HYS-32, a novel analogue of combretastatin A-4, enhances connexin43 expression and gap junction intercellular communication in rat astrocytes

Synthesis, Modeling, and Biological Evaluation of Anti-Tubulin Indole-Substituted Furanones

Due to the central role of tubulin in various cellular functions, it is a validated target for anti-cancer therapeutics. However, many of the current tubulin inhibitors are derived from complex natural products and suffer from multidrug resistance, low solubility, toxicity issues, and/or the lack of multi-cancer efficacy. As such, there is a continued need for the discovery and development of new anti-tubulin drugs to enter the pipeline. Herein we report on a group of indole-substituted furanones that were prepared and tested for anti-cancer activity. Molecular docking studies showed positive correlations between favorable binding in the colchicine binding site (CBS) of tubulin and anti-proliferative activity, and the most potent compound was found to inhibit tubulin polymerization. These compounds represent a promising new structural motif in the search for small heterocyclic CBS cancer inhibitors.

Discovery of an indole-substituted furanone with tubulin polymerization inhibition activity

Analogs of diarylpyrrolinone lead compound 1 were prepared and tested for anti-proliferative activity in U-937 cancer cells. Alterations of 1 focused on modifying the two nitrogen atoms: a) the pyrrolinone nitrogen atom was substituted with a propyl group or replaced with an oxygen atom (furanone), and b) the substituents on the indole nitrogen were varied. These changes led to the discovery of a furanone analog 3b with sub-micromolar anti-cancer potency and tubulin polymerization inhibition activity.

Can rodent models elucidate the pathomechanisms of genetic epilepsy?

Autosomal dominant sleep-related hypermotor epilepsy (ADSHE; previously autosomal dominant nocturnal frontal lobe epilepsy, ADNFLE), originally reported in 1994, was the first distinct genetic epilepsy shown to be caused by CHNRA4 mutation. In the past two decades, we have identified several functional abnormalities of mutant ion channels and their associated transmissions using several experiments involving single-cell and genetic animal (rodent) models. Currently, epileptologists understand that functional abnormalities underlying epileptogenesis/ictogenesis in humans and rodents are more complicated than previously believed and that the function of mutant molecules alone cannot contribute to the development of epileptogenesis/ictogenesis but play important roles in the development of epileptogenesis/ictogenesis through formation of abnormalities in various other transmission systems before epilepsy onset. Based on our recent findings using genetic rat ADSHE models, harbouring Chrna4 mutant, corresponding to human S284L-mutant CRHNA4, this review proposes a hypothesis associated with tripartite synaptic transmission in ADSHE pathomechanisms induced by mutant ACh receptors.

Activated spinal astrocytes contribute to the later phase of carrageenan-induced prostatitis pain

Background

Prostatodynia is the main symptom of chronic prostatitis and the main reason that patients go to the hospital for treatment. Although a variety of factors, including inflammatory immune response, nervous system sensitization, and psychological factors, have been shown to play important roles in the induction and development of chronic pain in prostatitis, the underlying cause of chronic prostatodynia maintenance in prostatitis patients remains unclear.

Methods

A mouse model of chronic prostatitis induced by carrageenan injection was used. The von Frey test was used to measure pain behavior. The microglial and astrocyte activations were immunohistochemically demonstrated with antibodies against Iba1 and GFAP. The expression of cytokine or signaling pathway was detected by enzyme-linked immunosorbent assay (ELISA) and Western blotting.

Results

In this study, we provide several lines of evidence to demonstrate that activated spinal astrocytes contribute to the later phase (5 weeks after carrageenan injection) of carrageenan-induced prostatitis pain. First, activation of spinal astrocytes but not microglia was found in the spinal cord dorsal horn at 5 weeks. Second, intrathecal injection of the astroglial toxin L-2-Aminoadipate acid (L-AA) but not microglial inhibitor minocycline reduced mechanical allodynia at 5 weeks. Third, chronic prostatitis induced a profound and persistent upregulation of connexin-43 hemichannels in spinal astrocytes, and spinal injection of the connexin-43 inhibitor carbenoxolone (CBX) effectively reduced pain symptoms. Fourth, increased expression and release of chemokine C-X-C motif ligand 1 (CXCL1) in the spinal dorsal horn and intrathecal injection of a CXCL1 neutralizing antibody or the CXCR2 (a major receptor of CXCL1) antagonist SB225002 significantly reduced mechanical allodynia at 5 weeks.

Conclusions

In this study, we found that a novel mechanism of activated spinal astrocytes plays a crucial role in maintaining chronic prostatitis-induced persistent pain via connexin-43-regulated CXCL1 production and secretion.

