abstract
Subtype-selective thyromimetics have potential as new pharmaceuticals for the prevention or treatment
of heart disease, high LDL cholesterol and obesity, but there are only a few methods that can detect
agonistic behavior of TR-active compounds. Among these are the rat pituitary GH3 cell assay and transcriptional
activation assays in engineered yeast and mammalian cells. We report the construction and
validation of a newly designed TRα-1 bacterial biosensor, which indicates the presence of thyroid active
compounds through their impacts on the growth of an engineered Escherichia coli strain in a simple
defined medium. This biosensor couples the configuration of a hormone receptor ligand-binding domain
to the activity of a thymidylate synthase reporter enzyme through an engineered allosteric fusion
protein. The result is a hormone-dependent growth phenotype in the expressing E. coli cells. This sensor
can be combined with our previously published TRβ-1 biosensor to detect potentially therapeutic
subtype-selective compounds such as GC-1 and KB-141. To demonstrate this capability, we determined
the half-maximal effective concentration (EC50) for the compounds T3, Triac, GC-1 and KB-141 using our
biosensors, and determined their relative potency in each biosensor strain. Our results are similar to
those reported by mammalian cell reporter gene assays, confirming the utility of our assay in identifying
TR subtype-selective therapeutics. This biosensor thus provides a high-throughput, receptor-specific,
and economical method (less than US$ 0.10 per well at laboratory scale) for identifying important
therapeutics against these targets.