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/mm
2. Employing this techni
que a 9-mer, 442,368-member peptide library (designed around the 13 amino acid α-MSH peptide se
quence) made up of 12 separate pools of 36,864 peptides/pool was assayed. Initially, a fraction (
10 % ) of each pool was scanned (
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 se
quenced by Edman degradation to determine the peptide se
quence. Re-synthesized peptides were re-examined against α-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.
