The efficacy and toxicity of ATM inhibition in glioblastoma initiating cells-driven tumor models.

The Ataxia Telangiectasia Mutated (ATM)-mediated DNA damage response (DDR) is a major mechanism of resistance of glioblastoma (GB) - initiating cells (GICs) to radiotherapy. The closely related Ataxia Telangiectasia and Rad3-related protein (ATR) is also involved in tumor resistance to radio- and chemotherapy. It has been shown that pharmacological inhibition of ATM protein may overcome the DDR-mediated resistance in GICs and significantly radiosensitize GIC-driven GB. Albeit not essential for life as shown by the decade-long lifespan of AT patients, the ATM protein may be involved in a number of important functions other than the response to DNA damage. We discuss our current knowledge about the toxicity of pharmacologic inhibition of ATM and ATR proteins.

Radiosensitization of orthotopic GIC-driven glioblastoma by doxycycline causes skin damage.

Doxycycline (DXC) is a tetracycline antibiotic which has been proposed as a breast cancer radiosensitizer by specifically reducing the expression of the DNA repair enzyme DNA PK in breast cancer initiating cells. Since DXC presents favorable pharmacokinetics properties including the capacity to cross the blood-brain barrier, it has been hypothesized that it could radiosensitize brain tumors as well. We have investigated the radiosensitizing capacity of DXC towards human glioma initiating cells (GIC)-driven orthotopic glioblastomas (GB) in NOD/SCID mice that faithfully mimic the growth properties of the clinical tumors of origin. DXC at 10 mg/Kg body weight was subcutaneously delivered daily, 5 days/week for 4 weeks. At the same time, radiotherapeutic fractions of 0.25 Gy to the head were delivered every 3-4 days (twice/week) for 15 weeks. No survival advantage was observed in DXC-treated mice as compared to vehicle-treated mice by this radiosensitizing protocol. On the contrary, skin damage with hair loss and deep ulcers were observed after 4 weeks in DXC-treated mice leading to discontinuation of drug treatment. These results do not support the use of DXC as a radiosensitizer for brain tumors and indicate skin damage as an important side effect of DXC.

Author Correction: Faithful animal modelling of human glioma by using primary initiating cells and its implications for radiosensitization therapy.

A correction to this article has been published and is linked from the HTML and PDF versions of this paper. The error has been fixed in the paper.

Faithful animal modelling of human glioma by using primary initiating cells and its implications for radiosensitization therapy [ARRIVE 1].

It has been reported that the ATM kinase inhibitor KU60019 preferentially radiosensitizes orthotopic high grade gliomas (HGG) driven by established U87 and U1242 cell lines bearing specific TP53 mutations. We wished to determine whether those results could be extended to tumors driven by primary glioma initiating cells (GIC) that closely mimic clinical tumors. Orthotopic HGG were developed in immunodeficient non-obese diabetic-severe combined immunodeficient (NOD-SCID) mice by intracranial injection of primary GIC isolated from the adult glioblastoma COMI (acronym of patient's name) and the pediatric anaplastic astrocytoma 239/12. Similar to the clinical tumors of origin, the orthotopic tumors COMI and 239/12 displayed different growth properties with a voluminous expansive lesion that exerted considerable mass effect on the adjacent structures and an infiltrating, gliomatosis-like growth pattern with limited compressive attitude, respectively. Significant elongations of median animal survival bearing the adult COMI tumor was observed after one KU60019 convection enhanced delivery followed by total 7.5 Gy of ionizing radiation delivered in fifteen 0.5 Gy fractions, as compared to animals treated with vehicle + ionizing radiation (105 vs 89 days; ratio: 0.847; 95% CI of ratio 0.4969 to 1.198; P:0.0417) [ARRIVE 16]. Similarly, a trend to increased median survival was observed with the radiosensitized pediatric tumor 239/12 (186 vs 167 days; ratio: 0.8978; 95% CI of ratio: 0.5352 to 1.260; P: 0.0891) [ARRIVE 16]. Our results indicate that radiosensitization by KU60019 is effective towards different orthotopic gliomas that faithfully mimic the clinical tumors and that multiple GIC-based animal models may be essential to develop novel therapeutic protocols for HGG transferable to the clinics.

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

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.

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

We have recently reported that glioblastoma (GB)-initiating cells (GIC) with low expression and/or mutation of TP53 and high expression of PI3K ("responder" genetic profile) can be effectively and safely radiosensitized by the ATM inhibitor KU60019. We report here on drug's diffusion and elimination from the animal body and brain, its effects on orthotopic GB and efficacy toward pediatric GIC. Healthy mice were infused by convection enhanced delivery (CED) with KU60019 and the drug kinetics followed by high performance liquid chromatography-mass spectrometry. Already at the end of CED, KU60019 had diffused from the injection site to the ipsilateral and, to a lower extent, controlateral hemisphere. After 24 hr, no drug could be detected all over the brain or in other organs, indicating rapid draining and excretion. After intraperitoneal injection, traces only of KU60019 could be detected in the brain, indicating inability to cross the brain-blood barrier. Consistent with the induction of cell cycle progression previously observed in vitro, KU60019 stimulated proliferation of orthotopic GB cells with the highest effect observed 96 hr after drug delivery. Adult GIC with high expression of TP53 and low expression of PI3K could be radiosensitized by KU60019, although less promptly than GIC bearing the "responder" profile. Consistent with the kinetics of proliferation induction, the highest radiosensitizing effect was observed 96 hr after delivery of KU60019 to GIC. Pediatric GIC could be similarly radiosensitized after exposure to KU60019. The results indicate that ATM inhibition may allow to radiosensitize a wide range of adult and pediatric high-grade gliomas.