Injectable chemotherapeutic microspheres and glioma I: enhanced survival following implantation into the cavity wall of debulked tumors

Adaptation of laser interstitial thermal therapy for tumor ablation under MRI monitoring in a rat orthotopic model of glioblastoma

BACKGROUND

Laser interstitial thermal therapy (LITT) under magnetic resonance imaging (MRI) monitoring is being increasingly used in cytoreductive surgery of recurrent brain tumors and tumors located in eloquent brain areas. The objective of this study was to adapt this technique to an animal glioma model.

METHODS

A rat model of U251 glioblastoma (GBM) was employed. Tumor location and extent were determined by MRI and dynamic contrast-enhanced (DCE) MRI. A day after assessing tumor appearance, tumors were ablated during diffusion-weighted imaging (DWI)-MRI using a Visualase LITT system (n = 5). Brain images were obtained immediately after ablation and again at 24 h post-ablation to confirm the efficacy of tumor cytoablation. Untreated tumors served as controls (n = 3). Rats were injected with fluorescent isothiocyanate (FITC) dextran and Evans blue that circulated for 10 min after post-LITT MRI. The brains were then removed for fluorescence microscopy and histopathology evaluations using hematoxylin and eosin (H&E) and major histocompatibility complex (MHC) staining.

RESULTS

All rats showed a space-occupying tumor with T2 and T1 contrast-enhancement at pre-LITT imaging. The rats that underwent the LITT procedure showed a well-demarcated ablation zone with near-complete ablation of tumor tissue and with peri-ablation contrast enhancement at 24 h post-ablation. Tumor cytoreduction by ablation as seen on MRI was confirmed by H&E and MHC staining.

CONCLUSIONS

Data showed that tumor cytoablation using MRI-monitored LITT was possible in preclinical glioma models. Real-time MRI monitoring facilitated visualizing and controlling the area of ablation as it is otherwise performed in clinical applications.

Local delivery to malignant brain tumors: potential biomaterial-based therapeutic/adjuvant strategies

Glioblastoma (GBM) is the most aggressive malignant brain tumor and is associated with a very poor prognosis. The standard treatment for newly diagnosed patients involves total tumor surgical resection (if possible), plus irradiation and adjuvant chemotherapy. Despite treatment, the prognosis is still poor, and the tumor often recurs within two centimeters of the original tumor. A promising approach to improving the efficacy of GBM therapeutics is to utilize biomaterials to deliver them locally at the tumor site. Local delivery to GBM offers several advantages over systemic administration, such as bypassing the blood-brain barrier and increasing the bioavailability of the therapeutic at the tumor site without causing systemic toxicity. Local delivery may also combat tumor recurrence by maintaining sufficient drug concentrations at and surrounding the original tumor area. Herein, we critically appraised the literature on local delivery systems based within the following categories: polymer-based implantable devices, polymeric injectable systems, and hydrogel drug delivery systems. We also discussed the negative effect of hypoxia on treatment strategies and how one might utilize local implantation of oxygen-generating biomaterials as an adjuvant to enhance current therapeutic strategies.

Polymeric Biomaterial Scaffolds for Tumoricidal Stem Cell Glioblastoma Therapy

Glioblastoma (GBM) is the most common primary brain tumor and has a poor prognosis; as such, there is an urgent need to develop innovative new therapies. Tumoricidal stem cells are an emerging therapy that has the potential to combat limitations of traditional local and systemic chemotherapeutic strategies for GBM by providing a source for high, sustained concentrations of tumoricidal agents locally to the tumor. One major roadblock for tumoricidal stem cell therapy is that the persistence of tumoricidal stem cells injected as a cell suspension into the GBM surgical resection cavity is limited. Polymeric biomaterial scaffolds have been utilized to enhance the delivery of tumoricidal stem cells in the surgical resection cavity and extend their persistence in the brain, ultimately increasing their therapeutic efficacy against GBM. In this review, we examine three main scaffold categories explored for tumoricidal stem cell therapy: microcapsules, hydrogels, and electrospun scaffolds. Furthermore, considering the significant impact of surgery on the brain and recurrent GBM, we survey a brief history of orthotopic models of GBM surgical resection.

