Modelling convection-enhanced delivery in normal and oedematous brain.

Convection-enhanced delivery (CED) could have clinical applications in the delivery of neuroprotective agents in brain injury states, such as ischaemic stroke. For CED to be safe and effective, a physician must have accurate knowledge of how concentration distributions will be affected by catheter location, flow rate and other similar parameters. In most clinical applications of CED, brain microstructures will be altered by pathological injury processes. Ischaemic stroke and other acute brain injury states are complicated by formation of cytotoxic oedema, in which cellular swelling decreases the fractional volume of the extracellular space (ECS). Such changes would be expected to significantly alter the distribution of neuroprotective agents delivered by CED. Quantitative characterization of these changes will help confirm this prediction and assist in efforts to model the distribution of therapeutic agents. Three-dimensional computational models based on a Nodal Point Integration (NPI) scheme were developed to model infusions in normal brain and brain with cytotoxic oedema. These models were compared to experimental data in which CED was studied in normal brain and in a middle cerebral artery (MCA) occlusion model of cytotoxic oedema. The computational models predicted concentration distributions with reasonable accuracy.

Inductively coupled microfluidic pressure meter for in vivo monitoring of cerebrospinal fluid shunt function.

A microfluidic pressure sensor with inductively coupled, wireless readout capability has been developed for integration into cerebrospinal fluid shunt valve implants. The sensor consists of a deformable PDMS film that is bonded over a microfluidic reservoir, forming a fluidic capacitor. Deflection of the capacitor membrane is detected remotely through a shift in the resonance frequency of a micro-fabricated LC circuit. Sensors were fabricated by a combination of conventional MEMS technologies and rapid soft lithography. A direct pattern transfer technique was used to pattern the deformable PDMS film with a metal coating for the capacitive readout. The mechanical response of the fluidic capacitor was characterized by measuring the deflection of the PDMS film using an extrinsic Fabry-Perot interferometer (EFPI), and wireless sensing was demonstrated by the shift in resonance frequency of the sensor via an inductively coupled antenna. The sensor transduces pressure into a change in resonant frequency with sensitivity > 3.4 ppm Pa⁻¹ and responsivity 4.6 kHz Pa⁻¹, over a dynamic range of 0~3 kPa.

Performance tests of a novel coaxial tube catheter in an in vitro model of intracranial cell delivery.

We have tested prototypes of a novel coaxial tube catheter in an in vitro gel model of cell delivery into the brain. Devices 1.6 and 2.0 mm outer diameter were used to deliver PC 12 cells (concentration = 106 cells ml⁻¹ at 1 µl min⁻¹ into a 5 ml sandwich of collagen and 0.1% agarose, with and without follow-on infusions of nerve growth factor (NGF). Post-infusion microscopic imaging (40X) at the infusion sites was then carried out over 7-day periods. The results showed that under these experimental conditions, it was possible to use these catheters to deliver cells without either leakage of trapped air into the gel or reflux of the cell suspension along the catheter insertion track. Differentiation of the NGF-treated cells was observed.

A novel coaxial tube catheter for central nervous system infusions: performance characteristics in brain phantom gel.

We tested a novel neurocatheter in a brain-tissue gel model of drug infusion via convection-enhanced delivery (CED) for the treatment of a variety of neurological diseases. CED is an alternative to systemic administration of agents by intravenous or oral routes, which are often less effective or carry risk of systemic side effects. We investigated two co-axial tube devices, with outer diameters of 1.6 mm and 2.0 mm. Bromophenol blue dye was infused into 400 ml of 0.6% agarose gel at 1 µl/min for 1 h, with/without the inner and outer tubes Luer-locked at the proximal end, with/without the inner tube primed, and with/without the inner tube preloaded into the outer tube upon insertion into the gel. The unlocked, primed, and unloaded configuration produced infusions that resulted in significantly less (p < 0.05) entrapped air escaping into the gel and resulted in no reflux of infusate.

Cytometric catheter for neurosurgical applications.

Implantation of neural progenitor cells into the central nervous system has attracted strong interest for treatment of a variety of pathologies. The replacement of dopamine-producing neural cells in the brain appears promising for the treatment of patients affected by Parkinson's disease. Previous studies of cell replacement strategies have shown that less than 10% of implanted cells were viable 24-48 hours following implantation. We present the design of an instrumented cell-delivery catheter that has been developed to facilitate the quantification of the cells delivered and determination of viability. The catheter uses a fibre optic probe to perform fluorescence-based cytometric measurements on cells exiting the port at the catheter tip. Results of fluorescence testing data are presented and show that the device can characterize the quantity of cell densities ranging from 60 000 to 600 000 cells ml(-1) with a coefficient of determination of 0.93 (p < 0.05, n = 6).

