Abstract 2110: WEE1 inhibition could reverse trastuzumab resistance by downregulation of PD-L1 in HER2-positive cancers

Abstract

Abstract Background: Trastuzumab in combination with chemotherapy is a standard of care for patients with HER2-positive breast and gastric cancer. Resistance mechanism to trastuzumab, anti-HER2 therapy, includes multiple pathways. Cancer cells could evade immune surveillance through high expression of programmed cell death ligand 1 (PD-L1) on cancer or immune cells. Among resistance mechanisms to trastuzumab, the role of PD-L1 modulation has not yet been discovered in HER2-positive cancers. WEE1 is involved in cell cycle progression and DNA damage response (DDR), and, interestingly, beyond DDR, it could modulate immunes. We aimed to evaluate the role of PD-L1 in trastuzumab resistance in HER2-positive cancers with/without immune cells and to explore WEE1 inhibitor as a trastuzumab resistance overcoming strategy by modulation of PD-L1. Methods: Four trastuzumab-resistant (HR) cells (SNU216HR, N87HR, SNU2670HR, SNU2773HR) were established from 2 HER2-amplified gastric cancer cells (SNU216, NCI-N87) and 2 HER2-amplified biliary tract cancer cells (SNU2670, SNU2773). For WEE1 inhibition, AZD1775 was used. MTT assay, colony formation assay, cell cycle analysis by FACS Calibur flow cytometer, and western blot were done. Results: All four HR cells showed PD-L1 upregulation compared with parental cells. When PD-L1 was knocked-down by transfection with si-PD-L1, anti-growth/proliferation effects were observed in MTT assay and colony forming assay. PD-L1 itself may promote cancer cell growth without interacting with immune cells. AZD1775 downregulated PD-L1 expression and induced cell cycle arrest at sub-G1 and G2/M phases in all 4 HR cells. The synergistic anti-proliferative effects were found in all 4 HR cells with co-treatment of trastuzumab and AZD1775. Conclusion: PD-L1 upregulation may contribute to trastuzumab resistance in HER2-positive cancer cells. Targeting WEE1-PD-L1 pathway might be a candidate strategy to overcome trastuzumab resistance in HER2-positive cancers. Citation Format: Meihua Jin, Ah-Rong Nam, Ji-Eun Park, Ju-Hee Bang, Kyoung-Seok Oh, Do-Youn Oh, Yung-Jue Bang. WEE1 inhibition could reverse trastuzumab resistance by downregulation of PD-L1 in HER2-positive cancers [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 2110.