Abstract
Glioblastoma is the deadliest adult brain cancer and all patients ultimately succumb to the disease. Radiation therapy (RT) provides survival benefit of 6 months over surgery alone but these results have not improved in decades. We report that radiation induces a glioma-initiating cell phenotype and identified trifluoperazine (TFP) as a compound that interferes with this phenotype conversion. TFP caused loss of radiation-induced Nanog mRNA expression, activation of GSK3 with consecutive post-translational reduction in p-Akt, Sox2 and β-catenin protein levels. TFP did not alter the intrinsic radiation sensitivity of glioma-initiating cells (GICs). Continuous treatment with TFP and a single dose of radiation reduced the number of GICs in vivo and prolonged survival in syngeneic and patient-derived orthotopic xenograft (PDOX) mouse models of glioblastoma. Our findings suggest that combination of a dopamine receptor antagonist with radiation enhances the efficacy of RT in glioblastoma by preventing radiation-induced phenotype conversion of radiosensitive non-GICs into treatment resistant, induced GICs.
Significance Glioblastoma is the most common and most deadly adult brain cancer. The current standard-of-care is surgery followed by RT and temozolomide, which results in a medium survival time of only 15 months. The efficacy of chemotherapies and targeted therapies in glioblastoma is very limited because most of these drugs do not pass the blood-brain-barrier. Ultimately, all patients succumb to the disease. Our study describes radiation-induced cellular plasticity as a novel resistance mechanism in glioblastoma. We identified a dopamine receptor antagonist as a readily available, FDA-approved drug, known to penetrate the blood-brain-barrier, which prevents phenotype conversion of glioma cells into glioma-initiating cells and prologs survival in mouse models of glioblastoma, thus suggesting that it will improve the efficacy RT without increasing toxicity.