Miriam Redondo

Phosphodiesterase 7 Inhibition Preserves Dopaminergic Neurons in Cellular and Rodent Models of Parkinson Disease

BACKGROUND Phosphodiesterase 7 plays a major role in down-regulation of protein kinase A activity by hydrolyzing cAMP in many cell types. This cyclic nucleotide plays a key role in signal transduction in a wide variety of cellular responses. In the brain, cAMP has been implicated in learning, memory processes and other brain functions. METHODOLOGY/PRINCIPAL FINDINGS Here we show a novel function of phosphodiesterase 7 inhibition on nigrostriatal dopaminergic neuronal death. We found that S14, a heterocyclic small molecule inhibitor of phosphodiesterase 7, conferred significant neuronal protection against different insults both in the human dopaminergic cell line SH-SY5Y and in primary rat mesencephalic cultures. S14 treatment also reduced microglial activation, protected dopaminergic neurons and improved motor function in the lipopolysaccharide rat model of Parkinson disease. Finally, S14 neuroprotective effects were reversed by blocking the cAMP signaling pathways that operate through cAMP-dependent protein kinase A. CONCLUSIONS/SIGNIFICANCE Our findings demonstrate that phosphodiesterase 7 inhibition can protect dopaminergic neurons against different insults, and they provide support for the therapeutic potential of phosphodiesterase 7 inhibitors in the treatment of neurodegenerative disorders, particularly Parkinson disease.

Phosphodiesterase 7 inhibitor reduced cognitive impairment and pathological hallmarks in a mouse model of Alzheimer's disease

Elevated levels of amyloid beta (Aβ) peptide, hyperphosphorylation of tau protein, and inflammation are pathological hallmarks in Alzheimers disease (AD). Phosphodiesterase 7 (PDE7) regulates the inflammatory response through the cyclic adenosine monophosphate signaling cascade, and thus plays a central role in AD. The aim of this study was to evaluate the efficacy of an inhibitor of PDE7, named S14, in a mouse model of AD. We report that APP/Ps1 mice treated daily for 4 weeks with S14 show: (1) significant attenuation in behavioral impairment; (2) decreased brain Aβ deposition; (3) enhanced astrocyte-mediated Aβ degradation; and (4) decreased tau phosphorylation. These effects are mediated via the cyclic adenosine monophosphate/cyclic adenosine monophosphate response element-binding protein signaling pathway, and inactivation of glycogen synthase kinase (GSK)3. Our data support the use of PDE7 inhibitors, and specifically S14, as effective therapeutic agents for the prevention and treatment of AD.

Protein kinase CK-1 inhibitors as new potential drugs for amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disease where motor neurons in cortex, brain stem, and spinal cord die progressively, resulting in muscle wasting, paralysis, and death. Currently, effective therapies for ALS are lacking; however, identification of pathological TAR DNA-binding protein 43 (TDP-43) as the hallmark lesion in sporadic ALS suggests new therapeutic targets for pharmacological intervention. Pathological TDP-43 phosphorylation appears to drive the onset and progression of ALS and may result from upregulation of the protein kinase CK-1 in affected neurons, resulting in postranslational TDP-43 modification. Consequently, brain penetrant specific CK-1 inhibitors may provide a new therapeutic strategy for treating ALS and other TDP-43 proteinopathies. Using a chemical genetic approach, we report the discovery and further optimization of a number of potent CK-1δ inhibitors. Moreover, these small heterocyclic molecules are able to prevent TDP-43 phosphorylation in cell cultures, to increase Drosophila lifespan by reduction of TDP-43 neurotoxicity, and are predicted to cross the blood–brain barrier. Thus, N-(benzothiazolyl)-2-phenyl-acetamides are valuable drug candidates for further studies and may be a new therapeutic approach for ALS and others pathologies in which TDP-43 is involved.

Effect of Phosphodiesterase 7 (PDE7) Inhibitors in Experimental Autoimmune Encephalomyelitis Mice. Discovery of a New Chemically Diverse Family of Compounds

Phosphodiesterase (PDE) 7 is involved in proinflammatory processes, being widely expressed both on lymphocytes and on certain brain regions. Specific inhibitors of PDE7 have been recently reported as potential new drugs for the treatment of neurological disorders because of their ability to increase intracellular levels of cAMP and thus to modulate the inflammatory process, as a neuroprotective well-established strategy. Multiple sclerosis is an unmet disease in which pathologies on the immune system, T-cells, and specific neural cells are involved simultaneously. Therefore, PDE7 inhibitors able to interfere with all these targets may represent an innovative therapy for this pathology. Here, we report a new chemically diverse family of heterocyclic PDE7 inhibitors, discovered and optimized by using molecular modeling studies, able to increase cAMP levels in cells, decrease inflammatory activation on primary neural cultures, and also attenuate the clinical symptoms in the experimental autoimmune encephalomyelitis (EAE) mouse model. These results led us to propose the use of PDE7 inhibitors as innovative therapeutic agents for the treatment of multiple sclerosis.