Injection of Chemotherapeutic Microspheres and Glioma III: Parameters to Optimize Efficacy

Injectable microspheres may provide a means of providing local, sustained exposure of glioma to chemotherapeutics to improve patient survival. Using a rodent model of surgically resected glioma, we previously demonstrated that direct injections of chemotherapeutic microspheres into the tissue surrounding a resection cavity provide superior survival effects over injections of the same microspheres directly into the surgical cavity. The present experiments extended this novel observation by exploring several parameters related to the use of intraparenchymal injections of chemotherapeutic microspheres to treat glioma. Using a rat model of resected glioma, several principles regarding the use of local sustained release carboplatin microspheres were established. First, an inverted U dose–response was observed, wherein further dose escalation beyond the optimal dose was not efficacious and indeed produced significant local toxicity. Second, it was necessary to expose approximately 40% of the tumor margin to sustained release carboplatin in order to increase survival in this model. Survival was not enhanced when the proportion of the tumor margin exposed to carboplatin was only 20%. Third, the distribution of the chemotherapeutic microsphere injections along the tumor perimeter was shown to be important, requiring that the entire perimeter be proportionately exposed to the chemotherapeutic agent. Together, these data continue to support the development of chemotherapeutic microspheres for treating glioma. However, they also caution that a number of fundamental parameters can profoundly influence the efficacy that might be expected from local sustained delivery. Careful attention to these principles is not only required if chemotherapeutic microspheres are to be used efficaciously, but these principles should provide a foundation to further optimize the potential of this and other polymeric delivery systems under development for local, intraparenchymal drug delivery to glioma.

Injection of Chemotherapeutic Microspheres and Glioma IV: Eradicating Tumors in Rats

Polymer microspheres can be easily injected into the brain to provide a local and sustained delivery of chemotherapeutics to a tumor or surrounding tissue subject to high rates of tumor recurrence following surgery. Building on previous studies that established the clear advantage of local, peritumoral injections of sustained release microspheres, the following experiments utilized two different approaches for maximizing the survival benefit in glioma-bearing rats. In the first experiment, a previously grown cortical tumor was debulked and animals received either one or two treatments with carboplatin-loaded microspheres (either 200 or 800 μg total carboplatin per treatment). In each case, the microspheres were injected along the perimeter of the resection cavity with each treatment separated by 20 days. Survival studies clearly demonstrated that two, temporally spaced injections were superior to a single series of injections. At the lowest dose tested (200 μg), median survival was increased an additional 40% over that in animals receiving one treatment. At the higher dose (800 μg), one third of the animals receiving two separate treatments were long-term survivors (>150 days) and showed complete eradication of the tumor on histological examination. In the second experiment, we directly compared the efficacy produced by sustained release carboplatin or 1,3-bis[2-chloroethyl]-1-nitrourea (BCNU) alone versus injecting carboplatin and BCNU-loaded micro-spheres blended together as a single suspension. Carboplatin and BCNU both enhanced survival, with BCNU being significantly less effective than carboplatin. However, the greatest improvements in survival were seen when a blended suspension of carboplatin and BCNU microspheres was injected around the surgical cavity. In contrast, spatially alternating injections of BCNU and carboplatin microspheres was significantly less effective and the increase in survival was no greater than that achieved with BCNU alone. These data offer further support for the potential utility of local, sustained release chemotherapeutic microspheres for treating glioma. Moreover, they suggest that injectable chemotherapeutic microspheres may offer important advantages by (a) permitting multiple, temporally spaced injections to be made, as needed, and (b) providing the opportunity to deliver combinations of several different efficacious drugs directly to the tumor site to enhance survival beyond what can be achieved with delivery of any single chemotherapeutic agent.

Spatial distribution and antitumor activities after intratumoral injection of fragmented fibers with loaded hydroxycamptothecin

There was only a small percentage of drug delivered to tumors after systemic administration, and solid tumors also have many barriers to prevent drug penetration within tumors. In the current study, intratumoral injection of drug-loaded fiber fragments was proposed to overcome these barriers, allowing drug accumulation at the target site to realize the therapeutic efficacy. Fragmented fibers with hydroxycamptothecin (HCPT) loaded were constructed by cryocutting of aligned electrospun fibers, and the fiber lengths of 5 (FF-5), 20 (FF-20), and 50μm (FF-50) could be easily controlled by adjusting the slice thickness. Fragmented fibers were homogeneously dispersed into 2% sodium alginate solution, and could be smoothly injected through 26G1/2 syringe needles. FF-5, FF-20 and FF-50 fiber fragments indicated similar release profiles except a lower burst release from FF-50. In vitro viability tests showed that FF-5 and FF-20 fiber fragments caused higher cytotoxicity and apoptosis rates than FF-50. After intratumoral injection into murine H22 subcutaneous tumors, fragmented fibers with longer lengths indicated a higher accumulation into tumors and a better retention at the injection site, but showed less apparent diffusion within tumor tissues. In addition to the elimination of invasive surgery, HCPT-loaded fiber fragments showed superior in vivo antitumor activities and fewer side effects than intratumoral implantation of drug-loaded fiber mats. Compared with FF-5 and FF-50, FF-20 fiber fragments indicated optimal spatial distribution of HCPT within tumors and achieved the most significant effects on the animal survival, tumor growth inhibition and tumor cell apoptosis induction. It is suggested that the intratumoral injection of drug-loaded fiber fragments provided an efficient strategy to improve patient compliance, allow the retention of fragmented fibers and spatial distribution of drugs within tumor tissues to achieve a low systemic toxicity and an optimal therapeutic efficacy.

