Current Medicinal Chemistry - Volume 21, Issue 10, 2014

Phosphodiesterases (PDEs), as key regulators of cyclic nucleotides, and their inhibitors have been emerged as new pharmacological targets and promising drug candidates for many diseases, including central nervous system pathologies. The high level of PDE10A expression in the striatal medium spiny neurons suggests a prominent function role for the isoenzyme. Basal ganglia dysfunction is associated with neuropsychiatric disorders and until recently the development of PDE10A inhibitors has been focused on schizophrenia. Currently, the pharmaceutical research on PDE10A inhibitors is moving to show the modulation of other functions associated with the basal ganglia such the motor control. Thus, PDE10A inhibitors may be important pharmacological agents for neurodegenerative disorders such as Parkinson’s and Huntington’s diseases. Recent data supporting new clues for PDE10A as therapeutic target together with a concise review of the chemical structures of its inhibitors are provided here. The goal of this manuscript is to provide new ideas for assistant pharmacologist and medicinal chemists in the search for PDE10A inhibitors as new disease modifying drugs for Parkinson’s disease.

The use of synthetic peptides as HIV-1 inhibitors has been the object of research over recent years. A large number of peptides that affect different stages of the HIV-1 life cycle have been and continue to be studied due to their possible clinical application in the fight against HIV-1 infection. The main advantages of synthetic peptides as therapeutic agents are their low systemic toxicity, the fact that structural modifications can be made to them and their resulting capacity to mimic certain substrates or epitopes. HIV-1-inhibiting peptides have been identified and/or developed using different methods. Some therapeutic peptides such as enfuvirtide—already approved for clinical use—are derived from HIV-1 itself. Others are natural peptides such as chemokines, defensins or the “virus inhibitory peptide”; while still others have been designed and synthesized based on crystallographic data on HIV-1 proteins or from peptide libraries. Initial attempts at therapeutic applications focused on HIV-coded enzymes (reverse transcriptase, protease and, more recently, integrase). However, structural HIV proteins and, more specifically, the mechanisms that involve the virus in cell infection and replication are now also considered therapeutic targets. Several chemical strategies to improve both the stability of peptides and their pharmacokinetics, including prolonging their half-life, have recently been described in the literature. There is growing an interest in inhibitors that prevent HIV entry into the host cell (fusion inhibitors) which could lead to the development of new antiviral agents. Knowledge of the mechanism of action of fusion inhibitors is essential not only for the development of future generations of entry inhibitors, but also to gain an understanding of the form and kinetics of membrane fusion induced by the virus. The physico-chemical processes involved at the interface between the lipid surface of cells and enveloped viruses (such as HIV-1) are essential to the action of peptides that prevent HIV-1 entry into the host cell. The interaction of these peptides with biological membranes may be related to their inhibition efficiency and to their mechanism of action, as the HIV-1 gp41 glycoprotein is bound and confined between the cellular membrane and the viral envelope.

Traumatic brain injury (TBI) is a major healthcare concern, constituting a major cause of death and disability throughout the world. Among the factors leading to TBI outcome are biochemical cascades which occur in response to primary and secondary injury. These mechanisms generate oxidative stress, an imbalance between oxidant and antioxidant agents that can result in neural dysfunction and death. After TBI, an assembly of oxidative stress markers (carbonylated proteins, lipid peroxides, reactive oxygen and reactive nitrogen species) are produced in the brain, while antioxidant defense enzymes decrease (GSH, ratio GSH/GSSG, GPx, GR, GST, G-6PD, SOD, CAT). This imbalance is directly related to the pathogenesis of TBI. Therefore, the development of antioxidant strategies is of primary interest in ongoing efforts to optimize brain injury treatment. The success of any drug intervention strategy relies, in part, on knowledge of the optimal dosage and therapeutic window for its administration. But while the enzymes involved in oxidative stress have been identified, the temporal course of this imbalance following TBI has yet to be determined. This would explain why most antioxidant strategies developed to treat patients with TBI have failed.

Neuritin (also known as candidate plasticity gene 15, cpg15) is an activity-induced glycosylphosphatidylinositol- anchored axonal protein and is mainly expressed in the brain. Neuritin mRNA expression is modulated by neurotrophic factors, synaptic activity, hormones, sensory experience, and electroconvulsive seizure therapy. Neuritin has several effects in the nervous system, such as promoting neurite outgrowth, modulating neurite outgrowth during neuronal differentiation, protecting motor neuron axons, promoting dendritic growth, shaping dendritic arbors of target neurons, regulating synaptic plasticity, stabilizing active synapses, promoting synaptic maturation and neuronal migration, promoting the development and maturation of visual cortical neurons, regulating apoptosis of proliferative neurons, and regenerating peripheral nerve and spinal axons. Neuritin is also implicated in cerebral ischemia, depression, and cognitive function in schizophrenia, and it upregulates transient outward K+ currents in neurons, suggesting that neuritin may be a potential therapeutic target in peripheral and central nervous system diseases. This review focuses on the expression, distribution, and physiological functions of neuritin in the nervous system.

