The effects of pluripotency on tumor formation and chemotherapy resistance in EGFR mutant NSCLC

A common mechanism of TKI resistance is through acquisition of secondary mutations in EGFR or met amplification. Also, it is associated with cellular differentiation state, and this can be influenced by the action of pluripotency factors such as SOX2, OCT4 and NANOG. In a murine model of mutant EGFR-driven, TKI-resistant lung cancer, induction of mutant EGFR in the lung correlated with increased SOX2 levels in tumors. Human NSCLC cell lines with EGFR mutations were treated with erlotinib and the expression of p-EGFR and SOX2 were examined. While erlotinib decreased p-EGFR, it exerted differential effects on SOX2 expression that depended on the cell line and growth conditions used. To determine the importance of SOX2, cells were infected with lentivirus containing SOX2 shRNA. Knockdown of SOX2 decreased proliferation rate in HCC827 cells but failed to affect in H1975. Furthermore, SOX2 loss did not alter their sensitivity to erlotinib and triciribine. In a limiting cell dilution assay in xenografts, HCC827 and H1975 cells with SOX2 knockdown formed tumors at the same rate as vector control cells. Because sustained activation of the PI3K/Akt pathway is associated with EGFR TKI resistance, cells were treated with PI3K/AKT inhibitors. PI3K/Akt inhibitors decreased SOX2 expression in a time-dependent manner. Furthermore, SOX2 expression was influenced by cell confluency in all the cell lines examined. SOX2 may be under the control of the PI3K/Akt pathway in EGFR mutant NSCLC and depend on cell density; however our data does not support a role for SOX2 in tumor formation or therapeutic resistance.