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The distribution of eukaryotic DNA topoisomerase I in the cell has been analyzed at four levels: (i) at the level of the nuclear matrix; (ii) at the cytological level by immunofluorescence of whole cells; (iii) at the electron microscopic level using the protein A/colloidal gold technique; and (iv) at the level of DNA to identify in situ the sequence upon which topoisomerase I is catalytically active. Although topoisomerase I is clearly distributed non‐randomly in the nucleus, the unique distribution of the enzyme is not related to the nuclear matrix. The data support the conclusion that topoisomerase I is heavily concentrated in the nucleolus of the cell; furthermore, particular regions within the nucleolus are depleted of topoisomerase. A technique has been developed which allows isolation and analysis of the cellular DNA sequences covalently attached to topoisomerase. Ribosomal DNA sequences are at least 20‐fold enriched in topoisomerase/DNA complexes isolated directly from a chromosomal setting, relative to total DNA. This is the first direct evidence that topoisomerase I is catalytically active on ribosomal DNA in vivo.

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Bovine somatotropin was studied with respect to thermal stability, quantitative thermal denaturation kinetics, and refolding potential following thermal denaturation using a panel of 6 monoclonal antibodies and the Conformation-Sensitive Immunoassay (CSI). The antibody panel consisted of 4 conformation-dependent and 2 sequence-specific antibodies. Each of the antibodies revealed unique thermal stability profiles for their respective epitopes suggesting that they each recognize different antigenic determinants. Comparing the thermal stability profiles generated with these antibodies allowed the stability of bovine somatotropin to be "dissected" based on individual structural features. The degree to which bovine somatotropin is stabilized by disulfide bonds was examined using CSI-based quantitative thermal denaturation kinetics profiles generated under reducing and nonreducing conditions. All of the conformational epitopes unfolded faster under reducing conditions indicating that the two disulfide bonds within the somatotropin molecule impart some degree of global stabilization. The ability of bovine somatotropin to refold after reducing or nonreducing thermal denaturation was also examined using the antibody panel and the CSI. The results show that, although significant refolding was evident for some epitopes, bovine somatotropin cannot refold to the native state following thermal denaturation under either reducing or nonreducing conditions.

The anti-IgG properties of two dual-specific (anti-dsDNA and anti-IgG) monoclonal NZB/NZW F1-derived autoantibodies, BV 17-45 and BV 16-13, were studied to resolve the location and possible commonality of the IgG epitope. To determine if BV 17-45 and BV 16-13 recognized the same IgG epitope, the relative temperature sensitivity of the conformational IgG epitopes were evaluated using the conformational sensitive immunoassay. Comparison of the temperature sensitivity of the conformational immunoglobulin epitopes over a temperature range of 25-100 degrees C suggested that the epitope recognized by BV 17-45 was the same as the IgG epitope recognized by BV 16-13. Further studies with papain- and pepsin-generated F(ab')2, Fab, and Fc fragments of BV 17-45 and BV 16-13 revealed that the dual-specific autoantibodies BV 17-45 and BV 16-13 both bound an epitope in the hinge region of the IgG molecule. The potential correlation between these studies and the pathogenic nature of dual-specific autoantibodies is discussed.

