Preclinical assessment of a noncooled MR thermometry-based neurosurgical laser therapy system.

OBJECTIVE: MRI-guided laser interstitial thermal therapy (MRgLITT) has recently gained interest as an ablative stereotactic procedure for intractable epilepsy, movement disorders, and brain tumors. Conventionally, a LITT system consists of a laser generator and cooled laser applicator, which is a fiber optic core surrounded by a sheath through which cooled fluid is pumped. However, this footprint can make the system bulky and nonmobile, limit the maximum depth of targeting, and increase the chances of breakdown. Herein, the authors conduct a preclinical assessment of a noncooled MRgLITT system in a porcine model. METHODS: Three-tesla MRI was used to guide the in vivo placement of noncooled laser applicators in the porcine brain. The study consisted of a survival arm and terminal arm. The laser was activated at a power of 4-7 W for ≤ 180 seconds. Temperature changes were monitored using the MR thermometry software ThermoGuide in the survival arm (n = 5) or both ThermoGuide software and adjacently inserted thermal probes in the terminal arm (n = 3). Thermal damage was determined by the software using the temperature-time relationship of cumulative equivalent minutes at 43°C (CEM43). Temperatures calculated by the software were compared with those recorded by the temperature probes. The dimensions of thermal damage thresholds (TDTs; 2-9, 10-59, 60-239, ≥ 240 CEM43 isolines) given by MR thermometry were compared with the dimensions of irreversible damage on histopathological analysis. RESULTS: There was a strong correlation between temperature recordings by ThermoGuide and those by thermal probes at both 4 mm (r = 0.96) and 8 mm (r = 0.80), with a mean absolute error of 0.76°C ± 2.13°C and 0.17°C ± 1.65°C at 4 and 8 mm, respectively. The area of 2-9 CEM43 was larger than the area of irreversible damage seen on histopathological analysis. The dimensions of the 10 and 60 CEM43 correlated well with dimensions of the lesion on histopathological analysis. A well-defined border (≤ 1 mm) was observed between the area of irreversible damage and healthy brain tissue. CONCLUSIONS: This preclinical assessment showed that the noncooled LITT system was able to precisely reach the target and create well-defined lesions within a margin of safety, without any adverse effects. MR thermometry software provided an accurate near-real-time temperature of the brain tissue, and dimensions of the lesion as visualized by the software correlated well with histopathological findings. Further studies to test the system's efficacy and safety in human subjects are in progress.

Learning Curve Associated with ClearPoint Neuronavigation System: A Case Series.

BACKGROUND: The ClearPoint neuronavigation system affords real-time magnetic resonance imaging (MRI) guidance during stereotactic procedures. While such information confers potential clinical benefits, additional operative time may be needed. METHODS: We conducted a retrospective analysis of procedural time associated with ClearPoint Stereotaxis, with hypothesis that this procedural time is comparable with that associated with frame-based biopsy. RESULTS: Of the 52 patients evaluated, the total procedural time for ClearPoint stereotactic biopsy averaged 150.0 (±40.4) minutes, of which 111.5 (±16.5) minutes were dedicated to real-time MRI acquisition and trajectory adjustment. This procedural time is within the range of those reported for frame-based needle biopsies. Approximately 5 minutes of the procedural time is related to the mounting of the MRI-compatible stereotactic frame. Based on the procedural time, we estimate that four cases are required in the learning curve to achieve this efficiency. Efficient algorithms for distortion corrections and isocenter localization are keys to ClearPoint stereotaxis. Routine quality assurance/control after each MRI software update and institutional information technology maintenance also contribute to efficiency. Real-time MRI is essential for definitive diagnosis in select cases. CONCLUSIONS: ClearPoint stereotactic needle biopsy can be achieved in time frames comparable to frame-based stereotaxis. However, procedural efficiency requires 4 "learning curve" cases as well as vigilance in terms of MR distortion correction and information technology maintenance.

In Vivo Efficacy of an Injectable Microsphere-Hydrogel Ocular Drug Delivery System.

