Inhibition of PI3K Pathway Reduces Invasiveness and Epithelial-to-Mesenchymal Transition in Squamous Lung Cancer Cell Lines Harboring PIK3CA Gene Alterations

A prominent role in the pathogenesis of squamous cell carcinoma of the lung (SQCLC) has been attributed to the aberrant activation of the PI3K signaling pathway, due to amplification or mutations of the p110a subunit of class I phosphatidylinositol 3-kinase (PIK3CA) gene. The aim of our study was to determine whether different genetic alterations of PIK3CA affect the biologic properties of SQCLC and to evaluate the response to specific targeting agents in vitro and in vivo. The effects of NVP-BEZ235, NVP-BKM120, and NVP-BYL719 on two-dimensional/three-dimensional (2D/3D) cellular growth, epithelial-to-mesenchymal transition, and invasiveness were evaluated in E545K or H1047R PIK3CA-mutated SQCLC cells and in newly generated clones carrying PIK3CA alterations, as well as in a xenograft model. PIK3CA mutated/amplified cells showed increased growth rate and enhanced migration and invasiveness, associated with an increased activity of RhoA family proteins and the acquisition of a mesenchymal phenotype. PI3K inhibitors reverted this aggressive phenotype by reducing metalloproteinase production, RhoA activity, and the expression of mesenchymal markers, with the specific PI3K inhibitors NVP-BKM120 and NVP-BYL719 being more effective than the dual PI3K/mTOR inhibitor NVP-BEZ235. A xenograft model of SQCLC confirmed that PIK3CA mutation promotes the acquisition of a mesenchymal phenotype in vivo and proved the efficacy of its specific targeting drug NVP-BYL719 in reducing the growth and the expression of mesenchymal markers in xenotransplanted tumors. These data indicate that PIK3CA mutation/amplification may represent a good predictive feature for the clinical application of specific PI3K inhibitors in SQCLC patients.