Lack of evidence for a high-affinity sarcosinamide carrier or a catecholamine carrier in Calu-1 lung-cancer cells, HT-29 colon-cancer cells, and DHF fibroblasts

We have previously demonstrated that uptake of the amino acid amide sarcosinamide by the glioma cell line SK-MG-1 occurs via the catecholamine carrier that accomodates epinephrine (Km=0.284mm; Vmax=0.154 nmol/106 cells/min). Sarcosinamide chloroethylnitrosourea (SarCNU), a new anticancer agent that exerts increased in vitro antitumor activity against gliomas as compared with BCNU (bis-chloroethylnitrosourea), the standard agent of choice, competitively inhibits sarcosinamide uptake by SK-MG-1 cells [inhibition constant (Ki)=3.26mm]. Using radiolabeledN-[3H]-sarcosinamide, we determined the transport of sarcosinamide in HT-29 coloncancer cells, in Calu-1 lung-cancer cells, and in normal foreskin DHF fibroblasts. Sarcosinamide transport was linear for up to 1 min at 22°C. In HT-29 cells and DHF fibroblasts, the uptake of sarcosinamide followed Michaelis-Menten kinetics of carrier-mediated transport. In HT-29 cells the Michaelis constant (Km) was 2.76±0.1mm and the maximal velocity (Vmax) was 2.03±0.1 nmol/106 celis/min, whereas in DHF fibroblasts the respective values were 6.58±3.90mm and 12.08±8.20 nmol/106 cells/min. In these two cell lines, neither epinephrine nor leucine significantly reduced sarcosinamide transport. In Calu-1 cells there was no evidence of carrier-mediated transport of either sarcosinamide or epinephrine. These nonglial cell lines lack a high-affinity catecholamine carrier. The increased cytotoxicity of SarCNU in gliomas may correlate with the presence of a high-affinity catecholamine carrier.