Prediction of metastatic potential in an animal model of prostate cancer: flow cytometric quantification of cell surface charge.

The natural history of clinically localized prostate cancer in individual patients is difficult to predict using currently available techniques. The majority of these patients will undergo treatment without knowledge of whether the tumor would have progressed during their lifetime. Because more patients are being diagnosed yearly with early stage prostate cancers it is becoming increasingly important to delineate factors that will clarify which patients have tumors with invasive potential. Using the Dunning R-3327 rat prostate animal tumor model we have previously shown that an increase in cell surface charge, as measured by individual cell electrophoresis, is associated with an increase in metastatic ability. This electrophoretic technique is limited by the small number of cells that can be analyzed during each assay. Therefore, we adapted a flow cytometric method for measurement of cell surface change, utilizing a large molecule (cationized ferritin) that binds quantitatively to the negative charges at the cell surface. With a fluorescent tag attached to the ferritin molecule, flow cytometric quantification of surface charge was possible, and this method was successful in identifying tumors with high metastatic ability in the Dunning prostate tumor model.