Combined PARP and ATR inhibition potentiates genome instability and cell death in ATM-deficient cancer cells

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.

DNA Repair and Ovarian Carcinogenesis: Impact on Risk, Prognosis and Therapy Outcome

“…Recent in vitro study on PARPi-resistant OvC cell lines from Burgess et al [207] confirms these results with ATR inhibitor VE-821, making treatment with ATRi a new promising approach to overcome PARPi-resistance in HR-deficient OvC. ATR inhibitor AZD6738 in combination with PARPi has revealed higher efficiency than PARPi alone [208,209]. Olaparib-approved by FDA and EMA for use in OvC therapy [144] Rucaparib-approved by FDA and EMA for use in OvC therapy [144] Niraparib-approved by FDA and EMA for use in OvC therapy [144] Veliparib-advanced clinical trials in combination with carboplatin and paclitaxel.…”

“…The CHEK1i V158411, PF-477736 and AZD7762 inhibited the proliferation of OvC cells [202] AZD7762 in combination with cisplatin suggested synergistic effects in ovarian clear cell carcinoma cell lines in vitro and suppressed growth of tumors in vivo [203] Prexasertib-effective in monotherapy in PARPi-resistant HGSOC cell lines and mouse xenografts [204] Combination of prexasertib mesylate monohydrate (LY2606368), a CHEK1 and CHEK2 inhibitor, and a PARPi, olaparib synergistically decreased cell viability in HGSOC cell lines (OVCAR3, OV90, PEO1 and PEO4) cell lines and induced greater DNA damage and apoptosis than the control and/or monotherapies [204,211] Prexasertib-effective in clinical phase II study in recurrent HGSOC [201] ATRi ATRi (VE-821, VE-822, AZ20) resensitized PARPi-resistant BRCA1-mutated human OvC cell line to PARPi [206] AZD6738 efficient in in ATM-deficient cells and in vivo in PDX mouse models with complete ATM loss [208] Combination PARPi with ATRi (AZD6738) and CHEK1i (MK8776) is more effective than PARPi alone in reducing tumor burden in BRCA1/2 mutated HGSOC cells and PDX models [209] Ongoing clinical PhaseII CAPRI Study of ATRi AZD6738 (ceralasertib) in combination with PARPi olaparib in HGSOC patients [212] ATMi ATMi KU55933 enhanced the response to ionizing radiation in A2780 and OVCAR3 OvC cells [213] WEE1i…”

Maintenance Therapy for ATM-Deficient Pancreatic Cancer by Multiple DNA Damage Response Interferences after Platinum-Based Chemotherapy

“…Moreover, it ablated already present metastases in the liver after FOLFIRINOX induction in line with the abrogation of escaper clones being more invasive. Therefore one might speculate that the triple inhibition of PARP, ATR, and DNA-PKcs in an HR deficient context could prevent the observed selection process upon prolonged FOLFIRINOX, probably by increasing DNA damage beyond a tolerable threshold due to the sensitizing effects of FOLFIRINOX [19]. This ablation of any escaper clones is likely responsible for reduced metastatic burden [36].…”

Targeting the DNA Damage Response to Overcome Cancer Drug Resistance in Glioblastoma

“…As discussed above for ATMi, also ATRi are able to increase toxicity more powerfully in cancer cells lacking ATM or that display a mutated form of p53 [ 54 , 55 , 56 ]. Coherently, ATM deficiency is one of the most advantageous biomarkers used for patient’s selection in clinical trials employing ATRi [ 40 , 49 , 57 ].…”