Differential responses of HER2-positive breast cancer cells to anti-HER2 treatment.

Abstract

e12095 Background: HER2 is a membrane tyrosine kinase receptor which promotes cells growth by activating downstream kinase pathways: RAS/MEK/ERK and PI3K/AKT. Given the fact that HER2 gene is amplified in certain population of breast cancer patients, therapeutic strategy has evolved to target HER2 function. However, it has been long controversial as to which patients are truly benefited from such treatment. In this study, we evaluate impact of HER2 overexpression on response to anti-HER2 treatment using a panel of breast cancer cell lines, and compared FISH vs. RT-PCR for their accuracy in predicting drug responses. Methods: Human breast cancer lines were obtained from ATCC or from cell repository bank at MD Anderson Cancer Center. RhuMAB HER2 was provided by Genentech. Her2 gene amplification was evaluated by FISH method using the PathVysion HER2/NeuDNA probe kit form Abbott. HER2 mRNA expression was analyzed by RT-PCR method. Growth inhibitory and cytotoxic effects of anti-HER2 antibody were determined by MTS assay. Apoptotic cell death was visualized with DAPI staining and quantified by Annexin V-based flow cytometric detection. Results: A total of 12 cell lines are chosen for this study, 4 of them are HER2-negative and 8 are HER2-positive as determined by FISH testing. Anti-HER2 antibody treatment inhibits growth of all cell lines tested, among them, 3 HER2-positive cell lines are identified to undergo apoptotic cell death. Re-culture in fresh medium restores cell growth potential in those non-apoptotic cells, but not in the apoptotic cell lines. FISH score has poor correlation with apoptotic cell death; in contrast, cell lines those expressing more than 20,000 copies of HER2 mRNA, as measured in 1 ng of total RNA, all show apoptosis. More interestingly, apoptotic death appears more severe as HER2 mRNA number increases. Conclusions: Accurate measurement of HER2 expression is essential for improving the outcome of anti-HER2 treatment. Our study suggests that RT-PCR technique seems to better fulfill the aim, and warrants future clinical trials of using RT-PCT to predict a positive response to anti-HER2 therapies.