Abstract
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.
Highlights
Supplementary information The online version of this article contains supplementary material, which is available to authorized users.Cambridge, UK 5 Quantitative Biology, Discovery Science, Oncology R&D, AstraZeneca, Cambridge, UK 6 Research and Early Development, Oncology R&D, AstraZeneca, Cambridge, UKInhibitors of core proteins involved in the DNA damage response (DDR) are being explored for their potential to selectively target cancer cells, such as by exploiting their high mutational burden and the principle of synthetic lethality [1,2,3]
We assessed the cytotoxicity of olaparib in combination with inhibitors against ataxiatelangiectasia mutated (ATM) (AZD0156), ATR (AZD6738) and WEE1 (AZD1775), across a panel of cell lines to identify synergistic combinations selective for genetic backgrounds including those with homologous recombination repair (HRR)- and ATM deficiencies (Fig. 1a and Supplementary Fig. 1A)
Abrogated ATM signalling in response to ionising radiation (IR), assessed by auto-phosphorylated ATM and phospho-KAP1, was observed in both the FaDu ATM-KO and NCIH23 cells, compared with functional signalling in their WT counterpart cells (Supplementary Fig. 2), suggesting that olaparib/AZD6738 combination activity is associated with
Summary
Inhibitors of other DDR factors are in development, including those targeting ATM, ataxia-telangiectasia mutated and Rad3-related (ATR), and DNA-dependent protein kinase (DNA-PK) These are fundamental kinases involved in the detection, signalling and DNA repair pathway choice, alongside regulating DDR processes including DNA damage checkpoint activation, senescence and apoptosis [16]. ATM-deficient cells are hypersensitive to ATR inhibition, at least partly due to a greater dependency on ATR for DNA repair and checkpoint control [27,28,29] This presents a clinical opportunity as ATM inactivation has been reported in a high proportion of metastatic prostate, lung, haematological, gastric and colorectal tumours [11, 30, 31]. We demonstrate that generation of mitosis-associated DNA damage and commitment to apoptosis occur earlier and at lower concentrations following combination treatment than with either single-agent, providing mechanistic insight and rationale for exploring combined PARP and ATR inhibition in the clinic
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