Current Drug Targets - Volume 14, Issue 7, 2013

Peroxisome Proliferator-Activated Receptors (PPARs) are a family of nuclear receptors whose activation modulates the gene expression that underlies both the glucid-lipid and the inflammation pathways. While many PPARs agonists have been used for years as medication for metabolic disorders, an increasing attention is being currently dedicated to these drugs for inflammation-related pathologies. Within the psychiatric field, it has recently appeared that inflammatory processes are highly suspected in the pathophysiology of several important disorders, such as schizophrenia and mood disorders. By their anti-inflammatory properties, PPARs might have a disease-modifying action that could help in improving the outcome of patients. Furthermore, recent data suggest that PPARs could also modulate the expression of some neurotransmission factors. Therefore, PPARs may directly modify the information processing, and have a potential symptomatic action on several psychiatric disorders. At last, PPARs action of metabolic regulation could have a role on corrective or even preventive strategies against the metabolic adverse events that are commonly observed with some current psychiatric medications, notably antipsychotics. This triple potential action profile of PPARs modulators is investigated in this article, successively for schizophrenia spectrum disorders and mood disorders. Theoretical involvements of PPARs are also discussed for the treatment of Post- Traumatic Stress Disorder and Personality Disorders. At the time of the emerging concept of psychoneuroimmunology, PPARs open original therapeutic prospects for the psychiatric research.

A major focus has developed for the discovery of proregenerative and neuroprotective therapeutic agents to help the millions of Americans who receive a CNS injury annually. Tribulations have been encountered along the way due to the complicated set of pathways that are initiated post-injury. To target this complicated multifaceted signaling cascade, the most promising therapeutics target multiple pathways involved in the secondary injury cascade, such as neuroinflammation, the generation of ROS and mitochondrial dysfunction. Compelling experimental data demonstrates that mitochondrial dysfunction is a pivotal link in the neuropathological sequelae of brain injury. A group of PPAR agonists, specifically rosiglitazone and pioglitazone, have shown an extreme amount of promise in the realm of drug discovery for CNS injury due to their ability to increase functional recovery and decrease lesion volumes following injury. The therapeutic effects of these PPAR agonists are thought to be a direct result of PPAR activity however new data is arising that shows some of the effects may be independent of PPAR activity, targeting a novel mitochondrial protein called mitoNEET. In this review, a thorough evaluation of the role of PPAR and mitoNEET in rosiglitazone and pioglitazone mediated neuroprotection will be completed in order to shed light on the mechanism of a new possible therapeutic intervention for CNS injury.

Parkinson’s disease (PD) is amongst the most frequent neurodegenerative disorders, the main pathologic hallmark of which is the degeneration of the substantia nigra pars compacta. Damage to multiple cellular components, such as mitochondrial dysfunction, oxidative stress, neuroinflammation, and proteasomal dysfunction, contribute to the progression of the neurodegenerative process. Peroxisome proliferator-activated receptor gamma (PPAR-γ) agonists, mainly thiazolidinediones, pioglitazone and rosiglitazone, have been successfully tested for their neuroprotective potential in PD experimental models, although the cellular target and underlying mechanism are currently a matter of debate. While the anti-inflammatory activity and attenuation of microgliosis have been proposed as a main mechanism of neuroprotection, other cellular targets might be involved, such as mitochondrial proteins controlling cellular bioenergetic and oxidative stress. Here, the current evidence of neuroprotection by PPAR-γ agonists in in vitro and in vivo experimental PD models is reported. Moreover, cellular pathways which have been investigated as potential targets of neuroprotection are reviewed. Taken together, the available data suggest that simultaneous targeting of multiple dysfunctional pathways may underlie the potent neuroprotective activity displayed by PPAR-γ agonists.

Stroke is one of the major causes of mortality and disability in adults in industrialized countries. Despite numerous preclinical studies and clinical trials in the field of cerebral ischemia, no pharmacological agent has been validated in the treatment of acute ischemic, except thrombolysis. Cerebral ischemia is not only a neuronal disease but it affects the entire neurovascular unit. The therapeutic strategy in stroke should be more global and combine preventive approaches, acute phase treatment and long-term care to improve recovery and prevent or treat affective and cognitive post-stroke consequences. There is an imperative need to develop disease-modifying drugs, which should be able to induce neuroprotection, to serve as adjuvants for thrombolysis by decreasing the hemorrhagic risk and to limit the long-term post-stroke consequences. This review presents the potential effects of Peroxisome Proliferator-Activated Receptors (PPARs) and of their agonists in stroke. We focus on each PPAR receptor and detail their implication in stroke. PPARs are nuclear receptors, acting as ligand-dependent transcription factors. They are expressed in the neurovascular unit that suggests that PPARs could play a role in stroke. Indeed, it has been shown that they are able to interfere with pathways implicated in the pathophysiology of stroke. They could be an answer to this disease-modifying drug concept, being able to act on the different phases of ischemia.

