the damage caused by neuronal death. During the past decade, considerable progress has been made in understanding the process of apoptosis and, significantly, a number of studies have shown that a variety of small molecules can activate or inhibit cell death by acting on crucial checkpoints of apoptosis. Here, we review evidence linking apoptosis to brain diseases and discuss how knowledge of the mechanisms of cell death has led to novel therapeutic strategies.

The purpose of this review is to discuss potential pathways involved in the pathogenesis of neurodegenerative diseases, highlighting current pharmacological drug targets in neuronal apoptosis prevention. The incidence of these disorders is expected to rise in the coming years and so finding effective treatments represents a significant challenge for medicine. Alzheimer's disease and Parkinson's disease were both described almost a century ago and are the most important neurodegenerative disorders in the developed world. However, the molecular mechanisms that lead to the development of the neuronal pathology in both diseases are unclear. For this reason, despite substantial research in the area, an effective treatment for these diseases does not yet exist. In the present study we discuss in depth the pathways involved in apoptosis and neuronal death in neurodegenerative diseases. We also examine drugs that may have a neuroprotective effect. Inhibition of apoptosis mediated by oxidative stress generation and mitochondrial alteration or by the blockade of NMDA receptors could constitute a suitable therapeutic strategy for Alzheimer's disease. A multiple therapy with antioxidants, cell cycle inhibitors, GSK3β inhibitors, and STATINS could, in the future, represent a suitable strategy for delaying the progression of neurodegenerative diseases. This research contributes to the development of new methods in the field of apoptosis inhibitors that could provide the future tools for the treatment of Alzheimer's and Parkinson's disease, as well as other neurodegenerative diseases.

The Bcl-2 protein family plays a central role in mitochondrial membrane permeabilization. This event and the ensuing release of cytochrome c are decisive in the apoptotic cascade. Therefore, a better knowledge of these processes and their regulation will probably lead to the development of novel therapeutic strategies for the treatment of apoptosis-related diseases. However, the mode of action of Bcl-2 protein family and its regulation are not completely understood. Yeast has proved to be a powerful tool to investigate the molecular aspects of several biological processes, including the steps of the apoptotic cascade involving mitochondria. The fact that yeast does not have obvious homologs of the mammalian Bcl-2 family proteins and that these proteins conserve some of their molecular and biochemical functions when expressed in yeast favor the use of this simpler model system to unravel some of the functions of this family. In this review we attempt to encompass the current knowledge regarding Bcl-2 family mode of action and regulation obtained using the yeast model system. Moreover, we discuss how this model system can be used in the future to gain new understanding about the intricate mechanisms of Bcl-2 family protein regulation, and highlight novel therapeutic targets revealed by this system. We believe that the studies summarized here also provide a proof of principle of yeast as an important tool to elucidate some of the complex mechanisms of apoptotic cell death in higher eukaryotes.

The deregulation of apoptosis and the cell cycle are important steps in the onset of cancer, giving cells unlimited reproductive potential and increasing their likelihood of survival. The cell cycle is an essential and tightly regulated four-stage process that effects the accurate duplication and transmission of genetic content to cells' progeny. Cyclin-dependent kinases (CDKs) are key elements of the mammalian cell cycle machinery. Their activity is normally regulated via cyclin binding, phosphorylation events, and interactions with endogenous CDK inhibitors. Malfunctions in the control of the cell cycle can be specifically countered using pharmacological CDK inhibitors. Importantly, CDK inhibitors are very effective against both rapidly dividing and quiescent cancer cells; this is particularly relevant in the treatment of malignancies such as chronic lymphatic leukemia (CLL) and multiple myeloma (MM) that exhibit both a low mitotic index and apoptotic defects. The high efficacy of pharmacological CDK inhibitors against CLL and MM is attributable to their ability to eliminate leukemic cells by apoptosis. Indeed, not only do pharmacological CDK inhibitors block cell cycle progression; they also promote apoptosis and thereby destroy irrevocably malignant cells. This article focuses on the impact of inhibiting individual cellular CDKs on apoptosis. We discuss in detail the molecular mechanisms by which CDK inhibitors are able to bypass chemoresistance in tumor cells and trigger apoptosis. Remarkably, recent findings suggest that the pharmacological utility of CDK inhibitors may not be restricted to the treatment of cancer: some may be efficacious in the treatment of patients with neurodegenerative and cardiovascular diseases.