Isolation of neuronal progenitor cells from the adult human neocortex.

BACKGROUND: The reliability of harvesting neuronal progenitor cells (NPCs) from the adult human neocortex has not been established, with respect to preparing autologous cell cultures for transplantation in stroke and traumatic brain injured patients. METHOD: Enriched NPC cultures have been generated from nonneurogenic regions of the adult rodent brain by buoyancy-dependent fractionation, but the feasibility of using such a method to isolate NPCs from the adult human cortex has not been reported previously. To determine if a starter population of human adult cortical NPCs could be isolated for in vitro expansion using this method, tissue samples from five patients undergoing cortical resection for either epilepsy or trauma were assayed. FINDINGS: Cultured cells generated from all patients predominately expressed both the NPC marker nestin and neuron-specific beta-tubulin III. The presence of NPCs was verified by in vitro BrdU/beta-tubulin III co-labeling and increasing beta-tubulin expression in differentiating conditions. Despite the formation of aggregates in monolayer culture, cell proliferation as measured by BrdU incorporation was not as prevalent as that reported from rodent cultures generated by this protocol. CONCLUSIONS: NPCs isolated from the adult human neocortex using this method expressed beta-tubulin III in larger percentages than has been previously reported for NPCs isolated using other methods. As such, these data suggest the possibility of culturing dividing neuroblasts from the adult neocortex for further manipulation as transplantable cells.

Equilibrium and non-equilibrium dynamics of the cranio-mandibular complex and cervical spine.

A dynamic model of the inverted pendulum characteristics of the head and cervical spine is presented. Using simple approximations and a single rotational-degree-of-freedom approach, the model is shown to conform to the classical mathematical description of an inverted pendulum motion. It also exhibits the well-known point of unstable equilibrium which is a standard property of such systems. Specific predictions of this theoretical description are compared against other values for the tilt, angular velocity and acceleration of the head during acceleration-sled testing, and with the Kapitza relation for mechanical-dither stabilization of an inverted pendulum. Numerical evaluations of the dynamic variables, resonant frequencies and time constants important to the problem are provided, and suggestions are made about how further results might be derived from extended versions of the model. This approach can now be refined to serve as a testing ground for analysing the biomechanics of traumatic neck injuries and for interpreting the possible roles that mandibular dysfunctions and dental malocclusion may play in disorders of the cervical spine. (Some background needed for exploring the latter possibility is presented.)

Membrane-type matrix metalloproteinases (MT-MMPs): expression and function during glioma invasion.

Membrane-type MMPs (MT-MMPs) constitute a growing subclass of recently identified matrix metalloproteinases (MMPs). In addition to the highly conserved MMP functional domains, the MT-MMPs have additional insertion sequences (IS) that confer unique functional roles. While most of the MMPs are secreted, the MT-MMPs are membrane associated and a number of these have cytoplasmic domains which may be important in cellular signaling. This membrane localization leads to focal areas of receptor recruitment and subsequent activity, thereby enhancing pericellular proteolysis in specific areas of contact within the brain interstitium. MT1-MMP is the best-characterized MT-MMP, the measure against which subsequently cloned homologues are compared. MT1-MMP activates proMMP2 via its interaction with TIMP2, which serves as an intermolecular bridge for proMMP2 binding to MT-MMPs. In addition to activation of proMMP2, MT-MMPs display intrinsic proteolytic activity towards extracellular matrix molecules (ECM), which is independent of MMP2 activation. The increased expression levels of several members of the MMP family have been shown to correlate with high-grade gliomas, including MTI-MMP. Despite improvements in the diagnosis and treatment of patients with glial tumors, they remain the most common and least curable brain cancer in adults. The ability of glioma cells to infiltrate surrounding brain tissue, and ultimately escape current therapeutic modalities, could potentially be minimized using anti-invasive therapies. Proteolysis is a necessary part of the invasion process, within which the MT-MMPs appear to play a central role. The development of pharmaceutical approaches that target expression and regulation of MT-MMPs may prove beneficial in targeting invading glioma cells.

The role of matrix metalloproteinase genes in glioma invasion: co-dependent and interactive proteolysis.

