Expression of Her-2/neu in human lung cancer cell lines by immunohistochemistry and fluorescence in situ hybridization and its relationship to in vitro cytotoxicity by trastuzumab and chemotherapeutic agents

Overexpression of the Her-2/neu oncogene and receptor protein was reported in similar to 20% of breast cancers and was associated with a poor prognosi s. Her-2/neu expression was a predictor for response to trastuzumab, a mono clonal antibody that recognizes the Her-2/neu cell surface receptor. Data r egarding the expression of Her-2/neu in lung cancer are far more limited, a nd there is little information regarding the influence of Her-2/neu express ion and response to trastuzumab alone or in combination with chemotherapeut ic agents. In this report we evaluated Her-2/neu gene expression by fluores cence in situ hybridization (FISH) and the cell surface expression of the H er-2/neu receptor by immunohistochemistry using the HercepTest and by FACS analysis in 31 lung cancer cell lines with 5 breast cancer cell lines as co ntrols. By FACS, we found Her-2/neu overexpression (mean fluorescence inten sity >8) in 2 of the 22 nonsmall cell lung cancer (NSCLC cell lines (9%), n one of 11 small cell lung cancer (SCLC cell lines, and 4 of 5 breast cancer cell lines. A positive HercepTest (2+ or 3+) was found in 6 of 19 NSCLC ce ll lines (26%, 2+; 5%, 3+), 1 of 3 SCLC cell lines (33%), and 4 of 5 breast cancer cell lines (80%). One of 6 NSCLC cell lines examined 17%) had gene amplification with > 32 copies of Her-2/neu/cell and had homogeneous staini ng regions. One NSCLC cell line had a maximum of 14 copies of Her-2/neu/cel l, and 3 had modest increases in Her-2/neu gene copy number without gene am plification (maximum 5-8 copies/cell). None of the SCLC cell lines had more than a maximum of 4 copies/cell, whereas the 2 breast cancer cell lines ha d maximum Her-2/neu copy numbers of 80 and 5, respectively. Aneusomy rather than true amplification was the major cause of increased Her-2/neu express ion in most of the NSCLC cell lines. There was a strong correlation when th e results of fluorescence-activated cell sorter, HercepTest results, and FI SH were compared in pairs. Furthermore, Trastuzumab produced a G(1) cell cy cle arrest and growth inhibition only in cell lines expressing Her-2/neu. T he IC50 for growth inhibition was correlated with cell surface Her-2/neu ex pression. The combination of trastuzumab and chemotherapeutic agents produc ed more than additive growth inhibition in cell lines expressing Her-2/neu, but the level of additivity was not related to the amount of Her-2/neu exp ression. These data indicate that trastuzumab alone and in combination with chemotherapeutic agents should be tested in NSCLC patients and that Her-2/ neu should be assessed by both immunohistochemistry and FISH methods in the se studies to determine which test is the best predictor of outcome.