Inhibiting glioma cell invasion by sequential photo-sonodynamic therapy

INTRODUCTION: Despite aggressive surgical resection and adjuvant chemoradiotherapy, malignant gliomas inevitably recur due to the persistence of infiltrative tumor cells at the resection margins. Although photodynamic therapy (PDT) has demonstrated the ability to inhibit glioma cell invasion, its clinical utility is limited by restricted light penetration and challenges associated with repeated intracranial application. Sonodynamic therapy (SDT), which utilizes low-intensity focused ultrasound (FUS) to activate a sonosensitizer, offers a non-invasive alternative capable of penetrating the skull and reaching deeply embedded tumor margins. This study evaluates the ability of sequential 5-aminolevulinic acid (ALA)-mediated PDT followed by repetitive SDT to inhibit glioma cell invasion using a three-dimensional spheroid-Matrigel migration model. METHODS: F98 glioma spheroids were formed and embedded between two layers of Matrigel. The embedded spheroids were incubated with ALA and treated with either PDT or SDT as single therapies as well as a sequential protocol consisting of a single PDT treatment followed by two repetitive SDT treatments at 24-hour intervals. Invasive distance from the spheroid edge into the surrounding matrix was measured at 4 and 7 days post-implantation under both 1% and 5% FBS conditions. RESULTS: Although ALA-mediated PDT and SDT individually inhibited glioma cell invasion in a dose-dependent manner, PDT did not significantly inhibit recurrence of invasive activity. Notably, sequential ALA-PDT followed by repetitive SDT produced sustained and highly significant inhibition of glioma cell invasion compared to either modality alone, without inducing sustained spheroid cytotoxicity. CONCLUSION: Sequential ALA-mediated PDT followed by repetitive SDT enhances inhibition of glioma cell invasion in vitro, suggesting the potential of a combined PDT-SDT strategy as a translatable, minimally invasive approach to suppress residual invasive tumor cells and improve post-operative outcomes of malignant glioma.