Drug encapsulated polymeric microspheres for intracranial tumor therapy: A review of the literature

Despite intensive surgical excision, radiation therapy, and chemotherapy, the current life expectancy for patients diagnosed with glioblastoma multiforme is only 12 to 15months. One of the approaches being explored to increase chemotherapeutic efficacy is to locally deliver chemotherapeutics encapsulated within degradable, polymeric microspheres. This review describes the techniques used to formulate drug encapsulated microspheres targeted for intracranial tumor therapy and how microsphere characteristics such as drug loading and encapsulation efficiency can be tuned based on formulation parameters. Further, the results of in vitro studies are discussed, detailing the varied drug release profiles obtained and validation of drug efficacy. Finally, in vivo results are summarized, highlighting the study design and the effectiveness of the drug encapsulated microspheres applied intracranially.

Co-delivery of chemosensitizing siRNA and an anticancer agent via multiple monocomplexation-induced hydrophobic association

Synergistic combination of gene targeting and chemotherapy by co-delivering siRNA and anticancer drugs has widely been investigated to develop siRNA-based therapeutics for cancer treatment. Despite clinical potential of this approach, big challenges still remain such as delivery efficiency or stability/biocompatibility of the siRNA delivery system. Here we report a simple and biocompatible co-delivering formulation based on a unique complexation method, i.e., multiple monocomplexation-induced hydrophobic association between Bcl-2 targeting siRNA and a monocationic anticancer agent (benzethonium chloride, BZT). A colloidal formulation of the hydrophobically associated multiple monocomplex (HMplex) composed of siRNA, BZT and Pluronic F-68 was spontaneously constructed by physical mixing of the ternary constituents. In vitro and in vivo studies revealed that the ternary HMplex with a low charge ratio (N/P=4) possesses a tightly complexed stable nanostructure with Pluronic surface and small colloidal size less than 10nm, which allowed for 1) suitable protection of siRNA in serum-rich physiological environment, 2) efficient intracellular transfection into the cytoplasm, and 3) successful peritumoral co-delivery into the tumor tissue with dense interstitial matrix. Compared to non-targeting HMplexes between scrambled siRNA and BZT, Bcl-2 targeting HMplexes enhanced significantly both mRNA down-regulation by siRNA and apoptosis induction by BZT, and thus greatly suppressed the tumor volume when administered to highly aggressive and resistant human breast cancer xenografts (MDA-MB-231) in mice. These results elucidate that the co-complexed siRNA and BZT were liberated by intracellular decomplexation to trigger a synergistically combined therapeutic action. The successful siRNA/chemodrug co-delivery in vivo via peritumoral route and the greatly promoted therapeutic efficacy thereby represent the clinical potential of HMplexes for adjuvant locoregional cancer treatment by gene-targeted combination therapy.

Validation of an imageable surgical resection animal model of Glioblastoma (GBM)

BACKGROUND

Glioblastoma (GBM) is the most common and malignant primary brain tumour having a median survival of just 12-18 months following standard therapy protocols. Local recurrence, post-resection and adjuvant therapy occurs in most cases.

NEW METHOD

U87MG-luc2-bearing GBM xenografts underwent 4.5mm craniectomy and tumour resection using microsurgical techniques. The cranial defect was repaired using a novel modified cranial window technique consisting of a circular microscope coverslip held in place with glue.

RESULTS

Immediate post-operative bioluminescence imaging (BLI) revealed a gross total resection rate of 75%. At censor point 4 weeks post-resection, Kaplan-Meier survival analysis revealed 100% survival in the surgical group compared to 0% in the non-surgical cohort (p=0.01). No neurological defects or infections in the surgical group were observed. GBM recurrence was reliably imaged using facile non-invasive optical bioluminescence (BLI) imaging with recurrence observed at week 4.

COMPARISON WITH EXISTING METHOD(S)

For the first time, we have used a novel cranial defect repair method to extend and improve intracranial surgical resection methods for application in translational GBM rodent disease models. Combining BLI and the cranial window technique described herein facilitates non-invasive serial imaging follow-up.

CONCLUSION

Within the current context we have developed a robust methodology for establishing a clinically relevant imageable GBM surgical resection model that appropriately mimics GBM recurrence post resection in patients.

Evaluation of biocompatibility and anti-glioma efficacy of doxorubicin and irinotecan drug-eluting bead suspensions in alginate

INTRODUCTION

Chemotherapeutic drug-eluting beads (DEBs) are microspheres that are in clinical use for intraarterial chemoembolisation of liver cancer. Here we report on the biocompatibility and anti-tumour efficacy of DEBs after intratumoral application in a rat BT4Ca glioma model.

