Neuroprotective profile of novel SRC kinase inhibitors in rodent models of cerebral ischemia

FDA-Approved Kinase Inhibitors in Preclinical and Clinical Trials for Neurological Disorders

Cancers and neurological disorders are two major types of diseases. We previously developed a new concept termed "Aberrant Cell Cycle Diseases" (ACCD), revealing that these two diseases share a common mechanism of aberrant cell cycle re-entry. The aberrant cell cycle re-entry is manifested as kinase/oncogene activation and tumor suppressor inactivation, which are hallmarks of both tumor growth in cancers and neuronal death in neurological disorders. Therefore, some cancer therapies (e.g., kinase inhibition, tumor suppressor elevation) can be leveraged for neurological treatments. The United States Food and Drug Administration (US FDA) has so far approved 74 kinase inhibitors, with numerous other kinase inhibitors in clinical trials, mostly for the treatment of cancers. In contrast, there are dire unmet needs of FDA-approved drugs for neurological treatments, such as Alzheimer's disease (AD), intracerebral hemorrhage (ICH), ischemic stroke (IS), traumatic brain injury (TBI), and others. In this review, we list these 74 FDA-approved kinase-targeted drugs and identify those that have been reported in preclinical and/or clinical trials for neurological disorders, with a purpose of discussing the feasibility and applicability of leveraging these cancer drugs (FDA-approved kinase inhibitors) for neurological treatments.

VEGF, a Key Factor for Blood Brain Barrier Injury After Cerebral Ischemic Stroke

Blood brain barrier (BBB) injury is an important factor affecting the prognosis of ischemic stroke. Extensive research on BBB injury has revealed that blood vessels and neural networks are interdependent and interrelated during and after the development of the brain. An array of signaling molecules, known as angioneurins, can affect both blood vessels and neural networks simultaneously. Angioneurins not only regulate the angiogenesis and remodeling process of the vascular system, but also act as neurotrophic and neuroprotective factors, or serve as guide molecules for axons. Vascular endothelial growth factor (VEGF) is a type of angioneurin that is expressed in neurons, astrocytes, macrophages, and vascular endothelial cells in ischemic and hypoxic brain tissues after cerebral ischemia. VEGF can increase and induce the destruction of the endothelial barrier in the early stages of cerebral ischemia. Both the upregulation of endogenous VEGF levels and the use of exogenous VEGF are harmful in the acute stage of stroke. However, the harmful effects of VEGF on vascular integrity are transient. Several studies have shown that VEGF regulates angiogenesis, neurogenesis, neurite growth and brain edema after cerebral ischemia. Therefore, it is crucial to understand the dual role of VEGF in ischemic stroke. The following will focus on the damage caused by VEGF to the BBB in the context of cerebral ischemic stroke, as well as therapeutic studies targeting VEGF.

Drug Repositioning in Friedreich Ataxia

Friedreich ataxia is a rare neurodegenerative disorder caused by insufficient levels of the essential mitochondrial protein frataxin. It is a severely debilitating disease that significantly impacts the quality of life of affected patients and reduces their life expectancy, however, an adequate cure is not yet available for patients. Frataxin function, although not thoroughly elucidated, is associated with assembly of iron-sulfur cluster and iron metabolism, therefore insufficient frataxin levels lead to reduced activity of many mitochondrial enzymes involved in the electron transport chain, impaired mitochondrial metabolism, reduced ATP production and inefficient anti-oxidant response. As a consequence, neurons progressively die and patients progressively lose their ability to coordinate movement and perform daily activities. Therapeutic strategies aim at restoring sufficient frataxin levels or at correcting some of the downstream consequences of frataxin deficiency. However, the classical pathways of drug discovery are challenging, require a significant amount of resources and time to reach the final approval, and present a high failure rate. Drug repositioning represents a viable alternative to boost the identification of a therapy, particularly for rare diseases where resources are often limited. In this review we will describe recent efforts aimed at the identification of a therapy for Friedreich ataxia through drug repositioning, and discuss the limitation of such strategies.

