The effects of lapatinib and neratinib on HER2 protein levels in breast cancer cell lines.

Abstract

637 Background: HER2, a member of the c-erbB receptor tyrosine kinase family, is over-expressed (HER2 gene amplification/IHC 3+, >30% cells) in approx. 25% of breast cancers. Pre-clinical studies have shown that the HER2-targeted small molecule tyrosine kinase inhibitor (TKI) lapatinib (LAP) can increase HER2 levels in cell line models and can potentiate trastuzumab-mediated antibody dependent cell-mediated cytotoxicity. To assess the potential effects of the next generation TKI neratinib (NER) on expression of HER2 in breast cancer, this study compares the effects of LAP and NER on HER2 protein levels in the HER2-amplified SKBR3 and HER2-non-amplified T47D cell lines in vitro. Methods: SKBR3 and T47D were treated with LAP or NER (0.2, 1 and 2 µM) for 12, 24 and 48 hours.HER2 protein levels were determined by ELISA, immunoblotting and high content analysis (HCA). HER2 protein was examined using two antibodies targeting the extracellular domain (ECD) and the intracellular domain (ICD) of HER2. pHER2, EGFR/pEGFR, MAPK/pMAPK and AKT/pAKT levels were determined by immunoblotting. Proliferation studies utilized an acid phosphatase-based assay. Results: ELISA analysis confirmedsignificantly lower HER2 expression in T47D (44 +/- 17 pg/µg) compared to SKBR3 (748 +/- 296 pg/µg), p = 0.015. NER proved a more potent inhibitor of pHER2 and pEGFR as analyzed by immunoblotting and in proliferation studies (NER IC50 - SKBR3 0.03 +/- 0.01 nM, T47D 199 +/- 70 nM, LAP IC50 - SKBR3 20 +/- 1 nM, T47D 1.2 +/- 0.2 µM). LAP induced an increase in both ECD and ICD-containing HER2 protein levels in SKBR3 and T47D cells. No increase in HER-2 levels was observed with NER treatment, as determined by HCA and immunoblotting. EGFR protein levels increased in response to lapatinib in both cell lines. Conclusions: Our results suggest that LAP and NER have differing effects on HER2 protein levels in the models examined. NER provides greater inhibition of HER2 signaling activity but does not increase HER2 protein levels as was observed with LAP. Further pre-clinical assessment of combinations of LAP and NER with HER2 and EGFR monoclonal antibody therapies is warranted in HER2-amplified, HER2-non-amplified and EGFR-expressing breast cancer models.