METHODS AND RESULTS

Doxorubicin and irinotecan-eluting DEBs were suspended in a Ca(2+)-free aqueous alginate solution that provides a sol-gel transition when injected into the Ca(2+) rich brain tissue. In this way the DEBs are immobilised at the implantation site. Forced elution studies in vitro using a USP-4 flow-through apparatus demonstrated that the alginate excipient helped to reduce the burst effect and rate the elution from the beads. From the in vivo evaluation, doxorubicin DEBs demonstrated a significant local toxicity, while irinotecan-loaded DEBs showed good local tissue compatibility. Doxorubicin at higher concentrations and irinotecan-loaded DEBs were found to decrease tumour volume, increase survival time and decrease the Ki67 proliferation index of the tumour. Doxorubicin was shown by fluorescent microscopy to diffuse into the peritumoral tissue, but also penetrates along white matter tracts, to more distant areas.

DISCUSSION

We conclude that the alginate suspension of irinotecan DEBs can be considered safe and effective in a clinical setting.

The efficacy of intracranial PLG-based vaccines is dependent on direct implantation into brain tissue

We previously engineered a macroporous, polymer-based vaccine that initially produces GM-CSF gradients to recruit local dendritic cells and subsequently presents CpG oligonucleotides, and tumor lysate to cell infiltrates to induce immune cell activation and immunity against tumor cells in peripheral tumor models. Here, we demonstrate that this system eradicates established intracranial glioma following implantation into brain tissue, whereas implantation in resection cavities obviates vaccine efficacy. Rats bearing seven-day old, intracranial glioma tumors were treated with PLG vaccines implanted into the tumor bed, resulting in retention of contralateral forelimb function (day 17) that is compromised by tumor formation in control animals, and 90% long-term survival (>100 days). Similar benefits were observed in animals receiving tumor resection plus vaccine implants into the adjacent parenchyma, but direct implantation of PLG vaccines into the resection cavity conferred no benefit. This dissociation of efficacy was likely related to GM-CSF distribution, as implantation of PLG vaccines within brain tissue produced significant GM-CSF gradients for prolonged periods, which was not detected after implantation in resection cavities. These studies demonstrate that PLG vaccine efficacy is correlated to GM-CSF gradient formation, which requires direct implantation into brain tissue, and justify further exploration of this approach for glioma treatment.

Three weeks release BCNU loaded hydrophilic-PLGA microspheres for interstitial chemotherapy: Development and activity against human glioblastoma cells

The aim of this study is the development of microspheres of BCNU for intracranial administration, as an alternative to marketed novel Gliadel Implant in the treatment of brain tumours. H poly-lactide-co-glycolide biodegradable microspheres of BCNU with a mean size of 33.5 + or - 1.8 microm were obtained by an oil-in-water emulsion solvent evaporation method. Their small size would allow their intracranial administration through a needle by cerebral stereotaxia if tumour recurrence occurs, without a surgical intervention, as Gliadel needs. BCNU was released from these microspheres during 21 days, mainly by a mechanism of diffusion from the polymer matrix (K = 2.91 mg days(-(1/2))). The cytotoxic effects of these microspheres on human glioblastoma cells were demonstrated all through 21 days and the value of percentage of viable cells was less than 40%. These microspheres should be commercialized as a freeze-dried product to keep at -20 degrees C. Three hundred and twenty milligrams of microspheres contain 61.6 mg of BCNU, the same amount of BCNU contained in 1600 mg or eight wafers of Gliadel usually implanted after the tumour resection.

In vitro and in vivo optimization of an anti-glioma modality based on synchrotron X-ray photoactivation of platinated drugs

For the past 5 years, a radio-chemotherapy approach based on the photoactivation of platinum atoms (PAT-Plat) consisting of treating tumors with platinated compounds and irradiating them above the platinum K edge (78.4 keV) has been developed at the European Synchrotron Radiation Facility (Grenoble, France). Compared to other preclinical modalities, PAT-Plat provides the highest survivals of rats bearing the rodent F98 glioma. However, further investigations are required to optimize its efficiency and to allow its clinical application. Here we examined in vitro and in vivo whether monochromatic X rays are more efficient than high-energy photons in producing the PAT-Plat effect by measuring DNA double-strand breaks (DSBs) and survival of glioma-bearing rats and whether an increase in the platinum concentration in the tumor results in increased rat survival. DSBs were assessed by pulsed-field gel electrophoresis with different DNA fragment migration programs and with gamma-H2AX immunofluorescence. In vivo, F98 glioma cells were injected intracerebrally, treated with a single intracranial injection of cisplatin or carboplatin 13 days after tumor implantation, and irradiated the day after with 78.8 keV X rays or 6 MV photons. Our results indicate that 78.8 keV X rays are more efficient than high-energy photons at producing the PAT-Plat effect. At low concentrations, cisplatin is more efficient than carboplatin; this is likely due to more efficient DNA binding and DSB repair inhibition. High concentrations of carboplatin inside tumors do not necessarily lead to protracted survival of rats. The therapeutic benefit of anti-glioma synchrotron strategies appears to be correlated with the percentage of unrepaired DSBs but not with the number of DSBs induced.

