Inhibition of beta-amyloid-induced neurotoxicity by imidazopyridoindoles derived from a synthetic combinatorial library.

Alzheimer's disease is a progressive neurodegenerative disorder characterized by the deposit of amyloid fibrils in the brain that result from the self-aggregative polymerization of the beta-amyloid peptide (Abeta). Evidence of a direct correlation between the ability of Abeta to form stable aggregates in aqueous solution and its neurotoxicity has been reported. The cytotoxic effects of Abeta have been attributed to the aggregation properties of a domain corresponding to the peptide fragment Abeta25-35. In an effort to generate novel inhibitors of Abeta neurotoxicity and/or aggregation, a mixture-based synthetic combinatorial library composed of 23 375 imidazopyridoindoles was generated and screened for inhibition of Abeta25-35 neurotoxicity toward the rat pheochromocytoma PC-12 cell line. The effect of the identified lead compounds on Abeta25-35 aggregation was then evaluated by means of circular dichroism (CD) and thioflavin-T fluorescence spectroscopy. Their activity against Abeta1-42 neurotoxicity toward the PC-12 cell line was also determined. The most active imidazopyridoindoles inhibited both Abeta25-35 and Abeta1-42 neurotoxicity in the low- to mid-micromolar range. Furthermore, inhibition of the random coil to beta-sheet transition and self-aggregation of Abeta25-35 was observed by CD and fluorescence spectroscopy, supporting the relationship between inhibition of the Abeta aggregation process and neurotoxicity.

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 sequences, and the calmodulin-peptide binding surface has been shown to be remarkably tolerant sterically. D-Amino acid peptides, therefore, represent potential 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 phosphodiesterase activity. Five hexapeptides were identified from a library containing over 52 million sequences. These peptides inhibited cell proliferation both in cell culture using normal rat kidney cells and by injection via the femoral vein following partial hepatectomy of rat liver cells. These hexapeptides showed no toxic effect on the cells. Despite their short length, the identified hexapeptides appear to adopt a partial helical conformation similar to other known calmodulin-binding peptides, as shown by CD spectroscopy in the presence of calmodulin and NMR spectroscopy in DMSO. The present peptides are the shortest peptide calmodulin antagonists reported to date showing potential in vivo activity.

Mixture-based heterocyclic combinatorial positional scanning libraries: discovery of bicyclic guanidines having potent antifungal activities against Candida albicans and Cryptococcus neoformans.

A mixture-based synthetic combinatorial library of more than 100,000 bicyclic guanidines was generated in a positional scanning format and assayed for activity against Candida albicans. Potent individual bicyclic guanidines were directly identified following the screening of the library. Time-kill curve studies indicated bactericidal activities for the individual bicyclic guanidines. These compounds also showed potent activity against Cryptococcus neoformans. These studies demonstrate the value of using mixture-based combinatorial positional scanning libraries made up of heterocyclic compounds for the rapid identification of novel classes of antifungal compounds.