Advancing Radioimmunotherapy for Brain Tumors Using In Vitro Assays

Abstract

Purpose: Glioblastoma is the most common and malignant primary brain tumor. Due to factors including resistance to treatment, local invasion, and high risk of recurrence, glioblastoma patient prognoses are often dismal, with median survival around 15 months. The current standard of care consists of radiation therapy and concurrent or adjuvant chemotherapy with temozolomide (TMZ). However, patient survival has only marginally improved, sounding a call for improved therapy for glioblastoma. More recently, triumphs using anticancer agents acting as immune-checkpoint inhibitors have garnered interest toward applying these agents to glioblastoma. One such agent, durvalumab, is undergoing phase I and II clinical trials in radioimmunotherapy for recurrent glioblastoma and high-grade glioma. However, with high potential may also exist unforeseen effects which may affect treatment outcomes. The purpose of this work is to bring these agents used in radioimmunotherapy applications to in vitro systems, where effects may be better observed, with the goal of developing effective combination modalities for glioblastoma, which has a 5-10% 5-year survival rate. Methods: Using a Faxitron CellRad cell irradiator and a commercially-available Electric Cell Impedance Sensor (ECIS), we quantified cell migration following the combination of radiotherapy and chemotherapy and now focus on the combination of radiotherapy and immunotherapy with durvalumab, a PD-L1 immune checkpoint inhibitor. Using clonogenic assays, we quantified glioblastoma cell survival following treatment with radioimmunotherapy. Results: Irradiated T98-G and U87 MG cells (glioblastoma) migrate significantly more (p<0.01) than untreated cells in the first 20-40 hours posttreatment, and the addition of chemotherapy increased migration rates for T98-G at the 5 Gy radiation dose (p<0.05). Treatment with durvalumab, however, did not significantly affect cell migration. Increased radiation dose led to increased cell death for T98-G (p<0.001) as measured using clonogenic assays, but the addition of TMZ and durvalumab did not significantly affect cell survival. Conclusions: Our results suggest that ECIS, morphometric analysis, and clonogenic assays can be used to explore effects of immunotherapy and radiotherapy on cell migration, aiding in the determination of effective therapeutic windows for glioblastoma while detecting changes to cell behavior. The methods used in this work may be applied to further studies in the interactions of radioimmunotherapy at the cellular level and may develop further to directly compare multimodal treatment strategies for determination of optimal treatment techniques.