Selenium cystine decreases the incorporation of S35 L-cystine by rat Murphy lymphosarcoma tumor cells both in vitro and in vivo. Selenium cystine also decreases the growth of the tumor in the intact animal.
Benzyl selenium cysteine does not inhibit the incorporation of S35 L-cystine by Murphy lymphosarcoma tumor cells in vitro nor does it affect tumor growth in the intact animal.
Thus the ability of selenium cystine to decrease the influx of S35 L-cystine into tumor cells in vitro is associated with the ability of this compound to inhibit tumor growth in the intact animal. Furthermore, the inhibitory effect of selenium cystine is not due solely to the presence of selenium within the molecule but is related to its structural identity with cystine.
The data are further suggestive of the importance of SH compounds in the growth of malignant cells.