PURPOSE: Demonstrate in vivo that controlled and extended release of a low dose of anti-vascular endothelial growth factor (anti-VEGF) from a microsphere-hydrogel drug delivery system (DDS) has a therapeutic effect in a laser-induced rat model of choroidal neovascularization (CNV). METHODS: Anti-VEGF (ranibizumab or aflibercept) was loaded into poly(lactic-co-glycolic acid) microspheres that were then suspended within an injectable poly(N-isopropylacrylamide)-based thermo-responsive hydrogel DDS.The DDS was shown previously to release bioactive anti-VEGF for ~200 days. CNV was induced using an Ar-green laser. The four experimental groups were as follows: (i) non-treated, (ii) drug-free DDS, (iii) anti-VEGF-loaded DDS, and (iv) bolus injection of anti-VEGF. CNV lesion areas were measured based on fluorescein angiograms and quantified using a multi-Otsu thresholding technique. Intraocular pressure (IOP) and dark-adapted electroretinogram (ERG) were also obtained pre- and post-treatment (1, 2, 4, 8, and 12 weeks). RESULTS: The anti-VEGF-loaded DDS group had significantly smaller (60%) CNV lesion areas than non-treated animals throughout the study. A small transient increase in IOP was seen immediately after injection; however, all IOP measurements at all time points were within the normal range. There were no significant changes in ERG maximal response compared to pre-treatment measurements for the drug-loaded DDS, which suggests no adverse effects on retinal cellular function. CONCLUSIONS: The current study demonstrates that the DDS can effectively decrease laser-induced CNV lesions in a murine model. Controlled and extended release from our DDS achieved greater treatment efficacy using an order of magnitude less drug than what is required with bolus administration. This suggests that our DDS may provide a significant advantage in the treatment of posterior segment eye diseases.

Controlled and Extended In Vitro Release of Bioactive Anti-Vascular Endothelial Growth Factors from a Microsphere-Hydrogel Drug Delivery System.

PURPOSE: To demonstrate controlled and extended release of bioactive anti-vascular endothelial growth factor (VEGF) agents (ranibizumab or aflibercept) from an injectable microsphere-hydrogel drug delivery system (DDS). METHODS: Anti-VEGF agents were radiolabeled with iodine-125 and loaded into poly(lactic-co-glycolic acid) (PLGA) 75:25 microspheres using a modified double-emulsion, solvent evaporation technique. Microspheres were then suspended in an injectable poly(N-isopropylacrylamide)-based thermo-responsive hydrogel to create a microsphere-hydrogel DDS. Release profiles were performed in phosphate buffered saline at 37°C and at predetermined intervals, release samples were collected. Microspheres were also made using non-radiolabeled anti-VEGFs to determine the bioactivity of the DDS throughout release. Bioactivity and cytotoxicity of release samples were determined using human umbilical vascular endothelial cells (HUVECs) under VEGF-induced proliferation. RESULTS: The DDS is capable of releasing either ranibizumab or aflibercept for 196 days with an initial burst (first 24 h) of 22.2 ± 2.2 and 13.1 ± 0.5 µg, respectively, followed by controlled release of 0.153 and 0.065 µg/day, respectively. Release samples showed no toxicity in HUVECs at any time. Both anti-VEGFs remained bioactive throughout release with significant inhibition of HUVEC proliferation compared to the drug-free DDS, which showed no inhibitory effect on HUVEC proliferation. CONCLUSIONS: Controlled, extended, and bioactive release for approximately 200 days was achieved for both ranibizumab and aflibercept in vitro. The use of anti-VEGF-loaded microspheres suspended within an injectable, thermo-responsive hydrogel may be an advantageous ocular DDS with the potential to improve upon current therapies.

Controlled and Extended Release of a Model Protein from a Microsphere-Hydrogel Drug Delivery System.

In extended ocular drug delivery applications, it is necessary to exert control over the release characteristics of the drug. Design considerations must be made to limit the initial burst (IB) and ensure complete release of drug from the drug delivery system (DDS). In this study, ovalbumin was used as a model protein to explore the effects on release of polymer formulation and fabrication technique in poly(lactic-co-glycolic acid) (PLGA) microspheres. Furthermore, the effect on release of suspending these microspheres in an injectable, thermo-responsive poly(N-isopropylacrylamide)-based hydrogel was determined. To characterize release, ovalbumin was radiolabeled with iodine-125. Regardless of polymer formulation or fabrication technique, pulsatile release was achieved with a second burst occurring after ~70 days for microspheres alone. Suspending PLGA 75:25 microspheres within hydrogel reduced the IB by ~75%, delayed the second burst by 28 days, and extended release out to ~200 days with steadier, consistent release throughout compared to microspheres alone. The combined microsphere-hydrogel DDS remains injectable through small-gauge needles and may have many applications, namely ocular drug delivery to the posterior segment.

Inverse relationship between the intraretinal concentration of bioavailable nitric oxide and blood glucose in early experimental diabetic retinopathy.

