Novel, potent calmodulin antagonists derived from an all-D hexapeptide combinatorial library that inhibit in vivo cell proliferation: activity and structural characterization

Calmodulin is known to bind to various amphipathic helical peptide sequence s, and the calmodulin-peptide binding surface has been shown to be remarkab ly tolerant sterically. D-Amino acid peptides, therefore, represent potenti al nonhydrolysable intracellular antagonists of calmodulin. In the present study, synthetic combinatorial libraries have been used to develop novel D- amino acid hexapeptide antagonists to calmodulin-regulated phosphodiesteras e activity. Five hexapeptides were identified from a library containing ove r 52 million sequences. These peptides inhibited cell proliferation both in cell culture using normal rat kidney cells and by injection via the femora l vein following partial hepatectomy of rat liver cells. These hexapeptides showed no toxic effect on the cells. Despite their short length, the ident ified hexapeptides appear to adopt a partial helical conformation similar t o other known calmodulin-binding peptides, as shown by CD spectroscopy in t he presence of calmodulin and NMR spectroscopy in DMSO. The present peptide s are the shortest peptide calmodulin antagonists reported to date showing potential in vivo activity.