Synthesis and screening of positional scanning combinatorial libraries.

This unit presents a combinatorial library method that consists of the synthesis and screening of mixture-based synthetic combinatorial libraries (SCL) of peptide molecules. The protocols employ peptide SCL to identify peptides recognized by mAbs and T cells. The first protocol uses a positional scanning SCL (PS-SCL) made up of hexapeptides to identify antigenic determinants recognized by mAbs. The 120 mixtures in the hexapeptide PS-SCL are tested for their inhibitory activity in a competitive ELISA. The second protocol uses a decapeptide PS-SCL to identify T cell peptide ligands. The 200 mixtures of the decapeptide PS-SCL are tested for their ability to induce proliferation. Support protocols cover optimization of the assay conditions for each mAb or T cell, to achieve the best level of sensitivity and reproducibility, and preparation of a hexapeptide PS-SCL, along with deconvolution approaches.

We report here, the design and synthesis of a positional scanning synthetic combinatorial library for the identification of novel peptide ligands targeted against the cancer-specific epidermal growth factor tyrosine kinase receptor mutation variant III (EGFRvIII). This receptor is expressed in several kinds of cancer, in particular, ovarian, glioblastomas, and breast cancer, but not in normal tissue. The library consisted of six individual positional sublibraries in the format, H-O(1-6)XXXXX-NH(2), O being one of the 19 proteinogenic amino acids (cysteine omitted) and X an equimolar mixture of these. The library consisted of 114 mixtures in total. Using a biotin-streptavidin assay, the binding of each sublibrary to NR6M, NR6W-A, and NR6 cells was tested. These cells express EGFRvIII, EGFR, and neither of the receptors, respectively. The result from each sublibrary was examined to identify the most active amino acid residue at each position. On the basis of this knowledge, eight peptides were synthesized and tested for binding to EGFRvIII. We identified one peptide, H-FALGEA-NH(2), that showed more selective binding to the mutated receptor than the EGFRvIII specific peptide PEPHC1. This study demonstrates the value of using mixture-based combinatorial positional scanning libraries for the identification of novel peptide ligands targeted against the cancer-specific EGFRvIII. Our best candidate H-FALGEA-NH(2) will be radioactively labeled and evaluated as an imaging agent for positron emission tomography investigation for diagnosis, staging, and monitoring of therapy of various types of cancer.

Screening of a synthetic peptide combinatorial library to identify inhibitors of the appressorium formation in Magnaporthe oryzae

159 - Identification of Antimelanogenic Peptides through Positional Scanning of a Synthetic Peptide Combinatorial Library

Combinatorial library synthesis and screening methods, which enable the rapid identification of highly active compounds, have revolutionized basic research and drug discovery. A number of different combinatorial approaches based on the principles of solid phase synthesis have been used to generate enormous molecular diversities, including peptides, peptidomimetics, and small organic molecules. The advantage of the various combinatorial approaches compared to traditional drug synthesis and screening methods is the very large number of compounds that can be simultaneously synthesized and rapidly screened in biological assays.

1 Molecular building principles in nature.- 2 Robotic equipment and microsystem technology in biological research.- 3 Components and systems for microliquid handling.- 4 Nanotiterplates for screening and synthesis.- 5 Chip technology for micro-separation.- 6 Rapid multisample PCR in miniaturized ultrathin-walled microwell plates.- 7 Generation of large libraries.- 8 Generation and screening of solution-phase synthetic peptide combinatorial libraries.- 9 Using oligonucleotide probe arrays to access genetic diversity.- 10 Generation of libraries by print technologies.- 11 Synthesis and screening of bead-based libraries.- 12 Sensors for biomolecular studies.- 13 Fluorescence detection of single molecules applicable to small volume assays.- 14 Fluorescence correlation spectrometry (FCS): Measuring biological interactions in microstructures.- 15 Scanning force microscopy: A microstructured device for imaging, probing, and manipulation of biomolecules at the nanometer scale.- 16 DNA resequencing, mutation detection and gene expression analysis of oligonucleotide microchips.- 17 Miniaturized arrays for DNA analysis.- 18 Manipulation of particles, cells and liquid droplets by high frequency electric fields.- 19 Optical trapping and manipulation.- 20 Computer modeling of protein, nucleic acid, and drug structures.- 21 Optimizing structure and function relationship of nucleic acid molecules.- 22 Optimisation of molecular function.- 23 Appendix.

BackgroundImmunotherapy offers many potential advantages to traditional chemotherapy, including high specificity and low toxicity. One of the goals of immunotherapy is to generate tumor-specific cytotoxic lymphocytes (CTLs), which have the...

BackgroundImmunotherapy offers many potential advantages to traditional chemotherapy, including high specificity and low toxicity. One of the goals of immunotherapy is to generate tumor-specific cytotoxic lymphocytes (CTLs), which have the...

Viral hemorrhagic fevers caused by the arenaviruses Lassa virus in Africa and Machupo, Guanarito, Junin, and Sabia virus in South America are among the most devastating emerging human diseases with fatality rates of 15-35% and a limited antiviral therapeutic repertoire available. Here we used high throughput screening of synthetic combinatorial small molecule libraries to identify inhibitors of arenavirus infection using pseudotyped virion particles bearing the glycoproteins (GPs) of highly pathogenic arenaviruses. Our screening efforts resulted in the discovery of a series of novel small molecule inhibitors of viral entry that are highly active against both Old World and New World hemorrhagic arenaviruses. We observed potent inhibition of infection of human and primate cells with live hemorrhagic arenaviruses (IC(50)=500-800 nm). Investigations of the mechanism of action revealed that the candidate compounds efficiently block pH-dependent fusion by the arenavirus GPs (IC(50) of 200-350 nm). Although our lead compounds were potent against phylogenetically distant arenaviruses, they did not show activity against other enveloped viruses with class I viral fusion proteins, indicating specificity for arenavirus GP-mediated membrane fusion.