A new underlying mechanism for the neuroprotective effect of bosutinib: Reverting toxicity-induced PARylation in SIN1-mediated neurotoxicity

Increased levels of reactive oxygen and nitrogen species play an important role in the development and progression of neurodegenerative diseases, such as Alzheimer's and Parkinson's disease. The overproduction of these highly reactive chemical species leads to DNA damage and subsequent activation of the poly(ADP-ribose)polymerase (PARP) enzyme. Several studies have demonstrated the potential use of PARP inhibitors for neuroprotection. We previously reported that the dual Src/Abl kinase inhibitor bosutinib (BOS) decreases PARP activity and acts as a chemosensitizer in cancer cells. In this study, we evaluated the neuroprotective potential of BOS with respect to its inhibitory effect on cellular poly(ADP-ribos)ylation (PARylation) using a 3-morpholinosydnonimine (SIN1)-mediated cellular toxicity model. Our data suggest that pretreatment with BOS, especially at lower doses, significantly decreased the level of SIN1-induced cellular PARylation. This regulation pattern of PARylation was found to be associated with the protective effect of BOS against SIN1 on the viability of retinoic acid-differentiated SH-SY5Y cells. Furthermore, while PARP-1 expression was decreased, phosphorylation of SAPK/JNK was not reverted at the observed neuroprotective doses of BOS. In conclusion, we suggest a novel mechanism for the neuroprotective effect of BOS involving the inhibition of cellular PARylation.

The retinal tyrosine kinome of diabetic Akimba mice highlights potential for specific Src family kinase inhibition in retinal vascular disease

Although anti-VEGF therapies have radically changed clinical practice, there is still an urgent demand for novel, integrative approaches for sight-threatening retinal vascular diseases. As we hypothesize that protein tyrosine kinases are key signaling mediators in retinal vascular disease, we performed a comprehensive activity-based tyrosine kinome profiling on retinal tissue of 12-week-old Akimba mice, a translational model displaying hallmarks of early and advanced diabetic retinopathy. Western blotting was used to confirm retinal tyrosine kinase activity in Akimba mice. HUVEC tube formation and murine organotypic choroidal sprouting assays were applied to compare tyrosine kinase inhibitors with different specificity profiles. HUVEC toxicity and proliferation were evaluated using the CellTox™ Green Cytotoxicity and PrestoBlue™ Assays. Our results indicate a shift of the Akimba retinal tyrosine kinome towards a hyperactive state. Functional network analysis of significantly hyperphosphorylated peptides and upstream kinase prediction revealed a central role for Src-FAK family kinases. Western blotting confirmed hyperactivity of this signaling node in the retina of Akimba mice. We demonstrated that not only Src but also FAK family kinase inhibitors with different selectivity profiles were able to suppress angiogenesis in vitro and ex vivo. In the latter model, the novel selective Src family kinase inhibitor eCF506 was able to achieve potent reduction of angiogenesis, comparable to the less specific inhibitor Dasatinib. None of the tested compounds demonstrated acute endothelial cell toxicity. Overall, the collected findings provide the first comprehensive overview of retinal tyrosine kinome changes in the Akimba model of diabetic retinopathy and for the first time highlight Src family kinase inhibition using highly specific inhibitors as an attractive therapeutic intervention for retinal vascular pathology.

miR-137 prevents inflammatory response, oxidative stress, neuronal injury and cognitive impairment via blockade of Src-mediated MAPK signaling pathway in ischemic stroke

Stroke is a leading cause of death and disability worldwide. The purpose of this study was to investigate the possible role of the microRNA (miRNA or miR) miR-137 in ischemic stroke. miRNAs are very stable in the blood and may serve as potential diagnostic and therapeutic markers. Wild-type, Src^-/- and miR-137^-/- mice were treated with p38 siRNA or Erk2 siRNA to identify their roles in the inflammatory response, oxidative stress, neuronal injury and cognitive impairment in brain tissues of mice following middle cerebral artery occlusion (MCAO) operation. We evaluated several factors including; inflammatory responses, oxidative stress, viability and apoptosis of astrocytes in order to identify the functions of miR-137 and Src in ischemic stroke. miR-137 alleviated the inflammatory response, oxidative stress, neuronal injury and cognitive impairment, and restricted apoptosis via targeting Src and inactivating the MAPK signaling pathway. Furthermore, up-regulation of miR-137 or inhibition of Src inhibited the secretion of inflammatory factors, suppressed oxidative stress, and reduced apoptosis of astrocytes. In conclusion, our work suggests that, in mice, miR-137 confers neuroprotective effects against ischemic stroke via attenuation of oxidative, apoptotic, and inflammatory pathways through inhibiting Src-dependent MAPK signaling pathway.

