Sonodynamic therapy inhibition of invasive glioma cells from tumor spheroids

• SDT significantly inhibits glioma cell invasion in a 3D Matrigel spheroid model. • Sublethal SDT reduces invasion independently of cytotoxic cell killing. • Pre-implantation SDT disrupts cell adhesion and prevents later matrix invasion. • Fractionated low-dose SDT matches inhibition from single high-dose exposure. • Ultrasound alone shows no anti-invasive effect without a sonosensitizer. Glioblastoma multiforme (GBM) is characterized by extensive tumor cell invasion into normal brain tissue leading to tumor recurrence despite present day treatment protocols. Photodynamic therapy (PDT) has been shown to inhibit glioma cell invasion, but the poor penetration of light in brain tissue has set limitations. Sonodynamic therapy (SDT), utilizing sensitizer activation by ultrasound (US), has been proposed as an alternative to PDT. The advantage of SDT is that US has much lower tissue attenuation compared to visible light, allowing treatment to tumor margins buried deep within the brain and non-invasively through the intact skull. This study evaluates the ability of SDT to inhibit glioma cell invasiveness in a 3D Matrigel matrix glioma cell assay. Glioma cell spheroids were embedded between 2 layers of Matrigel solution. After gelation, the embedded spheroids are incubated in a medium containing sonosensitizer for 18 hours and then exposed to varying intensities and durations of US. Measurements of cell invasion distance were taken 4 days after the spheroids were embedded. SDT significantly inhibited cell invasiveness compared to untreated spheroids and spheroids treated with only US. If administered pre-implantation, SDT also inhibited subsequent cell invasion into the deposited Matrigel matrix. The effects of SDT applied repetitively at lower intensities, had a greater inhibitory effect than single shot treatment. From this experimental study using GBM tumor spheroids, the results demonstrated that SDT significantly inhibited cell invasiveness and cell adhesion and had greater inhibitive effects when administered in repetitive form.