Matrix metalloproteinases (MMPs) are cation-dependent endopeptidases which have been implicated in the malignancy of gliomas. It is thought that the MMPs play a critical role in both metastasis and angiogenesis, and that interference with proteases might therefore deter local tumor dissemination and neovascularization. However, the attempt to control tumor-associated proteolysis will rely on better definition of the normal tissue function of MMPs, an area of study still in its infancy in the central nervous system (CNS). Understanding the role of MMP-mediated proteolysis in the brain relies heavily on advances in other areas of molecular neuroscience, most notably an understanding of extracellular matrix (ECM) composition and the function of cell adhesion molecules such as integrins, which communicate knowledge of ECM composition intracellularly. Recently, protease expression and function has been shown to be strongly influenced by the functional state and signaling properties of integrins. Here we review MMP function and expression in gliomas and present examples of MMP profiling studies in glioma tissues and cell lines by RT-PCR and Western blotting. Co-expression of MMPs and certain integrins substantiates the gathering evidence of a functional intersection between the two, and inhibition studies using recombinant TIMP-1 and integrin antisera demonstrate significant inhibition of glioma invasion in vitro. Use of promising new therapeutic compounds with anti-MMP and anti-invasion effects are discussed. These data underline the importance of functional interaction of MMPs with accessory proteins such as integrins during invasion, and the need for further studies to elucidate the molecular underpinnings of this process.

Intensity-modulated stereotactic radiosurgery using dynamic micro-multileaf collimation.

PURPOSE: The implementation of dynamic leaf motion on a micro-multileaf collimator system provides the capability for intensity-modulated stereotactic radiosurgery (IMSRS), and the consequent potential for improved dose distributions for irregularly shaped tumor volumes adjacent to critical organs. This study explores the use of IMSRS to provide improved tumor coverage and normal tissue sparing for small cranial tumors relative to plans based on multiple fixed uniform-intensity beams or traditional circular collimator arc-based stereotactic techniques. METHODS AND MATERIALS: Four patient cases involving small brain lesions are presented and analyzed. The cases were chosen to include a representative selection of target shapes, number of targets, and adjacent critical areas. Patient plans generated for these comparisons include standard arcs with multiple circular collimators, and fixed noncoplanar static fields with uniform-intensity beams and IMSRS. Parameters used for evaluation of the plans include the percentage of irradiated volume to tumor volume (PITV), normal tissue dose-volume histograms, and dose-homogeneity ratios. All IMSRS plans were computed using previously established IMRT techniques adapted for use with the BrainLAB M3 micro-multileaf collimator. The algorithms comprising the IMRT system for optimization of intensity distributions and conversion into leaf trajectories of the BrainLab M3 were developed at our institution. The ADAC Pinnacle(3) radiation treatment-planning system was used for dose calculations and for input of contours for target volumes and normal critical structures. RESULTS: For all cases, the IMSRS plans showed a high degree of conformity of the dose distribution with the target shape. The IMSRS plans provided either (1) a smaller volume of normal tissue irradiated to significant dose levels, generally taken as doses greater than 50% of the prescription, or (2) a lower dose to an important adjacent critical organ. The reduction in volume of normal tissue irradiated in the IMSRS plans ranged from 10% to 50% relative to the other arc and uniform fixed-field plans. CONCLUSION: The case studies presented for IMSRS demonstrate significant dosimetric improvements for small, irregularly shaped lesions of the brain when compared to treatments using multiple static fields or standard SRS arc techniques with circular collimators. For all cases, the IMSRS plan yielded a smaller volume of normal tissue irradiated, and/or a reduction in the volume of an adjacent critical organ (i.e., brainstem) irradiated to significant dose levels.

Quantitative three-dimensional analysis and diffusion modeling of oligonucleotide concentrations after direct intraparenchymal brain infusion.

We compared quantitative experimental results on the diffusion of 35S-labeled phosphorothioate oligonucleotide (PS-ODN) after intraparenchymal infusion in rat brain, with the distributions predicted by Fick's second law of diffusion. Fischer 344 rats underwent identical intracerebral infusions of 36S-PS-ODN. After 0, 5, 11, 23, and 47 h, groups of animals were sacrificed and sequential brain cryosections subjected to autoradiography. The resulting experimental data were compared to the predicted distributions, for estimation of the apparent free diffusion coefficient, D*. Volumes of distribution and total content of 36 S-PS-ODN in the parenchyma were also computed, to monitor loss of total material. The values for D* were within the expected range for the 21-mer PS-ODN used, but a progressive decrease in D* over time was noted. The model requires D* to remain constant and, thus, does not adequately explain the spread of 35S-PS-ODN following infusion. The progressive slowing of spread over time suggests that at later time points, 35S-PS-ODN may be fixed by tissue binding or cellular uptake in the brain. Loss of material via vascular and CSF clearance may also contribute to the lack of fit. Our results highlight issues to be addressed in the modeling and experimental design of the intraparenchymal infusion process.