Mechanisms underlying astrocytic connexin-43 autophagy degradation during cerebral ischemia injury and the effect on neuroinflammation and cell apoptosis

Connexin-43 (Cx43) is the most abundant gap junction protein in the nervous system. It enables cell communication and has important physiological roles including ion transport and substrate exchange, all of which have been implicated in cerebral ischemia injury. Our previous in vitro and in vivo studies have demonstrated that Cx43 is internalized and degraded during ischemia stress. However, the significance of ischemia-induced degradation of Cx43 remains unclear. Herein, we demonstrated that Cx43 degradation during ischemia injury is mediated by selective autophagy; additionally, we identified two related autophagy receptors-OPTN and NDP52. Cx43 degradation during ischemia requires its phosphorylation and ubiquitination, which are mediated by PKC, Src kinases, and ubiquitin kinase PINK1. Using point mutagenesis, we identified three phosphorylation sites underlying Cx43 autophagy degradation under ischemic stress. Cx43 degradation inhibition promoted the transition of astrocytes from a pro-inflammatory to an anti-inflammatory status, based on the levels of IL-10 and TNF in ischemia. Knockdown or accelerated degradation of Cx43 protected astrocytes from apoptosis under ischemic stress. These findings elucidate the underlying mechanism of astrocytic Cx43 autophagic degradation during ischemia. The study has identified potentially novel therapeutic strategies against ischemic stroke and evidence of crosstalk between autophagic degradation of Cx43, astrocytic apoptosis, and neuroinflammation.

Oxidative stress-induced activation of Abl and Src kinases rapidly induces P-glycoprotein internalization via phosphorylation of caveolin-1 on tyrosine-14, decreasing cortisol efflux at the blood-brain barrier

Exposure of the brain to high levels of glucocorticoids during ischemia-reperfusion induces neuronal cell death. Oxidative stress alters blood-brain barrier (BBB) function during ischemia-reperfusion, and so we hypothesized that it might impair P-glycoprotein (P-gp)-mediated efflux transport of glucocorticoids at the BBB. Therefore, the purpose of this study was to clarify the molecular mechanism of this putative decrease of P-gp-mediated efflux function. First, we established that H₂O₂ treatment of a human in vitro BBB model (hCMEC/D3) reduced both P-gp efflux transport activity and protein expression on the plasma membrane within 20 min. These results suggested that the rapid decrease of efflux function might be due to internalization of P-gp. Furthermore, H₂O₂ treatment markedly increased tyrosine-14-phosphorylated caveolin-1, which is involved in P-gp internalization. A brain perfusion study in rats showed that cortisol efflux at the BBB was markedly decreased by H₂O₂ administration, and inhibitors of Abl kinase and Src kinase, which phosphorylate tyrosine-14 in caveolin-1, suppressed this decrease. Overall, these findings support the idea that oxidative stress-induced activation of Abl kinase and Src kinase induces internalization of P-gp via the phosphorylation of tyrosine-14 in caveolin-1, leading to a rapid decrease of P-gp-mediated cortisol efflux at the BBB.

Dysfunction of 67-kDa Laminin Receptor Disrupts BBB Integrity via Impaired Dystrophin/AQP4 Complex and p38 MAPK/VEGF Activation Following Status Epilepticus

Status epilepticus (SE, a prolonged seizure activity) impairs brain-blood barrier (BBB) integrity, which results in secondary complications following SE. The non-integrin 67-kDa laminin receptor (67-kDa LR) plays a role in cell adherence to laminin (a major glycoprotein component in basement membrane), and participates laminin-mediated signaling pathways including p38 mitogen-activated protein kinase (p38 MAPK). Thus, we investigated the role of 67-kDa LR in SE-induced vasogenic edema formation in the rat piriform cortex (PC). SE diminished 67-kDa LR expression, but increased laminin expression, in endothelial cells accompanied by the reduced SMI-71 (a rat BBB barrier marker) expression. Astroglial 67-kDa LR expression was also reduced in the PC due to massive astroglial loss. 67-kDa LR neutralization led to serum extravasation in the PC concomitant with the reduced SMI-71 expression. 67-kDa LR neutralization also decreased expressions of dystrophin and aquaporin-4 (AQP4). In addition, it increased p38 MAPK phosphorylation and expressions of vascular endothelial growth factor (VEGF), laminin and endothelial nitric oxide synthase (eNOS), which were abrogated by SB202190, a p38 MAPK inhibitor. Therefore, our findings indicate that 67-kDa LR dysfunction may disrupt dystrophin-AQP4 complex, which would evoke vasogenic edema formation and subsequent laminin over-expression via activating p38 MAPK/VEGF axis.

Roles of astrocytic connexin-43, hemichannels, and gap junctions in oxygen-glucose deprivation/reperfusion injury induced neuroinflammation and the possible regulatory mechanisms of salvianolic acid B and carbenoxolone

Background

Glia-mediated neuroinflammation is related to brain injury exacerbation after cerebral ischemia/reperfusion (I/R) injury. Astrocytic hemichannels or gap junctions, which were mainly formed by connexin-43, have been implicated in I/R damage. However, the exact roles of astrocytic hemichannels and gap junction in neuroinflammatory responses induced by I/R injury remain unknown.

