Predictability, efficacy and safety of radiosensitization of glioblastoma-initiating cells by the ATM inhibitor KU-60019

Abstract

We have previously shown that pharmacological inhibition of ataxia telangiectasia mutated (ATM) protein sensitizes glioblastoma-initiating cells (GICs) to ionizing radiation (IR). Herein, we report the experimental conditions to overcome GIC radioresistance in vitro using the specific ATM inhibitor KU-60019, two major determinants of the tumor response to this drug and the absence of toxicity of this treatment in vitro and in vivo. Repeated treatments with KU-60019 followed by IR substantially delayed GIC proliferation in vitro and even eradicated radioresistant cells, whereas GIC treated with vehicle plus radiation recovered early and expanded. The tumor response to the drug occurred under a cutoff level of expression of TP53 and over a cutoff level of expression of phosphatidylinositol 3-kinase (PI3K). No increased clastogenicity or point mutagenicity was induced by KU-60019 plus radiation when compared to vehicle plus radiation. No significant histological changes to the brain or other organs were observed after prolonged infusion into the brain of KU-60019 at millimolar concentrations. Taken together, these findings suggest that GIC-driven tumors with low expression of TP53 and high expression of PI3K might be effectively and safely radiosensitized by KU-60019.Glioblastoma multiforme (GBM) is difficult to eradicate for its highly infiltrating nature and resistance to therapies (reviewed in Ref. 1). Autopsy findings have shown infiltration of tumoral cells even in the contralateral hemisphere, suggesting that GBM may be considered as a "whole brain disorder." 2,3 As a consequence, to eradicate high-grade gliomas we have to treat large portions or even the whole brain. This cannot be done with toxic treatments that would seriously affect patients' cognitive and physiological functions. To specifically target glioma-initiating cells (GICs) we have to

Pharmacokinetics, pharmacodynamics and efficacy on pediatric tumors of the glioma radiosensitizer KU60019

“…In particular, repeated treatments with the ATM inhibitor KU60019 followed by ionizing radiation substantially delay GIC proliferation in vitro and even eradicate radioresistant cells, whereas GIC treated with vehicle plus radiation recover early and expand. 2 Similar results and significant survival improvements of mice bearing orthotopic GB have been reported in two US-and one UKbased studies. [3][4][5] A relationship between tumor response to ATM inhibitors and low levels of TP53 tumor suppressor expression has been described 2,4 but these results have not been confirmed.…”

“…Pediatric GIC were cultured and characterized under the same conditions used for adult GIC. 2 Both 239/12 and 170/OG GIC expressed glial fibrillary acidic protein, vimentin and nestin by immunohistochemistry. Mutation analysis by direct-sequencing and multiplex ligation-dependent probe amplification demonstrated in both 239/12 and 170/OG loss of function mutations in the TP53 tumor suppressor gene.…”

“…2 GIC lines deriving from adult GB have been previously described. 2,6 The pediatric GIC lines 239/12 and 170/OG have been obtained from surgical resection of an anaplastic astrocytoma (WHO grade III) in a 14-year-old male and a GB (WHO grade IV) in a 12-year-old male, respectively. Both patients died because of the tumors within 3 years from the diagnosis.…”

“…2 The dose enhancement ratio (DER) on proliferation curves was determined as following: cell numbers were plotted as a function of time in linear coordinates and the mean proliferation capacity (MPC) was calculated as the area under the proliferation curve by definite integration, using in-housedeveloped software. The ratio MPC IR /MPC KU600191IR gives the radiation DER.…”

“…[1). To specifically target GB-initiating cells (GIC), we 2 and others [3][4][5] have identified a new radiosensitizing procedure. This is based on the capacity of ATM inhibitors such as KU60019 to specifically stimulate proliferation of quiescent GIC.…”