ATR kinase inhibitors NVP-BEZ235 and AZD6738 effectively penetrate the brain after systemic administration

Abstract

Ataxia Telangiectasia and Rad3 related protein (ATR) is a central mediator of the response to DNA damage that may cause the quiescent resistance of cancer initiating cells to genotoxic radiotherapy. NVP-BEZ235 is a dual PI3K/mTOR inhibitor that also effectively targets ATR with IC50 = 21 × 10− 9 M in cells. AZD6738 does not target significantly PI3K/mTOR-related kinases but specifically inhibits ATR with IC50 = 74 × 10− 9 M in cells. Both drugs have been proposed as radiosensitizers of different tumors including glioblastoma (GB), the most malignant brain tumor. In order to study the radiosensitizing properties of ATR inhibitors NVP-BEZ235 and AZD6738 towards GB, we have preliminarily investigated their capacity to penetrate the brain after systemic administration. Tumor-free CD-1 mice were inoculated i.p. with 25 mg/Kg body weight of NVP-BEZ235 or AZD6738. 1, 2, 6 and 8 h later, blood was collected by retro-orbital bleeding after which the mice were euthanized and the brains explanted. Blood and brain samples were then extracted and NVP-BEZ235 and AZD6738 concentrations determined by High Performance Liquid Chromatography/Mass Spectrometry. We found for NVP-BEZ235 and especially for AZD6738, elevated bioavailability and effective brain penetration after intraperitoneal administration. Albeit low drug and radiation dosages were used, a trend to toxicity of NVP-BEZ235 followed by ionizing radiation (IR) towards mice bearing primary glioma initiating cells (GIC)-driven orthotopic tumors was yet observed, as compared to AZD6738 + IR and vehicle+IR. Survival was never improved with median values of 99, 86 and 101 days for vehicle+IR, NVP-BEZ235 + IR and AZD6738 + IR-treated mice, respectively. Although the present results indicate favorable pharmacokinetics properties of ATR inhibitors NVP-BEZ235 and AZD6738, they do not lend support to their use as radiosensitizers of GB.

RETRACTED ARTICLE: The PI3K/mTOR dual inhibitor BEZ235 nanoparticles improve radiosensitization of hepatoma cells through apoptosis and regulation DNA repair pathway

“…Targeted delivery of BEZ235 to tumor tissues and cells is needed to decrease the toxic side effects of BEZ235 and enhance tumor response to irradiation. The radiotherapy resistance of HCC is mainly due to the occurrence of epithelial-mesenchymal transition (EMT) and cross-activation of Ras/Raf and phosphatidylinositol 3kinase (PI3K)/Akt/mTOR pathways in HCC [27,28]; excessive activation of the pathway can enhance HCC cell survival and inhibit cell death. Inhibition of Ras/Raf and PI3K/Akt/mTOR pathways regulates cell cycle of HCC, inhibits cell proliferation, promotes apoptosis, and enhances radiosensitivity of HCC [28][29][30].…”

“…The radiotherapy resistance of HCC is mainly due to the occurrence of epithelial-mesenchymal transition (EMT) and cross-activation of Ras/Raf and phosphatidylinositol 3kinase (PI3K)/Akt/mTOR pathways in HCC [27,28]; excessive activation of the pathway can enhance HCC cell survival and inhibit cell death. Inhibition of Ras/Raf and PI3K/Akt/mTOR pathways regulates cell cycle of HCC, inhibits cell proliferation, promotes apoptosis, and enhances radiosensitivity of HCC [28][29][30]. BEZ235 (PI3K/mTOR pathway inhibitor) causes significant cell death [29][30][31], but low concentrations of the drug in the target tissue results in poor therapeutic efficacy and need for more frequent dosing; on the other hand, high drug concentrations may cause toxicity, including stomatitis, hyperglycemia, non-infectious pneumonia, and immunosuppression.…”

Experimental glioma with high bHLH expression harbor increased replicative stress and are sensitive toward ATR inhibition

“…They induce double strand breaks. Of note, recent data indicate that the ATR inhibitor AZD6738 is able to penetrate the blood brain barrier, 36 and that ATR knockdown leads to significant sensitization to temozolomide in a glioma cell line. 37 This approach has also been studied in other cancers: ATR inhibition with AZD6738 combined with other therapies proved to be synergistic for pancreatic cancer (ATRi and Gemcitabine), 38 Her2-positive breast cancer (ATRi and Cisplatin), 39 and non-small cell lung cancer (ATRi and Cisplatin).…”

Contrast-enhanced, conebeam CT-based, fractionated radiotherapy and follow-up monitoring of orthotopic mouse glioblastoma: a proof-of-concept study

“…Here, we provide proof-of-concept for contrastenhanced, CBCT-based, fractionated radiotherapy and follow-up monitoring of orthotopic mouse glioblastoma with the help of a stand-alone small animal radiotherapy platform with integrated CBCT scanner. The radiation regimen closely resembling glioblastoma radiotherapy in the clinical routine is feasible, well tolerated, and may serve as a basis for combined modality treatment approaches with biologically targeted and/or immunotherapeutic agents in the context of preclinical target validation [20,21]. No other imaging modalities, such as MR, PET, or BL imaging, are needed for tumor localization, treatment planning, dose administration, and/or tumor volume follow-up.…”

“…We have also tested orthotopic xenotransplants of established human glioblastoma cell lines in immunocompromised mice with similar experiences (data not shown). However, the application of this methodology for orthotopic transplants of patient-derived, low-passage-number, glioma stem-like cell isolates which commonly show more invasive growth patterns will require further investigation [20,21,23,24].…”