CARRIER-MEDIATED TRANSPORT OF OLIGOPEPTIDES IN THE HUMAN FIBROSARCOMACELL-LINE HT1080

To explore the feasibility of targeting human tumor cells via their tr ansport systems, dipeptide uptake was studied in the human fibrosarcom a cell line HT1080 and the human fibroblast tell line IMR-90 by the us e of hydrolysis-resistant glycylsarcosine (Gly-Sar). The uptake of [C- 14]Gly-Sar into HT1080 was time dependent. Kinetic analysis of the con centration dependence of the initial rate of [C-14]Gly-Sar uptake show ed that a carrier-mediated transport system with a K-m of 11.4 +/- 3.3 mM and V-max of 26.8 +/- 4.0 (nmol/15 min/mg protein) and a nonsatura ble component (k(d) of 0.80 mu l/15 min/mg protein) were responsible f or the dipeptide uptake by HT1080 cells. The optimal pH for the maxima l uptake was around 6.0. [C-14]Gly-Sar uptake was inhibited by various di- and tripeptides and peptide-mimetic drugs, such as bestatin and c efadroxil. [C-14]Gly-Sar uptake was not affected by the presence of am ino acids or tetra-or pentapeptides. The uptake of cefadroxil was redu ced significantly by unlabeled Gly-Sar. Moreover, Gly-Gly and Gly-Leu produced an increase in the apparent K-m of the uptake of Gly-Sar with out altering V-max. On the other hand, dipeptide uptake hy IMR-90, whi ch is a normal diploid cell line (not malignant), showed no saturable transport. These results suggest that HT1080 cells take up dipeptides via a pH-dependent transporter. This is the first report showing that a dipeptide transport system, which is similar but not identical to th e well-characterized oligopeptide transporters PepT1 and PepT2, exists in fibroblast-derived tumor cells but not in normal fibroblasts. The present finding could be the basis of a novel strategy for the specifi c delivery of oligopeptide-mimetic anticancer drugs into tumor cells.