Fig. 6.

A central role for EGFRvIII and PI3Kp110δ in erlotinib resistance. Transient knockdown of EGFRvIII by specific siRNA led to a reduced proliferation of BS153^resE and restored sensitivity to erlotinib (A; **P < .005, *P = .05, t-test); RLU, relative luminescence units. At the protein level, EGFRvIII knockdown reduced downstream phosphorylation of PI3Kp110 and phosphorylation of Akt and ERK (B). Pharmacological interference with overall PI3K activity using PX-866 significantly reduced proliferation at concentrations above 1 µM for both cell lines after 6 d of incubation. Below 1 µM, only BS153^resE was significantly affected (C, grey asterisks). PX-866 inhibited proliferation of BS153^resE stronger than proliferation of BS153 at all concentrations tested. Specifically targeting p110δ by siRNA-mediated knockdown significantly decreased proliferation of BS153^resE. Additionally, BS153^resE was resensitized to treatment with erlotinib (D); values are means ± SD of octuplicate determinations. One of 3 independent experiments is shown.