Treatment of malignant gliomas with mitoxantrone-loaded poly (lactide-co-glycolide) microspheres

OBJECTIVE

Mitoxantrone (MTZ) has potent in vitro activity against malignant glioma cell lines, but it cannot be used effectively as a systemic agent for the treatment of brain tumors because of its poor central nervous system penetration. However, MTZ-loaded poly(lactide-co-glycolide) (PLGA) microspheres may be injected into the peritumoral area and into tumor tissue to provide effective and sustained local drug concentrations without causing systemic side effects.

METHODS

Fisher rats were randomized into three groups. The first group (n = 9) was concomitantly implanted with rat glioma (RG2) cells and blank PLGA microspheres. The second group (n = 6) was implanted with RG2 cells and MTZ-loaded PLGA microspheres. The third group (n = 9) was implanted with RG2 cells, and MTZ-loaded PLGA microspheres were injected into the same area after 7 days. Animals were sacrificed on Day 15 or 35. Tumor volumes were measured after hematoxylin and eosin staining. Distribution kinetics of MTZ in the brain was determined by high-performance liquid chromatography in nine rats injected with MTZ-loaded microspheres.

RESULTS

The tumor volumes were 76 +/- 11 and 107 +/- 11 mm (mean +/- standard error) on Days 15 (n = 6) and 35 (n = 3), respectively, in the control group. In rats treated with MTZ-loaded microspheres on Day 7, tumor volumes were significantly reduced to 17 +/- 4 and 23 +/- 2 mm on Days 15 (n = 6) and 35 (n = 3), respectively. No tumor formation was observed when glioma cells and MTZ-loaded PLGA microspheres were implanted concomitantly (n = 6). No systemic side effects or parenchymal inflammatory infiltration were observed in either group of rats. Brain MTZ concentration was highest at the injection site and declined with time and distance from the injection site and with time.

CONCLUSION

These data demonstrate that MTZ-loaded PLGA microspheres can deliver therapeutic concentrations of drug to the tumor and prevent glioma growth without causing side effects. This treatment method may increase the efficiency of antineoplastic therapy and positively impact survival.

Controlling delivery properties of a waterborne,in-situ-forming biomaterial

This study details efforts to transition an in-situ-gelling polymer for endovascular embolization from the bench-top to preclinical cerebral arteriovenous malformation animal model studies. The in-situ-forming gel is based on waterborne, reverse emulsion materials. For controlled embolization of vascular defects, it is crucial to understand the delivery properties of an in-situ-forming gel. Directing a liquid into a small cavity requires both precise control of the fluid flow, and depends upon minimal variability in the materials behavior. A 2(3) factorial experiment performed in the laboratory revealed that temperature, mixing time, and buffer strength are all significant factors affecting the gelation time of the specific system studied. All three factors were also seen to reduce the standard deviation on the gel times. Changing the temperature from 21.3 to 37.0 degrees C reduced the cross population variability from 6.0 +/- 3.3 min to 3.4 +/- 1.6 min. At 30-s premixing, the protocol produced an average gel time of 5.3 +/- 3.0 min, which was reduced to 3.3 +/- 1.2 min with 90 s. Finally, a 50 mM buffer solution provided a gel time of 6.5 +/- 3.2 min, which was reduced to 2.95 +/- 0.6 min at 100 mM. Viscosity data was analyzed to suggest a model for injection volume and viscosity.

Barriers to carrier mediated drug and gene delivery to brain tumors

Brain tumor patients face a poor prognosis despite significant advances in tumor imaging, neurosurgery and radiation therapy. Potent chemotherapeutic drugs fail when used to treat brain tumors because biochemical and physiological barriers limit drug delivery into the brain. In the past decade a number of strategies have been introduced to increase drug delivery into the brain parenchyma. In particular, direct drug administration into the brain tumor has shown promising results in both animal models and clinical trials. This technique is well suited for the delivery of liposome and polymer drug carriers, which have the potential to provide a sustained level of drug and to reach cellular targets with improved specificity. We will discuss the current approaches that have been used to increase drug delivery into the brain parenchyma in the context of fluid and solute transport into, through and from the brain, with a focus on liposome and polymer drug carriers.

