Second-Generation Terbium Products
Cisbio’s first-generation products use Europium cryptate to monitor reactions between biomolecules. In April, Cisbio launched its HTRF Terbium (Tb) platform for GPCR screening with the introduction of IP-One Tb and cAMP Tb. These assays are the first to incorporate Lumi4™-Tb cryptate for enhanced screening performance. Lumiphore developed Lumi4-Tb and licensed it exclusively to Cisbio for second-generation drug discovery assays.
Terbium cryptate shows different photophysical properties than Europium, and it is compatible with additional acceptors, including green-emitting ones. This allows for multiplexing of signals. Moreover, all Terbium products run on the same HTRF-compatible instruments as Europium ones.
Terbium is exceptionally bright—10 to 20 times brighter than Europium—lending itself to the exploration of cell surface receptors, according to Eric Trinquet, head of Cisbio’s technology and chemistry department. In proof-of-concept experiments, done in collaboration with researchers at the Institute of Functional Genomics, Trinquet found that ligand-binding assays that are selective for cell-surface receptors run more efficiently with Terbium than Europium cryptates. Additionally, Terbium assays run in much more cell-friendly experimental conditions than Europium assays, he noted.
“These new cryptates also perform outstandingly when used with suicide enzyme-labeling technologies like SNAP Tags from Covalys,” Trinquet said. His group has developed new substrates with enhanced reactivity for GPCR ligand-binding and oligomerization assays in living cells.
Cisbio is developing a new HTplex™ platform for the detection of two biological agents in the same microwell. The power of Terbium to multiplex was demonstrated in an experiment conducted in collaboration with Novartis, which aimed to identify the normal and mutant forms of the Huntington’s disease protein in neuronal cell lysates.
By using a common Terbium-labeled antibody directed against a conserved epitope on the protein and two other antibodies labeled with red and green acceptors, both the normal and mutant form of the Huntington’s protein were detected simultaneously (Figure 3). In this system, the Terbium cryptate acts as a fluorescence donor for both acceptors, and no overlap of their fluorescent signals occurred. “This first proof-of-concept of the HTplex technology worked well,” said Trinquet.
Cisbio will launch HTplex services by the end of this year, and new tools for exploring cell surface receptors should be out in 2009.