The Uptake of Proteins by Normal and Tumour Cells In Vitro

Abstract

THE concept that rapidly growing tumours are " nitrogen traps " has led to the suggestion that plasma and other proteins may be ingested intact by tumour cells to a much greater extent than by most normal cells (Henderson and LePage, 1959; Gey, 1956). Ingestion is generally assumed to occur by the process of pinocytosis, and increased pinocytotic activity would be consistent with increased cell surface activity of tumour cells which might be expected from their decreased adhesiveness (McCutcheon, Coman and Moore, 1948) poorer cell contacts (Mercer and Easty, 1961) and loss of contact inhibition (Abercrombie and Ambrose, 1958).The capacities of a number of normal and tumour cells to ingest fluorescent labelled proteins in vitro have been compared and the effects of population density, various media, including the addition of insulin, serum and antimetabolites, and temperature on the process have been investigated. Primary cultures were prepared by the usual techniques involving trypsinization of the chopped tissue followed by washing of the resultant cell suspensions. Aliquots, usually 2 ml., of cell suspension were added to the test tubes containing coverslips. When the cells were well attached the medium was changed and the cultures used 24 hours later. Care was taken to select replicate cultures with similar cell population densities.The fluorescent protein solution (usually 0X05 ml. of a 500 solution), together with any other reagents was added to the culture medium (2 ml.) in the test tubes. Control and treated cultures were removed from the incubator as required, washed twice with 5 ml. portions of culture medium, sealed on to a microscope slide with vaseline/paraffin wax mixture and examined by fluorescence microscopy. Labelling of proteinsThe proteins were conjugated with fluorescein or rhodamine B isothiocyanate using 20 parts of protein to 1 of dye, by the method of Riggs et al. (1958). Unconjugated dye was removed by passing the reaction mixture through a column of

Human ferritin for tumor detection and therapy

“…As far back as the 1960s, several research groups reported that human ferritin could be selectively taken up by tumor cells . Then, in the 1980s, Fargion et al found that H‐ferritin specifically binds to a protein of ∼100 kDa molecular weight .…”

Tissue distribution and tumour localization of 99m-technetium-labelled liposomes in cancer patients

“…Specific accumulation of liposomes in tumours, and particularly in tumour cells, would be of considerable advantage in improving the selectivity of anti-cancer drugs. Such a possibility seems feasible in view of reports that some tumour cells have a high endocytic activity (Busch et al, 1961;Ghose et al, 1962;Easty et al, 1964;Mego & McQueen, 1965;Trouet et al, 1972) which may enhance uptake of liposomes. Previous studies with animal models have shown that tumour localization of liposome markers is possible by a careful selection of the size and membrane properties of the liposome (Dapergolas et al, 1976;Richardson et al, 1977Richardson et al, , 1978b.…”

Lysosomes in cancer cells

“…Busch and Starbuck (1964), after injections of proteins labelled with radioactive isotopes, found that the specific activity of the protein within the tumour was higher than that in the liver and other normal tissues studied. Easty, Yarnell, and Andrews (1964) found that several tumour cell types, cultured in vitro, showed considerable uptake of fluorescein-labelled proteins. Ghose, Nairn, and Fothergill (1962) found in vivo a substantial amount of protein conjugate taken up by cells of ascites and solid tumours, although Easty (1964) has reported that uptake of fluorescent proteins into tumours in vivo frequently involves macrophages and stroma.…”