Methods

Primary cultured astrocytes were subjected to OGD/R injury, an in vitro model of I/R injury. Salvianolic acid B (SalB) or carbenoxolone (CBX) were applied for those astrocytes. Besides, Cx43 mimetic peptides Gap19 or Gap26 were also applied during OGD/R injury; Cx43 protein levels were determined by western blot and cytoimmunofluorescene staining, hemichannel activities by Ethidium bromide uptake and ATP concentration detection, and gap junction intercellular communication (GJIC) permeability by parachute assay. Further, astrocyte-conditioned medium (ACM) was collected and incubated with microglia. Meanwhile, ATP or apyrase were applied to explore the role of ATP during OGD/R injury. Microglial activation, M1/M2 phenotypes, and M1/M2-related cytokines were detected. Also, microglia-conditioned medium (MEM) was collected and incubated with astrocytes to further investigate its influence on astrocytic hemichannel activity and GJIC permeability. Lastly, effects of ACM and MCM on neuronal viability were detected by flow cytometry.

Results

We found that OGD/R induced abnormally opened hemichannels with increased ATP release and EtBr uptake but reduced GJIC permeability. WB tests showed decreased astrocytic plasma membrane’s Cx43, while showing an increase in cytoplasma. Treating OGD/R-injured microglia with ATP or OGD/R-ACM induced further microglial activation and secondary pro-inflammatory cytokine release, with the M1 phenotype predominating. Conversely, astrocytes incubated with OGD/R-MCM exhibited increased hemichannel opening but reduced GJIC coupling. Both SalB and CBX inhibited abnormal astrocytic hemichannel opening and ATP release and switched the activated microglial phenotype from M1 to M2, thus providing effective neuroprotection. Application of Gap19 or Gap26 showed similar results with CBX. We also found that OGD/R injury caused both plasma membrane p-Cx43(Ser265) and p-Src(Tyr416) significantly upregulated; application of SalB may be inhibiting Src kinase and attenuating Cx43 internalization. Meanwhile, CBX treatment induced obviously downregulation of p-Cx43(Ser368) and p-PKC(Ser729) protein levels in plasma membrane.

Conclusions

We propose a vicious cycle exists between astrocytic hemichannel and microglial activation after OGD/R injury, which would aggravate neuroinflammatory responses and neuronal damage. Astrocytic Cx43, hemichannels, and GJIC play critical roles in OGD/R injury-induced neuroinflammatory responses; treatment differentially targeting astrocytic Cx43, hemichannels, and GJIC may provide novel avenues for therapeutics during cerebral I/R injury.

Electronic supplementary material

The online version of this article (10.1186/s12974-018-1127-3) contains supplementary material, which is available to authorized users.

The role of non-receptor protein tyrosine kinases in the excitotoxicity induced by the overactivation of NMDA receptors

Protein tyrosine phosphorylation is one of the primary modes of regulation of N-methyl-d-aspartate (NMDA) receptors. The non-receptor tyrosine kinases are one of the two types of protein tyrosine kinases that are involved in this process. The overactivation of NMDA receptors is a primary reason for neuron death following cerebral ischemia. Many studies have illustrated the important role of non-receptor tyrosine kinases in ischemia insults. This review introduces the roles of Src, Fyn, focal adhesion kinase, and proline-rich tyrosine kinase 2 in the excitotoxicity induced by the overactivation of NMDA receptors following cerebral ischemia.

Translational gap in ongoing clinical trials for glioma

Despite the vast amounts of information gathered about gliomas, the overall survival of glioma patients has not improved in the last four decades. This could partially be due to an apparent failure to include basic concepts of glioma biology into clinical trials. Specifically, attempts to overcome the limitations of the blood brain barrier (BBB) and the chemoresistance of glioma stem cells (GSCs) were seldom included (a phenomenon known as the translational gap, TG) in a study involving 29 Phase I/II clinical trials (P2CT) published in 2011. The aim of this study was to re-evaluate this finding with a new series of 100 ongoing, but still unpublished, P2CT in order to determine if there is a TG reduction. As indicators, we evaluated in each P2CT the number of drugs tested, concomitant radiotherapy, and the ability of drugs to pass the BBB and to target GSCs. Compared to clinical trials published in 2011, we found that while in OCT there is an increase in the number of P2CT using two drugs (from 24.1% to 44.9%), and an increase in the number of drugs able to pass the BBB (7.14% versus 64.29%) and target GSCs (0% versus 16.3%), there was a decrease in the number of P2CT using concomitant radiotherapy (34.5% versus 18.37%). Overall our results suggest that there is only a modest improvement regarding reducing the TG because the vast majority of ongoing P2CT are still not including well known concepts of glioma biology important for a successful treatment.