Carboplatin Sustained Delivery System Using Injectable Microspheres

A controlled carboplatin delivery system using biodegradable polymer has been used in this study. The purpose was to evaluate the local and systemic effects of injectable, biodegradable microspheres containing carboplatin when injected as aqueous suspension subcutaneously in rats. Biocompatibility and toxicity of empty microspheres and microspheres loaded with carboplatin were evaluated by clinical and histological examination. The diffusion of carboplatin in tissues and time of drug release were evaluated by platinum determination in plasma and tissues over the time. The results of the study suggest that microspheres provide a sustained slow release of carboplatin and that multiple inoculations of microspheres containing drug and no evidence of local or systemic toxicity is found. This device may be useful in the treatment of solid tumours.

Spray-dried poly(D,L-lactide) microspheres containing carboplatin for veterinary use: in vitro and in vivo studies

The aim of this study was the development of a veterinary dosage form constituted by injectable biodegradable microspheres designed for the subcutaneous release of carboplatin, a chemotherapeutic drug. Poly(D,L-lactide) (PDLLA) microspheres were prepared by an emulsification/spray-drying method, using the drug-to-polymer weight ratios 1:9 and 1:5; blank microspheres (1% w/v) were prepared as a comparison. Microparticles were characterized in terms of morphology, encapsulation efficiency, and in vitro drug release behavior. In vivo tests were conducted on rats by subcutaneous injection of microsphere aqueous suspensions. Levels of carboplatin were evaluated both in the skin and in serum. The microparticles obtained had a spherical shape; particle size ranged from 5 to 7 microm, dependent on drug loading. Microspheres were able to control the in vitro release of the drug: approximately 90% to 100% of the carboplatin was released over 30 days. In vivo results showed that the microspheres were able to release high drug amounts locally, and sustained serum levels of drug were also achieved. Based on these results, carboplatin-loaded PDLLA microspheres may be useful for local delivery of the antineoplastic drug to the tumor, avoiding tumor recurrence in small animals, and may decrease the formation of distant metastases.

In vivo delivery of BCNU from a MEMS device to a tumor model

A drug delivery micrcoelectromechanical systems (MEMS) device was used to locally deliver a chemotherapeutic agent (BCNU) to an experimental tumor in rats. This MEMS device consists of an array of reservoirs etched into the silicon substrate. The drug release is achieved by the electrochemical dissolution of the gold membranes covering the reservoirs. A new Pyrex package was developed to improve the BCNU release kinetics and enhance device capacity. Co-formulation of BCNU with polyethylene glycol (PEG) led to complete and rapid release of drug in vivo. BCNU delivered from the MEMS device showed dose-dependent inhibiting effect on the tumor growth in the BCNU dosage range of 0.67 approximately 2 mg. BCNU delivered from the activated devices was as effective as equipotent subcutaneous injections of BCNU in inhibiting tumor growth. Further optimization using this MEMS device to deliver BCNU in combination with other therapeutic agents against the tumor challenge is possible because of the unique capability of the device to precisely control the temporal release profiles of multiple substances.

Drug delivery into the brain using poly(lactide-co-glycolide) microspheres

Among the strategies developed for drug delivery into the CNS, locally controlled drug release by the way of an implantable polymeric device has been developed in recent years. The first polymeric devices developed were macroscopic implants needing open surgery for implantation. Over the last few years, poly(lactide-co-glycolide) microspheres have been shown to be safe and promising for drug delivery into the brain. Poly(lactide-co-glycolide) is biodegradable and biocompatible with brain tissue. Due to their size, these microspheres can be easily implanted by stereotaxy in discrete, precise and functional areas of the brain without causing damage to the surrounding -tissue. Brain tumour treatments have been developed using this approach and clinical trials have been performed. Potential applications in neurodegenerative diseases have also been explored, particularly neurotrophic factor delivery and cell therapy.

Dynamic, three-dimensional optical tracking of an ablative laser beam

Surgical resection remains the treatment of choice for brain tumors with infiltrating margins but is currently limited by visual discrimination between normal and neoplastic marginal tissues during surgery. Imaging modalities such as computed tomography, magnetic resonance, positron emission tomography, and optical techniques can accurately localize tumor margins. We believe coupling the fine resolution of current imaging techniques with the precise cutting of midinfrared lasers through image-guided neurosurgery can greatly enhance tumor margin resection. This paper describes a feasibility study designed to optically track in three-dimensional space the articulated arm delivery of a noncontact ablative laser beam. To enable optical tracking of the laser beam focus, infrared-emitting diodes (IREDs) were attached to a handpiece machined for the distal end of the articulated arm of a surgical carbon dioxide laser. Crosstalk between the ablative laser beam and the tracking diodes was measured. The geometry of the adapted laser handpiece was characterized to track an externally attached passive tip and the laser beam focus. Target localization accuracies were assessed for both instrument points-of-interest and the sources of tracking errors were investigated. Stray infrared laser light did not affect optical tracking accuracy. The mean target registration errors while optically tracking the laser handpiece with a passive tip and the laser beam focus were 1.31+/-0.50 mm and 2.31+/-0.92 mm, respectively, and were equivalent to the errors tracking a 24-IRED pen probe from Northern Digital in a side-by-side comparison. The majority of error during ablation tracking derived from registration accuracy between physical space and the defined space of the ablation phantom and from an inability to freehand align the laser focus with the target in a consistent manner. While their magnitudes depend on spatial details of the tracking setup (e.g., number and distribution of fiducial points, working distance from the camera, etc.), these errors are inherent to any freehand laser surgery.

