Skip Navigation LinksHome > June 2008 - Volume 3 - Issue 6 > Tumor Dependence on the EGFR Signaling Pathway Expressed by...
Journal of Thoracic Oncology:
doi: 10.1097/JTO.0b013e3181753b24
Brief Report

Tumor Dependence on the EGFR Signaling Pathway Expressed by the p-EGFR:p-AKT Ratio Predicts Erlotinib Sensitivity in Human Non-small Cell Lung Cancer (NSCLC) Cells Expressing Wild-Type EGFR Gene

Li, Tianhong MD, PhD; Ling, Yi-He PhD; Perez-Soler, Roman MD

Free Access
Article Outline
Collapse Box

Author Information

Department of Oncology, Montefiore Medical Center and the Albert Einstein Cancer Center, Bronx, NY.

Disclosure: Tianhog Li: none; Yi-He Ling: none; Roman Perez-Soler:Grants/Research support from OSIP and NIH; Stockholder: OSIP, Genentech, Amgen, Novartis, Lilly, Transave, AstraZeneca; Consultant: OSIP, AstraZeneca, Genentech, Amgen, Novartis, Alza, Lilly, BMS, Transave.

Address for correspondence: Tianhong Li, MD, PhD, Department of Oncology, Montefiore Medical Center, Albert Einstein College of Medicine, 1825 Eastchester Road, 2 South, Room 55, Bronx, NY 10461. E-mail:

Supported by National Cancer Institute grants CA91784 and CA96515 and a grant from OSI Pharmaceuticals, Inc.

Collapse Box


Introduction: This study was undertaken to identify molecular determinants of tumor dependency on the epidermal growth factor receptor (EGFR) signaling pathway for predicting clinical benefit from erlotinib monotherapy in non-small cell lung cancer (NSCLC) patients with tumors expressing wild-type EGFR gene.

Methods: The effect of erlotinib on the total and phosphorylated protein expression of EGFR and key downstream signaling molecules was determined by immunoblots in a panel of NSCLC cells expressing wild-type EGFR gene. The parameters that correlate with cell sensitivity and resistance to erlotinib was analyzed.

Results: Individual assessment of total or phosphorylated protein expression of EGFR or a downstream signaling molecule does not correlate with sensitivity to erlotinib in these NSCLC tumors. Resistance of NSCLC cells to erlotinib is associated with failed inhibition of at least one phosphorylated downstream signaling molecule. The dependency of NSCLC cells on the activated EGFR axis was measured by the ratio of p-EGFR to a phosphorylated downstream protein. A high ratio should indicate that activation of a downstream signaling molecule primarily results from the activation of upstream EGFR; and a low ratio should indicate that activation of a downstream signaling molecule primarily results from the activation of a upstream receptors other than EGFR. The p-EGFR:p-AKT ratio was 10-fold higher in erlotinib-sensitive cells than erlotinib-resistant cells (p = 0.03). It was the best predictor of erlotinib sensitivity among all parameters analyzed in this panel of NSCLC cell lines.

Conclusions: The p-EGFR:p-AKT ratio deserves further investigation as a predictive parameter for clinical response to erlotinib in NSCLC tumors expressing wild-type EGFR gene.

Erlotinib, an oral epidermal growth factor receptor (EGFR) tyrosine kinase inhibitor (TKI), was approved by the US FDA in 2004 for unselected, advanced non-small cell lung cancer (NSCLC) patients who have failed first-line combination chemotherapy.1,2 About 10% of NSCLC patients whose tumors express high levels of EGFR protein as a result of the presence of tyrosine kinase-activating somatic mutations in the EGFR gene and/or high EGFR gene copy number exhibit a higher degree of dependence on the EGFR pathway and a higher tumor response to EGFR TKIs.3,4 However, acquired resistance to EGFR TKIs emerges in these tumors by at least two mechanisms: (1) the presence of a second somatic mutation T790M, which prevents drug binding to the TK domain of EGFR; and (2) activation of alternative signaling pathway(s) as an escape or survival response.5,6 The molecular mechanisms of sensitivity and resistance of NSCLC tumors expressing wild-type EGFR gene to EGFR TKIs are less clear, although a survival benefit is also observed in approximately 35% of NSCLC patients who have a robust and long-lasting stable disease (i.e., cytostatic effect) from erlotinib treatment.2,7 These patients, who achieve stable disease from erlotinib or gefitinib treatment have similar time to disease progression and overall survival compared with those NSCLC patients who achieve an objective response.8

To select this subgroup of NSCLC patients, this study was undertaken to identify molecular determinants of tumor dependency on the EGFR pathway and hence of erlotinib sensitivity in a panel of human NSCLC cell lines expressing the wild-type EGFR gene. The activity of EGFR signal transduction pathway was assessed by the expression of total and phosphorylated protein of EGFR and downstream signaling proteins by immunoblots. The parameters that could correlate with cell sensitivity and resistance to erlotinib were explored.

