GROWTH OF OVARIAN-CARCINOMA CELL-LINES AT PHYSIOLOGICAL FOLATE CONCENTRATION - EFFECT ON FOLATE-BINDING PROTEIN EXPRESSION IN-VITRO AND IN-VIVO

Ovarian-carcinoma cell lines (OVCAR3, IGROV1, OVCA432, SW626 and SKOV3 ), grown in standard medium containing supra-physiological (2.3 mu M) folate concentration, display different levels of reactivity with the anti-folate-binding-protein (FBP) monoclonal antibody MOv18, which rec ognizes the ol-isoform of the protein. Gel-filtration and absorption e xperiments indicated that on IGROV1 cells this molecule accounts for a ll folic-acid binding at nanomolar concentrations. The aim of the stud y was to investigate the effect of extracellular folate levels on cell s adapted to grow in medium containing physiological folate concentrat ion (20 nM). By the ternary complex assay, all cell lines showed a mar ked depletion of intracellular reduced folates, compared with those in standard folate medium. The monitoring of FBP by MOv18 showed on IGRO V1 cells a transient up-regulation of the protein, whereas on the othe r cell lines, except SKOV3, no changes were detected. These data sugge st that in these cells further over-expression of the molecule cannot generally be induced by lowering the extracellular folate concentratio n. On SKOV3, Scatchard analysis of I-125-MOv18 binding, as well as the evaluation of total folate binding capacity, showed a 2- to 3-fold st able increase of FBP expression after long-term growth in low-folate m edium. Reverse transcriptase-polymerase chain reaction (RT-PCR) analys is indicated in these cells a 1.5-fold increase in alpha-FBP mRNA. SKO V3 cells, maintained in vitro in medium containing supraphysiological and physiological (i.e., low-folate) concentrations were injected into nude mice. Weight differences, though not statistically significant, were observed in favour of low-folate-derived tumors. Immunohistochemi cal and immunochemical analysis of the tumor samples showed that in SK OV3 cells the receptor modulation can also be induced by restoring the physiological folate concentration in vivo. (C) 1995 Wiley-Liss, Inc.