Visualization of implanted GL261 glioma cells in living mouse brain slices using fluorescent 4-(4-(dimethylamino)-styryl)-N-methylpyridinium iodide (ASP+)

Brain Targeted Gold Liposomes Improve RNAi Delivery for Glioblastoma

INTRODUCTION

Glioblastoma (GBM) is the most common and lethal of the central nervous system (CNS) malignancies. The initiation, progression, and infiltration ability of GBMs are attributed in part to the dysregulation of microRNAs (miRNAs). Thus, targeting dysregulated miRNAs with RNA oligonucleotides (RNA interference, RNAi) has been proposed for GBM treatment. Despite promising results in the laboratory, RNA oligonucleotides have clinical limitations that include poor RNA stability and off-target effects. RNAi therapies against GBM confront an additional obstacle, as they need to cross the blood-brain barrier (BBB).

METHODS

Here, we developed gold-liposome nanoparticles conjugated with the brain targeting peptides apolipoprotein E (ApoE) and rabies virus glycoprotein (RVG). First, we functionalized gold nanoparticles with oligonucleotide miRNA inhibitors (OMIs), creating spherical nucleic acids (SNAs). Next, we encapsulated SNAs into ApoE, or RVG-conjugated liposomes, to obtain SNA-Liposome-ApoE and SNA-Liposome-RVG, respectively. We characterized each nanoparticle in terms of their size, charge, encapsulation efficiency, and delivery efficiency into U87 GBM cells in vitro. Then, they were administered intravenously (iv) in GBM syngeneic mice to evaluate their delivery efficiency to brain tumor tissue.

RESULTS

SNA-Liposomes of about 30-50 nm in diameter internalized U87 GBM cells and inhibited the expression of miRNA-92b, an aberrantly overexpressed miRNA in GBM cell lines and GBM tumors. Conjugating SNA-Liposomes with ApoE or RVG peptides increased their systemic delivery to the brain tumors of GBM syngeneic mice. SNA-Liposome-ApoE demonstrated to accumulate at higher extension in brain tumor tissues, when compared with non-treated controls, SNA-Liposomes, or SNA-Liposome-RVG.

DISCUSSION

SNA-Liposome-ApoE has the potential to advance the translation of miRNA-based therapies for GBM as well as other CNS disorders.

Temporal and spatial modulation of the tumor and systemic immune response in the murine Gl261 glioma model

Glioblastoma, the most aggressive form of glioma, has a 5-year survival rate of <5%. While radiation and immunotherapies are routinely studied in the murine Gl261 glioma model, little is known about its inherent immune response. This study quantifies the temporal and spatial localization of immune cell populations and mediators during glioma development. Eight-week old male C57Bl/6 mice were orthotopically inoculated with 1x106 Gl261 cells and tumor morphology, local and systemic immune cell populations, and plasma cytokines/chemokines assessed at day 0, 1, 3, 7, 14, and 21 post-inoculation by magnetic resonance imaging, chromogenic immunohistochemistry, multiplex immunofluorescent immunohistochemistry, flow cytometry and multiplex immunoassay respectively. From day 3 tumors were distinguishable with >30% Ki67 and increased tissue vascularization (p<0.05). Increasing tumor proliferation/malignancy and vascularization were associated with significant temporal changes in immune cell populations within the tumor (p<0.05) and systemic compartments (p = 0.02 to p<0.0001). Of note, at day 14 16/24 plasma cytokine/chemokines levels decreased coinciding with an increase in tumor cytotoxic T cells, natural killer and natural killer/T cells. Data derived provide baseline characterization of the local and systemic immune response during glioma development. They reveal that type II macrophages and myeloid-derived suppressor cells are more prevalent in tumors than regulatory T cells, highlighting these cell types for further therapeutic exploration.

Accumulation of Innate Amyloid Beta Peptide in Glioblastoma Tumors

Immunostaining with specific antibodies has shown that innate amyloid beta (Aβ) is accumulated naturally in glioma tumors and nearby blood vessels in a mouse model of glioma. In immunofluorescence images, Aβ peptide coincides with glioma cells, and enzyme-linked immunosorbent assay (ELISA) have shown that Aβ peptide is enriched in the membrane protein fraction of tumor cells. ELISAs have also confirmed that the Aβ(1–40) peptide is enriched in glioma tumor areas relative to healthy brain areas. Thioflavin staining revealed that at least some amyloid is present in glioma tumors in aggregated forms. We may suggest that the presence of aggregated amyloid in glioma tumors together with the presence of Aβ immunofluorescence coinciding with glioma cells and the nearby vasculature imply that the source of Aβ peptides in glioma can be systemic Aβ from blood vessels, but this question remains unresolved and needs additional studies.

