Abstract PO4-18-03: Combined Treatment with Pyrotinib and Chrysin Synergistically Improve the Autophagy Level in HER2-Positive Breast Cancer by Regulating the miR-16-5p/ZBTB16/G6PD Axis

Abstract Human epidermal growth factor receptor 2 (HER2)-positive breast cancer (BC) has been the most challenging subtype of BC, which consists of 20% of BC with an apparent correlation with poor prognosis. Despite that pyrotinib, a new HER2 inhibitor, has led to dramatic improvements in prognosis outcome, the efficacy of pyrotinib as monotherapy remain largely restricted due to its acquired resistance. Therefore, we aim at identifying a potent antitumor drug incorporated with pyrotinib for amplifying therapeutic efficacy for treating HER2-positive BC. Here, we reported a novel incorporation of pyrotinib in combination with chrysin, and explored its antitumor efficacy and the underlying mechanisms on HER2+ breast cancer. We determined that pyrotinib combined with chrysin yielded a potent synergistic effect to induce apoptosis and inhibit BT-474 and SK-BR-3 tumor cells, and suppressed in vivo tumor growth in tumor-bearing mice models. This may be mechanistically attributed to the induction of enhanced endoplasmic reticulum stress to increase the autophagy level. Furthermore, it was demonstrated that the combined treatment with pyrotinib and chrysin induced ubiquitination and G6PD degradation by regulating zinc finger and BTB/POZ domain-containing family protein 16 (ZBTB16) in tumorigenesis of BC. Besides, we identified that miR-16-5p is a potential upstream regulatory target of ZBTB16. Blocking miR-16-5p overexpression could inhibit HER2-positive tumorigenesis and significantly potentiate the efficacy of pyrotinib in combination with chrysin. Together, these findings demonstrate the utility of combined treatment with pyrotinib and chrysin as a potential option in the target treatment of HER2-positive BC through an unrecognized miR-16-5p/ZBTB16/G6PD axis. The miR-16-5p/ZBTB16/G6PD axis plays a crucial role in the pyrotinib plus chrysin-enabled anti HER2-positive BC Fig.1 a Cell viability of SK-BR-3 cells received various treatments. b Detection of cell cycle arrest of SK-BR-3 cells after various treatments. c Schematic diagram of the established protocol of the animal models. Photograph of resected tumor tissues, tumor volume (d), and tumor weight (e) of mice in different treatment groups during the whole testing period. f H&E, Ki67, and Tunel immunohistochemical staining of tumor sections of mice in various treatment groups. g Autophagy flux of SK-BR-3 cells labeled with mRFP-GFP-LC3 in the different treatment groups. h Expression level of ER stress markers in SK-BR-3 cells after various treatments via RT-qPCR and western blot. *P <0.05, compared with control group (DMSO), #P <0.05, compared with chrysin group, & P<0.05, compared with pyrotinib group. i Western blot analysis of the expression of G6PD in different treatment groups. j Fluorescence images of SK-BR-3 cells subjected to G6PD overexpression for the detection of autophagy level. k Ubibrowser database predicting the E3 ubiquitin ligases that may be involved in the regulation of G6PD ubiquitination. l Western blot analysis of G6PD protein half-life in SK-BR-3 cells with ZBTB16 silence. Cells were co-incubated with cycloheximide (CHX, 50μg/ml) for the indicated time. m Determination of the ubiquitination of G6PD in cells pretreated with 10 μM MG-132 for 3 h. Cells were transfected with ubiquitin after different treatments. The ubiquitinated G6PD was subjected to immunoprecipitation before western blot with ubiquitin antibody. n Dual-luciferase report verifying the targeting of ZBTB16 and miR-16-5p. o Transmission electron microscopy images of autophagosomes of tumors in various treatment groups (× 20000). p Immunohistochemical staining images of tumor slices for the determination of G6PD. q Schematic diagram for the underlying mechanism of pyrotinib combined chrysin against HER2-positive BC. Citation Format: Ting Luo, Xiaorong Zhong, Ping He, Dan Zheng, Yan Cheng, Kunrui Zhu. Combined Treatment with Pyrotinib and Chrysin Synergistically Improve the Autophagy Level in HER2-Positive Breast Cancer by Regulating the miR-16-5p/ZBTB16/G6PD Axis [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO4-18-03.