Stereotactic radiosurgery for glioblastoma--time to revisit this approach

Intracranial Sonodynamic Therapy With 5-Aminolevulinic Acid and Sodium Fluorescein: Safety Study in a Porcine Model

Background

Sonodynamic therapy (SDT) is an emerging ultrasound-based treatment modality for malignant gliomas which combines ultrasound with sonosensitizers to produce a localized cytotoxic and modulatory effect. Tumor-specificity of the treatment is achieved by the selective extravasation and accumulation of sonosensitizers in the tumor-bearing regions. The aim of this study is to demonstrate the safety of low-intensity ultrasonic irradiation of healthy brain tissue after the administration of FDA-approved sonosensitizers used for SDT in experimental studies in an in vivo large animal model.

Methods

In vivo safety of fluorescein (Na-Fl)- and 5 aminolevulinic acid (5-ALA)-mediated low-intensity ultrasound irradiation of healthy brain parenchyma was assessed in two sets of four healthy swine brains, using the magnetic resonance imaging (MRI)-guided Insightec ExAblate 4000 220 kHz system. After administration of the sonosensitizers, a wide fronto-parietal craniotomy was performed in pig skulls to allow transmission of ultrasonic beams. Sonication was performed on different spots within the thalamus and periventricular white matter with continuous thermal monitoring. Sonication-related effects were investigated with MRI and histological analysis.

Results

Post-treatment MRI images acquired within one hour following the last sonication, on day one, and day seven did not visualize any sign of brain damage. On histopathology, no signs of necrosis or apoptosis attributable to the ultrasonic treatments were shown in target areas.

Conclusions

The results of the present study suggest that either Na-FL or 5-ALA-mediated sonodynamic therapies under MRI-guidance with the current acoustic parameters are safe towards healthy brain tissue in a large in vivo model. These results further support growing interest in clinical translation of sonodynamic therapy for intracranial gliomas and other brain tumors.

Fluorescein-mediated sonodynamic therapy in a rat glioma model

INTRODUCTION

Malignant gliomas have a dismal prognosis and significant efforts are being made to develop more effective treatments. Sonodynamic therapy (SDT) is an emerging modality for cancer treatment which combines ultrasound with sonosensitizers to produce a localized cytotoxic effect. The aim of this study is to demonstrate the efficacy of SDT with fluorescein (FL) and low-intensity focused ultrasound in inhibiting the growth of ectopic gliomas implanted in the rat's subcutaneous tissue.

METHODS

In vivo cytotoxicity of FL-SDT was evaluated in C6 rat glioma cells which were inoculated subcutaneously. Tumor specific extracellular FL extravasation and accumulation was assessed with IVIS imaging in rats receiving systemic FL. Effects of FL-SDT with focused low-intensity ultrasound on tumor growth, and histological features of the rat's tumors were investigated. Treatment related apoptosis and necrosis were analyzed using hematoxylin & eosin, and apoptosis-specific staining.

RESULTS

IVIS imaging revealed a high degree of FL accumulation within the tumor, with a nearly threefold increase in tumoral epifluorescence signal over background. SDT significantly inhibited outgrowth of ectopic C6 gliomas across all three FUS exposure conditions. TUNEL and active caspase-3 staining did not reveal conclusive trends across control and SDT condition for apoptosis.

CONCLUSION

Our results suggest that SDT with FL and low-intensity FUS is effective in inhibiting the growth of ectopic malignant gliomas in rats. The selective FL extravasation and accumulation in the tumor areas where the blood-brain barrier is damaged suggests the tumor-specificity of the treatment. The possibility to use this treatment in intracranial models and in human gliomas will have to be explored in further studies.

Stereotactic Radiosurgery for Glioblastoma

Glioblastoma (GBM) is the most common primary malignant brain tumor in adults and one of the most aggressive of all human cancers. GBM tumors are highly infiltrative and relatively resistant to conventional therapies. Aggressive management of GBM using a combination of surgical resection, followed by fractionated radiotherapy and chemotherapy has been shown to improve overall survival; however, GBM tumors recur in the majority of patients and the disease is most often fatal. There is a need to develop new treatment regimens and technological innovations to improve the overall survival of GBM patients. The role of stereotactic radiosurgery (SRS) for the treatment of GBM has been explored and is controversial. SRS utilizes highly precise radiation techniques to allow dose escalation and delivery of ablative radiation doses to the tumor while minimizing dose to the adjacent normal structures. In some studies, SRS with concurrent chemotherapy has shown improved local control with acceptable toxicities in select GBM patients. However, because GBM is a highly infiltrative disease, skeptics argue that local therapies, such as SRS, do not improve overall survival. The purpose of this article is to review the literature regarding SRS in both newly diagnosed and recurrent GBM, to describe SRS techniques, potential eligible SRS candidates, and treatment-related toxicities. In addition, this article will propose promising areas for future research for SRS in the treatment of GBM.