The AP-1 complex regulates AXL expression and determines sensitivity to PI3Ka inhibition in esophagus and head and neck squamous cell carcinoma

Introduction

AXL overexpression is a common resistance mechanism to anti-cancer therapies, including the resistance to BYL719 (Alpelisib) – the p110a isoform specific inhibitor of phosphoinositide 3-kinase (PI3K) – in esophagus and head and neck squamous cell carcinoma (ESCC, HNSCC respectively). However, the mechanisms underlying AXL overexpression in resistance to BYL719 remain elusive.

Materials and methods:

To identify the transcription factors correlated with AXL overexpression in resistance to BYL719 we used RNA sequencing, western blot analysis (WB), immunohistochemistry (IHC), and quantitative real-time PCR methods. To study the role of c-JUN and c-FOS transcription factors in BYL719 resistance we performed gene silencing using siRNA, proliferation assays using specific inhibitors, and in-vivo experiments for efficacy of drug combinatios.

Results and discussion:

Here we demonstrated that the AP-1 transcription factors, c-JUN and c-FOS, regulate AXL overexpression in HNSCC and ESCC. The expression of AXL was correlated with that of c-JUN both in HNSCC patients and in HNSCC and ESCC cell lines. Silencing of c-JUN and c-FOS expression in tumor cells downregulated AXL expression and enhanced the sensitivity tumor cells to BYL719 in vitro. Blocking of the c-JUN N-terminal kinase (JNK) using SP600125 in combination with BYL719 showed a synergistic anti-proliferative effect in vitro, which was accompanied by AXL downregulation and potent inhibition of the mTOR pathway. In vivo, the BYL719–SP600125 drug combination led to the arrest of tumor growth in cell line-derived and patient-derived xenograft models, and in syngeneic head and neck murine cancer models.

Conclusion:

Collectively, our data suggests that JNK inhibition in combination with anti-PI3K therapy is a new therapeutic strategy that should be tested in HNSCC and ESCC patients.