Modulation of VEGF receptor 2 signaling by protein phosphatases

Phosphorylation of serines, threonines, and tyrosines is a central event in signal transduction cascades in eukaryotic cells. The phosphorylation state of any particular protein reflects a balance of activity between kinases and phosphatases. Kinase biology has been exhaustively studied and is reasonably well understood, however, much less is known about phosphatases. A large body of evidence now shows that protein phosphatases do not behave as indiscriminate signal terminators, but can function both as negative or positive regulators of specific signaling pathways. Genetic models have also shown that different protein phosphatases play precise biological roles in health and disease. Finally, genome sequencing has unveiled the existence of many protein phosphatases and associated regulatory subunits comparable in number to kinases. A wide variety of roles for protein phosphatase roles have been recently described in the context of cancer, diabetes, hereditary disorders and other diseases. In particular, there have been several recent advances in our understanding of phosphatases involved in regulation of vascular endothelial growth factor receptor 2 (VEGFR2) signaling. The receptor is the principal signaling molecule mediating a wide spectrum of VEGF signal and, thus, is of paramount significance in a wide variety of diseases ranging from cancer to cardiovascular to ophthalmic. This review focuses on the current knowledge about protein phosphatases' regulation of VEGFR2 signaling and how these enzymes can modulate its biological effects.

Methylphenidate-triggered ROS generation promotes caveolae-mediated transcytosis via Rac1 signaling and c-Src-dependent caveolin-1 phosphorylation in human brain endothelial cells

Methylphenidate (MPH) is an amphetamine-like stimulant commonly prescribed for attention deficit hyperactivity disorder. Despite its widespread use, the cellular/molecular effects of MPH remain elusive. Here, we report a novel direct role of MPH on the regulation of macromolecular flux through human brain endothelial cells (ECs). MPH significantly increased caveolae-mediated transcytosis of horseradish peroxidase through ECs without affecting paracellular permeability. Using FRET-based live cell imaging, together with pharmacological inhibitors and lentiviral-mediated shRNA knockdown, we demonstrate that MPH promoted ROS generation via activation of Rac1-dependent NADPH oxidase (NOX) and c-Src activation at the plasma membrane. c-Src in turn was shown to mediate the phosphorylation of caveolin-1 (Cav1) on Tyr14 leading to enhanced caveolae formation and transendothelial transport. Accordingly, the inhibition of Cav1 phosphorylation by overexpression of a phosphodefective Cav1Y14F mutant or knocking down Cav1 expression abrogated MPH-induced transcytosis. In addition, both vitamin C and inhibition of NOX blocked MPH-triggered vesicular transport. This study, therefore, identifies Rac1/NOX/c-Src-dependent signaling in MPH-induced increase in transendothelial permeability of brain endothelial cell monolayers via caveolae-mediated transcytosis.

The Role of New Tyrosine Kinase Inhibitors in Chronic Myeloid Leukemia

Imatinib mesylate was the first tyrosine kinase inhibitor (TKI) approved for the management of chronic myeloid leukemia. Imatinib produces acceptable responses in approximately 60% of patients, with approximately 20% discontinuing therapy because of intolerance and approximately 20% developing drug resistance. The advent of newer TKIs, such as nilotinib, dasatinib, bosutinib, and ponatinib, has provided multiple options for patients. These agents are more potent, have unique adverse effect profiles, and are more likely to achieve relevant milestones, such as early molecular responses (3-6 months) and optimal molecular responses (12 months). The acquisition of BCR-ABL kinase domain mutations is also reportedly lower with these drugs. Thus far, none of the randomized phase III clinical trials have shown a clinically significant survival difference between frontline imatinib versus newer TKIs. Cost and safety issues with the newer TKIs, such as vascular disease with nilotinib and ponatinib and pulmonary hypertension with dasatinib, have dampened the enthusiasm of using these drugs as frontline options. While the utility of new TKIs in the setting of imatinib failure or intolerance is clear, their use as frontline agents should factor in the age of the patient, additional comorbidities, risk stratification (Sokal score), and cost. Combination therapies and newer agents with potential to eradicate quiescent chronic myeloid leukemia stem cells offers future hope.

Tyrosine Kinase Inhibitor as a new Therapy for Ischemic Stroke and other Neurologic Diseases: is there any Hope for a Better Outcome?

