BackgroundPancreatic ductal adenocarcinoma (PDAC) carries an extremely poor prognosis, typically presenting with metastasis at the time of diagnosis and exhibiting profound resistance to existing therapies. The development of molecular markers and imaging probes for incipient PDAC would enable earlier detection and guide the development of interventive therapies. Here we sought to identify novel molecular markers and to test their potential as targeted imaging agents.Methods and FindingsHere, a phage display approach was used in a mouse model of PDAC to screen for peptides that specifically bind to cell surface antigens on PDAC cells. These screens yielded a motif that distinguishes PDAC cells from normal pancreatic duct cells in vitro, which, upon proteomics analysis, identified plectin-1 as a novel biomarker of PDAC. To assess their utility for in vivo imaging, the plectin-1 targeted peptides (PTP) were conjugated to magnetofluorescent nanoparticles. In conjunction with intravital confocal microscopy and MRI, these nanoparticles enabled detection of small PDAC and precursor lesions in engineered mouse models.ConclusionsOur approach exploited a well-defined model of PDAC, enabling rapid identification and validation of PTP. The developed specific imaging probe, along with the discovery of plectin-1 as a novel biomarker, may have clinical utility in the diagnosis and management of PDAC in humans.
Early detection and diagnosis of prostate cancer is key to designing effective treatment strategies. Microarrays have resulted in the discovery of hepsin (HPN) as a biomarker for detection of prostate cancer. In this study, we explore the development of HPN imaging probes for detection of prostate cancer. We used phage display to isolate HPN binding peptides with 190 + 2.2 nmol/L affinity in monomeric form and high specificity. The identified peptides were able to detect human prostate cancer on tissue microarrays and in cell-based assays. HPN-targeted imaging agents were synthesized by conjugating multiple peptides to fluorescent nanoparticles to further improve avidity through multivalency and to improve pharmacokinetics. When injected into mouse xenograft models, HPNtargeted nanoparticles bound specifically to HPN-expressing LNCaP xenografts compared with non-HPN-expressing PC3 xenografts. HPN imaging may provide a new method for detection of prostate cancer. [Cancer Res 2008;68(7):2286-91]
1183 Mesenchymal stem cells (MSCs) are a population of adult stem cells that constitute a promising source for therapeutic applications. MSCs exist in various adult tissues, such as bone marrow and umbilical cord blood. The most common method for MSC isolation relies on plastic adherence, however, this isolation procedure is hampered by the unpredictable influence of other co-cultured adhering cells. Phenotypic characterization of MSCs is usually carried out by FACS analysis of cell surface marker expression, but no unique marker has yet been identified. To circumvent these limitations, using granulocyte-colony stimulating factor (G-CSF) mobilized adult human peripheral blood (PB), we explored the use of Elutra® Cell Separation System (Caridian BCT) to isolate MSC enriched fractions based on their size and density. A group of 28 donors were studied after mobilization for two consecutive day of G-CSF injection (480μg/day subcutaneously). Total nucleated cells (TNC) were collected by apheresis on the third day. An average of 6-fold increase in MSCs in the post-mobilized sample was observed. At least 1 million TNC in pre- and post-mobilized PB were analyzed by FACS for the presence of MSCs by cell surface staining with antibodies to CD105, CD90, CD73, CD31, CD45 and CD34. Circa 3 × 1010 TNC were loaded onto the Elutra to fractionate the apheresis product into several distinct cell fractions. Typically, the MSCs were enriched in 2 fractions, and yielded about 5–10% of the initial loaded cell number. Following culturing and passage, cells from these 2 fractions were grown on plastic with low contamination by other cell types. The cultured cells showed spindle-shaped morphology. Cells were further characterized by FACS analysis and shown to stained positive for mesenchymal specific markers CD90 and CD105; and negative for hematopoietic markers of CD45 and CD34. Furthermore, after cells from all fractions were plated for colony forming unit-fibroblast assay (CFU-F), no colony formation were observed from other than the 2 fractions. In summary, we demonstrate that MSCs are mobilized into PB by G-CSF and can be collected by apheresis. Size-based Elutra fractionation of apheresis product in a closed system could provide a novel strategy for the large-scale isolation and expansion of human MSCs for autologous cell therapy *Dr. Marasco is a paid consultant for NeoStem and an equity holder. Disclosures: No relevant conflicts of interest to declare.
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