Screening
human stem cells which are now increasingly being used. Services at B’SYS include the rapid develop- ment of high-expression cell lines and include fluo- rescence activated cell sorting that represents an ideal method of clone selection (Figure 13).
High throughput screening of voltage-gated ion channels has been performed for close to a decade now and is an established tool in drug discovery. Ligand-gated ion channels have proved to be more difficult to incorporate into a high throughput screening model based on automated electrophysi- ology. A major limitation so far has been the need to rapidly apply compounds to the cells while con- tinuously measuring the signal. This is essential for being able to resolve rapidly activating and desen- sitising ion channel currents such as those pro-
duced by potential drug targets such as GABAA and nAchR. Furthermore, the compound applica- tion must be performed in such a way that record- ing duration and success rate is maximised. Using a microfluidic patch clamp technology, the Dynaflow®HT from Cellectricon (www.cellectri-
con.com) offers a low-cost and effective method to screen large number of compounds against both ligand- and voltage-gated targets. The microfluidic technology makes it possible to apply and remove compound very rapidly (low ms range) while not exposing the cells to strong forces that would dis- rupt the cell and terminate the recording. Before applying compound the chip is rinsed of non- trapped cells to avoid compound loss due to bind- ing to non-recordable cells. All cell handling is per- formed online to proven optimal cell conditions. The Dynaflow HT offers up to eight hours walk away time and provides excellent data quality and assay stability making it optimal for high through- put automated electrophysiology work (Figure 14).
ChanTest (
www.chantest.com) is a CRO specialis- ing in ion channels and their role in drug discov- ery and safety. Improvements in automated elec- trophysiology have made ion channels more acces- sible as drug targets. At ChanTest, all major volt- age- and ligand-gated ion channels are expressed in cell lines as replication-competent or division- arrested. Cell lines are validated on a large array of manual and automated patch clamp instru- ments and high throughput automated fluores- cence instruments. HTS at between 3,000 data points per day (dps/d) and 10,000 dps/d or greater has been achieved with automated megaohm seal patch clamping or automated fluorescence read- outs of membrane potential, calcium ion flux or potassium ion flux. Profiling and QSAR are done
Drug Discovery World Fall 2011
Figure 14: Image showing a cell trapping zone in the microfluidic patch clamp plate utilised in Cellectricon’s Dynaflow®HT system
on these instruments or with automated gigaohm seal patch clamping at throughputs between 100 and 300 dps/d. State of the art protocols are adapted for each type of instrument keeping in mind the differences in data quality between megaohm and gigaohm patch clamping and the absence of voltage control using fluorescence
Figure 15
Ion channel testing at ChanTest is undertaken using a wide variety of manual and automated patch clamp instruments and high throughput automated fluorescence imagers
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