RESEARCH

Our research is focused on microfluidic-based assays for high throughput drug screening and directed evolution of genetically-encoded drug candidates. Therefore, we develop novel microfluidic platforms as well as novel assays (cell-based and biochemical assays). In particular, we are currently addressing the following tasks:

Microfluidic platforms

Aqueous drops of a water-in-oil emulsion can be used as miniaturized reaction vessels for biological, biochemical and chemical reactions (Griffiths A.D. and Tawfik D.S. (2003) EMBO J. 22:24-35 ). Furthermore, applying microfluidic devices, these emulsions can be generated at very high speeds (several thousands drops per second). We are interested in using this technology for novel approaches in drug screening. We have developed microfluidic platforms allowing the long-term (several days) encapsulation of fully viable human cells and even multicellular organisms into aqueous microcompartments. Subsequent to an incubation step off-chip, a fluorescence readout of individual microcompartments can be performed at rates of up to 500/s. Noteworthy, all living organisms can be recovered and cultivated in ordinary culture flask subsequent to the encapsulation and readout.

Encapsulation of HEK293T cells (left) and C. Elegans (center) into aqueous microcompartments. Subsequent to an incubation step a fluorescence readout of individual microcompartments can be performed. The optical setup (right) allows acquisition rates of up to 500 samples per second.

We are currently establishing systems allowing to coencapsulate different drug candidates (synthetic or genetically-encoded) into each microcompartment. Hence the technology could replace conventional microtitre-based assays, strongly increase throughput and drastically decrease the assay costs. Ultimately, it should also allow the use of primary human cells (rather than transformed cell lines), which are arguably the most physiologically relevant model systems, but which generally cannot be obtained on the scale required for HTS.

Novel assays

We are continously developing novel assays compatible with the above described technology. This basically means that a desired property of a drug candidate (e.g. inhibition of viral cell-entry) has to be converted into a readout signal detectable on-chip (e.g. fluorescence). We have already developed corresponding assays for the inhibiton of viral cell-entry, fibrinolysis and the efficient killing of pathogens.

Assay for the inhibition of viral cell-entry. (PTC/GB2006/000316. (2006)) A) The indicator cells stably express a membrane-bound and HA-tagged form of tissue plasminogen activator (tPA). This enzyme converts plasminogen into active plasmin which subsequently turns a substrate into a fluorogenic product. The effector particles have packaged a vector encoding shRNA targeting the reporter gene. Hence upon cell-entry, the tPA fusion protein is downregulated and no fluorogenic product is generated. B) Fluorescence signal of HEK293T cell-derived indicator cells that have been incubated with MLV(VSV-G) effector particles in presence (dark blue) and absence(light blue) of 25µM AZT. X-axis: time in seconds, Y-axis: arbitrary fluorescence units in thousands.