The relevance of tyrosine kinase inhibitors (TKIs) in the treatment of malignancies has been already defined. Aberrant activation of tyrosine kinase signaling pathways has been causally linked not only to cancers but also to other non-oncological diseases. This review concentrates on the novel plausible usage of this group of drugs in neurological disorders, such as ischemic brain stroke, subarachnoid hemorrhage, Alzheimer’s disease, multiple sclerosis. The drugs considered here are representatives of both receptor and non-receptor TKIs. Among them imatinib and masitinib have the broadest spectrum of therapeutic usage. Both drugs are effective in ischemic brain stroke and multiple sclerosis, but only imatinib produces a therapeutic effect in subarachnoid hemorrhage. Masitinib and dasatinib reduce the symptoms of Alzheimer’s disease. In the case of multiple sclerosis several TKIs are useful, including apart from imatinib and masitinib, also sunitinib, sorafenib, lestaurtinib. Furthermore, the possible molecular targets for the drugs are described in connection with the underlying pathophysiological mechanisms in the diseases in question. The most frequent target for the TKIs is PDGFR which plays a pivotal role particularly in ischemic brain stroke and subarachnoid hemorrhage. The collected data indicates that TKIs are very promising candidates for new therapeutic interventions in neurological diseases.

Calpains and neuronal damage in the ischemic brain: The swiss knife in synaptic injury

The excessive extracellular accumulation of glutamate in the ischemic brain leads to an overactivation of glutamate receptors with consequent excitotoxic neuronal death. Neuronal demise is largely due to a sustained activation of NMDA receptors for glutamate, with a consequent increase in the intracellular Ca(2+) concentration and activation of calcium- dependent mechanisms. Calpains are a group of Ca(2+)-dependent proteases that truncate specific proteins, and some of the cleavage products remain in the cell, although with a distinct function. Numerous studies have shown pre- and post-synaptic effects of calpains on glutamatergic and GABAergic synapses, targeting membrane- associated proteins as well as intracellular proteins. The resulting changes in the presynaptic proteome alter neurotransmitter release, while the cleavage of postsynaptic proteins affects directly or indirectly the activity of neurotransmitter receptors and downstream mechanisms. These alterations also disturb the balance between excitatory and inhibitory neurotransmission in the brain, with an impact in neuronal demise. In this review we discuss the evidence pointing to a role for calpains in the dysregulation of excitatory and inhibitory synapses in brain ischemia, at the pre- and post-synaptic levels, as well as the functional consequences. Although targeting calpain-dependent mechanisms may constitute a good therapeutic approach for stroke, specific strategies should be developed to avoid non-specific effects given the important regulatory role played by these proteases under normal physiological conditions.

Src inhibitors modulate frataxin protein levels

Defective expression of frataxin is responsible for the inherited, progressive degenerative disease Friedreich's Ataxia (FRDA). There is currently no effective approved treatment for FRDA and patients die prematurely. Defective frataxin expression causes critical metabolic changes, including redox imbalance and ATP deficiency. As these alterations are known to regulate the tyrosine kinase Src, we investigated whether Src might in turn affect frataxin expression. We found that frataxin can be phosphorylated by Src. Phosphorylation occurs primarily on Y118 and promotes frataxin ubiquitination, a signal for degradation. Accordingly, Src inhibitors induce accumulation of frataxin but are ineffective on a non-phosphorylatable frataxin-Y118F mutant. Importantly, all the Src inhibitors tested, some of them already in the clinic, increase frataxin expression and rescue the aconitase defect in frataxin-deficient cells derived from FRDA patients. Thus, Src inhibitors emerge as a new class of drugs able to promote frataxin accumulation, suggesting their possible use as therapeutics in FRDA.

Tamoxifen and Src kinase inhibitors as neuroprotective/neuroregenerative drugs after spinal cord injury

Spinal cord injury (SCI) is a devastating condition that produces significant changes in the lifestyle of patients. Many molecular and cellular events are triggered after the initial physical impact to the cord. Two major phases have been described in the field of SCI: an acute phase and late phase. Most of the therapeutic strategies are focused on the late phase because this provides an opportunity to target cellular events like apoptosis, demyelination, scar formation and axonal outgrowth. In this mini-review, we will focus on two agents (tamoxifen and a Src kinase family inhibitor known as PP2) that have been shown in our laboratory to produce neuroprotective (increase cell survival) and/or regenerative (axonal outgrowth) actions. The animal model used in our laboratory is adult female rat (~250 g) with a moderate contusion (12.5 mm) to the spinal cord at the T₁₀ level, using the MASCIS impactor device. Tamoxifen or PP2 was administered by implantation of a 15 mg pellet (Innovative Research of America, Sarasota, FL, USA) or by intraperitoneal injections (1.5 mg/kg, every 3 days), respectively, to produce a long-term effect (28 days). Tamoxifen and the Src kinase inhibitor, PP2, are drugs that in rats with a moderate spinal cord injury promote functional locomotor recovery, increase spared white matter tissue, and stimulate axonal outgrowth. Moreover, tamoxifen reduces the formation of reactive oxygen species. Therefore, these drugs are possible therapeutic agents that have a neuroprotective/regenerative activity in vertebrates with SCI.

