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 accommodates
epinephrine (Km = 0.284 mM; Vmax = 0.154 nmol/10(6) 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) = 3.26 mM]. Using radiolabeled N-[3H]-
sarcosinamide, we determined the transport of
sarcosinamide in HT-29
colon-cancer cells, in Calu-1
lung-cancer cells, and in normal foreskin DHF fibroblasts.
Sarcosinamide transport was linear for up to 1 min at 22 degrees 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 +/- 0.1 mM and the maximal velocity (Vmax) was 2.03 +/- 0.1 nmol/10(6) cells/min, whereas in DHF fibroblasts the respective values were 6.58 +/- 3.90 mM and 12.08 +/- 8.20 nmol/10(6) 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.