Transferrin is an iron-carrying compound that stimulates cell growth and division by binding to specific receptors (TR) which are preferentially expressed by actively growing cells or by the malignant counterpart of normal cells. However, quiescent cells may not necessarily cease expressing TR. We evaluated TR expression by flow cytometric analysis utilizing a monoclonal antibody (OKT-9) specific for TR on six established human colon cancer cell lines with distinct degrees of phenotypic differentiation and growth rates at sequential stages of in vitro growth (exponential and stationary phase). There were no significant differences in the proportion of cells expressing TR among the fast and slow growing cell lines at any time point of the study, nor did the cultures change the proportion of TR positive cells in their transit from exponential into stationary phase of growth. Hence, direct measurements of TR expression in malignant cell populations may not provide a useful clinical marker to distinguish highly proliferative tumors from those with a slower growth resulting from a larger proportion of quiescent cells.
Antibodies, Monoclonal Cell Division