The effects of extra high dose rate irradiation on glioma stem-like cells

Abstract

Radiation therapy is an integral part of treatment for patients with glioblastoma. New technological advances in linear accelerators have made extra-high dose rate irradiation possible. This shortens patient treatment time significantly compared to standard dose rate irradiation, but the biologic effects of extra high dose rate irradiation are poorly understood. Glioma stem-like cells (GSCs) are resistant to standard radiation and contribute to tumor progression. Here, we assess the therapeutic effect of extra high dose rate vs. standard dose rate irradiation on GSCs. GSCs were exposed to 2, 4 and 6 Gy X-irradiation at dose rates of 4.2 Gy/min or 21.2 Gy/min (400 monitoring units (MU)/min or 2100 MU/min). We analyzed cell survival with cell growth assays, tumorsphere formation assays and colony formation assays. Cell kill and self-renewal were dependent on the total dose of radiation delivered. However, there was no difference in survival of GSCs or DNA damage repair in GSCs irradiated at different dose rates. GSCs exhibited significant G1 and G2/M phase arrest and increased apoptosis with higher doses of radiation but there was no difference between the two dose rates at each given dose. In a GSC-derived preclinical model of glioblastoma, radiation extended animal survival, but there was no difference in survival in mice receiving different dose rates of radiation. We conclude that GSCs respond to larger fractions of radiation, but extra high dose rate irradiation has no significant biologic advantage in comparison with standard dose rate irradiation.

Effectiveness of Flattening-Filter-Free versus Flattened Beams in V79 and Glioblastoma Patient-Derived Stem-like Cells

“…Hao et al [ 34 ] have assessed the therapeutic effect of 2, 4, and 6 Gy X-irradiation at dose rates of 4.2 Gy/min or 21.2 Gy/min on GSCs isolated from xenografts. The authors analyzed different endpoints (i.e., cell viability, tumor sphere formation, clonogenic survival, cell cycle apoptosis, and DNA damage).…”

Use of a Linear Accelerator for Conducting In Vitro Radiobiology Experiments

“…Because most patients are treated with high energy X-rays from linear accelerators, studies examining the biologic effects of a large range of dose rates performed on linear accelerators may be readily applied to patients. There have been several reports applying linear accelerators to radiation biology research, but results are mixed and additional studies are needed 13,14,15,16,19 .…”

“…There have been several studies that illustrate both dose and dose rate effects 12,13,14,15,16,17 . In these studies, both gamma-irradiation generated from radioactive isotopes or X-rays generated from linear accelerators were used.…”

“…A variety of cell lines representing lung cancer, cervical cancer, glioblastoma, and melanoma were used. Radiation effects on cell survival, cell cycle arrest, apoptosis and DNA damage were evaluated as readouts 12,13,14,15,16,17 . Here, we describe a method to define the biological effects of clinically relevant radiation dose and dose rates by delivering X-ray based radiation using a linear accelerator.…”

“…NOTE: Here, we show a representative cell cycle analysis 16 as an example of a biological assay following irradiation.…”