It has been a long story of the development of anticancer metallopharmaceuticals since the identification of cisplatin. Advances in metallodrugs discovery during the past 40 years have made it an ever-growing area of research in medicinal inorganic chemistry. Meanwhile, the emerging of N-heterocyclic carbene (NHC) chemistry has stimulated the newly burgeoning interests in the biomedical applications of metal-NHC complexes. This review will detail what have been achieved hitherto in the research of metal-NHC complexes as potential anti-tumor agents coupled with gold, silver, copper, platinum and palladium. Their mechanism of action will also be discussed. All the results obtained indicate that this promising approach is worthy of more focuses and further studies.

Human forkhead box class O (FoxO) transcription factors, activated in response to a wide range of external stimuli, like growth factors, insulin, nutrient levels and oxidative stress, are able to control several specific geneexpression programs. Besides their clear implication in metabolic processes, they appear to play a relevant role in tumour suppression by upregulation of genes involved in cell cycle arrest or apoptosis. Recent research efforts provide new insights into the molecular modulation of FoxO in liver cancer and disclose potential opportunities for developing new antitumor drugs. Through an intricate regulatory model, achieved via several post-translational modifications, including phosphorylation, acetylation, and ubiquitination, which control their subcellular localization and DNA binding activity, FoxO factors act as tumour suppressors. Low levels of FoxOs are associated with poor prognosis in cancer patients, and seem to confer chemotherapy resistance. Within FoxO members, FoxO3a appears to present anti-tumour properties in hepatocellular carcinoma, inducing the expression of pro-apoptotic genes, or interfering with signaling cascades commonly altered in this disease such as Wnt/β-catenin, PI3K/AKT/mTOR or MAPKs pathways. Here, we describe the main mechanisms of FoxO proteins regulation, and their cross-link with altered pathways in liver cancer. Moreover, based on the current knowledge of FoxO modulation, emphasis is placed on the development of novel agents which specifically activate FoxO family members and could be useful in the treatment of hepatocarcinoma.

Low molecular weight oligonucleotides have been discovered to have potential use for gene therapy by selectively inhibiting the expression of certain genes. Chemical conjugation of functional peptides to oligonucleotides can introduce desired properties to the oligonucleotides, such as cell-specific delivery, cellular uptake efficiency, and/or intracellular distribution. In this paper, targeting peptides are conjugated to antisense interleukin-6 via a copper (I) catalyzed alkyne-azide cycloaddition click reaction. A simple and reproducible solution-phase conjugation procedure was investigated. Oligonucleotide-peptide conjugations were characterized by reverse-phase high-pressure liquid chromatography and mass spectrometry. The results show that the targeting peptides can be used for targeting delivery of oligonucleotides using the aforementioned conjugation.

Epidemiological evidence has linked the development and progression of several cancers including melanoma with obesity. However, whether obesity impinges on responses of cancer cells to treatment remains less understood. Here we report that human adipocytes contribute to resistance of melanoma cells to various therapeutic agents. Exposure to media from adipocyte cultures (adipocyte media) increased cell proliferation and reduced sensitivity of melanoma cells to apoptosis induced by diverse chemotherapeutic drugs, including the DNA-damaging drug cisplatin, the microtubuletargeting agent docetaxel, and the histone deacetylase inhibitor SAHA. This was associated with increased activation of PI3K/Akt and MEK/ERK signaling, and was attenuated by a PI3K or MEK inhibitor. The effect of adipocyte media on melanoma cells was, at least in part, due to the interaction between the adipokine leptin and its long form receptor OB-Rb, in that immunodepletion of leptin in adipocyte media or siRNA knockdown of OB-Rb in melanoma cells reversed the increase in Akt and ERK activation, enhancement in cell proliferation, and importantly, protection of melanoma cells against the drugs. In support, recombinant leptin partially recapitulated the effect of adipocyte media on melanoma cells. Of note, OB-Rb was increased on the surface of melanoma cells compared to melanocytes, whereas leptin short form receptors appeared to be suppressed post-transcriptionally, suggesting that OB-Rb was selectively upregulated in melanoma cells. Collectively, these results indicate that adipocytes contribute to the resistance of melanoma cells to chemotherapeutic drugs and agents targeting the PI3K/Akt and MEK/ERK pathways, and suggest that inhibition of the leptin/ OB-Rb system may be useful to improve the efficacy of multiple therapeutic approaches in the treatment of melanoma.