Separation and Characterization of Neoplastic Cell Subpopulations of a Transplantable Rat Pancreatic Acinar Carcinoma

The transplantable pancreatic acinar carcinoma established in F344 rats demonstrates heterogeneity of cytodifferentiation with cell types ranging from those containing no zymogen granules to cells with mature zymogen differentiation. Two relatively homogeneous subpopulations of cells have been isolated by isopyknic Percoll gradient centrifugation from the heterogeneous cell population of this tumor. The subpopulation obtained at a density of 1.0987 g/ml was designated the granule-enriched fraction (GEF) and contained morphologically differentiated cells with abundant mature zymogen granules. The other subpopulation, obtained at a density of 1.0789 g/ml, consisted of poorly differentiated cells lacking zymogen maturation and was thus termed the granule-deficient fraction (GDF). In both fractions, greater than 97% of the cells were viable and maintained linear rates of [₃H]leucine and [₃H]thymidine incorporation into protein and DNA for up to 3 hr following isolation. High-resolution autoradiographic analysis of [₃H]thymidine incorporation revealed that 20% of the cells in GDF subpopulation and 12% of the cells in GEF subpopulation synthesize DNA. Morphological and morphometric analyses of the isolated GEF and GDF subpopulations of the acinar carcinoma revealed distinct differences in nuclear:cytoplasmic ratio, secretory granule content, and degree of polarity. The GEF subpopulation contained significant amounts of stored zymogen, as evidenced by higher levels of amylase and lipase activities. In contrast, the GDF subpopulation displayed very low levels of these enzymes. Both GDF and GEF subpopulations produced tumors when injected s.c. into F344 rats. Characterization of concanavalin A (Con A)-binding sites on the plasmalemma of the GDF and GEF subpopulations by the Con A:peroxidase method indicated the presence of Con A receptors on pancreatic carcinoma cells regardless of the extent of cytodifferentiation in contrast to normal pancreatic embryogenesis, in which Con A receptors are discerned only in acinar cells containing mature secretory granules. The presence of Con A receptors on all cells of the GDF and GEF acinar carcinoma cell subpopulations suggests either that neoplastic transformation results in altered genetic expression whereby progenitor “stem” cells, which lack Con A receptors during normal pancreatic embryogenesis, acquire such receptors or that the pancreatic carcinoma arises from dedifferentiation of mature acinar cell which normally possesses Con A receptors.