Concentrative Uptake of Azaserine by Neoplastic Plasma Cells and Lymphocytes2

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Abstract
Five ascites tumor strains were investigated for their ability to concentrate azaserine intracellularly in vitro. The azaserine-sensitive 70429/S plasma-cell tumor accumulated azaserine to intracellular concentrations as high as 30 times the external concentration. The 2 azaserine-resistant sublines, 70429/AZ-R-1 and 70429/AZ-R-5, concentrated the drug less efficiently than the sensitive parent strain at extracellular concentrations below 10 µg. per ml. At higher concentrations there was no correlation between drug sensitivity and drug uptake. The spontaneously resistant 6C3HED lymphosarcoma accumulated azaserine least efficiently: At all concentrations tested, azaserine uptake was less than that of the plasma-cell tumors. The rate and extent of azaserine uptake was inhibited by 2,4-dinitrophenol, sodium azide, and p-chloromercuribenzoic acid, which also reversed previous drug uptake by 50 percent or more. Many amino acids inhibit azaserine accumulation and displace it from its intracellular site; both D- and L-isomers are active. A free α-amino and carboxyl group appear essential for blocking activity.

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