Inhibitory Effects of Selenium on the Growth of L1210 Leukemic Cells1

Selenium has been shown to inhibit L1210 cells both in vitro and in vivo. The death of L1210 cells in vitro as indicated by trypan blue exclusion was dependent upon the form and con centration of selenium tested. Incubation of L1210 cells in buffer containing selenium at 1 jug/ml for 1 hr prior to inocula tion into mice significantly retarded the ability of the cells to propagate in vivo. Sodium selenite injected i.p. increased the longevity of mice inoculated with L1210 cells. Administration of 40 fig selenium as sodium selenite daily for 7 days resulted in a 65% increase in longevity of mice inoculated with 105 L1210 cells. Injections of sodium selenite at doses of 40 /ig/ day or less for 7 days did not significantly alter growth, liver weight, or red and white blood cell counts. The efficacy of selenium therapy was dependent upon the total number of tumor cells given in the initial inoculum. Selenium administra tion as sodium selenite was shown to be more effective in increasing the longevity of 11210-inoculated mice than was treatment with sodium selenate, selenocystine, or selenomethionine. Sodium selenite treatment at 20, 30, or 40 jug/day in mice inoculated with 102 cells resulted in 50, 80, and 90% cures, respectively. Supplementation of the drinking water with 3 ppm selenium as sodium selenite increased the longevity of L1210-inoculated mice by approximately 30%. Combined ther apy with selenium (30 /¿g/day) and methotrexate resulted in a significantly longer life span of L1210-treated mice than re sulted from either compound administered separately.