Suramin disrupts insulin-like growth factor-II (IGF-II) mediated autocrine growth in human SH-SY5Y neuroblastoma cells

Suppression of cell membrane permeability by suramin: involvement of its inhibitory actions on connexin 43 hemichannels

BACKGROUND AND PURPOSE

Suramin is a clinically prescribed drug for treatment of human African trypanosomiasis, cancer and infection. It is also a well-known pharmacological antagonist of P2 purinoceptors. Despite its clinical use and use in research, the biological actions of this molecule are still incompletely understood. Here, we investigated the effects of suramin on membrane channels, as exemplified by its actions on non-junctional connexin43 (Cx43) hemichannels, pore-forming α-haemolysin and channels involved in ATP release under hypotonic conditions.

EXPERIMENTAL APPROACH

Hemichannels were activated by removing extracellular Ca(2+) . The influences of suramin on hemichannel activities were evaluated by its effects on influx of fluorescent dyes and efflux of ATP. The membrane permeability and integrity were assessed through cellular retention of preloaded calcein and LDH release.

KEY RESULTS

Suramin blocked Cx43 hemichannel permeability induced by removal of extracellular Ca(2+) without much effect on Cx43 expression and gap junctional intercellular communication. This action of suramin was mimicked by its analogue NF023 and NF449 but not by another P2 purinoceptor antagonist PPADS. Besides hemichannels, suramin also significantly blocked intracellular and extracellular exchanges of small molecules caused by α-haemolysin from Staphylococcus aureus and by exposure of cells to hypotonic solution. Furthermore, it prevented α-haemolysin- and hypotonic stress-elicited cell injury.

CONCLUSION AND IMPLICATIONS

Suramin blocked membrane channels and protected cells against toxin- and hypotonic stress-elicited injury. Our finding provides novel mechanistic insights into the pharmacological actions of suramin. Suramin might be therapeutically exploited to protect membrane integrity under certain pathological situations.

Piper betle leaves: profiling phenolic compounds by HPLC/DAD-ESI/MS(n) and anti-cholinesterase activity

INTRODUCTION

Piper betle L. is a widely distributed plant in the tropical and subtropical regions, its leaves being largely consumed as a masticator and mouth freshener.

OBJECTIVE

The purposes of this work were to characterise the phenolic profile of this species and to improve knowledge of its anti-cholinesterase properties.

METHODS

The phenolic composition of P. betle leaf aqueous and ethanol extracts was characterised by HPLC coupled with a diode-array detector and combined with electrospray ionisation tandem MS, and in vitro cholinesterase inhibitory capacity of both extracts was assessed by spectrophotometric microassays. The effect on neuronal cells (SH-SY5Y) viability was evaluated by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide reduction and lactate dehydrogenase leakage.

RESULTS

Twelve phenolic compounds, comprising a phenylpropanoid, five cinnamoyl and six flavonoids derivatives were identified in P. betle leaves. Hydroxychavicol was the major compound in both extracts; however, the aqueous extract presented a greater diversity of compounds. Both extracts showed strong activity against both acetyl- and butyrylcholinesterase, which can be due, at least partially, to the phenolic composition. Furthermore, the aqueous extract proved to be cytotoxic to human neuroblastoma cells at concentrations higher than 500 µg/mL.

CONCLUSION

The results suggest that the consumption of P. betle leaves as an infusion can have a positive impact in the prevention and treatment of neurodegenerative diseases. Apigenin and luteolin derivatives are reported for the first time in this species.