Minimally invasive procedures. Advances in image-guided delivery of drug and cell therapies into the central nervous system.

Image-guided transparenchymal delivery of drugs is an emerging neurosurgical modality that holds the promise of delivering various agents directly across the blood-brain barrier. Potential large-scale applications for convection-enhanced delivery of drugs through the interstitial space include the delivery of chemotherapeutic agents and gene therapy vectors for the treatment of brain tumors and the delivery of neurotrophic factors and neurotransmitters for the treatment of neurodegenerative disorders. The related technique of direct intraparenchymal injection of cells provides a means for transplanting neural stem cells into the brain for the treatment of degenerative diseases. Significant advances in catheter design, infusion strategies, and imaging technology have brought these procedures into the mainstream of human clinical testing, with clinical applications potentially on the near horizon.

Cost-efficacy of MR-guided neurointerventions.

This article summarizes the available data on the cost-efficacy of interventional MR imaging and discusses its potential future role in the diagnosis and management of neurologic diseases and disorders.

Extracorporeal irradiation of tumorous calvaria. Case report.

This patient with recurrent meningioma grossly involving the frontal bone underwent craniotomy and tumor resection. During the procedure a bone flap was irradiated extracorporeally at a very high dose (120 Gy) sufficient to sterilize residual tumor cells, and the bone was then successfully replaced orthotopically for reconstruction. The use of autologous irradiated bone in this setting offers advantages over cadaveric transplantation and prosthetic implants. Radiation might cause less disruption of the bone's architecture than other techniques of tumor cell eradication.

Radiosensitization of rat glioma with bromodeoxycytidine and adenovirus expressing herpes simplex virus-thymidine kinase delivered by slow, rate-controlled positive pressure infusion.

Infection of rat RT2 glioma cells in vitro with an adenovirus (ADV-TK) expressing herpes simplex virus (HSV) thymidine kinase (TK) and subsequent exposure to 5-bromo-2'-deoxycytidine (BrdC), which is specifically incorporated into ADV-TK-infected cell DNA as 5-bromo-2'-deoxyuridine (BrdU), results in significant radiosensitization (sensitizer enhancement ratio: 1.4-2.3) compared with Ad beta gal-infected cells. Cell killing correlated well with increased BrdU DNA incorporation and with apoptosis. Whereas radiation (4 Gy) alone was relatively ineffective in inducing apoptosis, treatment with HSV-TK/BrdC resulted in BrdC dose- (10-100 microM) and time-dependent (24-48 hours) increases, and the combination of the two treatments produced a synergistic response (1.5- to 2-fold). To investigate the effects of the ADV-TK/BrdC treatment in vivo, RT2 cells were grown as soft tissue tumors in Fischer 344 rats and conditions for virus infusion were optimized by altering the volume and rate of infusion using a rate-controlled positive pressure device. We found that relatively large volumes (100-150 microL) of virus delivered at rates of < or = 1 microL/minute were optimal and gave uniform and reproducible results. Using these optimal infusion conditions, we were able to achieve 40% adenovirus infection in the tumor. Infection of RT2 tumors with ADV-TK and continuous administration of BrdC from an osmotic pump resulted in significant (.001 < P < .009) tumor regression 6 days after radiation (30 Gy delivered as 2 x 5 Gy over 3 days) compared with controls. In situ staining of sectioned tumors with anti-BrdU antibody or by high-performance liquid chromatography analysis of extracted and hydrolyzed tumor DNA confirmed that we obtained efficient and specific incorporation of BrdU into tumor cells. These results suggest that adenovirus-mediated delivery of HSV-TK in combination with BrdC and radiation can potentially be an efficient combination modality for the treatment of gliomas.

Hypofractionated stereotactic radiotherapy as an alternative to radiosurgery for the treatment of patients with brain metastases.

