Amphibian Melanophore Technology as a Functional Screen for Antagonists of G-Protein Coupled 7-Transmembrane Receptors

Functional cell-based uHTS in chemical genomic drug discovery

The availability of genomic information significantly increases the number of potential targets available for drug discovery, although the function of many targets and their relationship to disease is unknown. In a chemical genomic research approach, ultra-high throughput screening (uHTS) of genomic targets takes place early in the drug discovery process, before target validation. Target-selective modulators then provide drug leads and pharmacological research tools to validate target function. Effective implementation of a chemical genomic strategy requires assays that can perform uHTS for large numbers of genomic targets. Cell-based functional assays are capable of the uHTS throughput required for chemical genomic research, and their functional nature provides distinct advantages over ligand-binding assays in the identification of target-selective modulators.

Use of a cell-based, lawn format assay to rapidly screen a 442,368 bead-based peptide library

A cell-based, lawn format assay utilizing an in situ photocleavage method has been developed that allows the rapid examination of large bead-based compound libraries as discrete molecules. The format uses frog melanophore cells in a contiguous, adherent, confluent layer in small petri dishes covered with a 0.5-1-mm layer of agarose containing 130 micron diameter TentaGel beads at a density of 2-20 beads/mm2. Employing this technique a 9-mer, 442,368-member peptide library (designed around the 13 amino acid alpha-MSH peptide sequence) made up of 12 separate pools of 36,864 peptides/pool was assayed. Initially, a fraction (approximately 10%) of each pool was scanned (approximately 3700 beads from each pool) in 60-mm petri dishes to identify the most active pools. Upon direct photocleavage of the beads with UV light (365 nm), each petri dish was photographed over a 60-min period with a CCD camera to record changes in light intensity as an index of melanosome dispersion. Active beads were those that were surrounded by a localized decrease in light transmittance indicating melanosome dispersed cells. Upon examination with a dissecting microscope, single beads centrally located to a circular array of dispersed cells were identified and removed from the agarose and sequenced by Edman degradation to determine the peptide sequence. Re-synthesized peptides were re-examined against alpha-MSH receptor to confirm and quantify the activity. Several 9-mer peptides were identified with potencies similar to the natural 13-mer peptide. This method allows for the rapid screening of large bead-based photo-cleavable peptide libraries with the advantage that each compound is screened as a discrete molecule in a well-less format.