Biopolymer-mediated suramin chemotherapy in the treatment of experimental brain tumours

Suramin inhibits tumour growth and neoangiogenesis by blocking several growth factor receptors. In this study the toxicity and efficacy of intralesional delivery of suramin incorporated in a controlled-release polymer were assessed in a rat 9L tumour model. Initially, the toxicity of the compound was evaluated in adult Fisher 344 rats. The animals were intracerebrally implanted with an ethylene vinyl acetate copolymer. These experiments showed early toxicity in the rats implanted with a 50% load-polymer and 100% mortality within 48 h, whereas in rats implanted with a 33% load-polymer only transient behavioural changes were observed. In a second experiment the rats were stereotactically implanted with 9L cells in the frontal region. Two days after inoculation of cells, the animals were divided into two groups: one group received a 33% suramin load-biopolymer at the tumour implantation site, while the control group received polymer implants only. The interstitial release of suramin in the brain did not produce any improvement in survival of 9L tumour-bearing rats, with a mean survival of 14.2 +/- 1 days for the suramin-treated group versus 13.8 +/- 2 for the control group (p = 0.82). We conclude that intralesional polymer-mediated chemotherapy with suramin does not prolong survival in rats with intracerebral 9L tumours.

The chaperone activity of GRP94 toward insulin-like growth factor II is necessary for the stress response to serum deprivation

Insulin-like growth factor (IGF)-II is a hormone with mitogenic activity for many cell types and tissues. We demonstrate that its intracellular processing and secretion strictly depend on the endoplasmic reticulum chaperone glucose-regulated protein (GRP) 94. GRP94 interacts physically and transiently with pro-IGF-II intermediates, and its activity is essential for secretion of active IGF-II, thus establishing IGF-II as a client of GRP94. Embryonic stem (ES) cells that lack GRP94 are hypersensitive to stress conditions such as serum deprivation and die by apoptosis because they cannot respond to the stress by producing active IGF-II. This chaperone-client interaction may explain the previously documented antiapoptotic activity of GRP94 in a number of stress responses.

Suramin induces and enhances apoptosis in a model of hyperoxia-induced oligodendrocyte injury

Recent evidence suggests oxygen as a powerful trigger for cell death in the immature white matter, leading to periventricular leukomalacia (PVL) as a cause of adverse neurological outcome in survivors of preterm birth. This oligodendrocyte (OL) death is associated with oxidative stress, upregulation of apoptotic signaling factors (i.e., Fas, caspase-3) and decreased amounts of neurotrophins. In search of neuroprotective strategies we investigated whether the polysulfonated urea derivative suramin, recently identified as a potent inhibitor of Fas signaling, affords neuroprotection in an in vitro model of hyperoxia-induced injury to immature oligodendrocytes. Immature OLs (OLN-93) were subjected to 80% hyperoxia (48 h) in the presence or absence of suramin (0, 30, 60, 120 microM). Cell death was assessed by flow cytometry (Annexin V, caspase-3 activity assay) and immunohistochemistry for activated caspase-3. Immunoblotting for the death receptor Fas, cleaved caspase-8 and the phosphorylated isoform of the serine-threonin kinase Akt (pAkt) was performed. Suramin lead to OL apoptosis and potentiated hyperoxia-induced injury in a dose-dependent manner. Immunoblotting revealed increased Fas and caspase-8 expression by suramin treatment. This effect was significantly enhanced when suramin was combined with hyperoxia. Furthermore, pAkt levels decreased following suramin exposure, indicating interference with neurotrophin-dependent growth factor signaling. These data indicate that suramin causes apoptotic cell death and aggravates hyperoxia-induced cell death in immature OLs. Its mechanism of action includes an increase of previously described hyperoxia-induced expression of pro-apoptotic factors and deprivation of growth factor dependent signaling components.

Low-dose cisplatin protects human neuroblastoma SH-SY5Y cells from paclitaxel-induced apoptosis

Combined anticancer therapy using platinum compounds and antitubulins has increased the risk of neurotoxicity. However, the combination of low-dose cisplatin (CDDP) with toxic doses of paclitaxel significantly reduces cellular death in a human neuroblastoma SH-SY5Y cell line. To analyze the mechanisms of this protection, we evaluated various signaling molecules possibly involved in apoptosis and some relevant cell cycle regulatory proteins. CDDP does not interfere with the tubulin-stabilizing action of paclitaxel. The evaluation of molecular pathways involved in apoptosis indicates that the Bcl-2 but not the caspases may be involved in the CDDP protection of paclitaxel-induced apoptosis. The increase in p53 protein and its nuclear accumulation suggests a possible involvement of p53 in CDDP protection. The use of the chemical inhibitor of p53, pifithrin alpha, excluded this possibility. The study of cyclins and the flow cytometric analysis (fluorescence-activated cell sorting) suggest that CDDP exerts a protective action by blocking cells early in the cell cycle. The determination of the mitotic index indicates that CDDP prevents cells from reaching the mitosis. We concluded that low doses of CDDP are protective against toxic doses of paclitaxel and that the possible mechanism of this protection is that the CDDP prevents human neuroblastoma SH-SY5Y cells from achieving mitosis.