Back to Top | Article Outline


Back to Top | Article Outline
Drug, Antibodies, and Cell Lines.

Erlotinib (Tarceva, formerly OSI 774) was obtained from OSI pharmaceuticals and processed as described before.9 Most of the antibodies used for immunoblots were purchased from Cell Signaling (Beverly, MA). Antibodies against extracellular signal-responsive kinase (ERK)1/2 and p-ERK1/2 were obtained from Promega (Seattle, WA). All human tumor cell lines used in this study, except HN5 human head and neck carcinoma cell line (a generous gift from OSI Pharmaceuticals) were purchased from the American Type Culture Collection (Manassas, VA) and maintained routinely in RPMI 1640 medium supplemented with 10% fetal bovine serum.

Growth inhibition assay and immunoblot analysis were performed as previously described.9

Back to Top | Article Outline


Neither Total EGFR nor p-EGFR Expression Predicts Erlotinib Sensitivity

We confirmed our previous findings that NSCLC cell lines expressing wild-type EGFR gene displayed a variable, dose-dependent sensitivity to erlotinib9 in a panel of nine human NSCLC cell lines with different clinical and histologic features (H23, H322, H358, H460, H522, A549, H596, H661, and H1299) (IC50: 0.8 to >20 μM, data not shown). There was no absolute intrinsic resistance to erlotinib observed, although at 2 μM, the median plasma concentration in patients taking a standard dose of erlotinib 150 mg daily,10 only two of nine NSCLC cell lines showed a >50% growth inhibition (data not shown). We further characterized the effect of EGF and erlotinib on the EGFR expression in four erlotinib-sensitive tumor cell lines (H322, H358, HN5 and A431; IC50 <2 μM) and four erlotinib-resistant NSCLC cell lines (H460, A549, H596 and H1299; IC50 ≥2 μM) by immunoblots (Figure 1). The cytotoxicity of HN5 and A431 cells to erlotinib was used as positive controls since they express high level of EGFR protein and are known to be sensitive to EGFR TKIs.11–13

Figure 1
Figure 1
Image Tools

The expression of p-EGFR at tyrosine (Y1068) was measured as it is the binding site for the PI3K and MAPK interacting protein Gab1, which mediates the activation of downstream PI3K/AKT and MAP/ERK signal pathways. The baseline expression of p-EGFR was barely detectable in all tested cell lines deprived of serum (Figure 1A, lane 1), suggesting that these NSCLC cells have low constitutive EGFR activation in the absence of ligands. Addition of EGF to the cell culture media dramatically induced the phosphorylation of EGFR in both erlotinib-sensitive and erlotinib-resistant tumor cell lines (Figure 1A, lane 2), suggesting that the EGFR pathway can be activated in response to EGF in all tested NSCLC cell lines although this modulation does not alter the sensitivity to erlotinib. With increasing concentrations of erlotinib, the expression of p-EGFR (upper panels) was inhibited to a much greater extent as compared with that of t-EGFR (lower panels) in each cell line (Figure 1A, lanes 3–6). Two μM of erlotinib inhibited p-EGFR expression by about 90% in all NSCLC cell lines, except for H1299, regardless of their sensitivity to erlotinib (Figure 1B). Of note, 20 μM of erlotinib only inhibited p-EGFR expression by only approximately 80% in HN5 cells that were sensitive to erlotinib (Figure 1B, legend ♢). Thus, neither the expression of p-EGFR nor t-EGFR correlates with the sensitivity of these human NSCLC cells to erlotinib. We did not find any correlation between the level of total and phosphorylated ErbB-2 or ErbB-3 protein expression and erlotinib sensitivity in the cell lines studied (data not shown), although only a few cell lines were analyzed.

Back to Top | Article Outline
Lack of Inhibition of Phosphorylated Downstream Signaling Proteins of EGFR Predicts Resistance of NSCLCL Cells to Erlotinib

Three major signaling pathways mediate the downstream effects of EGFR activation: the cell proliferation pathway (Ras/ERK) and survival pathways [PI3K/AKT and Jak/STAT]. Figure 2 illustrates that the concentrations of erlotinib required to inhibit the activity of downstream p-AKT, p-ERK1/2, and p-STAT3 proteins were higher than those required to inhibit p-EGFR protein in both erlotinib-sensitive and erlotinib-resistant cells (p < 0.05), although they varied considerably. Compared with erlotinib-sensitive cell lines, erlotinib-resistant NSCLC cell lines had at least one phosphorylated downstream signaling protein that was refractory to erlotinib inhibition: A549 (p-AKT, p-ERK1/2, p-STAT3), H1299 (p-AKT, p-ERK1/2), H596 (p-AKT), and H460 (p-STAT3). These data suggest that alternative activation of growth and survival mechanisms via an EGFR-independent pathway(s) might also be a common mechanism of erlotinib resistance in these NSCLC cells harboring wild-type EGFR gene. Among the three major activated downstream EGFR signaling proteins, lack of inhibition of p-AKT expression was most commonly associated with erlotinib resistance in these NSCLC cell lines. This is consistent with the key role of p-AKT in mediating the effect of erlotinib alone and in combination with at least some cytotoxic agents.9,14–16