This review examines the growing literature on the role of peroxisome proliferator-activated receptors (PPARs) in addiction. There are two subtypes of PPAR receptors that have been studied in addiction: PPAR-α and PPAR-γ. The role of each PPAR subtype in common models of addictive behavior, mainly pre-clinical models, is summarized. In particular, studies are reviewed that investigated the effects of PPAR-α agonists on relapse, sensitization, conditioned place preference, withdrawal and drug intake, and effects of PPAR-γ agonists on relapse, withdrawal and drug intake. Finally, studies that investigated the effects of PPAR agonists on neural pathways of addiction are reviewed. Taken together these preclinical data indicate that PPAR agonists are promising new medications for drug addiction treatment.

CPT-11 (irinotecan), a DNA topoisomerase I inhibitor is one of the main treatments for colorectal cancer. The main dose limiting toxicities are neutropenia and late onset diarrhea. Though neutropenia is manageable, CPT-11 induced diarrhea is frequently severe, resulting in hospitalizations, dose reductions or omissions leading to ineffective treatment administration. Many potential agents have been tested in preclinical and clinical studies to prevent or ameliorate CPT-11 induced late onset diarrhea. It is predicted that prophylaxis of CPT-11 induced diarrhea will reduce sub-therapeutic dosing as well as hospitalizations and will eventually lead to dose escalations resulting in better response rates. This article reviews various experimental agents and strategies employed to prevent this debilitating toxicity. Covered topics include schedule/dose modification, intestinal alkalization, structural/chemical modification, genetic testing, anti-diarrheal therapies, transporter (ABCB1, ABCC2, BCRP2) inhibitors, enzyme (β-glucuronidase, UGT1A1, CYP3A4, carboxylesterase, COX-2) inducers and inhibitors, probiotics, antibiotics, adsorbing agents, cytokine and growth factor activators and inhibitors and other miscellaneous agents.

Endogenous opioid peptides have been studied extensively as potential therapeutics for the treatment of pain. The major problems of using natural opioid peptides as drug candidates are their poor receptor specificity, metabolic instability and inability to reach the brain after systemic administration. A lot of synthetic efforts have been made to opioid analogs with improved pharmacological properties. One important structural modification leading to such analogs is cyclization of linear sequences. Intramolecular cyclization has been shown to improve biological properties of various bioactive peptides. Cyclization reduces conformational freedom responsible for the simultaneous activation of two or more receptors, increases metabolic stability and lipophilicity which may result in a longer half-life and easier penetration across biological membranes. This review deals with various strategies that have been employed to synthesize cyclic analogs of opioid peptides. Discussed are such bridging bonds as amide and amine linkages, sulfur-containing bonds, including monosulfide, disulfide and dithioether bridges, bismethylene bonds, monosulfide bridges of lanthionine and, finally, carbonyl and guanidine linkages. Opioid affinities and activities of cyclic analogs are given and compared with linear opioid peptides. Analgesic activities of analogs evaluated in the in vivo pain tests are also discussed.

Epidermal growth factor receptors (EGFRs) belong to the ErbB family of receptor tyrosine kinases (TKs) involved in the proliferation of normal and malignant cells. As mutations and overexpression of ErbB TKs are implicated in carcinoma and glioblastoma and are related to both a very strong resistance to chemotherapy and a poor survival means that ErbB receptors are targets of considerable importance for anti-cancer drug design. Besides using monoclonal antibodies for anti-EGFR-related cancer therapeutics, small molecules - tyrosine kinase inhibitors are being considered as well. Some of these therapies have entered clinical trials or have been approved for clinical use. Based on experimental methods (radiometry, immunofluoroscence or luminescence, electrophoresis) that are mainly employed for measuring and interpreting the selectivity of protein kinase inhibitors, routine accomplishment of selectivity of small molecules for particular protein kinases is a substantial challenge. In light of this, we herein elaborate a computer-based protein engineering approach demonstrating its potential to be a viable supplement to experiment in modulating the affinity of ligand molecules for EGFR in an efficient manner. The structural basis of the remarkable strategy is also elucidated using our recent results obtained by means of molecular docking and molecular dynamics simulations. A few critical implications for successful structure-based design of prospective drug candidates against EGFR-related cancers are consequently discussed.