Pharmacology of Src family kinases and therapeutic implications of their modulators

Src family kinases (SFKs), the largest family of nonreceptor tyrosine kinases, include 10 members. Src was the first gene product discovered to have intrinsic protein tyrosine kinase activity. Src is widely expressed in many cell types and can have different locations within a cell; the subcellular location of Src can affect its function. Src can associate with cellular membranes, such as the plasma membrane, the perinuclear membrane, and the endosomal membrane. SFKs actions on mammalian cells are pleiotropic and include effect on cell morphology, adhesion, migration, invasion, proliferation, differentiation, and survival. SFKs at one end have been documented to play some important physiological functions; on the other end, they have been described in the pathophysiology of some disorders. In this review article, an exhaustive attempt has been made to unearth pharmacology of SFKs and therapeutic implications of SFKs modulators.

Long-term treatment with PP2 after spinal cord injury resulted in functional locomotor recovery and increased spared tissue

The spinal cord has the ability to regenerate but the microenvironment generated after trauma reduces that capacity. An increase in Src family kinase (SFK) activity has been implicated in neuropathological conditions associated with central nervous system trauma. Therefore, we hypothesized that a decrease in SFK activation by a long-term treatment with 4-amino-5-(4-chlorophenyl)-7-(t-butyl)pyrazolo[3,4-d]pyramidine (PP2), a selective SFK inhibitor, after spinal cord contusion with the New York University (NYU) impactor device would generate a permissive environment that improves axonal sprouting and/or behavioral activity. Results demonstrated that long-term blockade of SFK activation with PP2 increases locomotor activity at 7, 14, 21 and 28 days post-injury in the Basso, Beattie, and Bresnahan open field test, round and square beam crossing tests. In addition, an increase in white matter spared tissue and serotonin fiber density was observed in animals treated with PP2. However, blockade of SFK activity did not change the astrocytic response or infiltration of cells from the immune system at 28 days post-injury. Moreover, a reduced SFK activity with PP2 diminished Ephexin (a guanine nucleotide exchange factor) phosphorylation in the acute phase (4 days post-injury) after trauma. Together, these findings suggest a potential role of SFK in the regulation of spared tissue and/or axonal outgrowth that may result in functional locomotor recovery during the pathophysiology generated after spinal cord injury. Our study also points out that ephexin1 phosphorylation (activation) by SFK action may be involved in the repulsive microenvironment generated after spinal cord injury.

CD44 regulates dendrite morphogenesis through Src tyrosine kinase-dependent positioning of the Golgi

The acquisition of proper dendrite morphology is a crucial aspect of neuronal development towards the formation of a functional network. The role of the extracellular matrix and its cellular receptors in this process has remained enigmatic. We report that the CD44 adhesion molecule, the main hyaluronan receptor, is localized in dendrites and plays a crucial inhibitory role in dendritic tree arborization in vitro and in vivo. This novel function is exerted by the activation of Src tyrosine kinase, leading to the alteration of Golgi morphology. The mechanism operates during normal brain development, but its inhibition might have a protective influence on dendritic trees under toxic conditions, during which the silencing of CD44 expression prevents dendritic shortening induced by glutamate exposure. Overall, our results indicate a novel role for CD44 as an essential regulator of dendritic arbor complexity in both health and disease.

Omega-3 polyunsaturated fatty acids enhance cerebral angiogenesis and provide long-term protection after stroke

Stroke is a devastating neurological disorder and one of the leading causes of death and serious disability. After cerebral ischemia, revascularization in the ischemic boundary zone provides nutritive blood flow as well as various growth factors to promote the survival and activity of neurons and neural progenitor cells. Enhancement of angiogenesis and the resulting improvement of cerebral microcirculation are key restorative mechanisms and represent an important therapeutic strategy for ischemic stroke. In the present study, we tested the hypothesis that post-stroke angiogenesis would be enhanced by omega-3 polyunsaturated fatty acids (n-3 PUFAs), a major component of dietary fish oil. To this end, we found that transgenic fat-1 mice that overproduce n-3 PUFAs exhibited long-term behavioral and histological protection against transient focal cerebral ischemia (tFCI). Importantly, fat-1 transgenic mice also exhibited robust improvements in revascularization and angiogenesis compared to wild type littermates, suggesting a potential role for n-3 fatty acids in post-stroke cerebrovascular remodeling. Mechanistically, n-3 PUFAs induced upregulation of angiopoietin 2 (Ang 2) in astrocytes after tFCI and stimulated extracellular Ang 2 release from cultured astrocytes after oxygen and glucose deprivation. Ang 2 facilitated endothelial proliferation and barrier formation in vitro by potentiating the effects of VEGF on phospholipase Cγ1 and Src signaling. Consistent with these findings, blockade of Src activity in post-stroke fat-1 mice impaired n-3 PUFA-induced angiogenesis and exacerbated long-term neurological outcomes. Taken together, our findings strongly suggest that n-3 PUFA supplementation is a potential angiogenic treatment capable of augmenting brain repair and improving long-term functional recovery after cerebral ischemia.

