The novel CXCR4 antagonist, PRX177561, reduces tumor cell proliferation and accelerates cancer stem cell differentiation in glioblastoma preclinical models.

Glioblastoma is the most frequent and the most lethal primary brain tumor among adults. Standard of care is the association of radiotherapy with concomitant or adjuvant temozolomide. However, to date, recurrence is inevitable. The CXCL12/CXCR4 pathway is upregulated in the glioblastoma tumor microenvironment regulating tumor cell proliferation, local invasion, angiogenesis, and the efficacy of radio-chemotherapy. In this study, we evaluated the effects of the novel CXCR4 antagonist, PRX177561, in preclinical models of glioblastoma. CXCR4 expression and PRX177561 effects were assessed on a panel of 12 human glioblastoma cells lines and 5 patient-derived glioblastoma stem cell cultures. Next, the effect of PRX177561 was tested in vivo, using subcutaneous injection of U87MG, U251, and T98G cells as well as orthotopic intrabrain inoculation of luciferase-transfected U87MG cells. Here we found that PRX177561 impairs the proliferation of human glioblastoma cell lines, increases apoptosis, and reduces CXCR4 expression and cell migration in response to stromal cell-derived factor 1alpha in vitro. PRX177561 reduced the expression of stem cell markers and increased that of E-cadherin and glial fibrillary acidic protein in U87MG cells consistent with a reduction in cancer stem cells. In vivo, PRX177561 reduced the weight and increased the time to progression of glioblastoma subcutaneous tumors while increasing disease-free survival and overall survival of mice bearing orthotopic tumors. Our findings suggest that targeting stromal cell-derived factor 1 alpha/CXCR4 axis by PRX177561 might represent a novel therapeutic approach against glioblastoma and support further investigation of this compound in more complex preclinical settings in order to determine its therapeutic potential.

The brain-penetrating CXCR4 antagonist, PRX177561, increases the antitumor effects of bevacizumab and sunitinib in preclinical models of human glioblastoma.

BACKGROUND: Glioblastoma recurrence after treatment with the anti-vascular endothelial growth factor (VEGF) antibody bevacizumab is characterized by a highly infiltrative and malignant behavior that renders surgical excision and chemotherapy ineffective. It has been demonstrated that anti-VEGF/VEGFR therapies control the invasive phenotype and that relapse occurs through the increased activity of CXCR4. We therefore hypothesized that combining bevacizumab or sunitinib with the novel CXCR4 antagonist, PRX177561, would have superior antitumor activity. METHODS: The effects of bevacizumab, sunitinib, and PRX177561 were tested alone or in combination in subcutaneous xenografts of U87MG, U251, and T98G cells as well as on intracranial xenografts of luciferase tagged U87MG cells injected in CD1-nu/nu mice. Animals were randomized to receive vehicle, bevacizumab (4 mg/kg iv every 4 days), sunitinib (40 mg/kg po qd), or PRX177561 (50 mg/kg po qd). RESULTS: The in vivo experiments demonstrated that bevacizumab and sunitinib increase the in vivo expression of CXCR4, SDF-1α, and TGFß1. In addition, we demonstrate that the co-administration of the novel brain-penetrating CXCR4 antagonist, PRX177561, with bevacizumab or sunitinib inhibited tumor growth and reduced the inflammation. The combination of PRX177561 with bevacizumab resulted in a synergistic reduction of tumor growth with an increase of disease-free survival (DSF) and overall survival (OS), whereas the combination of PRX177561 with sunitinib showed a mild additive effect. CONCLUSIONS: The CXC4 antagonist PRX177561 may be a valid therapeutic complement to anti-angiogenic therapy, particularly when used in combination with VEGF/VEGFR inhibitors. Therefore, this compound deserves to be considered for future clinical evaluation.

Abeta(1-42) reduces synapse number and inhibits neurite outgrowth in primary cortical and hippocampal neurons: a quantitative analysis.

Synaptic loss represents one of the earliest signs of neuronal damage and is observed within both Alzheimer's disease patients and transgenic mouse models of the disease. We have developed a novel in vitro assay using high content screening technology to measure changes in a number of cell physiological parameters simultaneously within a neuronal population. Using Hoechst-33342 to label nuclei, betaIII-tubulin as a neuron-specific marker, and synapsin-I as an indicator of pre-synaptic sites, we have designed software to interrogate triple-labelled images, counting only those synaptic puncta associated with tubulin-positive structures. Here we demonstrate that addition of amyloid beta peptide (Abeta(1-42)), to either primary hippocampal or cortical neurons for 4 days in vitro has deleterious effects upon synapse formation, neurite outgrowth and arborisation in a concentration-dependent manner. Control reverse peptide showed no effect over the same concentration range. The effects of Abeta(1-42) were inhibited by D-KLVFFA, which contains residues 16-20 of Abeta that function as a self-recognition element during Abeta assembly and bind to the homologous region of Abeta and block its oligomerisation. These effects of Abeta(1-42) on synapse number and neurite outgrowth are similar to those described within AD patient pathology and transgenic mouse models.

Hippocalcin functions as a calcium sensor in hippocampal LTD.

It is not fully understood how NMDAR-dependent LTD causes Ca(2+)-dependent endocytosis of AMPARs. Here we show that the neuronal Ca(2+) sensor hippocalcin binds the beta2-adaptin subunit of the AP2 adaptor complex and that along with GluR2 these coimmunoprecipitate in a Ca(2+)-sensitive manner. Infusion of a truncated mutant of hippocalcin (HIP(2-72)) that lacks the Ca(2+) binding domains prevents synaptically evoked LTD but has no effect on LTP. These data indicate that the AP2-hippocalcin complex acts as a Ca(2+) sensor that couples NMDAR-dependent activation to regulated endocytosis of AMPARs during LTD.