DNA-encoded chemical libraries (DECLs) are collections of compounds, individually coupled to DNA tags serving as amplifiable identification barcodes. Since individual compounds can be identified by the associated DNA tag, they can be stored as a mixture, allowing the synthesis and screening of combinatorial libraries of unprecedented size, facilitated by the implementation of split-and-pool synthetic procedures or other experimental methodologies. In this review, we briefly present relevant concepts and technologies, which are required for the implementation and interpretation of screening procedures with DNA-encoded chemical libraries. Moreover, we illustrate some success stories, detailing how novel ligands were discovered from encoded libraries. Finally, we critically review what can realistically be achieved with the technology at the present time, highlighting challenges and opportunities for the future.

The use of water-soluble synthetic peptide combinatorial libraries permits the systematic examination of tens to hundreds of millions of peptides in existing microdilution assays. In the present study, we prepared and determined the antistaphylococcal activities of two new synthetic peptide combinatorial libraries (one N-acetylated, the other not) composed of tetrapeptides having one position defined and the remaining three positions made up of mixtures of L-, D-, and unnatural amino acids (a total of 58 different amino acids). These libraries, when used in conjunction with an iterative selection process, allowed for the development of a series of individually defined tetrapeptides with high levels of activity against Staphylococcus aureus. The activities of the final individual peptides against two additional strains of gram-positive bacteria (methicillin-resistant S. aureus and Streptococcus sanguis), a gram-negative bacterium (Escherichia coli), as well as the yeast Candida albicans were also determined. Cell viability assays showed that the identified peptides are bacteriostatic against both S. aureus and E. coli.

We describe a new method for encoded synthesis, efficient on-resin screening, and rapid unambiguous sequencing of combinatorial peptide libraries. An improved binary tag system for encoding peptide libraries during synthesis was designed to facilitate unequivocal assignment of isobaric residues by MALDI-TOF MS analysis. The improved method for encoded library synthesis was combined with a new versatile on-resin screening strategy that permitted multiple stages and types of screening to be employed successively on one library under mild conditions. The new method facilitated a combinatorial study of transglutaminase (TGase) enzyme substrate peptides, revealing new details of the effect of amino acid composition on TGase substrates. The approach was first demonstrated for an encoded library (130,321 compounds) of lysine pentapeptide substrates of TGase, synthesized using the "split-mix" method. The library was reacted on-resin with TGase enzyme and a soluble desthiobiotin labeled glutamine substrate. Initial screening was performed by adsorbing streptavidin-coated magnetic microparticles onto library beads, followed by magnetic separation. The differential binding affinities of desthiobiotin and biotin for streptavidin were exploited to release the magnetic microparticles and regenerate the desthiobiotin-labeled resin beads for further screening by flow-cytometry-based automated bead sorting, resulting in 345 beads that were sequenced by MALDI-TOF MS analysis. A second library consisted of encoded glutamine hexapeptide substrates, which was reacted on-resin with TGase enzyme and a soluble desthiobiotin-labeled cadaverine. Two-stage screening identified 267 glutamine peptides as TGase-reactive, of which 21 were further analyzed by solution-phase enzyme kinetics. Kinetic results indicated that the peptide PQQQYV from the library has a 68-fold greater substrate specificity than the best known glutamine substrate QQIV. The new encoding and screening strategies described here are expected to be broadly applicable to synthesis and screening of combinatorial peptide libraries in the future.

In less than one minute the catalytic activity and selectivity of a single catalyst was measured in combinatorial libraries of ternary Rh-Pd-Pt-Cu alloys. Only slightly more than two hours were needed to complete a library with 136 elements. The elements of the libraries (ca. 2-4 μg of material) are contained in a two-dimensional array synthesized by a thin-film technique. The analysis was performed by a scanning mass spectrometer (see picture).

Application of a dual color detection scheme in the screening of a random combinatorial peptide library

Synthesis and screening of combinatorial libraries for pharmaceutical lead discovery is a rapidly expanding field. Oligo-N-substituted glycines (NSGs) were one of the earliest sources of molecular diversity in combinatorial libraries. In one of the first demonstrations of the power of combinatorial chemistry, two NSG trimers, CHIR-2279 and CHIR-4531, were identified as nM ligands for two 7-transmembrane G-protein-coupled receptors. The NMR characterization of these two lead compounds was undertaken to verify covalent connectivity and to determine solution conformations, if any. The sequential chemical shift assignments were performed using a new strategy for assigning 1H and 13C resonances of NSGs. The conformational preferences were then determined in both an aqueous co-solvent system and an organic solvent to probe the effects of hydrophobic collapse. NSGs are expected to be more flexible than peptides due to the tertiary amide, with both cis and trans amide bond conformations being accessible. Solution NMR studies indicate that although CHIR-2279 and CHIR-4531 have identical backbones and termini, and very similar side chains, they do not display the same solution conformational characteristics.