Micro-osmotic pumps for continuous release of the tyrosine kinase inhibitor bosutinib in juvenile rats and its impact on bone growth

Background

Bosutinib is a third-generation dual tyrosine kinase inhibitor (TKI) inhibiting Abl and Src kinases. It was developed to act on up-regulated tyrosine kinases (TKs) like BCR-ABL in Philadelphia chromosome positive (Ph+) chronic myeloid leukemia (CML) when resistance to first- and second-generation TKIs developed. However, first- and second-generation TKIs show off-target effects on bone metabolism, whereas studies on skeletal adverse effects of bosutinib are still lacking. Therefore, it was the aim of this study to continuously expose juvenile rats to bosutinib and to analyze its influence on the growing bone.

Material/Methods

Starting after weaning, 4-week-old Wistar rats were chronically exposed over a 28-day period to varying concentrations of bosutinib, which were continuously administered subcutaneously via implanted Alzet^® micro-osmotic pumps. After necropsy, the length of the femora and tibiae were analyzed.

Results

Continuous administration of bosutinib by micro-osmotic pumps led to serum drug levels in the lower therapeutic range, was well tolerated, and exhibited only minor adverse effects on the growing skeleton.

Conclusions

Micro-osmotic pumps represent a convenient system for continuous TKI release in young growing rats. Compared to first- and second-generation TKIs, bosutinib seems to exert fewer adverse effects on the growing bone.

A truncated fragment of Src protein kinase generated by calpain-mediated cleavage is a mediator of neuronal death in excitotoxicity

Excitotoxicity resulting from overstimulation of glutamate receptors is a major cause of neuronal death in cerebral ischemic stroke. The overstimulated ionotropic glutamate receptors exert their neurotoxic effects in part by overactivation of calpains, which induce neuronal death by catalyzing limited proteolysis of specific cellular proteins. Here, we report that in cultured cortical neurons and in vivo in a rat model of focal ischemic stroke, the tyrosine kinase Src is cleaved by calpains at a site in the N-terminal unique domain. This generates a truncated Src fragment of ~52 kDa, which we localized predominantly to the cytosol. A cell membrane-permeable fusion peptide derived from the unique domain of Src prevents calpain from cleaving Src in neurons and protects against excitotoxic neuronal death. To explore the role of the truncated Src fragment in neuronal death, we expressed a recombinant truncated Src fragment in cultured neurons and examined how it affects neuronal survival. Expression of this fragment, which lacks the myristoylation motif and unique domain, was sufficient to induce neuronal death. Furthermore, inactivation of the prosurvival kinase Akt is a key step in its neurotoxic signaling pathway. Because Src maintains neuronal survival, our results implicate calpain cleavage as a molecular switch converting Src from a promoter of cell survival to a mediator of neuronal death in excitotoxicity. Besides unveiling a new pathological action of Src, our discovery of the neurotoxic action of the truncated Src fragment suggests new therapeutic strategies with the potential to minimize brain damage in ischemic stroke.

Ionotropic receptors and ion channels in ischemic neuronal death and dysfunction

Loss of energy supply to neurons during stroke induces a rapid loss of membrane potential that is called the anoxic depolarization. Anoxic depolarizations result in tremendous physiological stress on the neurons because of the dysregulation of ionic fluxes and the loss of ATP to drive ion pumps that maintain electrochemical gradients. In this review, we present an overview of some of the ionotropic receptors and ion channels that are thought to contribute to the anoxic depolarization of neurons and subsequently, to cell death. The ionotropic receptors for glutamate and ATP that function as ligand-gated cation channels are critical in the death and dysfunction of neurons. Interestingly, two of these receptors (P2X7 and NMDAR) have been shown to couple to the pannexin-1 (Panx1) ion channel. We also discuss the important roles of transient receptor potential (TRP) channels and acid-sensing ion channels (ASICs) in responses to ischemia. The central challenge that emerges from our current understanding of the anoxic depolarization is the need to elucidate the mechanistic and temporal interrelations of these ion channels to fully appreciate their impact on neurons during stroke.