We recently showed that the ATM inhibitor (ATMi), KU-60019, is a potent radiosensitizer, the first report published on this novel compound. Briefly, KU-60019 is a very specific ATM kinase inhibitor and superior over its predecessor KU-55933 and shows at least 10-fold better efficacy in vitro for radio sensitizing human glioma cells. In addition, pro-survival signaling through the AKT and ERK pathways is also inhibited by KU-60019. The ATMi does so irrespective of PTEN and p53 status. Our studies also showed that glioma cells migration and invasion in vitro were inhibited to a large extent perhaps by interfering with AKT and ERK signaling in the presence of ATMi. Thus, the potential benefit of KU-60019 as a radiosensitizer for GBM is not limited to its ability to block the DDR and potently radiosensitize glioma cells but also having the ability to inhibit invasion and spread of the cancer. Preclinical testing of KU-60019 as a radiosensitizer for glioma is ongoing. We would now like to determine whether the PARP inhibitor (PARPi) AZD2281/KU-59436 alone, in combination with KU-60019 and/or radiation would show improved therapeutic efficacy in a preclinical glioma model. AZD2281 targets and kills tumor cells with mutations in BRCA1/BRCA2, or cells that are defective in homologous recombination repair (HRR) failing to repair DNA double-strand breaks (DSBs) during replication. Thus, synergistic killing should occur in glioma cells treated with AZD2281 and KU-60019 during DNA synthesis even in the absence of radiation. Low dose radiation (d 2 Gy) is expected to enhance the toxicity to AZD2281 and KU-60019 and further increase killing and promote radiosensitization of cells in S-phase, the most radioresistant cell cycle phase. In fact, our preliminary data show that this multi-pronged approach kills human glioma cells with little to no toxicity to normal cells in co-cultures. Thus, proof-of-principle testing of this strategy in an animal glioma model is warranted. Except for stem cells and neural progenitors (NPs), the brain consists mostly of terminally differentiated cells that do not proliferate. Thus, aggressively growing glial brain tumors residing in the brain parenchyma would be very favorable for therapeutic intervention with AZD2281 in combination with the ATMi with radiation perhaps providing further potentiation. However, it is very important to examine what impact this treatment might have on the NPs so that appropriate steps can be taken to spare normal brain. Little is known about the molecular processes occurring in normal brain in response to radiation but in general it is believed that radiation of neural stem cell compartments results in impaired neurogenesis due to radiation late effects and inflammation. We hope that insights gained from the proposed animal studies will demonstrate proof-of-principle of a novel drug combination strategy for the treatment of GBM that would be effective and safe and with the full support of KuDOS Pharmaceuticals/AstraZeneca can relatively quickly be translated into a clinical trial.
At best, standard treatment of glioblastoma multiforme (GBM) prolongs patient survival by a little more than a year. Thus, there is great need for developing and testing novel therapeutic approaches to combat this dreadful disease. We have developed a multi-pronged strategy targeting invasion, pro-survival signaling as well as DNA repair for treating GBM and now propose to test this approach for proof-of-principle in an animal model.
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