S100B suppression alters polarization of infiltrating myeloid-derived cells in gliomas and inhibits tumor growth

S100B, a member of the multigene family of Ca²⁺-binding proteins, is overexpressed by most malignant gliomas but its biological role in gliomagenesis is unclear. Recently, we demonstrated that low concentrations of S100B attenuated microglia activation through the induction of STAT3. Furthermore, S100B downregulation in a murine glioma model inhibited macrophage trafficking and tumor growth. Based on these observations, we hypothesized that S100B inhibitors may have antiglioma properties through modulation of tumor microenvironment.

To discover novel S100B inhibitors, we developed a high-throughput screening cell-based S100B promoter-driven luciferase reporter assay. Initial screening of 768 compounds in the NIH library identified 36 hits with >85% S100B inhibitory activity. Duloxetine (Dul, an SNRI) was selected for the initial proof-of-concept studies. At low concentrations (1–5 μM) Dul inhibited S100B and CCL2 production in mouse GL261 glioma cells, but had minimal cytotoxic activity in vitro. In vivo, however, Dul (30 mg/kg/14 days) inhibited S100B production, altered the polarization and trafficking of tumor-associated myeloid-derived cells, and inhibited the growth of intracranial GL261 gliomas. Dul therapeutic efficacy, however, was not observed in the K-Luc glioma model that expresses low levels of S100B. These findings affirm the role of S100B in gliomagenesis and justify the development of more potent S100B inhibitors for glioma therapy.

Platelets are responsible for the accumulation of β-amyloid in blood clots inside and around blood vessels in mouse brain after thrombosis

INTRODUCTION

Platelets contain beta-amyloid precursor protein (APP) as well as Aβ peptide (Aβ) that can be released upon activation. During thrombosis, platelets are concentrated in clots and activated.

METHODS

We used in vivo fluorescent analysis and electron microscopy in mice to determine to what degree platelets are concentrated in clots. We used immunostaining to visualize Aβ after photothrombosis in mouse brains.

RESULTS

Both in vivo results and electron microscopy revealed that platelets were 300-500 times more concentrated in clots than in non-clotted blood. After thrombosis in control mice, but not in thrombocytopenic animals, Aβ immunofluorescence was present inside blood vessels in the visual cortex and around capillaries in the entorhinal cortex.

CONCLUSION

The increased concentration of platelets allows enhanced release of Aβ during thrombosis, suggesting an additional source of Aβ in the brains of Alzheimer's patients that may arise if frequent micro-thrombosis events occur in their brains.

Pulsed and oscillating gradient MRI for assessment of cell size and extracellular space (POMACE) in mouse gliomas

Solid tumor microstructure is related to the aggressiveness of the tumor, interstitial pressure and drug delivery pathways, which are closely associated with treatment response, metastatic spread and prognosis. In this study, we introduce a novel diffusion MRI data analysis framework, pulsed and oscillating gradient MRI for assessment of cell size and extracellular space (POMACE), and demonstrate its feasibility in a mouse tumor model. In vivo and ex vivo POMACE experiments were performed on mice bearing the GL261 murine glioma model (n = 8). Since the complete diffusion time dependence is in general non-analytical, the tumor microstructure was modeled in an appropriate time/frequency regime by impermeable spheres (radius Rcell , intracellular diffusivity Dics ) surrounded by extracellular space (ECS) (approximated by constant apparent diffusivity Decs in volume fraction ECS). POMACE parametric maps (ECS, Rcell , Dics , Decs ) were compared with conventional diffusion-weighted imaging metrics, electron microscopy (EM), alternative ECS determination based on effective medium theory (EMT), and optical microscopy performed on the same samples. It was shown that Decs can be approximated by its long time tortuosity limit in the range [1/(88 Hz)-31 ms]. ECS estimations (44 ± 7% in vivo and 54 ± 11% ex vivo) were in agreement with EMT-based ECS and literature on brain gliomas. Ex vivo, ECS maps correlated well with optical microscopy. Cell sizes (Rcell  = 4.8 ± 1.3 in vivo and 4.3 ± 1.4 µm ex vivo) were consistent with EM measurements (4.7 ± 1.8 µm). In conclusion, Rcell and ECS can be quantified and mapped in vivo and ex vivo in brain tumors using the proposed POMACE method. Our experimental results support the view that POMACE provides a way to interpret the frequency or time dependence of the diffusion coefficient in tumors in terms of objective biophysical parameters of neuronal tissue, which can be used for non-invasive monitoring of preclinical cancer studies and treatment efficacy. Copyright © 2016 John Wiley & Sons, Ltd.

