UVB-induced lesions in mammalian cellular DNA can, through the process of mutagenesis, lead to carcinogenesis. However, eukaryotic cells have evolved complex mechanisms of genomic surveillance and DNA damage repair to counteract the effects of UVB radiation. We show that following UVB DNA damage, there is an overall inhibition of protein synthesis and translational reprogramming. This reprogramming allows selective synthesis of DDR proteins, such as ERCC1, ERCC5, DDB1, XPA, XPD, and OGG1 and relies on upstream ORFs in the 59 untranslated region of these mRNAs. Experiments with DNA-PKcs-deficient cell lines and a specific DNA-PKcs inhibitor demonstrate that both the general repression of mRNA translation and the preferential translation of specific mRNAs depend on DNA-PKcs activity, and therefore our data establish a link between a key DNA damage signaling component and protein synthesis.[Keywords: DNA damage; translation; upstream ORF] Supplemental material is available at http://www.genesdev.org.

The poly (ADP-ribose) polymerase (PARP) inhibitor olaparib is FDA approved for the treatment of BRCA-mutated breast, ovarian and pancreatic cancers. Olaparib inhibits PARP1/2 enzymatic activity and traps PARP1 on DNA at single-strand breaks, leading to replication-induced DNA damage that requires BRCA1/2-dependent homologous recombination repair. Moreover, DNA damage response pathways mediated by the ataxia-telangiectasia mutated (ATM) and ataxia-telangiectasia mutated and Rad3-related (ATR) kinases are hypothesised to be important survival pathways in response to PARP-inhibitor treatment. Here, we show that olaparib combines synergistically with the ATR-inhibitor AZD6738 (ceralasertib), in vitro, leading to selective cell death in ATM-deficient cells. We observe that 24 h olaparib treatment causes cells to accumulate in G2-M of the cell cycle, however, co-administration with AZD6738 releases the olaparib-treated cells from G2 arrest. Selectively in ATM-knockout cells, we show that combined olaparib/AZD6738 treatment induces more chromosomal aberrations and achieves this at lower concentrations and earlier treatment time-points than either monotherapy. Furthermore, single-agent olaparib efficacy in vitro requires PARP inhibition throughout multiple rounds of replication. Here, we demonstrate in several ATM-deficient cell lines that the olaparib and AZD6738 combination induces cell death within 1-2 cell divisions, suggesting that combined treatment could circumvent the need for prolonged drug exposure. Finally, we demonstrate in vivo combination activity of olaparib and AZD6738 in xenograft and PDX mouse models with complete ATM loss. Collectively, these data provide a mechanistic understanding of combined PARP and ATR inhibition in ATM-deficient models, and support the clinical development of AZD6738 in combination with olaparib.

DNA damage checkpoint kinases ATR and WEE1 are among key regulators of DNA damage response pathways protecting cells from replication stress, a hallmark of cancer that has potential to be exploited for therapeutic use. ATR and WEE1 inhibitors are in early clinical trials and success will require greater understanding of both their mechanism of action and biomarkers for patient selection. Here, we report selective antitumor activity of ATR and WEE1 inhibitors in a subset of non-germinal center B-cell (GCB) diffuse large B-cell lymphoma (DLBCL) cell lines, characterized by high MYC protein expression and CDKN2A/B deletion. Activity correlated with the induction of replication stress, indicated by increased origin firing and retardation of replication fork progression. However, ATR and WEE1 inhibitors caused different amounts of DNA damage and cell death in distinct phases of the cell cycle, underlying the increased potency observed with WEE1 inhibition. ATR inhibition caused DNA damage to manifest as 53BP1 nuclear bodies in daughter G 1 cells leading to G 1 arrest, whereas WEE1 inhibition caused DNA damage and arrest in S phase, leading to earlier onset apoptosis. In vivo xenograft DLBCL models confirmed differences in single-agent antitumor activity, but also showed potential for effective ATR inhibitor combinations. Importantly, insights into the different inhibitor mechanisms may guide differentiated clinical development strategies aimed at exploiting specific vulnerabilities of tumor cells while maximizing therapeutic index. Our data therefore highlight clinical development opportunities for both ATR and WEE1 inhibitors in non-GCB DLBCL subtypes that represent an area of unmet clinical need.Significance: ATR and WEE1 inhibitors demonstrate effective antitumor activity in preclinical models of DLBCL associated with replication stress, but new mechanistic insights and biomarkers of response support a differentiated clinical development strategy.

