Abstract 337: The PARP inhibitor olaparib is synergistic with the ATR inhibitor AZD6738 in ATM deficient cancer cells

Abstract

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.

Discovery and Characterization of AZD6738, a Potent Inhibitor of Ataxia Telangiectasia Mutated and Rad3 Related (ATR) Kinase with Application as an Anticancer Agent

“…The observed levels are expected to drive significant ATR inhibition, with cover increasing in a dose dependent manner up to ATR IC 96 . Preclinical work has demonstrated further potential for combination therapy with, for example, olaparib . Early data from dose escalation studies with combination partners olaparib and durvalumab were presented recently showing good tolerance for compound 2 in combination dose escalation and preliminary signals of antitumor activity, with no evidence of drug–drug interactions (DDI); in 44 patients treated at various doses of compound 2 (60–240 mg QD) in combination with olaparib, 1 RECIST complete response (CR) and 6 partial responses (PR; 1 unconfirmed) were observed in patients with BRCA1 or BRCA2 mutations independent of ATM status, in advanced breast (3 patients), and 1 each of ovarian, prostate, pancreatic, and ampullary cancer; and in 25 patients treated at various doses (80 mg through 240 mg BD) in combination with durvalumab, 1 RECIST CR and 3 PRs, in patients with advanced NSCLC (3 patients) and HNSCC (1 patient), independent of tumor PD-L1 expression were observed …”

PARP Inhibition Increases the Reliance on ATR/CHK1 Checkpoint Signaling Leading to Synthetic Lethality—An Alternative Treatment Strategy for Epithelial Ovarian Cancer Cells Independent from HR Effectiveness

“…Moreover, olaparib acts synergistically with ATRi (AZD6738) in ATM deficient cancer cells [ 41 ]. Combined treatment with ATRi and PARPi caused 84% cell death of ATM deficient cancer cells in contrast to only 37% growth inhibition in ATM-proficient wild-type cells [ 42 ]. The ATRi VE-821 sensitizes OVCAR-8, SKOV-3, and PEO-1 ovarian cancer cells to common chemotherapeutics, such as cisplatin, topotecan, and veliparib [ 26 ].…”

Poly(ADP-Ribose) Polymerase Inhibitors in Pancreatic Cancer: A New Treatment Paradigms and Future Implications

“…Inhibition of CDK12 leads to downregulation of DDR genes [114] and reverses resistance to PARPi in breast cancer [115] and multiple myeloma in vitro [116]. PARPi-induced DNA damage can activate the ATR-mediated G2/M checkpoint facilitating DNA repair which can be reversed by ATR inhibition leading to cell death [117]. Similarly, Wee1 inhibition can allow unrepaired DNA enter mitosis via the G2/M checkpoint but the results of phase I study with olaparib with Wee1 inhibitor in unselected were disappointing with ORR of only 11% [118].…”