George T. Gillies

Nanoscale thermometry via the fluorescence of YAG:Ce phosphor particles: measurements from 7 to 77?C

The laser-induced fluorescence lifetime of 30 nm particles of YAG:Ce was measured as a function of temperature from 7 to 77°C. The fluorescence decay lifetimes for the nanoparticles of this phosphor varied from ≈18 to 27 ns, i.e. ≈33% relative to the longest lifetime measured. This large variation in lifetime, coupled with the high signal strength that was observed, suggest that YAG:Ce nanoparticles will be useful thermographic phosphors. We describe the material and the apparatus used to characterize its fluorescence, present the results of measurements made over the range of temperatures tested and comment on some possible applications for this novel material.

Magnetic guidance of ferrofluidic nanoparticles in an in vitro model of intraocular retinal repair

Agarose gel at a concentration of 0.6% was used to simulate the vitreous body of the eye during the infusion of a ferrofluid and the subsequent magnetic concentration of it onto a surrogate retinal surface. The 10 nm Fe3O4 particles in the ferrofluid served to mimic the cobalt particles in a silicone magnetic fluid that is being developed for use as a tamponading agent in magnetic fluid therapies designed to alleviate retinal detachments and other types of retinopathy. Magnetically guided interstitial diffusion of the nanoparticles through up to 20 mm of the gel over periods of 72 h was shown to be possible, thus demonstrating that essentially all points on the retinal surface are reachable from elsewhere in the ocular interior. The nanodynamics of the magnetic and viscous forces at work on the particles during movement through the gel are discussed; in particular the diffusion speeds of the particles are estimated and compared with observations.

Antiproliferative effect of c-myc antisense phosphorothioate oligodeoxynucleotides in malignant glioma cells

OBJECTIVEnTo improve the prognosis for primary malignant tumors of the central nervous system, new therapeutic strategies are needed. Antisense oligodeoxynucleotides (ODNs) offer the potential to block the expression of specific genes within cells. The proto-oncogene c-myc has long been implicated in the control of normal cell growth and its deregulation in the development of neoplasia. We therefore reasoned that a strategy using ODNs complementary to c-myc messenger ribonucleic acid would be a potent inhibitor of glioma cell proliferation.nnnMETHODSnA variety of antisense, sense, and scrambled (15-mer) phosphorothioate ODNs targeted to rat and human c-myc messenger ribonucleic acid were synthesized and added to the media of cultured RT-2 cells (a rat glioblastoma cell line). Cell growth was assessed by 3-[4,5-dimethylthiazol-2yl]-2,5-diphenyltetrazolium bromide dye assay 1 to 5 days after adding the ODNs. c-Myc protein expression was analyzed by Western blot analysis. The stability of the ODNs was confirmed by gel electrophoresis.nnnRESULTSnCompared with cultures containing standard media, two of three antisense ODNs significantly inhibited the growth of glioma cells, whereas sense and scrambled sequence ODNs did not significantly affect cell growth at the concentrations tested. A human c-myc antisense sequence, which differed from the rat sequence by one base substitution, also had an inhibitory effect on RT-2 cells. Western blot analysis demonstrated that expression of immunoreactive c-Myc protein was also greatly reduced in the rat antisense ODN-treated cells (and not in sense-, scrambled-, or control-treated cells). The degree of reduction of c-Myc protein expression correlated well with the decrease in cell growth observed with several antisense ODNs. Phosphorothioate ODNs were stable in cell culture media for at least 5 days.nnnCONCLUSIONnThese results suggest that c-Myc plays a critical role in glioma cell proliferation and demonstrate that antisense ODNs can suppress proto-oncogene expression and inhibit the proliferation of glioma cells. Our results indicate that the antiproliferative activity of these ODNs was mediated predominantly through sequence-specific antisense mechanisms, but that sequence-specific nonantisense effects may also contribute to the strongest effects demonstrated. These findings support a potential role for antisense strategies designed to inhibit c-myc expression in the treatment of malignant gliomas.