Background AZD0156 and AZD6738 are potent and selective inhibitors of ataxia-telangiectasia-kinase (ATM) and ataxia-telangiectasia-mutated and Rad3-related (ATR), respectively, important sensors/signallers of DNA damage. Methods We used multiplexed targeted-mass-spectrometry to select pRAD50(Ser635) as a pharmacodynamic biomarker for AZD0156-mediated ATM inhibition from a panel of 45 peptides, then developed and tested a clinically applicable immunohistochemistry assay for pRAD50(Ser635) detection in FFPE tissue. Results We found moderate pRAD50 baseline levels across cancer indications. pRAD50 was detectable in 100% gastric cancers ( n = 23), 99% colorectal cancers ( n = 102), 95% triple-negative-breast cancers (TNBC) ( n = 40) and 87.5% glioblastoma-multiformes ( n = 16). We demonstrated AZD0156 target inhibition in TNBC patient-derived xenograft models; where AZD0156 monotherapy or post olaparib treatment, resulted in a 34–72% reduction in pRAD50. Similar inhibition of pRAD50 (68%) was observed following ATM inhibitor treatment post irinotecan in a colorectal cancer xenograft model. ATR inhibition, using AZD6738, increased pRAD50 in the ATM-proficient models whilst in ATM-deficient models the opposite was observed, suggesting pRAD50 pharmacodynamics post ATR inhibition may be ATM-dependent and could be useful to determine ATM functionality in patients treated with ATR inhibitors. Conclusion Together these data support clinical utilisation of pRAD50 as a biomarker of AZD0156 and AZD6738 pharmacology to elucidate clinical pharmacokinetic/pharmacodynamic relationships, thereby informing recommended Phase 2 dose/schedule.

AZD6738 (ceralasertib) is a potent and selective orally bioavailable inhibitor of ataxia telangiectasia and rad3-related (ATR) kinase. ATR is activated in response to stalled DNA replication forks to promote G2/M-cell cycle checkpoints and fork restart. Here, we found AZD6738 modulated CHK1 phosphorylation and induced ATM-dependent signaling (pRAD50) and the DNA damage marker γH2AX. AZD6738 inhibited breakinduced replication (BIR) and homologous recombination repair (HRR). In vitro sensitivity to AZD6738 was elevated in, but not exclusive to, cells with defects in the ATM-pathway or that harbor putative drivers of replication stress such as CCNE1amplification. This translated to in vivo anti-tumor activity, with tumor control requiring continuous dosing and free plasma exposures which correlated with induction of pCHK1, pRAD50, and γH2AX. AZD6738 showed combinatorial efficacy with agents associated with replication fork stalling and collapse such as carboplatin and irinotecan and the PARP inhibitor olaparib. These combinations required optimisation of dose and schedules in vivo and showed superior anti-tumor activity at lower doses compared to that required for monotherapy. Tumor regressions required at least 2 days of daily dosing of AZD6738 concurrent with carboplatin, while twicedaily dosing was required following irinotecan. In a BRCA2-mutant patient-derived triple-negative breast cancer (TNBC) xenograft model, complete tumor regression was achieved with 3-5 days of daily AZD6738 per week concurrent with olaparib. Increasing olaparib dosage or AZD6738 dosing to twice-daily allowed complete tumor regression even in a BRCA wild-type TNBC xenograft model. These preclinical data provide rationale for clinical evaluation of AZD6738 as a monotherapy or combinatorial agent.

