Abstract 4270: ErbB inhibitors in bladder cancer cell lines: Effectiveness in cells that express high levels but low activity of the ErbB receptors.
Authors: Mooso Benjamin A. , de Vere White Ralph W. , Ghosh Paramita M. 
Published: August 2014

Background: Various studies demonstrated increased expression of EGF-receptor (EGFR/HER1/ErbB1) and related receptors ErbB2/HER2/Neu, ErbB3/HER3 and ErbB4/HER4 in bladder cancer. Despite this, clinical trials using drugs inhibiting EGFR (erlotinib), ErbB2 (trastuzumab) or dual EGFR/ErbB2 inhibitors (lapatinib) were all deemed ineffective. Since ErbB receptors require dimerization with other members of this family, each of which regulate cell growth and survival, we hypothesized that all four receptors must be simultaneously suppressed to achieve lasting effects. Here we compare the effects of erlotinib, trastuzumab and lapatinib to a novel pan-ErbB inhibitor dacomitinib in four bladder cancer cell lines expressing high and low levels of these receptors.

Methods: The bladder cancer cell lines T24, TCCSUP, J82 and HTB-2FT4 were used to evaluate the efficacy of erlotinib (Tarceva), trastuzumab (Herceptin), lapatinib (Tykerb, GW572016) and dacomitinib (PF00299804). Cell growth was estimated by MTT or crystal-violet staining. Protein expression was determined by western blotting and apoptosis was determined by flow cytometry after seventy-two hour incubation with the indicated treatment.

Results: Comparison of the T24, TCCSUP, J82 and HTB-2FT4 bladder cancer cells with C4-2 (prostate) and MCF-7 (breast) cells showed that all but the HTB-2FT4 bladder cancer cells expressed high levels of EGFR and ErbB3 but not ErbB2, while HTB-2FT4 cells expressed only EGFR and TCCSUP cells had higher ErbB levels than T24. Interestingly, ErbB2 and ErbB3 are readily activated by EGF in T24 cells compared to TCCSUP. MTT demonstrated the efficacy of dacomitinib and erlotinib, primarily EGFR inhibitors, compared to lapatinib, primarily an ErbB2 inhibitor with anti-EGFR activity at higher concentrations, while the ErbB2 inhibitor, trastuzumab, had little effect. The trastuzumab and erlotinib combination performed worse than erlotinib alone in T24 cells; hence trastuzumab studies were not pursued further. Crystal-violet staining after treatment with erlotinib, lapatinib and dacomitinib indicated higher efficacy of dacomitinib after seven days in the T24 and TCCSUP cell lines. MTT and flow cytometry showed that lapatinib was ineffective alone but, in combination with dacomitinib, significantly decreased cell viability in TCCSUP cells. In contrast, combining erlotinib, lapatinib and dacomitinib proved most effective in T24 cells.

Conclusions: We demonstrate that all ErbB receptors must be simultaneously inhibited to prevent proliferation of both high and low ErbB expressing bladder lines. Inhibition of ErbB2 alone had a deleterious effect, likely due to ErbB2 inhibition stimulating the activation of the other ErbB receptors. While high levels of ErbB kinases sensitized cells to the inhibitors, the drugs were more effective in cells that had lower activation of the receptors.

Citation Format: Benjamin A. Mooso, Ralph W. deVere White, Paramita M. Ghosh. ErbB inhibitors in bladder cancer cell lines: Effectiveness in cells that express high levels but low activity of the ErbB receptors. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 4270. doi:10.1158/1538-7445.AM2013-4270