Screening method for identification of novel G protein coupled receptor ligands with focus on class B modulators
The family of G protein-coupled receptors (GPCRs) has been proven to provide valuable targets for the development of therapeutics. Nevertheless, identification of synthetic ligands to modulate class B GPCRs has been hardly achieved. In human the class B GPCRs (also class 2 GPCRs / secretin-like family of GPCRs) consists of fifteen members. Type B receptors are built from a seven-helical transmembrane domain and an extracellular N-terminal domain that usually mediates high affinity binding of endogenous peptidic ligands. Activation of these receptors is achieved through a distinct part of the ligand in a subsequent binding step to the receptor’s activation domain that resides in its transmembrane domain. Class B GPCRs play an important role e.g. in glucose metabolism (GLP1R) or as a key regulator of the hypothalamicpituitary-adrenal axis (CRF1R) rendering them potential targets for the development of new drugs.
Scientists from the Max-Plack-Institute of Psychiatry in Munich developed a screening method for the identificiation of novel class B GPCR modulators that is also applicable to other GPCR classes. This approach is based on a separation of the binding and activation domain of endogenous class B ligands. Using a „click“ chemistry approach (azide-alkyne bioconjugation) different compounds (e.g. peptides, synthetic peptides or small molecules) can be attached to a preselected binding domain yielding a library of different „binding domain - compound“ fusions. This fusion facilitates interaction of the compound with the receptor’s activation domain and therefore the investigation of its capacity to modulate the GPCR (Fig. 1B). Since purification of these fusions can be substantially reduced to a minimum without affecting activity, this method allows for an efficient screening approach.
As proof of concept, a novel and high affine peptidic ligand for the CRF1 receptor has been developed. The ligand acts as specific activator of this particular receptor even in the absence of the binding domain used during the screening/optimization phase. The obtained biomimetic peptide was fully functional in vivo further emphasizing the value of this screening approach.
An international application (WO2008/022716A2) has been filed that already entered national/regional phases in US and Europe.