Identification of neuroprotective properties of anti-MAG antibody: a novel approach for the treatment of stroke?

The inhibitory activity of myelin-associated glycoprotein (MAG) on neurons is thought to contribute to the lack of regenerative capacity of the CNS after injury. The interaction of MAG and its neuronal receptors mediates bidirectional signaling between neurons and oligodendrocytes. The novel finding that an anti-MAG monoclonal antibody not only possesses the ability to neutralise the inhibitory effect of MAG on neurons but also directly protects oligodendrocytes from glutamate-mediated oxidative stress-induced cell death is reported here. Furthermore, administration of anti-MAG antibody (centrally and systemically) starting 1 hour after middle cerebral artery occlusion in the rat significantly reduced lesion volume at 7 days. This neuroprotection was associated with a robust improvement in motor function compared with animals receiving control IgG1. Together, these data highlight the potential for the use of anti-MAG antibodies as therapeutic agents for the treatment of stroke.

KCNQ/M currents in sensory neurons: significance for pain therapy.

Neuronal hyperexcitability is a feature of epilepsy and both inflammatory and neuropathic pain. M currents [IK(M)] play a key role in regulating neuronal excitability, and mutations in neuronal KCNQ2/3 subunits, the molecular correlates of IK(M), have previously been linked to benign familial neonatal epilepsy. Here, we demonstrate that KCNQ/M channels are also present in nociceptive sensory systems. IK(M) was identified, on the basis of biophysical and pharmacological properties, in cultured neurons isolated from dorsal root ganglia (DRGs) from 17-d-old rats. Currents were inhibited by the M-channel blockers linopirdine (IC50, 2.1 microm) and XE991 (IC50, 0.26 microm) and enhanced by retigabine (10 microm). The expression of neuronal KCNQ subunits in DRG neurons was confirmed using reverse transcription-PCR and single-cell PCR analysis and by immunofluorescence. Retigabine, applied to the dorsal spinal cord, inhibited C and Adelta fiber-mediated responses of dorsal horn neurons evoked by natural or electrical afferent stimulation and the progressive "windup" discharge with repetitive stimulation in normal rats and in rats subjected to spinal nerve ligation. Retigabine also inhibited responses to intrapaw application of carrageenan in a rat model of chronic pain; this was reversed by XE991. It is suggested that IK(M) plays a key role in controlling the excitability of nociceptors and may represent a novel analgesic target.

Lipid rafts mediate the interaction between myelin-associated glycoprotein (MAG) on myelin and MAG-receptors on neurons.

The interaction between myelin-associated glycoprotein (MAG), expressed at the periaxonal membrane of myelin, and receptors on neurons initiates a bidirectional signalling system that results in inhibition of neurite outgrowth and maintenance of myelin integrity. We show that this involves a lipid-raft to lipid-raft interaction on opposing cell membranes. MAG is exclusively located in low buoyancy Lubrol WX-insoluble membrane fractions isolated from whole brain, primary oligodendrocytes, or MAG-expressing CHO cells. Localisation within these domains is dependent on cellular cholesterol and occurs following terminal glycosylation in the trans-Golgi network, characteristics of association with lipid rafts. Furthermore, a recombinant form of MAG interacts specifically with lipid-raft fractions from whole brain and cultured cerebellar granule cells, containing functional MAG receptors GT1b and Nogo-66 receptor and molecules required for transduction of signal from MAG into neurons. The localisation of both MAG and MAG receptors within lipid rafts on the surface of opposing cells may create discrete areas of high avidity multivalent interaction, known to be critical for signalling into both cell types. Localisation within lipid rafts may provide a molecular environment that facilitates the interaction between MAG and multiple receptors and also between MAG ligands and molecules involved in signal transduction.

Molecular cloning, distribution and functional analysis of the NA(V)1.6. Voltage-gated sodium channel from human brain.

We have cloned and expressed the full-length human Na(V)1.6 sodium channel cDNA. Northern analysis showed that the hNa(V)1.6 gene, like its rodent orthologues, is abundantly expressed in adult brain but not other tissues including heart and skeletal muscle. Within the adult brain, hNa(V)1.6 mRNA is widely expressed with particularly high levels in the cerebellum, occipital pole and frontal lobe. When stably expressed in human embryonic kidney cells (HEK293), the hNa(V)1.6 channel was found to be very similar in its biophysical properties to human Na(V)1.2 and Na(V)1.3 channels [Eur. J. Neurosci. 12 (2000) 4281-4289; Pflügers Arch. 441 (2001) 425-433]. Only relatively subtle differences were observed, for example, in the voltage dependence of gating. Like hNa(V)1.3 channels, hNa(V)1.6 produced sodium currents with a prominent persistent component when expressed in HEK293 cells. These persistent currents were similar to those reported for the rat Na(V)1.2 channel [Neuron 19 (1997) 443-452], although they were not dependent on over-expression of G protein betagamma subunits. These data are consistent with the proposal that Na(V)1.6 channels may generate the persistent currents observed in cerebellar Purkinje neurons [J. Neurosci. 17 (1997) 4157-4536]. However, in our hNa(V)1.6 cell line we have been unable to detect the resurgent currents that have also been described in Purkinje cells. Although Na(V)1.6 channels have been implicated in producing these resurgent currents [Neuron 19 (1997) 881-891], our data suggest that this may require modification of the Na(V)1.6 alpha subunit by additional factors found in Purkinje neurons but not in HEK293 cells.