It is not yet clear whether lapatinib will be subject to the same pitfalls; the first phase analysis of the lapatinib clinical trial cannot answer that question. signaling were resistant to inhibition of fatty acid synthesis, whereas introduction of a constitutively active mutant form of EGFR, EGFRvIII, sensitized tumor xenografts in mice to cell death, which was augmented by the hydroxymethylglutaryl-CoA (HMG-CoA) reductase inhibitor atorvastatin. These results identify a previously undescribed EGFR-mediated pro-survival metabolic pathway, and suggest new therapeutic approaches to treating EGFR-activated glioblastomas. == INTRODUCTION == Glioblastomas (GBMs) aggressively invade the surrounding brain, making complete surgical excision impossible. Unfortunately, GBMs FKBP4 are also among the most radiation- and chemotherapy-resistant of all cancers. On average, GBM patients survive 12 to 15 months from the time of initial diagnosis (1,2). The epidermal growth factor receptor (EGFR), which is usually amplified in up to 45% of GBM patients (3), has oncogenic activity (4,5). However, EGFR inhibitors have been ineffective in the clinic (6). Maintenance of signal flux through the phosphatidylinositol-3-kinase (PI3K)-Akt-mammalian target of rapamycin complex 1 (mTORC1) pathway, either as a consequence of PTEN (phosphatase and tension homolog deleted from chromosome 10) loss (7,8), a key unfavorable regulator of PI3K signaling, or through co-activation of other receptor tyrosine kinases (RTKs) (9), together with failure to block EGFR-mediated changes in cellular metabolism, have been suggested as possible explanations for the resistance of multiple cancers, including GBMs, to inhibitors of EGFR Losartan tyrosine kinase activity (1013). However, attempts to determine the clinical importance of EGFR signaling in GBM have been hampered by a lack of studies designed to assess the acute effects of EGFR inhibitors on signal transduction and tumor metabolism in patients. Here we analyzed GBM clinical samples, cell lines and a mouse model to identify an EGFR- and Akt-dependent, rapamycin-insensitive signaling pathway that promotes GBM cell survival through sterol regulatory element-binding protein 1 (SREBP-1) -dependent fatty acid synthesis. == RESULTS == == Inhibition of EGFR-PI3K-Akt signaling suppresses SREBP-1 nuclear translocation in GBM patients treated with lapatinib == As part of a Phase II clinical trial for the EGFR inhibitor lapatinib, we performed quantitative immunohistochemical analysis of tumor tissue from the first nine GBM patients for whom tissue was available both at initial diagnosis (medical procedures Losartan 1) and after a 7 to 10 day course of treatment (surgery 2) (Fig. 1A). We have previously Losartan demonstrated the effectiveness of this assay in measuring drug-specific effects in GBM patients (14). Access to pre- and post-treatment samples for each patient facilitated intra-patient comparison of molecular endpoints, enhancing the statistical power to detect changes in this small sample size. Immunohistochemical staining for EGFR phosphorylated on Tyr1086(p-EGFR), a measure of EGFR activation (Fig. 1, B and C), was significantly decreased in tumors from lapatinib-treated patients (p<0.05). Decreased p-EGFR was detected in tumors from 6 of 9 patients (Fig. 1D), with increased intra-tumor lapatinib concentration in tumors that exhibited decreased EGFR phosphorylation (table S1). Staining for Akt phosphorylated on Ser473(p-Akt), a measure of PI3K pathway activity (15), was also significantly decreased after lapatinib treatment (p<0.01) (Fig. 1, B and C), consistent with the decrease in p-EGFR (p<0.01) (Fig. 1D). Thus, lapatinib inhibited EGFR signaling through Akt in glioblastomas from the majority of patients examined. == Fig. 1. == EGFR and Akt signaling and nuclear SREBP-1 accumulation response data in the first set of 9 GBM patients receiving lapatinib in a Phase II clinical trial. (A) Tumor tissue was analyzed from 9 GBM patients before and after treatment with the EGFR inhibitor lapatinib. (B) Immunohistochemical staining (reddish brown) of phospho-EGFR Tyr1086, phospho-Akt Ser473and SREBP-1 before and after treatment with lapatinib from a representative patient (#1). Nuclei were counterstained with hematoxylin (blue). Inset shows nuclear SREBP-1 staining indicated by green arrow. Scale bar = 20 um. (C) Quantification of immunohistochemical staining from >1000 cells from at least five representative areas of each tumor before and after lapatinib treatment,P-values were determined by Wilcoxon text (7). Each diamond represents an individual patient. (D) Reduction of p-EGFR, p-Akt and nuclear SREBP-1 staining for each GBM patient before (S1) and after (S2) treatment with lapatinib. (E) Correlation between inhibition of p-EGFR and inhibition of nuclear SREBP-1 staining. (F) Analysis of tumor tissue from 9 GBM patients before and after.