Albumin loaded microsphere of amphiphilic poly(ethylene glycol)/ poly(α-ester) multiblock copolymer

The purpose of this study is to investigate the microspheres (MS) based on (AB)(n) type amphiphilic multiblock copolymers for sustained and complete release of a model protein, bovine serum albumin (BSA). The MS were prepared by a modified water-in-oil-in-water (W/O/W) double emulsion method using amphiphilic multiblock copolymers consisting of poly(ethylene glycol) (PEG) and a poly(alpha-ester), poly(epsilon-caprolactone) (PCL) or poly(l-lactic acid) (PLLA). The size of MS and encapsulation efficiency of BSA within MS were not noticeably influenced by the copolymer composition used in this experiment. While BSA was completely released from PEG/PLLA MS through matrix erosion and the diffusion of BSA, it was released only to an extent of 60% from PEG/PCL MS solely through the diffusion process. However, the release of BSA from PEG/PCL MS dramatically increased and then reached 100% release in 10 days after thermal treatment of the MS at 50 degrees C for 30 min in the middle of release test (on day 15).

Therapeutic effectiveness of novel 5-fluorouracil-loaded poly(methylidene malonate 2.1.2)-based microspheres on F98 glioma-bearing rats

BACKGROUND

Drug delivery to the central nervous system (CNS) remains a real challenge for neurosurgeons and neurologists, because many molecules cannot cross the blood-brain barrier (BBB). In recent years, solid polymeric materials have been implanted into animal and human brains either by surgery or using stereotactic methods to assure the controlled release of a drug over a determined period, thus circumventing the difficulties posed by the BBB. Poly(methylidene malonate 2.1.2) (PMM 2.1.2) is a new polymer that was described a few years ago and that allows the fabrication of novel, 5-fluorouracil (5-FU)-loaded PMM 2.1.2 microspheres. The objective of the current study was to assess the therapeutic effectiveness of those particles in a rat brain tumor model, the F98 glioma.

METHODS

Forty-three rats were used in this study. First, a histologic evaluation of the F98 tumor model was performed on Fischer female rats. Thereafter, different groups of rats were injected and were treated with 5-FU microspheres in 2 different suspension media: carboxymethylcellulose (CMC) aqueous solution with or without 5-FU.

RESULTS

The tumor was confirmed as extremely aggressive and invasive, even in early development. The 5-FU-loaded microspheres improved rat median survival significantly compared with untreated animals, CMC-treated animals, and 5-FU solution-treated animals when injected in CMC without 5-FU, demonstrating the interest of a sustained release and the efficacy of intratumoral chemotherapy against an established tumor.

CONCLUSIONS

PMM 2.1.2 microspheres appeared to be a promising system, because their degradation rate in vivo was longer compared with many polymers, and they may be capable of long-term delivery.

BCNU-loaded poly(D, L-lactide-co-glycolide) wafer and antitumor activity against XF-498 human CNS tumor cells in vitro

Implantable polymeric device that can release chemotherapeutic agent directly into central nervous system (CNS) has had an impact on malignant glioma therapy. The purpose of our study was to develop an implantable polymeric device, which can release intact 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU) for long-term period over 1 month, and to evaluate its cytotoxicity against XF 498 human CNS tumor cells in vitro. BCNU was incorporated into biodegradable poly(D,L-lactide-co-glycolide) (PLGA), by using spray-drying method. BCNU-loaded PLGA microparticles were characterized by scanning electron microscopy (SEM), powder X-ray diffraction, and differential scanning calorimetry. SEM observation of the microparticles showed that the microparticles were spherical, i.e. microspheres. Homogeneous distribution of BCNU in PLGA microsphere was confirmed by significant reduction of crystallinity of BCNU. Microspheres were fabricated into wafers with flat and smooth surface by direct compression method. In vitro release of BCNU in pH 7.4 phosphate buffered saline was prolonged up to 8 weeks after short initial burst period. Antitumor activity of BCNU-loaded PLGA wafer against XF 498 human CNS tumor cells continued over 1 month and, PLGA only did not affect the growth of the cells. Meanwhile, the cytotoxic activity of BCNU powder disappeared within 12 h. These results strongly suggest that the BCNU/PLGA formulations increase release period of carmustine in vivo and also be useful in the development of implantable polymeric device for malignant glioma.