PURPOSE: Modeling studies have demonstrated a potential biologic advantage of fractionated stereotactic radiotherapy for malignant brain tumors as compared to radiosurgery (SRS), even when only a few fractions are utilized. We prospectively evaluated the feasibility, toxicity, efficacy and cost of hypofractionated stereotactic radiotherapy (HSRT) in the treatment of selected radiosurgery-eligible patients with brain metastases. METHODS AND MATERIALS: Patients with a limited number of brain metastases not involving the brainstem or optic chiasm underwent linac-based HSRT delivered in 3 fractions using a relocatable stereotactic frame. Depth-helmet and reference point measurements were recorded to address treatment accuracy. All patients underwent whole brain radiotherapy to a dose of 30 Gy. Toxicity, response, and survival duration were recorded for each patient. Prognostic factors were assessed by Cox regression analysis. Cost comparisons with a cohort of SRS treated patients were performed. RESULTS: Thirty-two patients with 57 brain metastases were treated with HSRT. Twenty-three and 9 patients underwent HSRT for upfront and salvage treatment, respectively. The median dose delivered was 27 Gy, given in 3 fractions of 9 Gy. From 3328 depth-helmet measurements, the absolute median setup deviation in AP, lateral, and vertical orientations was approximately 1.0 mm. No significant acute toxicity was seen. Late toxicities included seizures in four patients, and radionecrosis in two patients. The median survival duration from treatment was 12 months. KPS (p = 0.039) and RTOG-RPA class (p = 0.039) were identified as significant prognostic factors for survival. HSRT was $4119 less costly than SRS. CONCLUSION: HSRT, as delivered in this study, is more comfortable for patients and less costly than SRS in the treatment of selected patients with brain metastases. Proper dose selection and radiobiologic/toxicity trade-offs with SRS await further study.

Central nervous system leiomyosarcoma in patients with acquired immunodeficiency syndrome. Report of two cases.

Leiomyosarcomas (LMSs) of the central nervous system are extremely rare; however, they are becoming more prevalent in immunocompromised patients. The authors present the cases of two patients with acquired immunodeficiency syndrome: one with LMS of the thoracic vertebral body and the other with LMS originating from the region of the cavernous sinus. The epidemiological and histological characteristics of LMS and its association with latent Epstein-Barr virus are discussed, as well as the treatments for this neoplasm.

Determination of intracranial tumor volumes in a rodent brain using magnetic resonance imaging, Evans blue, and histology: a comparative study.

The measurement of tumor volumes is a practical and objective method of assessing the efficacy of a therapeutic agent. However, the relative accuracy of different methods of assessing tumor volume has been unclear. Using T1-weighted, gadolinium-enhanced magnetic resonance Imaging (T1-MRI), Evans Blue infusion and histology we measured intracranial tumor volumes in a rodent brain tumor model (RT2) at days 10, 16 and 18 after implantation of cells in the caudate putamen. There is a good correlation between tumor volumes comparing T1-MRI and Evans Blue (r2 = 0.99), T1-MRI and Histology (r2 = 0.98) and histology and Evans Blue (r2 = 0.93). Each of these methods is reliable in estimating tumor volumes in laboratory animals. There was significant uptake of gadolinium and Evans Blue in the tumor suggesting a wide disruption of the blood-brain barrier.

Enhanced radiosensitivity of malignant glioma cells after adenoviral p53 transduction.

OBJECT: The goal of this study was to determine whether adenoviral vector-mediated expression of human wildtype p53 can enhance the radiosensitivity of malignant glioma cells that express native wild-type p53. The p53 gene is thought to function abnormally in the majority of malignant gliomas, although it has been demonstrated to be mutated in only approximately 30%. This has led to studies in which adenoviral transduction with wild-type human p53 has been investigated in an attempt to slow tumor cell growth. Recent studies suggest that reconstitution of wild-type p53 can render cells more susceptible to radiation-mediated death, primarily by p53-mediated apoptosis. METHODS: Rat RT2 glioma cells were analyzed for native p53 status by reverse transcriptase-polymerase chain reaction and sequence analysis and for p53 expression by Western blot analysis. Clonogenic survival and the terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick-end labeling assay were used to characterize RT2 cell radiosensitivity and apoptosis, respectively, with and without prior transduction with p53-containing and control adenoviral vectors. Animal survival length was monitored after intracerebral implantation with transduced and nontransduced RT2 cells, with and without cranial radiation. The RT2 cells were demonstrated to express native rat wild-type p53 and to markedly overexpress human p53 following adenoviral p53 transduction. The combination of p53 transduction followed by radiation resulted in marked decreases in RT2 cell survival and increases in apoptosis at radiation doses from 2 to 6 Gy. Animals receiving cranial radiation after intracerebral implantation with RT2 cells previously transduced with p53 survived significantly longer than control animals (p<0.01). CONCLUSIONS: The ability to enhance the radiosensitivity of malignant glioma cells that express wild-type p53 by using adenoviral transduction to induce overexpression of p53 offers hope for this approach as a therapeutic strategy, not only in human gliomas that express mutant p53, but also in those that express wild-type p53.