Abstract 1190: Differences in responsiveness of drug-sensitive and drug-resistant human bladder cancer cells to specific EGFR inhibitors

Abstract

Abstract Bladder cancer is a common genitourinary malignant disease in the USA. EGFR and/or HER2 are overexpressed in these cancers, and EGFR/HER2 inhibitors are suggested as treatment. Gefitinib (i.e., Iressa) is a selective inhibitor of the epidermal growth factor receptor (EGFR) and Lapatinib is a dual inhibitor of both the EGFR and HER2/neu (Human EGFR type 2) receptor. Both compounds compete with the binding of ATP to the tyrosine kinase domain of the respective receptors to inhibit autophosphorylation causing suppression of signal transduction. Unfortunately, resistance to these inhibitors is a problem. The purpose of this study was to compare the signaling pathway(s) induced by Gefitinib and Lapatinib, in UM-UC-5 (Gefitinib-sensitive) and UM-UC-14 (Gefitinib-resistant) bladder cancer cells and to identify molecular markers that might be useful predictors of efficacy. Each cell line was cultured to 90% confluence and then incubated 24 h in serum-free media. They were treated, respectively, with 2.5 μM Gefitinib or Lapatinib for 24 h and harvested. Cell lysates were subjected to Proteome Profiler™ Arrays (R&D, Minneapolis, MN) including RTK, phospho-MAP kinase, phospho-kinase, and apoptosis arrays. Results indicate that Gefitinib and Lapatinib had differential effects on proteins known to play a role in apoptosis. Iressa appeared to decrease anti-apoptotic Bcl2, whereas Lapatinib increased pro-apoptotic Bax expression. Lapatinib, but not Iressa, also suppressed anti-apoptotic clusterin. Both agents decreased anti-apoptotic claspin, survivin, and XIAP expression but the effect of Lapatinib was 2- to 8-fold greater than Iressa. Notably, in the drug-resistant UM-UC-14 cells, Iressa had little affect whereas Lapatinib induced pro-apoptotic BAD and inhibited expression of anti-apoptotic Bcl2, Bcl-XL, and clusterin. Perhaps the most notable difference between these two drugs, was the effectiveness of Lapatinib in suppressing EGFR/HER2 expression in both cell lines. In the sensitive line, Lapatinib suppressed EGFR/HER2 expression 2-3 fold more than did Iressa and was almost as effective in the resistant line, whereas Iressa had no effect on UM-UC-14 cells. In contrast, Iressa was at least 8-fold more effective than Lapatinib in suppressing ERK1/2 expression in drug-sensitive cell lines but neither compound affected ERKs in resistant cells. Overall, the effect of these compounds on MAP kinase signaling appeared to be similar in sensitive cells; however, Lapatinib was able to suppress some MAP kinase signaling in the resistant line. Other notable differences included increased phosphorylation of p53, p27 and p70S6 kinase only by Lapatinib and decreased phosphorylation of eNOS only by Iressa in sensitive cells. Overall results suggest that human bladder cancer cells display some similarity but also marked heterogeneity in response to “specific” EGFR inhibitors ex vivo. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 1190.