Microglia Activate Migration of Glioma Cells through a Pyk2 Intracellular Pathway

Glioblastoma is one of the most aggressive and fatal brain cancers due to the highly invasive nature of glioma cells. Microglia infiltrate most glioma tumors and, therefore, make up an important component of the glioma microenvironment. In the tumor environment, microglia release factors that lead to the degradation of the extracellular matrix and stimulate signaling pathways to promote glioma cell invasion. In the present study, we demonstrated that microglia can promote glioma migration through a mechanism independent of extracellular matrix degradation. Using western blot analysis, we found upregulation of proline rich tyrosine kinase 2 (Pyk2) protein phosphorylated at Tyr579/580 in glioma cells treated with microglia conditioned medium. This upregulation occurred in rodent C6 and GL261 as well as in human glioma cell lines with varying levels of invasiveness (U-87MG, A172, and HS683). siRNA knock-down of Pyk2 protein and pharmacological blockade by the Pyk2/focal-adhesion kinase (FAK) inhibitor PF-562,271 reversed the stimulatory effect of microglia on glioma migration in all cell lines. A lower concentration of PF-562,271 that selectively inhibits FAK, but not Pyk2, did not have any effect on glioma cell migration. Moreover, with the use of the CD11b-HSVTK microglia ablation mouse model we demonstrated that elimination of microglia in the implanted tumors (GL261 glioma cells were used for brain implantation) by the local in-tumor administration of Ganciclovir, significantly reduced the phosphorylation of Pyk2 at Tyr579/580 in implanted tumor cells. Taken together, these data indicate that microglial cells activate glioma cell migration/dispersal through the pro-migratory Pyk2 signaling pathway in glioma cells.

Demeclocycline as a contrast agent for detecting brain neoplasms using confocal microscopy

Complete resection of brain tumors improves life expectancy and quality. Thus, there is a strong need for high-resolution detection and microscopically controlled removal of brain neoplasms. The goal of this study was to test demeclocycline as a contrast enhancer for the intraoperative detection of brain tumors. We have imaged benign and cancerous brain tumors using multimodal confocal microscopy. The tumors investigated included pituitary adenoma, meningiomas, glioblastomas, and metastatic brain cancers. Freshly excised brain tissues were stained in 0.75 mg ml(-1) aqueous solution of demeclocyline. Reflectance images were acquired at 402 nm. Fluorescence signals were excited at 402 nm and registered between 500 and 540 nm. After imaging, histological sections were processed from the imaged specimens and compared to the optical images. Fluorescence images highlighted normal and cancerous brain cells, while reflectance images emphasized the morphology of connective tissue. The optical and histological images were in accordance with each other for all types of tumors investigated. Demeclocyline shows promise as a contrast agent for intraoperative detection of brain tumors.

Electron microscopy in rat brain slices reveals rapid accumulation of Cisplatin on ribosomes and other cellular components only in glia

Cisplatin is a widely used, effective anticancer drug. Its use, however, is associated with several side effects including nephrotoxicity and neurotoxicity. It is known that cisplatin is accumulated in cells by the organic cation transport system and reacts with nucleotides, damaging them, but the precise target of cisplatin-induced neurotoxicity remains obscure. Here we report direct visualization of cisplatin inside brain cells using in vivo "cisplatin staining," a technique that takes advantage of the high electron density of cisplatin, which contains platinum (atomic mass = 195). After applying 0.1% cisplatin to living brain slices for 30 min, we fixed the tissue and observed the accumulated cisplatin using electron microscopy. We found that cisplatin was localized mainly to ribosomes associated with endoplasmic reticulum (EPR) in glial cells and to the myelin sheath formed by oligodendrocytes around neuronal axons. Staining of nuclear DNA was moderate. Our in vivo "cisplatin staining" method validated that the main target of cisplatin is a direct attack on myelin and the RNA contained in ribosomes.