The ability to produce and collect Circulating Tumor Cells (CTCs) from cultured metastatic tumor tissue and established pancreatic cancer cell lines using a 3D perfusion culture system is demonstrated. The culture system used, the RealBio D4 ™ Culture System, incorporates low-sheer, tangential flow of nutrient medium above and below an open synthetic 3D cell scaffold, and gas-permeable membranes above and below the nutrient flow compartments to facilitate creation of in vivo-like gradients of nutrients, growth factors, and gasses that promote the recreation of an in vivo-like environment. This design allows CTCs generated within the cultures to migrate out of the cultured tissue or cell mass into the circulating nutrient medium in a manner reminiscent of the migration of CTCs out of tumors and into the blood stream in vivo. Once in the medium, the CTCs can be easily collected for characterization and further study. Human metastatic pancreatic (to liver) tumor tissue from a mouse xenograft, and established human pancreatic cancer cell lines were cultured in the RealBio D4™ Culture System for at least 30 days. Cells migrating from the cultured tissues into the circulating culture medium were collected periodically throughout the study and characterized with respect to functional and cell surface CTC markers using a commercially available CTC technology designed for detecting CTCs in whole human blood (Vita-Assay™, Vitatex Inc., Stony Brook, NY). CTC's were positively identified in the circulating medium at all time points examined. CTCs were produced by the cultured primary tumor tissue at a rate of more than 100 CTCs per culture per day after 30 days accounting for nearly 10% of all viable cells shed into the medium. Highly metastatic cell lines (MIA PaCa-2 and AsPC-1) produced as many as 6,000 CTCs per day accounting for 22% of the viable cells migrating from the cultures. In contrast, poorly metastatic cell lines (PL45 and Capan-2) produced no more than 20 CTCs per day representing no more than about 3% of the viable cells. The results presented here demonstrate that CTCs can be produced in vitro by heterogeneous tumor tissue cultures. The results also show that CTCs can be produced in large numbers by highly metastatic cancer cell lines grown in vitro, but that poorly metastatic cancer cell lines produce far fewer CTCs when cultured under the same conditions. The methods described here represent a valuable new approach for the study of CTCs in vitro with direct applicability for developing improved diagnostic assays for CTCs, the study of factors that affect their formation and migration from tumor tissue, and development of therapies targeting CTCs. Citation Format: William P. Pfund, George Martin, Paul A. Neeb. In vitro production of circulating tumor cells (CTCs) using 3D cultures of human tumor tissues and established tumor cell lines. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 1456. doi:10.1158/1538-7445.AM2013-1456

Development of a biologically relevant in vitro tumor model is a complex undertaking which requires culturing heterogeneous cell populations in a realistic 3D arrangement such that interactions normally occurring between different cell types (e.g., stromal cells and cancer cells) may be promoted in vitro. This level of complexity requires establishing and maintaining varied microenvironments in the culture that simulate the various microenvironmental niches present within the original tumor. Here, we demonstrate significant progress to this end by reporting results of successful efforts to co-culture heterogeneous cell populations derived from a metastatic pancreatic carcinoma tumor for 3 months using a novel, 3D perfusion culture system. The design of the culture system incorporates low-sheer, tangential flow of nutrient medium above and below an open synthetic 3D cell scaffold and exchange of metabolic gasses via gas-permeable membranes which separate the core of the culture chamber from gassing chambers located above and below the nutrient flow compartments. This design allows for the establishment of realistic gas and nutrient gradients across the culture scaffold that mimic nutrient, waste and gas gradients present in vivo. Primary tumor cultures were initiated in the 3D perfusion culture system and T-75 flasks (2D control cultures) after mechanical/enzymatic dissociation of a mouse xenograft tumor originating from a human pancreatic carcinoma that had metastasized to the liver. Each culture was seeded with an aliquot of the total tumor dispersion and maintained in culture for up to 90 days. The 3D perfusion cultures were maintained by performing partial medium exchanges as needed based on glucose concentration levels measured in the circulating medium while the 2D control cultures were maintained using traditional subculturing techniques as necessary based on confluence of the cell monolayers. A trend of increasing glucose consumption rate was observed throughout the duration of the study in the 3D tumor cultures suggesting continuous expansion of the cultured cell population without the need for subculturing. The cell populations observed in the 3D perfusion culture remained diverse throughout the 3 month culture period and the cells were found to arrange in a manner resembling the cellular organization of a corresponding tumor in vivo. 2D cultures established using cells removed from the 3D perfusion culture after 3 months closely resemble early passages of the 2D control cultures with respect to the composition and arrangement of cells. In contrast, the diversity of cell types present in the 2D control cultures decreased noticeably during the course of the study. These data suggest that the novel 3D perfusion culture system represents significant advancement over traditional culture technologies towards recapitulating human tumors in vitro. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 4239. doi:1538-7445.AM2012-4239