Abstract 1075: AXL is a potential druggable target in trastuzumab resistance in HER2+ breast cancer patients
Authors: Adam-Artigues Anna , Cervera Raimundo , Arenas Enrique Javier , Brasó-Maristany Fara , Martinez-Sabadell Alex , Tormo Eduardo , Hernando Cristina , Martinez Maria Teresa , Simon Soraya , Poveda Jesús , Burgués Octavio , Rovira Ana , Rojo Federico , Albanell Joan , Bermejo Begoña , Lluch Ana , Eroles Pilar , Prat Aleix , Arribas Joaquin , Cejalvo Juan Miguel 
Published: July 2021

Abstract
Introduction HER2+ correlates with aggressive phenotype and poor prognosis. The use of several antiHER2 drugs has dramatically improved prognosis and survival of HER2+ breast cancer (BC) patients. However, ≈20% of these patients will present resistance to antiHER2 therapies and relapse. The purpose of this study is to explore the role of AXL in antiHER2 treatment resistance and its potential as a druggable biomarker in HER2+ BC.
Methods We generated 2 trastuzumab (T) resistant models from a HER2+ BC patient. The first one was a PDX derived resistant cell line established by chronic treatment for 6 months with T in vitro (TR1 and TR2). The second resistant model (TR4) was established by chronic treatment with T for 4 months and two serial passages in mice. The prognostic value of AXL was evaluated in primary tumor cohort of HER2+ BC patients treated by standard guidelines (n=51). AXL was also explored in a cohort from PAMELA trial, a neoadjuvant phase II study. Patients were given lapatinib and T for 18 weeks (Luminal-HER2+ patients were additionally given hormonotherapy). Tumor samples were collected at baseline, day 14 and surgery (n= 96).
Results PDX resistant cell lines (TR1 and TR2) and resistant tumors (TR4) exhibit upregulation of AXL in comparison to the parental cells (PDX118). In vitro, the combination of an AXL inhibitor (TP-0903) + T resensitized resistant cells to T. In 3D organoids models from TR4, the combination decreased cell number in organoids more than both single agents. In TR4 in vivo model, TP-0903 + T completely abrogate tumor growth for more than 2 months.To validate our preclinical findings, we analyzed the level of AXL in our retrospectively cohort of patients. AXL level was significantly upregulated in patients who relapsed (p&lt;0.0001). Patients with high levels of AXL had significantly shorter disease-free survival (DFS) and overall survival (OS) (log-rank p&lt;0.0001; HR=15.78; 95% CI 3.89-19.80 for DFS; log-rank p=0.013; HR= 5.43; 95% CI 1.35-13.07 for OS). The median DFS and OS were 36 and 77 months in patients with high AXL level, whereas patients with low AXL level presented 92.5 and 92.5 months.To identify early molecular changes induced by dual HER2 blockade in patients with HER2+ disease, AXL was analyzed in PAMELA trial cohort. A significant increase of AXL was detected at day 14 compared to baseline (p=5.8e-20). This effect was observed in both luminal and non-luminal HER2+ BC patients and across all PAM50 subtypes. This rapid response suggests the implication of AXL as a mechanism of antiHER2 resistance. Levels of AXL decreased as long as treatment was on hold at surgery compared to day 14 (p=6.04e-14).
Conclusion AXL level was correlated with poor outcome of HER2+ BC patients. On our preclinical models, we showed that combination of TP-0903 and T abrogate tumor growth in acquired resistant models to T in PDXs. We postulate AXL as a promising new therapeutic strategy to overcome resistance to antiHER2 therapies
Citation Format: Anna Adam-Artigues, Raimundo Cervera, Enrique Javier Arenas, Fara Brasó-Maristany, Alex Martinez-Sabadell, Eduardo Tormo, Cristina Hernando, Maria Teresa Martinez, Soraya Simon, Jesús Poveda, Octavio Burgués, Ana Rovira, Federico Rojo, Joan Albanell, Begoña Bermejo, Ana Lluch, Pilar Eroles, Aleix Prat, Joaquin Arribas, Juan Miguel Cejalvo. AXL is a potential druggable target in trastuzumab resistance in HER2+ breast cancer patients [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 1075.