Preclinical data highlight AZD1390 as a potentially powerful new therapy to enhance brain tumor patient responses to radiotherapy.

AZD0156 is a potent and selective, bioavailable inhibitor of ataxia-telangiectasia mutated (ATM) protein, a signaling kinase involved in the DNA damage response. We present preclinical data demonstrating abrogation of irradiation-induced ATM signaling by low doses of AZD0156, as measured by phosphorylation of ATM substrates. AZD0156 is a strong radiosensitizer in vitro, and using a lung xenograft model, we show that systemic delivery of AZD0156 enhances the tumor growth inhibitory effects of radiation treatment in vivo. Because ATM deficiency contributes to PARP inhibitor sensitivity, preclinically, we evaluated the effect of combining AZD0156 with the PARP inhibitor olaparib. Using ATM isogenic FaDu cells, we demonstrate that AZD0156 impedes the repair of olaparib-induced DNA damage, resulting in elevated DNA double-strand break signaling, cellcycle arrest, and apoptosis. Preclinically, AZD0156 potentiated the effects of olaparib across a panel of lung, gastric, and breast cancer cell lines in vitro, and improved the efficacy of olaparib in two patient-derived triple-negative breast cancer xenograft models. AZD0156 is currently being evaluated in phase I studies (NCT02588105).

Physical and chemical agents that induce DNA double-strand breaks (DSBs) are among the most potent mutagens. The mammalian cell response to DSB comprises a highly co-ordinated, yet complex network of proteins that have been categorized as sensors, signal transducers, mediators and effectors of damage and repair. While this provides an accessible classification system, review of the literature indicates that many proteins satisfy the criteria of more than one category, pointing towards a series of highly co-operative pathways with overlapping function. In summary, the MRE11-NBS1-RAD50 complex is necessary for achieving optimal activation of ataxia-telangiectasia-mutated (ATM) kinase, which catalyses a phosphorylation-mediated signal transduction cascade. Among the subset of proteins phosphorylated by ATM are histone H2AX (H2AX), mediator of damage checkpoint protein 1, nibrin (NBS1), P53-binding protein 1 and breast cancer protein 1, all of which subsequently redistribute into DSB-containing sub-nuclear compartments. Post-translational modification of DSB responding proteins achieves a rapid and reversible change in protein behaviour and mediates damage-specific interactions, hence imparting a high degree of vigilance to the cell. This review highlights events fundamental in maintaining genetic integrity with emphasis on early stages of the DSB response.

Inhibition of ataxia-telangiectasia mutated (ATM) during radiotherapy of glioblastoma multiforme (GBM) may improve tumor control by short-circuiting the response to radiation-induced DNA damage. A major impediment for clinical implementation is that current inhibitors have limited central nervous system (CNS) bioavailability; thus, the goal was to identify ATM inhibitors (ATMi) with improved CNS penetration. Drug screens and refinement of lead compounds identified AZ31 and AZ32. The compounds were then tested for efficacy and impact on tumor and healthy brain. Both AZ31 and AZ32 blocked the DNA damage response and radiosensitized GBM cells AZ32, with enhanced blood-brain barrier (BBB) penetration, was highly efficient as radiosensitizer in syngeneic and human, orthotopic mouse glioma model compared with AZ31. Furthermore, human glioma cell lines expressing mutant p53 or having checkpoint-defective mutations were particularly sensitive to ATMi radiosensitization. The mechanism for this p53 effect involves a propensity to undergo mitotic catastrophe relative to cells with wild-type p53., apoptosis was >6-fold higher in tumor relative to healthy brain after exposure to AZ32 and low-dose radiation. AZ32 is the first ATMi with oral bioavailability shown to radiosensitize glioma and improve survival in orthotopic mouse models. These findings support the development of a clinical-grade, BBB-penetrating ATMi for the treatment of GBM. Importantly, because many GBMs have defective p53 signaling, the use of an ATMi concurrent with standard radiotherapy is expected to be cancer-specific, increase the therapeutic ratio, and maintain full therapeutic effect at lower radiation doses. .

Four poly(ADP-ribose) polymerase (PARP) inhibitors have now presented phase 3 monotherapy data showing compelling benefit of targeting tumours enriched with DNA damage response (DDR) pathway deficiencies, including BRCA gene mutations. Indirect treatment comparisons using the published clinical data from these late stage trials suggest similar levels of monotherapy efficacy are observed in spite of reported differences in PARP trapping potency. However, there is greater diversity in the observed safety profiles. To try and understand these observations, we have carried out a head-to-head comparison of these four PARP inhibitors (olaparib, niraparib, rucaparib and talazoparib) as well as veliparib, which recently reported phase 3 chemotherapy combination data. In our studies, we included an assessment of molecular mechanism of action that included PAR inhibition, PARP trapping and synthetic lethality in isogenic BRCA mutant and wild type models. In addition, an assessment of selectivity in terms of both inhibition of PARP family members using a novel chemoproteomic approach, as well as secondary (off-target) activities was performed. Finally, effects on human haematopoietic stem cell viability and bio-distribution to bone marrow in the rat were tested and compared. A detailed correlation of our datasets with the observed clinical results, including adverse events, suggests these preclinical experiments provide an excellent predictor of clinical response and could be used to assess emerging as well as novel PARP inhibitors. OlaparibVeliparibRucaparibNiraparibTalazoparibCompanyAZAbbVieClovisTesaroPfizerPhaseApprovedIIIApprovedApprovedIIIPARP1 SPR Kd (µM)0.0010.0070.0010.0130.002PARP2 SPR Kd (µM)0.0010.0140.0230.0430.005PARPs with Proteomic Kd <1 µM1,2,3,4,131,2,3,4,131,2,3,4,10,131,2,131,2,3,4,5a,13, 16Sec. Pharm. #, top hit µM0/855/85 5HT7, 0.513/85 5HT4, 0.517/84 DAT, 0.040/85Monotherapy dose (mg)300 bd (tablet)500 bd600 bd300 od1 od Citation Format: Elisabetta Leo, Jeffrey Johannes, Giuditta Illuzzi, Andrew Zhang, Paul Hemsley, Michal J. Bista, Jonathan P. Orme, Verity A. Talbot, Ana J. Narvaez, Elizabeth Underwood, Andrew Pike, Jenni K. Nikkila, Lucy Riches, Sinbad Sweeney, Frida Gustafsson, Anna Cronin, Piero Ricchiuto, Debora A. Roaquin, Fiona Pachl, Eric Miele, Ruth MacDonald, Glen Hawthorne, Andrew N. Mead, Mark J. O'Connor. A head-to-head comparison of the properties of five clinical PARP inhibitors identifies new insights that can explain both the observed clinical efficacy and safety profiles [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr LB-273.