Barasertib (AZD1152), a pro-drug of the highly potent and selective Aurora B kinase inhibitor AZD2811, showed promising clinical activity in relapsed/refractory diffuse large B-cell lymphoma (DLBCL) patients administered as a 4-day infusion. To improve potential therapeutic benefit of Aurora B kinase inhibition, a nanoparticle formulation of AZD2811 has been developed to address limitations of repeated intravenous infusion. One of the challenges with the use of nanoparticles for chronic treatment of tumors is optimizing dose and schedule required to enable repeat administration to sustain tumor growth inhibition. AZD2811 gives potent cell growth inhibition across a range of DLBCL cells lines in vitro. In vivo, repeat administration of the AZD2811 nanoparticle gave antitumor activity at half the dose intensity of AZD1152. Compared with AZD1152, a single dose of AZD2811 nanoparticle gave less reduction in pHH3, but increased apoptosis and reduction of cells in G1 and G 2 -M, albeit at later time points, suggesting that duration and depth of target inhibition influence the nature of the tumor cell response to drug. Further exploration of the influence of dose and schedule on efficacy revealed that AZD2811 nanoparticle can be used flexibly with repeat administration of 25 mg/kg administered up to 7 days apart being sufficient to maintain equivalent tumor control. Timing of repeat administration could be varied with 50 mg/kg every 2 weeks controlling tumor control as effectively as 25 mg/kg every week. AZD2811 nanoparticle can be administered with very different doses and schedules to inhibit DLBCL tumor growth, although maximal tumor growth inhibition was achieved with the highest dose intensities.

Bruton tyrosine kinase (BTK) is an essential kinase in the B-cell receptor (BCR) signalling pathway. Acalabrutinib is a potent and highly selective irreversible BTK inhibitor that received accelerated approval by FDA for the treatment of Relapsed/Refractory Mantle Cell Lymphoma. It is proposed to be combined with the Ataxia telangiectasia and Rad3-related (ATR) kinase inhibitor AZD6738, in a Phase I/II proof of concept clinical trial to assess safety and efficacy in patients with B-cell malignancies. ATR is a key regulator of DNA replication, repair and cell cycle checkpoints. The Activated B-Cell (ABC) subtype of Diffuse Large B-Cell Lymphoma (DLBCL) is associated with chronic active BCR signalling, and given our previous identification of sensitivity to AZD6738 in ABC-DLBCL cell lines, we hypothesised that combination with acalabrutinib may have additional therapeutic benefit. Here we report preliminary data to support combination efficacy in models of ABC-type DLBCL. The growth inhibitory and cell kill effect of AZD6738 and acalabrutinib in combination was assessed in 3 ABC and 4 GCB DLBCL cell lines. Combination activity and cell kill was detected specifically in the ABC-type TMD8 cell line. Using flow cytometry, we show that the cell kill effects of the drug combination were dependent on dose and schedule. Single agent treatment with 5 nM acalabrutinib or 0.5 µM AZD6738 for 72 h, caused cell death in 12% and 17% of cells respectively. The equivalent doses given in combination for 72 h induced cell death in 39% of cells, indicative of a greater than additive effect. Cell killing was increased with longer co-exposure to the combination, shown by an increase in cell death from 18% at 24 h, to 30% at 48 h. Acalabrutinib is dosed on a BID schedule, thus we tested whether its activity in combination with AZD6738 was affected by pre- or post-addition of acalabrutinib. A 24 h pre-treatment of cells with acalabrutinib, followed by the combination of AZD6738 and acalabrutinib for 48 h resulted in 20% cell death, whereas 48 h combination treatment followed by 24 h acalabrutinib monotherapy caused a similar 27% increase in death, suggesting that combination efficacy is not dependent on sequence of drug administration. Furthermore, the mRNA expression of BTK target genes in ABC-DLBCL cell lines was modulated by acalabrutinib, however there was no additional modulation to this pathway by the combination with AZD6738, suggesting the two agents kill cells through different mechanisms of action. In the TMD8 xenograft mouse model, daily dosing of AZD6738 (25 mg/kg) with twice daily dosing of acalabrutinib (20 mg/kg) was well tolerated and resulted in complete and durable tumor regressions (8/8 tumors), whereas single agent treatments resulted in tumor growth delay. Collectively, our preliminary data support a rationale for combining BTK and ATR inhibitors for an effective and alternative treatment option in ABC-DLBCL. Citation Format: Lucy A. Young, Oona Delpuech, Brandon Willis, Alexandra Bussey, Zena Wilson, Michelle Dupont, Carlos Grajales, Andrew Bloecher, Todd Covey, Kate Wills, Alan Lau, Simon J. Hollingsworth. Preclinical efficacy of the ATR inhibitor AZD6738 in combination with the BTK inhibitor acalabrutinib in ABC-DLBCL models [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-263.

