Kathryn A. Brown

Response to trastuzumab, erlotinib, and bevacizumab, alone and in combination, is correlated with the level of human epidermal growth factor receptor-2 expression in human breast cancer cell lines

Human epidermal growth factor receptor-2 (HER2) and epidermal growth factor receptor (EGFR) heterodimerize to activate mitogenic signaling pathways. We have shown previously, using MCF7 subcloned cell lines with graded levels of HER2 expression, that responsiveness to trastuzumab and AG1478 (an anti-EGFR agent), varied directly with levels of HER2 expression. HER2 and EGFR up-regulate vascular endothelial growth factor (VEGF), a growth factor that promotes angiogenesis and participates in autocrine growth-stimulatory pathways that might be active in vitro. Here, we show that trastuzumab, erlotinib, and bevacizumab, individually and in combination, inhibit cell proliferation in a panel of unrelated human breast cancer cell lines, in proportion to their levels of HER2 expression. The combination of all three drugs provided a greater suppression of growth than any single drug or two-drug combination in the high HER2–expressing cell lines (P < 0.001). Combination index analysis suggested that the effects of these drugs in combination were additive. The pretreatment net level of VEGF production in each cell line was correlated with the level of HER2 expression (r = 0.883, P = 0.016). Trastuzumab and erlotinib each reduced total net VEGF production in all cell lines. Multiparameter flow cytometry studies indicated that erlotinib alone and the triple drug combination produced a prolonged but reversible blockade of cells in G1, but did not increase apoptosis substantially. These studies suggest that the effects of two and three-drug combinations of trastuzumab, erlotinib, and bevacizumab might offer potential therapeutic advantages in HER2-overexpressing breast cancers, although these effects are of low magnitude, and are likely to be transient. [Mol Cancer Ther 2007;6(10):2664–74]

Multiparameter analysis of human epithelial tumor cell lines by laser scanning cytometry

Laser scanning cytometry (LSC) is a relatively new slide-based technology developed for commercial use by CompuCyte (Cambridge, MA) for performing multiple fluorescence measurements on individual cells. Because techniques developed for performing four or more measurements on individual lymphoid cells based on light scatter as a triggering parameter for cell identification are not suitable for the identification of fixed epithelial tumor cells, an alternative approach is required for the analysis of such cells by LSC. Methods for sample preparation, event triggering, and the performance of multiple LSC measurements on disaggregated fixed human cells were developed using normal lymphocytes and two human breast cancer cell lines, JC-1939 and MCF-7, as test populations. Optimal conditions for individual cell identification by LSC were found to depend on several factors, including deposited cell density (cells per unit area), the dynamic range of probe fluorescence intensities, and intracellular distribution of the fluorescent probe. Sparsely deposited cells exhibited the least cell overlap and the brightest immunofluorescent staining. Major advantages of using DNA probes over a cytoplasmic immunofluorescent protein marker such as tubulin for event triggering are that the former exhibit greater fluorescence intensity within a relatively sharply demarcated nuclear region. The DNA-binding dye LDS-751 was found to be suboptimal for quantitative DNA measurements but useful as a triggering measurement that permits the performance of simultaneous fluorescein isothiocyanate-, phycoerythrin-, and indodicarbocyanine-based measurements on each cell. A major potential advantage of LSC over flow cytometry is the high yields of analyzable cells by LSC, permitting the performance of multiple panels of multicolor measurements on each tumor. In conclusion, we have developed and optimized a technique for performing multiple fluorescence measurements on fixed epithelial cells by LSC based on event triggering using the DNA-binding dye LDS 751. Although not ideal for quantitative measurements of cell DNA content, the large Stokes shift of this dye permits the performance of three or more additional fluorescence measurements on each cell.

A Suitable Method for Identifying Cell Aggregates in Laser Scanning Cytometry Listmode Data for Analyzing Disaggregated Cell Suspensions Obtained from Human Cancers

The presence of cell aggregates in cell suspensions obtained from human solid tumors can interfere with the measurement of cell DNA content of cell singlets, and can confound multiparameter analysis of other measurements on the same cells. Flow cytometric corrections for cell aggregates based on signal pulse shape have not proven to be reliable. Mathematical models have been developed to correct for cell aggregates in binned DNA histogram data, but they are not suitable for the correction of correlated non‐DNA measurements obtained on the same cells.

Guidelines for improving the reproducibility of quantitative multiparameter immunofluorescence measurements by laser scanning cytometry on fixed cell suspensions from human solid tumors.

Laser scanning Cytometry (LSC) is a versatile technology that makes it possible to perform multiple measurements on individual cells and correlate them cell by cell with other cellular features. It would be highly desirable to be able to perform reproducible, quantitative, correlated cell‐based immunofluorescence studies on individual cells from human solid tumors. However, such studies can be challenging because of the presence of large numbers of cell aggregates and other confounding factors. Techniques have been developed to deal with cell aggregates in data sets collected by LSC. Experience has also been gained in addressing other key technical and methodological issues that can affect the reproducibility of such cell‐based immunofluorescence measurements.

Breast Cancer: Expression of HER-2 and Epidermal Growth Factor Receptor as Clinical Markers for Response to Targeted Therapy

In this chapter we consider the relationships that involve both HER-2 and epidermal growth factor receptor (EGFR), with a particular focus on the potential use of these two transmembrane growth factor receptors as biomarkers for predicting response to targeted therapeutic agents directed at either or both of them. Effective clinical use of these receptors as biomarkers depends both on an understanding of their complex biological interactions, and an awareness of the shortcomings of current methods of measuring these two cellular constituents in the clinical setting. Here we will review selected aspects of these two topics, and attempt to develop working hypotheses and organizing principles that might be useful in translating basic knowledge into clinical practice. CELL AND MOLECULAR BIOLOGY OF HER-2/EPIDERMAL GROWTH FACTOR RECEPTOR INTERACTIONS