Repression of AXL expression by AP-1/JNK blockage overcomes resistance to PI3Ka therapy

Background: The phosphatidylinositol-4, 5-bisphosphate 3-kinase (PI3K) pathway, which regulates cell proliferation and survival, is hyper-activated or mutated in over 50% of HPV-related head and neck squamous cell carcinoma (HNSCC). Blocking the isoform specific of the PI3K, p110a, using BYL719 showed a promising anti-tumor activity in PIK3CA-mutated HNSCC. However, intrinsic or acquired-resistance was observed in pre-clinical models and in-patients. We previously showed that upregulation of receptor tyrosine kinase AXL induced resistance to BYL719 in vitro, in vivo and in patients.

Objectives: To uncover the molecular machinery leading to AXL up-regulation following BYL719.

Methods: Western blot analysis was performed to determine the correlation between AXL expression and transcription factors like c-JUN in HPV-related HNSCC cell lines. Cell proliferation assay was performed to determine the role of AXL and c-JUN in the response to BYL719 in vitro. Immunohistochemistry was used to measure AXL and c-JUN expression in tissue sections.

Results: A good correlation between AXL and c-JUN expression in HPV-related HNSCC cell lines was observed. Knockdown of c-JUN using siRNA was sufficient to re-sensitize HPV-related HNSCC tumor cells to BYL719 in vitro. In vitro, inhibition of BYL719 and JNK inhibitors (inhibits c-JUN) showed a synergistic anti-tumor effect. Mechanistically, inhibition of the JNK pathway prevents AXL expression following BYL719.

Conclusions: AXL/c-JUN levels determine sensitivity to PI3Ka inhibition. AXL expression levels are regulated by c-JUN. Blocking c-JUN using JNK inhibitors re-sensitized tumor cells to BYL719.