Use of a highly parallel microfluidic flow cell array to determine therapeutic drug dose response curves.

A high-throughput, microfluidic flow cell array (MFCA) system has been modified to enable drug screening against small-volume cell-, and tissue cultures. The MFCA is composed of a 3D channel network that simultaneously flows fluids through forty-eight 830 µm by 500 µm flow cells, which physically divide and fluidically seal an existing culture into multiple compartments when docked onto the surface of a cell or tissue culture dish. The modified system provides temperature (37 °C) and CO2/pH level controls, while continuously flowing solutions (media or other liquid such as drug suspensions) over the cells/tissues. These assays were enhanced and validated using inverted microscopy and fluorescent staining techniques which also allow real time viability and toxicity assessments. This work presents the results of this new generation in vitro drug testing assay performed using this modified MFCA system. This setup allows the testing of 48 drug combinations on 48 different cell-, tissue specimen at once under flow conditions. All 48 flow cells were utilized to test 5 different concentrations of cisplatin (CDDP). CDDP solutions in various concentrations were continually flowed over cultured human ovarian cancer cells for 48 h. Viability assessments were performed using red-orange calcein and SYTOX ® Green nucleic acid stains. Cells were imaged at the beginning and end of the experiment (48 h). In order to compare and validate MFCAs suitability as drug screening assay, MTT assays were performed on cells. We found that both, MTT and MFCA assays generated dose-response curves with similar profiles. Innovative advantages of the MFCA system include the ability of handling smaller amounts of solutions compared to conventional and current state of the art drug screening and cell viability/toxicity methods. It also provides the ability to continually deliver fresh solution to the cell samples, while eliminating wastes that are produced. Based on our here reported findings MFCA may have a strong potential of providing a more physiological model than current state of the art static MTT assays.

Shift in a large river fish assemblage: body-size and trophic structure dynamics.

As the intensity and speed of environmental change increase at both local and global scales it is imperative that we gain a better understanding of the ecological implications of community shifts. While there has been substantial progress toward understanding the drivers and subsequent responses of community change (e.g. lake trophic state), the ecological impacts of food web changes are far less understood. We analyzed Wabash River fish assemblage data collected from 1974-2008, to evaluate temporal variation in body-size structure and functional group composition. Two parameters derived from annual community size-spectra were our major response variables: (1) the regression slope is an index of ecological efficiency and predator-prey biomass ratios, and (2) spectral elevation (regression midpoint height) is a proxy for food web capacity. We detected a large assemblage shift, over at least a seven year period, defined by dramatic changes in abundance (measured as catch-per-unit-effort) of the dominant functional feeding groups among two time periods; from an assemblage dominated by planktivore-omnivores to benthic invertivores. There was a concurrent increase in ecological efficiency (slopes increased over time) following the shift associated with an increase in large-bodied low trophic level fish. Food web capacity remained relatively stable with no clear temporal trends. Thus, increased ecological efficiency occurred simultaneous to a compensatory response that shifted biomass among functional feeding groups.