ATR Inhibitors VE-821 and VX-970 Sensitize Cancer Cells to Topoisomerase I Inhibitors by Disabling DNA Replication Initiation and Fork Elongation Responses

Abstract

Camptothecin and its derivatives, topotecan and irinotecan are specific topoisomerase I (Top1) inhibitors and potent anticancer drugs killing cancer cells by producing replication-associated DNA double-strand breaks, and the indenoisoquinoline LMP-400 (indotecan) is a novel Top1 inhibitor in clinical trial. To develop novel drug combinations, we conducted a synthetic lethal siRNA screen using a library that targets nearly 7,000 human genes. Depletion of ATR, the main transducer of replication stress came as a top candidate gene for camptothecin synthetic lethality. Validation studies using ATR siRNA and the ATR inhibitor VE-821, confirmed marked antiproliferative synergy with camptothecin, and even greater synergy with LMP-400. Single cell analyses and DNA fiber combing assays showed that VE-821 abrogates the S-phase replication elongation checkpoint and the replication origin-firing check point induced by camptothecin and LMP-400. As expected, the combination ofTop1 inhibitors with VE-821 inhibited the phosphorylation of ATR and Chk1; however, it strongly induced γH2AX. In cells treated with the combination, the γH2AX pattern changed overtime from the well-defined Top1-induced damage foci to an intense peripheral and diffuse nuclear staining, which could be used as response biomarker. Finally, the clinical derivative of VE-821, VX-970 enhanced the in vivo tumor response to irinotecan without additional toxicity. Akey implication of our work is the mechanistic rationale and proof-of-principle it provides to evaluate the combination of Top1 inhibitors with ATR inhibitors in clinical trials.

Targeting DNA damage in SCLC

“…In the same study VX-970 increased sensitivity to cisplatin in six out of seven NSCLC PDX models [94]. In addition, ATR inhibitors have been shown to increase sensitivity to topoisomerase I inhibitors in colorectal cancer cell lines in vitro and in vivo [95], rationalising the combination of ATR inhibitors and topotecan in early phase clinical trials in SCLC. Summary of DNA damage pathways and therapeutics (Fig.…”

Distinct but Concerted Roles of ATR, DNA-PK, and Chk1 in Countering Replication Stress during S Phase

“…Nevertheless, how replication stress can be measured in normal and cancer cells remains elusive. Because multiple ATRi and Chk1i are being tested in clinical trials for cancer therapy (Foote et al, 2013; Josse et al, 2014; Karp et al, 2012; Ma et al, 2013; Sausville et al, 2014; Seto et al, 2013), understanding the mechanisms of action and unique properties of these inhibitors may help to guide their applications in clinical settings.…”

The cell cycle checkpoint inhibitors in the treatment of leukemias

“…In vivo studies using both VE-821 and VX-970 showed robust results. Indeed, these two ATR inhibitors synergized with radiotherapy and gemcitabine in pancreatic cancer xenograft models [76, 77] and with irinotecan in a colorectal cancer model [79]. Nowadays, different clinical trials are ongoing against solid tumors to assess the safety, tolerability, and pharmacokinetics of VX-970 in combination with cytotoxic chemotherapy (NCT02157792, NCT02595931, NCT02567422, and NCT02595892).…”