PURPOSE: To directly measure in vivo retinal nitric oxide (NO) concentration in experimental early diabetic retinopathy and correlate measurements with blood glucose to determine how intraretinal NO changes with severity of diabetes. METHODS: Long-Evans rats were made diabetic with streptozotocin (STZ). Three weeks post STZ injection, intraretinal NO concentration profiles were recorded using a dual NO/electroretinogram microelectrode. Diabetic profiles were compared with profiles from healthy controls, healthy rats injected with the NO synthase inhibitor L-NG-nitroarginine methyl ester (L-NAME), and healthy rats that received acute glucose injections ("acute hyperglycemia"). The NO values at the retina/RPE boundary (100% retinal depth) and retinal surface (0% depth) were analyzed for correlation with blood glucose. RESULTS: The average NO concentrations in the outer retina, inner retina, and vitreous humor of mild diabetic rats (250-400 mg/dL) were significantly higher than controls by 73%, 47%, and 70%, respectively. The average NO concentrations in the outer retina, inner retina, and vitreous humor of severe diabetic rats (500-600 mg/dL) were lower than controls, with NO at 41%, 36%, and 36% of controls, respectively, similar to L-NAME-treated eyes (38%, 36%, 20% of control). The NO levels in moderate diabetic rats (400-500 mg/dL) and acute hyperglycemia rats were similar to controls. The NO was significantly and inversely correlated with blood glucose for diabetic rats at 100% depth (R = -0.91) and 0% depth (R = -0.79) but not for acute hyperglycemia rats. CONCLUSIONS: The higher-than-control level of NO in mild diabetic rats and lower-than-control level in severe diabetic rats show that severity of diabetes is an important factor when measuring the bioavailability of NO in diabetic retinopathy.

Advances in ocular drug delivery: emphasis on the posterior segment.

INTRODUCTION: Recent advances in pharmacological therapies to treat ocular diseases such as glaucoma, age-related macular degeneration, diabetic macular edema and retinal vascular occlusions have greatly improved the prognosis for these diseases. Due to these advances in pharmacological therapy, there is a great deal of interest in minimally invasive delivery methods, which has generated rapid developments in the field of ocular drug delivery. AREAS COVERED: This review will summarize currently available and recent developments for ocular drug delivery to both the anterior and posterior segments. Modes of delivery, including topical, systemic, transcleral/periocular and intravitreal, will be discussed and corresponding examples will be given. This review will highlight the advantages and disadvantages of each mode of delivery and discuss strategies to address these issues. EXPERT OPINION: An ideal therapy should maintain effective levels of drug for the intended duration of treatment following a single application, yet a significant number of months of therapy may be required. There are numerous approaches under investigation to improve treatment options. From the use of novel biomaterial implants and depots for sustained release, to prodrug formations, to iontophoresis to improve drug delivery, the main emphasis will continue to be placed on less invasive, longer acting, sustained release formulations in the treatment of numerous ocular disorders.

Objective area measurement technique for choroidal neovascularization from fluorescein angiography.

The purpose of this study was to develop a non-biased method of quantitatively measuring choroidal neovascularization (CNV) areas based on late-phase fluorescein angiography (FA) images. Experimental CNV was induced in Long Evans rats by laser disruption of the Bruch's membrane. FA was performed weekly for 5weeks. Multi-Otsu thresholding (MOT) was used to quantify CNV in late-phase FA images from both experimental rodent CNV and wet age-related macular degeneration (wAMD) patients. Images were automatically thresholded into three levels based on the image histogram, with the highest level containing CNV. To determine the technique's ability to quantify CNV areas, rats were given either triamcinolone acetonide or dexamethasone sodium phosphate to treat CNV and compared to untreated rats. The rat CNV lesion areas measured from 5-week histology sections from each treatment group were compared to areas measured from the corresponding FA images. MOT was able to detect statistical decreases in rodent CNV area in the treatment groups versus control from weeks 3 through 5. The ratio of CNV area measured from histology to area measured from FA images was not statistically different between groups. Finally, to determine the usefulness of MOT on pathological morphologies of CNV, MOT was performed on late-phase FA images from patients with classic and diffuse CNV. The technique was able to segment classical CNV in wAMD patients, but performed poorly with diffuse CNV. MOT provides a robust, objective, and quantifiable area measurement of CNV lesion area in both experimentally-induced and pathological CNV. The results indicate that MOT could be a useful research tool in helping evaluate the effects of therapeutics on CNV growth.