Comparative assessment of PDE 4 and 7 inhibitors as therapeutic agents in experimental autoimmune encephalomyelitis

PDE4 inhibition suppresses experimental autoimmune encephalomyelitis (EAE), an animal model of multiple sclerosis (MS). However, side effects hinder PDE4 inhibitors clinical use. PDE7 inhibition might constitute an alternative therapeutic strategy, but few data about the anti‐inflammatory potential of PDE7 inhibitors are currently available. We have used the EAE model to perform a comparative evaluation of PDE4 and PDE7 inhibition as strategies for MS treatment.

Phosphodiesterase 10 Inhibitors: New Disease Modifying Drugs for Parkinson’s Disease?

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 Parkinsons and Huntingtons 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 Parkinsons disease.

Identification in silico and experimental validation of novel phosphodiesterase 7 inhibitors with efficacy in experimental autoimmune encephalomyelitis mice.

A neural network model has been developed to predict the inhibitory capacity of any chemical structure to be a phosphodiesterase 7 (PDE7) inhibitor, a new promising kind of drugs for the treatment of neurological disorders. The numerical definition of the structures was achieved using CODES program. Through the validation of this neural network model, a novel family of 5-imino-1,2,4-thiadiazoles (ITDZs) has been identified as inhibitors of PDE7. Experimental extensive biological studies have demonstrated the ability of ITDZs to inhibit PDE7 and to increase intracellular levels of cAMP. Among them, the derivative 15 showed a high in vitro potency with desirable pharmacokinetic profile (safe genotoxicity and blood brain barrier penetration). Administration of ITDZ 15 in an experimental autoimmune encephalomyelitis (EAE) mouse model results in a significant attenuation of clinical symptoms, showing the potential of ITDZs, especially compound 15, for the effective treatment of multiple sclerosis.

5-Imino-1,2-4-thiadiazoles and quinazolines derivatives as glycogen synthase kinase 3β (GSK-3β) and phosphodiesterase 7 (PDE7) inhibitors: determination of blood-brain barrier penetration and binding to human serum albumin.

5-Imino-1,2,4-thiadiazoles and quinazolines derivatives as glycogen synthase kinase 3β (GSK-3β) and phosphodiesterase 7 (PDE7) inhibitors were characterized for their ability to pass the blood-brain barrier (BBB) together with their human serum albumin (HSA) binding using high-performance liquid affinity chromatography (HPLAC) and circular dichroism (CD). To study the blood-brain barrier penetration, a parallel artificial membrane permeability assay (PAMPA) using a porcine brain lipid was employed. For the HPLAC investigation, HSA was previously covalently immobilized to the silica matrix of the HPLC column. This HSA-based column was used to characterize the high affinity binding sites of 5-imino-1,2,4-thiadiazoles and quinazolines derivatives to HSA. Displacement experiments in the presence of increasing concentrations of competitors known to bind selectively to the main binding sites of HSA were carried out to determine their possible binding site. The same drug-protein system was studied by CD. The analysed compounds were able to pass BBB, they present good drug-like properties and they showed a high affinity to HSA. Competition experiments showed an anticooperative interaction at sites I and II, and an independent binding at bilirubin binding site on HSA.

Crosstalk between phosphodiesterase 7 and glycogen synthase kinase-3: two relevant therapeutic targets for neurological disorders.

Chronic neuroinflammation has been increasingly recognized as a primary mechanism underlying acute brain injury and neurodegenerative diseases. Enhanced expression of diverse pro-inflammatory agents in glial cells has been shown to contribute to the cell death that takes place in these disorders. Previous data from our group have shown that different inhibitors of the cyclic adenosine monophosphate (cAMP) specific phosphodiesterase 7 (PDE7) and glycogen synthase kinase-3 (GSK-3) enzymes are potent anti-inflammatory agents in different models of brain injury. In this study, we investigated cross-talk between PDE7 and GSK-3, two relevant therapeutic targets for neurological disorders, using a chemical approach. To this end, we compared specific inhibitors of GSK-3 and PDE7 with dual inhibitors of both enzymes with regard to anti-inflammatory effects in primary cultures of glial cells treated with lipopolysaccharide. Our results show that the GSK-3 inhibitors act exclusively by inhibition of this enzyme. By contrast, PDE7 inhibitors exert their effects via inhibition of PDE7 to increase intracellular cAMP levels but also through indirect inhibition of GSK-3. Activation of protein kinase A by cAMP results in phosphorylation of Ser9 of GSK-3 and subsequent inhibition. Our results indicate that the indirect inhibition of GSK-3 by PDE7 inhibitors is an important mechanism that should be considered in the future development of pharmacological treatments.

PDE7 inhibitor TC3.6 ameliorates symptomatology in a model of primary progressive multiple sclerosis

cAMP plays an important role in the transduction of signalling pathways involved in neuroprotection and immune regulation. Control of the levels of this nucleotide by inhibition of cAMP‐specific PDEs such as PDE7 may affect the pathological processes of neuroinflammatory diseases like multiple sclerosis (MS). In the present study, we evaluated the therapeutic potential of the selective PDE7 inhibitor, TC3.6, in a model of primary progressive multiple sclerosis (PPMS), a rare and severe variant of MS.