Targeted suppression of glioma by ultralow-dose x-ray–induced photodynamic therapy and gold-based nanoclusters in preclinical models

The diffuse and infiltrative nature of high-grade gliomas poses ongoing challenges in treatment and management. Radiotherapy is an important glioma treatment, with a standard radiotherapy dose of 60 gray. However, high-dose radiotherapy is associated with radiation-induced side effects on normal tissue. Scintillator-mediated low-dose x-ray–induced photodynamic therapy using kilovoltage x-rays has been shown to be effective for multiple tumor types without causing damage to healthy tissue. However, x-ray–induced photodynamic therapy is yet to be explored in glioma because of the inability of the photosensitizers to cross the blood-brain barrier. Here, we present an integrated gold clustoluminogen containing protein-protected gold nanoclusters conjugated to a photosensitizer and a cell-penetrating peptide. Using intravital imaging, we showed that gold clustoluminogen crossed the intact blood-brain barrier in healthy animals and accumulated in tumors in two murine intracranial orthotopic glioma models. Gold clustoluminogen efficiently suppressed glioma growth and prolonged animal survival under ultralow-dose x-ray treatment (total 2 gray, megavoltage x-ray) using the same protocol as that used for clinical megavoltage radiotherapy. Moreover, gold clustoluminogen potently inhibited tumor growth in an orthotopic patient-derived xenograft glioma model with prolonged animal survival under ultralow-dose x-ray treatment. Gold clustoluminogen was eliminated through hepatic and renal excretion, with no observed toxicity. These results highlight new opportunities to develop clinically relevant glioma therapies with reduced side effects.