The discovery of small molecule inhibitors of cytotoxicity induced by amyloid-β (Aβ) oligomers, either applied extracellularly or accumulated intraneuronally, is an important goal of drug development for Alzheimer's disease (AD), but has been limited by the lack of efficient screening methods. Here we describe our approach using two cell-based methods. The first method takes advantage of the unique ability of extracellularly applied Aβ oligomers to rapidly induce the exocytosis of formazan formed by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT). We employed a short protocol to quantify this toxicity, and quickly identified two novel inhibitors, code-named CP2 and A5, from two compound libraries. A second independent screen of the same libraries using our previously published MC65 protection assay, which identifies inhibitors of toxicity related to intracellular Aβ oligomers, also selected the same two leads, suggesting that both assays select for the same anti-Aβ oligomer properties displayed by these compounds. We further demonstrated that A5 attenuated the progressive aggregation of existing Aβ oligomers, reduced the level of intracellular Aβ oligomers, and prevented the Aβ oligomer-induced death of primary cortical neurons, effects similar to those demonstrated by CP2. Our results suggest that, when combined, the two methods would generate fewer false results and give a high likelihood of identifying leads that show promises in ameliorating Aβ oligomer-induced toxicities within both intraneuronal and extracellular sites. Both assays are simple, suitable for rapid screening of a large number of medicinal libraries, and amenable for automation.

The αvβ3 integrin, expressed on the surface of various normal and cancer cells, is involved in numerous physiological processes such as angiogenesis, apoptosis, and bone resorption. Because this integrin plays a key role in angiogenesis and metastasis of human tumors, αvβ3 integrin ligands are of great interest to advances in targeted-therapy and cancer imaging. In this report, one-bead-one-compound (OBOC) combinatorial libraries containing the RGD motif were designed and screened against K562 myeloid leukemia cells that had been transfected with human αvβ3 integrin gene. Cyclic peptide LXW7 was identified as a leading ligand with a build-in handle that binds specifically to αvβ3 and showed comparable binding affinity (IC50 = 0.68±0.08 μM) to some of the well-known RGD “head-to-tail” cyclic pentapeptide ligands reported in the literature. The biotinylated form of LXW7 ligand showed similar binding strength as LXW7 against αvβ3 integrin, whereas biotinylated RGD cyclopentapeptide ligands revealed a 2 to 8 fold weaker binding affinity than their free forms. LXW7 was able to bind to both U-87MG glioblastoma and A375M melanoma cell lines, both of which express high levels of αvβ3 integrin. In vivo and ex vivo optical imaging studies with biotinylated-ligand/streptavidin-Cy5.5 complex in nude mice bearing U-87MG or A375M xenografts revealed preferential uptake of biotinylated LXW7 in tumor. When compared with biotinylated RGD cyclopentapeptide ligands, biotinylated LXW7 showed higher tumor uptake but lower liver uptake.

Four "One-bead one-compound" (OBOC) combinatorial libraries were designed, synthesized, and screened against MDA-MB-231 breast cancer cells. A novel cyclic peptide 1 (LXY1) with high binding specificity to α3 integrin, was identified. Molecular interactions between α3 integrin and 1 were characterized by using a series of K562 cells transfected with various mutant α3 integrins. Using analytic flow cytometry, the binding affinity (Kd) of 1 to α3 integrin on MDA-MB-231 breast cancer cells was determined to be approximately 0.4 μM. Based on the established structure-activity relationship (SAR) study, two highly focused cyclic peptide libraries were further designed, synthesized, and screened against MDA-MB-231 breast cancer cells under stringent conditions. A novel cyclic peptide 2 (LXY3) with a high binding affinity (IC 50 =57 nM) was identified. Moreover, the targeting efficiency and specificity of 2 to the breast adenocarcinoma tumors in mouse xenografts was further confirmed by in vivo and ex vivo near infra-red fluorescence optical imaging.

Purpose-Patients with glioblastoma usually have a very poor prognosis. Even with a combination of radiotherapy plus temozolomide, the median survival of these patients is only 14.6 months. New treatment approaches to this cancer are needed. Our purpose is to develop new cell-surface binding ligands for glioblastoma cells, and use them as targeted imaging and therapeutic agents for this deadly disease.Methods-One-bead one-compound combinatorial cyclic peptide libraries were screened with live human glioblastoma U-87MG cells. The binding affinity and targeting specificity of peptides identified were tested with in vitro experiments on cells and in vivo, and ex vivo experiments on U-87MG xegnograft mouse model.Results-A cyclic peptide, LXY1, was identified and shown to be binding to the α3 integrin of U-87MG cells with moderately high affinity (Kd = 0.5+/−0.1 μM) and high specificity. Biotinylated LXY1, when complexed with streptavidin-Cy5.5 (SA-Cy5.5) conjugate, targeted both subcutaneous and orthotopic U-87MG xenograft implants in nude mice. The in vivo targeting specificity was further verified by strong inhibition of tumor uptake of LXY1-biotin-SA-Cy5.5 complex when intravenously injecting the animals with anti-α3 integrin antibody or excess unlabeled LXY1 prior to administrating the imaging probe. The smaller univalent LXY1-Cy5.5 conjugate (2279 Da) was found to have a faster accumulation in the U-87MG tumor and shorter retention time compared with the larger tetravalent LXY1-biotin-SA-Cy5.5 complex (~ 64 KDa).Conclusions-Collectively, the data reveals that LXY1 has the potential to be developed into an effective imaging and therapeutic targeting agent for human glioblastoma.