The Propeptide Domain of Lysyl Oxidase Induces Phenotypic Reversion of Ras-transformed Cells

Lysyl oxidase is an extracellular enzyme critical for the normal biosynthesis of collagens and elastin. In addition, lysyl oxidase reverts ras-mediated transformation, and lysyl oxidase expression is down-regulated in human cancers. Since suramin inhibits growth factor signaling pathways and induces lysyl oxidase in ras-transformed NIH3T3 cells (RS485 cells), we sought to investigate the effects of suramin on the phenotype of transformed cells and the role of lysyl oxidase in mediating these effects. Suramin treatment resulted in a more normal phenotype as judged by growth rate, cell cycle parameters, and morphology. beta-aminopropionitrile, the selective inhibitor of lysyl oxidase enzyme activity, was remarkably unable to block suramin-induced reversion. By contrast, ectopic antisense lysyl oxidase demonstrated that lysyl oxidase gene expression mediated phenotypic reversion. Since lysyl oxidase is synthesized as a 50 kDa precursor and processed to a 30 kDa active enzyme and 18 kDa propeptide, the effects of these two products on the transformed phenotype of RS485 cells were then directly assessed in the absence of suramin. Here we report, for the first time, that the lysyl oxidase propeptide, and not the lysyl oxidase enzyme, inhibits ras-dependent transformation as determined by effects on cell proliferation assays, growth in soft agar, and Akt-dependent induction of NF-kappaB activity. Thus, the lysyl oxidase propeptide, which is released during extracellular proteolytic processing of pro-lysyl oxidase, functions to inhibit ras-dependent cell transformation.

Autocrine growth factor regulation of lysyl oxidase expression in transformed fibroblasts

Lysyl oxidase catalyzes oxidative deamination of peptidyl-lysine and hydroxylysine residues in collagens and lysine residues in elastin to form peptidyl aldehydes that are required for the formation of covalent cross-links in normal extracellular matrix biosynthesis. Lysyl oxidase in addition has tumor suppressor activity, and phenotypic reversion of transformed cell lines is accompanied by increased lysyl oxidase expression. The mechanism of low expression of lysyl oxidase in tumor cells is unknown. The present study investigates the hypothesis that autocrine growth factor pathways maintain low lysyl oxidase expression levels in c-H-ras-transformed fibroblasts (RS485 cell line). Autocrine pathways were blocked with suramin, a general inhibitor of growth factor receptor binding, and resulted in more than a 10-fold increase in lysyl oxidase expression and proenzyme production. This regulation was found to be reversible and occurred at the transcriptional level determined using lysyl oxidase promoter/reporter gene assays. Function blocking anti-fibroblast growth factor-2 (FGF-2) antibody enhanced lysyl oxidase expression in the absence of suramin. Finally, the addition of FGF-2 to suramin-treated cells completely reversed suramin stimulation of lysyl oxidase mRNA levels. Data support that an FGF-2 autocrine pathway inhibits lysyl oxidase transcription in the tumorigenic-transformed RS485 cell line. This finding may be of therapeutic significance and, in addition, provides a new experimental approach to investigate the mechanism of the tumor suppressor activity of lysyl oxidase.

Recent advances in drug-induced neuropathies

PURPOSE OF REVIEW

Peripheral neuropathy is a common neurotoxic effect of medications. When medications are used to treat life-threatening illnesses, balancing the toxic effects of peripheral neuropathy with the therapeutic benefits of the drug can be difficult. This article examines recent research into the cellular mechanisms associated with neuropathy after treatment with medications to treat cancer, and HIV, and to prevent transplant rejection.