Figure 2
Figure 2
Image Tools
Back to Top | Article Outline
Ratios Quantifying the Dependency of NSCLC Tumors on the EGFR Signaling Pathway Predict Erlotinib Sensitivity

We explored the ratios of activated upstream to downstream signaling proteins to quantify the dependency of NSCLC tumors on the EGFR signaling pathway. The assumption was that in cases of high EGFR dependence, the likelihood that the activation of a downstream signaling protein is mainly from the activation of upstream EGFR should be higher than in cases of low EGFR dependence, where downstream activation occurs not as a consequence of upstream EGFR activation. Figure 3A illustrates the expression of phosphorylated and total EGFR and AKT by immunoblots in erlotinib-sensitive tumor cell lines (n = 4) and erlotinib-resistant NSCLC cell lines (n = 7) treated with EGF. The mean of relative amount of each protein expression was normalized to the expression in H322 (as 1) and illustrated under each band. The ratio of p-EGFR expression to p-AKT alone (i.e., p-EGFR:p-AKT) was 10-fold higher in erlotinib-sensitive cells than in erlotinib-resistant cells (6.0 ± 2.8 and 0.6 ± 0.5, respectively, p = 0.03, Mann-Whitney U test), followed by the ratio of their levels relative to total EGFR and total AKT, respectively [i.e., (p-EGFR:EGFR):(p-AKT:AKT)] (6-fold higher: 2.4 ± 1.1 and 0.4 ± 0.2, respectively, p = 0.02) and the ratio of p-EGFR to t-EGFR (3-fold higher) (1.4 ± 0.1 and 0.4 ± 0.1, respectively, p = 0.02) (Figure 3B). Thus, the ratio of p-EGFR:p-AKT best correlates with the sensitivity of these NSCLC cells to erlotinib.

Figure 3
Figure 3
Image Tools

In summary, we here report that only the activated (phosphorylated) form of EGFR and downstream signaling proteins are the targets of erlotinib inhibition. The expression levels of total EGFR and downstream AKT or ERK or STAT3 proteins are not significantly altered by erlotinib treatment and do not correlate with the sensitivity of NSCLC cells to erlotinib. These data do not support determining the expression of total amount of a protein to predict the clinical efficacy of EGFR TKI.17,18 Effective inhibition of all activated EGFR downstream signaling molecules (such as p-AKT, p-ERK, and p-STAT3) by erlotinib was associated with sensitivity to erlotinib, whereas lack of inhibition of at least one downstream signaling protein by erlotinib was associated with resistance to erlotinib, reflecting the cell’s ability to use or trigger an EGFR-independent pathway to maintain cell growth and survival. The p-EGFR:p-AKT ratio, which vertically couples the activity of upstream and downstream EGFR signaling molecules, is a parameter indicative of tumor dependency on the EGFR pathway. Although there are still technical hurdles to overcome, these results support our current effort in developing assays for clinical application and validation of the p-EGFR:p-AKT ratio as a predictive biomarker in retrospective and prospective clinical studies in NSCLC.

Back to Top | Article Outline


1. Perez-Soler R. The role of erlotinib (Tarceva, OSI 774) in the treatment of non-small cell lung cancer. Clin Cancer Res 2004;10:S4238–S4240.

2. Shepherd FA, Rodrigues Pereira J, Ciuleanu T, et al. Erlotinib in previously treated non-small-cell lung cancer. N Engl J Med 2005;353:123–132.

3. Baselga J, Arteaga CL. Critical update and emerging trends in epidermal growth factor receptor targeting in cancer. J Clin Oncol 2005;23:2445–2459.

4. Sequist LV, Bell DW, Lynch TJ, Haber DA. Molecular predictors of response to epidermal growth factor receptor antagonists in non-small-cell lung cancer. J Clin Oncol 2007;25:587–595.

5. Kobayashi S, Ji H, Yuza Y, et al. An alternative inhibitor overcomes resistance caused by a mutation of the epidermal growth factor receptor. Cancer Res 2005;65:7096–7101.

6. Pao W, Miller VA, Politi KA, et al. Acquired resistance of lung adenocarcinomas to gefitinib or erlotinib is associated with a second mutation in the EGFR kinase domain. PLoS Med 2005;2:e73.

