Abstract P1-13-15: Elevated TCEAL9 Expression Is Correlated With Trastuzumab-based Neoadjuvant Chemotherapy Resistance In HER2-positive Breast Cancer
Authors: Goh Chih Wan , Chi Wei-Ru , Zhang Liyi , Zhang Qi , Chen Ming , Xiong Min , Liu Douwaner , Ren Hengyu , Xiu Bingqiu , Xue Jingyan , Chi Yayun , Wu Jiong 
Published: March 2023

Background: -Trastuzumab-based neoadjuvant chemotherapy has shown to have remarkable clinical benefits for HER2-positive breast cancer patients who had higher tumor burden. -Patients who achieved pathological complete response (pCR) are known to have better prognosis. -However, certain patients have little response or are not sensitive to trastuzumab-based treatment regimens. -Understanding the mechanism of trastuzumab resistance is crucial for the development of new therapeutic strategy. Objectives: To investigate the role of TCEAL9 in developing trastuzumab resistance in HER2-positive breast cancer Methods: A total of 83 patients who received paclitaxel, carboplatin and trastuzumab neoadjuvant chemotherapy in Fudan University Shanghai Cancer Center(FUSCC) from 2016 to 2018 were enrolled in this study. After completed neoadjuvant chemotherapy and surgery, gene expressions were compared between the pCR and non-pCR groups. Total RNA from formalin-fixed paraffin-embedded tissue sections was isolated and RNA-sequencing was performed. Gene sets from GEO dataset GSE52707 were used to analyze TCEAL9 expression in resistant and non-resistant cell lines. Gene expression levels were converted into log2 values and row-wised standardized. BT-474 and SK-BR-3 cell lines were transduced with each expression lentivirus, followed by selection with puromycin for stable expression. TCEAL9 mRNA and protein level evaluation was evaluated by qPCR and western blot. The influence of TCEAL9 expression on proliferation and sensitivity to HER2-targeted therapy was evaluated by CCK8. BT-474 and SK-BR-3 transfected cells were plated in 96-well plates with 4,000 cells per well. After 3 or 5 days of incubation with trastuzumab, pertuzumab or lapatinib, the viability of cells was measured using Cell Proliferation Assay. Comparisons between Kaplan-Meier curves were performed using the long-rank test. Results: TCEAL9 was elevated significantly (P&lt; 0.05) in non-pCR patients in the FUSCC cohort and was associated with lapatinib resistance in GSE52707 from GEO datasets. Patients with elevated TCEAL9 expression had worse recurrence-free survival (RFS), distant metastasis-free survival (DMFS) and progression-free survival (PPS) (all P&lt; 0.05)by using KM-plotter. Overexpression of TCEAL9 was associated with lapatinib(IC50= 5.56 vs 10.90nM) and trastuzumab + pertuzumab(IC50= 745 vs 635nM) resistance in BT-474 and SK-BR-3 respectively, but has no influence in proliferation. In this study, we found that TCEAL9 could induce HER2-positive breast cancer cells resistance to HER2-targeted therapy through the activation of mTOR signaling pathway. After EGFR stimulation, TCEAL9 has a higher mTOR phosphorylation level in BT-474 cells. TCEAL9 elevation also increased HER2 and mTOR phosphorylation after lapatinib treatment in SK-BR-3 cells. In addition, the elevation of TCEAL9 has a positive correlation with HER2 signaling pathways such as EGFR, PIK3R1, FOXO1 and AKT3 in TCGA datasets. Conclusions: TCEAL9 expression correlates with trastuzumab resistance and high TCEAL9 expression is associated with poor prognosis in HER2-positive breast cancer patients.

Citation Format: Chih Wan Goh, Wei-Ru Chi, Liyi Zhang, Qi Zhang, Ming Chen, Min Xiong, Douwaner Liu, Hengyu Ren, Bingqiu Xiu, Jingyan Xue, Yayun Chi, Jiong Wu. Elevated TCEAL9 Expression Is Correlated With Trastuzumab-based Neoadjuvant Chemotherapy Resistance In HER2-positive Breast Cancer [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P1-13-15.