New approach to tumor therapy for inoperable areas of the brain: chronic intraparenchymal drug delivery

Because the brainstem has little functional redundancy, diffuse lesions have been regarded as inoperable. To determine whether local drug therapy can prolong survival in a rodent model of a tumor in such eloquent tissue, lethal doses of F98 and 9L tumor cells were injected into the brainstems of Fischer 344 rats. Five days after inoculations, 0.5 mg/ml solutions of carboplatin were infused at 1 microl/h for 7 days. Compared to control groups that survived 13-17 days with F98 tumors and 22-23 days with 9L tumors, animals locally infused with 0.1 mg of carboplatin survived 27-30 days (Prob > Chi Sq = 0.0003), and 32 days (Prob > Chi Sq = 0.01), respectively. Measurements of tissue platinum levels at autopsy suggested that infusions distributed pharmacologically relevant levels of carboplatin through a volume of tissue at least 0.5 cm in diameter. The results suggest that chronic low-flow infusions provide a promising approach to therapy for CNS lesions in tissues considered to be inoperable.

Sustained release chemotherapeutic microspheres provide superior efficacy over systemic therapy and local bolus infusions

PURPOSE

The present studies evaluated the ability of injectable, biodegradable microspheres releasing carboplatin, doxorubicin, or 5-fluorouracil to suppress the growth of solid tumors implanted subcutaneously or intramuscularly.

METHODS

Seven to 10 days after implantation of MATB-III cells, rats received systemic chemotherapy, intratumoral bolus chemotherapy, or injections of chemotherapeutic microspheres into the tumor center or multiple sites along the outer perimeter of the tumor.

RESULTS

A single treatment with carboplatin, doxorubicin, or 5-fluorouracil microspheres along the perimeter of the tumors produced a significant, dose-related suppression in tumor growth, relative to injections directly into the tumor center. Moreover, five temporally-spaced microsphere treatments along the tumor perimeter (with either doxorubicin or 5-fluorouracil microspheres) completely eradicated 100% of the subcutaneous tumors and 40-53% of the intramuscular tumors. Polypharmacy, accomplished by blending doxorubicin- and 5-fluorouracil-loaded microspheres and injecting them into the tumors was even more efficacious than sustained delivery of either drug alone. Comparable doses of systemic chemotherapy or intratumoral bolus chemotherapy were ineffective.

CONCLUSIONS

Injectable microspheres might be ideal for local, sustained delivery of chemotherapeutic agents to solid tumors. However, attention must be paid to the placement of the microspheres, for injections around the tumor perimeter may be required for efficacy.

The process and development of image-guided procedures

Medical imaging has been used primarily for diagnosis. In the past 15 years there has been an emergence of the use of images for the guidance of therapy. This process requires three-dimensional localization devices, the ability to register medical images to physical space, and the ability to display position and trajectory on those images. This paper examines the development and state of the art in those processes.

Injectable chemotherapeutic microspheres and glioma II: enhanced survival following implantation into deep inoperable tumors

PURPOSE

Delivery of chemotherapeutics using implantable, biodegradable polymers provides a potentially powerful method of treating brain tumors. The present studies examined the ability of injectable microspheres, formulated to release carboplatin or BCNU for 2-3 weeks, to enhance survival in a rodent model of deep, inoperable glioma.

METHODS

Rat glioma (RG2) cells were implanted into the striatum of rats. In a first experiment, the tumors were allowed to grow for 3 days, followed by either no treatment, bolus chemotherapy (100 microg), or implantation of microspheres containing 10, 50, or 100 microg of carboplatin. The microspheres were implanted, via hypodermic injection, directly into the center of the small, 3-day-old tumors. In a second experiment, tumors grew for 8 days prior to treatment with either carboplatin- or BCNU-loaded microspheres. The microspheres were then injected either directly into the center of these larger tumors or into three sites along the perimeter of the tumor. Separate sets of animals received bolus chemotherapy (100 microg) into either the tumor center or around the tumor perimeter.

RESULTS

Injection of carboplatin-loaded microspheres into the center of the small 3 day old, tumors produced dose-related increases in survival. When injections of carboplatin- or BCNU-loaded microspheres were made into the center of the larger, 8-day-old tumors, survival was not enhanced. However, when the microspheres were injected along the perimeter of the larger tumors, sustained-release chemotherapy did significantly prolong survival. Bolus chemotherapy was less effective than sustained release chemotherapy.

CONCLUSIONS

Together, these data: (1) demonstrate that sustained delivery of chemotherapy in or near the tumor site is superior to equipotent bolus doses in inoperable tumors, (2) demonstrate that injection of sustained release microspheres into the tissue surrounding a growing tumor may provide superior effects over injections directly into the tumor mass, and (3) suggest that this approach may provide a useful means of selectively delivering chemotherapeutics to tumors or portions of tumors that cannot otherwise be treated with conventional surgical approaches.