MEMBRANE-TRANSPORT OF METHOTREXATE IN A SQUAMOUS CARCINOMA CELL-LINE ADAPTED TO LOW FOLATE CONCENTRATIONS

Membrane transport characteristics of the folate analogue methotrexate (MTX) were studied in a human squamous carcinoma cell line of the head and neck (HNSCC) adapted to grow in tissue culture media with nanomolar reduced folate concentrations (SCC-11B-LF), as compared to SCC-11B cells grown in standard medium containing high folate concentrations.We observed that SCC-11B-LF cells exhibited a 10.5-fold increased uptake of [H-3]-MTX via the reduced folate/MTX carrier system compared to SCC-11B cells. Affinity labelling of the reduced folate \MTX carrier system suggests that the up-regulation of [H-3]-MTX transport mainly results from an increased rate of carrier translocation, and only to a minor extent (15-20%) from an increased amount of carrier protein. The upregulation of MTX transport resulted in a 2.4-fold increased growth inhibitory effect by MTX.These results suggest that membrane transport may play a more important role in MTX-cytotoxicity when SCC-11B cells in vitro are grown in more physiological folate concentrations.