Science & Technology
Cellular drug screening
An industrial application of particular importance is the generation of cell lines stably expressing target gene products that are toxic to cells. Expressing such genes under Tet control allows expansion of cells to high density before turning on expression of the target gene product. This way, even toxic gene products can be generated in sufficient amounts to support e.g. high throughput screening.
Another successful example of this strategy is the development of 2 cell lines: HepAD38 and HepAD79 in 1997/98 by 'Avid Therapeutics' which contain, stably integrated, the entire genome of Hepatitis B virus (HBV) under Tet control . The search for anti-Hepatitis therapeutics has been severly hampered by the lack of a cell culture replication system for these viruses. In the HepAD cell lines, commencement of viral replication is strictly regulated by Tet and leads to a high level of HBV DNA production after the cells become confluent. In contrast to another cell line (HepG2 2.2.15) available at the time and used to assay compounds for anti-HBV activity, the level of HBV production in HepAD38 is significantly higher and sufficient to support 96-well microtiter plate-based high throughput screens for inhibitors of HBV replication. Since numerous highly pathogenic viruses exploit similar replication mechanisms, it was assumed that drug candidates for different pathogens could also be identified with the help of these cell lines. In fact, they were used to discover and to characterize several novel antiviral substances targeting reverse transcriptase, a crucial enzyme in the replication of HBV, HCV and HIV. As such, 'Gilead' analyzed 'Tenofovir' a potent drug against HBV via the HepAD cell lines and markets the nucleoside analogue for the treatment of HIV disease under the trade name 'Viread'. The pharmaceutical company 'Pharmasset, Inc.' which is committed to the discovery and development of drugs to fight viral infections has used the mentioned Tet cell lines for several years e.g. during development of 'Reverset', an anti-HIV drug. Finally, biopharmaceutical company 'Genelabs Technologies' (now part of 'GlaxoSmithKline') is focusing on the discovery and development of novel compounds for viral infections and has used the HepAD38 cell line for its Hepatitis research program.
Until today HepAD 38 and HepAD79 cell lines are still widely used in drug discovery or drug development to evaluate the inhibitory effect of compounds for viral replication.