ABSTRACT
OBJECTIVE: Neoadjuvant chemoradiotherapy (neo-CRT) prior to surgery is the standard of care for oesophageal adenocarcinoma (OAC) patients. Unfortunately, most patients fail to respond to treatment. MiR-187 was previously shown to be downregulated in neo-CRT non-responders, whist in vitro miR-187 overexpression enhanced radiosensitivity and upregulated PTEN. This study evaluates the role of miR-187 and downstream PI3K signalling in radiation response in OAC. METHODS: The effect of miR-187 overexpression on downstream PI3K signalling was evaluated in OAC cell lines by qPCR and Western blotting. PTEN expression was analysed in OAC pre-treatment biopsies of neo-CRT responders and non-responders. Pharmacological inhibition of PI3K using GDC-0941 was evaluated in combination with radiotherapy in two-dimensional and three-dimensional OAC models in vitro and as a single agent in vivo. Radiation response in vitro was assessed via clonogenic assay. RESULTS: PTEN expression was significantly decreased in neo-CRT non-responders. MiR-187 overexpression significantly upregulated PTEN expression and inhibited downstream PI3K signalling in vitro. GDC-0941 significantly reduced viability and enhanced radiation response in vitro and led to tumour growth inhibition as a single agent in vivo. CONCLUSION: Targeting of PI3K signalling is a promising therapeutic strategy for OAC patients who have repressed miR-187 expression and do not respond to conventional neo-CRT. ADVANCES IN KNOWLEDGE: This is the first study evaluating the effect of PI3K inhibition on radiosensitivity in OAC, with a particular focus on patients that do not respond to neo-CRT. We have shown for the first time that targeting of PI3K signalling is a promising alternative therapeutic strategy for OAC patients who do not respond to conventional neo-CRT.