The poly(ADP-ribose polymerase) (PARP) inhibitor olaparib is FDA approved for the treatment of BRCA-mutated ovarian cancers. Olaparib inhibits PARP function during DNA single-strand-break repair and also by trapping of PARP on DNA to create lesions. These complexes cause replication-associated DNA damage including stalling and collapse of DNA replication forks. Cells which have lost BRCA1/2-dependent homologous recombination repair are highly sensitive to olaparib. In addition, other DNA damage response (DDR) pathways mediated by the ataxia telangiectasia mutated (ATM) and ataxia telangiectasia mutated and Rad3-related (ATR) kinases are hypothesised to be important survival pathways in response to PARP inhibitor treatment. Here we show that olaparib combines synergistically with the orally bioavailable ATR inhibitor AZD6738, in vitro, leading to cell death in ATM-deficient backgrounds. The growth inhibitory and cell kill effect of a range of concentrations of AZD6738 (0.01-1 µM) and olaparib (0.03-3 µM) were assessed using the Loewe model of additivity in the isogenic ATM knockout (KO) and wildtype (WT) FaDu head and neck cancer cell lines. The combination of AZD6738 and olaparib induced cell death in the ATM KO cells across a wide range of concentrations, with 3 µM olaparib plus 1 µM AZD6738 inducing 84% cell kill, in contrast to only 37% growth inhibition in the ATM WT cells. The observed combination synergy in the ATM KO cells is a result of increased DNA replication-associated DNA damage together with abrogation of the G2-M checkpoint activated by olaparib. Olaparib treatment led to a 10 and 20% increase in G2 cells at 24 hours in the ATM KO and ATM WT FaDu cell lines respectively, however co-administration of AZD6738 (0.1-0.3 µM) completely released the olaparib treated cells from the G2 arrest. DNA metaphase spread analysis showed that combination treatment with olaparib (1 µM) plus AZD6738 (0.1 µM) in the ATM KO cells caused 12.8 chromosomal DNA aberrations per cell compared to 4.4 or 3.3 aberrations per cell when treated with olaparib or AZD6738 alone respectively (n = 2). In contrast, in the ATM WT cells the olaparib plus AZD6738 combination treatment caused only 1.5 chromosomal aberrations per cell. Collectively, these data show that olaparib-induced DNA damage activates an ATR-dependent G2-M checkpoint allowing time to repair damaged DNA, and that AZD6738 abrogates this checkpoint, permitting cells to undergo mitosis in the presence of DNA damage leading to increased chromosomal aberrations. These data provide a mechanistic understanding of the combination and supports the clinical line of sight for the development of AZD6738 in combination with olaparib. Citation Format: Rebecca Lloyd, Katarynza Falenta, Paul W. Wijnhoven, Christophe Chabbert, Jonathan Stott, James Yates, Alan Y. Lau, Lucy A. Young, Simon J. Hollingsworth. The PARP inhibitor olaparib is synergistic with the ATR inhibitor AZD6738 in ATM deficient cancer cells [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 337.