Characterization of the catecholamine extraneuronal uptake, carrier in human glioma cell lines SK-MG-1 and SKI-1 in relation to (2-chloroethyl)-3-sarcosinamide-1-nitrosourea (SarCNU) selective cytotoxicity

Transport of (2-chloroethyl)-3-sarcosinamide-1-nitrosourea (SarCNU) and (-)-norepinephrine was investigated in SarCNU-sensitive SK-MG-1 and -resistant SKI-1 human glioma cell lines. [H-3]SarCNU influx was inhibited by SarCNU, sarcosinamide, and (+/-)-epinephrine in SK-MG-1 cells with competitive inhibition observed by (+/-)-epinephrine (K-i = 140 +/- 12 mu M) and (+/-)-norepinephrine (K-i = 255 +/- 41 mu M). No effect on influx was detected in SKI-1 cells. [H-3](-)-Norepinephrine influx was linear to 15 sec in both cell lines and temperature dependent only in SK-MG-1 cells. Influx of [H-3](-)-norepinephrine was found to be saturable in SK-MG-1 (K-m = 148 +/- 28 mu M, V-max = 1.23 +/- 0.18 pmol/mu L intracellular water/sec) but not in SKI-1 cells. In SK-MG-1 cells, [H-3](-)-norepinephrine influx was found to be inhibited competitively by (-)-epinephrine (K-i = 111 +/- 7 mu M) and SarCNU (K-i = 1.48 +/- 0.22 mM). Ouabain and KCl were able to inhibit the: [H-3]norepinephrine influx in SK-MG-1 cells, consistent with influx being driven by membrane potential. Several catecholamine uptake(2) inhibitors were able to reduce significantly the influx of [H-3](-)-norepinephrine and [H-3]SarCNU with no inhibition by a catecholarnine uptake(2) inhibitor. These findings suggest that increased sensitivity of SK-MG-1 to SarCNU is secondary to enhanced accumulation of SarCNU mediated via the catecholamine extraneuronal uptake(2) transporter, which is not detectable in SKI-1 cells. The introduction of SarCNU into clinical trials will confirm ii increased uptake via the catecholamine extraneuronal uptake(2) transporter will result in increased antitumor activity.