Apoptosis plays an important role in development, growth, differentiation, altered gravity conditions, tissue homeostasis, immune defense, and cancer. It can be initiated by external signals via death receptors, but may also emerge from mitochondria. Today most of the key players in cellular apoptosis regulation are identified and can be targeted by therapeutic strategies. In this review we focus on recent development of drugs, which interfere with apoptosis and are currently used or tested for treatment of breast cancer. These novel agents include those targeting the extrinsic pathway such as Fas, tumor necrosis factor-alpha and tumor necrosis factor related apoptosisinducing ligand, as well as drugs targeting the intrinsic Bcl-2 family pathway, or drugs inhibiting repair enzymes such as Poly (ADPribose) polymerase (PARP) inhibitors. Their function will be explained, their role in tumor biology and actual clinical studies will be discussed.

Glial tumors are the main primary adult brain tumor. Even with the most advanced treatments, which include stereotactic microscope aided surgical resection, internal and external radiation therapy and local and systemic chemotherapy, median survival time for patients diagnosed with these malignancies is about 12 months. We explore here the possibility that the endoplasmic reticulum stress response (ERSR) could be a possible target to develop chemotherapeutic agents to induce toxicity in glioma cells. ERSR has the dual capacity of activating repair and/or cytotoxic mechanisms. ERSR is triggered by the accumulation of unfolded proteins in the ER. The presence of unfolded proteins in the ER regulates, via a complex biochemical cascade, the upregulation of molecular chaperones, inhibition of protein synthesis, and an increase of proteasome mediated unfolded protein degradation. ERSR in particular conditions can also contribute to cell death via activation of programmed cell death. Apoptosis activation during ERSR is usually caused by the activation of one or a combination of three biochemical cascades. Induction of these pathways ultimately leads to caspase 3 activation culminating in apoptosis. Glioma cells are in a condition of constant low grade ERSR, which possibly contributes to their resistance to treatment protocols. It is conceivable that small molecules that interact with this phenomenon ultimately could be used to modulate the system to activate apoptosis and cause gliotoxicity. We will discuss here ERSR biochemically relevant features to death mechanisms and already identified small molecules that by modulating ERSR are able to activate glioma cell death.

The recent elucidation of molecular regulators of apoptosis and their roles in cellular oncogenesis has motivated the development of biomacromolecular anticancer therapeutics that can activate intracellular apoptotic signaling pathways. Pharmaceutical scientists have employed a variety of classes of biologics toward this goal, including antisense oligodeoxynucleotides, small interfering RNA, proteins, antibodies, and peptides. However, stability in the in vivo environment, tumor-specific biodistribution, cell internalization, and localization to the intracellular microenvironment where the targeted molecule is localized pose significant challenges that limit the ability to directly apply intracellular-acting, pro-apoptotic biologics for therapeutic use. Thus, approaches to improve the pharmaceutical properties of therapeutic biomacromolecules are of great significance and have included chemically modifying the bioactive molecule itself or formulation with auxiliary compounds. Recently, promising advances in delivery of pro-apoptotic biomacromolecular agents have been made using tools such as peptide “stapling”, cell penetrating peptides, fusogenic peptides, liposomes, nanoparticles, smart polymers, and synergistic combinations of these components. This review will discuss the molecular mediators of cellular apoptosis, the respective mechanisms by which these mediators are dysregulated in cellular oncogenesis, the history and development of both nucleic-acid and amino-acid based drugs, and techniques to achieve intracellular delivery of these biologics. Finally, recent applications where proapoptotic functionality has been achieved through delivery of intracellular-acting biomacromolecular drugs will be highlighted.