RECENT FINDINGS

Cisplatin and suramin induce a length, dose, and time-dependent axonal sensorimotor polyneuropathy. Cisplatin and suramin both result in apoptosis in dorsal root ganglion neurons that may partially explain the neuropathy that develops with treatment. In contrast, nerve growth factor prevents initiation of the programmed cell death associated with cisplatin neurotoxicity. Suramin causes accumulation of lamellar inclusion bodies in dorsal root ganglion neurons related to dose of administration and severity of the neuropathy. Nucleoside reverse transcriptase inhibitors affect mitochondrial function and lead to depletion of the nerve's mitochondrial DNA and inhibition of DNA polymerase. These effects on the mitochondrion may be related to the polyneuropathy that develops in these patients. In contrast to the axonal neuropathies, tacrolimus and rarely suramin can result in a demyelinating neuropathy that may mimic Guillain-Barré syndrome or chronic inflammatory demyelinating polyneuropathy. Many of these neuropathies can be reversed by early recognition of the symptoms or by using sensitive electrophysiological testing. In certain instances, specific therapies may ameliorate the neuropathy. Glutamine may reduce paclitaxel-induced toxicity, while some patients with tacrolimus or suramin-induced demyelinating neuropathy may respond to intravenous immunoglobulin or plasmapheresis.

SUMMARY

Improved understanding of neurotoxic mechanisms in the peripheral nervous system associated with chemotherapeutic and anti-HIV medications, coupled with early improved diagnosis, promises to help limit neurotoxicity associated with these medications.

The IGF/IGFBP system in CNS malignancy

The insulin-like growth factor (IGF) system includes IGF-I and IGF-II, the type I and type II IGF receptors, and specific IGF binding proteins (IGFBP-1 to IGFBP-6). These factors regulate both normal and malignant brain growth. Enhanced expression of IGF-I and IGF-II mRNA transcripts has been demonstrated in gliomas, meniningiomas, and other tumours. Abnormal imprinting of IGF-II occurs in gliomas, medulloblastomas, and meningiomas. Both types of IGF receptor are expressed in gliomas and, in particular, the type I IGF receptor appears to be upregulated in malignant brain tissue. Antisense IGF-I receptor mRNA induces an antitumour response, resulting in complete brain tumour regression. Clinical trials for the treatment of brain tumours in humans based on a gene transfer protocol using IGF-I receptor antisense are under way. All six IGFBPs are expressed to a variable extent in brain tumours. High concentrations of IGFBP-2 are found in cerebrospinal fluid from patients with malignant central nervous system tumours; therefore, IGFBP-2 might be a useful marker for these tumours. IGFBP-4 appears to be a negative regulator of tumour proliferation. Both in vitro and in vivo experiments suggest that the IGF system represents an important target for the treatment of malignant central nervous system tumours and the ongoing trials should provide valuable information for future therapeutic approaches.

Insulin-like growth factors regulate neuronal differentiation and survival

Insulin-like growth factor I (IGF-I) and IGF-II are potent trophic factors for motor and sensory neurons and glial cells. The actions of IGF-I and IGF-II are mediated via the IGF-I receptor (IGF-IR). IGF:IGF-IR binding activates distinct signaling cascades, which in turn mediate the trophic effects of the IGFs. We discuss three main IGF coupled events: growth cone motility, long-term neurite outgrowth, and neuroprotection. Our data suggest that IGF-I enhances growth cone motility by promoting reorganization of actin and activation of focal adhesion proteins via the phosphatidylinositol-3 kinase (Pl-3K) pathway. Long-term treatment with IGF-I activates the mitogen-activated protein (MAP) kinase cascade and promotes neurite outgrowth. A separable, but likely linked, action of the IGFs via Pl-3K is protection of neurons from apoptosis. These pleotrophic effects of IGFs suggest that this family of growth factors may have potential clinical utility in the treatment of neurological disorders.