Loss of Cx43-Mediated Functional Gap Junction Communication in Meningeal Fibroblasts Following Mouse Hepatitis Virus Infection

Mouse hepatitis virus (MHV) infection causes meningoencephalitis by disrupting the neuro-glial and glial-pial homeostasis. Recent studies suggest that MHV infection alters gap junction protein connexin 43 (Cx43)-mediated intercellular communication in brain and primary cultured astrocytes. In addition to astrocytes, meningeal fibroblasts also express high levels of Cx43. Fibroblasts in the meninges together with the basal lamina and the astrocyte endfeet forms the glial limitans superficialis as part of the blood-brain barrier (BBB). Alteration of glial-pial gap junction intercellular communication (GJIC) in MHV infection has the potential to affect the integrity of BBB. Till date, it is not known if viral infection can modulate Cx43 expression and function in cells of the brain meninges and thus affect BBB permeability. In the present study, we have investigated the effect of MHV infection on Cx43 localization and function in mouse brain meningeal cells and primary meningeal fibroblasts. Our results show that MHV infection reduces total Cx43 levels and causes its intracellular retention in the perinuclear compartments reducing its surface expression. Reduced trafficking of Cx43 to the cell surface in MHV-infected cells is associated with loss functional GJIC. Together, these data suggest that MHV infection can directly affect expression and cellular distribution of Cx43 resulting in loss of Cx43-mediated GJIC in meningeal fibroblasts, which may be associated with altered BBB function observed in acute infection.

Connexin 43 contributes to ectopic orofacial pain following inferior alveolar nerve injury

Background

Clinically, it is well known that injury of mandibular nerve fiber induces persistent ectopic pain which can spread to a wide area of the orofacial region innervated by the uninjured trigeminal nerve branches. However, the exact mechanism of such persistent ectopic orofacial pain is not still known. The present study was undertaken to determine the role of connexin 43 in the trigeminal ganglion on mechanical hypersensitivity in rat whisker pad skin induced by inferior alveolar nerve injury. Here, we examined changes in orofacial mechanical sensitivity following inferior alveolar nerve injury. Furthermore, changes in connexin 43 expression in the trigeminal ganglion and its localization in the trigeminal ganglion were also examined. In addition, we investigated the functional significance of connexin 43 in relation to mechanical allodynia by using a selective gap junction blocker (Gap27).

Results

Long-lasting mechanical allodynia in the whisker pad skin and the upper eyelid skin, and activation of satellite glial cells in the trigeminal ganglion, were induced after inferior alveolar nerve injury. Connexin 43 was expressed in the activated satellite glial cells encircling trigeminal ganglion neurons innervating the whisker pad skin, and the connexin 43 protein expression was significantly increased after inferior alveolar nerve injury. Administration of Gap27 in the trigeminal ganglion significantly reduced satellite glial cell activation and mechanical hypersensitivity in the whisker pad skin. Moreover, the marked activation of satellite glial cells encircling trigeminal ganglion neurons innervating the whisker pad skin following inferior alveolar nerve injury implies that the satellite glial cell activation exerts a major influence on the excitability of nociceptive trigeminal ganglion neurons.

Conclusions

These findings indicate that the propagation of satellite glial cell activation throughout the trigeminal ganglion via gap junctions, which are composed of connexin 43, plays a pivotal role in ectopic mechanical hypersensitivity in whisker pad skin following inferior alveolar nerve injury.

Mouse Hepatitis Virus Infection Remodels Connexin43-Mediated Gap Junction Intercellular Communication In Vitro and In Vivo

Gap junctions (GJs) form intercellular channels which directly connect the cytoplasm between neighboring cells to facilitate the transfer of ions and small molecules. GJs play a major role in the pathogenesis of infection-associated inflammation. Mutations of gap junction proteins, connexins (Cxs), cause dysmyelination and leukoencephalopathy. In multiple sclerosis (MS) patients and its animal model experimental autoimmune encephalitis (EAE), Cx43 was shown to be modulated in the central nervous system (CNS). The mechanism behind Cx43 alteration and its role in MS remains unexplored. Mouse hepatitis virus (MHV) infection-induced demyelination is one of the best-studied experimental animal models for MS. Our studies demonstrated that MHV infection downregulated Cx43 expression at protein and mRNA levels in vitro in primary astrocytes obtained from neonatal mouse brains. After infection, a significant amount of Cx43 was retained in endoplasmic reticulum/endoplasmic reticulum Golgi intermediate complex (ER/ERGIC) and GJ plaque formation was impaired at the cell surface, as evidenced by a reduction of the Triton X-100 insoluble fraction of Cx43. Altered trafficking and impairment of GJ plaque formation may cause the loss of functional channel formation in MHV-infected primary astrocytes, as demonstrated by a reduced number of dye-coupled cells after a scrape-loading Lucifer yellow dye transfer assay. Upon MHV infection, a significant downregulation of Cx43 was observed in the virus-infected mouse brain. This study demonstrates that astrocytic Cx43 expression and function can be modulated due to virus stress and can be an appropriate model to understand the basis of cellular mechanisms involved in the alteration of gap junction intercellular communication (GJIC) in CNS neuroinflammation.