A spinal cord surrogate with nanoscale porosity for in vitro simulations of restorative neurosurgical techniques

The development of strategies for the regrowth of axons through a section of damaged spinal cord could benefit from the availability of an in vitro model in which the potential clinical utility of candidate techniques could be assessed preliminarily. We have designed a spinal cord surrogate for this purpose; it uses 0.6% agarose gel as the parenchymal component and has a fibrous-like longitudinal structure. At this concentration, the pore size distribution of the homogeneous gel ranges from less than 10 nm to more than 1000 nm while the average pore size ranges from 100 to 300 nm. The average pore size is larger than that of the extracellular space in the tissues of the central nervous system, which is of the order of 20 nm. However, the addition of fibres to the surrogate gel model significantly modifies its longitudinal permeability, as assessed by monitoring the distribution of marker dye material during direct infusion into the surrogate. This makes the model useful for evaluating infusion-based techniques that will ultimately be employed for the delivery of growth factors and other agents to the growing axonal processes in injured spinal cord. The role foreseen for this type of surrogate in investigations of the nanomechanics of restorative neurosurgical procedures is discussed.

Atomic force microscopy observations of tumour cell invadopodia: novel cellular nanomorphologies on collagen substrates

Atomic force microscopy was used to map the surface topographies and the fine details of cells from the T98 human glioblastoma brain tumour cell line. The cells were plated on collagen substrate within growth media, and then exposed to air during the microscopy sessions. Over the course of these studies an example of a cytostructural invadopodia was observed extending in a straight line from one cell to another over a distance of approximately 80 µm, but with an estimated deviation from linearity over the length of its path of only ≈ 8 nm µm−1, i.e., < 1%. The remarkable straightness of its path suggests that strong cell-to-cell signalling processes are at work during even this earliest stage of tumorigenesis. A better understanding of the nanoscale morphologies and mechanics of novel cytostructural elements like this particular form of invadopodia may provide insights on new modalities of brain tumour treatment.

Atomic force microscopy measurement of cytostructural elements involved in the nanodynamics of tumour cell invasion

Cytostructural features associated with the invasive characteristics of brain tumour cells have been inspected and measured with atomic force microscopy. In one case the invadopodia extended from a T98 human glioblastoma cell departed from a linear path by 1 mrad for each 240 nm of axial extension from the point where its curvature began. In another cell, diametrically opposed invadopodia were projected over the collagen substrate and were co-aligned to within < 175 mrad (10°) of a common axis. In the latter case, an estimate of the torque that would be needed to overcome the adhesion forces and rotate the cell via moments applied by the invadopodia led to a value of 7 nN µm. From measurements by others of the interactions between glioma cells and collagen, the implied adhesion force for this cell was ≈ 0.5 nN, which was consistent with still other values reported in the literature. The measured mean radius of the cell was roughly 15 µm. The implications of these results for understanding and slowing the invasion of tumour cells through the extracellular matrix of the brain are discussed.

Intratumoral Administration and Convection-Enhanced Delivery

ABSTRACT: Convection-enhanced delivery is a means of localized drug delivery to the central nervous system. The therapeutic agent, infused via a catheter, is carried (convectus, latin) by bulk flow though the interstitial space. This method has proved to be a useful laboratory technique for targeted, wide-spread distribution of a broad range of agents including small molecules and gene therapy vectors, such as viruses and liposomes. The success in the lab has translated into a significant number of clinical studies which combine the use of convection-enhanced delivery and elegantly devised molecular strategies. Additionally, several studies suggest that convection-enhanced delivery can be accurately predicted with mathematical models, allowing precise planning of dosage and distribution in the clinical setting. Taken together the results of these investigations hint at the promise of an expanded armantarium against brain tumors.

Phosphor thermometry signal analysis and interpretation

Since the last International Temperature Symposium, phosphor thermometry has continued to mature with considerable attention given to combustion and turbine engine applications. More recently the utility to problems on the micro-and nano-scales has appreciated, particularly in regard to biological and biomedical situations. The method is therefore used for a wide range of situations. Signal interpretation is important and experience teaches that without sufficient care phosphor signals can be misleading. In order to advance the method, signal analysis investigations should prove fruitful. The specific aspect addressed here is the question of waveform sampling. A simple phenomenological approach is described that explores how the number of points digitized per waveform affects the measurement repeatability and accuracy. This is demonstrated for single shot signals and the average of 512 sequential waveforms. A bright temperature-independent luminescence signal from YVO4:Eu is sampled every 800 ps (1.25 GS/...