Glioblastoma development in mouse brain: general reduction of OCTs and mislocalization of OCT3 transporter and subsequent uptake of ASP+ substrate to the nuclei

Organic cation transporters (OCTs) were first found and then isolated from cultured glioma cells. When glioma cells are implanted into brain the fate of OCTs varies with time after implantation and transporter type. Here we report that OCT1, OCT2 and OCT3 immunofluorescence is significantly reduced over time in implanted GL261 glioma cells, during tumor development in the brain. By day 21 after glioma implantation, OCT1, OCT2 and OCT3 immunofluorescence was reduced more than 10-fold in the cytoplasm of glioma cells, while OCT3 immunofluorescence became concentrated in the nucleus. The well-known fluorescent substrate for OCT transporters, 4-(4-(dimethylamino)-styryl)-N-methylpyridinium iodide (ASP⁺), previously shown to accumulate in glioma-cell cytoplasm in in vivo slices, began to accumulate in the nucleus of these cells, but not in cytoplasm, after 21 days post-implantation. Considering this mislocalization phenomenon, and other literature on similar nuclear mislocalization of different transporters, receptors and channels in glioma cells, we suggest that it is one of the "omens" preceding the motility and aggressivity changes in glioma behavior.

APP+, a fluorescent analogue of the neurotoxin MPP+, is a marker of catecholamine neurons in brain tissue, but not a fluorescent false neurotransmitter

We have previously introduced fluorescent false neurotransmitters (FFNs) as optical reporters that enable visualization of individual dopaminergic presynaptic terminals and their activity in the brain. In this context, we examined the fluorescent pyridinium dye 4-(4-dimethylamino)phenyl-1-methylpyridinium (APP+), a fluorescent analogue of the dopaminergic neurotoxin MPP+, in acute mouse brain tissue. APP+ is a substrate for the dopamine transporter (DAT), norepinephrine transporter (NET), and serotonin transporter (SERT), and as such represented a candidate for the development of new FFN probes. Here we report that APP+ labels cell bodies of catecholaminergic neurons in the midbrain in a DAT- and NET-dependent manner, as well as fine dopaminergic axonal processes in the dorsal striatum. APP+ destaining from presynaptic terminals in the dorsal striatum was also examined under the conditions inducing depolarization and exocytotic neurotransmitter release. Application of KCl led to a small but significant degree of destaining (approximately 15% compared to control), which stands in contrast to a nearly complete destaining of the new generation FFN agent, FFN102. Electrical stimulation of brain slices at 10 Hz afforded no significant change in the APP+ signal. These results indicate that the majority of the APP+ signal in axonal processes originates from labeled organelles including mitochondria, whereas only a minor component of the APP+ signal represents the releasable synaptic vesicular pool. These results also show that APP+ may serve as a useful probe for identifying catecholaminergic innervations in the brain, although it is a poor candidate for the development of FFNs.

Neurovascular coupling: in vivo optical techniques for functional brain imaging

Optical imaging techniques reflect different biochemical processes in the brain, which is closely related with neural activity. Scientists and clinicians employ a variety of optical imaging technologies to visualize and study the relationship between neurons, glial cells and blood vessels. In this paper, we present an overview of the current optical approaches used for the in vivo imaging of neurovascular coupling events in small animal models. These techniques include 2-photon microscopy, laser speckle contrast imaging (LSCI), voltage-sensitive dye imaging (VSDi), functional photoacoustic microscopy (fPAM), functional near-infrared spectroscopy imaging (fNIRS) and multimodal imaging techniques. The basic principles of each technique are described in detail, followed by examples of current applications from cutting-edge studies of cerebral neurovascular coupling functions and metabolic. Moreover, we provide a glimpse of the possible ways in which these techniques might be translated to human studies for clinical investigations of pathophysiology and disease. In vivo optical imaging techniques continue to expand and evolve, allowing us to discover fundamental basis of neurovascular coupling roles in cerebral physiology and pathophysiology.