7. Tsao MS, Sakurada A, Cutz JC, et al. Erlotinib in lung cancer-molecular and clinical predictors of outcome. N Engl J Med 2005;353:133–144.

8. Pronzato P, Loprevite M, Brianti A, et al. Disease stabilization (SD) as a surrogate end-point in advanced non-small cell lung cancer (NSCLC) patients treated with erlotinib (E) or gefitinib (G). J Clin Oncol 2007;25:18115.

9. Li T, Ling YH, Goldman ID, Perez-Soler R. Schedule-dependent cytotoxic synergism of pemetrexed and erlotinib in human non-small cell lung cancer cells. Clin Cancer Res 2007;13:3413–3422.

10. Hidalgo M, Siu LL, Nemunaitis J, et al. Phase I and pharmacologic study of OSI-774, an epidermal growth factor receptor tyrosine kinase inhibitor, in patients with advanced solid malignancies. J Clin Oncol 2001;19: 3267–3279.

11. Modjtahedi H, Affleck K, Stubberfield C, Dean C. EGFR blockade by tyrosine kinase inhibitor or monoclonal antibody inhibits growth, directs terminal differentiation and induces apoptosis in the human squamous cell carcinoma HN5. Int J Oncol 1998;13:335–342.

12. Kawamoto T, Mendelsohn J, Le A, Sato GH, Lazar CS, Gill GN. Relation of epidermal growth factor receptor concentration to growth of human epidermoid carcinoma A431 cells. J Biol Chem 1984;259:7761–7766.

13. Kawamoto T, Sato JD, Le A, Polikoff J, Sato GH, Mendelsohn J. Growth stimulation of A431 cells by epidermal growth factor: identification of high-affinity receptors for epidermal growth factor by an anti-receptor monoclonal antibody. Proc Natl Acad Sci USA 1983;80:1337–1341.

14. Sordella R, Bell DW, Haber DA, Settleman J. Gefitinib-sensitizing EGFR mutations in lung cancer activate anti-apoptotic pathways. Science 2004;305:1163–1167.

15. Amann J, Kalyankrishna S, Massion PP, et al. Aberrant epidermal growth factor receptor signaling and enhanced sensitivity to EGFR inhibitors in lung cancer. Cancer Res 2005;65:226–235.

16. Tracy S, Mukohara T, Hansen M, Meyerson M, Johnson BE, Janne PA. Gefitinib induces apoptosis in the EGFRL858R non-small-cell lung cancer cell line H3255. Cancer Res 2004;64:7241–7244.

17. Baselga J, Albanell J, Ruiz A, et al. Phase II and tumor pharmacodynamic study of gefitinib in patients with advanced breast cancer. J Clin Oncol 2005;23:5323–5333.

18. Tan AR, Yang X, Hewitt SM, et al. Evaluation of biologic end points and pharmacokinetics in patients with metastatic breast cancer after treatment with erlotinib, an epidermal growth factor receptor tyrosine kinase inhibitor. J Clin Oncol 2004;22:3080–3090.

Cited By:

This article has been cited 4 time(s).

Lung Cancer
EGFR-tyrosine kinase inhibitor treatment beyond progression in long-term Caucasian responders to erlotinib in advanced non-small cell lung cancer: A case-control study of overall survival
Faehling, M; Eckert, R; Kamp, T; Kuom, S; Griese, U; Strater, J; Ott, G; Spengler, W
Lung Cancer, 80(3): 306-312.
Cancer Biology & Therapy
Combined MEK and EGFR inhibition demonstrates synergistic activity in EGFR-dependent NSCLC
Balko, JM; Jones, BR; Coakley, VL; Black, EP
Cancer Biology & Therapy, 8(6): 522-530.

World Journal of Gastroenterology
Genomic-wide analysis of lymphatic metastasis-associated genes in human hepatocellular carcinoma
Lee, CF; Ling, ZQ; Zhao, T; Fang, SH; Chang, WC; Lee, SC; Lee, KR
World Journal of Gastroenterology, 15(3): 356-365.
Genistein Enhances the Effect of Epidermal Growth Factor Receptor Tyrosine Kinase Inhibitors and Inhibits Nuclear Factor Kappa B in Nonsmall Cell Lung Cancer Cell Lines
Gadgeel, SM; Ali, S; Philip, PA; Wozniak, A; Sarkar, FH
Cancer, 115(): 2165-2176.
Back to Top | Article Outline

Erlotinib; Small molecule tyrosine kinase inhibitor; EGFR; NSCLC; Wild-type EGFR gene

© 2008International Association for the Study of Lung Cancer


Article Tools



Search for Similar Articles
You may search for similar articles that contain these same keywords or you may modify the keyword list to augment your search.

Other Ways to Connect



Visit on your smartphone. Scan this code (QR reader app required) with your phone and be taken directly to the site.

 For additional oncology content, visit LWW Oncology Journals on Facebook.