IMPORTANCE

We found that MHV infection leads to the downregulation of Cx43 in vivo in the CNS. In addition, results show that MHV infection impairs Cx43 expression in addition to gap junction communication in primary astrocytes. After infection, Cx43 did not traffic normally to the membrane to form gap junction plaques, and that could be the basis of reduced functional gap junction coupling between astrocytes. This is an important first step toward understanding how viruses affect Cx43 expression and trafficking at the cellular level. This may provide a basis for understanding how structural alterations of astrocytic gap junctions can disrupt gap junction communication between other CNS cells in altered CNS environments due to infection and inflammation. More specifically, alteration of Cx43 may be the basis of the destabilization of Cx47 in oligodendrocytes seen in and around inflammatory demyelinating plaques in MS patients.

Combretastatins: more than just vascular targeting agents?

Several prodrugs of the naturally occurring combretastatins have undergone extensive clinical evaluation as vascular targeting agents (VTAs). Their increased selectivity toward endothelial cells together with their innate ability to rapidly induce vascular shutdown and inhibit tumor growth at doses up to 10-fold less than the maximum tolerated dose led to the clinical evaluation of combretastatins as VTAs. Tubulin is well established as the molecular target of the combretastatins and the vast majority of its synthetic derivatives. Furthermore, tubulin is a highly validated molecular target of many direct anticancer agents routinely used as front-line chemotherapeutics. The unique vascular targeting properties of the combretastatins have somewhat overshadowed their development as direct anticancer agents and the delineation of the various cell death pathways and anticancer properties associated with such chemotherapeutics. Moreover, the ongoing clinical trial of OXi4503 (combretastatin-A1 diphosphate) together with preliminary preclinical evaluation for the treatment of refractory acute myelogenous leukemia has successfully highlighted both the indirect and direct anticancer properties of combretastatins. In this review, we discuss the development of the combretastatins from nature to the clinic. The various mechanisms underlying combretastatin-induced cell cycle arrest, mitotic catastrophe, cell death, and survival are also reviewed in an attempt to further enhance the clinical prospects of this unique class of VTAs.

Connexin 43 mediates PFOS-induced apoptosis in astrocytes

Perfluorooctane sulfonate (PFOS) is a man-made environmental pollutant that is toxic to mammals. However, the neurotoxic effects of PFOS remain largely unexplored. In this study, we determined the role of an astrocyte specific gap junction protein, connexin 43 (Cx43), in PFOS-induced apoptosis. The rate of astrocyte apoptosis was higher in cortex astrocytes after PFOS treatment. These astrocytes also showed up-regulated expression of Cx43 and higher levels of cleaved caspase-3. Elevated ROS accumulation and decreased ΔΨm also confirmed the presence of PFOS-induced apoptosis. However, the exposure of astrocytes to PFOS together with carbenoxolone (CBX) significantly reduced both Cx43 and cleaved caspase-3 levels. These results indicate that Cx43 plays a proapoptotic role in PFOS-induced apoptosis in cortex astrocyte cells.

HYS-32-Induced Microtubule Catastrophes in Rat Astrocytes Involves the PI3K-GSK3beta Signaling Pathway

HYS-32 is a novel derivative of combretastatin-A4 (CA-4) previously shown to induce microtubule coiling in rat primary astrocytes. In this study, we further investigated the signaling mechanism and EB1, a microtubule-associated end binding protein, involved in HYS-32-induced microtubule catastrophes. Confocal microscopy with double immunofluorescence staining revealed that EB1 accumulates at the growing microtubule plus ends, where they exhibit a bright comet-like staining pattern in control astrocytes. HYS-32 induced microtubule catastrophes in both a dose- and time-dependent manner and dramatically increased the distances between microtubule tips and the cell border. Treatment of HYS-32 (5 μM) eliminated EB1 localization at the microtubule plus ends and resulted in an extensive redistribution of EB1 to the microtubule lattice without affecting the β-tubulin or EB1 protein expression. Time-lapse experiments with immunoprecipitation further displayed that the association between EB-1 and β-tubulin was significantly decreased following a short-term treatment (2 h), but gradually increased in a prolonged treatment (6-24 h) with HYS-32. Further, HYS-32 treatment induced GSK3β phosphorylation at Y216 and S9, where the ratio of GSK3β-pY216 to GSK3β-pS9 was first elevated followed by a decrease over time. Co-treatment of astrocytes with HYS-32 and GSK3β inhibitor SB415286 attenuated the HYS-32-induced microtubule catastrophes and partially prevented EB1 dissociation from the plus end of microtubules. Furthermore, co-treatment with PI3K inhibitor LY294002 inhibited HYS-32-induced GSK3β-pS9 and partially restored EB1 distribution from the microtubule lattice to plus ends. Together these findings suggest that HYS-32 induces microtubule catastrophes by preventing EB1 from targeting to microtubule plus ends through the GSK3β signaling pathway.