BKM120 Treated WHIMs_17 Model Cohort

Aberrant activation of PI3K pathway is frequently observed in triple negative breast cancer (TNBC). However single agent PI3K inhibitors have shown modest anti-tumor activity. To investigate biomarkers of response, we tested 17 TNBC PDX models with diverse genetic and proteomic background, with varying PI3K pathway signaling activities for their tumor growth response to the pan-PI3K inhibitor BKM120 as well as baseline and treatment induced proteomic changes as assessed by reverse phase protein array (RPPA). We demonstrated that PI3K inhibition induces varying degrees of tumor growth inhibition (TGI), with 5 models demonstrating over 80% TGI. BKM120 consistently reduced PI3K pathway activity as demonstrated by reduced pAKT following therapy. Several biomarkers showed significant association with resistance, including baseline levels of growth factor receptors (EGFR, pHER3 Y1197), PI3Kp85 regulatory subunit, anti-apoptotic protein BclXL, EMT (Vimentin, MMP9, IntegrinaV), NFKB pathway (IkappaB, RANKL), and intracellular signaling molecules including Caveolin, CBP, and KLF4, as well as treatment induced increase in the levels of phosphorylated forms of Aurora kinases. Sensitivity was associated with higher baseline levels of proapoptotic markers (Bak and Caspase 3) and higher number of markers being changed following BKM120 therapy. Interestingly, markers indicating PI3K pathway signaling activation at baseline were not significantly correlated to %TGI. These results provide important insights in biomarker development for PI3K inhibitors in TNBC. Molecular profiling was completed on 54 microarrays representing different passages and human counterparts for 17 triple negative breast cancer models using 2 channel (tumor:reference) whole human genome Agilent arrays.