Abstract 1526: WEE1 inhibition suppresses esophageal adenocarcinoma tumor growth both in vitro and in vivo

Abstract

Abstract Esophageal adenocarcinoma (EAC) has seen a 400% increase in incidence over the past 30 years. The 5-year survival rate is under 20% due to ineffective therapeutics and a lack of actionable oncogenic drivers, necessitating novel therapeutic avenues in this disease. Genomic analysis indicates that a subset of EAC tumors have alterations in the G2/M cell cycle check point and DNA damage response governed by mutations in TP53 or other hits in this pathway, suggesting targeting the G2/M pathway might be a viable option in EAC. We and others have demonstrated that the WEE1 inhibitor AZD1775 is effective both in vitro and in vivo against tumors with DNA damage response alterations, and this drug is currently in clinical trials across a number of tumor types. We hypothesized that inhibition of WEE1 would induce DNA damage and cell death in EAC tumors, and provide a rational therapeutic avenue against this deadly disease. Across multiple EAC cell lines, AZD1775 suppressed tumor cell growth either as a monotherapy or in combination with DNA-damaging therapies. The growth suppression was accompanied by persistent DNA damage as determined by γH2AX and the induction of apoptosis. FLO-1 cells, responsive to monotherapy AZD1775, showed a dramatic reduction in G2 cells 24 hours post AZD1775 exposure with concomitant increases in cells in G0 and S phases of the cycle; while SK-GT-4, resistant to monotherapy AZD1775, showed an initial reduction in cells in G2 but recovered to normal levels 24 hours post-exposure. To assess AZD1775 in vivo, we generated a patient-derived xenograft (PDX) model of an EAC tumor excised at our institution. Combinations of AZD1775 with radiation or cisplatin significantly reduced in vivo tumor growth compared to vehicle, and the combination of AZD1775 with cisplatin was as effective as standard-of-care treatment (cisplatin + docetaxel + radiation), a therapeutic avenue plagued by toxicity in humans. Exposure to AZD1775 in combination with cisplatin showed suppression of phospho-CDC2 (target-hit) and induction of γH2AX in vivo compared to vehicle. Towards understanding a mechanism for lack of response of certain EAC cell lines to AZD1775 monotherapy, we explored the PI3K pathway that has been previously implicated in AZD1775 resistance. SK-GT-4 cells, which are unresponsive to AZD1775 monotherapy, demonstrated elevated phospho-AKT and phospho-p70S6K protein levels compared to other cell lines and were found more sensitive to PI3K or MTOR inhibition, suggesting a dependence on this pathway for tumor cell survival. Collectively, our data suggest that AZD1775, both alone and in combination with standard-of-care DNA damage, may be an effective therapeutic strategy for those EAC tumors dependent on the G2/M checkpoint. Citation Format: Mylan Blomquist, Vashti M. Carson, Ross M. Bremner, Timothy G. Whitsett, Landon J. Inge. WEE1 inhibition suppresses esophageal adenocarcinoma tumor growth both in vitro and in vivo [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 1526.