10.
Cell-based bioassays have been suggested for screening of hormones and drug bioactivities. They are a plausible alternative
to animal based methods. The technique used is called receptor/reporter system. Receptor/reporter system was initially developed
as a research technique to understand gene function. Often reporter constructs containing viral promoters were used because
they could be expressed with very 'high' magnitude in a variety of cell types in the laboratory. On the other hand mammalian
genes are expressed in a cell/tissue specific manner, which makes them (
i.e. cells/tissues) specialized for specific function
in vivo. Therefore, if the receptor/reporter system is to be used as a cell-based screen for testing of hormones and drugs for human
therapy then the choice of cell line as well as the promoter in the reporter module is of prime importance so as to get a
realistic measure of the bioactivities of 'test' compounds. We evaluated two conventionally used viral promoters and a natural
mammalian promoter, regulated by steroid hormone progesterone, in a cell-based receptor/reporter system. The promoters were
spliced into vectors expressing enzyme CAT (chloramphenicol acetyl transferase), which served as a reporter of their magnitudes
and consistencies in controlling gene expressions. They were introduced into breast cell lines T47D and MCF-7, which served
as a cell-based source of progesterone receptors. The yardstick of their reliability was highest magnitude as well as consistency
in CAT expression on induction by sequential doses of progesterone. All the promoters responded to induction by progesterone
doses ranging from 10
-12 to 10
-6 molar by expressing CAT enzyme, albeit with varying magnitudes and consistencies. The natural mammalian promoter showed the
most coherence in magnitude as well as dose dependent expression profile in both the cell lines. Our study casts doubts on
use of viral promoters in a cell-based bioassay for measuring bioactivities of drugs and hormones for human therapy and suggests
caution regardingtranslation
in toto, of a research technique as a cell-based bioassay for drug screening.
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