Process bottlenecks in high-throughput screening (HTS) can significantly diminish the productivity of a drug discovery program. One major and costly bottleneck within the drug discovery process is the creation of the modified cells needed for HTS cell-based assays for screening drug candidate libraries. A related bottleneck is the inability to transfect certain cells types and to load relevant agents such as mRNA, proteins, and small molecules.
Cells for HTS cell-based assays are commonly modified to express genes that produce proteins for drug targets. Traditionally, cell lines are modified for stable integration and expression of the target gene; this process can be long and time-consuming, often taking several months to create a stable clone. Another option is to transfect cells with the target genes to produce a transient response of several days. Drug discovery groups are increasingly using transiently transfected cells because of the savings in time and other resources versus the creation of stable cell lines.
Among commonly used transient transfection techniques are transfection with lipid-based reagents and cell transduction with viral vectors. Both methods have significant limitations. Reagents for transfecting cells on the multibillion cell scale required for HTS campaigns are expensive, and not appropriate for all cell types and loading agents. Limitations of viral vector-based transductions include the time and cost of vector production and scale-up, cell defense responses to viral vectors, and a limited range of transducible cell types.
To expand the range of cell and loading agent combinations and to overcome the limitations of other transient transfection methods, MaxCyte has introduced the MaxCyte® STX™ Scalable Transfection System, based on its flow electroporation technology.
How STX Transfection for HTS Works
The MaxCyte STX (Figure 1) is a benchtop instrument controlled by an integrated computer. To prepare cells for HTS runs, the MaxCyte STX uses a simple, sterile procedure to transfect up to 10 billion cells in under 30 minutes. First, cells harvested from large-scale culture systems, along with the molecules to be transfected, are suspended in MaxCyte’s protein-free electroporation buffer.
The suspended cells are aseptically transferred to a sterile processing assembly, which is then installed on the MaxCyte STX. The MaxCyte STX computer comes preprogrammed with transfection protocols for common HTS cell types such as HEK293 and CHO cells. The user selects a cell transfection protocol and clicks the start button. This activates computer-controlled valves and an air pressure system that regulates the flow of cells through the MaxCyte STX electroporation chamber.
Inside the chamber, a series of electrical pulses tailored to the selected cell type loads the molecules into the cells as they flow between the electrodes. Cells emerging from the electroporation chamber then flow into a cell collection chamber. After a short incubation, the cells are ready for culture or cryopreservation. This MaxCyte STX instrument can also be used in a small-scale static mode to modify cells in the quantities appropriate for assay development.