Effects of cysteine upon tumor cells

Cysteine had been reported to increase survival time in thymoma-bearing mice and the interpretation suggested was that this was due to inhibition of a collagenase activity associated with some tumor cells by a chelating action of cysteine. In the present work it was shown that cysteine was a particularly potent inhibitor of amino acid transport into S37 ascites tumor cells, raising another possible interpretation of the earlier data. Sarcomas have previously been reported to lack collagenase activity; a survival study using S37 cells was therefore undertaken in an attempt to distinguish between possible interpretations of the earlier data involving thymomas. A null result was obtained with either cysteine or EDTA, reinforcing the earlier interpretation that survival enhancement with thymoma-bearing mice was due to an effect on collagenase. Other sulfhydryl analogs were found to inhibit transport also, and the effect was more pronounced with system L than system A. The reason for cysteine's particularly potent action on amino acid transport may be associated either with chelation of a metal ion involved in transport, or the involvement of the gamma-glutamyl cycle in the support of amino acid transport.