Sonodynamic Therapy for Gliomas. Perspectives and Prospects of Selective Sonosensitization of Glioma Cells

Malignant glial tumors (gliomas) are the second (after cerebral stroke) cause of death from diseases of the central nervous system. The current routine therapy, involving a combination of tumor resection, radio-, and chemo-therapy, only modestly improves survival. Sonodynamic therapy (SDT) has been broadly defined as a synergistic effect of sonication applied in combination with substances referred to as "sonosensitizers". The current review focuses on the possibility of the use of tumor-seeking sonosensitizers, in particular 5-aminolevulinic acid, to control recurring gliomas. In this application, SDT employs a principle similar to that of the more widely-known photodynamic therapy of superficially located cancers, the difference being the use of ultrasound instead of light to deliver the energy necessary to eliminate the sensitized malignant cells. The ability of ultrasound to penetrate brain tissues makes it possible to reach deeply localized intracranial tumors such as gliomas. The major potential advantage of this variant of SDT is its relative non-invasiveness and possibility of repeated application. Until now, there have been no clinical data regarding the efficacy and safety of such treatment for malignant gliomas, but the preclinical data are encouraging.